Page 71 - Tunable Lasers Handbook

52 R. C. Sze and D. G. Harris

FIGURE 1 5 Confocal positive-branch unstable resonator.

I I
10 20
IvIAGNIFICATION (Mi
FIGURE 1 6 Time to reach diffraction limit and gain as a function of magnification.

Consider, for example, a plot oft and gc. for a cavity design where the gain
length is La = 20 cm and, due to mechanical or other constraints, the cavity sepa-
ration is L = 76 cm. We calculate g, for cases where A = 20 and 30. All of the
excimer laser transitions should have the A parameter lying within this range.
Figure 16 shows that at a magnification of 20 we can have small-signal gains as
high as 0.3 cm-1. In short-pulse discharge excimer laser systems, the measured
small-signal gain lies between 0.2 to 0.3 cm-1. We see that the problem here lies
in the time required to reach the diffraction limit. With the cavity separation at