Efim A. Khazanov

200 TW 45 fs laser based on optical parametric chirped pulse amplification

200 TW peak power has been achieved experimentally using a Cr:forsterite master oscillator at 1250 nm, a stretcher, three optical parametrical amplifiers based on KD*P (DKDP) crystals providing 14.5 J energy in the chirped pulse at 910 nm central wavelength, and a vacuum compressor. The final parametrical amplifier and the compressor are described in detail. Scaling of such architecture to multipetawatt power is discussed.

Investigation of self-induced depolarization of laser radiation in terbium gallium garnet

Absorption of laser radiation in magnetooptical materials results in a temperature gradient which induces depolarization due to both the temperature dependence of the Verdet constant and the photoelastic effect of thermal strains. This results in a limitation of the isolation ratio of Faraday isolators in high average power lasers. Here, we derive expressions for the isolation ratio as a function of beam power, beam radius, angle between incident polarization and crystal axis, and characteristics of the magnetooptical material. The theoretical results are compared with experiments for a terbium gallium garnet crystal. Our results allow us to choose the optimal parameters to maximize the isolation ratio and to compare different materials from this point of view.

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.

Exawatt-Zettawatt pulse generation and applications

A new amplification method, weaving the three basic compression techniques, Chirped Pulse Amplification (CPA), Optical Parametric Chirped Pulse Amplification (OPCPA) and Plasma Compression by Backward Raman Amplification (BRA) in plasma, is proposed. It is called C3 for Cascaded Conversion Compression. It has the capability to compress with good efficiency kilojoule to megajoule, nanosecond laser pulses into femtosecond pulses, to produce exawatt and beyond peak power. In the future, C3 could be used at large-scale facilities such as the National Ignition Facility (NIF) or the Laser Megajoule (LMJ) and open the way to zettawatt level pulses. The beam will be focused to a wavelength spot size with a f#1. The very small beam size, i.e. few centimeters, along with the low laser repetition rate laser system will make possible the use of inexpensive, precision, disposable optics. The resulting intensity will approach the Schwinger value, thus opening up new possibilities in fundamental physics.

Faraday Rotators With Short Magneto-Optical Elements for 50-kW Laser Power

Faraday rotators with short magneto-optical elements are created and experimentally studied. The magneto-optical elements are made three to four times shorter either by cooling them to nitrogen temperatures or by increasing the magnetic field. These ways are shown to increase maximum average laser power passing through the Faraday isolators up to 50 kW

Thermally induced birefringence in Nd:YAG ceramics.

Analytical expressions for eigenpolarizations and phase delays in grains of thermally loaded Nd:YAG ceramic rods have been derived. It is shown that the depolarization of radiation in polycrystalline ceramics results in beam modulation with a characteristic size of the order of the ceramic grain size. It is reasonable to increase the ratio of rod length to grain length both to diminish this modulation depth and to compensate for birefringence by use of known techniques.

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 thermally induced depolarization in Faraday isolators for high average power lasers

A compensation scheme for thermally induced birefringence in Faraday isolators is proposed. With the use of this scheme a 36-fold increase of the isolation degree was attained in experiment. A comparative analysis of the considered scheme and the earlier Faraday isolator schemes with high average radiation power is performed. A method for optimizing the earlier Faraday isolator scheme with birefringence compensation is developed.

Single cycle thin film compressor opening the door to Zeptosecond-Exawatt physics

This article demonstrates a new compression scheme that has the potential to compress a high energy pulse as high as a few hundred Joules in a pulse as short as one optical cycle at 0.8 μm producing a true ultra-relativistic λ3 pulse. This pulse would have a focused intensity of 1024 W/cm2 or a0 of 1000. On interaction with a solid target, this pulse could form an efficient, 10%, relativistic mirror that could further compress the pulse to the atto-zeptosecond regime, with an upshifted wavelength of 1–10 keV. This technique could be a watershed enabling the compression of petawatt pulses into the exawatt and zeptosecond regime possible.