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22Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2018
STIMULATED RAMAN SCATTERING AND TWO PLASMON DECAY INSTABILITIES IN INHOMOGENEOUS FEMTOSECOND LASER PLASMA
Tsymbalov I.N.,*1 Gorlova D.A.1, Sen'kevich A. M.1, Shulyapov S.A.,1 Ivanov K.A.,1 Ksenofontov P.A.,2 Brantov A.V.,2 Savel'ev A.B.,1 Bychenkov V.Yu.2
Faculty of Physics and International Laser Center of Lomonosov Moscow State University, Moscow, Russia 2P.N. Lebedev Physical Institute, Russian Academy of Sciences, Moscow, Russia
Plasma wave excitation in inhomogeneous femtosecond laser plasma due to the combined effect of two plasmon decay instability and stimulated Raman scattering is demonstrated. PIC simulation results and their experimental validation are presented.
1. Introduction
Electron acceleration in femtosecond laser plasma with scalelength LA~1 is due to nonlinear plasma wave excitation [1]. Optimization of high energy electrons generation requires study of nonlinear laser-plasma interaction and wave excitation. Radiation scattered by waves carries information about their frequencies, wave numbers and space localization and can be used for plasma wave diagnostics. Studies of instability in femtosecond plasma have already been carried out in papers [2], a feature of this work is the short plasma gradient (LA~1) and subrelativistic intensities of the laser pulse.
2. Simulation parameters and experimental setup.
We made interaction simulations using the fully relativistic 3D3V PIC code Mandor. The spatial resolution was A/100, temporal resolution was 3*10-3fs. The planar foil target consisting of cold ions and electrons. A p-polarized laser pulse with duration of 50 - 200 fs (FWHM) entered the simulation box. Varying the laser pulse intensity, the initial electron density scale length (0.5-10A) and incident angle (150-750) we found the dependences of the plasmon parameters
and optical harmonics yield on these parameters. In our experiments we used Ti: Sapphire
18 2
laser system (pulse duration - 50 - 200 fs, maximal intensity on target - 5-1010W/cmz). The laser radiation was focused by off-axis parabolic mirror (F~5cm) onto the obliquely metal target. To create pre-plasma layer on the target surface we use Nd:YAG laser(maximal intensity on target -1012W/cm ). The fiber spectrometers and CCD cameras with different interference filters were used to measure the plasma emission in visible and infrared ranges at different angles.
3. Results
The PIC simulation showed that the main feature of the oblique incidence laser pulse interaction with short plasma gradient is refraction, which leads to the appearance of new components in the spatial spectrum. So, the instability pump wave should now be considered as a sum of plane waves, and this leads to the appearance of new features for instability growth rate. The analysis of electromagnetic fields showed that in addition to the electrostatic component in the ponderomotive forces corresponding to the TPD, there is an electromagnetic component corresponding to SRS. SRS and TPD have a common plasma wave. This agrees with the observed values of the plasmon wave vector kx=1.1-1.6k0 [3] The scattering of the fundamental wave by plasma generates a radiation source with an even broader spectral ky component and a rather narrow kx component, which determines the angular distributions of the scattered radiation at frequencies 3/2ro and 1/2ro. The angular distributions of 3/2ro radiation from PIC simulation are in good agreement with the experimental data. Supported by RFBR grants #16-02-00263, #18-32-00868
1. K. Ivanov, I. Tsymbalov, S. Shulyapov, D. Krestovskikh, A. Brantov, V.Y. Bychenkov, R. Volkov, and A. Savel'ev, Phys. Plasmas 24, 063109(2017)
2. A. Tarasevitch, C. Dietrich, C. Blome, K. Sokolowski-Tinten, and D. von der Linde, Phys. Rev. E 68, 026410 (2003)
3. B. Quesnel, P. Mora, J.C. Adam, A. Heron, and G. Laval, Phys. Plasmas 4, 3358 (1997).
