E. V. Pestryakov

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.

BeAl6O10:Cr3+ (Ti3+, Ni2+) laser crystals and their spectroscopic characteristics

Abstract The EPR, optical absorption, luminescence spectra, and lasing characteristics of Cr 3+ , Ti 3+ , and Ni 2+ ions in BeAl 6 O 10 (beryllium hexaaluminate, BHA) crystals are studied. The spectroscopic data show that the BHA crystals have an orthorhombic structure with the space group Pbcm. The temperature dependence of luminescence lifetime of the excited state of Cr 3+ ions ( τ ≈13×10 −6 s at 300 K) is investigated. The energy gap between the 2 E- and 4 T 2 -levels of Cr 3+ (∼236 cm −1 ) and the nonradiative relaxation activation energy ( E a ≈1667 cm −1 ) are determined. High-efficient tunable radiation of a new BeAl 6 O 10 :Cr 3+ laser crystal is demonstrated in the region of 0.78–0.92 μm at 300 K. It is shown that the doped BHA crystals are promising active media for tunable solid state lasers in the spectral regions of 0.7–1.0 μm (Cr 3+ ) and 1.35–1.65 μm (Ni 2+ ).

Highly nonlinear fundamental mechanisms of excitation and coloring of wide-gap crystals by intense femtosecond laser pulses

Analysis of the spatial distribution of the color centers formed in wide-gap LiF and MgF2 crystals in a laser beam channel has shown that these centers are formed in numerous longitudinal filaments into which a laser beam splits when propagating in a medium. The luminescence of the produced color centers is photoluminescence, which is excited by the supercontinuum radiation in the filaments.

High-intensity femtosecond laser systems based on coherent combining of optical fields

The basic design principles of high-intensity laser systems based on coherent combining of radiation of multichannel laser facilities are considered. The influence of the instability of parameters of individual beams on coherent combining efficiency is analyzed, and requirements on their values for realization of high-efficiency coherent combining are determined. The fundamental possibility of coherent combining of parametrically amplified femtosecond pulses is experimentally demonstrated for the first time. Combining pulses with an energy of ∼1 mJ (pulse duration of 25–30 fs) with an efficiency exceeding 83% is realized by using a spherical mirror and a specially developed high-precision electro-optical relative time jitter stabilization scheme, which ensures its stability at ∼170 as level. The analysis conducted and the experimental data confirm that there are no fundamental limitations on intensity scaling of the high-intensity laser system based on coherent combining being developed at the Institute of Laser Physics of the Siberian Branch of the Russian Academy of Sciences.

Design of high gain OPCPA for multiterawatt and petawatt class systems on large aperture LBO crystals

Comparative analysis of optimal scheme of non-collinear optical chirped-pulse parametric amplification of fewcycle femtosecond pulses from Ti:Sa laser in LBO and DKDP crystals pumped by picosecond pulses up to petawatt level is presented. A flexible code, based on the extended model of parametric amplification, which takes into account the large set of effects such as saturation, phase self-modulation, influence of beam divergence, thermal effects, and amplification of spontaneous emission was realized. A way of creating nearly 1 PW system based on LBO crystals with transform-limited pulse duration about 9 fs has been demonstrated. Comparison between DKDP and LBO crystal showed that the latter is much better for OPCPA petawatt system design than DKDP.

PHYSICAL PROPERTIES OF BEAL6O10 SINGLE CRYSTALS

Single crystals of BeAl6O10, beryllium hexaaluminate, were grown by the Czochralski method. The optical, acousto-optical, elastic, and a number of thermo-mechanical properties of bulk crystals of BeAl6O10 were investigated in comparison with crystal of BeAl2O4, chrysoberyl. It has been demonstrated that this material is the promising host for active media of tunable solid state lasers.

Laser-driven plasma wakefield electron acceleration and coherent femtosecond pulse generation in X-ray and gamma ranges

The laser wakefield acceleration (LWFA) of electrons in capillaries and gas jets followed by inverse Compton scattering of high intensity femtosecond laser pulses is discussed. The drive and scattered pulses will be produced by the two-channel multi-terawatt laser system developed in ILP SB RAS.

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.

Laser ceramics with disordered crystalline structure

New ceramic materials based on yttrium oxide Y2O3 with isovalent (Yb2O3, Nd2 O3, and Lu2O3) and heterovalent (ZrO2 and HfO2) components are synthesized, and their spectroscopic properties are investigated. Possible channels of losses in the gain of stimulated radiation in the radiative transitions of Nd3+ and Yb3+ ions in ceramics with heterovalent additives are studied. The results of measurements of Y2O3 ceramics doped with zirconium and hafnium ions, the emission bandwidth and the lifetimes of the 4F3/2 and 2F5/2 levels of Nd3+ and Yb3+ ions, respectively, are presented. It is shown that the nonradiative population of the 4F3/2 levels of neodymium ions is due to their dipole-dipole interaction with Zr3+ and Hf3+ ions. Laser generation in [(Yb0.01Lu0.24Y0.75)2O3]0.88(ZrO2)0.12 ceramics with disordered crystalline structure was achieved at a wavelength of 1034 nm with a differential efficiency of 29%.