Low phase noise diode laser oscillator for 1S-2S spectroscopy in atomic hydrogen

TL;DR

This paper presents a stabilized diode laser oscillator with ultra-low phase noise at 972 nm, enabling high-precision 1S-2S spectroscopy in atomic hydrogen without efficiency loss from phase noise.

Contribution

The authors developed a high-power, low-noise diode laser with a novel intra-cavity electro-optical modulator and demonstrated its effectiveness in atomic hydrogen spectroscopy.

Findings

Achieved 99.9% power in the laser carrier.

RMS phase noise of 1 mrad^2 in 10 MHz bandwidth.

No significant phase noise impact on 1S-2S excitation efficiency.

Abstract

We report on a low-noise diode laser oscillator at 972 nm actively stabilized to an ultra-stable vibrationally- and thermally compensated reference cavity. To increase the fraction of laser power in the carrier we designed a 20 cm long external cavity diode laser with an intra-cavity electro-optical modulator. The fractional power in the carrier reaches 99.9% which corresponds to a rms phase noise of $\phi^2_\textrm{rms}=1\,\textrm{mrad}^2$ in 10\,MHz bandwidth. Using this oscillator we recorded 1S-2S spectra in atomic hydrogen and have not observed any significant loss of the excitation efficiency due to phase noise multiplication in the three consecutive 2-photon processes.