Experimental study of bremsstrahlung and characteristic radiation spectra from laser targets irradiated with ultrashort
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Experimental Study of Bremsstrahlung and Characteristic Radiation Spectra from Laser Targets Irradiated with Ultrashort Laser Pulses with Intensities of up to ~1019 W/cm2 P. A. Tolstoukhov, D. A. Vikhlyaev, D. S. Gavrilov, A. G. Kakshin, E. A. Loboda, V. A. Lykov, V. Yu. Politov, A. V. Potapov, V. A. Pronin, V. N. Saprykin, and K. V. Safronov Zababakhin AllRussian Research Institute of Technical Physics, Russian Federal Nuclear Center, ul. Vasil’eva 13, Snezhinsk, Chelyabinsk oblast, 456770 Russia Received February 18, 2010; in final form, December 23, 2010
Abstract—Results from experimental studies of bremsstrahlung and characteristic radiation spectra from laser targets irradiated with ultrashort laser pulses with intensities of up to ~1019 W/cm2 are presented. The continuous spectra of hard Xray emission from Ta and Al targets and the line spectrum of copper were mea sured. The temperature of fast electrons was obtained from the measured hard Xray spectra, and the Kα radi ation yield from Ta was measured. The energy conversion efficiency of laser radiation into the copper char acteristic radiation was obtained from the measured yield of Kα radiation. DOI: 10.1134/S1063780X11080083
1. INTRODUCTION The interaction of an ultrashort laser pulse with a solid target results in the production of a thin layer of hot dense plasma on the target surface. The extremely strong electric and magnetic fields generated in this interaction accelerate plasma particles to high ener gies. Thus, for laser intensities of 1017–1019 W/cm2, the energy of fast electrons can reach several tens of keV [1]. Fast electrons decelerated in the target produce continuous and characteristic radiation. In this case, about 1% of the total electron energy is converted into the characteristic Кα radiation. Studies of Xray emission from the laserproduced plasma provide important information on the plasma parameters and unsteady processes occurring in this plasma. Moreover, intense ultrashort laser pulses can be used to create plasma Xray sources [1, 2]. The processes occurring in laserproduced plasmas are conventionally described using two electron veloc ity distributions having different temperatures. The temperature Te of less than 1 keV is usually ascribed to the thermal electron component, while the distribu tion of hot electrons is characterized by the parameter Thot, which corresponds to the average energy of hot electrons and describes the exponential tail of the electron velocity distribution. The average electron energy (temperature) Thot depends on the product of the laser intensity I [W/cm2] by the square of the laser
( )
α
wavelength λ [μm] as follows: Thot ~ I λ 2 . Soft Xray emission in a hot plasma is generated due to thermal electrons with the temperature Te,
whereas hard Xray (HXR) emission is associated with hot electrons, the temperature Thot of which increases rapidly with increasing laser intensity. Measurements of continuous HXR emission make it possible to determine the temperature Thot and obtain imp
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