Self-frequency doubling in a laser-active whispering-gallery resonator

Lasing and self-frequency doubling are achieved in a millimeter-sized laser-active whispering-gallery resonator made of neodymium-doped lithium niobate. A low-cost 808-nm laser diode without external frequency stabilization is sufficient to pump the neodymium ions. Laser oscillation around 1.08 mm drives a frequency-doubling process within the same cavity providing green light. The electrical-optical efficiency of the system reaches up to 2×10−4. To the best of our knowledge, this is the first demonstration of combining lasing and 𝜒(2) frequency conversion in a single high-𝑄 whispering-gallery resonator. This approach is general and can be applied to other materials and other nonlinear optical processes.