The monochromators, which are able to separate a specific wavelength light from a complex spectrum and a continuous spectrum light source, have been widely used in optical measurements. As one crucial specification, wavelength accuracy has always been a research theme for monochromator users around the world. When the monochromator is utilized for calibrating the wavelength in the ultraviolet, visible, and near-infrared regions, low-pressure discharged lamps, such as mercury lamps, are usually employed to obtain wavelength deviations at certain wavelength points of atomic emission lines of lamps,which are well-known recognized. For the requirement of monochromator wavelength calibration, a light path based on the low-pressure discharged lamp method was constructed. Three strong radiation flux lines of the mercury lamps were selected and tested,whose wavelength values were 365.015 nm, 435.833 nm, and 546.075 nm. Meanwhile a new method based on continuous spectrum light source and Fourier transform spectrometer was proposed and light path was also built. Near the wavelength value points of the selected atomic emission lines of mercury lamp, a measurement experiment was performed both on the same monochromator and the same experimental conditions, and the wavelength deviation values of the monochromator was obtained. The consistency of the two methods was good, and the best repeatability error was better than 0.005nm. The work of this article is of positive for those measurement laboratories to select suitable approach to perform their monochromators wavelength calibrations.
The monochromator has been widely used in the field of optical precision measurement. It can effectively separate the monochromatic light of the specific wavelength required for the experiment from a complex spectrum and a continuous spectrum light source. The wavelength accuracy of a monochromator is an important indicator of its performance，and the research of wavelength accuracy calibration methods to improve measurement accuracy is a hot theme for researchers around the world.When the monochromator is utilized for calibrating the wavelength in the ultraviolet, visible, and near-infrared region, low-pressure discharged lamps, such as mercury lamps and neon lamps, are usually used to calibrate on the well-known limited atomic emission lines of lamp to obtain the wavelength deviation value at the wavelength points of these lines.For some high-precision requirements, for example, when measuring the spectral responsivity of a reference solar cell using a tunable laser as light source, it is difficult for these discrete and finite lines to fully satisfy the demand.To solve this problem, a new method based on combination of continuous spectrum light source and fourier transform spectroradiometer was used. A calibrated experimental optical path was successfully built, and the wavelength deviation values of 322 wavelength points from 400 nm to 2000 nm were obtained. The optimal measurement repeatability reached 0.3 pm, which met the need for high-precision measurement requirement. As a comparison, a low-pressure discharged lamp method was also used. Using a mercury lamp and a neon lamp, a wavelength calibration experiment was performed on the same monochromator in the same wavelength range, and only 20 wavelength deviation values were obtained at its atomic emission lines wavelength point. The number of wavelength deviation values is less than 6.5% of that of the new method.The new method proposed in this paper,which not only can significantly improve the quality of the monochromator calibration wavelength deviation values, but in which the obtained values are able to establish traceability to the international SI unit system, is an ideal wavelength accuracy calibration method.
Based on a testing method of spatial frequency response(SFR), a setup for characteristics measurements of the infrared defect tester,which can also be called electroluminescence tester(EL tester), a machine examining defects of photovoltaic (PV) panel, was built. The influences of focusing plane adjustments and infrared light box arrangements on resolution measurement of EL tester in full field of view were analyzed. For different types of EL testers, portable and fixed, testing methods and procedures were presented. Especially, a novel testing method for portable EL was claimed, which could do the work well without reference background. Based on method claimed and setup built, the resolutions of different types of EL testers were obtained and stable results were achieved. This setup is portable designed to meet online measurements requirements of PV industry.
Spectral mismatch error should be carefully considered during the calibration of solar cells by means of solar simulator
and calibrated reference cell. Even test and reference cells with the same type should be also considered spectral mismatch
error to achieve good measurement results. Spectral mismatch error can be calculated with the relative spectral response
of the test and reference cells, and the relative spectral irradiance of the simulator and reference solar. The reference solar
spectral irradiance distribution was given according to IEC60904-3:2008. Experimental results, two cells, one test and
one ref, with two different spectra solar simulators, were presented. The calculation method and experimental data
presented could be positive reference to photovoltaic labs to obtain good calibration and test results of solar cells.
