Super-Spectral-Resolution Raman Spectroscopy for Advanced Diamond Characterization and Identification

As the field of diamond devices grows, and the methods of growing diamond proliferate, more advanced spectroscopic methods are needed to characterize, identify, and distinguish between diamond samples. Raman spectroscopy is an extremely powerful laser-based method for characterizing materials based on their unique inelastic scattering spectrum and it is an excellent tool for characterizing diamond, diamond impurities, and nano-diamond powders, etc., however, the power of the technique is limited by the resolution of the spectrometer. Here we introduce Super-Spectral-Resolution Raman Spectroscopy (SSR-RS), a method which greatly improves the spectral resolution of the Raman spectrometer and demonstrate that with SSR-RS we can distinguish between natural and lab-grown diamonds. In SSR-RS, a Fabry–Perot (F-P) Etalon filter (Finesse &gt; 30, FSR = 2 cm^-1), mounted on an angle-tunable motor, is added to the classical micro-Raman setup, and Raman spectra are automatically acquired for many different angles of the F-P filter. In previous published super-resolution Raman experiments, the mirror distances "d" within the F-P were varied [1, 2]. Here, the F-P etalon itself is fabricated as monolithic structure, plane and parallel by design through a set of innovations developed by Light-Machinary. With a low-resolution grating of 150 g/mm, which by itself exhibited a best-case resolution of 40 cm^-1, we applied the SSR-RS technique to diamond to obtain a linewidth fit parameter of less than 1 cm^-1 . To baseline SSR-RS, we used the super-spectral-resolution method to extract the linewidth of the laser excitation itself and obtained a laser linewidth of better than 0.007 cm^-1. In essence, the modelling aspect of SSR-RS is a kind of “point-spread-function” fitting of the spectrum. Further investigations were carried out on the spectra of a natural diamond compared to a lab-grown diamond, where in both cases, a spectral resolution improvement of at least 40X of the original spectrum has been obtained. Using SSR-RS, we were able to observe differences between natural vs. lab-grown diamond due to different Raman shifts and Raman shift linewidths. The SSR-RS technique promises to be an important spectroscopic technique for characterizing advanced diamond devices and differentiating between seemingly indistinguishable diamond samples.<br/><br/><b>References</b><br/> <br/>[1] Malka D, Adler-Berke B, Tischler Y, Zalevsky Z, Improving Raman spectra of pure silicon using super-resolved method, <i>Journal of Optics.</i> (2019); <b>21</b>, 075801<br/>[2] Malka D, Berkovic G, Tischler Y, Zalevsky Z, Super-resolved Raman Spectra of toluene and toluene-chlorobenzene mixture, <i>Spectroscopy Letters.</i> (2015); <b>48</b>(6), 431-435.