[Research on Small-Type and High-Spectral-Resolution Grating Monochromator].

Monochromator is the necessary equipment for spectral imager to calibrate the spectrum continuously. In order to calibrate the hyperspectral imaging spectrometer continuously, a small-type and high-spectral-resolution grating monochromator is designed. The grating monochromator with horizontal Czerny-Turner structure is designed with high-spectral-resolution as a starting point, and the design idea is discussed in detail from choosing the grating, calculating the focal length, the sizes of entrance slit and exit slit, among others. Using this method, the necessary structure parameters are determined, and the impact of the necessary structure parameters for spectral resolution and volume is given. According to the optical characteristics of the grating monochromator, the mechanical structures of the instrument are designed for small and handy from the components of the entrance slit, the collimator lens and imaging objective lens, the scanning structures, the fuselage and so on. The relationship of the sine mechanism parameters for output wavelength and wavelength scanning accuracy is given. The design and adjustment of the instrument are completed. The visible spectrums of mercury lamp are used as calibration lines, and the calibration curve is acquired by using least square method. This paper gives a method that combining the limit error of the step number and the calibration curve to evaluate the wavelength repeatability and wavelength precision. The datum of experiment shows that the spectral resolution of the instrument is better than 0.1 nm in the wavelength band from 400 to 800 nm. Simultaneously the wave-length repeatability reach to ± 0.96 6 nm and the precision reach to ± 0.096 9 nm.

[Study on the Design of Prism Hyperspectral Imaging System Based on Off-Axis Two-Mirror Littrow Configuration].

In order to meet the requirements of high spectral resolution and high image quality on the hyperspectral imaging system, and to meet the new demands of miniaturization, light weight, and high optical efficiency in practical applications, a prism known as hyperspectral imaging system based on Littrow configuration is designed. The use of off-axis two-mirror Littrow configuration is to reduce the size of the optical system and provide a collimated beam for the plane prisms. To avoid the optical path interference, the macro programming optimization is applied. The application of two correct lens and aspheric mirrors can correct the spectral smile and the keystone of the hyperspectral imaging system. It is indicated that the distortion is less than 2.1 µm and the spectral bend is less than 1.3 µm, both are controlled within 18% pixel. The analytical results indicate that the MTF in the visible-near infrared(VNIR) spectral region from 400 to 1 080 nm is above 0.9 while spectrum resolution is about 1.6～5.0 nm, the spectral transmittance more than 51.5%. The results show that the system has high transmittance and image quality within the whole spectral range.

[Full-field and automatic methodology of spectral calibration for PGP imaging spectrometer].

In order to analyze spectral data quantitatively which is obtained by prism-grating-prism imaging spectrometer, spectral calibration is required in order to determine spectral characteristics of PGP imaging spectrometer, such as the center wavelength of every spectral channel, spectral resolution and spectral bending. A spectral calibration system of full field based on collimated monochromatic light method is designed. Spherical mirror is used to provide collimated light, and a freely sliding and rotating folding mirror is adopted to change the angle of incident light in order to realize full field and automatic calibration of imaging spectrometer. Experiments of spectral calibration have been done for PGP imaging spectrometer to obtain parameters of spectral performance, and accuracy analysis combined with the structural features of the entire spectral calibration system have been done. Analysis results indicate that spectral calibration accuracy of the calibration system reaches 0.1 nm, and the bandwidth accuracy reaches 1.3%. The calibration system has merits of small size, better commonality, high precision and so on, and because of adopting the control of automation, the additional errors which are caused by human are avoided. The calibration system can be used for spectral calibration of other imaging spectrometers whose structures are similar to PGP.

[Model design and stray light suppression technology of stray-light testing equipment for plane grating].

Grating scatter is an important performance index for plane grating, and its measurement is a difficult problem for grating research field. In order to achieve stray-light of the instrument itself to be less than 10(-8) so that the grating scatter can be accurately measured, stray light in diffraction grating monochromators has been studied and an opto-mechanical model of measure instrument for plane grating is designed, which works in parallel light environment and based on the scalar diffraction theory and classical Fresnel-Kirchhoff diffraction theory. Main pathway of the instrumentation's stray light is calculated and analyzed by the simulation of stray-light testing equipment with ASAP software. Accordingly, four stray-light suppression structures including blocking rings, vanes, aperture stops and light traps are proposed to reduce instrument's scattered light and grating's multiple diffraction. Finally, contrast analysis of the instrumentation's stray light is made before and after adding stray-light suppression structures. Simulation and analysis results show that the max of instrument's stray light reduces from more than 10(-6) to less than 10(-8) after adding stray-light suppression structures and has met the stray-light testing equipment's design requirements whose goal is to realize accurate measurement greater than or equal to 10(-7) for grating scatter with grating's groove density changing from 300 to 3 600 gr x mm(-1). The research methods and results above will provide a theoretical basis for the research and development of the stray-light testing equipment for plane grating.

