Vladimir E. Yashin

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.

Picosecond, terawatt, all-Nd:glass CPA laser system

Abstract An all-Nd:glass fiberless chirped-pulse-amplification laser system capable of producing 1.2 ps pulses of 2 TW in power is presented. A potential for obtaining a high (≥ 10 8 ) long-time scale contrast ratio of a pulse by the use of an electro-optic deflector as well as good focusability of a high-power beam of rectangular cross-section produced by a single-pass grating compressor are demonstrated.

Enhancement of laser/EUV conversion by shaped laser pulse interacting with Li-contained targets for EUV lithography

The advantages of droplet and claster Li-contained targets for debris free EUV generation are estimated on base of analytical modeling and simulation. Conversion efficiency of laser energy into EUV energy from such targets is found to reach a few percents. The laser prepulse is proposed to enhance the laser energy conversion into emission at wavelength of 13.5 nm.

Femtosecond laser based on Yb:KYW crystals with suppression of spectral narrowing in a regenerative amplifier by spectral profiling of the pulse

This paper describes a femtosecond laser regenerative amplifier based on two Yb:KYW crystals with direct longitudinal pumping by powerful linear arrays of semiconductor injection lasers having fiber output. To prevent spectral narrowing during amplification and the corresponding lengthening of the amplified pulse when it is compressed, a combination of two Yb:KYW crystals were used, with the spectral maxima of the amplification shifted relative to each other and with spectral profiling of the amplified radiation. The mean power of the laser before compression reached 12 W at a pulse-repetition rate in the range 50–500 kHz and a spectral width of 10 nm, which is about a factor of 2 greater than the spectral width without profiling. The pulse width after compression in the compressor equalled 182 fs, while the mean power exceeded 8 W. The laser system thus developed can be used as a source of powerful femtosecond light pulses for the microprocessing of materials and for biomedical applications.

Application of Yb:KGd(WO4)2 crystals to lasers with high brightness beams

We report the experimental investigation of the thermo-optical effects that limit the brightness of radiation in the diode-end-pumped lasers with Ng- and Np-cut Yb:KGW anisotropic crystals. It is shown that the geometry of laser crystals and their relative positioning in relation to the directions of radiation propagation and polarization vector influence essentially the laser output power and beam quality at high pump power. By optimizing the crystal configuration we obtained the output power of 22 W in Q-switched mode and that of 17 W at regenerative amplification of chirped pulses with a beam quality of M2 < 1.1.

Femtosecond oscillator on Yb:KYW crystal pumped by laser diode with fiber output

A femtosecond laser based on an Yb:KYW crystal with direct longitudinal pumping by a high-power semiconductor injection laser with a fiber output is described. Femtosecond pulses were generated in the self-longitudinal-mode-locking operating condition due to the use of a semiconductor saturable absorber. The average power of the oscillator was as high as 3.5 W at a central wavelength of 1035 nm, the pulse length and pulse repetition rate being 200 fs and 85.5 MHz, respectively. The product of the pulse length and the radiation spectrum width was 1.3 times higher than the theoretical limit for the pulse shape described by the function sech2. The designed master oscillator can be also used as a stand-alone source of femtosecond radiation pulses for material microprocessing and primary source for femtosecond laser amplification systems.

Holographic diffraction gratings with multilayer insulator coatings

Based on numerical modeling of metallized diffraction gratings with multilayer insulator coatings, the diffraction efficiency of such gratings is investigated, assuming that the initial profile of the metallized grat-ing is not reproduced in the course of sequential deposition of coating layers. From comparison of experimental and calculated data, it is concluded that the initial grating relief is subject to considerable smoothing. The new nontraditional range of the optimum values of layer thicknesses, which provides a high diffraction efficiency in the operating wavelength range of 1.06 μm, is suggested. The stability of the diffraction efficiency with respect to random errors in the thickness of insulator layers deposited is investigated numerically.

1-TW Nd:glass laser system

The construction of 1 TW Nd:glass laser system with pulse compression is described. The laser system consists of master oscillator with self-mode locking and negative feed-back, stretcher, regenerative amplifier, two preamplifiers, amplifier chain and diffraction gratings compressor. The possibilities of improving the laser system parameters are discussed.

A compact femtosecond generator based on an Yb:KYW crystal with direct laser-diode pumping

This paper describes a femtosecond laser based on Yb:KYW with direct pumping by a semiconductor injection laser. The Yb:KYW laser crystal was pumped longitudinally with the radiation of an InGaAs semiconductor injection laser with fiber output of the radiation. The spatial structure of the radiation of the semiconductor laser was reshaped by a lens-based optical system in order to maximize its power concentration in the volume of the laser medium. Femtosecond pulses were generated in the longitudinal mode-locking regime by using a semiconductor saturable absorber. The generator’s mean power exceeded 1W at the central wavelength of 1043nm, with a pulse about 90fs wide. The master oscillator thus developed can be used both as a self-contained source of femtosecond light pulses and as a priming source for femtosecond laser amplifier systems.

Diffraction gratings for lasers with pulse compression: comparative research

Diffraction gratings are key elements of laser systems with pulse compression. For providing of high peak power subpicosecond pulses these gratings should have a high damage threshold, large aperture and high optical quality. In the present work comparison holographic and ruled gratings for systems of pulse compression is spent. Ruled gratings had spatial frequency 1740 grooves/mm, and holographic--1700 grooves/mm and were covered by gold, that provided 90% diffraction efficiency to the first diffraction order. Measurements of damage thresholds for 1 ps and 0.5 ns pulses have shown that for ruled grating it more than for holographic. It was probably connected to a thicker layer of metal for ruled gratings. To increase of a gratings damage threshold additional multi layer dielectric coatings were used. Computer calculations have shown that by changing of amount, material and thickness of layers it is possible to significantly improve damage thresholds. Experimental measurements have shown that for four layers there is the increase of thresholds in 2 times. Received thresholds show, that for the being available sizes as ruled (170 X 170 mm), and holographic (200 X 400 mm) gratings generation of multiterrawatt laser pulses in CPA laser systems is possible.