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Do you now how build a correlator?

Ch.

  --- s_egorov <s_egorov@...> escribió:

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Hi there,

We are currently using a Coherent MIRA mode-locked system (0.8 W
output at 800 nm, 76 MHz repetition rate, 150 fs pulse duration)
pumped by an Ar-ion laser (Coherent Innova 310, 8 W, multiline).
After many years of good service, the Ar-ion tube has ceased
operation. Given the circumstances, we are presently considering the
option of upgrading to diode technology. Coherent offers a diode-
based alternative (Verdi V6, 6W output) at ca. Euro 66,000 + TAX
(about Euro 80,000 total). We wonder whether there are cheaper (yet
reliable) alternatives to this option. Any thoughts, suggestions, or
experience in these matters will be greatly appreciated.

Thanks,

Felix (F.Fernandez-Alonso@...)

Date: Tue, 11 May 2004 10:16:05 +0100
From: "Steve Meech" <s.meech@...>

I would be grateful if you could bring this advert to the attention
of any likely contacts.
Many thanks, and apologies for cross postings

Steve Meech

Post-doctoral Research Associate in Ultrafast Spectroscopy
School of Chemical Sciences and Pharmacy, UEA, Norwich, UK

Applications are invited for a post-doctoral research position in
nonlinear optical studies of the ultrafast dynamics of surfaces and
interfaces. The work will be carried out in a new ultrafast laser
laboratory in the group of Stephen Meech at the University of East
Anglia, Norwich, England.

The individual we will appoint will be creative, highly motivated
and capable of independent research.  They will hold a PhD in
physical chemistry, physics or a related subject.  The candidate we
are seeking must also have demonstrated expertise in one or more of
the following subjects:  design and construction of ultrafast lasers
and ultrafast laser experiments; nonlinear optics; ultrafast laser
spectroscopy.

The position will be available from 1st October 2004, and will be
for three years.  Preliminary enquiries, including a CV, should be
made to Dr Meech (s.meech@...).

An application form should be obtained from the Personnel Office,
University of East Anglia, Norwich, NR4 7TJ (Internet:
http://www.uea.ac.uk/personnel/jobs/ or e-mail: personnel@...
or answer phone: 01603 593493), to be returned by 1 July 2004.
Please quote reference RA44.

****************************************************

Stephen Meech
School of Chemical Sciences and Pharmacy
University of East Anglia
Norwich NR4 7TJ, UK
Tele: 44(0)1603 593141
Fax: 44(0)1603 592003
****************************************************

Postdoctoral Position in Ultrafast Spectroscopy

A postdoctoral position is currently available in Dr. Jie Shan's
group
in
the Physics Department at Case Western Reserve University
http://www.phys.cwru.edu (Cleveland, Ohio).  The project involves
ultrafast
spectroscopy, with an emphasis on terahertz time-domain
measurements.
Prior
experience in ultrafast spectroscopy and background in condensed
matter
physics / materials research are highly desirable.

The position provides a unique opportunity to work in a new and fully
functional lab equipped with a state-of-the-art Ti:sapphire
femtosecond
amplifier system and complete capabilities for THz pump-probe
spectroscopy.
  Applications, including a current CV and a list of three
references,
should
be sent to jie.shan@...

Or
Dr. Jie Shan
Department of Physics
Case Western Reserve University
10900 Euclid Avenue
Cleveland, OH 44106
Email: jie.shan@...
Tel: 216-368-4240
Fax: 216-368-4671

Do you know?

http://www.femtosecondsystems.com/femtoforum/

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14th International Conference
on Ultrafast Phenomena
July 25-30, 2004
Niigata, Japan
http://www.osa.org/meetings/topicals/UP/

Near Infrared Tunable Femtosecond Cr:Forsterite (Cr:F) Laser system
at 1250 nm with Ytterbium Fiber Laser Pump: For Research and
Industrial Applications

The femtosecond Cr:Forsterite (Cr:F) laser system from Del Mar
Ventures is a mode-locked ultrashort laser producing pulses in near
infrared ~1250 nm range. A laser is mode-locked when many
longitudinal modes inside the laser cavity are held in phase by
constructive interference producing the femtosecond (10 -15s) pulse
[1].  Forsterite based on Cr4+ are the first tunable lasers operating
in 1150 to 1300 nm range [2,3,4,5].  The extremely short time
duration of a femtosecond pulse gives enormous peak powers and power
densities. Femtosecond lasers are being used in a rapidly growing
number of applications, including ultrafast photochemistry,
photophysics, photoablation, micromachining, imaging condensed
matter, semiconductor device physics, and other areas.

The  Cr:F gain medium is pumped by a 6-10W Ytterbium Fiber Laser
giving an all solid state laser system that is  an  affordable source
of femtosecond pulses in 1230 - 1270nm region.  The combination of
Ytterbium Fiber Laser and Cr:F oscillator gives pulses in the sub-65
femtosecond range at a repetition rate of 120/76 MHz and delivers
power between 180-250mW.

The femtosecond Cr:Forsterite laser is tunable over wavelengths from
1230 to 1270 nm,  making it ideal for imaging condensed matter and
biomedical applications [6,7].  Frequency doubling can produce wave
lengths in the visible at ~630 nm and supercontinuum generation
produce pulses in the infrared and visible range.

New Photochemistry and Photobiology

With the high bandwidth and extremely short pulse duration of
femtosecond lasers researchers are pushing the bounds of chemical and
biological imaging.  Laser spectroscopy involves the use of
femtosecond laser pulses to study the properties of matter. The short
pulse duration allows the detection and study of short-lived
transient chemical reaction at very high resolutions.8

Optical coherence tomography (OCT) employs the coherent properties of
the Cr:Forsterite light source to study the morphological structures
and functions of biological samples on micron scale, such as cellular
development with very high resolution [9].  Because the axial
resolution depends primarily on the bandwidth of the light source,
high bandwidth femtosecond  Cr:Forsterite lasers can give resolutions
in the 5-10  um range with imaging depths of 2-3 mm.  Cells as small
as 15um have been successfully imaged using Cr:Forsterite lasers and
OCT [7 ].

The Cr:Forsterite generates femtosecond pulses at wavelengths from
1230 to 1270 nm. These wavelengths are less damaging to biological
samples than the shorter wavelengths produced by other femtosecond
lasers. This allows in vivo imaging of cells and other biological
samples.  With wavelength above 1200nm it is possible to image tissue
samples that are non transparent at shorter wavelengths. This
wavelength is ideal to heat water in tissues for welding, stress
release, cornea shaping and other applications.


Material processing

The femtosecond pulse duration is very short making even low energy
pulses produce extremely high peak power. This limits low energy
threshold thermal and mechanical side effects.  The high peak power
of the femtosecond pulse allows multiple photons to be absorbed,
creating an electron plasma in the material.   As the plasma expands
material is ejected from the target area [10].  Because this material
ablation is not a thermal effect, cavitations and laser induced
pressure transients are reduced.
Femtosecond lasers are used to produce micro-gratings and multi-
dimension periodic nano structures in a variety of materials
including dielectrics, semiconductors, metals, plastics and resins
[11]. Multiphoton absorption allows for processing of materials that
are not very photosensitive.
Below the ablation threshold the high pulse energies can introduce
structural changes resulting in a change in the index of refraction
of the material. All optical wave guides and photonic devices are
manufactured using these techniques [12].

Medical Applications

Femtosecond lasers are finding many uses in the medical field where
they are finding use in applications ranging from biopsy imaging to
eye surgery.

