M. S. Brodyn

Techniques to Characterize the Nonlinear Optical Response of Doped Nematic Liquid Crystals

ABSTRACT We have examined the efficiency of various techniques for the determination of the nonlinear optical response (NLO) of dye-doped liquid crystals. The intensity ranges where each technique is optimal are defined. We propose an approach for precise and detailed NLO response measurements as a function of dye concentration when the optical parameters of samples vary in a wide range and change significantly after the light-induced Freedericksz transition.

Impact of incorporated anatase nanoparticles on the second harmonic generation in KDP single crystals

The second harmonic generation efficiency was studied for the single crystalline potassium dihydrogen phosphate matrix with incorporated TiO2 nanocrystals in the field of the mode-locked Nd:YAG laser pulses. For the first time the frequency conversion efficiency gain was observed for KDP:TiO2 single crystal (SC) instead of KDP SC due to the internal self-focusing effect of the pump beam caused by the giant cubic nonlinear optical response of the embedded nanoparticles.

Interplay of Quadratic and Cubic Nonlinear Optical Responses in KDP Single Crystals with Incorporated TiO2 Nanoparticles

We have obtained the significant enhancement (up to 70 %) of the second harmonic generation efficiency in the novel composite material based on KDP single crystalline matrix with incorporated anatase nanoparticles under the mode-locked YAG:Nd laser pulsed excitation. The effect is explained by the internal self-focusing at moderate pump peak intensity due to giant cubic nonlinear optical response of anatase nanoparticles. The possibility to control quadratic and cubic nonlinear optical responses with selection of the nanoparticles concentration and growth sector of the crystal was shown. The nonlinear optical refractive index variation is a very sensitive tool to perform the diagnostics of the KDP and KDP:TiO2 single crystals within CW and pulsed picosecond range laser radiation due to the resonant excitation of the transient intrinsic defect states of the crystal matrix and surface states at the anatase nanoparticles interface.

The Effect of Sintering Temperature on Linear and Nonlinear Optical Properties of YAG Nanoceramics

Recent improvements in powder synthesis and ceramics sintering made it possible to fabricate high-quality optical materials. The work is devoted to the structural and optical characterization of the (\({Y_3}{Al_5}{O_{12}}\), YAG) ceramics prepared by high-pressure low-temperature technique. The structural properties of the studied ceramic samples was obtained by X-ray diffraction. The studies of the total and in-line transmittance as well as optical scattering indicatrices were performed in visible and NIR ranges. The scatterer size \(\sim200\) nm was estimated by Rayleigh–Gans–Debye model. It was shown that the studied samples demonstrate high transparency at 1064 nm. The nonlinear optical characterization of the samples was done by the self-action of the picosecond laser pulses at 1064 nm. The measured nonlinear optical response (\( \operatorname{Im}({{\chi }^{(3)}})\,\sim \,{{10}^{-11}}\,\text{esu} \) esu) showed significant dependence on the sintering temperature variation.

Diagnostics of optical nonlinearities: spatial beam distortion technique and its application to semiconductors and novel materials

Development of nonlinear refraction diagnostics methods based on spatial beam distortions technique and nonlinear absorption measurements is illustrated with wide-gap semiconductors experimental data. With picosecond Z-scan technique we have studied competitive optical nonlinearities -- intraband direct equilibrium carriers transitions saturation and interband two-photon absorption (TPA) for a α-SiC(6H) crystal, and enhanced state absorption, absorption saturation and TPA -- of epoxy polymer based on diglicidyl ether of bisphenol A in a wide pumping intensities range (10 MW/cm2 - 20 GW/cm2) at 532 nm. The complexity of the analysis was dealt with the nonlinearities signatures recognition problem and selection the part of the Z-scan curve which corresponds to the dominant contribution of the proper nonlinear mechanism on the background of competitive others. The TPA coefficient is β = 3.2 ± 0.3 cm/GW for the α-SiC(6H) crystal. The TPA coefficient is β = 4.0 ± 0.5 cm/GW for the polymer. At very high laser intensities (>7 GW/cm2) photoinduced transformation into some new configuration is taken place that is more absorbent at 532 nm. The TPA coefficient is β = 16.7 ± 3 cm/GW for the photoproduct. Up to pumping irradiance of 20 GW/cm2 no optical damage of the polymer was observed.

