Self-calibration micro-light radiance meter based on 355nm pumping and measuring method

Abstract

This invention provides a self-calibrated low-light radiance meter and measurement method based on 355nm pumping, including self-calibration and radiation observation. In self-calibration mode, the multiplexed optical path module periodically imports spontaneous parametric downconversion correlated photons, and the photon counting and coincidence detection modules calibrate the absolute quantum efficiency of the three channels. In radiation observation mode, the multiplexed optical path module imports the low-light target radiation, and simultaneously acquires the absolute spectral radiance of the observed target in the 460nm–1550nm band. The calibration coefficients obtained in the self-calibration mode are used to correct the observation results. This invention starts from the basic principle of calibrating the quantum efficiency of single-photon detectors based on the correlated photon method of spontaneous parametric downconversion, realizing high-precision observation of low-light spectral radiance in the visible to near-infrared bands. It solves the scientific problem of traceability of low-light observation instruments on space platforms and plays an important role in climate monitoring, low-light radiation metrology, and single-photon source radiance measurement.

Description

Technical Field

[0001] This invention relates to the fields of climate monitoring, low-light radiation metrology, and single-photon source radiance measurement, and particularly to a self-calibrating low-light radiance meter and measurement method based on 355nm pump. Background Technology

[0002] With the rapid increase in the number of satellite remote sensors and the development of optoelectronic technology, low-light radiometric calibration research for quantitative remote sensing satellites has received widespread attention. The current technique of independently calibrating each payload is becoming less feasible. Differences in calibration timing, meteorological conditions, calibration equipment, and calibration procedures among different payloads lead to unavoidable difficulties in comparing the absolute values ​​of observation data. For the radiometric calibration accuracy of optical payloads, the absolute accuracy requirement for visible to near-infrared light has generally increased from the current 7%–10% to better than 5%, with some special scientific applications such as climate monitoring requiring ultra-high accuracy better than 0.1%. Facing the technical challenge of ultra-high precision radiometric measurement and ensuring the traceability of remote sensor observation data, it is essential to research and apply radiometric reference source technology specifically for low-light detection.

[0003] Over the past 30 years, domestic and international researchers have gradually established and successfully implemented three main calibration techniques: on-orbit field calibration, satellite calibration, and laboratory calibration, to determine and correct for changes in the response characteristics of remote sensors. The S-NPP satellite, carrying the Visible-Infrared Imaging Radiometer VIIRS, achieves radiometric calibration through a three-stage gain-stage transfer calibration method, achieving a design uncertainty of 15% under weak moonlight conditions. The low-light camera developed by the Beijing Institute of Space Electromechanical Engineering uses a three-stage cascaded integrator sphere transfer model, leveraging the constant spectrum of a uniform light source at each output radiance level. It measures the spectral radiance at various levels of low light using a transfer measurement method, achieving a measurement uncertainty of 18% in the 450-1000 nm range. From the perspective of improving the accuracy of low-light radiance measurement, replacing physical standards with objective physical effects reduces the progressively accumulated errors introduced by the standard transfer chain, thus improving the accuracy of low-light radiometric measurements. Absolute calibration of the detector responsivity through spontaneous parametric downconversion effects enables absolute radiometric observations without relying on external references.

[0004] Currently, the two main post-launch calibration techniques—on-orbit site calibration and satellite calibration—require the establishment of high-precision primary standards and a standard transfer chain to ensure that all optical radiation detectors can be traced back to a common benchmark. This limits the effective improvement of detector accuracy. Primary standards are generally established and maintained only by national standards and metrology departments to ensure their accuracy, stability, and authority. However, the actual application fields, operating platforms, and usage conditions of photoelectric detectors vary greatly, necessitating the design and establishment of different transfer chains. This increases calibration time and costs, and inevitably causes accuracy to decrease progressively with each transfer link. Furthermore, the inherent uncertainties of each level of standard are also transferred step by step, ultimately accumulating on the user's detector. If spectral calibration is required, the spectral transmittance of the spectrometer (monochromator, filter, etc.) within its transmission band must be precisely measured, which remains a significant factor limiting accuracy improvement.

