Characterization of commercially available vertical-cavity surface-emitting lasers tuned on Cs D1 line at 894.6 nm for miniature atomic clocks

Abstract

We report on the metrological characterization of novel commercially available 894.6 nm vertical-cavity surface-emitting lasers (VCSELs), dedicated to Cs D₁ line spectroscopy experiments. The thermal behavior of the VCSELs is reported, highlighting the existence of a minimum threshold current and maximum output power in the 55°C-60°C range. The laser relative intensity noise, measured to be -108 dB/Hz at 10 Hz Fourier frequency f for a laser power of 25 μW, is reduced with increased power. The VCSELs frequency noise is 10⁸ Hz²/Hz at f=100 Hz. The spectral linewidth of the VCSELs is about 30 MHz. VCSELs injection current can be directly modulated at 4.596 GHz with microwave power in the range of -10 to +0 dBm to generate optical sidebands. A VCSEL was used in a microcell-based Cs atomic clock based on coherent population trapping. A preliminary clock short-term fractional frequency stability of 8×10^-11τ^-1/2 up to about 100 s is reported, demonstrating the suitability of these VCSELs for miniature atomic clock applications.