Research On Technology Of Opto-mechanical System Of Handhelded Raman Spectrometer

With the features of rich information, strong analytical ability, fast processingspeed, without sample pretreatment and easy to use, handheld Raman spectrometeris widely used in water pollution monitoring, drug smuggling, air quality monitoring,cultural identification, drug testing and other areas. The technology of handheldRaman spectrum is relatively mature abroad, and series of excellent products havebeen applied. In China, the domestic applications are still in its infancy. The keytechnology of handheld Raman spectrometer is hard to break is the main blockingreason.In this paper, basing on the current technical condition, two main parts ofhandheld Raman spectrometer, the optical system of Raman probe and the gratingspectrometer, are studied. In terms of Raman probe, an optical system of handheldRaman probe with the total length of15cm, small field of view and large objectnumerical aperture has been designed. The object numerical aperture of collectingsystem is0.33using spherical optical technology and0.4using non-spherical opticaltechnology. The telephoto structure with the telephoto ratio of0.59has been used inconverging system. Meanwhile, the further analysis of stray light in optical systemof Raman probe has been investigated. By real ray tracing, a reasonable stray lightanalysis model has been established. Several technologies of eliminating the scattering stray light caused by the laser reflecting and scattering on lens surfacehave been proposed, such as the technology of notch filter, the technology of blackspots, the technology of aperture matching and so on. Using the optical simulationsoftware Tracepro, the opto-mechanical model of handheld Raman spectrometer hasbeen simulated. The simulation result shows that stray light suppression level meetsthe Raman spectral measuring requirements while using the eliminating stray lighttechnologies above. In terms of grating spectrometer, for coma-free Czerny-Turnerstructure the formula of determining the structure by the image size has beenproposed. Basing on this formula, the spectrometer with a high resolution of0.6nmand satisfying application requirements of Raman spectroscopy has been designed.In astigmatism-free Czerny-Turner structure, the zero-order and first-orderastigmatism-free conditions in crossed astigmatism-free structure have been derived,and the restricted conditions on system construction are presented. Thecorrespondent crossed coma-free Czerny-Turner structure has also been built up forthe comparison. It is shown in both of theoretical calculation and softwaresimulation, that the astigmatism-free crossed C-T structure has a superior opticalperformance, with RMS of spot diagram only12%to52%of that in thecorrespondent coma-free Czerny-Turner structure at the working wavelength. Theformer is easy to obtain good optimized results. In order to improve designefficiency, and to make work more intelligent and reliable, the initial structuremodels of coma-free and astigmatism-free have also been established by GUI inMatlab to directly communicating with Zemax, which make it convenient byautomatically input instead of manually input. Finally, we get the results of thespectral resolution better than0.6nm and the Raman spectral range from781nm to1014nm, with the prototype size of243mm×25mm×71mm. The five characteristicpeaks of Raman spectrum of CCL4have been successfully measured by theprototype of the Raman spectrometer, which verifies the feasibility and therationality of the optical design of the whole Raman spectrometer system. Thesehave established a good technical foundation of handheld Raman spectrometer for further development in reducing instrument size and improving excellentperformance.