Submitted In Total Fullment Of The Requirements For The Degree Of Master In Optical Engineering

Liquid chromatography system is the most influential, fastest-growing and widely used modern analytical systems, which enjoys its popularity in petroleum chemical in-dustry, organic synthesis, physiology, biochemistry, medicine, health, and even space exploration and other applications in almost all fields of science. The fluorescence detector, as the "eye" of the system, is a key component of liquid chromatography system, which is crucial for reliability and accuracy of qualitative and quantitative analysis results. However, domestic fluorescence detector demand rely mainly on im-ports, for the absence of effective domestic R & D, this paper make a in-depth study of the fluorescence detector signal detection system as well as its stray light inhibition.The main work of this paper including:1. Fluorescence is an extremely weak optical signal, while the design of weak sig-nal detection system involves considerable carefulness of any minor electrical noise that may be introduced in from anywhere. This paper set up the model of the whole detection circuit, from the photomultiplier tubes to the ADC sampling module, and a detailed analysis of bandwidth and amplitude of the signal and noise is made and then verified by experiment. The final overall circuit noise is limited in 31.7μV,and the detection accuracy of light-current is up to 6.4pA, equivalent to 25.6mlm light detection precision. The system's performance is as equal as the similar high-level foreign products.2. AΔ-Σtype ADC is the mainstream design in fluorescence detection signal ac-quisition system for its high precision and integration. This paper uses CS5532 ADC to successfully set up a 24 bit ADC system, whose digital accuracy reaches 18 bit. However,the low word output rate is the by-product of the high precision, which is the main restriction of the scanning speed of the system. To address this problem, this paper has proposed and implements a new ADC system based on over-sampling and matching hardware digital filter module. The new sheme could offer a 60 (～) 250k word output rate and flexible 16 (～) 22 bit effective precision according to different demands. The significant advantage of this new ADC design was to enable the flexibility of make the best compromise between system precision and wavelength scanning speed.3. The most popular control system is based on MCU which suffers from poor real-time performance, slow operation speed and low system integration. This paper introduces and implements the SOPC control system instead of MCU, whose on-chip user-defined peripheral modules enjoys excellent realtime performance, strong computing power and high-integration. In This paper, a custom-defined ADC driver, which avoid ADC-speed-loss in traditional driving design, is de-signed to speeds up the systematic sampling rate for 10%. A user-defined UART controller which enable at-one-time 24bit data-bus transferring is designed to increase the bus bandwidth utilization by 3 times. And also, an embedded hard-ware IIR digital co-processor is designed which can effectively inhibit the noise by 53%. The new system integrates these different features in a single chip, which greatly simplifies external circuit design and reduces costs.4. To study the influence of the stray light from monochromator on system perfor-mance, this paper, for the first time, builds up a model of the monochromator in ASAP for ray-tracing and stray light analysis, and for the first time, introduces monochromator- spectral-transfer-function to define its influence on optical sig-nal. Some experiments are made to verify the correctness of the simulation mod-els. And on the analysis of the "critical surface" in the optical path, this paper puts forward several stray light suppression structure as using field diaphragm and aperture diaphragm, multi-level leaf structure, and unique structures for grating incident light,and the simulation shows stray light rejection ratio of above structure are 2.7×10(-5),7.6×10(-5), and 0.33×10(-5)respectively, which could provide some meaningful guide for practical improvements. end (enumerate) In summary, this paper makes an in-depth study and design of the signal detec-tion system of the fluorescence detector, presents a precision-speed adjustable new ADC scheme, introduces SOPC control system which break though the speed and performance bottlenecks of traditional control system, and for the first time, analyze the stray light from fluorescence detector monochromator in software, as well as puts forward several effective suppression structurer. In the end, this paper developed a fluorescence detector prototype, whose SNR of Raman peak of water under 350nm excitation light reaches 63.