[0005] The main advantages of adopting the correlated photon spontaneous parametric downconversion working mode are: (1) The correlated photon source has technical characteristics such as temporal and spatial correlation, natural wide spectrum and reproducible absolute values, and has sufficiently high absolute accuracy; (2) The integrated design of self-calibration and radiation observation allows for real-time monitoring and correction of changes in response characteristics, maintaining long-term stability of response characteristics and improving the traceability and accuracy of observation data. Key technologies to be addressed include the preparation and value transfer of correlated photon sources, suppression of pump stray light, high-precision and high-efficiency coupling of correlated photons, ultraviolet radiation resistance and packaging hardening processes for space single-photon detectors, and the integrated design of self-calibration and radiation observation. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a self-calibrating micro-radiance meter based on 355nm pumping and a measurement method thereof, with a radiance measurement range of 1×10⁻⁶. -9 W / (cm 2 ·sr·nm)~1×10 -6 W / (cm 2 The observation process (·sr·nm) includes self-calibration and radiation observation. In self-calibration mode, the multiplexed optical path module periodically imports spontaneous parametric downconversion correlated photons, and the photon counting and coincidence detection modules calibrate the absolute quantum efficiency of the three channels. In radiation observation mode, the multiplexed optical path module imports the radiation from the low-light target, and simultaneously acquires the absolute spectral radiance of the observed target in the 460nm–1550nm band. The observation results are then corrected using calibration coefficients obtained from the self-calibration mode.

[0007] This invention starts from the basic principle of calibrating the quantum efficiency of single-photon detectors based on the correlation photon method of spontaneous parametric downconversion, and realizes high-precision observation of the spectral radiance of low light in the visible to near-infrared bands. It solves the scientific problem of traceability of measurement values ​​of low light observation instruments on space platforms and plays an important role in climate monitoring, low light radiation metrology, and single-photon source radiance measurement.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A self-calibrating micro-radiance meter based on 355nm pump includes a correlated photon generation module, a self-calibration and radiation observation multiplexing module, a photon counting and coincidence counting measurement module, and a signal acquisition and processing module;

[0010] The correlated photon generation module includes a 355nm pump laser, a Glan Taylor prism, a half-wave plate, a converging lens, and a BBO crystal. The laser pumps the nonlinear crystal to generate phase-matched correlated photons in the 460nm to 1550nm wavelength range.

[0011] The self-calibration and radiation observation multiplexing module includes a scanning switching mirror driven by a motor, an off-axis parabolic mirror, a figure-eight filter module, and a dichroic mirror. Correlated photons or faint light are reflected by the mode switching mirror and collimated by the off-axis parabolic mirror before entering the figure-eight filter module. After being reflected and transmitted by two dichroic mirrors, light in the 460nm-685nm, 737nm-910nm, and 1550nm wavelength bands enters the three converging channels.

[0012] The photon counting and coincidence counting measurement module includes a first beam-shrinking lens group, a second beam-shrinking lens group, a first converging lens group, a second converging lens group, a third converging lens group, a first photon counting detector, a second photon counting detector, a third photon counting detector, and a coincidence measuring instrument. The first and second beam-shrinking lens groups are composed of two lenses to further compress related photons or micro-light spots. The first, second, and third converging lens groups couple the light beam into the photosensitive surfaces of the first, second, and third photon counting detectors, respectively. The first, second, and third photon counting detectors count the photons of the signal light and the idle light, respectively. The coincidence measuring instrument records the related photon events when the signal light and the idle light arrive simultaneously.

[0013] The signal acquisition and processing module includes a data acquisition unit and a host computer measurement software, which completes high-speed acquisition and storage of count values ​​for each channel, as well as timing control of the system measurement process. The host computer measurement software automatically controls and processes the various physical quantities obtained in the self-calibration mode and radiation observation mode.

[0014] This invention also provides a measurement method for a self-calibrating micro-radiance meter based on 355nm pump, comprising the following steps:

[0015] Step (1) Turn on the power control box to preheat the 355nm pump laser, half-wave plate, crystal displacement stage, scanning switching mirror, first filter wheel, second filter wheel, first photon counting detector, second photon counting detector, third photon counting detector, coincidence measuring instrument, data acquisition unit, and host computer for 30 minutes.

