Quasi-continuous-wave long-pulsed, all-solid-state Nd:YAG modeless laser

We demonstrate the quasi-continuous-wave long-pulsed operation of a compact all-solid-state modeless laser based on intracavity frequency-shifted feedback by an acousto-optic modulator. The laser active medium is an Nd:YAG crystal rod, side-pumped by high-brightness laser diodes of 808 nm. When the pump repetition and duration are 200 Hz & 250 mu s, the maximum single pulse energy of 85 mJ is produced at an optical conversion efficiency of similar to 34%, and also a good beam quality of M-X(2) = 1.80 & M-Y(2) = 1.78 is obtained in the horizontal & vertical directions respectively. Moreover, a narrow continuous spectrum is achieved with the 3-dB linewidth of 75 pm (i.e. 20 GHz) and the center wavelength of 1064.16 nm. Via the sum frequency generation, such a long-pulse (several hundred mu s), narrow-linewidth modeless laser source is preferred for solving the major problem of saturation of the mesospheric sodium atoms and can create a much brighter sodium guide star to meet the needs of adaptive imaging applications in astronomy.