T. Usmanov

Nonlinear susceptibilities, absorption coefficients and refractive indices of colloidal metals

The investigations of the nonlinear optical parameters of Au, Ag, Pt and Cu colloidal solutions using the Z-scan method and third-harmonic generation (THG) are presented. The nonlinear refractive indices, nonlinear absorption coefficients and Kerr-induced nonlinear susceptibilities (χ(3)(-ω;ω,-ω,ω)) of these solutions on the wavelengths of picosecond and nanosecond Nd:YAG laser radiation (λ = 1064 nm) and its second harmonic (λ = 532 nm) have been measured. A tenfold increase of nonlinear susceptibilities on the wavelength of 532 nm in comparison with λ = 1064 nm is shown for these colloidal metals. The application of colloidal metals as optical limiters of picosecond and nanosecond radiation (λ = 1064 nm and 532 nm) was studied. The influence of aggregation of colloidal clusters on optical limiting in these media was considered. It was shown that the appearance of the long-wave wing of absorption at the final stages of aggregation led to the nonlinear absorption of picosecond pulses. The investigations of the THG of picosecond Nd:YAG laser radiation in colloidal metals (Pt and Cu) are presented. THG efficiency was found to be 7×10-7 for colloidal platinum. Nonlinear susceptibilities χ(3)(-3ω;ω,ω,ω) of colloidal platinum and copper were measured to be (1.5±0.75)×10-14 esu and (1±0.5)×10-14 esu, respectively.

Optical harmonics generation in low-temperature laser-produced plasmas

Abstract Results of odd harmonics generation (up to eleventh, λ = 96 nm) of laser radiation (λ = 1.054 nm, τ = 3 ps) in a low-temperature atmospheric plasma and a surface plasma in vacuum are reported. Maximum efficiency was achieved for third harmonics generation (η = 10−3). High-order harmonics generation and frequency conversion optimization depending on radiation and nonlinear media characteristics are considered.

Nonlinear optical characteristics of C60 and C70 films and solutions

Abstract Investigations of nonlinear optical parameters of C 60 and C 70 films and solutions by Z -scan method are presented. Nonlinear refractive indices on the wavelength of Nd:YAG laser radiation ( λ =1064 nm) have been measured. Two-photon absorption and nonlinear susceptibilities of fullerene-doped films and solutions have been studied.

Limitation of second-harmonic generation of femtosecond Ti:sapphire laser pulses

The second-harmonic generation of 50-fs Ti:sapphire laser pulses in 1- and 2-mm KDP crystals at 350 mJ of incident energy is measured experimentally and analyzed theoretically. A frequency-conversion efficiency of ∼40% is reached. The limiting influence of self-phase modulation and fundamental phase modulation is demonstrated. The deep modulation of a frequency-doubled spectrum at a high incident intensity is observed. Methods to increase conversion efficiency are proposed.

Non-linear optical properties of metal nanoparticles implanted in silicate glass

Copper nanoparticles have been synthesized in silica and soda-lime glasses by 50 keV Cu þ ion implantation with doses of 8.0 � 10 16 ion/cm 2 . Nanoparticles were characterised by well developed absorption band of surface plasmon resonance in visible range. Metal nanoparticle composite glasses were analyzed by the Z-scan method at the IR wavelength of Nd:YAG laser radiation 1064 nm. The Z-scan scheme with an open and closed aperture allowed to determined non-linear refractive indices, third order non-linear susceptibilities and non-linear absorption coefficients of the synthesized materials. The third order non-linear susceptibility in the analyzed medium with simultaneous nonlinear refraction and absorption were considered as a complex values. It is suggested that the samples with non-linear absorption is perspective ones for optical limiting application. 2003 Elsevier Science B.V. All rights reserved.

