High-Resolution Investigation of a Grating-Stabilized Laser with a Fabry-Perot Interferometer

A diode-based external cavity diode laser (ECDL) is built in Littrow configuration and its modal behavior as well as its current and temperature-induced wavelength shift is investigated. The ECDL is based on a laser diode (LD) in the blue spectral range with a straight ridge and low-reflectivity front facet. A high-resolution grating spectrometer (SPEX 1404 0.85 m double spectrometer) as well as a scanning Fabry-Perot Interferometer (FPI, Burleigh RC-110 with RG-93 ramp generator) are used for spectral characterization. With the high resolution of the FPI, an upper bound of the ECDL linewidth of about 50 fm is found, which is 75 MHz in terms of frequency. The spectral shifts with temperature and with driving current are determined. The shift of 1.15 pm mA(-1) of the individual mode of the external cavity is caused by a change of the group refractive index and corresponding change of the effective cavity length. The shift of 2.7 pm mA(-1) of the spectral center of gravity can be explained by the faster shift of the internal modes. The single-mode shift with temperature of 16.71 pm K-1 is consistently measured both by the spectrometer and the FPI.