Measurement of hard X-ray spectra on femtosecond laser facility
Properties of hard x-rays from tantalum targets, irradiated by femtosecond laser, were investigated experimentally. During experiments, focal spot size have been varied from 3 um to 10 um, laser pulse intensity on target changed from 10^19 W/cm^2 to 10^20 W/cm^2. Two spectrometers based on gray filters methods were employed for investigation of hard x-ray yield. Spectrometer on image plates was applied for detection in photon energy range E=100-600 keV, scintillation spectrometer was applied for detection in the range E>400 keV. Using scintillation spectrometer, spectrum temperature and relative hard x-ray yield in every laser shot were quantified. By placing spectrometer at different angles to laser radiation axis, an x ray direction pattern was investigated. All in all it was found that: - x-ray spectrum temperature in intensity range from 10^19 to 10^20 W/cm^2 equals to ~1 MeV independently on direction; - conversion of laser pulse energy into x-rays in the range from 0.1 to 1 MeV equals to ~5•10^(-4) 1/sr; - X-ray yield has maximum in the direction of laser radiation propagation.