M.M. Denariez-Roberge

Photoexcited azo-dye induced torque in nematic liquid crystals

We study molecule reorientation initiated by absorption of resonant light, in D2 azo dye doped nematic liquid crystals. The photoexcitation of the dye subsystem creates a torque on the host, that is not collinear with the traditional dielectric torque. The temporal and geometrical characteristics of these torques are also different. Transient three dimensional molecular reorientation is detected through different paths for excitation and relaxation regimes. The complex coupling of the photoisomerizing dye with the nematic host is probably the origin of the observed phenomena.

Diffusion of photoexcited azo dye in a liquid-crystal host

Dynamic holograms are created and studied in a D2 azo-dye-doped nematic liquid crystal. The dependence of diffraction on the excitation and probe polarizations is observed. The efficiency of excitation and the corresponding relaxation time depend also on the period and orientation of the light-interference pattern with respect to the initial molecular orientation. The excitation and diffusion of dye molecules are suggested to be the origin of these phenomena.

Influence of the intensity of the exciting radiation on decay time and polarization of the fluorescence of some dyes in solution

Abstract We measured fluorescence depolarization of cryptocyanine in methanol and acetone and of DDI in methanol, using Q switched ruby laser exciting light. We show that, for weak excitation, we can deduce spontaneous fluorescence decay times from these measurements. With strong laser excitation, the induced polarization observed in cryptocyanine is related to stimulated emission.

Observation du “hole burning” dans une solution de cryptocyanine dans le methanol

Abstract A hole-burning effect is observed spectroscopically in a solution of cryptocyanine in methanol, when excited by a mode-locked ruby laser. The hole width is about 5 A. A transverse relaxation time of 5 psec is deduced and its significance is discussed.

Degenerated six-wave-mixing using high order Bragg diffraction in semiconductor-doped glass

Abstract High order Bragg diffraction was used to perform degenerated six-wave-mixing. The experiment has been performed in a semi- conductor doped glass (Corning 3–68) using picosecond pulses at 532 nm. The dependence of the signal on the intensity of each beam and the angular selectivity of the grating have been investigated.

Action laser dans le perylene a 4730 Å

Abstract Laser action at 4730 A has been observed in perylene dissolved in benzene when excited by the second harmonic of a Q -switched ruby laser. Laser action is observed for concentrations between 10 -4 and 5×10 -3 M/ Characteristics of emission are presented.

Effet laser dans quelques composes organiques entre 3700 ET 5000 Å

Abstract We wish to report laser action in some organic compounds when pumped by the second harmonic of a ruby laser: αNPD or 2-(1-naphtyl)-5-phenyl, 1,3,4, oxadiazole; αNBE or trans -1-(4-biphenyl)-2-(1-naphthyl)-ethylene; 1,3,4,8 tetraphenyl-pyrene; 1,1,4,4 tetraphenyl-butadiene. The spectral characteristics of the stimulated on emission are presented and discussed.

Degenerate four-wave mixing in organic azo dyes chrysoidin and benzopurpurin 4B.

Phase-conjugate reflectivity obtained by degenerate four-wave mixing are measured in different azo dye solutions. A reflectivity up to 80% was achieved. Values of the nonlinear susceptibility chi((3)) are calculated, and its origin is discussed.

Thermal gratings written in glycerol with CO 2 laser radiation

Real time holographic recording has been performed in glycerol using CO(2) laser beams for the writing. The dynamics of the grating formation was monitored with a reading beam at 632.8 nm. Particular attention has been paid on temporal behavior.

External laser triggering of a saturable absorption Q-switching system

The jitter of a passively Q‐switched ruby laser was reduced to less than 50 ns by using external dye laser triggering.