Efficient, tunable near-infrared solid-state dye laser with good beam quality

We have demonstrated a laser-pumped, near-infrared solid-state dye laser (SSDL) with a slope efficiency congruent to 35%, tunability over congruent to 40 nm (from 710 to 750 nm) and M-2 < 1.3. This device utilizes a folded three-mirror resonator containing a tight focus for the gain medium and a collimated section for the tuning element. The folded cavity is astigmatically compensated through proper choice of sample thickness and cavity fold angle. We achieved low-threshold operation through the tight intracavity focus and by mounting the sample at Brewster's angle. Two pump lasers were used in this study: (L) a flashlamp-pumped dye laser (FPDL) with an output wavelength of 630 nm and a pulse duration of congruent to 1 mu s; and (2.) a pulsed red diode laser with an output wavelength of 671 nm and a pulse duration of congruent to 200 ns. The gain medium consists of the near-infrared dye Oxazine 725 in the solid host modified PMMA. With the FPDL as the pump source, slope efficiencies up to congruent to 35% were measured at the center of the tuning range. A single-plate birefringent filter (BRF) was used to tune the output from congruent to 7 10 to 750 nm with a single output wavelength. The BRF narrowed the spectral output from congruent to 15 to congruent to 0.8 nm, and provided smooth, continuous tuning over the 40-nm range. Lasing was observed outside this range, but the output consisted of two wavelengths separated by congruent to 50 mn (the free spectral range of the BRF). Time-resolved data showed that, for these cases, the laser switches from the shorter to the longer wavelength during the pulse. Input/output curves were generated as a function of resonator feedback for several output wavelengths. Findlay-Clay analyses were used to determine the round-trip cavity loss at each wavelength. The results correlate well with known losses in the resonator, including dye self-absorption losses. Beam-quality measurements were made near the peak of the tuning curve (lambda congruent to 727 nm) with a cavity feedback of 95%. At 1.5x threshold, the laser output had an M-2 value of congruent to 1.06. At 7x threshold, the beam quality degraded slightly to M-2 =1.26. Good temporal tracking was observed between the pump and output pulses, once the SSDL turned on. With design improvements to reduce the threshold, the tunable SSDL was also lased using the diode laser as the pump source. Further characterization of this device under direct diode-puniping is in process.