Active Optical Filter.

An active optical filter comprising a device which utilizes a phenomenon known as 'total internal reflection.' Two prisms are provided with a medium interposed between them. The index of refraction of the interposed medium is one which will change and decrease the light-transmitting properties of the filter with an increase in intensity of the incident light to form an optical switch which limits the transmitted light above certain power levels. These power levels are often found in Q-switched laser pulses. (Author)