The Study Of Hadamard Mask Modification To Optimize The Performance Of DMD Hadamard Transform Near-Infrared Spectrometer

In the 1970s,the Hadamard Transform?HT?was proposed and formed a relatively mature theory^[1].With the emergence of mechanical encoding mask,the Hadamard Transform has been applied in the Near-Infrared?NIR?spectrometer.Encoding mask is an important device in the spectrometer.Adopting a mechanical mask,the spectrometer often has a complex structure,low resolution,and short life.Compared with the traditional instrument,it has no advantage.The development of HT spectrometer is restricted by encoding mask.Until the appearance of digital micro-mirror device?DMD?,DMD has been applied in the HT spectrometer as an encoding mask.Because of the HT spectrometer based on DMD has several advantages such as higher SNR?Singal Nosise Ratio?,wider spectral range and low cost^[2-3],DMD based HT spectrometers has attracted the attention of researchers.At present,the HT spectrometer's performance has experienced the great improvement,but it still has some defects.Such as the grating diffraction of spectrometer,2-D grating diffraction of DMD and the spectral efficiency of light source and so on,these defects would make the spectral energy distribution uneven.Then the influence of stray light on the whole spectrum absorbance will be various,the lower the spectral energy is,the more seriously is influenced by the stray light.The spectral band with low energy has low SNR,low liner and low absorbance.While the spectral band with high energy has good performance in that aspect.In this paper,the chapter 1 and chapter 2 demonstrate the background and the relavant principles of the NIR spectroscopy and Hadamard Transform NIR spectroscopy.In chapter 3 there are some analysis and discussion about a series problem of HT spectroscopy.A Hadamard mask of variable-width-stripe is proposed to improve the SNR of spectrometer.Meanwhile,we analyze the impact of the defect based on HT spectrometer.It is found that the lower the spectral energy is,the more seriously influenced by the stray light.In order to solve this problem,our research team propose a split wave band scan mode.Through doing some simulations and experiments,the results show that with the new scan mode and Hadamard mask,the influence of stray light is restrained or reduced.The SNR of spectrometer is increased,especially the SNR of the low-energy spectral band.