Apparatus and method for stabilizing the frequency of lasers

A method of stabilizing a single laser frequency f utilizing an etalon having a resonant frequency approximating the laser frequency f and having an FSR, and utilizing a frequency reference generator providing a reference frequency fREF approximating the FSR, the method comprising the steps of:

• (a) locking the frequency f to the resonant frequency of the etalon;
• (b) generating sidebands at frequencies f−fFSR* and f+fFSR* wherein fFSR* approximates the FSR of the etalon;
• (c) temporally dithering the sideband frequencies f−fFSR* and f+fFSR* by a small magnitude fD at frequency fM;
• (d) detecting the intensity response (transmission or reflection) of the etalon at the sideband frequencies f−fFSR* and f+fFSR* at dither frequency fM;
• (e) comparing the phase of the intensity response at frequency fM with the phase of the dither signal at frequency fM to generate a first error signal;
• (f) adjusting fFSR* to minimize the magnitude of the first error signal;
• (g) comparing fFSR* to a reference frequency fREF to generate a second error signal;
• (h) adjusting the etalon FSR to minimize the magnitude of the second error signal.

Apparatus for stabilizing the frequency f of a single laser utilizing an etalon, and a stable reference frequency fREF, the apparatus comprising:

• a phase modulator for generating sidebands at frequencies f−fFSR* and f+fFSR* wherein fFSR* approximates the FSR of the single etalon;
• a first servo loop configured to match the laser frequency f to a resonant frequency of the etalon;
• a second servo loop configured to adjust fFSR* to match the etalon FSR;
• and
• a third servo loop configured to adjust the etalon FSR to cause fFSR* to match fREF.