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

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Facchin_2022_ACSPhotonics_Refractive_CC.pdf (1.288Mb)
Date
16/03/2022
Author
Facchin, Morgan
Bruce, Graham David
Dholakia, Kishan
Funder
The Leverhulme Trust
EPSRC
Grant ID
RPG-2017-197
EP/P030017/1
Keywords
Speckle
Metrology
Refractive index
Integrating sphere
QC Physics
QD Chemistry
DAS
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Abstract
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.
Citation
Facchin , M , Bruce , G D & Dholakia , K 2022 , ' Measurement of variations in gas refractive index with 10 -9 resolution using laser speckle ' , ACS Photonics , vol. 9 , no. 3 , pp. 830-836 . https://doi.org/10.1021/acsphotonics.1c01355
Publication
ACS Photonics
Status
Peer reviewed
DOI
https://doi.org/10.1021/acsphotonics.1c01355
ISSN
2330-4022
Type
Journal article
Rights
Copyright © 2022 American Chemical Society. Open Access article licensed under Creative Commons Attribution CC-BY 4.0.
Description
Funding: This work was supported by funding from the Leverhulme Trust (RPG-2017-197) and the UK Engineering and Physical Sciences Research Council (EP/P030017/1).
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  • University of St Andrews Research
URI
http://hdl.handle.net/10023/25273

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