Sub 23 μHz instantaneous linewidth and frequency stability measurements of the beat note from an offset phase locked single frequency heterodyned Nd:YAG laser system.

Abstract

We report, what is to the best of our knowledge, the narrowest instantaneous linewidth measurement of the beat frequency between two phase locked heterodyned 1.319 μm Nd:YAG lasers. At both 65 kHz and 31.7 GHz beat frequencies, we measured the instantaneous 3 dB linewidth of the optically-generated microwave tones to be < 22.8 μHz, limited only by the minimum instrument resolution. Allan deviation measurements indicate that the laser system follows a 5 MHz quartz reference oscillator to stability levels of σy (1s) = 8.4 × 10-12. At 10.24 GHz, the laser system follows a sapphire loaded cavity oscillator to stability levels of σy (1s) = 1.6 × 10-11. For these measurements, the optical beat note closely follows the linewidth and stability of the driving microwave frequency reference.