Alexander S. Kuzhelev

250-W average-power Nd:YAG laser with self-adaptive cavity completed by dynamic refractive-index gratings

A high average power laser oscillator with a cavity completed by a nonlinear mirror formed by refractive index gratings which accompany population gratings induced in Nd:YAG laser crystals by generating beams themselves is investigated numerically and experimentally. The role of different noise sources at the initial stage of nonlinear cavity formation is studied. The adaptation of the cavity formed by nonlinear dynamic mirrors to intracavity distortions is demonstrated. The generation of beams with average power up to 250 W, near-diffraction-limited divergence, and long coherence length has been achieved.

Pulse repetitive Nd:YAG laser with distributed feedback by self-induced population grating

We present a self-starting Nd:YAG laser-oscillator with a cavity formed by refractive index grating caused by population grating induced in the laser crystal by the generating beams themselves. Different configurations of the cavity (linear, loop and multi-loop) have been investigated. The laser-oscillator with a nonlinear mirror displays self-adaptivity to strong thermally induced intracavity distortions. Generation of single transverse mode beams with diffraction quality in the millisecond pulse-repetitive regime with 12 W average power has been achieved.

Self-pumped phase conjugation of the heterogeneous light beam in the inverted Nd:YAG-rod with nonreciprocal feedback

Abstract Parametric self-pumped phase conjugation of the space heterogeneous light beam in an inverted Nd:YAG-rod with nonreciprocal feedback is investigated. The effect was realized in the geometry of the near-corunning mutually-incoherent pumping beams (incident and passing through the feedback loop with phase and amplitude nonreciprocities). Phase conjugation was observed both for the linearly polarized pumping beams and for their circular polarizations.

Formation of dynamic cavity in a self-starting high-average-power Nd:YAG laser oscillator

Self-organization of the dynamic cavity completed by holographic gratings in the novel laser oscillator was studied experimentally and numerically. A key role of the resonant grating of refractive index induced by generating beams in an Nd:YAG laser crystal was determined. Stabilization of the generated pulses and an increase in output power were achieved by use of a vibrating intracavity mirror.

Stimulated resonance scattering of light waves in laser crystals with a population inversion

A new type of stimulated scattering of light is discovered in a Nd:YAG laser crystal with a population inversion. The scattering occurs for light at the resonance frequency of the laser transition, with a small anti-Stokes shift. It is shown that the effect is due to the appearance of a wave of population of the metastable level and the associated traveling index grating in a laser medium with different polarizability of the excited and unexcited atoms.

Degenerate four-wave mixing measurements of the ?(3) non-linear optical properties of poly(arylene-ethynylenesilylene)s

The third-order optical non-linearity in solution of a series of poly(arylene-ethynylenesilylene)s containing a variety of backbone arylene groups and substituents at silicon has been studied by using the degenerate four-wave mixing technique at 1064 nm with a 6 ns pulse duration. Thermal grating effects may be neglected under the experimental set-ups employed. The results obtained are greater by more than two orders of magnitude than those previously measured for some of the polymers using the Z-scan technique at the same wavelength. The electronic contribution to the fast non-linearity is greater than the nuclear (orientational) contribution by a factor of at least 4. The presence of a single 8-(dimethylamino)naphthyl ligand at silicon affording pentacoordination has a beneficial effect on the X (3) properties. The high X (3) properties of the polymers (e.g. [Re(X (3) )]=9.5 × 10 -12 esu for [-C≡C-SiPh 2 -C≡C - (1,4-C 6 H 4 )-] n in chloroform [5 g] l -1 ]) confirm the presence of extensive through-Si conjugation along the backbone.

