Half-Watt single frequency yellow 561 nm and yellow-green 553 nm DPSS lasers with record 19% optical conversion efficiency

Since the first introduction of DPSS lasers at 561 nm in 2004, the power level required by some biotechnical applications has always increased. Oxxius has contributed to fulfill the demand thanks to the introduction of the SLIM-561 100mW in 2008 and of the SLIM-561 200mW and 300mW in 2009. More recently, new dyes or nano-dots have required shorter wavelengths (such as 553 nm) and new applications such as Laser Doppler Velocimetry requiring both high power and single frequency operation have appeared. In this presentation, we demonstrate how to further increase the power. 553nm and 561 nm emission are obtained by frequency doubling the 1106 nm and 1123 nm lines of Nd:YAG. The latter transitions are significantly weaker than the 1064 nm line. As a consequence, any loss in the cavity significantly increases the laser threshold. Because of the perfect alignment of the crystal interfaces and the low divergence of the intracavity beam, monolithic cavities demonstrate significantly reduced round-trip losses compared to standard cavities. Consequently, laser threshold can be dramatically reduced and the nonlinear loss, responsible for the visible emission, can easily dominate the linear losses. We have taken standard monolithic cavities of our commercial SLIM-561 products and have increased the pumping power up to 2.8 W. Yellow and Yellow-green powers have not shown any sign of saturation and 0.5 W could be achieved at both wavelengths. This results in a record 18% pump to signal optical efficiency. We have checked that the emission remained single frequency whatever the pumping power.