Rudolf R. Gerke

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.

100-TW Femtosecond Laser Based on Parametric Amplification

In experiments on the parametrical amplification of femtosecond pulses in wide-aperture DKDP crystals, a power of more than 100 TW has been reached, which is much higher than the record level achieved in such lasers. The energy efficiency obtained for the parametric amplifier is equal to 27%. The energy of a 72-fs pulse is equal to 10 J.

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.

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.

Methods and means of superstrong field formation on multiterawatt laser facility “Progress-P”

We present the parameters of compressor and focusing systems of 30-TW Nd:glass laser facility “Progress-P” and results of experimental investigation of beam propagation through this systems. Near diffraction-limited beam quality is obtained at output laser amplifier chain by use the low-thermal phosphate Nd:glass and high quality optical elements. Output 180 mm beam is compressed using two holographic gratings with dimensions 420×210 mm and focused on targets by means on-axis parabolic mirror with focal length of 200 mm. About 50% energy is obtained in 8 μm focal spot in target chamber for low power beam. Investigations of the focal spot characteristics for high-power beam are under way.

Toward Petawatt Laser Based on Optical Parametrical Amplification: Status Quo and Perspectives

Laser power of more than 100TW (70fs, 10J) has been achieved in experiments on optical parametric amplification of femtosecond pulses in KD*P crystals. Energy conversion efficiency of optical parametric amplifier is 27%.

On the effect of nonequidistance of dielectric coatings and the groove profile on the energy characteristics of holographic diffraction gratings

The diffraction efficiency and the resistance to radiation damage of gratings with a multilayer dielectric coating, which are used for compression of high-power laser pulses, are studied. The effect of smoothing of the profile of the metallized surface of the grating upon deposition of dielectric coatings on the energy characteristics of the grating at the wavelength λ=1.05 μm is analyzed. Gratings with various profiles of the metallic surface relief and with different contrast of the refractive indices of the dielectrics forming the coating are considered.

Diffraction efficiency and damage threshold of the holographic grating with a multilayer dielectric coating

In the process of creation of multi-layered coating through evaporation of the dielectric occurs considerable smoothing of an initial grating relief. The smoothing results in reduce of the diffraction efficiency and damage threshold of the grating at the working wavelength. The value of the smoothing is measured. Calculation of the structure parameters of the grating by real smoothing is made to improve the diffraction efficiency and damage threshold.

Optimization of the structure parameters of high-efficiency gratings with multilayer dielectric coating for laser pulse compression

Optimization of the grating structure parameters at the working wavelength 1.06 (mu) is made on the basis of the calculation method for the diffraction gratings with nonequidistant coatings. The comparison of the experimental and calculation data has revealed the considerable smoothing of an initial grating relief by evaporation of multi-layered coating. On the basis of theoretical estimations the untraditional area of optimum layer thickness is suggested. The theoretical diffraction efficiency for this area at real relief smoothing is 96%.

Photosensitivity of As-S-based chalcogenide photoresists in the recording of relief phase holograms

The photosensitivity of AsxSb(Ge)yS100-x-y (x equals 35 - 45, y equals 0 - 6) films to light with wavelength 488 nm was investigated. The value of photosensitivity was quantified using the results of chemical etching in amine solutions for as-deposited and exposed films. It was found the exposure required to obtain the optimal relief depth, which is from 0.1 to 0.3 micrometer for holographic gratings, decreases with both sulfur and antimony content from about 2 J/cm2 for As2S3 to about 0.3 J/cm2 for As30Sb4S66. The photosensitivity of the Ge doped films is sharp decreased with Ge content. A model of effect of additives on the change of dissolution kinetics was proposed. It is based on the consideration of a photopolymerization of films leading to the formation of the insoluble network of AsS3/2 structural units.