Behavior of radiation of Nd:YAP and Nd:YAG in a resonator with extremely low Q-value have been studied. The light pulses of the form discrete spikes around 1.08 micrometers have been observed using a relatively low pumping energies in Nd:YAP. The formation of these pulses has threshold character. Additional measurement such as second harmonic generation, far field distribution and spectral behavior have shown that emitted pulses have a typical laser character. Derived value of threshold gain parameter with material losses (g0 - (alpha) ) for threshold energy is 0.581 cm-1. No similar effect was observed for Nd:YAG, even for four timeshigher value of threshold energy than Nd:YAP. Obtained results demonstrate the cooperative effects of Nd3+ ions in Nd:YAP through a correlation between electromagnetic and crystal field.
Michael P. Koselja,
"Cooperation effect of radiation in Nd:YAP", Proc. SPIE 1864, Solid State Lasers IV, (17 June 1993); doi: 10.1117/12.146886; https://doi.org/10.1117/12.146886