We describe the molecular engineering of new highly efficient two-photon photolabile cages, based on dissymmetrical
donor-acceptor and symmetrical donor-donor systems. Complete characterizations of these new cages, based on a
biphenyl, fluorenyl or a 2,5-diphenylthienyl central core will be presented. In vitro photochemistry will be described
(uncaging quantum yield, two-photon uncaging action cross-section,...) and we will then focus on biological results
obtained in cell culture and on acute brain slices (with glutamate and fluorescence uncaging).
Having shown the feasibility of passive daytime observation on board of a 155mm gyrostabilized artillery shell, the French-German Research Institute of Saint-Louis (ISL) has started working on projectile boarded night vision systems. Laser illumination was preferred over the use of passive IR imaging mainly for reasons of detector performance and cost. The active imaging system designed for artillery shells will have to undergo accelerations of the order of 15000 g. It will begin the observation of the target area about 1000 m before impact and transmit the images to the ground station before its destruction. A laser illuminator with a peak power of 1 kW before beam shaping and a pulse duration of 50 μs with a repetition rate of 25Hz has been developed for this application. It is based on a laser diode stack emitting at 800nm. A special atten-tion has been given to the beam shaping operation. The beam divergence closely matches the field of view of the imaging optic and has a constant and homogeneous intensity profile over the target. Other fundamental criteria have also been taken into account, such as a compact size, simplicity and low cost, without losing the efficiency of the collimator. A prototype of the active imaging system with a field of view of 10° has been built, tested and validated on the ground. Integration of the illuminator into a 155 mm shell has begun.
Some experiments concerning color holography and color holographic interferometry have been conducted at ISL. In a first stage, static holograms have been recorded with c.w. lasers in PFG-03C silver-halide panchromatic holographic plates. Color holographic interferometry is at present experimented and developed. Quantitative measurements by double-exposure holography are not possible. An example, on a cantilever plate, showing the achromatic fringe, is visualized on the reconstructed image. Quantitative deformations of the plate are presented. An experimental set-up designed for the real-time holographic interferometry of phase objects is also presented. A video film, recorded at 25 frames per second and relating laboratory experiments on some fluid mechanics flows, is shown. New difficulties occur when these experiments are carried out by using pulsed lasers. Our first tests on this technique are presented. Three pulsed lasers have been used: a ruby laser, a frequency doubled YAG laser and a frequency doubled titanium-sapphire laser. Ruby and YAG lasers, delivering red and green waves, are commercially available. A special frequency doubled titanium-sapphire laser, built as ISL produces the blue line. Preliminary results are presented and discussed.
Night vision capability has become an indispensable tool for military and civilian surveillance operations. Low-light- level television (LLLTV) and Forward-Looking-IR (FLIR) devices have long been used for these applications. Nevertheless, both have their shortcomings when the identification of the target is essential for the success of the mission. LLLTV cannot provide god image resolution in ultra low-light level conditions and is very sensitivity to parasitic light. FLIR system have poor resolution when the temperature difference contrast conditions are not met.
KNbO3 yields very high non-linear coefficients. This material is attractive and widely used for the frequency doubling of cw and quasi cw near infrared laser sources. However it is not commonly used for pulsed applications. Frequency doubling of a pulsed high peak power titanium doped sapphire (Ti:S) laser with KNbO3 has been investigated. Close to 60% conversion efficiencies have been obtained in external cavity single shot operation. Factors limiting the conversion efficiency in a repetitive mode and with longer crystals have been identified. Quadrature second harmonic generation technique has been shown to overcome some of these limitations compared to single crystal technique. First experimental results for frequency doubling the Nd:YAG and Nd:YAlO 4F3/2-4I9/2 laser transition in the pulsed nanosecond regime with KNbO3 are also presented.
KEYWORDS: Holography, Holograms, Chemical process control, Diffraction, Silver, 3D image reconstruction, Helium neon lasers, Photography, Chemical reactions, Light
Using three pulsed lasers we have recorded color holograms and double exposure holograms on silver halide panchromatic PFG03C plates. The first results are shown. Quality of these holograms is less good than the quality of color holograms recorded with CW lasers. But however the obtained results are significant and promising.
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