The Research Of High Throughput,High-resolution And Broadband Spatial Heterodyne Raman Spectroscopy

As one inelastic scattering of spectroscopy,Raman spectroscopy has its own position,shape and relative intensity,which can provide detailed information about microstructure and internal structure of sample,has characteristic of a fingerprint to identify molecules and called“Raman fingerprint”.Raman spectroscopy is one of the molecular spectroscopy,and the primaty advantages of the technieuqes are no sample preparation required,non-contact,non-destructive,safe,rapid analusis and water can be used as solvent.These advantages greatly expand the capability to apply to a varity of fields,including physcis,chemistry,biomedicine,geology and materials.With the great development of spectral data processing method,spectrometers and the performances of lasers and detectors,the more requirments were developed from the perspective of the users and scientists with regard to what is necessary to achieve sample identification of unknown samples.Spatial Heterodyne Raman Spectroscopy?SHRS?is one of new type of Fourier transform spectroscopy,based on the Michelson interferometer,in which mirrors has been replaced by two gratings.The SHRS has large throughput,high resolution.Not only the SHRS could be field widened,but also has no moving parts,so it has a compact package.SHRS has become one of the research hot spots in the related fields of the applications of Raman detection.However,for the conventional SHRS,it has inverse realationship between the bandpass and spectral resolution.The lower the bandpass,the higer the spectral resolution;the hiher the bandpass,the lower the spectral resolution.This relationship is one of the biggest problems for the SHRS:the spectral resolution is so high that the bandpass is hindered greatly.The reasonable science objects for Raman spectrometer are a spectral resolution of less than 4 cm^-1 and a spectral range of more than 4000 cm^-1.According to the requirements of Raman measurement,it's necessary for the Raman spectrometer to be established to meet the requirements of high spectral resolution and broadband coverage.Three different types of spatial heterodyne Raman spectrometer are developed for the simultaneous high resolution and broadband Raman measurements to slove the inverse relationship between the spectal resolution and the spectral range.The instrument exhibits good performance for high-resolution broadband Raman measurements.The main contens of the dissertation are as follows:1.The basic principle of the Raman spectroscopy is presented.According to the presented problems of Raman spctrocopy,the performances and types of the Raman spectrometer should be taken into consideration to sutiable for the requirements of Raman spectroscopy.The development tendency of SHRS is introduced and summarized.The problems of typical SHRS are discussed.2.Based on the theory of interference and Snell's law,the mathematical mode of the field widened SHRS is built.In the three-dimensional space corrdiante system,the light is pass throuth the beamsplitter,prisms and grating,in which the positions of intersection of each optical surface can be obtained by using the ray tracing method.Fianlly,the light is received by the CCD camera and the optical path difference could be calculated.It provides the theoretical rational for the suitable refractive index and apex angle of the prism.3.A two-dimensional?2-D?SHRS that uses a field widening prism to effectively increase the throughput or sensitivity without sacrificing the spectral resolution for Raman measurements while broadening the bandpass.The signal-to-noise ratio?SNR?is measured under different integrations or laser powers and shows that the system exhibits good stability and fair repeatability.Raman spectra obtained from the field-widened SHRS and a commercialized Raman instrument are compared and the intensity could be impoved about 178 times,and the resolution of the field-widened SHRS and the SHRS using the same instrumental parameters without field widening are also compared and the Raman intensity can be increased by 2.58 times.The results of Raman spectroscopy of sulfur,CCl₄,sulfate is investigated in two states:solid salt and aqueous solution show that the field-widened SHRS exhibits a good performance to successfully perform wide-field Raman measurements.4.A SHRS with an echelle-mirror structure that employs multiple diffraction orders to achieve a broad spectral coverage and high spectral resolution simultaneously is proposed.The SHRS takes advantage of the multiple orders of the echelle grating to obtain a broad spectral range that meets the requirements of Raman detection.To avoid the mixture of bandpass,each diffraction order has its own covering,echelle grating should be roated by x-axis carefully so that evey coverings could be separated.Four orders are used and one covering is 1071 cm^-1 with spectral resolution 1.051 cm^-1.The total bandpass is 4278 cm^-1.Another new broadband Raman spectrometer has been developed using an echelle spatial heterodyne Raman spectrometer.The instrument is based on a Michelson interferometer,which is constructed using two echelle gratings to replace the mirrors in two arms.Masks are used to remove the shadow ghosts caused by the different orders of the two echelle gratings.After the calibration and Raman experiments,three orders are used and total covering is 3590 cm^-1 with spectral resolution 1.21 cm^-1.The two techniques solve the problem of the inverse relationship between the bandpass and spectral resolution..5.A field-widened spatial heterodyne Raman spectrometer with a mosaic grating structure is developed for the simultaneous sensitivity enhancement and broadband transmission Raman measurements.We optimize the etendue to maximize the signals collected from the samples by using field-widening prisms and employ two mosaic gratings to achieve broadband operation,covering 5638 cm^-1 with 2.865 cm^-1 spectral resolution.The signal-to-noise ratios are improved by a factor of more than 11 and show a good stability and fair repeatability.6.Based on the techniques we proposed above,a field-widened spatial heterodyne Raman spectrometer with a mosaic grating structure is used to investigate the broadband Raman spectra of sulfate minerals,sulfate on solid state and in aqueous solutions.The main v₁ mode can be probed by the spatial heterodyne Raman spectroscopy to determine concentration of sulfate and unambiguous identification of different sulfate minerals,solid sulfate.All these applications show the excellet prospect in water pollution,geology,ocean,mars exploration and other fields.