[0016] Step (2) The 355nm pump laser is incident into the BBO crystal after passing through a Glan Taylor prism, a half-wave plate, and a converging lens. The motor-controlled scanning switching mirror is rotated into the relevant photon calibration optical path.

[0017] Step (3): After the relevant photon source is collimated by reflection from the off-axis parabolic mirror, it passes through the figure-eight filter module and the first dichroic mirror. The reflected light from the common optical path is then converged by the first beam-shrinking lens group, the first bandpass filter, and the first converging lens group before being received by the first photon counting detector. The transmitted light from the common optical path passes through the second dichroic mirror, and the reflected light is then converged by the second beam-shrinking lens group, the second bandpass filter, and the second converging lens group before being received by the second photon counting detector. The transmitted light is then converged by the third converging lens group before being received by the third photon counting detector.

[0018] Step (4) Measure the photon number rate of paired correlated photons and the coincidence measurement photon number rate using a coincidence measurement instrument, a data acquisition unit, and a host computer, respectively, to obtain the quantum efficiency and the photon number rate of the correlated photon spectrum of the shared channel for self-calibration and radiation observation;

[0019] Step (5) Rotate the motor-controlled scanning switching mirror into the observation optical path, and use the micro-light integrating sphere to conduct radiation observation. The propagation direction of the optical path is consistent with the propagation direction of the relevant photons. The micro-light radiance data is obtained through the measurement software of the host computer.

[0020] The beneficial effects of this invention are:

[0021] This invention establishes a self-calibrating low-light radiance meter based on spontaneous parametric downconversion correlated photons. It periodically and accurately calibrates the radiation observation optical path, enabling precise measurement of radiance in the 460nm–1550nm band of low-light instruments. This fundamentally solves the limitations imposed by errors in the transmission of radiation reference values ​​and the impact of optical and electronic decay in the observation optical path on the accuracy of low-light radiance measurements. Existing visible-near-infrared payloads, whether calibrated in the laboratory before launch or on-board after launch, have an absolute accuracy of approximately 3%–7%, with very limited potential for further improvement, making it difficult to meet the increasing calibration accuracy requirements of climate observation. Correlated photon-based calibration eliminates the need to trace high-precision primary standards and lengthy standard transfer chains in the laboratory. By utilizing correlated photons generated during the parametric downconversion process, a calibration source with temporal, spatial, and polarization correlations can be obtained, leading to higher calibration accuracy. Attached Figure Description

[0022] Figure 1 A traceability diagram of self-calibrated micro-radiance measurement values;

[0023] Figure 2 This is a schematic diagram of the principle of the self-calibrating micro-radiance meter based on 355nm pump of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0025] like Figure 1 As shown, the transmission link of a self-calibrating low-light radiance meter based on 355nm pump according to the present invention includes four parts: a correlated photon standard source, a self-calibrating low-light radiance meter, a low-light integrating sphere, and a low-light instrument. The transmission process is as follows: after the correlated photon standard source achieves correlated photon self-calibration through the self-calibrating low-light transmission radiometer, the radiometric observation of the low-light integrating sphere source is performed by switching modes, and finally applied to the low-light instrument, thereby obtaining the quantum efficiency of the shared channel for self-calibration and radiometric observation, the radiance of the low-light source, and the calibration coefficient of the low-light instrument in sequence.

[0026] like Figure 2 As shown, a self-calibrating micro-radiance meter based on 355nm pump according to the present invention includes a correlated photon generation module, a self-calibration and radiation observation multiplexing module, a photon counting and coincidence counting measurement module, and a signal acquisition and processing module.

[0027] The correlated photon generation module mainly consists of a 355nm pump laser 1, a Glan Taylor prism 2, a half-wave plate 3, a converging lens 4, a BBO crystal 5, and a crystal displacement stage 6. Based on the second-order nonlinear effect of nonlinear optics and the type I phase-matching condition of crystals, phase-matched correlated photons in the 460nm to 1550nm wavelength range are generated by pumping the nonlinear crystal with the laser. The correlated photons have strict correlations in terms of photon number rate, emission direction, time, frequency, and polarization. Determining one photon allows the prediction of the existence of its corresponding other photon.

