Abstract: In an instrument for measuring the energy of optical radiation, particularly laser radiation, a number of radiation absorbing plate-like foraminous elements are disposed in a tubular housing such that the radiation entering at one end of the housing is successively absorbed by the radiation absorbing elements which are heated thereby, and a fan disposed at the other end of the housing moves cooling air through the housing and through the radiation absorbing elements whereby the air is heated. From the temperature increase of the cooling air which is measured by a temperature measuring element, the energy of the optical radiation entering the housing is determined.

Abstract: In a pulsed gas laser apparatus for operation at ambient pressure comprising a laser module having a tubular window open at its distal end for the coupling or uncoupling of a laser beam, the tubular window has a volume which is at least equal to, or a multiple of, the volume change of the laser gas in the module during pulsed laser operation and extends essentially vertically from the laser module. The window includes a mixing zone in which during pulsed laser operation both laser gas and ambient gas are present, the window extending downwardly if the laser gas is lighter than the ambient gas and upwardly if the laser gas is heavier than the ambient gas thereby to counteract infiltration of ambient gas into the window. Also, means are provided for controlling the laser gas volume supplied to the module such that the concentration of the ambient gas in the mixing zone in the window remains below a predetermined limit.