The same properties that make femtosecond lasers useful for material
processing can also be used for a variety of surgical applications.
One of the first commercially successful applications of femtosecond
lasers is their use in the LASIK (Laser in situ keratomileusis) eye
surgery procedure. Cr4+ lasers in 1110-1500 nm range offer safer
wavelengths than Ti:sapphire femtosecond lasers at 800 nm to reduce
potential retinal damage. The Ultrafast laser replaces the
microkeratome mechanical knife that makes the initial cut in the
cornea.  This offers a highly controlled cut of uniform thickness
that is not possible with a mechanical knife [13].  Dental
applications and surgery on the inner ear are areas where the
extremely clean material processing abilities of femtosecond lasers
offer an alternative to mechanical drills or CW lasers that leave
micro cracks and cause thermal stress in tooth enamel and tissue
damage in the inner ear [13,14].

Work has also been done using femtosecond lasers to treat
atherosclerosis. The build up of plaque causes arteries to harden,
restricting blood flow.  By ablating tissue from the artery wall the
elasticity of the artery can be restored.  Blood pressure forces the
artery to expand once wall material has been removed.  This procedure
would be used in place of balloon angioplasty or Stenting procedures.
The use of laser ablation offers the advantage of being less damaging
to the structural integrity of the artery than other procedures.13


References

1. L.  Qian, X. Liu, F. Wise," Femtosecond Kerr-lens mode
locking with negative nonlinear phase shifts," Opt. Lett. Vol. 24,
No. 3, (1999).

2. V. Petricevic, S. K. Gayen, and R. R. Alfano, "Laser Action
in Chromium-Activated Forsterite for Near-Infrared Excitation: Is
Cr4+ the Lasing Ion?" Appl. Phys. Lett. 53, 2590 (1988).

3. V. Petricevic, A. Seas, and R. R. Alfano, "Slope Efficiency
Measurements of Chromium-Doped Forsterite Laser", Opt. Lett. 16, 811
(1991).

4. A. Seas, V. Petricevic, and R. R. Alfano, "Generation of Sub-
100-fs Pulses From a Continuous-Wave Mode-Locked Chromium-Doped
Forsterite Laser", Opt. Lett. 17, 937 (1992).

5. J. M. Evans, V. Petricevic, A. B. Bykov, A. Delgado, and R.
R. Alfano, "Direct Diode-Pumped Continuous-Wave Near-Infrared Tunable
Laser Operation of Cr4+:forsterite and Cr4+:Ca2GeO4", Opt. Lett. 22,
1171 (1997).

6. S. Boppart, W. Drexler, U. Morgner, F. Kartner, J.
Fujimoto, "Ultrahigh Resolution and Spectroscopic OCT Imaging of
Cellular Morphology and Function," Proc. Inter-Institute Workshop on
In Vivo Optical Imaging at the National Institutes of Health. Ed. A.
H. Gandjbakhche. September 16-17, pp. 56-61, 1999.

7. W. Drexler, U. Morgner, F. Kartner, C. Pitris, S. Boppart, X.
Li, J. Fujimoto, "In vivo  ultrahigh-resolution optical coherence
tomography,"  Opt. Lett. Vol. 24, No. 17, (1999).

8. W. Sibbett, D. Reid, M. Ebrahimzadeh, "Versatile femtosecond
laser sources for time-resolved studies: configurations and
characterizations," Phil. Trans. R. Soc. Lond. A 356, 283-296, (1998)

9. A. Nejadmalayeri, "Optical Coherence Tomography," (2001)

10. V. Mizeikis et al., J. Nishii, S. Matsuo et al.," Femtosecond
laser micro-fabrication for tailoring photonic crystals in resins and
silica," Journal Photochemistry and Photobiology A: Chem. 145, (2001)

11. M. Hirano, K. Kawamura, H. Hosona, " Encoding of holographic
grating and periodic nano-structure by femtosecond laser pulse,"
Applied Surface Science 197-198, 688-698 (2002).

12. K. Minoshima, A. Kowaleviez, E. Ippen, J.
Fujimoto, "Fabrication of coupled mode photonic devices in glass by
nonlinear femtosecond laser materials processing," Optics Express
645, Vol.10, No.15, (2002).

13. H. Lubatschowski,  A. Heisterkamp,  F. Will,  A. Singh,  J.
Serbin,  A. Ostendorf,  O. Kermani,  R. Heermann, H. Welling, W.
Ertmer, "Medical applications for ultrashort laser pulses," RIKEN
Rev., No. 50 (2003).

14. A. Rode, E. Gamaly, B. Luther-Davis, A. Chan, R. Lowe, P.
Hannaford, "Subpicosecond laser ablation of dental enamel," J.
Applied Physics Vol. 92, No. 4, (2002).

A postdoctoral position is open for an experienced individual in the
area of optical properties of materials at Wayne State University
Department of Chemistry. A candidate is sought to apply femto-second
time-resolved spectroscopy to organic opto-electronic Materials
(molecules, dendrimers,and polymers).  The successful candidate will
have experience with pump-probe spectroscopy, interfacing electronic
equipment, femtosecond lasers and optics.

For more information candidates should contact: Dr. Theodore Goodson
III at tgoodson@...


--
Theodore Goodson III  Ph.D.
Assistant Professor of Chemistry
Department of Chemistry, room 59
Wayne State University
Detroit, Michigan 48202
Tel. 313-577-6918
Fax  313-577-8822
tgoodson@...

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Carefully-shaped femtosecond pulses of light can now enhance the
yield of chemical reactions and synthesize novel molecules. Gustav
Gerber, one of the pioneers of laser chemistry, talks to Rob van den
Berg about his work.

Coherent control
For hundreds of years chemists have been heating, stirring and
pressurizing their reaction mixtures to encourage molecules to
undergo specific changes. Unfortunately, such "shake and bake"
techniques are not always particularly selective or efficient,
especially when it comes to the synthesis of complicated molecules
which may require many processing steps.

Recent optical research by chemists and physicists around the world
looks set to change that situation. For several years, scientists
have been quietly developing ways to directly manipulate the
electronic structure of the molecule using laser pulses, forcing
individual bonds to break and reattach.

The ultimate aim is to establish optical synthesis techniques that
can deliver a higher yield with less unwanted by-products, or produce
molecules that are hard to make by other means. The idea is that
laser pulses aligned to the exact frequency of a chemical bond can
deliver just enough energy to cause selective breakage of bonds.

In initial experiments, unfortunately, this selectivity was lost due
to the rapid redistribution of energy within the molecule. As a
result, laser excitation became simply an expensive method of heating
up the entire molecule. However, the use of femtosecond Ti:sapphire
lasers, pulse-shaping devices and sophisticated feedback algorithms
now looks set to change the situation.

Coherent control

Today's state-of-the-art approach to laser chemistry is called
coherent control. It involves making an initial guess at the shape of
the optical pulse that will excite the molecules and start the
reaction. The pulse is generated and the reaction products that form
as a result are detected and analysed by a learning algorithm. It
then adjusts the pulse's duration, phase and amplitude to increase
the yield of the reaction. After several iterations the best pulse
shape for the reaction is found. In a typical experiment, it takes a
matter of minutes to test thousands of different laser pulses and
find the most suitable pulse parameters.


Compounds
Gustav Gerber, a professor of experimental physics at the University
of Würzburg, Germany, is one of the technique's pioneers. Gerber
thinks that the technique offers many possibilities - creating novel
stable or metastable molecules, obtaining better image-quality in
microscopy and improving optical data transfer, for instance. "This
scheme was first applied to increase the fluorescence of a large dye
molecule, but already, one year later, we have used it to optimize
the outcome of a dissociation reaction," Gerber said.