Impact of Merocyanine Dye Concentration in Ultrathin Polymer Films on Nonlinear Optical Response Due to the Aggregation Effect

Nonlinear optical properties of thin films of the organic merocyanine dye derived from the class of malonodinitrile dyes, as well as its solid guest-host systems based on polymethyl methacrylate are studied. The optical absorption spectra of films with different dye concentrations and of the dye solutions in non-polar solvents are measured. The scattering indicatrices of films are presented. The films demonstrated the efficient photoinduced variation of the refractive index under the pulsed and continuous wave laser excitations. A nonlinear optical response of films under the picosecond range pulsed laser excitation points to the aggregation effects at the 10-wt.% dye concentration and higher.

Vector Holograms Recorded in Epoxy-Based Polymer With 4-Aminoazobenzene by Pulsed Laser Light

Both scalar and vector gratings were recorded in an epoxy-based polymer with 4-amino-azobenzene depending on the geometry of the recording by the second harmonic of a pulsed Nd:YAG laser. A new mechanism of nonlinear refraction (striction) is suggested and is experimentally observed for the first time in the medium under study.

Laser chemical vapor deposition of nanometric structures and their electrical and optical properties

Laser chemical vapor deposition (LCVD) method based on Ar+ laser radiation was applied for the synthesis of nanometric structures based on iron oxides Fe2O3-x (0 < or = x < or = 1) in the form of thin films. These structures were formed while deposition of elements from iron carbonyl vapors (Fe(CO)5). The thickness of deposited films was no more than 30 nm while deposition on the Si substrate surface and on the SiO2 substrate surface. Deposited thin films demonstrated typical semiconductor trends of specific conductivity in the range (340-170)K. Obtained semiconductor thin films based on iron oxides had the band gap for intrinsic conductivity (Eg) less than 1.0 eV. It was found out that electrical properties of these films were determined by the surface morphology of them and their content of iron oxides. Deposited films demonstrated a large third-order nonlinear optical (NLO) susceptibility (x(3)). While pumping of narrow band gap semiconductor thin film with a frequency-doubled mode-locked Nd:YAG laser (λL=532 nm) and pulse duration of 30 ps (FWHM) at power density less than 100 MW/cm2, the meaning of x(3) was about 5×10-6 e.s.u.

Size Dependence of the Third-Order Optical Nonlinear Susceptibility of PbS Nanocrystals in PVA

We have synthesized a composite material containing semiconductor nanocrystals with a high third-order optical nonlinear susceptibility χ(3) (ω) = (6.5±2.3) · 10−16 m2/V2 (PbS-18 nm) at λ = 1.064 nm in the case where the nanocrystal size approaches the Bohr radius of an exciton in the material.

Nonlinear optical properties of substituted pyridostyryl dye base films

The paper presents the results of the complex investigation of linear and nonlinear parameters of new organic compound type - polymethine dye base (PDB) - 1-pentafluorophenyl-4-phenyl-5,6,7,8-tetrahydro-8-[(4-dimethylaminophenyl)methylene]-quinoline. For the first time thin films on glass substrate from this material were deposited by physical evaporation in vacuum. Linear absorption spectra of base films and base solutions were investigated in the wavelength range 300 - 1100 nm. Nonlinear properties of three films with thickness of 247, 350, 535 nm were studied with Z-scan and spatial profile analysis techniques in picosecond range of pumping pulses duration at the fundamental wavelength of YAG:Nd3+ laser 1064 nm. We observed darkening/bleaching effects of different magnitude (2 - 20%) of total transmittance in dependence on films thickness. It was estimated effective third order nonlinear susceptibility χ(3) ≈ 10-5 esu. Such high nonlinear response can be explained by presumable cascade process of PDB molecule excitation which is simultaneously in resonance with pump wavelength 1064 nm (1.17 eV) and its harmonics 355 nm (3.48 eV).