Integrating Sphere Light Source Research Articles

Small Integrating Sphere Light Source with High Radiance Uniformity

Small Integrating Sphere Light Source with High Radiance Uniformity

Characterization of Imaging System for Satellite-Borne Polarization Camera Based on Scientific Grade CCD

The cloud and aerosol polarization camera (CAPC) is an ultrawide angle satellite-borne polarization sensor, which adopts a scientific-grade array charge-coupled device (CCD) with the feature of smearing effect. To realize shorter exposure time and increase the dynamic range for the CCD imaging box of CAPC, the idea of charge dumping is introduced into the CCD timing driving design. Then, the design of power supply, driving timing, and analog front-end (AFE) is studied in detail. Finally, the comprehensive performance of the CCD imaging box is compared by utilizing the large aperture integrating sphere light source. The measurement results indicate that the exposure time of CCD is controlled between 5 and 80 ms, and the linearity error of CAPC at various bands is lower than 0.5%. Under the condition of 90% saturation exposure, the signal-to-noise ratio (SNR) of CAPC is 52.63 dB. The CCD dynamic range can achieve 62.91 dB. The experimental results meet the working requirements of the CAPC and verify the effectiveness of the CCD imaging design.

Retrieving nighttime aerosol optical depth using combined measurements of satellite low light channels and ground-based integrating spheres

ABSTRACT The aerosol optical depth, as an aerosol optical property, is a key physical quantity used to characterize the degree of atmospheric turbidity. The radiance of the integrating sphere light source after radiometric calibration is relatively stable. Compared with the original use of city lights to invert the night-time aerosol optical depth (AOD), the use of the integrating sphere can effectively reduce the change of the emission source and improve the inversion accuracy. A model to retrieve night-time AOD based on combined measurements of satellite low light channels and ground-based integrating spheres was established by the night-time artificial observation experiment in the Dunhuang radiation correction field (DRCF) for 38 consecutive days from October to November 2018. After excluding cloud pollution and moonlight pollution, the calculated results are compared with the Moderate Resolution Imaging Spectroradiometer (MODIS) data and the Visible/Infrared Imaging Radiometer Suite (VIIRS) night-time aerosol data. The average root mean square error of the processed data is 0.11 and 0.23, and the correlation coefficient reaches 0.85 and 0.46, respectively. The experimental results preliminarily show that the retrieval AOD is in good agreement with the satellite data, and it is feasible to retrieve AOD based on combined measurements of satellite low light channels and ground-based integrating spheres.

Radiometric calibration of a multiphoton microscope capable of measuring absolute photon flux of single photon sources

Precise photon flux measurement of single photon sources (SPSs) is essential to the successful application of SPSs. In this work, a novel method, to our knowledge, was proposed for direct measurement of the absolute photon flux of single photon sources with a femtosecond laser multiphoton microscope. A secondary 2-mm-diameter aperture was installed under the microscope objective to define the numerical aperture (NA) of the microscope. The defined NA was precisely measured to be 0.447. An LED-based miniaturized integrating sphere light source (LED-ISLS) was used as a standard radiance source to calibrate the photon flux responsivity of the multiphoton microscope, with the defined NA. The combined standard uncertainty of the measured photon flux responsivity was 1.97%. Absolute photon flux from a quantum-dot based emitter was measured by the multiphoton microscope. The uncertainty of the photon flux was evaluated to be 2.1%. This work offers a new, to our knowledge, radiometric method for fast calibration of photon flux responsivity of microscopes, and absolute photon flux calibration of single photon sources.

Synchronous measurement method of a multi-angle scattered light field.

A synchronous multi-angle scattered light field measurement system is constructed in this study to overcome issues with current systems in the field of multi-angle remote sensing. A mathematical model of the scattered light field measurement was established. An off-axis catadioptric optical system was designed to satisfy hemispheric spatial scattered light field measurements in a zenith angle range of 68°. The off-axis calibration model was established, and the spatial relationship was calibrated. The measurement accuracy was calibrated via an integrating sphere light source, and the maximum measurement relative error was -3.71%. The scattered light field of the reference diffuse reflective target plate Labsphere Permaflect-50 and 304 stainless steel was simulated under an incident light irradiation range within the zenith angle of -23.5∘ to +23.5∘, and synchronous measurement of the multi-angle scattered light field of the sample was realized. The measurement system could provide technical support for building the complex model of multi-angle reflection/radiation from the earth's surface, multi-angle sensor radiation calibration, and improvement of the physical parameter inversion accuracy of observation targets.