In the coherent control method, two diffraction gratings and a liquid-
crystal multi-channel modulator (LCM) are used to adjust the shape of
the optical pulse. The first grating separates the individual
wavelengths within the pulse, while the multi-channel modulator gives
each wavelength a specific phase delay. Finally, the wavelengths are
recombined into a single pulse by the second grating. The process not
only reshapes the pulse but also reorders the wavelengths within it
so that they strike molecules in a predetermined sequence.

But because the LCM has 128 channels that can each be set at 4000
different levels, an astronomical number of different laser pulse
shapes can be generated. To find the optimal shape, an evolutionary
algorithm is used. Each pulse is labelled by the setting of the
individual modulator channels. This setting works as a kind of
genetic code and forms the basis for a process similar to natural
selection.


Schematic
Using a random setting of the individual modulator channels, the
chemical reaction in question is initiated, and its products are
detected. The reaction is then performed again using slightly
different settings. A computer analyses the results and determines
which are the most "successful" pulses - that is, which have
generated the largest quantity of the desired product. Only the most
successful pulses are used to generate offspring, becoming
the "parents" for the next generation of pulses. After a surprisingly
small number of generations, the optimal pulse shape is reached.

The system acts rather like a very efficient analogue computer,
solving the problem depending on the conditions set by the
experimenter. "Basically, it is the system itself that determines
what it needs at each instant of time," said Gerber."It is as if the
molecule effectively solves the Schrödinger equation, and determines
at what time it needs what frequencies."

On the experimental side, in the last four years Gerber's group has
discovered numerous examples of reactions in which the product yield
may be enhanced using the coherent control technique.


Pulse shaping
"For instance, in the molecule CH2ClBr it is very difficult to break
only the C-Cl bond and leave the C-Br bond intact," said Gerber. "Our
method proved to be four times better than conventional synthetic
chemistry." His group has obtained a similar enhancement in the
removal of a carbonyl ligand (CO) from organometallic complexes like
Fe(CO)5.

"In the pharmaceutical industry synthetic chemists use acid groups to
protect certain parts of a molecule during reactions," said
Gerber. "After that you have to get rid of these acid groups, but
unfortunately, other molecular groups often break off at the same
time and are lost."

Gerber has succeeded in decreasing this unwanted loss by a factor of
five. He was also the first to make the method work in liquids by
selectively exciting complex dye molecules that have overlapping
absorption spectra. It had been thought that the complex interactions
between the excited molecule and surrounding solvent molecules would
cause problems, but this has not turned out to be the case.

Theoretical success

Researchers now want to take a step further, and find out what it is
that determines the optimal laser field (pulse shape). For relatively
simple processes, like the ionization of a calcium atom, Gerber
succeeded in finding out why the laser pulse came out as it did. But
he admitted: "If we want to try to understand what the molecules are
telling us, we need the help of theoreticians."

A group from the Free University of Berlin led by Ludger Wöste and
Jörn Manz has recently managed to decipher the reaction dynamics
underlying the optimal laser field as determined by coherent
control. "With ab initio quantum calculations and simulations of wave
packet dynamics we were able to decode the optimal femtosecond pulse
generated by adaptive learning techniques," explained Wöste. "That
was our main goal: to understand exactly what the light pulse does to
the molecule. The first part of the pulse is for excitation and the
second for ionization."


Pulse shaping (2)
Gerber also explains that a common criticism of laser chemistry -
that it is a technique that will never be suitable for generating
macroscopic quantities of a product - is also no longer an issue. His
approach is as follows:

"We first determine the optimal laser field with a 1 kHz laser in the
gas phase, but then copy this on a different system with a much
higher repetition-rate and perform the same experiment in the liquid
phase at a much higher density," said Gerber. "In this way we are
able to produce the same microgram to milligram quantities in 24
hours as 'classic' synthesis of a complicated substance, which
requires many separate steps. And the operating costs of a laser are
much lower."

Gerber and his team are now looking into using LCMs to change the
polarization state of each laser pulse. In this way they hope to be
able to address the 3D properties of molecules and pull a chemical
bond in a specific direction. Ultimately, this may enable synthesis
of either the left or right-handed form of molecules - a capability
that can be crucial for making pharmaceutical compounds, where often
only one of the two forms is biologically active.

Ultimately, the pulse-shaping techniques developed for laser
chemistry could also have important applications in other fields. In
telecommunications, the shape of a light pulse travelling along an
optical fibre tends to distort over long distances. The effect, known
as dispersion, might be preventable by pre-compensating the light
pulses with a pulse shaper developed for laser chemistry.

In biological imaging, multi-photon laser microscopes use femtosecond
pulses to generate 3D images of a sample. The images from deeper
layers tend to be poor-quality, because the laser light is distorted
as it passes through the upper layers.

"With a pre-compensated pulse, we might be able to correct for this,
increasing the resolution and contrast ratio of the images," said
Gerber. He sees similar benefits in the fields of materials
micromachining with lasers and laser surgery.

About the author

Rob van den Berg is a freelance science and technology journalist
based in the Netherlands.

A bit of hopefully on-topic self advertising :

A key part for pump probe experiments is a synchronizing
controller.
Our laser sync controller is able to synchronize a picosecond
or femtosecond laser to a synthesizer with a phase noise better
than 1ps rms.

While the current series is recommended up to 200MHz, a new
controller targeted for frequencies of 500MHz or higher is
under development.

http://www.ibrtses.com/products/sync.html

Rene

The Femtosecond Kit FemtoStart from Del Mar Ventures represent an
excellent compromise between time and cost. Containing all necessary
optical and mechanical elements together with a thorough instruction,
it enables the user to achieve stable femtosecond lasing after a
short period of time. FemtoStart kit can be used as introductory
system in colleges and universities for undergraduate and graduate
training.
FemtoStart Kit is an excellent tool for research groups who would
like to learn more about opportunities of using femtosecond laser
pulses in a variety of applications including physics, chemistry,
biochemistry, biology, new material research, semiconductor physics
and optical communications, space research and medicine.

Basic FemtoStart Kit's configuration correspond to 100, 50 or 20
femtosecond Ti : sapphire lasers. Optional configurations are also
possible.  FemtoStart kit has several advantages compared to fixed
setups; e.g. repetition rates may be varied from 70 to 140 MHz. We
recommend 5 W diode pumped solid state (DPSS) laser (Verdi from
Coherent or Millenia from Spectra-Physics) as a pumping source,
however any Ar-ion laser or diode-pumped solid-state laser with 3 –5W
output power will do the job.

Del Mar Ventures product portfolio includes many innovative products
for scientific and applied research as well as standard optical,
laser and detector components. We supply MCP based detectors and
imaging systems, IR viewers, femtosecond lasers and systems, optical
components including crystal, holographic and diffractive optics and
other products. Please visit our web site at http://www.sciner.com/.
Here you'll find further information about our newest developments
and product details.
OpticsLand, a presicion optics division of Del Mar Ventures, produces
precision ultraviolet, visible and infrared optics from fused silica,
crystal quartz, calcium fluoride, barium fluoride, magnesium
fluoride, sapphire, germanium, calcite, glass and other materials.
The product line includes lenses, windows, prisms, mirrors,
polarizers, retarders, beamsplitters, filters, etalons etc.
OpticsLand provides engineering and contract manufacturing of
precision optical components and systems.

For more information, visit Del Mar Ventures' Web site at:
http://www.sciner.com/CDP/kit.htm e-mail at: femto@...

