[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.

[Optimal Design of Light Folding Imaging Spectrometer Based on Dyson Concentric System].

Concave grating spectrometer based on Dyson concentric optical system has advantages of low aberration, large aperture and compact structure. The object plane and image plane of concentric spectrometer subsystem must be reunited into one plane while the distance between the object point and image point is relatively small. Thus it is difficult to satisfy this requirement for the existing focal plane of detection technology and assembly technology. In order to solve the assembly problem of the object and detector, the traditional Dyson concentric spectrometer was improved by introducing the off-axis mirror to shift the image light beam. The results show that the object plane and image plane of the improved system are separated successfully by the beam folding, and the aberration at all wavelengths is more rational distribution.

[Algorithm for Background Removal in Spectral Image of Echelle Spectrometer].

Echelle spectrometer gets full spectrum by transient direct reading because of the characteristic of cross-dispersion. The two-dimension spectra received by flat-plane detector needs to be reduced to one-dimension spectra so that the effective wavelength can be detected. Because of huge original data and few effective data, background removal plays an important role of decreasing the amount of data and improving data processing speed. The two-dimension spectrum of echelle spectrometer is analyzed and a suitable background removal algorithms is came up. The edge detection method is applied to diffuse spot detection. Selecting appropriate operator to convolute original image to get edge image and calculating global threshold to segment edge image which can be used to map original image to get the background removed image. Two-dimensional spectral images based on different elements at different integration time are used to judge the effect of different background removal algorithm and different operator are analyzed to figure out their effect of speed and accuracy for algorithm. Experimental result shows that the algorithm came up by this letter is better for image background removal than the others. The background removed image can be used in spectrum reductionand the speed of data processing is notable promoted.

[An Effective Wavelength Detection Method Based on Echelle Spectra Reduction].

Echelle spectrometer with high dispersion, high resolution, wide spectral coverage, full spectrum transient direct-reading and many other advantages, is one of the representative of the advanced spectrometer. In the commercialization trend of echelle spectrometer, the method of two-dimension spectra image processing is becoming more and more important. Currently, centroid extraction algorithm often be used first to detect the centroid position of effective facula and then combined with echelle spectrum reduction method to detect the effective wavelength, but this method is more difficult to achieve the desired requirements. To improve the speed, accuracy and the ability of imaging error correction during detecting the effective wavelength, an effective wavelength detection method based on spectra reduction is coming up. At the beginning, the two-dimension spectra will be converted to a one-dimension image using echelle spectra reduction method instead of finding centroid of effective facula. And then by setting appropriate threshold the one-dimension image is easy to be dealing with than the two-dimension spectra image and all of the pixel points stand for effective wavelength can be detected at one time. Based on this new idea, the speed and accuracy of image processing have been improved, at the same time a range of imaging errors can be compensated. Using the echelle spectrograph make a test applying this algorithm for data processing to check whether this method is fit for the spectra image processing or not. Choosing a standard mercury lamp as a light source during the test because the standard mercury lamp have a number of known characteristic lines which can be used to examine the accuracy of wavelength detection. According to experimental result, this method not only increase operation speed but improve accuracy of wavelength detection, also the imaging error lower than 0.05 mm (two pixel) can be corrected, and the wavelength accuracy would up to 0.02 nm which can satisfy the requirements of echelle spectrograph for image processing.

[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.

[Research on influencing factors and compensation method of testing results for concave gratings diffraction efficiency].

The present paper aimed at the question that the beam cross-section changes according to the rotation of concave grating during the measuring process, and the appropriate supplement to the principle of the program was done. The appropriate supplement to the principle lay the foundation for the derivation of the beam cross-section k(theta), and the whole analytical expression of changes factor of the beam cross-section k (theta) for concave grating was derived. Because of the relationship between the theoretical values and the factors which affect the diffraction efficiency measuring accuracy was nonlinear, the quadratic nonlinear regression analysis was introduced and the compensating formula was established. The results show further correction to diffraction efficiency measurements for concave grating, the range of differences between the compensated values and the theoretical values was reduced from +/- 2.5% to less than +/- 0.3%, compared with the linear regression analysis, and the quadratic nonlinear regression analysis significantly reduces the variation between the compensated values and the theoretical values, which further ensures the accurate measurement of the diffraction efficiency for concave gratings. The compensating process is embedded in the measurement program; this method is strongly real-time, which can satisfy the requirements of simple operation, testing speediness and preciseness.

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.

[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.

[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.

[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.

[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.

[Optical design and performance analysis of light and small echelle spectrograph].

The present paper analyzed the influence of the pinhole diameter, grating parameters, CCD pixel size, prism parameters, system aberrations and found that the first three are the main factors, and then deduced the mutual restraint relationship among them. On this basis, a portable high-resolution echelle spectrograph was designed. Applying this design, aberration was fully corrected and spectral resolution achieved the demand. With the Hg lamp calibrated and restored, the actual resolution gets up to 0.038 nm which is significantly better than target (0.05@200 nm), while the ordinary grating spectrometers need 500 mm focal length to achieve this resolution. From this result, the advantages of the portable echelle spectrograph are fully demonstrated.

Illumination system using LED sources for pocket-size projectors.

An illumination system using LED sources for pocket-size projectors is designed. Its color gamut is much larger than the sRGB standard. The maximum theoretical efficiency of this system is 29.98% by non-imaging theory-based calculations. To analyze the system model, 1.5 x 10(6) rays are traced by using the LightTools software. The total light flux that illuminates the digital micromirror device is 44 lm and the American National Standards Institute 13-point uniformity on the surface is 91.55%, -91.15% with a system efficiency of 28.3%. The calculations are in good agreement with the simulation results. The illumination system can be used for personal pocket-size projectors providing a 15-20 in. (38-51 cm) color display with the brightness comparable with a laptop.