The human eye has the ability to distinguish millions of colors, with this feature we can identify very
subtle color differences, and the measurement of human eye color difference threshold can provide a
visual function diagnosis for testee. In recent years, people begin to focus on studies on visual
threshold diagnostic equipment. This paper proposes a human eye color difference threshold
measurement system which is based on dual integrating sphere. The system includes two pairs of dual
integrating sphere and color control module. Dual integrating sphere uses to mix and produce color,
and palette unit which produces primary colors (red (R), green (G), blue (B)) is embedded in dual
integrating sphere. At the same time, the embedded palette unit which produces cyan (C), magenta (M),
and yellow (Y) expands color area that the system can generate. One optical path based on dual
integrating sphere generates standard color, the other path produces the matching color which is similar
to a standard color. In the high-precision closed-loop color control module, photoelectric switch records
stepper motor’s origin position and limits move displacement. Precision stepper motor pushes the
light-blocking panel of the palette unit to a predetermined position, while real-time monitoring the
position of the light-blocking panel and mixing the ideal controllable color. Two colors that the system
generates are projected onto the same target area. Subjects make a judgment on color difference
threshold by observing the target eventually.
An advanced fiber point diffraction interferometer (FPDI) is built for measuring spherical mirror surface and spherical
lens wave front aberration with high precision. This new interferometer is based on point diffraction technique. Using
short coherence length laser as light source, the perfect spherical wave diffracts from fiber point resource as reference
wave. And the spherical wave is interfered with object wave to achieve higher accuracy. A phase shifting point
diffraction interferometer with one single-mode-optical-fiber is built for measuring concave spherical mirror surface. A
concave spherical mirror is measured by the experimental facility. The interferograms are collected by CCD and
analyzed by computer. The PV values and RMS values of resulted surface error are compared with the result acquired by
digital wave front interferometer. The measured surface is fitted and represented by Zernike polynomials. The results
compared with Zygo GPI interferometer are proximately the same. Finally the differences between them are discussed in
detail. To measure the aberration of spherical lens, a two single-mode-optical-fibers point diffraction interferometer is
built by adding another single mode optical fiber. A convex lens is measured. The interferograms is presented.
Due to the phasing effects, the measurements of Minimum Resolvable Temperature Difference (MRTD) for Staring
array thermal imagers often get abnormal results when the targets approaching system Nyquist frequency (fn). To
simulate the relations between MRTD values and four-bar targets' frequencies, this paper introduces the concept of best
contrast. Clearly, the MRTD results are inversely proportional to the best contrasts under optimum phases, higher
contrast corresponding to a lower MRTD. On the other hand, with the spatial frequencies increasing, the target's
opening area shrinking and leads the effective infrared eradiation decreasing, this means the MRTD results are inversely
proportional to the opening area of the target. Based on these two assumptions, and through numerical simulations, this
paper depicts the tendency chart of MRTD under optimum phases to the four-bar targets' spatial frequencies. The
tendency chart adequately explains the hump curve happens at frequencies between 0.6fn and fn. From the simulations,
the maximum of MRTD values can be predicted at the frequency of 0.89fn. The tendency chart illustrated by numerical
simulation is consistent with the MRTD results get in laboratory. While in Dynamic Minimum Resolvable Temperature
Difference (DMRTD) testing, moving the four-bar targets introduces temporal effects not present in static MRTD test.
Simulation reveals that DMRTD test can get more realistic shape of the curve between 0.6fn and fn, the characteristic
hump in the static MRTD curve between 0.6fn and fn is not seen.
An absolute measurement method of spherical lens with Fiber Point Diffraction Interferometer (FPDI) was developed.