Spectral diagnostic system for light impurity transport study in J-TEXT Tokamak

A light impurity diagnostic system is developed for the J-TEXT tokamak. This diagnostic system consists of carbon V (227.09 nm), carbon III (464.7 nm) and edge rotation diagnostics. The carbon V diagnostic consists of a 12-core fiber bundle for light collection, an aberration-corrected monochromator, and a 12-channel photomultiplier tube array. The carbon III diagnostic adopts three identical 18-channel Si photodiode arrays to cover the edge region of the high-field side (HFS), low-field side (LFS) and limiter regions at different toroidal positions, with a specified front filter. The carbon VI (529.26 nm) diagnostic consists of a 10-core fiber bundle, an aberration-corrected monochromator, and an electron-multiplying CCD camera. The system coverage range is 0.2 m to 0.07 m of the HFS. A high-resolution spectroscopic diagnostic can detect carbon III (229.69 nm) and carbon V (227.09 nm) radiation intensities in the LFS. An accurate absolute calibration is carried out by an integrating sphere light source, and a relative position calibration is developed for all diagnoses. Combining the impurity emission profile which derived from inversion and plasma parameter profile, the impurity density of each ion stage and impurity transport coefficients are obtained by a one-dimensional impurity transport code.

基于积分球光源的能见度测量系统设计及实现

基于积分球光源的能见度测量系统设计及实现

Research on radiation uniformity of annular baffle integrating sphere light source

Research on radiation uniformity of annular baffle integrating sphere light source

Theory and analysis of a large field polarization imaging system with obliquely incident light.

Polarization imaging technology provides information about not only the irradiance of a target but also the polarization degree and angle of polarization, which indicates extensive application potential. However, polarization imaging theory is based on paraxial optics. When a beam of obliquely incident light passes an analyser, the direction of light propagation is not perpendicular to the surface of the analyser and the applicability of the traditional paraxial optical polarization imaging theory is challenged. This paper investigates a theoretical model of a polarization imaging system with obliquely incident light and establishes a polarization imaging transmission model with a large field of obliquely incident light. In an imaging experiment with an integrating sphere light source and rotatable polarizer, the polarization imaging transmission model is verified and analysed for two cases of natural light and linearly polarized light incidence. Although the results indicate that the theoretical model is consistent with the experimental results, the theoretical model distinctly differs from the traditional paraxial approximation model. The results prove the accuracy and necessity of the theoretical model and the theoretical guiding significance for theoretical and systematic research of large field polarization imaging.

Programmable LED-based integrating sphere light source for wide-field fluorescence microscopy

Wide-field fluorescence microscopy commonly uses a mercury lamp, which has limited spectral capabilities. We designed and built a programmable integrating sphere light (PISL) source which consists of nine LEDs, light-collecting optics, a commercially available integrating sphere and a baffle. The PISL source is tuneable in the range 365–490nm with a uniform spatial profile and a sufficient power at the objective to carry out spectral imaging. We retrofitted a standard fluorescence inverted microscope DM IRB (Leica) with a PISL source by mounting it together with a highly sensitive low- noise CMOS camera. The capabilities of the setup have been demonstrated by carrying out multispectral autofluorescence imaging of live BV2 cells.

