Abstract

Nd:YAG is one of the most important solid state gain media for cw and pulsed lasers and in the last few years it has also been the preferred medium in diode-pumped laser systems. Recently we explored the concept of producing a compact mode-locked Nd:YAG laser at 1.06 µm using synchropumping techniques. Although synchropumping of Nd:YAG is generally thought to be unfeasible due to the long upper laser level lifetime (hundreds of microseconds), we recently demonstrated such mode-locked operation¹ based on gain modulation through pump band to upper laser level transitions. To determine the limitations and effectiveness of synchropumped mode locking, we have measured this non-radiative lifetime for the first time using a pump-probe technique in a standard (1%) doped Nd:YAG sample. The ⁴G_7/2 pump band manifold was excited with 2.3-mJ. 40-ps, λ = 0.53-µm pulses and the population of the upper laser level (⁴F_3/2) was monitored by measuring the gain as a function of time delay for a weak 55-ps, λ = 1.06-µm pulse. The gain was observed to rise with a single exponential temporal characteristic and a time constant of 470 ps at 300 K. This time was observed to be essentially constant for temperatures between 150 and 450 K.

© 1989 Optical Society of America