Dr. Sergey Egorov
Del Mar Ventures
12595 Ruette Alliante #148
San Diego CA 92130
V/fax +1 (509) 752-0123
delmar@...
http://www.sciner.com/

FROM:
Monique Martin
Directeur de recherche au CNRS
UMR ENS CNRS 8640, PASTEUR
Departement de Chimie
Ecole Normale Superieure
----------------------------------------------------------------

VIth International Conference on Femtochemistry
(FEMTOCHEMISTRY VI) to be held in Paris, France, from Sunday July 6
to Thursday July 10, 2003. It is the 6th in a series on the latest
research in femtosecond and picosecond molecular processes in
Chemistry and Biology, an ever-growing field, where new research
areas are constantly opening up, and one which both stimulates and
accompanies the development of ultrafast technologies.
http://www.chimie.ens.fr/w3femto6/

Rapid measurement of high fields.
From PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 614  November 20, 2002   by Phillip F. Schewe, Ben Stein, and
James Riordon


Physicists from the Tata Institute and the Institute for Plasma
Research in India have recorded in detail, for the first time, the
huge magnetic spike encountered by atoms in a sample bearing the
brunt of an intense laser shot.
Fields as great as 27 megagauss, roughly 50 million times the
strength of Earth's magnetic field, come about very quickly in the
following way: the 10^16-watt/cm^2 pump laser beam strikes an
aluminum target, the surface layer of atoms is quickly ionized, and a
stream of very fast electrons is released into the body of the
target, inducing the huge field. Many high-power lasers around the
world study the effects of intense light upon a solid sample. The
chief achievement of the Indian researchers is to look at this
process with unprecedented temporal precision, monitoring the rising
magnetic field in femtosecond intervals by watching the polarization
of a delayed secondary laser beam reflected from the particle plasma
engulfing the sample.
Femtosecond knowledge of megagauss fields might have a bearing on
designs for nuclear fusion reactions, and  for studying other
subjects where high magnetic fields are important—NMR, Hall effect,
and perhaps even fast magnetic information storage and switching
devices. (Sandhu et al., Physical Review Letters 25 November 2002;
contact G. Ravindra Kumar, Tata Institute, grk@...; 91-22-
2152971 x 2381; www.tifr.res.in )

Terahertz waves penetrate the world of imaging

Foiling terrorists, detecting cancer and designing new drugs are just
some of the potential applications for equipment that exploits the
unique properties of terahertz waves. Oliver Graydon looks behind the
scenes at one of the hottest sectors in photonics research today.

From Opto & Laser Europe October 2002.
Detecting weapons concealed underneath clothing, analysing the
contents of suspicious-looking envelopes, or even spotting the onset
of cancer: these are just some of the exciting prospects that have
been turning terahertz wave research into one of the most talked-
about topics in photonics.
Terahertz waves are electromagnetic waves that have a frequency of
between 100 GHz and 30 THz and lie between the infrared and microwave
parts of the spectrum. What makes these waves so fascinating to
scientists is their ability to penetrate materials that are usually
opaque to both visible and infrared radiation.
For example, terahertz waves can pass through fog, fabrics, plastic,
wood, ceramics and even a few centimetres of brick - although they
can be blocked by a metal object or a thin layer of water. The way in
which terahertz waves interact with living matter has potential for
highlighting the early signs of tooth decay and skin or breast
cancer, or understanding cell dynamics.
Growing demand
The list of potential customers for terahertz wave technology is
growing all the time. The military wants high terahertz and
millimetre-wave imagers that are able to "see through" bad weather;
chemists want spectroscopy equipment for analysing the structure of
new drugs; and airports arguably need better security-screening
equipment.
As a result, research on terahertz waves is fast evolving beyond
being a mere scientific curiosity. There is now a buzz of activity as
researchers around the world race to build the first practical
terahertz imaging and spectroscopy equipment.
"The field has exploded - it's incredible," said Paul Planken from
Delft University of Technology, who is an active researcher in the
field. "A number of years ago I tried to make a list of all the
papers published on terahertz generation and detection. I started
with 1969 and there was just one paper. Now I see so many papers
being published that I refuse to believe that 10 years from now there
will be no real-life applications for terahertz technology."
The Delft team has built a state-of-the-art system for generating and
detecting terahertz waves and has already applied it to various
imaging tasks, such as filming the diffusion of a gas through
polystyrene foam. The team is now investigating biomedical
applications and has recently demonstrated a method of dramatically
improving the resolution of a terahertz imaging system.
Powerful potential
Although the majority of the initial research on terahertz imaging
was carried out by Martin Nuss and colleagues at Bell Labs in the
early 1990s, today the leading research group in the field is
undoubtedly Xi Cheng Zhang's group at Rensselaer Polytechnic
Institute, US. For more than a decade the group has been pushing back
the frontiers of terahertz technology and has published a huge number
of papers on the topic. The Institute has recently established a
dedicated facility for terahertz studies, the Center for Terahertz
Research, and has received a $1m (€1.03m) donation from the W M Keck
Foundation.
At this year's CLEO conference in May in California, Zhang and co-
workers from the University of Adelaide, Australia, and the New York
State Department of Health, US, reported initial results on the use
of terahertz waves to screen potential biohazards.
The team found that terahertz waves could detect and classify unknown
powders that were sealed inside an envelope. Using a transmission
terahertz imaging technique operating at 0.3 THz, the team
successfully detected and distinguished between samples of flour,
salt, baking soda and bacterial spores placed inside a paper
envelope.
Outside academia, one of the first companies attempting to cash in on
the market potential and commercialize terahertz technology is
Teraview, a start-up based in Cambridge, UK. With a headcount of 13,
the firm was spun out of Toshiba Europe's Research Laboratory in
April 2001 to develop equipment for medical imaging, drug development
and security screening.
The start-up has not wasted any time. Having built prototype medical-
imaging equipment, the Cambridge-based firm has tested its terahertz
technique for skin-cancer detection in field trials at UK hospitals,
as well as using it to image semiconductor chips for electronics
companies.
"Although there are lots of universities carrying out research in the
field, we are the first company dedicated to commercializing
terahertz technology," claimed Don Arnone, Teraview's chief executive
officer. "We're starting to bring products to market and will have a
product launch shortly."
Teraview's prototype medical imager, the TPI Scan, resembles a
photocopier on wheels. It squeezes the laser, optics and electronics
needed for terahertz imaging into a self-contained 1 m long, 1 m high
and 60 cm wide trolley that weighs 150 kg. The TPI Scan can scan a
sample of up to 25 x 25 mm in size in less than 1 min, and features
an integral camera that simultaneously generates a visible image of
the sample. The resolution of the scanning is 200 µm in one axis and
20 µm in the other.
The equipment is likely to retail for around Ł250,000 (€395,000) and
will be used to help diagnose skin lesions and plan surgery. It
features an external CD writer, USB port and network connection for
data transfer.
As for customers, Teraview has already signed a distribution
agreement with Bruckner, which makes analysis equipment for the
pharmaceuticals industry. "We're looking to align ourselves with
established players, such as Bruckner, in each of our key markets,"
said Arnone. "We'll produce a terahertz engine [a module for emitting
and detecting terahertz waves] and then supply it to commercial
collaborators for them to market."
Teraview is also working closely with the semiconductor group at
Cambridge University to develop a semiconductor laser that operates
in the terahertz region. To date, terahertz waves are usually
generated by illuminating a piece of semiconductor, such as gallium
arsenide, with femtosecond pulses from a solid-state laser such as a
Ti:sapphire laser. Although this approach works well and femtosecond
lasers are getting smaller and cheaper all the time, it is still a
relatively bulky and expensive solution. Ultimately, the preferred
source for many commercial applications would be a compact
semiconductor laser.
Quantum leap
The development of such emitters has recently taken a leap forward,
thanks to the invention at Bell Labs, US, of the quantum-cascade
laser, which emits in the mid-infrared at around 4 µm. Semiconductor
scientists are now adapting the technology to design lasers that are
operational in the far-infrared and terahertz regions.
Earlier this year, researchers from Teraview, the University of
Cambridge, and the National Institute for the Physics of Matter
(INFM) in Italy made a series of quantum cascade lasers that operate
in pulsed and continuous-wave mode at 4.4 THz (wavelength 68 µm).
Although the lasers can only currently work at low temperatures of up
to 50 K, they emit up to 2 mW of singlemode terahertz radiation. The
challenge now is to raise the operational temperature, which,
although it may take several years, is definitely feasible.
"I think the development of a quantum cascade laser is a major
milestone, certainly - if they are able to make one that works at
room temperature," said Planken. "Up until recently most people
generated terahertz radiation by illuminating GaAs with femtosecond
laser pulses or by optical rectification with telluride electro-optic
crystals. Now they have a third candidate."
Whether it will be its applications in medicine, security or
pharmaceuticals that take off first is hard to predict, but once
terahertz technology has a toehold in one market it is likely to
quickly spread to others.
"Some people say that terahertz radiation will replace X-rays, but
that's not true," said Planken. "It will not happen because the human
body is made up mostly of water, so you do not get much penetration.
Water is a very good terahertz application killer."