[0028] The self-calibration and radiation observation multiplexing module mainly consists of a mode-switching reflector 7 driven by a motor, a low-light integrating sphere light source 8, an off-axis parabolic reflector 9, a figure-eight filter module 10, a first dichroic mirror 11, and a second dichroic mirror 16. Correlated photons (or low-light sources) are reflected by the mode-switching reflector and collimated by the off-axis parabolic reflector before entering the figure-eight filter module 10. They are then reflected and transmitted through the first dichroic mirror 11 and the second dichroic mirror 16, forming light in the 460nm–685nm, 737nm–910nm, and 1550nm wavelength bands, which then enter the three converging channels.

[0029] The photon counting and coincidence counting measurement module mainly consists of a first beam-shrinking lens group 12, a second beam-shrinking lens group 17, a first filter wheel 13, a second filter wheel 18, a first converging lens group 14, a second converging lens group 19, a third converging lens group 21, a first photon counting detector 15 (Si single-photon detector), a second photon counting detector 20 (Si single-photon detector), a third photon counting detector 22 (InGaAs single-photon detector), and a coincidence measuring instrument 23. The first beam-shrinking lens group 12 and the second beam-shrinking lens group 17 each consist of two lenses to achieve correlation of light. Further compression of the light beam or micro-light spot, the first filter wheel 13 and the second filter wheel 18 achieve light filtering. The first converging lens group 14, the second converging lens group 19 and the third converging lens group 21 couple the light beam into the photosensitive surfaces of the first photon counting detector 15, the second photon counting detector 20 and the third photon counting detector 22 respectively. The first photon counting detector 15, the second photon counting detector 20 and the third photon counting detector 22 count the photons of the signal light and the idle light respectively. The coincidence measuring instrument 23 records the relevant photon events of the simultaneous arrival of the signal light and the idle light.

[0030] The signal acquisition and processing module mainly consists of a data acquisition unit 24 and a measurement software of a host computer 25. It completes the high-speed acquisition and storage of count values ​​of each channel, as well as the timing control of the system measurement process. The measurement software of the host computer 25 performs automated control and processing of various physical quantities obtained in self-calibration mode and radiation observation mode.

[0031] The measurement method of a self-calibrating micro-radiance meter based on 355nm pump according to the present invention includes the following steps:

[0032] Step (1) Turn on the power control box to preheat the 355nm pump laser 1, half-wave plate 3, crystal displacement stage 6, scanning and switching mirror 7, first filter wheel 13, second filter wheel 18, first photon counting detector 15, second photon counting detector 20, third photon counting detector 22, coincidence measuring instrument 23, data acquisition device 24, and host computer 25 for 30 minutes;

[0033] Step (2) The 355nm pump laser 1 is incident into the BBO crystal 5 through the Glan Taylor prism 2, half-wave plate 3, and converging lens 4. The motor-controlled scanning switching mirror 7 is rotated into the relevant photon calibration optical path.

[0034] Step (3): After the relevant photon source is collimated by reflection from the off-axis parabolic mirror, it passes through the figure-eight filter module 10 and the first dichroic mirror 11. The reflected light from the common optical path is converged by the first beam shrinking mirror group 12, the first filter wheel 13, and the first converging lens group 14 and then received by the first photon counting detector 15. The transmitted light from the common optical path passes through the second dichroic mirror 16. The reflected light is converged by the second beam shrinking mirror group 17, the second filter wheel 18, and the second converging lens group 19 and then received by the second photon counting detector 20. The transmitted light is converged by the third converging lens group 21 and then received by the third photon counting detector 22.

[0035] Step (4) Measure the photon number rate of paired correlated photons and the coincidence measurement photon number rate using coincidence measurement instrument 23, data acquisition device 24, and host computer 25 respectively, and obtain the quantum efficiency and the photon number rate of correlated photon spectrum of the shared channel for self-calibration and radiation observation.

[0036] Step (5) Rotate the motor-controlled scanning switching reflector 7 into the observation optical path, and use the micro-light integrating sphere light source 8 to perform radiation observation. The propagation direction of the optical path is consistent with the propagation direction of the relevant photons. The micro-light radiance data is obtained through the built-in software of the host computer 25.

[0037] The figure-eight filter module 10 includes two dichroic mirrors placed at a 45° angle, with a narrow-band interference filter placed in the middle to filter out the remaining pump stray light, while transmitting correlated photons and low-light radiation light with maximum efficiency.

