V. E. Leshchenko

Coherent combining of femtosecond pulses parametrically amplified in BBO crystals.

We report on the first experimental realization of coherent combining of parametrically amplified femtosecond pulses. The proposed and implemented two-loop active stabilization system allows us to achieve 110 as relative timing jitter between combined pulses, which is necessary for efficient coherent beam combining. In each channel of the two-channel laser setup, pulses were parametrically amplified in β-BaB2O4 (BBO) crystals to 50 μJ energy, compressed to 49 fs duration, and then coherently combined with efficiency as high as 97%. Currently, it is the shortest duration of amplified pulses for which coherent combining is demonstrated.

Coherent combining of multimillijoule parametric-amplified femtosecond pulses

We report on the first experimental realization of the coherent combining of multimillijoule parametric-amplified femtosecond pulses. An original two-channel laser system based on parametric amplification in β-BaB2O4 and LiB3O5 crystals was created. High-contrast laser pulses, with up to 100 mJ of energy and with a pulse duration of 23 fs, were generated in both channels. An original setup for active timing-jitter stabilization was developed. It allowed reduction of the relative timing jitter of the amplified pulses to 40 as, which enabled coherent combining with an efficiency as high as 95%. At the present time, this work demonstrates coherent combining of femtosecond pulses with both the highest energy and the shortest pulse duration.

Coherent combining efficiency in tiled and filled aperture approaches.

Different approaches to qualify coherent beam combining performance in tiled and filled aperture combining experiments are discussed. The dependence of the combining efficiency on different misalignments and the number of combining pulses has been investigated and analytical equations for its evaluation have been obtained. The results provide design guidelines for laser systems based on coherent beam combining and allow comparison of experiments performed in different combining approaches. The analysis shows that there are good prospects to scale achieved peak intensity.

Guiding femtosecond high-intensity high-contrast laser pulses by copper capillaries

Propagation of high-intensity, high-contrast ( <10−8), 50 fs laser pulses through triangular copper capillaries is experimentally studied. The relative transmission through 20-mm-long, about 50 μm wide capillaries is directly measured to be 70% for input intensities up to 1017 W/cm2. The copper reflectivity in vacuum, helium, and air is measured in the intensity range of 1010–1017 W/cm2. No reflectivity decrease in vacuum and helium is observed, which leads to the conclusion that copper capillary waveguides can efficiently guide laser pulses of intensities greater than 1019 W/cm2 on the capillary axis (that corresponds to 1017 W/cm2 on the walls). The reduction of the transmission efficiency to zero after a number of transmitted pulses is observed, which is caused by plug formation inside the capillary. The dependence of the capillary lifetime on the pulse energy is measured.

Aberration-free broadband stretcher-compressor system for femtosecond petawatt-level laser system based on parametric amplification

An optimal stretcher-compressor scheme is designed for laser facilities based onbased on optical parametric chirped-pulse amplification under picosecond (∼100 ps) pumping, which enables one to attain petawatt peak power of pulses less than 10 fs with high contrast and low aberrations. The stretcher design is based on an Öfner telescope with spherical mirrors and two diffraction gratings, one being placed at the center of the spherical mirrors. It is shown to be the only possible aberration-free stretcher design. The simulation performed has shown that a compressor consisting of four transmission diffraction gratings with an aperture 112 × 125 mm, a thickness of 3 mm, and chirped mirrors with 100-mm aperture that introduce −4500 fs2 dispersion allows amplified pulse compression down to <10 fs length and 1 PW peak power with the total B-integral lower than 1. The designed stretcher-compressor system is planned to be implemented in the high power femtosecond laser system being developed at ILP SB RAS.

High-energy few-cycle pulses for relativistic laser-matter interaction: Status of the Petawatt Field Synthesizer

The Petawatt Field Synthesizer (PFS) light source has been under development at the Max-Planck-Institut für Quantenoptik (Garching, Germany) for several years [1]. Its aim is to deliver few-cycle, waveform-controlled light pulses with unprecedented peak power at 10 Hz repetition rate from a compact (laboratory-scale) system.

Current status and development of the 10 Hz, 1 picosecond, 2 J and 10 J Yb:YAG CPA amplifiers of the Petawatt Field Synthesizer

The Petawatt Field Synthesizer (PFS) is an OPCPA driven light source that is currently being developed at the Max-Planck-Institut für Quantenoptik in Garching, Germany. The target parameters are few-cycle, waveform-controlled light pulses with a repetition rate of 10 Hz and a peak power in the Petawatt regime [1]. The system relies on a cascaded broadband OPCPA that is pumped by a picosecond, all-diode-pumped Yb:YAG chirped-pulse-amplification (CPA) laser chain, the PFS pumplaser. In its final version, the pumplaser has to deliver nanosecond pulses with energies above 10 J at a wavelength of 1030 nm that can be compressed down to 1 picosecond and converted to 515 nm. Here, we report on the design and current performance of the new 2 J amplifier and discuss the design and ongoing development of the final 10 J amplifier.

Generation and characterization of surface high harmonics with a few cycle laser — First results and future plans

High harmonics generated on solid surfaces (SHHG) promise a much higher efficiency compared to harmonics generated in gases. In case of ROM (Relativistically Oscillating Mirror) mechanism [1], conversion efficiencies up to the percent level are predicted [2]. An interesting property of ROM is that the maximum photon energy scales with the laser intensity. In addition an isolated attosecond (as) pulse can be generated when using a few-cycle driver pulse. However, for ROM, relativistic laser intensities above 1 × 1018 W/cm2 are required, which in combination with the few-cycle pulse duration is not readily available.

Dual-channel multiterawatt laser system with coherent beam combining

The dual-channel femtosecond laser system with each channel consisting of three BBO and LBO crystals based broadband parametric amplification stages of Ti:Sa laser radiation and relative jitter stabilization system to 110 as level is presented. For the first time coherent combining of two sequences of parametrically amplified femtosecond pulses with energy of ~ 150 mJ, 10 Hz repetition rate is experimentally realized. Coherent combining efficiency of over 90% is reached. Experimental results of parametrically amplified contrast measurement are presented with further comparison with simulation results based on the model of parametric luminescence evolution developed by us. In order to achieve petawatt power level schemes of multibeam pumping of the booster cascade of developed laser system are considered.