T-rays explained
The powerful nature of terahertz analysis stems from the fact that it
is a coherent technique that can make both amplitude and phase
measurements. Unlike common optical spectroscopic techniques that
only measure the intensity of light at specific frequencies,
terahertz experiments often measure the temporal electric field of
terahertz pulses that have interacted with (i.e. reflected off or
passed through) a sample.
A Fourier transformation of this time-domain data discloses the
amplitude and phase of the pulse and reveals a wealth of information
about the sample. For example, it allows precise measurements of the
refractive index and absorption coefficient of a sample. Molecules
also have unique rotation and vibration resonance lines in the
terahertz spectrum that can be used as terahertz fingerprints.
The most popular way to generate terahertz waves is to illuminate a
carefully engineered semiconductor crystal, such as GaAs, with
femtosecond pulses of visible light. This bombardment creates
ultrashort pulses of terahertz radiation (typically of the order 100
fs) that can be used for imaging and spectroscopy.
As the pulses reflect from different depths within an object,
an "image slice" at a desired depth can be built up by carefully
controlling the timing of the pulse detection. A 3D image can be
constructed by putting together a number of these sliced images.
Coherent detection of the pulses is achieved by illuminating a second
crystal with both the terahertz pulses and a portion of the visible
femtosecond pulses that is split off from the original beam and has
undergone a suitable time delay.


Breakthrough in resolution
Paul Planken and Nick van der Valk at Delft University of Technology
in the Netherlands have improved the resolution of a terahertz
imaging system by a factor of almost 1000. The development is
significant because it could open the door to terahertz studies of
tiny structures, such as living cells.
Imaging systems conventionally have a diffraction-limited resolution
(spot size) that is equal to about half of the optical wavelength. In
the case of terahertz waves, which have a wavelength of about 1 mm,
this corresponds to a resolution of about 0.5 mm - far too big for
cell imaging. However, the Delft team has now demonstrated that it
can create and measure terahertz spot sizes as small as 8 µm, and
that 1 µm may ultimately be possible.
The Dutch researchers achieve such small focal spots by using a sharp
metal tip to locally bend and concentrate the electric field of the
terahertz beam near the surface of a GaP crystal. The mechanism is
analogous to how a lightning rod acts to bend electrical field lines.
In the future the method could be used with a terahertz pump to probe
experiments by placing thin samples on the crystal underneath the
tip. The sample is illuminated by the pump beam from above and a
tightly focused probe beam from below. The crystal is then raster
scanned under the tip to generate a 2D terahertz image.

ULTRAFAST LASER SURGERY

The Center for Ultrafast Optical Science of the University of Michigan
announces the use of femtosecond laser pulses on surgery, in
particular for ophthalmology.
Ultrashort pulsed lasers allow for non-thermal laser-tissue
interaction.
Cuts can be made with little collateral damage. Users of surgical
lasers will recall that incisions made with thermal lasers often do
not bleed because the tissue is locally coagulated or cauterized.
Skin or other vascular tissues will bleed if cut with an ultrashort
pulsed laser. For certain applications, the type of cut produced by
ultrashort lasers is useful. This laser-tissue interaction is known
as photodisruption.  The high intensity of the beam transforms
ordinary matter into a micro-plasma extremely rapidly. The energy in
the plasma is reabsorbed by surrounding tissue, which may cause
undesired collateral damage. However, if the parameters are chosen
correctly, a very clean cut can be made. The usual goal is to exploit
the ability of femtosecond pulses to produce photodisruption with
very small pulse energies, and therefore, very small
collateral tissue damage.

More information: http://www.eecs.umich.edu/USL/Medical/

From:
IMAAC/UNIDO VIRTUAL LASER MATERIALS PROCESSING FORUM
---------------------------------------------------
News
---------------------------------------------------
Number 11

Do you want to share your ideas about future femto/atto/zeptosecond
lasers? Here is an article from Opto & Laser Europe June 2002:

Racing against the clock
Wilson Sibbett, the father of femtosecond laser physics, talks to
Jacqueline Hewett about his quest to generate ultrashort pulses of
light and put them to good use.


