High power DFB lasers for D1 and D2 rubidium absorption spectroscopy and atomic clocks

Abstract

Distributed feedback ridge-waveguide lasers have been developed. The distributed feedback is provided by a second order grating, formed into an InGaP/GaAsP/InGaP multilayer structure. A threshold current of 40 mA and a differential quantum efficiency of 0.8 W/A is achieved. The lasers emit up to 200 mW in a single lateral and longitudinal mode around 794.7 nm and 780.0 nm. These wavelength regions are of particular interest for applications in absorption spectroscopy of the rubidium D1 and D2 lines and atomic clocks. These applications require a stable lasing wavelength with small spectral line width and possibility of a fine tuning. By changing the output power with current and / or the heatsink temperature the wavelength can be tuned to reveal the hyperfine structure of the rubidium lines. This was verified by passing the laser emission through a 80 mm long rubidium cell and measuring the transmitted power versus current and temperature. It is shown, that a hyperfine structure measurement of the rubidium lines can be performed in a less than 9 μs. Due to the large side mode suppression ratio of >45 dB and the small spectral line width of ~ 200 kHz these lasers are ideally suited for absorption spectroscopy