Abstract: A mode-monitoring system used in connection with discrete beam frequency tunable laser provides optical feedback that can be used for adjusting the laser or for other processing associated with the use of the laser. For example, the output of a frequency tunable source for a frequency-shifting interferometer can be monitored to support the acquisition or processing of more accurate interference data. A first interferometer for taking desired measurements of optical path length differences traveled by different portions of a measuring beam can be linked to a second interferometer for taking measurements of the measuring beam itself. The additional interference data can be interpreted in accordance with the invention to provide measures of beam frequency and intensity.

Abstract: A frequency-shifting interferometer gathers intensity data from a set of interference patterns produced at different measuring beam frequencies. A periodic function is matched to the intensity data gathered from the set of interference patterns over a corresponding range of measuring beam frequencies. Localized correlations involving phase offsets between the interfering portions of the measuring beam are used to inform a determination of a rate of phase change with measuring beam frequency corresponding to the optical path length difference between the interfering beam portions.

Abstract: A frequency tuning system for a laser includes mode-matched lasing and feedback cavities. A reflective facet of the feedback cavity is adjustable for retroreflecting different feedback frequencies to the lasing cavity without changing a fixed length of the feedback cavity. A selection among resonant frequencies of the feedback cavity provides for tuning the laser through discrete resonant frequencies of the lasing cavity.