# Infrared Laser Locking to Rubidium Saturated Absorption Spectrum via a Photonic Chip Frequency Doubler

## TL;DR

This paper demonstrates the first successful locking of an infrared laser to rubidium saturated absorption lines using a photonic chip frequency doubler, showcasing compact and stable frequency conversion with tunable bandwidth.

## Contribution

It introduces a novel method of IR laser locking to Rb lines via a photonic integrated frequency doubler, expanding the application of integrated resonators in atomic spectroscopy.

## Key findings

- Generated strong second-harmonic signals up to microwatts.
- Achieved tunable SHG bandwidth covering Rb D2 lines.
- Successfully locked IR laser to Rb saturated absorption lines.

## Abstract

Photonic integrated resonators stand out as reliable frequency converters due to their compactness and stability, with second-harmonic generation (SHG) efficiencies of up to 17000%/W reported recently in aluminum nitride microrings. In this work, a sufficiently strong second-harmonic (SH) signal up to microwatts was generated by a photonic integrated frequency doubler using a milliwatt infrared (IR) laser source. Furthermore, increased SHG bandwidth covering $^{85}$Rb and $^{87}$Rb D$_2$ transition lines as well as saturated absorption spectroscopy (SAS) were demonstrated by tuning the pump power and chip temperature. Here, we present, to the best of our knowledge, the first successful locking of an IR laser to Rb saturated absorption lines via a photonic chip frequency doubler.