Raman spectroscopy has been shown to be a powerful spectroscopic approach for detecting gases. It is capable of detecting gases that possess no infrared absorption feature, such as diatomics, and it also does not suffer from signal saturation as can be the case for transmission measurements. However, the Achilles heel of Raman based gas detection is the low scattering cross section. Here we show that introducing gas into an optical open micro-cavity (OMC) can greatly enhance the Raman signal. The enhancement comes from 2 factors: namely confining the light longer in the gas containing volume, hence strengthening the light-matter interaction, and also directing the Raman scattering in a more collimated fashion towards the detector. The OMC has been designed such that the separation between the mirrors is piezo controlled, hence it is possible to scan the micro-cavity resonances and tune the OMC to a particular Raman transition. Using the OMC, with laser excitation at 532 nm, we show detection of several gases simultaneously such as nitrogen and oxygen, and discuss prospects for boosting the limit of detection.
The presentation will cover the design consideration of the Tip, Tilt, Z microcavity having a range of 40 micron and a positioning resolution of 10 nm. The design comprises an intrinsic position to allow close loop operation. Response time is in the msec range to facilitate fast scanning.
The spectrometer set up will be presented as well as representative experimental results.