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 R
1
line and R
2
line 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 R
2
operation the threshold is adjusted to a suitable value by rotating the loss plate to give an attenuation L
2
/pass. The filter is then reset for R
1
operation and a different (larger) attenuation L
1
must be introduced by the loss plate to raise the R
1
threshold to the same level. An analysis of the threshold populations of the
²
E
levels 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
\log L_{1}
, against
\log L_{2}
.