Page 314 - Tunable Lasers Handbook

274 Norman P. Barnes

As the quality of laser materials increases, more nearly stoichiometric laser mate-
rial should become available, which should mitigate this problem.
The quantum efficiency of these materials is relatively high. Quantum effi-
ciency has been measured for GSGG and found to be nearly unity [52]. Little evi-
dence of concentration quenching for either GSGG or GSAG has been reported.
Upper laser level lifetimes are compatible with flashlamp pumping. Upper
laser level lifetimes at room temperature are 120 and 160 ps for GSGG and
GSAG, respectively [49,50]. Upper laser level lifetime was measured as a func-
tion of temperature for GSAG and appears in Fig. 26. Lack of a precipitous
decrease in the upper laser level lifetime as a function of temperature tends to
support the contention that nonradiative decay effects are small. A two-level
model can represent the data well. From this curve fit, the lifetime of the 4TT, and
the weighted average of the ?E and ATl levels are 57 and 304 ps, respectively.
Emission spectra from these materials display a single broad peak with little
evidence of R line emission at room temperature. Emission peaks for GSGG and
GSAG occur at about 0.760 and 0.765 pm with widths of about 0.10 and 0.11
pm, respectively [49.50]. Emission spectra also appear in Figs. 24 and 25.
Because of the ground state absorption, the wavelengths corresponding to peak
laser emission are somewhat longer. Peak laser emission wavelengths for
GSGG, YSAG. and GSAG are 0.785, 0.767. and 0.784 pm, respectively [53]. At
reduced temperatures. R line emission can be observed at wavelengths slightly
shorter than about 0.7 pm.
Normal mode lasing has been achieved using flashlamp pumping of GSGG
and GSAG. Initial results using GSGG produced a threshold of about 25 J and a
slope efficiency of about 0.0005 [49]. However by filtering the flashlamp radia-
tion with a K,CrO, solution, performance was substantially increased [5]. The
threshold did not vary significantly. but the slope efficiency increased to about

m
Experimental Points
-Theoretical Two Level Model

10
Temperature (K)
FIGURE 26 Upper laser level lifetime of Cr:GSAG verws temperature.