Study On Key Technologies Of Near-infrared Polarization Interference Spectroscopy

Near-infrared spectral analysis is a conventional and quantitative analysis technique, its core is spectroscopy. Study on novel Fourier transforms spectroscopy having higher stability and suitable for on-line analysis and process control, has important theoretical and practical significance.Based on introduction to application background, research status home and abroad,advantages and disadvantages of different near-infrared spectroscopies, key technologies of near-infrared polarization interference spectroscopy with a common path are studied.Interferometer is the key component of the Fourier transform spectroscopy. For the inherent shortcomings of the Michelson interferometer and its derivative forms, a mechanical compensation-typed polarization interferometer with a common path is proposed. The basic principle and key specification of polarization interferometer are studied using wave theory, and the theoretical expression of optical intensity of polarization interference is derived, the single wavelength and 0.8~1.7 μm composite light interference curves are simulated as well as. Study on the regularity of modulation and luminous flux affected by transmission axis angle of polarizer and analyzer is proposed. Through the calculation of influence of angle maladjustment, a parameter configuration method achieved maximum modulation and luminous flux is proposed. Contrastive study on principles and characteristics of polarization interferometer are proposed by wave theory, Jones vector and Stokes vector methods, results show that although three have their own advantages and disadvantages, but all roads lead to Rome. Jones matrix and Mueller matrix of polariztion interferometer are derived, and the interference light’s Jones vector and Stokes vector expressions in theory are given. Accordingly, the vector expressions can be used to study the transmission characteristics for different polarization beams in the interferometer, and the influence of different polarization components’ angle on the interference can be analyzed, providing theoretical guidance for the project development.The basic parameters and the stability of the phase compensator are calculated and analyzed, and the performance evaluation of the phase compensator is presented. The influence of crystal material and optical axis orientation on the performance is studied, and the formula for calculating the dimension and resolution of the optical axis is derived. The optical path difference sensitivity, uniform of scanning velocity, tilted error tolerance, oblique incidence angle error tolerance and temperature adaptability etc. are analyzed and calculated,and the corresponding calculated formulas are derived. By comparison, the anti-interference ability of the moving optical wedge is 2/Δnsinθ times stronger than the classical Michelson interferometer. The ability of the moving wedge to resist the inclination of is 1.75/Δn times higher than classic Michelson interferometer. Due to the birefringence difference of the crystal material is usually very small, therefore the stability advantages of polarized interferometer are very obvious.After the incidence with small angle, there are no additional optical path difference are produced. In addition, the angle of the wedge is also an important parameter to affect the phase compensator, so it is necessary to seek a balance between performance, size and cost. Based on the theoretical analysis of the phase compensator, a design example is given, and the propagation properties of polarized light in the phase compensator are simulated, the comparison shows that the ray trace results and the theoretical calculation is consistent.According to the practical requirements, design scheme of a near-infrared polarization interference spectrometer is presented, the design wavelength is 0.8~1.7μm, the spectral resolution is 8cm-1. Starting from the specifications, design parameters are calculated, optical system of polarization interference spectrometer using near infrared fiber-coupled light, off-axis parabolic mirror, Glan-Thompson prisms and phase compensator made by calcite is designed, and then the quality evaluation from the point of spot diagram, geometry encircled energy and lateral color is carried on. The non-parallelism of collimated light and defocusing effects of detector are investigated and analyzed. The optical system’s thermal stability of-20℃~85℃ is evaluated using multiple structure method. The influence of the off axis parabolic mirror’s misalignment on optical system is simulated. For the deficiency of existing optical structure, a kind of improved structure is put forward, which can reduce the use of two slices of cold mirrors leading to reduce the assembly difficulties and stray light effects. Opto-mechanic integrated simulation of the spectrometer is proposed, results show that point source formed by fiber-coupled light source combined with off-axis parabolic mirror can achieve more advantages on reducing stray light than surface light source. The defocusing influence of optical fiber head on the distribution of light energy is analyzed, providing guidance for the adjustment of the optical fiber head. A correction method of spectrum reconstruction for polarization interference.The influencing factors of spectral reconstruction and tilted errors of moving wedge is simulated, results show that the sampling interval, maximum optical path difference, wavelength and apodization function can impact the accuracy of spectral reconstruction. Influence of tilted error of moving wedge on spectral reconstruction are affected by beam aperture and wavelength, smaller diameter and longer wavelength due to smaller inclined error, when lambda is 0.8μm, beam diameter is 10.8mm, the moving wedge’s tilted tolerance is 24.04 ", the recovered spectral peak energy down to 90% of the theoretical value, which is consistent with the simulation result. A prototype system is build, and the verification experiments are carried on, based on which He-Ne laser’s interference curve is obtained. The spectral curve of He-Ne laser is recovered using trigonometric function of apodization, which is coincident with the simulation result, show that spetral data processing method is reasonable and feasible. The interference curves of He-Ne laser and near infrared light are collected at the same time, the repeated appearance of zero point of the reference laser with high frequency can provide accurate and equal sampling interval for interference curves of composite light, and the interference curve distribution of composite light is coincident with simulation results.