Abstract
Due to the coupling between longitudinal modes in the intracavity doubled diode-pumped solid-state (DPSS) laser, large amplitude fluctuations have been observed in the green output. It restricts the development and applications of intracavity doubled DPSS laser, and this phenomenon knows as the “Green Problem”. In order to improve the applications of intracavity doubled DPSS laser, solving the green problem is the first target. According to the rate-equations which were done in the previous work, we simulate the behavior of the Type I phase matching green output. In the experiment, we design two kinds of laser cavities, individually including self-frequency doubling crystal (Nd︰YCOB) laser system and Nd︰GdVO4 & BIBO double crystals laser system. We try to reduce the green noise which caused by coupling between different polarization modes by operating at g=0, but it cannot restrain the coupling modes in the same polarization when the number of modes in the laser cavity is larger than one. So, if we want to lower the Type I phase matching green noise, the most efficient method is single mode operation. Finally, we hope to reduce the green noise by putting a Volumetric Bragg Grating into the cavity. In the experimental results, we really observe the stable green output when single mode operation in the laser cavity; also we can observe green noise when two modes survive in the cavity. Consequently, the method of putting a Volumetric Bragg Grating into the cavity is really reducing the number of modes in the cavity, and possible to obtain single mode operation.