Novel materials from bis(arene)metal-containing polyacrylonitrile

Novel bis(arene)metal-containing polyacrylonitrile materials have been prepared by the polycyanoethylation reaction between acrylonitrile and (arene) 2 M (M = Cr or V; arene = PhH, C 6 H 4 Et 2 or mesitylene) in the absence of solvent. The resulting star-shaped molecules consist of a central (arene) 2 M species with up to four polyacrylonitrile arms covalently bonded to the arene ligands. The materials are readily soluble and films can be cast from solutions in acetonitrile. The IR and solid state 13 C NMR spectra (or EPR spectrum for the oxidized chromium-containing polymer) are consistent with the presence of a metal-arene bond and confirm the persistence of the sandwich structure. The properties of the thermolysed materials are consistent with the formation of conjugated naphthyridine-type structures. The value of |n 2 | determined by the degenerate four-wave mixing technique at 1064 nm with a 6 ns pulse duration for a solution in conc. H 2 SO 4 (1 g l -1 ) of the chromium-containing polymer pyrolysed at 350 °C was found to be 0.8 × 10 -13 cm 2 W -1 corresponding to |Re X (3) | = 0.4 x 10 -11 esu.

NONDEGENERATE FOUR-WAVE-MIXING MEASUREMENTS OF A RESONANTLY INDUCED REFRACTIVE-INDEX GRATING IN A ND:YAG AMPLIFIER

Two optical waves (at 1064 nm) were used to resonantly induce a population grating in a flash-lamp-pumped Nd:YAG rod, and a nonresonant wave (at 1054 or 694 nm) was used to read (with a diffraction efficiency of as much as 1% or 0.3%, respectively) the refractive-index grating caused by the difference in the polarizability of the excited and the unexcited Nd ions. Comparisons of experimental results and numerical calculations gave the dependence of the ratio of the real and the imaginary parts of the resonant susceptibility of Nd:YAG at 1064 nm on the pump power.

High-average-power solid state lasers with cavity formed by self-induced refractive index gratings

We present a self-starting Nd:YAG laser-oscillator with cavity formed by refractive index gratings and gain gratings accompanying population gratings which are induced in the laser crystal by generating beams themselves. The spatio- temporal and spectral characteristics of the laser including two Nd:YAG-amplifiers, a saturable absorber and a Sagnac interferometer are investigated. The laser-oscillator with a nonlinear mirror has displayed self-adaptivity to strong thermally induced intracavity distortions. Generation of single mode beams with up to 60 W average power and near- diffraction limited quality has been achieved.

Thin film Z-scan measurements of the nonlinear response of novel conjugated silicon-ethynylene polymers and metal-containing complexes incorporated into polymeric matrices

The third-order optical nonlinearities of new conjugated poly[(arylene)(ethynylene)silylene]s, and a variety of chromium, neodymium or cobalt complexes incorporated into polymeric matrices as thin sol-gel or polyacrylonitrile films have been determined by using a single beam Z-scan technique. The samples were pumped by a single ultrashort pulse of a mode-locked Nd-phosphate glass laser (wavelength 1054 nm) with a 5ps pulse duration (full width at half- maximum), the repetition rate of the Gaussian beam being low (0.3Hz) ro avoid thermal effects. The spot radius of the focused pulse was ca. 60micrometers , its beam waist being in the sample (intensity up to 4x1013 Wm-2). Calibration was done with chloroform and benzene, the value of N2 for the latter (2x10-12esu) being similar to that previously reported. A small-aperture Z-scan (S=0.03) was used to measure the magnitude and the sign of the nonlinear refractive index, n2. Very high nonlinear refractive indices were found for a film containing (a) a poly[(arylene)(ethynylene)silylene]s with pentacoordinated silicon (c 5 gl-1) in a sol-gel matrix (N2 = 6 x 10-13 cm2W-1), (b) a film containing a poly[(arylene)(ethynylene)silylene] with tetracoordinated silicon (c 0.5 gl-1) and a very small proportion of fullerene-C70 incorporated into an NH2-containing sol-gel matrix (n2 = 5x10-13 cm2W-1, and (c) a thin polyacrylonitrile film of polycyanoethylate bis-arenechromium(I) hydroxide (n2 = -5 x 10-12 cm(superscript 2W-1.