An astigmatic wavelength meter

An astigmatic scheme of a laser wavelength meter based on a single air-gap Fizeau interferometer is described. For a multimode laser, the accuracy in determining the center of gravity of a spectrum is within 1 GHz. Two comple mentary testing techniques are proposed for the instrument. By using them, it was shown for the first time that, for this type of meters, a systematic error arises and increases with a decrease in the radiation-spectrum width . The effect is periodic in the lasing frequency and results from a weak be am that is brought about by a reflection from the front surface of the inte rferometer. Moreover, in the previously designed optical schemes, this effe ct is so strong that unambiguous determination of the wavelength of a singl e-frequency radiation is impossible. The use of an astigmatic scheme helps additionally attenuate the influence of the third beam, thus eliminating th e ambiguity in the results and reducing the absolute error to a value of +/ -1.5 GHz.