Spectral linewidth and tuning requirements of sources for gas sensing in space-based applications at 935 nm

The spectral linewidth and tuning requirements of an external cavity laser (ECL) in the Littrow architecture and a distributed feedback (DFB) device for space-based gas sensing were investigated. The wavelengths of both devices were in the 935 nm range and different linewidth measurement techniques were explored for the two sources. The linewidth of the ECL was measured using a short-arm homodyne technique, while the linewidth of the DFB was measured with a heterodyne technique using the ECL as a local oscillator. The spectral linewidth of the ECL was measured to be <300 kHz with <5 MHz for the DFB device. The emission wavelength tuning characteristics, including the overall tuning range and the free running stability of the ECL, were also examined. The full frequency drift of the ECL measured over a 36-hour period was found to be approximately 540 MHz, while it showed approximately 0.4 nm continuous mode-hop free wavelength tuning.