The program objective is to develop an efficient spectrograph for ultraviolet resonance Raman spectroscopy (UVRRS). UVRRS is a superb technique for efficient structure and dynamics studies of biological macromolecules and is useful for taxonomic identification. UVRRS can also detect muM concentrations of species and can be used for quantitative analysis. However, UVRRS suffers from the need for large spectrographs and loss of spectral range due to difficulties in removing intense scattered UV excitation laser frequencies, a problem inherent in Raman spectroscopy. A unique filter is proposed which utilizes atomic absorption lines from metal vapors to absorb the scattered laser light while transmitting the resonance Raman signals. Narrow band widths of absorption lines guarantees little loss of spectral information. The filters will be used with a novel, high resolution compact spectrograph using an echelle grating coupled to a CCD camera for collection of the entire spectral range. The Phase I program successfully demonstrated the capabilities of a vapor rejection filter to selectively remove scattered laser light while maintaining high throughput for the Raman signal. Spectral collection on an echelle at a UV wavelength of interest successfully enabled collection of a complete Raman spectrum at high resolution. The Phase II objective will be to develop a series of vapor rejection filters for utilization of many UV wavelengths. In addition, a prototype echelle spectrograph with a UV-enhanced CCD will be developed which incorporates the vapor rejection filters to allow usage of laser wavelengths down to 200 nm.
Applications for a commercial UVRRS echelle spectrograph are extensive and exist in clinical, academic, and industrial laboratories. UVRRS can determine nucleic acid base pair ratios for taxonomic identification, analyze amino acid bands to determine protein structural information, and quantitative polymer or coating analyses. The novel filters allow access to low frequency structural and dynamical information not obtainable with conventional UV Raman methods.
