Measurement of variations in gas refractive index with 10-9 resolution using laser speckle

Morgan Facchin*, Graham David Bruce, Kishan Dholakia

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)
3 Downloads (Pure)


Highly-resolved determination of refractive index is vital in fields ranging from biosensing through to laser range-finding. Laser speckle is known to be a sensitive probe of the properties of the light and the environment, but to date speckle-based refractive index measurements have been restricted to 10^-6 resolution. In this work we identify a strategy to optimise the sensitivity of speckle to refractive index changes, namely by maximising the width of the distribution of optical path lengths in the medium. We show that this can be realised experimentally by encapsulating the medium of interest within an integrating sphere. We demonstrate that variations of the refractive index of air as small as 4.5x10-9 can be resolved with an uncertainty of 7x10-10. This is an improvement of three orders of magnitude when compared to previous speckle-based methods.
Original languageEnglish
Pages (from-to)830-836
Number of pages7
JournalACS Photonics
Issue number3
Early online date16 Feb 2022
Publication statusPublished - 16 Mar 2022


  • Speckle
  • Metrology
  • Refractive index
  • Integrating sphere


Dive into the research topics of 'Measurement of variations in gas refractive index with 10-9 resolution using laser speckle'. Together they form a unique fingerprint.

Cite this