Laser devices are now well known, and it is likewise well known that laser devices can provide relatively high power outputs. In addition, it is known that transmissive optics can be utilized intracavity in a laser device, and such use is shown, by way of example, in FIG. 1, illustrating, typically, a laser 5 having a laser cavity 7 extending between mirrors 9 and 11 with lens 13 positioned in the laser cavity between mirror 9 and Brewster window 15 of a laser medium 17 (shown in FIG. 1 as a gas laser medium within the laser cavity).
Power degradation in laser devices due to contamination buildup on intracavity optical surfaces has, however, been a serious problem in many applications, and often dictates the service interval for current commercial instrumentation that is based on low-loss laser devices.
It has been observed that mirror surfaces, for example, show lower apparent degradation rates than anti-reflection coated surfaces of transmissive optics, even when in similar environments. This observation is consistent with the contamination that consists of substantially non-absorbing (or dielectric) Material that condenses to form relatively uniform films oil intracavity surfaces.
A dielectric film deposited on a mirror surface will typically degrade its nominally high reflectance only a small amount, while a dielectric film deposited on an anti-reflection coated surface, or on a Brewster surface, normally raises its nominally low reflectance, and at least in some cases, does so quite dramaticaly.
Currently, increased reflectance on the surfaces of transmissive optics has been ignored, or at least inadequately handled, in laser based devices, and this has caused degradation of the performance of such devices. In particular, the curvature and orientation of surfaces of transmissive optics are now commonly chosen without regard to how light reflected from the surface propagates with respect to the cavity mode, and hence the light reflected from the surface is lost from the laser cavity, resulting in power losses.