High purity efficient first Stokes Raman laser

The subject of the solid-state Raman frequency conversion to the yellow frequency spectra has been an active topic since the mid 1990’s, because of its application in bio-medical and astronomy fields. However, the yellow laser performance is often limited because of the cascade conversion to second or higher Stokes. This cascade conversion not only limits the conversion efficiency and the output power of the first Stokes, but also degrades the pulse and the beam profile of the first Stokes. We present a type of polarization coupled Raman resonator, in which the higher order ( the second Stokes and higher ) laser output can be dramatically suppressed. Our Raman resonator is pumped by a Q-switched and frequency doubled slab laser, and we can get an almost pure (P 559 /(P 559 +P 532 )>99%) 559 nm yellow light output with an efficiency over 39% from 532 nm to 559 nm. The resonator includes a high reflection rear mirror, a KGW crystal, a polarization coupled input/output element, and a high reflection output coupler of 559 nm (R 559 nm = 0.6). Furthermore, we have proposed an improvement of this polarization coupled Raman resonator. The theoretical calculations of the temporal and spatial dependent Raman conversion equations show that the conversion efficiency of the first order Stokes is greatly enhanced with an additionalλ/2 waveplate for 589 nm and the BBO crystal.