1-watt single-frequency 689 nm VECSEL for quantum technologies

Single-frequency AlGaInP-based VECSELs are high-brightness, low-noise lasers with capacity for compact power scaling, making them excellent candidates for quantum technology applications based on cold strontium (Sr) atoms, which require high-power, low-noise light at 689 nm. We demonstrate lateral power-scaling of an AlGaInP-VECSEL, producing multimode output power of 2 W around 689 nm and 1 W single-frequency at the Sr ¹S₀ → ³P₁ cooling transition frequency (434.82 THz) using intracavity filtering. Relative to previous reports, this system offers an increase in multimode output power of >350%. The thermal resistance of the system is estimated as 4.3(1) K/W, consistent with other AlGaInP-VECSEL reports. Single-frequency output power and wavelength stability are observed as 4.3% and 445 fm (280 MHz) rms over a 1-hour period, respectively. The single-frequency VECSEL was also locked to a Fabry-Perot reference cavity, demonstrating ultra-low relative intensity noise (RIN) of <-152.9 dBc/Hz for frequencies above 1 kHz. Further frequency noise measurements resulted in estimated free-running and locked linewidths of 71(1) kHz (0.02 s) and 7.26(1) kHz (20 s), respectively, demonstrating suitability for high-power quantum applications based on cold Sr.