Improved 2nd harmonic rise-time in a thermal-lens-dominated extended-cavity micro-laser

Many commercially available compact, micro-cavity diode-pumped solid-state lasers achieve a stable resonator condition following the formation of an intra-cavity thermal lens. Typically, this thermal lens forms as a result of localized thermal expansion in the host material due to the very high optical power of the infrared pump beam. Additionally, most common DPSS host media, such as Nd:YAG and Nd:YVO4 exhibit high dn/dT, change in refractive index with temperature. Thermal lens formation time dominates stable resonator establishment and, thus, the rise-time of the intra-cavity-generated visible second-harmonic output light. Thermal lens formation time may range from 10´s of microseconds to several milliseconds, depending on pump power, the host material dn/dT, and the volume and length of the host material. This paper describes a unique approach that improves the second-harmonic rise-time - and, thus, the modulation bandwidth - for high-power VECSELs by several orders of magnitude. This approach, while typically used in some laser systems for other purposes, allows direct modulation of high-power VECSELs to greater than 100 megahertz with second-harmonic rise-time of a few nanoseconds.