[Integration design and diffraction characteristics analysis of prism-grating-prism].

Prism-grating-prism (PGP) module is the important dispersing component in the hyper spectral imager. In order to effectively predict the distribution of diffraction efficiency of the whole PGP component and its diffraction characteristics before fabrication, a method of the PGP integration design is proposed. From the point of view of the volume phase holographic grating (VPHG) design, combined with the restrictive correlation between the various parameters of prisms and grating, we compiled the analysis software for calculating the whole PGP's diffraction efficiency. Furthermore, the effects of the structure parameters of prisms and grating on the PGP's diffraction characteristics were researched in detail. In particular we discussed the Bragg wavelength shift behaviour of the grating and a broadband PGP spectral component with high diffraction efficiency was designed for the imaging spectrometers. The result of simulation indicated that the spectral bandwidth of the PGP becomes narrower with the dispersion coefficient of prism 1 material decreasing; Bragg wavelength shift characteristics broaden the bandwidth of VPHG both spectrally and angularly, higher angular selectivity is desirable for selection requirements of the prism 1 material, and it can be easily tuned to achieve spectral bandwidth suitable for imaging PGP spectrograph; the vertex angle of prism 1, the film thickness and relative permittivity modulation of the grating have a significant impact on the distribution of PGP's diffraction efficiency, so precision control is necessary when fabrication. The diffraction efficiency of the whole PGP component designed by this method is no less than 50% in the wavelength range from 400 to 1000 nm, the specific design parameters have been given in this paper that have a certain reference value for PGP fabrication.

Use of metal-enhanced fluorescence spectroscopy for detection of polycyclic aromatic hydrocarbons in diesel oil emulsions in artificial seawater.

In this study, we employed the metal-enhanced fluorescence (MEF) method for the detection of polycyclic aromatic hydrocarbons (PAHs) in diesel oil emulsions in artificial seawater. Silver nanoparticles with an average diameter of 80 nm were immobilized onto silanized quartz as MEF substrates. Excited by illumination at 355 nm, a 4.6-fold increase in the fluorescence signals of PAHs was recorded when MEF substrates were used. The finite-difference time-domain (FDTD) method was used to provide mechanistic insights into the fluorescence enhancement. Monitoring water pollution has environmental significance and MEF spectroscopy is finding direct applications in this field.

[High-precision 3D morphology measurement by digital gatling method based on structured light].

In order to measure the microscopic 3D morphology of the objects with high-precision, a 3D texture measurement system of digital gatling based on structured light was designed, which can calculate the 3D height information with the analytic phase method. First, the authors collected sixteen equal step phase images by the four-step equal step method, and calculated their main value by dividing them into four groups. Then, the authors found the average as the final phase main value. The pretreatment on the fringe was done by the adaptive Wiener filter and wavelet multi-threshold method to eliminate the various effects of noise, projector distortion and CCD camera distortion. Besides, gradient-oriented phase unwrapping algorithm based on multifrequency was introduced to avoid phase discontinuity point in the course phase unwrapping, and it was proven to be effective and stable. Experiments showed that the system's 3D resolution was 2.75 microm, and the high degree accuracy was better than 0.5 microm, when the system was running with the fringe parameter p0 = 22.7 mm(-1). In addition, the system has many advantages such as fast measuring, simple operation and non-contact, which can meet the need of the high precision measurement requirements for the microscopic 3D morphology.

[A method of precise adjustment and calibration for high-resolution echelle spectrograph].

Echelle spectrograph is a new type of high-resolution, high-precise spectrograph, and its resolution can be up to tens of thousands to hundreds of thousands. In this case, a little error of the structure will affect the resolution and precision greatly, so an accurate adjustment is of importance for the echelle spectrograph. According to the design features, the present paper discusses the adjustment method for echelle spectrograph. This is an uncomplicated, quick method, and adapts to mini, airproof structure of echelle spectrograph. Using this method, the actual state is consistent with the design result. The result of wavelength calibration is given out, and the error is less than 0.002 nm, which satisfies the requirement of the system.

