CN100416237C - Method and device for realizing high-precision radiance benchmark based on standard detector - Google Patents

Abstract

The invention relates to a method and device for realizing a novel high-precision radiance reference based on a standard detector in the visible light band. The invention uses a low-temperature radiometer as the primary benchmark for optical radiation flux measurement, adopts a multi-band filter type radiance meter based on an optical trap structure, and realizes the standard transfer from the low-temperature absolute radiometer to the Trap standard detector. The multi-band filter type radiance meter of the present invention has compact structure, high long-term stability, is designed with a precise constant temperature control system, can be used in different ambient temperatures without reducing the measurement accuracy, and is very suitable as a laboratory benchmark for radiance It is very convenient for long-term storage or as a daily work standard. It can greatly reduce the uncertainty of existing radiance benchmarks, and provides a new set of ideas and methods for the establishment of radiometric high-precision measurement benchmarks.

Description

Method and device for realizing high-precision radiance benchmark based on standard detector

technical field

The invention belongs to the technical field of precise measurement of optical radiation in radiometry, and in particular relates to a novel device and method for realizing a high-precision radiance detection reference based on a standard detector.

Background technique

Until now, radiance benchmarks have generally been implemented using a radiation source-based approach. The primary standard using this method is based on the absolute blackbody theory and determined by Planck's law. The working standard in the visible-short-wave infrared band is the radiance standard lamp of various uncertainty levels. According to Planck's black body radiation law, the emission spectral radiance of a black body corresponds to the temperature of the black body at a specific wavelength. The existing radiance benchmark is based on this principle, and the radiance benchmark is established by accurately measuring the temperature of the black body. Therefore, in the process of establishing the primary radiance benchmark based on the high-temperature blackbody (1500K-3200K), the accurate measurement of the temperature of the high-temperature blackbody is the most important uncertain factor. In fact, the measurement of high-temperature black body temperature is technically difficult, the required equipment is complicated, and the accuracy is difficult to improve. Therefore, the absolute accuracy of the existing primary benchmark of radiance itself is not high, and the uncertainty is large, about It is about 1% to 4%; after multi-level standard transmission, it finally reaches the user's working standard, and its absolute accuracy is even worse, with an uncertainty of about 5% to 10%. Due to the low accuracy of the existing radiance working standard itself, the further improvement of the measurement accuracy of various types of spectral radiance meters on the market is limited, and the measurement and measurement level of spectral radiance is currently at a low level, seriously constraining The development needs of those industries that require high accuracy of radiance measurement indicators.

Contents of the invention

The object of the present invention is to invent a new method and device for realizing a high-precision radiance detection benchmark based on a standard detector. The primary standard of the radiation source adopts the device with the highest precision for measuring the optical radiation flux in the world - the low-temperature absolute radiometer, and the transfer standard and working standard of the radiance both adopt the filter-type radiance meter based on the silicon trap detector . The accuracy of this method is much better than the existing method based on radiation sources, and because the standard transfer chain is short, the uncertain factors in the standard transfer process can be greatly reduced.

The present invention invents a set of novel devices for realizing the radiance detection reference—a multi-band optical filter type radiance meter. It adopts the unique design of the light trap structure, small size, light weight, compact structure, easy operation, very suitable for use as a daily radiance transfer standard and working standard.

