Wide-tuning-range Littman-type external-cavity diode laser for spectroscopy of GaAs band-edge and impurity-level transitions

We report the design and implementation of a compact external-cavity diode laser (ECDL) for wavelength-tunable excitation around the GaAs bandgap. By modifying a commercial laser kit and redesigning key optomechanics, we achieve wide wavelength tunability over 790–870 nm. We describe a geometrical-optics design procedure that accounts for the tuning-mirror pivot constraint, together with practical assembly and interference-mitigation measures for wavelength-scanned operation. The ECDL operates in a single longitudinal mode with a linewidth below several tens of MHz (measurement-limited) and delivers an optical output power of tens of mW across the tuning range. Free-running frequency drifts are on the order of 50 MHz over tens of seconds and 500 MHz over tens of minutes without active feedback.