Abstract

Power scaling of solid-state laser sources is limited by thermal effects inside the gain medium induced by optical pumping. These issues, which strongly affect the beam quality and laser performance, require a careful design and a particular attention to the thermal management. The most fundamental way to reduce the thermal load inside a laser gain medium is to reduce the so-called quantum defect. In Nd³⁺-doped YAG, the quantum defect is in general of 24 % when a pump laser diode at 808 nm is used and the emission is at 1064 nm. However, a successful demonstration of heat reduction is possible by directly pumping in the emitting levels around 869 nm or 885 nm [1]. To further reduce the quantum defect, it is possible to pump Nd³⁺ ion directly from the last upper level of the ground state manifold at 938 nm or 946 nm. A first demonstration has been recently reported [2] with a Ti:Sapphire laser as a pump source at 946 nm. As the absorption peaks are very low at 946 nm and at 938 nm with a spectral width of only 1 nm in both cases, the diffraction limited beam and narrow spectral linewidth of the Ti:Sapphire laser was very useful. Nevertheless, the use of diode laser source as pump source is more relevant is term of compactness and overall efficiency. We present the first demonstration to our knowledge of diode-pumped Nd:YAG laser at 938 nm.

© 2009 IEEE