A novel method for realizing a high-precision radiance benchmark based on a standard detector in the visible light band comprises the following steps: (1), designing a multi-band filter-type radiance meter, which actually consists of It consists of three parts: the cylindrical aperture tube part, the Trap detector part and the circuit acquisition control part, (2), the field diaphragm, the stray light removal diaphragm, and the aperture are installed in the cylindrical aperture tube in sequence. Diaphragm and narrow-band interference filter, and then the diaphragm tube is installed on a box body, and a polyhedral structure Trap skeleton is installed on the side of the box close to the narrow-band interference filter, and the Trap skeleton is close to the diaphragm tube A circular light incident hole is left on the surface, and a silicon photodiode is respectively fixed on each of the remaining three surfaces. These three surfaces are respectively set as the bottom surface, the left side, and the right side. The position relationship is: the plane where the light entrance hole is located is vertical to the bottom surface, the right side is at a 45-degree angle to the plane where the light entrance hole is located, and the right side is perpendicular to the bottom surface, the left side is at a 45-degree angle to the bottom surface, and the left side is at a 45-degree angle to the bottom surface. The side is perpendicular to the plane where the light incident hole is located, and the three silicon photodiodes fixed on the Trap polyhedral skeleton are connected in parallel on the circuit. The photocurrent signal output by the three parallel photodiodes is changed by the pre-amplifier circuit for I-V and Amplified, converted into a voltage signal, and then sent to the A/D conversion and signal processing unit part controlled by the single-chip microcomputer system after being pre-processed by the signal conditioning circuit, (3), the radiance described in (1), (2) The polyhedral structure Trap skeleton in the meter and the op amp circuit at the back end together constitute a Trap detector with an optical trap structure; several wavelengths of lasers are selected in the visible light range, and at each wavelength point, the low temperature absolute radiometer is used to and the HP34970A 6.5-digit digital voltmeter to measure the incident laser radiation flux and the output voltage signal of the Trap detector entering the optical trap structure Trap detector respectively, and establish the input optical radiation flux and The one-to-one correspondence between the output voltages, through internal difference and extrapolation, calculates the absolute spectral responsivity of the Trap detector in the entire visible light band; after the absolute calibration of the above-mentioned cryogenic absolute radiometer, the Trap detector becomes a A light radiation power standard detector; (4), according to the definition of radiation power and radiance, radiation power (radiation flux) φ refers to the radiation energy dQ of a certain space position per unit time dt, has: φ=dQ/dt; The radiance L refers to the radiant flux dΦ on the unit solid angle dΩ and the unit projected area dScosθ leaving, arriving at or passing through a certain surface, there is: L=dφ/dΩ·dS·cosθ; compare the definitions of radiant flux and radiance It can be seen that compared with the radiant flux, there is only one more geometric factor (dΩ·dS·cosθ) in the definition of radiance, and this geometric factor is actually determined by the incident aperture and solid angle ; That is, the measurement of radiance relative to the measurement of radiant flux has only one more accurate determination of the geometric factor determined jointly by the entrance aperture and the solid angle; Aperture and solid angle of the cylindrical diaphragm tube, and after the incident aperture and solid angle are accurately measured, the Trap optical radiation power standard detector can be transformed into a radiance standard detector through strict calculation of the formula; ( 5) When actually measuring a certain Lambertian target, the temperature of the radiance standard detector is controlled by the temperature control system at the temperature when the Trap optical power standard detector is calibrated with respect to the cryogenic radiometer in (3) for absolute power calibration, so far , the radiance standard based on the standard detector is established.

By freely replacing narrow-band interference filters with different central wavelengths, the radiance detection benchmarks with different central wavelengths can be formed.

The device for realizing the high-precision radiance detection reference is characterized in that it includes: a stray light stop, a precision temperature sensor, a field stop, an aperture stop, a narrow-band interference filter, a VFD fluorescent digital display screen, Keypad on the front panel, RS232-C serial interface and Trap detector based on optical trap structure.

The core part of the Trap detector adopts an ingenious optical trap structure. This design structure makes the incident light undergo multiple reflections and absorptions inside the Trap, and almost all of the incident light can be accepted by the detector to complete photoelectric conversion. Moreover, the Trap detector is polarization-insensitive, and the measurement results will not be affected by the different polarization states of the incident light during multiple measurements.

The multi-band filter type radiance meter is designed with a precise constant temperature control system based on semiconductor refrigeration technology. Abandoning the traditional method of temperature control water jacket, using semiconductor cooler Peltier, digital temperature sensor DS18B20. The digital temperature sensor DS18B20 is fixedly installed on the radiometer, and is bonded with thermal silica gel, and the radiometer, temperature sensor and Peltier are bonded with thermally conductive epoxy resin or soldered with low-temperature solder.

The multi-band filter type radiance meter has a friendly man-machine exchange interface and can be set to a remote computer automatic control mode or a local working mode. With power-off non-volatile memory, when set to the automatic measurement state, the radiance meter of the present invention can automatically complete the acquisition and measurement, and the results are stored in the on-chip memory, and can be transferred to the upper PC through the RS232C serial port after the measurement is completed Statistical analysis and processing of later data.

The primary reference of the radiation source of the present invention adopts the device with the highest precision in measuring the optical radiation flux in the world—the low-temperature absolute radiometer. Cryogenic absolute radiometers use the principle of electrical substitution to measure the absolute power of optical radiation. The incident light raises the temperature of the receiving cavity inside the radiometer, and blocks the incident light after reaching thermal equilibrium. The electric power required to generate the same temperature rise by electric heating is equal to the actual incident light power, and the temperature and electric heating power are respectively measured by a germanium resistance thermometer And bridge precision measurement. The inner wall of the cone-shaped receiving cavity inside the radiometer is coated with a high-absorption material, and the incident light is almost completely absorbed after being reflected many times. The cavity is under the double-layer cold shield of liquid nitrogen (77K) and liquid helium (4.2K), which isolates the ambient heat radiation and also makes the light and electric heating process extremely high equivalence. At low temperature, the wires and joints are in a superconducting state, and their ohmic losses can be ignored. The above-mentioned design features of the low temperature radiometer make it very accurate for optical radiation measurement, and the measurement uncertainty can reach 0.01%.