[Wavelength calibration research on the automatic grating monochromator for orthogonal Czerny-Turner structure].

The wavelength calibration research on the automatic grating monochromator for orthogonal Czerny-Turner structure was investigated. Combined with the structure parameters and characteristic of this monochromator, the sinusoid that accords with the grating equation was proposed as the function of the wavelength calibration. Based on the principle of the least square method, the formula of the fitting residual error of the wavelength calibration was given. Using the Nelder-Mead simplex method, the undetermined coefficient of the fitting residual error was solved, which founded the precise formula between the wavelength and the grating turning angle. The accuracy of the method was verified through the experiment. The calibrated wavelength precision of the monochromator is less than 0.1 nm, which satisfies the application requirement. Applied in the wavelength calibration of the automatic grating monochromator with orthogonal Czerny-Turner structure, this method is simple to apply and easy for implementation. Using this method, the wavelength calibration can be realized quickly and real-timely, but it is only needed to modify the control program of the stepping motor slightly, which shows a better practicability.

[A technology of real-time image compression for convex grating imaging spectrometer].

The huge amount of convex grating imaging spectrometer image data brings much pressure to data transmission and storage, so the image must be compressed in real time. Firstly, the image characteristics were analyzed according to the imaging principle, and the compression approach to removing spatial correlation and spectral correlation was achieved; Secondly, the compression algorithms were analyzed and the 3-D compression scheme of one-order linear compression in spectral dimension and JPEG2000 compression in spatial dimension was proposed. Finally, a real-time compression system based on FPGA and ADV212 was designed, in which FPGA was used for logic control and implementation of prediction algorithm, and ADV212 was used for JPEG2000 compression. The analysis result shows that the system has the ability of lossless and lossy compression, enabling real-time image compression.

[Optical system design of plane grating double monochromator].

The plane grating double monochromator is the important part of the instrument for testing diffraction efficiency of plane grating, and in order to accomplish the research of the instrument, the optical system design and simulation of the plane grating double monochromator was investigated. The instrument mainly consists of light source, front monochromator, testing monochromator and detector, and combined with the practical requirement, the corresponding light source, detector and the structure of the optical path were selected. According to the design requirement, the design and simulation of the optical system of the front monochromator and testing monochromator were done respectively, and the spot diagram of the image surface and the results of real ray trace were given. The analysis showed that in the front monochromator the maximum width of the exit spot and the maximum height of the exit spot were 0.33 and 1.83 mm respectively. On the other hand, in the testing monochromator, the maximum width of the exit spot and the maximum height of the exit spot were 0.66 and 7.27 mm, respectively. Through selecting the size of the exit slit properly, the system can work without luminous flux lost, which guarantees the testing precision of the optical system of the instrument.

[The integrative design for imaging spectrometer].

The hyperspectrum imaging spectrometer will achieve miniaturization and high spectrum resolution and high space resolution along with development of the hyperspectrum imaging technology that is becoming a trend. This trend requires the designers to improve and optimize their designing constantly in designing the instruments. The present paper carried out a method of integrative design for imaging spectrometer. This method suggested that the design and optimization work of the disperse systems of imaging spectrometers would take into account the whole systems, but not consider themselves only. It would get a perfect result by using this method. This paper also explained in details how the method can be used in the design course of imaging spectrometer with convex grating which has been used widely recently. Finally, this paper validated the method by testing the imaging spectrometer with convex grating, which was developed using this method.

[Position acquiring of signal spots in the echelle spectrograph].

It is important for the echelle spectrograph to acquire the exact positions of the spots in the two-dimension spectra image, which directly influence the precision of spectral analysis. With the target of high resolution, which is 15 000 in the echelle spectrograph being discussed, the acquired positional error must be less than 0.03 mm-which equals 2 pixels. According to the characters of the two-dimensional spectra, a position-acquiring method for the signal spots based on the centroid computing algorithm was put forward. Applying this method, the signal spots were distinguished from the noise spots and their positions can be acquired accurately and swiftly, with the positional error less than 2 pixels and wavelength error 0.02 nm, which satisfy the requirements of the echelle spectrograph.

[Solving resolution of diffraction gratings using coefficients of Zernike polynomials].

