Research On Design And Testing Error Compensation Of Wide Spectral Coverage Test Instrument For Plane Grating Diffraction Efficiency

In order to develop high spectral resolution spectroscopy and carry out the keytechnical research on prototype instruments of hyper-spectral remote sensing, thenget the ability of monitoring and testing the atmospheric composition，2012Changchun Institute of Optics, fine mechanics and physics take on the carbon starspayload of with CO2detector with high spatial and hyper spectral resolution.Atmospheric CO2detector introduces the large blaze angle reflection plane gratingas the core component. Diffraction efficiency of the grating play a decisive role tothe energy transfer capability of the instrument, thereby affecting the detectionaccuracy and precision of the inversion for CO2concentration of atmospheric CO2detector, so atmospheric CO2detector also made the target to its diffractionefficiency of the large-size flat grating, but the existing testing equipment bear therestriction of wavelength range and detection of the test grating size, cannot achievethe testing diffraction efficiency of large-size flat grating; Meanwhile, the testingvalue for large size of the grating in the existing equipment cannot accurately reflectthe energy transmission performance at its work state in atmospheric CO2detector.Related structures have reported that using a tunable laser as a light source, selectseveral points at the grating surface in the space to measure the grating diffraction efficiency, but this method cannot achieve the full aperture efficiency in the practiceworking condition, and therefore cannot fully measure the diffraction efficiency ofthe test grating. Meanwhile, the tester exit slit size and the detector sensitive areaalso limits the detecting of the flux of the testing element.Given these reasons, according to the requirement of CO2detecting instrument tothe large-scale plane grating, we deeply study the instrument in these aspects, whichincluding the optical system design, the optics assembly method, the efficiencymeasurement method and the error compensation method. The chief research workon the instrument is as following. Firstly, in allusion to the working condition andthe requirement of large-size grating, according to the principle of grating efficiencymeasurement, adopting the structure of double-monochromator to design theinstrument. For the requirement of wide spectral coverage, we put forward thedesign of the pre-monochromator gratings group. According to the actual result ofray tracing, we know that the wide spectral coverage diffraction efficiencyinstrument can satisfy the efficiency measurements of large size plane grating.Secondly, because the existing detector photosensitive area is restricted, bring on theenergy integral method to collect the exit flux, and validate the correctness of themeasurement method. At the same time, in view of the practical problems, weanalyze them theoretically according to the principle of measuring grating efficiency,and determine the adjustment method of optical elements. Thirdly, the gratingefficiency obtained from the instrument is a relative value, and the measuringaccuracy of its value is affected by the measurement process and the compensationmethod. To improve the measuring accuracy of the grating efficiency, this paperfurther investigates the main factors influencing the measurement accuracy, deducethe analytic expression for the change factor of beam cross section (k(θ)). And thenput forward the compensation formula of improving efficiency measurementaccuracy. Through embedding the compensation procedures in the measuringsoftware, the method can get real-time results, and meet the requirement of theinstrument for accurate measurements. Fourthly, through the analysis of the performance of optical system, we put forward the alignment method, with whichthe optical element precision alignment and the detection signal identification of themicroscope can be combined. Using this method, we achieve a precise alignment forthe wide spectral plane grating diffraction efficiency instrument on the basis of thedouble monochromator. And then, according to the measurement process of gratingefficiency, the operating software is developed, which has the functions of thewavelengths calibration and scanning, the optical system alignment and testing, andthe error compensation of the results. And this software provides convenience forvarious kinds of grating efficiency test.