Three-wavelength laser light source for absolute, sub-Angstrom, two point source interferometer

摘要

We report on the progress of the development of a three-wavelength light source for an earlier published absolute, two point source interferometer to measure absolute optical path differences (OPD) with angstrom accuracy over the range of millimeters. The light source system should produce three different wavelengths between 630nm and 640nm simultaneously, providing two synthetic wavelengths that enable the absolute OPD measurement. Due to requirements of the detection system, the frequencies of two of these lasers have to be stabilized with an accuracy of the order of 10~(-7), while the third laser is stabilized to better than 10~(-8). For the former, tuneable external cavity diode lasers are used, whereas the latter is a commercial, frequency stabilized HeNe laser. Two different locking schemes and their relative merits are evaluated: Molecular absorption locking, guaranteeing long-term stability, versus Fabry Perot locking, with the flexibility of choice of the desired frequencies. Recent measurement results for both locking schemes are presented.