A precision wavelength meter for a pulsed laser

Abstract

A precision wavelength meter has been developed for the calibration of a pulsed laser system, for making measurements of its relative wavelength and wavelength change. The device, based on a Fabry-Perot interferometer, has been used with CW lasers and with pulsed laser sources operating at pulse repetition rates up to 10 Hz. Its operational accuracy has been demonstrated to be about 0.01 pm, used at a wavelength of 589 nm, or about 1 part in 50 million. A single unit of the present design is only able to measure relative wavelength changes. To obtain a measure of absolute wavelength, three similar units would be required in which the etalon gaps are in non-commensurate ratios. A second method of obtaining precision absolute wavelength is to use a single Fabry-Perot unit to enhance the precision obtainable from a second wavelength meter based on a Fizeau interferometer. Alternatively, when required to operate only within a specific small free-spectral range (up to perhaps 10-20 pm), the single Fabry-Perot unit could be periodically calibrated against a spectral source (calibration lamp) of known and essentially constant absolute wavelength.