[0038] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A self-calibrating micro-radiance meter based on 355nm pump, characterized in that: This includes a related photon generation module, a self-calibration and radiation observation multiplexing module, a photon counting and coincidence counting measurement module, and a signal acquisition and processing module; The correlated photon generation module includes a 355nm pump laser, a Glan Taylor prism, a half-wave plate, a converging lens, and a BBO crystal. The laser pumps four nonlinear crystals to generate phase-matched correlated photons in the 460nm to 1550nm wavelength range. The self-calibration and radiation observation multiplexing module includes a scanning switching mirror driven by a motor, an off-axis parabolic mirror, a figure-eight filter module, and a dichroic mirror. Correlated photons or faint light are reflected by the scanning switching mirror and collimated by the off-axis parabolic mirror before entering the figure-eight filter module. After being reflected and transmitted by two dichroic mirrors, light in the 460nm~685nm, 737nm~910nm, and 1550nm wavelength bands enters three converging channels. The reflected light from the first dichroic mirror (460nm~685nm) enters the first photon counting detector after passing through the first beam-shrinking lens group and the first converging lens group. The transmitted light is split into reflected light of 737nm~910nm after entering the second dichroic mirror. The reflected light then enters the second photon counting detector through the second beam shrinking mirror group and the second converging lens group. The directly transmitted 1550nm band light enters the third photon counting detector through the third converging lens group. The photon counting and coincidence counting measurement module includes a first beam-shrinking lens group, a second beam-shrinking lens group, a first converging lens group, a second converging lens group, a third converging lens group, a first photon counting detector, a second photon counting detector, a third photon counting detector, and a coincidence measuring instrument. The first and second beam-shrinking lens groups each consist of two lenses to further compress related photons or micro-light spots. The first, second, and third converging lens groups couple the light beam into the photosensitive surfaces of the first, second, and third photon counting detectors, respectively. The first, second, and third photon counting detectors detect signal light and idle light photons, respectively. The coincidence measuring instrument records related photon events where the signal light and idle light arrive simultaneously. The signal acquisition and processing module includes a data acquisition unit and a host computer measurement software, which completes high-speed acquisition and storage of count values ​​for each channel, as well as timing control of the system measurement process. The host computer measurement software automatically controls and processes the various physical quantities obtained in the self-calibration mode and radiation observation mode.

2. The measurement method of a self-calibrating micro-radiance meter based on 355nm pump according to claim 1, characterized in that, Includes the following steps: Step (1) Turn on the power control box to preheat the 355nm pump laser, half-wave plate, crystal displacement stage, scanning switching mirror, first filter wheel, second filter wheel, first photon counting detector, second photon counting detector, third photon counting detector, coincidence measuring instrument, data acquisition device, and host computer for 30 minutes. Step (2) The 355nm pump laser is incident into the BBO crystal after passing through a Glan Taylor prism, a half-wave plate, and a converging lens. The motor-controlled scanning switching mirror is rotated into the relevant photon calibration optical path. Step (3): After the relevant photon source is collimated by reflection from the off-axis parabolic mirror, it passes through the figure-eight filter module and the first dichroic mirror. The reflected light from the common optical path is then converged by the first beam-shrinking mirror group, the first filter wheel, and the first converging lens group before being received by the first photon counting detector. The transmitted light from the common optical path passes through the second dichroic mirror, and the reflected light is then converged by the second beam-shrinking mirror group, the second filter wheel, and the second converging lens group before being received by the second photon counting detector. The transmitted light is then converged by the third converging lens group before being received by the third photon counting detector. Step (4) Measure the photon number rate of paired correlated photons and the coincidence measurement photon number rate using a coincidence measurement instrument, a data acquisition unit, and a host computer, respectively, to obtain the quantum efficiency and the photon number rate of the correlated photon spectrum of the shared channel for self-calibration and radiation observation; Step (5) Rotate the motor-controlled scanning switching mirror into the observation optical path, and use the micro-light integrating sphere light source to conduct radiation observation. The propagation direction of the optical path is consistent with the propagation direction of the relevant photons. The micro-light radiance data is obtained through the measurement software of the host computer.

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