  Wilson Sibbett
When Wilson Sibbett was embarking on his academic career in the mid-
1960s, the idea that femtosecond lasers would one day be put to use
as precision scalpels for cutting microscopic holes in materials must
have seemed far-fetched.
Little did Sibbett realize that some 30 years later he would become
the first person to generate femtosecond pulses using Kerr-Lens
modelocking (KLM), a technique that has now been adopted worldwide
and has earned him international recognition in the laser community.
Sibbett describes the history of ultrashort pulse-generation as
resembling a staircase. "You make a step up and then you consolidate,
making incremental developments and thinking up lateral
applications," he explained. "And then some bright spark makes a
quantum leap into the next regime and you go up again. Today the
staircase is still moving. I have every expectation that it will
continue to deliver absolutely fascinating science in the future."
Beyond attoseconds
This steady rate of progress means that pulses of just a few
attoseconds in duration (10_18 s) - a time regime that was
unimaginable five to 10 years ago - are fast becoming familiar
territory. In fact, optical scientists are now striving to crack the
next challenge and produce pulses as short as a zeptosecond (10_21
s). This may sound like science fiction, but Sibbett says that it is
well on the way to becoming reality.
Current theories suggest that it might be possible to exploit the
polarization properties of petawatt lasers to enter the zeptosecond
regime. Once there, studying the inner workings of atomic nuclei
becomes a real possibility. "It's really starting to become very
exciting fundamental physics," commented Sibbett. "Depending on the
spectral region in which we generate the pulses, a variety of new and
different experiments will emerge."
During the past 30 years, Sibbett has earned himself an international
reputation in the field of ultrashort pulses, and has built up an
enormous bank of knowledge. Asked if he has ever considered other
career avenues, he gives a surprising response. "I was tempted to go
back to farming and in fact did go back for a short time," he
admitted. "One of my original career objectives was to be a science
teacher and a farmer as a sort of joint occupation. The farming
instinct didn't leave, but I was persuaded to return to science."
Today, lasers that produce ultrashort pulses are finding applications
in biology and materials processing. Most of these applications hinge
on the KLM discovery that Sibbett made in 1990. This gave researchers
the ability to generate picosecond and femtosecond pulses with high
average and peak powers over a broad spectral range. At the time,
this was a great improvement on the femtosecond dye lasers that were
then commonplace.
Laying the foundations
In fact, it was the discovery of dye lasers some 20 years earlier
that had first inspired Sibbett to embark on an academic career in
the world of optics. In particular, it was the study of short pulses
that appealed to his engineering instincts. He started a PhD at
Queens University in Belfast, Northern Ireland (completing it at
Imperial College, London), looking into methods of generation and
instrumentation to measure ultrashort pulses. "The idea of having a 1
ps pulse, or even a sub-picosecond pulse, was quite a fascination.
The problem was deciding how to measure them," explained Sibbett.
Sibbett's research into short-pulse continuous-wave dye lasers at
Imperial College continued for 14 years. But there was a problem.
These lasers did not have the tunability to access the wavelengths
needed for optical communications. To overcome this problem, Sibbett
began exploring colour-centre lasers working at liquid-helium
temperatures and emitting in the telecoms band between 1.4 and 1.6
µm. But as this research continued, other considerations entered the
equation.
From a domestic point of view, Sibbett found that his quality of life
was suffering in London. He had never intended to remain in the
capital, and moved north in 1985 to continue his research at St
Andrews University in Scotland.
In Scotland Sibbett managed to raise the working temperature of his
lasers to match that of liquid nitrogen (77 K), and this achievement
transformed his work. For the first time, Sibbett's research on so-
called "coupled-cavity modelocking" and colour-centre lasers was
yielding results that were competitive with those of the leading US
research centres, such as the Bell laboratories in New Jersey.
Tempted by the lure of greater bandwidth and tunability, however,
Sibbett shifted the focus of his research to a newer gain medium,
Ti:sapphire, and began duplicating some of his coupled-cavity
modelocking experiments that relied on pieces of customized optical
fibre. The discovery that was looming would be revolutionary.
"We made the amazing observation that we didn't need the fibre at all
to get the modelocking effect working," explained Sibbett. "We found
that the nonlinearity was in the Ti:sapphire crystal itself." This
simplified everything: combining the gain of the crystal and its
inherent nonlinearity yielded modelocking in one resonator working at
room temperature.
"It was such a staggering breakthrough that it was almost
unbelievable," said Sibbett. "Some people called it magic because it
was just so different." Sibbett and colleagues had witnessed the
first generation of femtosecond pulses using KLM.
Today, the optical nonlinearities that give rise to modelocking can
be accessed using tiny, compact lasers. Femtosecond pulses with
average powers of 20 mW are readily achieved by pumping a CR:LiSAF
crystal using the everyday red diodes that are found in the DVD
industry. Such a system also has the inherent advantages of
portability and self-containment. The latest compact versions of
these diode-pumped femtosecond lasers can be powered with "AA"
batteries and operate at a total input electrical energy of just 1 W.
Sibbett has plans to use this sort of system to mimic the UVA and UVB
components of sunlight. "We can apply this in areas of oncology where
you might want to look at the damage caused within tissue in that
part of the spectrum," he explained. Other medical applications
include corneal surgery for vision correction, in which this compact
system could replace conventional excimer laser systems.
Femtosecond networks
Another application set to benefit from ultrashort pulse lasers is
data communications. As director of the ultrafast photonics
collaboration (OLE November 2000 p28), Sibbett is driving this area
forward. But in order for femtosecond lasers to succeed in this vein,
he admits that a breakthrough in semiconductor materials is required.
"We are thinking that the combination of quantum confinement with
various semiconductor structures, and also the combination of
photonic band-gap structures, might enable us to get both optical and
optoelectronic hybrid devices that would allow us to take this
technology into the next regime," said Sibbett. If integration can be
achieved, this opens the door for femtosecond networks.
Sibbett recalls a time during his days at Imperial College when
someone to whom he was introduced asked him: "I believe you work with
short pulses?" Wanting to impress, he replied that pulses of around
100 fs were now feasible. His enquirer's response was somewhat
unexpected: "That's a bit long for us. What would be really nice
would be if you could get down to 10_38 s. That gets you into some of
the theories that relate to the big bang."
Even if light pulses never reach that milestone, one thing is for
sure: as long as physicists' fascination with ever-shorter pulses
continues, there will be more breakthroughs, leading to more chapters
of physics textbooks being rewritten.

Del Mar Ventures offers Yb:GdCOB single crystals of high overall
material quality grown using recently improved techniques.
Ytterbium-doped calcium oxoborate of Yb3+:Ca4GdO(BO3)3, known as
Yb:GdCOB, has recently shown promising spectral qualities resulting
in impressive femtosecond lasing performance [1-5]. Yb:GdCOB single
crystals have a fortunate relationship between emission cross-
section, lifetime and bandwidth and are thus prime candidates for a
new generation of high peak power lasers. With a very long upper-
state lifetime, Yb:GdCOB lasers tend to store a lot of energy in the
upper laser level.
For additional information about Yb:GdCOB crystals or to request a
quotation please contact us at the address below.

Del Mar Ventures product portfolio include many innovative products
for scientific and applied research as well as standard optical,
laser and detector components. We supply MCP based detectors and
imaging systems, IR viewers, femtosecond lasers and systems, optical
components including crystal, holographic and diffractive optics and
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Here you'll find further information about our newest developments
and product details.
OpticsLand, a precision optics division of Del Mar Ventures, produces
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crystal quartz, calcium fluoride, barium fluoride, magnesium
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The product line includes lenses, windows, prisms, mirrors,
polarizers, retarders, beamsplitters, filters, etalons etc. Del Mar
Ventures provides engineering and contract manufacturing of precision
optical components and systems.

[1] A. Kemp, "Yb:GdCOB as a Gain Material in Ultra-compact
Femtosecond Lasers: A Review of Existing Work," University of St.
Andrews, St. Andrews 2000.
[2]  F. Druon, F. Auge, F. Balembois, P. Georges, A. Brun, A. Aron,
F. Mougel, G. Aka, and D. Vivien, "Efficient, tunable, zero-line
diode-pumped, continuous-wave Yb3+: Ca(4)LnO(BO3)(3) (Ln = Gd,Y)
lasers at room temperature and application to miniature lasers,"
Journal of the Optical Society of America B-Optical Physics, vol. 17,
pp. 18-22, 2000.
[3]  F. Druon, F. Balembois, P. Georges, A. Brun, A. Courjaud, C.
Honninger, F. Salin, A. Aron, F. Mougel, G. Aka, and D.
Vivien, "Generation of 90-fs pulses from a mode-locked diode-pumped
Yb3+: Ca4GdO(BO3)(3) laser," Optics Letters, vol. 25, pp. 423-425,
2000.
[4]  F. Mougel, K. Dardenne, G. Aka, A. Kahn-Harari, and D.
Vivien, "Ytterbium-doped Ca4GdO(BO3)(3): An efficient infrared laser
and self-frequency doubling crystal," Journal of the Optical Society
of America B-Optical Physics, vol. 16, pp. 164-172, 1999.
[5]  F. Auge, F. Balembois, P. Georges, A. Brun, F. Mougel, G. Aka,
A. Kahn-Harari, and D. Vivien, "Efficient and tunable continuous-wave
diode-pumped Yb3+: Ca4GdO(BO3)(3) laser," Applied Optics, vol. 38,
pp. 976-979, 1999.

Del Mar Ventures
12595 Ruette Alliante #148
San Diego, CA 92130
v/fax: (509)752-0123
femto@...