To achieve a high accuracy, several key techniques are discussed such as: short coherence length laser, interferogram
collecting, experiment set up, and reconstruction of wave front. Through these techniques an experiment system has been
built. The 5-step phase shifting interferograms are collected. The wave front is fitted by Zernike polynomials and
reconstructed. The repeated measurement result has a good performance compared to a Zygo GPI interferometer.
This paper presents Zernike polynomials fitting wave front which is detected by fiber point diffraction interferometer (FPDI). To confirm that Zernike polynomials are suitable for fitting concave spherical mirror surface, different orders of Zernike polynomials were used to fit several different surfaces which are produced by computer. Fitting result errors were evaluated by residual standard deviation. It is illuminated that Zernike polynomials are suitable for fitting surface which changes smoothly but not suitable for fitting surface with sharp fluctuating. When the shape changes dramatically Zernike polynomials are unable to correctly fit. Choosing appropriate term of polynomials, more terms don't mean higher precision. A metal coated concave spherical mirror, curvature radius 580mm, caliber 70mm, was measured as a sample. The five-step phase shifting interferograms of good quality were detected by an experimental FPDI which was built in lab. Measured wave front was fitted by 36 terms of Zernike polynomials from phase map which were unwrapped from five-step phase shifting interferograms. The measurement result was obtained and compared with that by Zygo interferometer when measured the same mirror. The 2 represented wave fronts have same characters such as centers bulging and marginal trough.
The point diffraction interferometer (PDI) is the technology which realizes the absolute interferometric measurement
without the use of reference surface. Pinhole is mostly used to generate the ideal spherical wavefront traditionally. While
using the single mode optical fiber instead of pinhole can easily introduce phase-shifting ability for PDI measurement.
This paper mainly discusses the merits and disadvantages of two kinds of fiber phase shifting point diffraction
interferometer (FPS/PDI). Two fibers FPS/PDI is a separated-path configuration. Although it's easy to adjust, it's more
sensitive to environment influence, and the thickness of fiber cladding will induce an off-axis error during measurement.
Single fiber FPS/PDI is a common-path configuration, thus it is robuster than the front, but the maximum visibility is
now one half. Its accuracy is mainly affected by factors such as the fiber core diameter, slight ellipticity and oblique face.
The paper lastly compares the single fiber PDI with ZYGO interferometer based on measurement data about a sphere
surface, the single interference pattern collected by our experimental fiber PDI apparatus is analyzed and the major error
sources are also discussed.
The primary restriction on the precision of spherical figure measurement is the imperfectness of the reference spherical
wavefront. Using the nearly perfect spherical wavefront diffracting from a single mode fiber as the reference, the
accuracy of spherical figure measurement can be greatly improved. To get good contrast of interference fringe, the
extraneous interference should be eliminated, and the intensity of the reference beam must match to the measuring beam
at the same time. Using the short coherence length laser source can avoid most of the extraneous interference. The
principles through stretching the resonant cavity length to shorten the coherence length are discussed; the effects are
validated by constructing a Twymann-Green interferometer using the cavity length tunable YAG solid state laser.
Calculations on light intensity show that only through controlling the attenuation of the measuring beam, can it match to
the reference beam. Coating the fiber tips with semi-metallic film can substantially improve the contrast of the
interference fringe. Comparing to the measurement results of ZYGO interferometer, the single interference pattern
collected by our experimental fiber PDI apparatus is analyzed and the major error sources are also discussed.
The key technology that the attenuators of the continuous values are designed, manufactured and calibrated to calibrate the range of Laser Range Finder is discussed in this paper. The transmittance control technology of designing the continuous attenuator with a large caliber and 0.2dB-10dB attenuation continuously is sets forth, and the means of orthogonal polynomial surface fitting for continuous attenuation values are analyzed, the utility calibrating results are also presented.
A computer-aided alignment method is put forward in this paper. It combines laser shearing interferometry and computer- aided optimization, accurately measures the alignment of the optical elements of the system being aligned and gives the adjustment project to control the wavefront quality. The theoretical analysis and experiments demonstrate the ability and effectiveness of this computer-aided alignment method and it especially suits for the on-site alignment of large and complex optical system.