Nonlinear optical parameters and optical limitation in cobalt-doped polyvinylpyrrolidone solutions

Nonlinear optical parameters (nonlinear refractive indices and nonlinear absorption coefficients) of solutions of polyvinylpyrrolidone doped by cobalt to various concentrations are measured at the lasing and second-harmonic wavelengths of a picosecond Nd:YAG laser (λ=1064 and 532 nm, respectively, and τ=35 ps). Data on optical limitation in these solutions are presented. The absence of nonlinear absorption in the IR spectral range and its significant effect in the visible range are demonstrated. Optical limitation at a wavelength of 1064 nm is related to defocusing, whereas at 532 nm, this effect is caused by two-photon absorption and partially by inverse saturated absorption and defocusing. Nonlinear optical parameters of metal-polymer complexes are reported.     

Nonlinear optical parameters of colloidal silver at various stages of aggregation

The Z-scan method is used to study the variation in the nonlinear susceptibility χ⁽³⁾ (−gw; ω, ω, −ω) and nonlinear refractive index of colloidal silver with the degree of aggregation under the action of picosecond and nanosecond radiation (λ=1064 nm). The values of χ⁽³⁾ for aggregated silver that are defined by Kerr nonlinearity and thermal self-focusing are found to be −1.5×10⁻¹⁴ and −4.4×10⁻¹¹ esu, respectively. The time evolution of the picosecond pulses passing through the colloid is investigated.     

Optical limiting in cobalt-doped polyvinylpyrrolidone

The results of optical limiting investigations of cobalt-doped polyvinylpyrrolidone solutions are presented. The optical limiting studies have shown that this process is due to self-defocusing at the wavelength of 1064 nm and also due to reverse saturable absorption and self-defocusing at the wavelength of 532 nm. The results of measurements on the non-linear optical characteristics of organometallic complexes are presented. Received: 10 July 2001 / Revised version: 15 October 2001 / Published online: 29 November 2001     

The use of three-photon absorption for optical limiting of laser radiation

The results of a study of nonlinear refraction and nonlinear absorption at a wavelength of 532 nm in an LGO (Li₂Ge₂O₁₅) crystal by Z-scan methods are presented. It is shown that the nonlinear refraction is caused by self-focusing of the laser radiation, whereas the nonlinear absorption is three-photon in nature. The possibility of using an LGO crystal for producing the optical limiting of laser radiation of picosecond duration is demonstrated.     

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.     

On the analysis of factors limiting third harmonic generation of Nd:YAlO<Subscript>3</Subscript> laser radiation in barium vapor

The efficiency of generation of the third harmonic (THG) of Nd:YAlO³ laser radiation in barium vapor is analyzed. The influence of the following factors is taken into consideration: the interference of transformed radiation in the case of THG via two channels ω+ω+ω→3ω and 2ω+2ω?ω →3ω, the Kerr effect, two-photon absorption, and the relationship between the energies of the first and second harmonics of radiation. It is shown that the Kerr effect, on the one hand, violates the phase matching conditions in the direct channel but, on the other hand, increases the conversion efficiency due to a defocusing action of the medium, which reduces the influence of the phase detuning between the pumping waves on the process of harmonic generation in the case of generation of difference frequencies. At the same time, the two-photon absorption leads to the depletion of one of the interacting waves (in this case, the second harmonic) and to the prevalence of third harmonic generation through the direct channel.     

Third-harmonic generation in polyvinylpirrolidone-based metallic complexes

The third-order nonlinear susceptibilities of the aqueous solutions of polyvinylpirrolidone doped with iron and zinc were studied by the method of third-harmonic generation with 1064-nm Nd:YAG laser radiation. The efficiencies of transformation into the third harmonic in these metallic complexes were 8×10^?7 and 5×10^?7, respectively. To determine the role of the Kerr effect in the transformation process, the nonlinear refractive index of the iron-doped polyvinylpirrolidone solution was measured by the Z-scan method and a value of n ₂=?6.7×10^?13 cgs unit was obtained.     

Radiowave propagation on short meteor radio links

We present experimental results obtained on meteor radio links with lengths of 100 and 250 km. The advantage of the “lateral propagation” is demonstrated. Using the “KAMET” computer model, we simulated the propagation of radiowaves along radio links, of up to 600 km. An effective version is proposed for working on radio links of up to 300 km, which is called “tracking the meteor activity maximum.” State University, Kazan’, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 6, pp. 693–703, June, 1997.     

Nonlinear refraction and nonlinear absorption of silver aggregates in a polymeric matrix

The nonlinear optical characteristics of silver aggregates in a polymeric matrix are studied by the Z-scan method at the wavelength λ = 1064 nm. The nonlinear refractive index and the third-order nonlinear susceptibility of a sample with silver aggregates are measured. It is shown that the nonlinear refraction in the sample is related to the Kerr effect. The character of the nonlinear absorption process is discussed.