Abstract

In the last decade diode-pumped Cr:LiSAF lasers have attracted much interest as compact all-solid-state efficient sources of tunable radiation in the near-infrared (800-950 nm) as well as for the generation of femtosecond pulses. Non-diffraction limited, broad-area laser diodes used as pump sources introduce some limitation in the performance of Cr:LiSAF tunable lasers, such as efficiency reduction owing to upconversion and excited-state parasitic processes enhanced by imperfect mode-matching. Up to date, the highest efficiency reported was obtained pumping Cr:LiSAF with a nearly diffraction-limited MOPA [1]. However, these devices are quite expensive and share, with more affordable broad-area single emitters, a significantly reduced lifetime with respect to AlGaAs laser diodes (or aluminum-free laser diodes) emitting at 808 nm [2]. An alternative high-quality source of radiation at 671 nm (near the peak absorption of Cr³⁺ ions in LiSAF crystals) is the intracavity doubled Nd:YVO₄ laser emitting at 1342 nm fundamental wavelength. Using a highly reliable 10-W fiber-coupled diode array at 808 nm as excitation source, and a 15-mm type II LBO for non-critically phase-matched intracavity second-harmonic conversion, we developed an efficient Z-folded oscillator generating as much as 760 mW at 671 nm, linearly polarized and with M²<1.2 (fig. 1). The amplitude stability of the red beam was better than 0.1 %, owing to multi-longitudinal-mode operation. To the best of our knowledge this is currently the highest cw power generated with high-brightness diode-pumped lasers near 670 nm. Considering the dollars per watt per hour of operation, this design can be significantly cost-effective as compared with MOPA devices, and nearly as competitive as single-emitter pump diodes (at least ensuring a significantly extended operating lifetime). Furthermore, the temperature-controlled LBO crystal achieves noncritical phase-matching at 671 nm at nearly room temperature (≈35 °C), which is definitely more manageable than the ≈160 °C required by doubling at 532 nm with type I LBO.

© 2001 EPS