A nonlinear transformation of femtosecond laser pulses

1. Frequency conversion
A new method of frequency conversion of femtosecond laser pulses based on the stimulated Raman scattering (SRS) has been developed.
1. "A generation of Stokes pulses of less than 100 fs at SRS in a barium nitrate crystal," A.V.Konyaschenko, L.L.Losev, S.Yu.Tenyakov, Quantum Electronics, 2010, Volume 40, № 8, p. 700-703.
Abstract
Generation of 72-fs pulses at a frequency of the first Stokes component at SRS in a barium nitrate crystal of  laser pulse on Al2O3: Ti3 within 50 fs has been carried out.
Energy conversion efficiency is 20%.
The optical pumping scheme of a barium nitrate crystal by two consecutive orthogonally polarized chirped pulses with a subsequent temporary compression of the Stokes radiation pulse was used.
2. "Generation of the second Stokes component at SRS of the chirped laser pulses" A.V.Konyaschenko, L.L.Losev, S.Yu.Tenyakov, Quantum Electronics, 2011, Volume 41, № 5, p. 459-464.
Abstract
Experimental study of the optical schemes of the second Stokes component at SRS of broadband chirped laser pulses in compressed gases has been held. Energy conversion efficiency and spatial characteristics of a light beam of the second Stokes component at single and double focusing of the pump radiation into a gas-filled cuvette, as well as in circuits using a quartz capillary and two gas cuvettes have been measured.
It is shown that the maximum energy efficiency of conversion to the second Stokes component is achieved at cascade generation in the optical circuit with two cuvettes with compressed gases. In this scheme at SRS in hydrogen a laser radiation on sapphire with titanium with a wavelength of 0.79 microns is converted to the second Stokes component with a wavelength of 2.3 microns with an efficiency of 8.5%.

2. Temporary compression

A method of temporary compression of femtosecond laser pulses based on the process of spectral broadening at pulse propagation in a gas-filled capillary has been investigated.

1. " The compression degree and energy efficiency of a capillary compressor of femtosecond laser pulses" A.V.Konyaschenko, P.V.Kostryukov, L.L.Losev, S.Yu.Tenyakov, Quantum Electronics, 2011, Volume 41, № 11, p. 989-992.

Abstract

For temporary compressors of femtosecond laser pulses, based on the effect of spectral broadening in a gas-filled capillary, a ratio between the compression degree and energy efficiency of compressor has been derived. It is shown that the maximum compression degree is achieved at the energy efficiency of 15% - 30%. 15-fold laser pulse compression within 290 fs with the energy efficiency of 24% has been implemented.
2. "A capillary compressor of femtosecond laser pulses with a nonlinear rotation of the polarization ellipse" A.V.Konyaschenko, P.V.Kostryukov, L.L.Losev, S.Yu.Tenyakov, Quantum Electronics, 2012, Volume 42, № 3, p. 231-234.
Abstract

A process of nonlinear rotation of the laser-radiation polarization ellipse running concurrently with the pulse spectral broadening at a nonlinear self- phase modulation in a gas-filled capillary has been investigated. It is shown that the spectral components experience the greatest rotation of the polarization ellipse offset to short wavelengths relative to the central wavelength of the initial laser pulse.
Eightfold increase of the energy contrast of a light pulse within 28 fs obtained by compression of the radiation pulse of ytterbium laser within 290 fs has been implemented using a rotation effect of the polarization ellipse.