An inexpensive diode-pumped mode-locked Nd:YVO4 laser for nonlinear optical microscopy

We report an inexpensive diode-pumped Nd:YVO4 laser mode-locked with combined effects of nonlinear mirror (NLM) and cascaded second-order optical nonlinearities (CSON) in a KTP crystal. Detailed analysis, which takes into account the transverse effect of cavity modes, shows that the CSON effect dominates the mode locking process. The resulting self-defocusing lens couples with an aperture appearing in the gain medium and then produces a cavity loss modulation. The mode locking self starts at a pump power of 2.2 W with a 35% transmission output coupler and generates pulses with a duration of 14 ps and an averaged power of 350 mW. The laser was shown to be useful for probing polar structures of nonlinear optical materials with second harmonic microscopy. (C) 2000 Elsevier Science B.V. All rights reserved.