Vladimir V. Lozhkarev

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.

Adaptive acousto-optic technique for femtosecond laser pulse shaping

We discuss the theoretical and experimental investigation of acousto-optic dispersive tunable filters, based on quasi-collinear geometry of light-sound interaction in a tellurium dioxide single crystal. The geometry uses the effect of strong acoustic anisotropy in the paratellurite as well as peculiarities of acoustic wave reflections at the free boundary of the crystal. A mathematical concept for determination of optical, electrical, and constructional parameters of the filters is developed. Different experimental acousto-optic filters intended for femtosecond pulse shaping are designed and tested. Preliminary experiments are performed in a subpetawatt optical parametric chirped pulse amplification laser system. The experimental data conform completely with the predicted data.

High-efficiency second-harmonic generation of superintense ultrashort laser pulses

The effect of instantaneous cubic nonlinearity on second-harmonic generation of femtosecond laser pulses is investigated. The possibility of improving generation efficiency and shortening pulse duration is analyzed. Energy conversion efficiency of 60% was obtained in an experiment in a 1 mm thickness KDP crystal at the peak intensity of 0.6 TW/cm(2) and the duration of 60 fs.

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.

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.

Second-Harmonic Generation of Super Powerful Femtosecond Pulses Under Strong Influence of Cubic Nonlinearity

A theoretical model of second-harmonic generation (SHG) under strong influence of cubic nonlinearity was verified in experiment. Effective energy conversion in thin potassium dihydrogen phosphate crystals at peak intensity up to 5 TW/cm2 (B-integral equaled 6.4) was demonstrated and no crystal damage was observed. Comparative analysis of SHG of radiation at the fundamental wavelengths of 910 and 800 nm showed the major advantages of the first one. The double-pass geometry of SHG in an ultrathin crystal on a substrate is discussed in detail. Additional correction of parabolic spectral phase of the SH radiation allows pulse duration to be shortened from 20 to 9 fs for 910 nm fundamental wavelength and from 20 to 12 fs for 800 nm.

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.

A method for obtaining inverted images

A method for obtaining a brightness-inverted image of opaque objects is described. The factor of conversion of images from negative into positive was up to 350% relative to the average intensity level of the incident beam, which is in agreement with numerical calculations.

Deep tomography of biological tissues by optoacoustic method

The results of theoretical and experimental investigations of pulsed optoacoustic (OA) method for tomography of biological objects in the frequency range 1-10 MHz at the depths of up to 5 centimeters are presented. Some key imaging problems - reducing of effect of surface OA pulse and light shock on the received signal, enhancing of the uniformity of light distribution inside the object keeping light irradiation at the reliable level - can be solved by choice of experiment configuration and spatial scanning. Taking into account distortions of OA signal due to frequency dependence of tissue properties and receiving/amplifying circuits the acoustical source position can be found using signal processing e.g. inverse filtering algorithm. The next step to the high-quality imaging is in use of reconstructive tomographic algorithms. The experimental setup was designed for OA tomographic investigation of phantoms (artificial objects and biotissue samples) as well as in vivo objects. The received signals were amplified, digitized and stored in PC. The experiments with the model objects were carried out to elaborate principles of multichannel receiving by weakly-directed probes and to study the methods for reconstruction of 2D tomograms. The results show that post-processing and choice of experiment geometry allow to improve significantly the quality of optoacoustic tomograms. This work was supported by RFBR (Project #00-02-16600).

Development of eye-safe IR lidar emitter and detector technologies

Lidar systems developed over the last decade have demonstrated impressive results when applied to the detection of specific volatile chemicals. MOst of these systems are limited to a single wavelength or, at best, a narrow wavelength band. Exceptions are DIAL systems, CO2 lidars, and dye laser sources. Currently under development at INEEL and PASSAT Ltd. are technologies that convert Nd:YAG laser energy to the 8-11 micrometers band with an output of 20 millijoules/pulse or higher. Wavelength shifting is accomplished using a tunable optical parametric oscillator and amplifier, and stimulated Raman scattering cells as the emitter. This system can be made tunable continuously from 6-11 microns which makes this an eyesafe laser system. In addition, identical SRS cells are used as low noise, narrow band receivers that are sensitive to extremely low levels of scattered laser radiation. Use of this technology is to generate a pair of pulses at different wavelengths for DIAL applications. A description of this system will be provided along with test results.