Diode-pumped 2 μm lasers are highly suitable for many applications, notably coherent laser radar systems. As a CW diode-pumped laser Tm:YAG behaves very well, but we and others have also noted that these lasers are less than perfect under Q-switched conditions, for two reasons. The upper laser level lifetime is shortened significantly if the laser is pumped intensely, as a result of non-linear optical processes which tend to depopulate the upper laser level. Previously available laser materials were also susceptible to bulk optical damage, which frequently occured at low internal energy fluences. Our previous demonstration of 1 mJ pulses relied on finding a "good" spot on the crystal. At the 1 mJ energy level the effective storage time was about 3.2 ms, more than a factor of 3 shorter than the 11 ms fluorescence lifetime. Improved performance was predicted if a) the laser mode volume is pumped as uniformly as possible, i.e. with a near-circular pump spot, and b) cleaner crystals were used, since it was strongly suspected that the bulk damage resulted from the rapid heating of particulate inclusions.
© 1991 Optical Society of AmericaPDF Article