Abstract: An aerodynamic window for a gas laser, comprising a chamber positioned at one end of a structure forming part of a laser cavity in which lasing action can take place the chamber having first and second apertures aligned with the optical axis of the laser cavity and its longitudinal axis at an acute angle to the optical axis of the optical cavity and means whereby the chamber can be continuously evacuated, wherein the chamber is of uniform cross section and the apertures are situated in a side wall and an end wall of the chamber respectively.Preferably, the second aperture is displaced from the longitudinal axis of the chamber towards the first aperture.

Abstract: A transverse flow gas transport laser including a closed loop of ducting through which a gaseous lasing medium can be circulated so as to pass continuously through a lasing region of the ducting in which it can be excited into lasing activity, in which there is included means for extracting a portion of the gaseous lasing medium from a region of the ducting other than the lasing region, comprising the said portion of the lasing medium and injecting it back into the remainder of the lasing medium thereby to induce flow of the gaseous medium through the lasing region of the ducting.

Abstract: A laser having an unstable optical cavity including an output mirror having an off-axis hole therein through which laser radiation can pass to maintain lasing action in an active medium situated in the laser optical cavity, wherein the output mirror is so shaped and positioned as to present an elliptical profile to laser radiation incident upon it, the major axis of the ellipse extending in the direction of offset of the hole in the output mirror.

Abstract: A control device for a segmented anode gas discharge laser adapted to sense the onset of arcing in a region of the anode, switch off that portion of the anode and reenergize it when the arcing has ceased.

Abstract: A transverse flow gas discharge laser in which the cathode has an elongated cross-section the larger dimension of which is positioned at an angle to the direction of flow of the gaseous lasing medium. The anode of the laser is of modular construction and consists of an array of individually ballasted cylindrical buttons. Both the anode and the cathode are so positioned that they intereact aerodynamically with the adjacent duct wall to produce a stable electric discharge between them.