Optical limiting in fullerenes, colloidal metal solutions, and semiconductors in the field of pico-and nanosecond pulses of an Nd:YAG laser

Optical limiting of pico-and nanosecond pulsed radiation of a Nd:YAG laser (λ=1064 and 532 nm) is studied in solutions of fullerenes (C60 and C70), semiconductor crystals and films (GaAs, As2S3, As20S80, 2As2S3/As2Se3, and 3As2S3/As2Se3), and colloidal solutions of metals (Au, Ag, Pt, and Cu). The effect of the particle aggregation in silver solutions on the optical limiting is considered. Optical limiting mechanisms, specifically, reverse saturable absorption, two-photon absorption, and self-action effects, are discussed. Nonlinear absorption coefficients of the studied materials are measured.

Low-order harmonic generation in metal ablation plasmas in nanosecond and picosecond laser regimes

Low-order harmonics, third and fifth, of IR (1064 nm) laser emission have been produced in laser ablation plasmas of the metals manganese, copper and silver. The harmonics were generated in a process triggered by laser ablation followed by frequency up-conversion of a fundamental laser beam that propagates parallel to the target surface. These studies were carried out in two temporal regimes by creating the ablation plasma using either nanosecond or picosecond pulses and then probing the plasma plume with pulses of the same duration. The spatiotemporal behavior of the generated harmonics was characterized and reveals the distinct composition and dynamics of the plasma species that act as nonlinear media, allowing the comparison of different processes that control the generation efficiency. These results serve to guide the choice of laser ablation plasmas to be used for efficient high harmonic generation of laser radiation.

Nonlinear properties of composites based on dielectric layers containing copper and silver nanoparticles

Nonlinear optical characteristics of copper and silver nanoparticles in glass host matrices are studied by the Z-scan method at the wavelength of a Nd:YAG laser (λ=1064 nm) in a field of picosecond pulses. It is found that the third-order nonlinear susceptibility is more pronounced in glasses with copper nanoparticles than in glasses with silver nanoparticles. On the basis of experimental data obtained for samples with copper nanoparticles synthesized by ion implantation, it is shown for the first time that the nonlinear absorption of laser radiation with a wavelength lying out of the plasmon resonance region can be caused by a two-photon effect in metal particles. The character of the optical limiting process in the samples with copper nanoparticles when two-photon absorption is involved is discussed.

Frequency conversion of picosecond radiation in fullerene-doped polyimide films and colloidal metals

Investigations of third-harmonic generation (THG) of picosecond Nd:YAG laser radiation in C70-doped polyimide films and colloidal metals (Pt and Cu) are presented. The nonlinear susceptibility χ(3)(-3ω;ω,ω,ω) of the fullerene-doped film was measured to be (9±4.5)×10-13 esu (for 0.5% C70 in polyimide 6B film). The influence of nonlinear refraction of fullerene-doped films on the phase-matching conditions of THG was responsible for deviation from the cubic power dependence of the third-harmonic signal on the fundamental radiation intensity I3ω(Iω) and restriction of THG efficiency in 0.5% C70-doped polyimide film. THG efficiencies were found to be 6×10-6 and 7×10-7 for 0.5% C70-doped polyimide film and colloidal platinum respectively. The maximal predicted efficiency of THG in 0.5% C70-doped polyimide film at weak focusing has been achieved. Nonlinear susceptibilities χ(3)(-3ω;ω,ω,ω) of colloidal platinum and copper were measured to be (1.5±0.75)×10-14 and (1±0.5)×10-14 esu respectively.

Analysis of third-order nonlinear susceptibilities of quadratic nonlinear optical crystals

The relations between the tensor components of the nonlinear susceptibilities responsible for self-action processes are measured in KDP, deuterated KDP, and LiNbO3 crystals at the Nd:YAG laser wavelength (lambda=1064 nm). The measurements are conducted on the basis of the analysis of the polarization dependences of focused radiation transmittance with the z-scan scheme. The obtained polarization dependences in KDP corresponded to the fourth-rank tensor of Kerr nonlinearity. The obtained values of nonlinear refractive indices are compared with the known experimental data.