Diagnosing hot electron production by short pulse, high intensity lasers using photonuclear reactions

Solid targets irradiated with 10(19) W/cm(2) or greater of 1 mu m light in picosecond pulses are found to be radioactive. The strongest activities obs erved are the result of photonuclear reactions in which an energetic photon excites the nucleus sufficiently to produce particle emission leaving a ra dioactive daughter. The photoreaction cross sections are known for a wide r ange of nuclei and provide a quantitative measure of the photon flux produc ed in the target. Both the delayed daughter activities and measurements of the prompt particles emitted in the reaction can be used as diagnostics. Ex amples of these techniques applied in diagnosing experiments at the Nova la ser facility adapted to generate petawatt pulses using chirped pulse amplif ication will be presented. These results will be compared with bremsstrahlu ng photon spectra calculated using electron spectra measured in a magnetic spectrograph. (C) 1999 American Institute of Physics. [S0034-6748(99)59601- 9].