Tunable single-frequency lasing in a microresonator

Whispering-gallery-mode resonators made of laser-active materials can serve as efficient microphotonic coherent light sources. However, the majority of experimental realizations relies on expensive pump light sources like narrow-linewidth or pulsed laser systems, which is inappropriate for most applications. In order to overcome this, we present a whispering-gallery laser system without the need for an expensive pump light source and at the same time with unprecedented laser performance: A laser-active resonator made of Nd:YVO  4 is non-resonantly excited, employing a low-cost laser diode without any external frequency stabilization, emitting up to 100 mW optical power around 810 nm wavelength. Continuous-wave single-frequency lasing at 1064 nm wavelength is achieved with directed laser light emission in the mW-regime. The temporal power and frequency stability are within ±1.5 % and ±30 MHz, respectively. Modehop-free frequency fine-tuning is achieved exceeding 11 GHz tuning range by changing the temperature of the cavity. Faster tuning can be expected when applying geometric or electro-optic instead of thermal tuning.