Lasers lick dentists' drills

6 August 2002

Dentists could soon swap their drills for painless tools based on
pulsed infrared lasers. Andrei Rode of the Australian National
University and colleagues have shown that ultrashort pulses of
radiation from powerful modern lasers can safely remove material from
a tooth without damaging the surrounding area. Previous attempts to
develop this technique have failed because they used longer-lasting
laser pulses that heated and cracked healthy parts of the tooth (A
Rode et al 2002 J. Appl. Phys. 92 2153).
Lasers are widely used in medicine to remove soft biological tissue,
and scientists are keen to develop a laser-based tool to replace
dentists' drills. But hard dental material can only be removed by
very powerful lasers.
Such high powers have been achieved in previous studies by using
laser pulses lasting several picoseconds, or 10-12 seconds.
These 'heat ablation' techniques proved unsuccessful because they
were too hard to control - strong thermal shocks led to uneven
removal of material and made the teeth crack.
But lasers have now been developed that emit more powerful bursts of
radiation that last just tens of femtoseconds, or 10-15 seconds.
Using such pulses, Rode's team has successfully removed dental enamel
without the excessive heating that can damage healthy tissue. In
contrast with earlier attempts, the new technique removes matter by a
process known as electrostatic ablation.
The team used two titanium-sapphire lasers that emitted infrared
pulses with a frequency of 1 kHz. One laser emitted pulses lasting 95
fs with an average power of 0.5-0.6 W, and the other one emitted
pulses lasting 150 fs with an average power of 0.8-1.0 W. Healthy
human teeth - donated for medical research - were used in the study.
Rode and co-workers found that these laser pulses were powerful
enough to eject electrons from atoms on the surface of the teeth,
ionzing the atoms and molecules in the dental enamel. This ionization
created a local electric field strong enough to remove the ions from
the enamel altogether. Since the laser pulses are shorter than the
characteristic heat conduction time of dental matter, there is no
time for heat ablation - and its damaging effects - to occur.
The researchers admit that their technique removes enamel around a
hundred times more slowly than mechanical drills, but they say that
decayed dental material - which is softer than the healthy teeth used
in their experiment - could be removed ten times faster than this.
Author
Katie Pennicott is Editor of PhysicsWeb

> 			 Summer School on
>
> 	 Coherent Control in Atomic and Molecular Systems
>
> 		 monday 30 sept - saturday 5 oct 2002
>
> 			    CARGESE (Corsica, France)
>
> The past few years have seen a surge in activity aimed at manipulating
quantum interference phenomena with lasers in order to control molecular,
atomic, and optical processes. In particular, use of coherent light in the
weak and strong field regimes, in a field termed quantum coherent control
has been shown to lead to great selectivity of molecular photo-dissociation;
atomic and molecular photo-ionization; phase dependent current
directionality in semiconductors; adaptive pulse-shaping control of
branching reactions; chiral molecules separation; nanodeposition of
predetermined patterns by purely optical means; and control of High
Harmonics generation.
> Simultaneously with the above, great progress has been made in using
quantum systems as computation and storage devices; to secure information
transmission; and even for teleportation. The resulting field, often called
quantum information is strongly linked and often has similar objectives to
those of quantum control.
>  The goal of the Summer School is to deliver the basics and the recent
issues of the field to Young Researchers (PhD students, post-doctorates,
young scientists...) and new comers to the field.
>
> Registration and Details :
> http://www.irsamc.ups-tlse.fr/irsamc/cargese/princip.htm
>
>
> Topics include :
> 1) Introductory Lectures (IL) giving (or recalling) the ground bases which
should be known to understand the main topics of the school :
> 	 Introduction to light-matter interaction
> 				 photodissociation and scattering theory
> 				 Pulse shaping techniques
> 				 wave packet propagation techniques
>
> 2) General Lectures (GL) giving the essential of each kind of Control or
Laser matter interaction scheme :
> 	 Principles of  Coherent Control
> 			 Optimal Control
> 			 Strong Field Phenomenology
> 			 STIRAP
>
> 3) Case Studies (CS) giving application examples of each topic covered in
the General Lectures :
> 	 Case studies of Coherent Control
> 				     Optimal Control
> 				     strong field physics
> 				     STIRAP
>
> 4)  New Routes (NR), where new fields in which Coherent Control starts to
be applied, or could be applied :
> 	 Laser induced transparency and dark state polaritons (NR)
> 	 Quantum information (NR)
> 	 Decoherence and learning control  (NR)
> 	 Application to solid state physics (NR)
> 	 Control schemes in Laser Cooling (NR)
>
> Preliminary list of speakers
> Th. Amand (F), A. Aspect (F), K. Bergmann (D), A. Beswick (F), P.
Bucksbaum (USA), C. Dorrer (USA), M. Fleischhauer (D), G. Gerber (D), M.
Ivanov (Can), M. Shapiro (Is), B. Shore (USA), D. Tannor (Is), R. de
Vivie-Riedle (D), I. Walmsley (UK),
>
> a Poster session will be organized in order for the participants to
present their own results and to know each other.
>
> Conference fees and housing :
>  470 Euros double room
>  500 Euros single room
>  This includes registration fees and housing in small appartments (in the
village), lunches at the Institute from monday 30th lunch to sunday 6th oct
morning.
>
> 	 Early Registration (before july 15th) : 30 Euros discount
>
> Chairmen
>  Pr. Bertrand Girard, Toulouse (France)
>  Pr. Moshe Shapiro, Weizmann (Israel)
>
> Scientific committee>
>  Pr. Klaas Bergmann, Kaiserslautern (Germany)
>  Pr. Bertrand Girard, Toulouse (France)
>  Pr. Moshe Shapiro, Weizmann Inst. (Israel)
>
> Local organizing committee
> V. Blanchet, M.A. Bouchene, B. de Beauvoir, J. Degert, B. Girard, C.
Meier, M.F. Rolland
>
> Financial support from ESF ULTRA programme and European Union HCM
programme through the COCOMO research network.
>
>
>
> Bertrand Girard
> Laboratoire Collisions Agrégats Réactivité
> IRSAMC UMR 5589
> Université Paul Sabatier
> 118 Route de Narbonne
> 31062 TOULOUSE CEDEX
> FRANCE
> Phone (33) 5 61 55 64 98
> Fax (33) 5 61 55 83 17
> bertrand.girard@...
> http://www.irsamc.ups-tlse.fr/irsamc/UMR5589/300/femtoweb/principal.html
>
>

From OpticsExpress.org

Picosecond time-gated microscopy of UV-damaged plant tissue
S. Rehman and Philip B. Lukins, Univ. of Sydney

Abstract
We demonstrate that picosecond time-gated fluorescence microscopy can
be used to monitor subtle changes in the kinetics and spatial
distribution of perturbations to the molecular and cellular structure
of plant tissue caused by ultraviolet radiation. Single-molecule
experiments on Photosystem II and chloroplast preparations give
picosecond fluorescence decay kinetics that are similar to those
obtained previously on bulk samples. For green plant leaves,
localized and well-defined cellular structure is seen for normal
material whereas relatively diffuse and non-specific features are
seen after UV-irradiation indicating significant UV-induced rupture
of the cellular structure. The changes in the chlorophyll
fluorescence decay kinetics indicate uncoupling of chlorophyll
molecules in the light-harvesting system leading to inhibition of
energy reorganization and transfer in the antennae and subsequent
exciton transfer to the reaction centers.


Vol. 10, No. 8 - April 22, 2002 OpticsExpress
http://www.opticsexpress.org/

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     Postdoctoral position in
  Coherent control and femtosecond dynamics in atoms and molecules
     University of Toulouse (FRANCE)

http://www.irsamc.ups-tlse.fr/irsamc/UMR5589/300/femtoweb/principal.html
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Funded by the European Community in the frame of the COCOMO network
(Programme: IHP-RTN-99-1)
(http://www.physik.uni-kl.de/w_bergma/CoCoMoNetwork/home.html)
Reserved to citizens of European Union and Associated states
One-year postdoctoral position (extendable to two-years)

The COCOMO network projects build on recent breakthroughs that allow
unprecedented control of atomic and molecular processes by means of coherent
laser radiation. By controlling the relative phase of coherent fields, or by
careful timing of pulse sequences, one can prepare a single preselected
quantum state, or one can control branching in photoionisation or
fragmentation processes or in chemical reaction into a specified channel.

