Abstract: In a method of operating and controlling hysteresis motors energized by a three-phase power supply and individually monitored by an operating monitoring system, whereby the effective power output of the individual motors is determined and the three-phase voltage is changed if the effective power output deviates from a predetermined range, the hysteresis motors are first energized at an intermediate range voltage until they reach nominal speed and are then running at synchronous speed, the supply voltage is then increased to an upper range, where the remanent magnet pole strength is impressed on the armature and then reduced to a lower range for continuous operation of the motors, the power output of the individual motors is monitored and, if it drops below a threshold indicating a switch to asynchronous operation, the operating voltage is again increased to the intermediate range for renewed synchronization.

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 an optically stable laser resonator which includes at one end a fully reflective mirror, a partially reflective mirror serving as an uncoupling window at the other end and a pair of spherical optical mirrors one being diverging and the other being converging to provide an expanded beam at the uncoupling window wherein the beam axis has an incidence angle w.sub.1 with the diverging lens axis which is between 10.degree. and 45.degree. and the axis of the beam extending between the spherical mirrors has an incidence angle with the converging mirror axis which, depending on the mirror distance and the focal length of the mirrors, is so calculated that astigmatism is essentially eliminated.

Abstract: In a method for uniformly removing layers from a coated surface, a laser beam is used for scanning the surface along parallel scanning lines wherein the laser beam has a surface illuminating cross-section with a central area defined between parallel lines extending transverse to the scanning lines and tapered marginal end areas extending from the transverse opposite ends of the central area to a predetermined distance and the scanning line distance is so selected that the central areas of the surface illuminating cross-sections of adjacent scanning lines are spaced by the predetermined distance and the tapered marginal end areas of the beam overlap between the scanning lines and together provide, in the overlap area, for essentially the same laser beam exposure as in the central area.