Measurement and unfolding of MeV x-ray spectra from high-intensity laser-solid interactions*

During the interaction between a high-intensity laser (∼ 10²¹ W/cm²) and a mm-thick solid target, a population of hot electrons is generated which travel through the target and create MeV photons via bremsstrahlung radiation. Such high-energy photons are useful in imaging applications, so it is important to optimize the energy and yield of this process. At an experiment performed at the Texas Petawatt laser, the target type (bare, plastic coating, nanowires), laser energy (50 J – 140 J), and pulse duration (120 fs – 600 fs) were varied to study the effects on the produced X-ray spectra. These spectra were measured with an assortment of diagnostics measuring radiation from the front and back sides of the target surface. An advantage of several of these diagnostics is that they can function at a high repetition rate, which allows them to monitor the X-ray spectra across thousands of shots during high repetition rate applications. Here we report on the unfolded spectra from two of these diagnostics: a scintillating attenuation spectrometer and a scintillating screen with a filter array.