Optical Sensing and Metrology

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!

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 accurate measurements of laser parameters, such as attometre-resolved wavelength measurement and characterisation of
the orbital angular momentum and polarisation of the light beam. Moreover, we can use speckle to probe environmental changes, such as resolving changes of refractive index at 10^-9 and picometre-level displacements of the scattering medium.