Sensitive large-area calorimeter for measuring the energy of laser-produced plasma soft X radiation

A thermoelectric detector for measuring the energy of laser-produced plasma soft X radiation is described. The measurements are made in the wave length range, lambda=1.5 to 14 A. A small thickness of the detecting element (approximately 100 mcm Al), great number of copper-constantan thermocouples and large area (about 25 cm2) allow to obtain a high sensitivity of the instrument equal to 10-4 J/cm2. The absolute calibration of the instrument was performed in a vacuum chamber at a pressure < or approximately 0.1 torr by the substitution method. Total error when measuring the X radiation energy of about 10-4 J is 15%; for the energy of about 10-2 J it is 5%. The conversion coefficient of the laser radiation into the plasma X radiation for a teflon target has been determined to be about 3%