The group in Toulouse develops particularly :
- Studies of different coherent control schemes in simple systems (atoms,
diatomic molecules). These schemes are based on chirped or shaped ultrashort
pulses (or sequences of pulses). Our approach favors a carefull analysis of
the system in order to design the best suited scheme or shape.

- Time resolved photofragment imaging and/or photoelectron spectroscopy in
molecules. Studies of photodissociation, internal conversion, isomerisation
processes

- Combining the two previous approaches, coherent control schemes will be
developed in progressively more complex systems

Motivated candidates should have obtained their PhD in atomic/molecular
physics and/or ultrashort laser studies.
Moreover, an expertise in one or several of the following experimental
techniques will be appreciated :
molecular beam techniques, electron/ion imaging techniques, femtosecond
laser development, pulse shaping ...

Gross monthly salary : 3600 euros
IF YOU WOULD LIKE to join us, SEND email to :
bertrand@...
or
val@...

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Toulouse is a very nice middle size city (500 000 inhabitants) located in
the South-West of France, with a strong university tradition (more than 100
000 students).
It is the center of french (and European) aircraft and space industry
(Airbus, Ariane ..).

It is nicely located at
1h30' from the Mediterranean sea
2h30' from the Atlantic Ocean
LEss than 2h from many ski (and hiking) resorts in the Pyrenees

Many middle-age villages can be found within 1H driving in any direction.
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Recent publications of the group :

[1] V. Blanchet, C. Nicole, M. A. Bouchene and B. Girard, “Temporal coherent
control in two-photon transitions : from optical interferences to quantum
interferences,” Phys. Rev. Lett. 78 (14), 2716-9 (1997).
[2] V. Blanchet, M. A. Bouchene and B. Girard, “Temporal coherent control in
the photoionization of Cs2 : Theory and Experiment,” J. Chem. Phys. 108,
4862 (1998).
[3] V. Blanchet, M. Zgierski, T. Seidemann and A. Stolow, “Discerning
Vibronic Molecular Dynamics using time-resolved photoelectron Spectroscopy,”
Nature 401, 52 (1999).
[4] C. Nicole, M. A. Bouchene, S. Zamith, N. Melikechi and B. Girard,
“Saturation of wave-packet interferences : Direct observation of spin
precession in potassium atoms,” Phys. Rev. A 60, R1755 (1999).
[5] C. Dorrer, B. de Beauvoir, C. Le Blanc, S. Ranc, J. P. Rousseau, P.
Rousseau, J. P. Chambaret and F. Salin, “Single-shot real-time
characterization of chirped-pulse amplification systems by spectral phase
interferometry for direct electric-field reconstruction,” Opt. Lett. 24,
1644 (1999).
[6] E. Sokell, S. Zamith, M. A. Bouchene and B. Girard, “Polarization
dependent pump-probe studies in atomic fine structure levels : towards the
production of spin-polarized electrons.,” J. Phys. B 33, 2005 (2000).
[7] K. Resch, V. Blanchet, A. Stolow and T. Seidemann, “Toward Polyatomic
Wave Packet Decomposition: Final State Effects,” J. Phys. Chem. A 105, 2756
(2001).
[8] J. Degert, C. Meier, B. Girard and M. J. J. Vrakking, “Time-dependent
fragment distributions detected via pump-probe ionization: a theoretical
approach,” Eur. Phys. J. D 14, 257 (2001).
[9] S. Zamith, J. Degert, S. Stock, B. De Beauvoir, V. Blanchet, M. A.
Bouchene and B. Girard, “Observation of Coherent Transients in Ultrashort
Chirped Excitation of an undamped Two-Level System,” Phys. Rev. Lett. 87,
033001 (2001).


Bertrand Girard
Laboratoire Collisions Agrégats Réactivité
IRSAMC UMR 5589
Université Paul Sabatier
118 Route de Narbonne
31062 TOULOUSE CEDEX
FRANCE
Phone (33) 5 61 55 64 98
Fax (33) 5 61 55 83 17
bertrand.girard@...
http://www.irsamc.ups-tlse.fr/irsamc/UMR5589/300/femtoweb/principal.html

The main research subject of the Institute of Materials Chemistry
(Tampere University of Technology, Finland) leaded by Prof. Helge
Lemmetyinen is photochemistry of organic and bio-organic functional
molecules and molecular systems. This includes investigation of
primary processes of photo-excitation, excited state relaxation,
energy and charge transfer of natural and artificial molecular
systems.
The time-resolved studies of the emission dynamics is on of the key
tools for this type of research work. The instrument for the ultra-
fast emission measurements (FOG-100, CDP,
http://www.sciner.com/CDP/fog.htm ) was set up in 1997. It utilizes
the up-conversion method and in combination with 50 fs Ti:sapphire
laser (TiF50, CDP http://www.sciner.com/CDP/fstis.htm ) allows to
achieve time resolution of 100-200 fs depending on the type of
sample. This time resolution was important for investigations of the
photoinduced electron transfer of covalently linked phytochlorin-
fullerene dyad, where combination of emission and absorption time
resolved techniques was crucial in order to elucidate the mechanism
of the electron transfer and to separate the exciplex and complete
charge transfer states [1, 2].
The photoinduced electron transfer mediated by DNA was also
successfully studied by monitoring emission dynamics of the dye
molecules intercalated into DNA structure [3]. The femtosecond time
resolution and high accuracy of the emission measurements is
important for quantitative analysis of the dynamics of the studied
system. Therefore, the measured data analysis is supported by a home-
made fitting program which can account for instrument response
(measured or simulated) and can acquire global data fitting in order
to obtain the model best suitable for the complete set of the
experimental results.

1. N. V. Tkachenko, L. Rantala, A. Y. Tauber, J. Helaja, P. H.
Hynninen,
H. Lemmetyinen, Photoinduced electron transfer in phytochlorin-[60]
fulleren dyads.
J. Am. Chem. Soc. (1999), 121, 9378-9387.
2. V. Vehmanen, N. V. Tkachenko, A. Y. Tauber, P. H. Hynninen,
H. Lemmetyinen, Ultrafast charge transfer in phytochlorin-[60]
fullerene
dyads: influence of the attachment position, Chem. Phys. Lett.,
(2001) 345:3-4, 213-218.
3. A. I. Kononov, E. B. Moroshkina, N. Tkachenko, H. Lemmetyinen,
Photophysical processes in the complexes of DNA with ethidium bromide
and acridine orange: A femtosecond study, J. Phys.Chem. B, (2001)
105, 535-541.

==============================
Nikolai V. Tkachenko, Ph.D.
Institute of Materials Chemistry
Tampere University of Technology, Finland
fax: +358-3-31152108
e-mail: nikolai.tkachenko@...
WWW: http://www.tut.fi/~tkatchen

Dear Colleagues,
When nuclear reaction occur, for example neutron capture,  electron
structure of an atom significatly changes. Does anybody aware of the
experimental research on the ultrafast dynamic of atomic changes
after nuclear reaction? What is the time scale of these events? Is it
possible to observe, for example, dynamics of optical spectra changes
after nuclear reaction?

Thank you,
Dr. Sergey Egorov
Research Scientist
Del Mar Ventures
http://www.sciner.com/