Optimization And Development Of A Miniature Ultraviolet Flat-field Spectrometer

The differential optical absorption spectroscopy (DOAS) analyzer is an important instrument to detect the trace gases in atmosphere. The ultraviolet (UV) spectrometer, which is a crucial part of the DOAS analyzer, has decisive influence on the detection limit and accuracy. Based on the requirements of DOAS analyzer, this dissertation develops a prototype of the miniature UV flat-field Czerny-Turner spectrometer, including optimization of the optical design, manufacture of the prototype and experiment after assembly.First of all, to minimize the error of the detection limit, an optimal resolution (0.5~0.7nm) is derived through differential signal to noise (D-SNR), a new conception inversely proportional to the error. To ensure that this resolution would be attained at a wide spectral region, the aberrations of the basic design and the fold design of the Czerny-Turner spectrometer are both studied. Thus a new law that the resolution at any wavelength of the basic design of the Czerny-Turner spectrometer would also be improved to an approximate same level as the central wavelength, where if the primary coma is eliminated, is revealed. The structure parameters of the basic design of the Czerny-Turner spectrometer are further optimized to reduce astigmatism and increase light efficiency. Then, based on the above-mentioned conclusions and some existing design methods, a complete design process of the miniature spectrometer is presented. Accordingly, a basic Czerny-Turner design with a flat field, a consistent high resolution and high efficiency over the whole UV region is accomplished.The mechanical design of spectrometer is carried out according to the dispersive optics and adjustment requirements, consisting of such key structures as fiber coupling, grating and mirrors regulation. Due to the detection limit and the analysis of the differential noise, a proper detector is selected, thus the refrigeration circuit with a negative feedback to reduce the noise, and the timing-driving module are both devised.Experiments about the aberrations and resolutions of the Czerny-Turner spectrometer are conducted, and the relationships of aberrations, resolutions and wavelengths in different designs are verified accordingly. The assembly of the miniature flat-field UV spectrometer and the Hg spectrum experiments are both carried out; results show that the prototype has satisfied the requirements of the optimal resolution.