Solid-state lasers directly pumped by InGaN diode lasers: Ti:sapphire and Pr³⁺:LiYF4 lasers

We report our recent progress of solid-state lasers, the titanium-doped sapphire laser and the praseodymium-doped LiYF4 (Pr³⁺:LiYF4) laser, directly pumped by InGaN diode lasers of green and blue. While the titanium-doped sapphire laser can be pumped by both blue and green diode lasers because of its broad absorption spectrum, we find 450-nm diode laser pumping inefficient for its power scaling owing to the onset of an additional absorption loss induced by the blue pump laser. The degradation of the performance of a Ti:sapphire laser induced by a 450-nm diode pumping is experimentally revealed. Furthermore, we demonstrate a passively mode-locked Ti:sapphire laser pumped by two green diode lasers of 1-W, and 74 fs pulses at a repetition rate of 120 MHz with an averaged output power of 45 mW are obtained. The Pr³⁺:LiYF4 laser, one of the most promising candidates as a visible laser, has become possible to be pumped directly by blue diode lasers of 440-nm wavelength. We demonstrate the power scaling at 523 and 640 nm oscillation, a passive Q-switching at 640 nm with a Cr⁴⁺:YAG saturable absorber by utilizing polarization-combined blue diode lasers as the pump source.