7B1 - Ruby laser loss measurement by comparison of R1, R2thresholds

A simple method of measuring the losses of a ruby laser resonant cavity has been developed in which the thresholds for R1line and R2line operation are compared. A quartz birefringent filter is placed in the cavity with quartz disk cut to allow Brewster-angle operation and of such a thickness that the separation between pass bands of the filter analyzer combination is 28 Å. The analyzer, placed between the filter and the output mirror, consists of a stack of fused quartz plates at the Brewster-angle. A known loss is introduced into the cavity by means of a plate inclined to the laser beam at a known angle. With the filter set for R2operation the threshold is adjusted to a suitable value by rotating the loss plate to give an attenuation L2/pass. The filter is then reset for R1operation and a different (larger) attenuation L1must be introduced by the loss plate to raise the R1threshold to the same level. An analysis of the threshold populations of the2Elevels shows that the losses of the cavity due to aU sources of loss other than the loss plate may be obtained from a plot of L₁, against L₂.