Harnessing speckle for high-precision optical measurement

When monochromatic light strikes a rough surface it produces a distinctive grainy interference pattern called speckle. This disordered pattern is often thought of as detrimental to optical systems, and has historically been predominantly studied by optical engineers seeking to remove or reduce its effects. However, the interference pattern produced is extremely sensitive to changes of the properties of the light, the scattering medium and the environment, and has begun to see increased use as a tool to perform precision measurements in a compact setup.

For example, in St Andrews we have developed a state-of-the-art speckle wavemeter, by passing coherent light through an integrating sphere [1] or a step-index multimode fibre [2]. By tracking changes in the speckle with multivariate analysis techniques such as Principal Component Analysis [2] or Convolutional Neural Networks [3], we can track changes in wavelength on the attometre scale, and can extend our device to simultaneously measure the wavelength of multiple lasers [4].

Wavelength is not the only property of the light that can be tracked, and we also recently demonstrated precision measurement of the polarisation states of multiple laser beams [5].

In this project, you will develop new applications and new techniques for precision measurements with speckle. This will include simultaneous tracking of multiple properties of the light and testing the capability of speckle to measure environmental changes such as temperature and pressure in real-world environments and for trace-gas detection.