Stable solar-pumped TEM00-mode 1064Â nm laser emission by a monolithic fused silica twisted light guide

To improve TEM00-mode solar-pumped laser output power stability, a monolithic fused silica twisted light guide was firstly produced and then combined with both a 2D-CPC (Compound Parabolic Concentrator) and a 2 V-shaped cavity to achieve uniform pumping along a 3 mm diameter, 50 mm length, 1.0 at.% Nd3+:YAG rod through an heliostat-parabolic mirror system. Based on both refractive and total internal reflection principles, the light guide provided an effective solution to both guiding and redistributing highly concentrated solar radiations. A near-Gaussian profile focal spot was transformed into a uniform rectangular-shaped light column, facilitating further pump light coupling into the long and thin laser rod within the 2 V-shaped pump cavity. Optimum pumping parameters and solar laser output powers were found through both ZEMAX© non-sequential ray-tracing and LASCAD© laser cavity analysis codes. The light guide reduced considerably the thermal lensing effects of the solar laser. 2.7 W continuous-wave TEM00-mode (M2 ≤ 1.05) 1064 nm solar laser emission with 2.3 W/m2 collection efficiency and, more importantly, with 1.7% stability was finally achieved, being significantly more stable than the previous TEM00-mode solar lasers.