HIGH RESOLUTION LUMINESCENCE AND RAMAN 3D HYPERSPECTRAL IMAGING OF GEMSTONES (Invited Presentation)

2D imaging of luminescent defects in gemstones, in particular diamond, has become a powerful tool to acquire information about growth and treatments. General bulk spectroscopy is extended by acquiring a spectrum at each spatial point, which can then allow specific spectral signatures to be identified, which can have different applications based on the defect. Related to this is Raman mapping, where a Raman spectrum is acquired at each point, which can then be fitted to acquire information relating to different minerals but is also applicable to measuring strain fields and temperature sensing. This 2D imaging, sometimes called hyperspectral imaging, requires advanced microscopes and lasers to be effectively deployed and can take considerable time to measure large areas of a sample. This means that bulk spectroscopy techniques are still much more common.

The next generation of imaging systems takes the dimensionality to the next level, by allowing for large 3D volumes of samples to be acquired with the same spectral information, resulting in 4D data sets (a spectrum from each point in 3D). This opens a new door to explore samples, allowing for full rotation of the acquired data space, enabling study of the growth in significantly higher detail. Whereas historically only small regions of the sample can be measured, this new development of an instrument at GIA allows large fields of view (FOV) to be measured, with an example size being 2.2 X 3.5 X 3.1 mm, with micron level sampling. At each of these voxels (3D pixels), a spectrum is still present, which can either show luminescent or Raman features. This newly developed instrument is approximately 10 times faster than commercially available devices, which now makes it practical to analyze volumes that could otherwise require month-long measurements. Here, we will present data collected from diamond, showing growth structure, strain related features, and inclusions using Raman spectroscopy, for large 3D volumes at micron level resolution. Specifically, we will briefly overview the instrument and its design principles, before showing its application to diamond.