# Harnessing speckle for a sub-femtometre resolved broadband wavemeter and laser stabilization

## TL;DR

This paper introduces a broadband speckle-based wavemeter capable of sub-femtometre resolution and uses it to stabilize a diode laser with a linewidth under 1 MHz, surpassing conventional methods.

## Contribution

It demonstrates a novel speckle-based approach for high-resolution wavelength measurement and laser stabilization across a broad spectrum.

## Key findings

- Achieved sub-femtometre wavelength resolution at 780 nm.
- Measured wavelengths from 488 to 1064 nm with high accuracy.
- Stabilized a diode laser to a linewidth below 1 MHz.

## Abstract

The accurate determination and control of the wavelength of light is fundamental to many fields of science. Speckle patterns resulting from the interference of multiple reflections in disordered media are well-known to scramble the information content of light by complex but linear processes. However, these patterns are, in fact, exceptionally rich in information about the illuminating source. We use a fibre-coupled integrating sphere to generate wavelength-dependent speckle patterns, in combination with algorithms based on the transmission matrix method and principal component analysis, to realize a broadband and sensitive wavemeter. We demonstrate sub-femtometre wavelength resolution at a centre wavelength of 780 nm and a broad calibrated measurement range from 488 to 1064 nm. This is comparable with or exceeding the performance of conventional wavemeters. Using this speckle wavemeter as part of a feedback loop, we stabilize a 780 nm diode laser to achieve a linewidth better than 1 MHz.