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.

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The conceptual design of ultra-high intensity multichannel laser system with coherent beam combining is presented. Design of 1 PW and 10 PW laser channels with pulse repetition rate of 10 Hz based on optical parametric amplification in LBO crystals is considered. Requirements of the most critical pulse parameters for high efficiency coherent beam combining and their dependence on the number of channels is analyzed. Experimentally coherent beam combining of parametrically amplified compressed femtosecond pulses is demonstrated for the first time. Original two-loop relative timing jitter active stabilization scheme is proposed and experimentally investigated. 97% coherent beam combining efficiency is achieved with 110 as relative timing jitter.

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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.

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