Development of a Near-Market-Ready Miniature Raman Probe

Raman probes are fibre-coupled devices that use fibre optics to transmit excitation laser light to a sample, capture the resulting Raman signal, and transmit that signal back to a spectrometer for analysis. As such, they provide versatility in terms of sample positioning relative to a Raman spectrometer. Conventional Raman probes have dimensions measured in cm's, but there are applications in areas such as healthcare, manufacturing, and metrology, that require mm-scale and even sub-mm Raman probes.

The manufacture of miniature fibre-coupled Raman probes is not trivial, as they usually consist of multiple micro-optic components for focusing, collimating, and filtering the pump and Raman signals, and although mm-scale probes have been demonstrated, they have proven to be too expensive for widespread commercial applications. Recently, we demonstrated how miniature Raman probes can be manufactured using an emerging manufacturing technique known as Ultrafast-Laser-Assisted Etching (ULAE), which relies on the nonlinear absorption of ultrashort laser pulses to directly write structural modifications inside a dielectric material such as fused silica glass. If correctly controlled, the laser-modified material can exhibit a ~1000-fold increase in KOH chemical etch rate compared to the pristine material, enabling fabrication of exquisite mm-scale fused silica micro-optic components with micron-scale precision. In addition to facilitating the manufacture of freeform micro-optics that would be difficult to realise with conventional approaches, a key advantage of ULAE is that the micro-optics can be monolithically integrated with passive alignment structures for fibres and other parts. This aspect could be particularly advantageous for volume manufacturing, to circumvent the time and cost involved in active alignment.

We have recently demonstrated the use of ULAE to manufacture a prototype sub-mm fibre-coupled Raman probe that exhibits many performance aspects required for a commercial offering. There remains, however, several Technology Readiness Level (TRL) and Market Readiness Level (MRL) aspects that require development to take the current Raman probe to a near-market-ready state. This project will address these aspects by (i) demonstrating the integration of spatially selective multi-layer coatings onto the Raman probe, (ii) demonstrating the CO2 laser polishing of the Raman probe's optical surfaces, (iii) demonstrating that Raman probes can be manufactured at scale, and (iv) quantifying the performance of the Raman probe technology in collaboration with our project partners. Our aim is that the Raman probe will be "product one" for a company that we will spin-out from Heriot-Watt University (HWU) shortly after the end of the project.