Observation of transmission enhancement phenomena in a laser resonant cavity

We present the experimental observation of a phenomenon in which the reflection loss, induced by an uncoated glass sample placed in a laser cavity, significantly reduces at a series of incident angles. The light amplification condition for a laser to work can be satisfied by means of this phenomenon, though the gain is less than the loss when the sample is placed in the normal incidence. The angle ranges for the laser can keep working are intermittent, and both of the lasing range and no-lasing range become narrow with the incident angle increasing. Six kinds of optical glass samples and one birefringent sample have been tested, and three types of lasers are used to confirm this phenomenon. This phenomenon may make the anti-reflection film be not necessary for a transparent sample in some techniques or instruments based on the characteristics of laser resonant cavity. Principle and properties of this phenomenon are analyzed, and the theoretical analyses are coincident to the experimental observations. Three conditions for this phenomenon to occur, as well as the potential applications, are given finally.