ИСТИНА

Use of the melted gallium target in the experiments on the interaction of super-intense femtosecond laser radiation with dense matter is very convenient, as it has been shown previously [1]. First, there is no need to displace the target after each laser shot due to restoration of melted gallium surface. Moreover, the interaction of the laser pulse having moderate intensity and inhomogeneous energy fluence with melted gallium surface leads to formation of several dense microjets of matter above the target surface. So, if the main femtosecond laser pulse has a moderate-intense prepulse, which comes several nanoseconds before the main pulse, dynamical microstructuring of the target surface occurs [1,2]. The Interaction of the main sub-relativistic femtosecond laser pulse with microstructured by the prepulse melted gallium surface provides an efficient electron acceleration and, as a result, efficient generation of hard x-rays and gamma-radiation [2]. Since in previous experiments the inhomogeneity in the laser energy distribution within the focal spot was due to the aberrations at the beam optical path, there was no ability to control the distribution of the energy glance at the target surface. To overcome this restriction we calculated and manufactured binary-phase diffractive optical elements (DOEs), which provide high-order Gauss-Hermite modes generation of the femtosecond laser pulses at a central wavelength of 800 nm. In this paper, we present the results of experiments on the microjet generation above the melted gallium surface by the femtosecond laser pulses with different Gauss-Hermite intensity profiles formed by means of the DOEs. In the experiments, laser pulses were delivered by the Ti: Sa laser system of ILC MSU (pulse duration of 50 fs, pulse energy up to 120 mJ at 10 Hz repetition rate). The microjet formation was investigated with the optical pump-probe shadowgraphy technique at different times after the laser pulse interaction with target surface. The beam intensity profile and the pulse energy were additionally controlled in each laser shot. This work was supported by RFBR under grants 16-32-00143, 16-02-00302. 1. D.S. Uryupina. Phys. Plasmas, 19, 013104 (2012) 2. A. Lar'kin. Phys. Plasmas, 21, 093103 (2014)