基于多光源的光谱分布可调谐光源系统

A spectrum-tunable integrating sphere light source based on a Light Emitting diode (LED) and basis sources was developed to eliminate the effect of spectral non-matching between calibration source and an on-orbit detecting target on the calibration accuracy of space optical remote sensor in a laboratory. The developed source was used to produce typical ground object spectra and to calibrate space optical remote sensors, which significantly diminishes the absolute radiometric calibration error caused by spectral non-matching mentioned above. Firstly, the affecting mechanism of the spectral non-matching on the absolute radiometric calibration accuracy of space optical remote sensor was analyzed. Then, the design scheme of the spectrum-tunable light source was given according to technical requirements. The scheme was mainly divided into four key issues: the determination of light source and design of spectral matching algorithm, the design of light source drive circuit and control system, the matching of target spectrum and spectral adjustment, and the optical-mechanical design of spectrum-tunable light source. In the end, the performance of calibrated spectrum-tunable light source was tested. The results show that the spectral non-matching errors of equi-energy spectrum and 6000 K blackbody spectrum are 6.37% and 8.76% respectively, the irradiance non-uniformity is 0.53%, the irradiance instability of the spectrum-tunable light source within 30 min is 0.03%, and the radiance angular non-uniformity of the spectrum-tunable light source within horizontally 30 is 0.80%. Moreover, it offers the spectral radiance above 0.07 W/(m2srnm) and the integral radiance in 410-900 nm of 58.3 W/(m2sr). These data all meet the design requirements of spectrum-tunable light sources.

Outdoor relative radiometric calibration method using gray scale targets

The radiometric calibration of remote sensors is a basis and prerequisite of information quantification in remote sensing. This paper proposes a method for outdoor relative radiometric calibration using gray scale targets. In this method, the idea of two substitutions is adopted. Sunlight is used to replace the integrating sphere light source, and gray scale targets are used to replace the diffuser. In this way, images at different radiance levels obtained outdoors can calculate the relative radiometric calibration coefficients using the least square method. The characteristics of this method are as follows. Firstly, compared with laboratory calibration, it greatly reduces the complexity of the calibration method and the test cost. Secondly, compared with the existing outdoor relative radiometric calibration of a single radiance level, it uses test images of different radiance levels to reduce errors. Thirdly, it is easy to operate with fewer environmental requirements, has obvious advantages in the rapid calibration of airborne remote sensors before or after flight and is practical in engineering. This paper theoretically and experimentally proves the feasibility of this method. Calibration experiments were conducted on the wide-view multispectral imager (WVMI) using this method, and the precision of this method was evaluated by analyzing the corrected images of large uniform targets on ground. The experiment results have demonstrated that the new method is effective and its precision meets the requirement of the absolute radiometric calibration. relative radiometric calibration, relative radiometric correction, precision evaluation, gray scale target

基于溴钨灯和LED积分球光源的可调谐光谱分布及光谱匹配

The mixed-lamps of bromine tungsten lamps and LEDs were proposed to serve as integrating sphere inner source and LEDs were driven by constant current.Simulated Annealing(SA) algorithm was introduced to study the spectral matching technique of spectrum-tunable integrating sphere light source(STIS).The simulation experiment indicated that mixed-lamps could not only mimic CIE-D65 and equi-energy spectra successfully,but also improve the performance of STIS.The numbers of LEDs reducing 79.8% and 82.9%,respectively,and the average relative error reducing 10% and 40.5%,comparied with LEDs simulation results.A feasible mixed-lamps scheme for Ф 0.5 m integrating sphere,whose maximal radiance between 380 nm and 900 nm is no less than 50 W/(m2·sr).The validating experiment indicated that the SA algorithm and constant current drive mode would be feasible in STIS' engineering practice.

Realizations of the units of luminance and spectral radiance at the HUT

Realizations of the units of luminance and spectral radiance at the Helsinki University of Technology (HUT) are presented. These realizations are linked to HUT units of luminous intensity and spectral irradiance using a characterized photometer, a spectroradiometer and an integrating-sphere light source. A new method for determining the spatial uniformity of the output of the integrating-sphere source is described. The uncertainty analysis indicates a relative expanded uncertainty of 3.6 × 10−3 (coverage factor k = 2) for the realization of the unit of luminance. The expanded uncertainty for the realization of the unit of spectral radiance varies between 6 × 10−3 and 2.5 × 10−2 in the wavelength region 360 nm to 830 nm.