# Speckle spectrometer with integrating sphere reaches 6 fm resolution at 780 nm

- Published: 2026-11-08 18:21 UTC
- Section: Science › Instruments & experiments
- Tags: speckle spectrometer, 6 fm resolution, integrating sphere, resolving power, rubidium-85 hyperfine structure, D2 transition, electro-optic modulator sidebands, microwave photonics, Adelaide University, Nature Communications
- URL: https://realtech.media/news/rt-8868f9ee8bd0c1f1fbf725b4_speckle_spectrometer_with/

**Researchers from Adelaide University, ENS Paris and St Andrews report a laboratory speckle spectrometer about 80 times finer than earlier versions, resolving rubidium hyperfine structure.**

![Speckle spectrometer with integrating sphere reaches 6 fm resolution at 780 nm](https://realtech.media/media/2026/11/9fc559e13b3708e8.jpg)
*Wolfgang der Bastler, Wikimedia Commons, CC BY-SA 3.0*

A team from Adelaide University, the Laboratoire Kastler Brossel in Paris and the University of St Andrews has built a speckle spectrometer with a resolution of 6 fm at a wavelength of 780 nm. The work was published in Nature Communications on 7 November 2026 [1]. The resolving power is 1.3 × 10^8, which the authors describe as an approximately 80-fold improvement over previous implementations [1].

Laser speckle is a granular intensity pattern that arises from random optical interference. It encodes spectral information in many dimensions, and this can be used for precision measurements. Speckle-based spectrometers are compact, mechanically robust and insensitive to alignment, but their spectral resolution had stayed at the picometre scale [1].

## Integrating sphere as a scattering cavity

To go beyond this limit, the authors used an integrating sphere as a multiply scattering cavity. The sphere gives access to a wide range of path lengths, which increases the spectral sensitivity of the device [1]. At 780 nm this gave the 6 fm resolution reported in the paper.

The authors used a sphere with a standard Thorlabs part number and an electro-optic modulator in the setup. The modulator served as a source of known spectral structure for testing the instrument [1].

## Sidebands and rubidium hyperfine structure

The resolution was enough to clearly separate the laser sidebands generated by the electro-optical modulator. The sideband powers extracted from the speckle agreed with the expected values to within 1% [1].

The spectrometer was also used for a direct speckle-based measurement of the hyperfine structure of the D2 transition in 85Rb. The resulting transmission spectra differed by no more than 3.7% from independent measurements referenced to a wavemeter [1].

The authors state that these results establish speckle as a platform for ultra-high precision spectroscopy, radio-frequency spectrometry and microwave photonics [1]. The paper describes a laboratory demonstration at a single wavelength of 780 nm.

## Sources

1. [Nature Communications](https://doi.org/10.1038/s41467-026-78325-y)

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