Nikolay Andreev

Compensation of thermally induced modal distortions in Faraday isolators

Two methods of compensation of thermal lensing in high-power terbium gallium garnet (TGG) Faraday isolators have been investigated in detail: compensation by means of an ordinary negative lens and compensation using FK51 Schott glass possessing a negative dn/dT. Key thermooptic constants for TGG crystals and FK51 glass were measured. We find that the contribution of the photoelastic effect to the total thermal lens cannot be neglected for either TGG or FK51. We define a figure of merit for compensating glass and show that for FK51, an ordinary negative lens with an optimal focus is more efficient, but requires physical repositioning of the lens for different laser powers. In contrast, the use of FK51 as a compensating element is passive and works at any laser power, but is less effective than simple telescopic compensation. The efficiency of adaptive compensation can be considerably enhanced by using a compensating glass with figure of merit more than 50, a crystal with natural birefringence or gel.

Suppression of self-induced depolarization of high-power laser radiation in glass-based Faraday isolators

Light absorption in optical elements of Faraday rotators results in a nonuniform cross-sectional temperature distribution that leads to depolarization of laser radiation and, consequently, limits the isolation ratio of optical Faraday isolators. We show experimentally that the influence of the temperature dependence of the Verdet constant on the isolation ratio is negligibly small when compared with the influence of the photoelastic effect. We also present two novel methods of optical isolation that significantly reduce the depolarization caused by the photoelastic effect and increase the isolation ratio by two orders of magnitude in comparison with the conventional method. Our results confirm the possibility of magneto-optical glass-based Faraday isolators with isolation ratios of 30 dB for average laser powers of hundreds of watts.

Applications of Brillouin cells to high repetition rate solid-state lasers

A review is given of possible applications for Brillouin cells in solid-state lasers operating at higher pulse repetition frequencies. Brillouin cells are used to reduce beam divergence, improve intensity distribution in the near field, and provide phase locking of light beams pulse compression, and pulse shape control. >

Compensation of birefringence in active elements with a novel Faraday mirror operating at high average power

A decrease in the depolarization ratio by more than one order of magnitude by use of a recently proposed Faraday mirror (FM) in comparison with the traditional FM has been demonstrated experimentally. At a high average laser power, the possibility of an increase in the accuracy of compensation of depolarization in the active element by means of a lambda/4 plate with both the traditional and the novel FM is shown.

Phase conjugation of single photons

Phase conjugation (PC) of extremely weak signals using a phase-conjugate mirror based on Mandelstam-Brillouin-enhanced four-wave mixing, coupled with an optical quantum amplifier, is considered. PC of a pulse with energy 4*10/sup -17/ J is achieved. PC conditions for amplified superluminescence noise of the optical quantum amplifier are specified and the limiting parameters are estimated. It is shown experimentally that if the signal-to-noise ratio (S/N) is equal to unity, the energy of an input signal for which phase conjugation is possible corresponds to 30 photons per transverse mode. >

New scheme of a petawatt laser based on nondegenerate parametric amplification of chirped pulses in DKDP crystals

The ultra-broadband phase matching was experimentally observed in a DKDP crystal upon parametric amplification of signal radiation with a wavelength of 911 nm in a pump field with a wavelength of 527 nm. The original scheme was used to excite the first parametric amplification stage by chirped pulses of idler radiation with a wavelength of 1250 nm. The saturated gain of a three-stage parametric amplifier was equal to 108.

A two-channel repetitively pulsed Nd:YAG laser operating at 25 Hz with diffraction-limited beam quality

A two-channel, repetitively pulsed laser was studied. The main features of this laser were the compensation of aberration and polarization distortions in Nd:YAG crystals and the summation of two channels of radiation into a single diffraction-limited beam with a pulse energy up to 5 J.

Parametric amplification of chirped laser pulses at 911-nm and 1250-nm wavelengths

The analysis of tuning characteristics for parametric amplification in KD*P has shown that the application of KD*P crystals may considerably enhance the possibilities of certain optical parametric amplifiers of both terawatt and petawatt level. For instance, at pumping with a wavelength of (lambda) 3 equals 0.527 micrometers , which is most promising for the creation of such systems, the KD*P-based amplifiers may work far from the degenerate mode, e.g., at (lambda) s- 0.911 micrometers and (lambda) i-1.25 micrometers . For operation at these wavelengths there are currently master oscillator of femtosecond pulses with pulse duration of up to 30 fs. In this paper elements of the system are discussed, and their parameters are optimized.

Use of self-focusing for measurements of ultrasmall (less than λ/3000) wave-front distortions

Results of the use of self-focusing in Kerr liquids for the measurement of small wave-front distortions transmitted through a transparent optical sample are presented. Using controlled self-focusing to decrease the spot size of the deflected beam, we have been able to improve the measurement resolution by an order of magnitude compared with that achieved with a conventional Hartmann detector. We examine a variety of materials to determine the optimal nonlinear medium and demonstrate measurements of absolute wave-front deviations at the level of λ/3000. A prototype of a new device, the scanning nonlinear Hartmann sensor, is described.

Multicascade boradband optical parametric chirped pulse amplifier based on KD*P crystals

We have experimentally demonstrated the existence of super-broadband non-degenerated phase matching for a signal with a wavelength of 911 nm in KD*P crystal pumped with wavelength of 527nm. Parametric amplification coefficient of more than 107 in three cascades is achieved. This resulted in pulse energy 10mJ at the output of third cascade. It is shown that in the KD*P crystal chirped pulses of conventional femtosecond sources (a Ti:Sa laser at 911 nm and a Cr:forsterite laser at 1250 nm) can be amplified up to the level that ensures multipetawatt power after compression.