Ultra-intense gamma-rays created using the Texas Petawatt Laser

In a series of experiments at the Texas Petawatt Laser (TPW) in Austin, TX, we have used attenuation spectrometers, dosimeters, and a new Forward Compton Electron Spectrometer (FCES) to measure and characterize the angular distribution, flux, and energy spectrum of the X-rays and gamma rays produced by the TPW striking multi-millimeter thick gold targets. Our results represent the first such measurements at laser intensities ≥10²¹W×cm^-2 and pulse durations ≤150fs. We obtain a maximum yield of X-ray and gamma ray energy with respect to laser energy of 4% and a mean yield of 2%. We further obtain a Full Width Half Maximum (FWHM) of the gamma angular distribution of 33°. We were able to characterize the gamma-ray spectrum from 3MeV to 50MeV using a Forward Compton Electron Spectrometer, with an energy resolution of 10-15% and mean bremsstrahlung effective kT of ~6MeV. We were able to characterize the spectrum from 1 to 5MeV using a Filter Stack (attenuation) Spectrometer, measuring a mean X-ray temperature for the spectrum from 3 to 5MeV of 2.1MeV, suggesting that the low-energy gammas are bremsstrahlung from secondary electrons.