Synthetic FM triplet for AM-free precision laser stabilization and spectroscopy

Abstract

The Pound–Drever–Hall (PDH) cavity-locking scheme has found prevalent uses in precision optical interferometry and laser frequency stabilization. A form of frequency modulation spectroscopy, PDH enjoys superior signal-to-noise recovery, large acquisition dynamic range, wide servo bandwidth, and robust rejection of spurious effects. However, residual amplitude modulation at the signal frequency, while significantly suppressed, still presents an important concern for further advancing the state-of-the-art performances. Here we present a simplified and improved scheme for PDH using an acousto-optic modulator to generate digital phase reference sidebands instead of the traditionally used electro-optic modulator approach. We demonstrate four key advantages: (1) the carrier and two modulation tones are individually synthesized and easily reconfigured, (2) robust and orthogonal control of the modulated optical field is applied directly to the amplitude and phase quadratures, (3) modulation synthesis, demodulation, and feedback are implemented in a self-contained and easily reproducible electronic unit, and (4) superior active and passive control of residual amplitude modulation is achieved, especially when the carrier power is vanishingly low. These distinct merits stimulate new ideas on how we optimally enact PDH for a wide range of applications.

Monolithic optical resonator for ultrastable laser and photonic millimeter-wave synthesis

“…Though the free-running RAM is highly up to the PDH setup and the temperature control of the EOM, such an amount of RAM contribution would need a relatively long averaging time to dominate the overall stability performance. For further development of this resonator with more deterministic linear drift or with drift cancellation 36 , 43 by which the FFS can be maintained on 10 −14 level, the RAM stabilization 42 , 44 would be necessary.…”