Optical Design Of Raman Spectrometer For Veterinary Drugs Detection

Veterinary drugs can effectively control animal disease. They play an important role in promoting the healthy development of animal husbandry. However, some enterprises illegally adulterate veterinary drugs with other material, which has delayed treatment and caused huge losses to farmers. The bogus drugs are difficult to distinguish, so professional instruments are needed.Detection and analysis technique should be accurate, rapid, simple and cheap, or its promotion will be limited. Chemical method, chromatography and spectrometry are the main methods for bogus drugs detection at present. Raman spectroscopy is a kind of spectrometry based on Raman scattering. It is rapid, non-contact, nondestructive, and it requires less samples which needn’t to be pre-treated, so its suitable for bogus drugs detection. With the emergence of portable Raman spectrometer and the development of chemometrics, the advantages of Raman spectroscopy are highlighted.In this paper, Raman spectrum experiment is conducted to detecting adulterated veterinary drugs, and an optical system for Raman system is designed. The main contents of this paper are as follows:(1) Through a combination of Raman spectrum experiment and chemometrics, this paper studied the veterinary drugs detection based on Raman spectroscopy, which provided guidance for the design of Raman spectrometer. The basic theory of qualitative discrimination and quantitative analysis using partial least squares(PLS) is introduced. Qualitative and quantitative analysis is done of Penicillin adulterated with glucose and starch based on partial least squares. The research contains the establishment of calibration set, the elimination of singular sample, the impact analysis of different pretreatment and its combination, and so on.(2) Based on the requirement of veterinary drugs detection, this paper designed a Raman probe for portable Raman spectrometer. The Raman probe includes two parts of excitation and collection. The excitation system has a numerical aperture of 0.22, which matches with the fiber. Its magnification is 1:1. The radius of the spot diagram is almost the same as the Airy disk. The numerical aperture of the collection system reaches 0.44, which allows large-angle light to enter the system. The spot diagram of zero field of view and 50μm field of view are 3.949μm and 5.074μm respectively. The 10μm encircled energy exceeds 95%.(3) In this paper, an optical system for Raman spectrometer is designed using transmission volume holographic grating. The diffraction efficiency of the grating is analyzed based on Kogelnik’s coupled wave theory. A transmission optical system for Raman spectrometer is designed. The length of the system is less than 10 cm. The numerical aperture reaches 0.22 and the resolution is 0.6nm in the range of 790-1014 nm.