Optical Sensing and Metrology

We harness light to probe the chemical structure of materials from bacteria to whiskey using Raman spectroscopy. We also develop innovative methods to measure properties of the light itself, by scrambling it into grainy speckle patterns. 

Raman Spectroscopy

Laser light can excite molecules to emit Raman photons which contain important chemical fingerprints of the samples. Wavelength modulated Raman spectroscopy (WMRS) efficiently removes the auto-fluorescence from biological samples, such as cells or tissue, therefore hugely enhances the signal to noise level and its detection ability. We use this for analysis of chemicals ranging from bacteria to whiskey!

  • THROUGH-BOTTLE WHISKY SENSING AND CLASSIFICATION USING RAMAN SPECTROSCOPY IN AN AXICON-BASED BACKSCATTERING CONFIGURATION
    H. Fleming, M. Chen, G. D. Bruce and K. Dholakia, advanced online publication in Anal. Methods / arXiv: 2005.13538
  • REAL-TIME MONITORING OF LIVE MYCOBACTERIA WITH A MICROFLUIDIC ACOUSTIC-RAMAN PLATFORM
    V. O. Baron, M. Chen, B. Hammarström, R. J. H. Hammond, P. Glynne-Jones, S. H. Gillespie and K. Dholakia, Commun. Bio. 3, 235 (2020)
  • TOWARDS AUTOMATED CANCER SCREENING: LABEL-FREE CLASSIFICATION OF FIXED CELL SAMPLES USING WAVELENGTH MODULATED RAMAN SPECTROSCOPY
    L. Woolford, M. Chen, K. Dholakia and C. S. Herrington, Journal of Biophotonics 11, e201700244 (2018)
  • RAMAN IMAGING THROUGH A SINGLE MULTIMODE FIBRE
    I. Gusachenko, M. Chen and K. Dholakia, Opt. Express 25, 13782 (2017)

Speckle Metrology

When laser light hits a rough surface, the light is scattered in many directions and the resultant interference pattern has a grainy appearance which we call speckle. This speckle is often considered as a loss of any information contained in the laser light, as much research has been devoted to avoiding it. However, the speckle is actually rich in information about both the laser and the scatterer. We have used this phenomenon to perform highly accuarate measurements of laser parameters, such as attometre-resolved wavelength measurement and characterisation of the orbital angular momentum contained in the light beam.

  • SPECKLE-BASED DETERMINATION OF THE POLARISATION STATE OF SINGLE AND MULTIPLE LASER BEAMS
    M. Facchin, G. D. Bruce and K. Dholakia, OSA Continuum 3, 1302-1313 (2020)
  • FEMTOMETER-RESOLVED SIMULTANEOUS MEASUREMENT OF MULTIPLE LASER WAVELENGTHS IN A SPECKLE WAVEMETER
    G. D. Bruce, L. O’Donnell, M. Chen, M. Facchin and K. Dholakia, Opt. Lett. 45, 1926 (2020)
  • DEEP LEARNING ENABLED LASER SPECKLE WAVEMETER WITH A HIGH DYNAMIC RANGE
    R. K. Gupta, G. D. Bruce, S. J. Powis and K. Dholakia, arXiv: 1910.10702
  • OVERCOMING THE SPECKLE CORRELATION LIMIT TO ACHIEVE A FIBER WAVEMETER WITH ATTOMETER RESOLUTION
    G. D. Bruce, L . O’Donnell, M. Chen and K. Dholakia, Opt. Lett. 44, 1367 (2019)
  • HARNESSING SPECKLE FOR A SUB-FEMTOMETRE RESOLVED BROADBAND WAVEMETER AND LASER STABILIZATION
    N. K. Metzger, R. Spesyvtsev, G. D. Bruce, B. Miller, G. T. Maker, G. Malcolm, M. Mazilu and K. Dholakia, Nat. Commun. 8, 15610 (2017)
  • MODAL CHARACTERIZATION USING PRINCIPAL COMPONENT ANALYSIS: APPLICATION TO BESSEL, HIGHER-ORDER GAUSSIAN BEAMS AND THEIR SUPERPOSITION
    A. Mourka, M. Mazilu, E. M. Wright and K. Dholakia, Sci. Rep. 3, 1422 (2013)