Lensless Fourier-Transform Method for Optical Holography

Fig. 2. A. Instrumental response. B. Excitation spectrum of the 1.93-1L fluorescence of 1I2-atom percent Tm+3 in Er20 3• C. Excitation spectrum of the 1.93-1L fluorescence of 1/2-atom percent Tm+3 in Y203' times as intense as the emission from 1/2% Tm+3 in Y20 3 at 77°K under tungsten excitation. The laser experiments were conducted with a sample approximately 1 cm in length with flat and parallel silvered ends using a fast gold-doped germanium detector. The threshold was less than 3 joules into a I-in. straight xenon flash lamp in close proximity to the liquid nitrogen dewar containing the sample. No laser operation could be obtained from the nearby fluorescent lines at an energy input of 20 joules. The lifetime of the fluorescence is 2.9 msec at 77°K with a build-up time of about 200 f..tsec. Nearthreshold laser emission is observed 50 f..tsec after the 250-f..tsec lamp pulse is over, an effect which is a consequence of this build-up time. CW operation was observed using 500-W quartziodine tungsten lamps as the pumping source. In the configuration used, the liquid nitrogen dewar containing the sample was surrounded by an array of 12 lamps. Threshold was reached with three lamps. The crystals were grown by A. C. Pastor and K. Arita under the direction of R. C. Pastor. We thank D. Roberts for the use of the CW laser housing, C. R. Duncan for technical assistance, and]. Mikiska for the coatings.