It is hard and costly to test resolution directly, because the focal length of testing equipment could be nearly ten meters. Solving resolution by diffraction wavefront aberration indirectly is an effective solution to this problem. A normalization model of solving resolution using fitting coefficients of Zernike polynomials was established based on the spectral imaging theory of Fourier optics. The relationship between resolution and wavefront aberration of diffraction gratings was illustrated by this model. Finally, a new method of testing resolution using fitting coefficients of Zernike polynomials was proposed. According to this method, the resolution of a grating is tested by ZYGO interferometer indirectly. Compared with direct method, results indicate that the error of indirect method is less than 4.22%, and this method could be an effective way to avoid the difficulty of direct method to solve resolution. Meanwhile, this method can be used in ZYGO interferometer to solve resolution by wavefront testing easily.

[Small imaging spectrometer for the inspection of fruit quality].

Imaging spectrometer can acquire spatial and spectral information of the target at the same time, achieve high-precision, non-destructive, non-contamination and large area instantaneous inspection of the fruit. In order to get the imaging spectrum of the fruit, compact imaging spectrometer with convex grating produced by self was designed, it has the advantages of good performance, small volume and low weight, its resolution at 578 nm is 2.1 nm, and spectral line bend and chromatic distortion are both smaller than 0.6%. Laboratory test of the imaging spectrometer and the experiment of getting the imaging spectrum of apple were done, and the result shows that the imaging spectrometer satisfies the design requirement and can acquire the imaging spectrum of apple rapidly with high precision for inspection of fruit quality.

[A review of Dyson optical system in the measure of infrared imaging spectrum].

It is difficult for the traditional infrared imaging spectrometers to satisfy the requirement of high signal to noise ratio (SNR) and small size simultaneously. The new infrared remote sensing imaging spectrometers based on Dyson concentric optical configuration have the advantages of high aperture, high SNR, simpleness small volume and low weight. The Dyson imaging spectrometers can achieve high SNR, which is difficult for the traditional imaging spectrometers for infrared imaging spectrum. The present review introduces the beginning, the development and the present research of the Dyson imaging spectrometers, especially illustrates the principle of Dyson concentric spectrometer, difficulty during its manufacture and the application in the high-performance infrared remote sensing imaging spectrometers, providing a reference for the high-performance research of infrared remote sensing imaging spectrometers.

[Optimization of broad-band flat-field holographic concave grating without astigmatism].

The desirable imaging locations of the flat-field holographic concave gratings should be in a plane. And the object can be imaged perfectly by the grating when the tangential focal curve and sagittal focal curve both superpose the intersection of the image plane and dispersion plane. But actually, the defocus can not be eliminated over the entire wavelength range, while the astigmatism vanishes when the grating parameters satisfy some conditions. An optimization method for broad-band flat-field holographic concave gratings with absolute astigmatism correction was proposed. The ray tracing software ZEMAX was used for investigating the imaging properties of the grating. And we made a comparison between spectral performance of gratings designed by this new method and that by conventional method, respectively. The results indicated that the spectral performance of gratings designed by using the absolute astigmatism correction method can be as good as gratings designed with the conventional method. And the focusing performance in the sagittal direction is much better, so that the S/N ratio can be greatly improved.

[Effect of curvature radius error on the flat-field holographic concave grating resolution and its compensation].

The spectral resolution of the spectrometer will be seriously deteriorated by radius error which is inevitable in the flat-field holographic concave grating fabrication. In order to give theoretical guidance to the design and assembly of the spectrometers, the geometric ray-tracing method was used to calculate and analyze the variation of the spectral image width with different radius error. It was discovered that in a wide range of the radius error, the position of the tangential focal curve moves forward or backward as the radius changes, while the shape of the tangential focal curve remains almost unchanged. As is shown through the calculation, the radius error can be compensated by adjustment of the detector's position or entrance slit distance. The simulation results indicate that with proper modification of the using structure, the grating can have a spectral resolution as good as the designed results.

[Achievement of the noninvasive measurement for human blood glucose with NIR diffusion reflectance spectrum method].

The noninvasive measurement of human blood glucose was achieved with NIR diffusion reflectance spectrum method. The thumb fingertip NIR diffusion reflectance spectra of six different age healthy volunteers were collected using Nexus-870 and its NIR fiber port smart accessory. The test was implemented with changing the blood glucose concentration for the limosis and satiation of every volunteer. The calibration model was set up using PLS method with the smoothing, baseline correction and first derivatives pretreatment spectrum in the 7500-8500 cm(-1) region for single volunteer, the same age combination and that of different age. When the spectrum was obtained, the actual blood glucose value of every spectrun sample was demarcated using ultraviolet spectrophotometer. The correlation between the calibration value and true value for single volunteer is better than that for the combination of volunteers, the correlative coefficients are all over 0.90471, RMSECs are all less than 0.171.