The multi-band filter type radiance meter of the present invention is characterized in that it adopts a unique structural design of an optical trap. This optical trap design structure uses three planar silicon photodiodes. According to the principle of mirror reflection, the reflected light incident on the first silicon photodiode hits the second silicon photodiode, and the reflected light on the second silicon photodiode The light then hits the third silicon photodiode, and the reflected light on the third silicon photodiode returns to the second silicon photodiode through the original path, and the resulting reflection on the second silicon photodiode The light hits the first silicon photodiode. In this way, part of the light lost due to reflection on each silicon photodiode will be received by the next silicon photodiode, and so on. The principle is as follows:

For a single silicon photodiode, there are:

I _f =η(1-ρ)(λe/hc)·P

Therefore, the optical trap structure has:

I _f =[η ₁ (1-ρ ₁ )+η ₂ ρ ₂ (1-ρ ₁ )+η ₃ ρ ₁ ρ ₂ (1-ρ ₃ )+η ₂ ρ ₁ ρ ₂ ρ ₃

(1-ρ ₂ )+η ₁ ρ ₁ ρ ₂ ρ ₂ ρ ₃ (1-ρ ₁ )]·(λe/h c)·P

In the formula: _If is the photogenerated current; P is the incident light power; λ is the incident light wavelength; h is the Plank constant; _c is the speed of light _{in vacuum} ; The internal quantum efficiency of the photodiode;

ρ ₁ and ρ ₂ are the reflectivity of photodiodes 1# and 2# when the incident angle is 45°, and ρ ₃ is the reflectivity of photodiode 3# when the incident angle is normal.

In fact, since photodiodes of the same type are used, there are: η ₁ =η ₂ =η ₃ and ρ ₁ =ρ ₂ =ρ ₃ , then the above formula can be simplified as:

I _f =η(1-ρ ₅ )(λe/hc)·P

This creates a light trap with greatly reduced surface reflectivity compared to monolithic silicon photodiodes, and the three-piece structure also greatly reduces the polarization sensitivity of a single device to radiation, i.e. minimizes The surface reflectivity of the silicon photodiode detection device is affected by the different incident angles on the measurement and the uncertainty of the radiation measurement caused by the polarization sensitivity, which can greatly improve the measurement accuracy.

In the filter-type radiance meter of the present invention, the light-splitting element adopts a narrow-band interference filter, and the assembly structure adopts a design structure that is convenient for replacing filters with different central wavelengths. For the different required bands, it can be realized by replacing the filters with different center wavelengths.

Because the key parameters such as the central wavelength and transmittance of the optical filter will drift with the change of the ambient temperature, the measurement accuracy of the radiance meter will be reduced. Therefore, the filter-type radiance meter of the present invention is designed with a complete intelligent Temperature monitoring and control system, which can realize precise constant temperature control of the filter.

The optical filter type radiance meter of the present invention is designed with a friendly human-computer interaction interface and an RS232C computer serial interface. The small keyboard on the front panel is used to input relevant setting parameters; the high-brightness vacuum fluorescent display VFD is used to display operation prompt information, working status information and measurement results in real time. The radiometer can be set to local working mode or computer remote control mode.

Description of drawings

Fig. 1 is a schematic diagram of the transmission chain of the radiance standard of the present invention.

Fig. 2 is a schematic diagram of the optical trap structure of the present invention.

Fig. 3 is a structural schematic diagram of the multi-band filter type radiance meter of the present invention.

Figure 4 is a diagram of the temperature control system of the multi-band filter type radiance meter.

Detailed ways

See Figure 1, Figure 2, Figure 3, Figure 4.

The method for realizing the novel high-precision radiance standard based on the standard detector of the present invention is shown in FIG. 1 . The cryogenic radiometer is currently the device with the highest absolute accuracy in measuring optical radiation power in the world. In the method of the present invention, it is used as the primary benchmark of optical radiation flux measurement. Because the cryogenic absolute radiometer is expensive, bulky, and complicated to operate, it is not convenient to use it as a daily work standard. Therefore, the present invention has designed and developed a Trap detector based on an optical trap structure, which has superior performance and is small in size. It is easy to use, has good long-term stability, and is very suitable for use as a transfer standard. In the visible light band, lasers of different wavelengths are used to perform absolute calibration on the response of the Trap detector relative to the cryogenic absolute radiometer, and then based on the spectral response curve of the Trap detector, it can be calculated by extrapolation and interpolation algorithms Absolute spectral responsivity of Trap detectors over the entire continuum of visible light range. In this way, the Trap detector becomes a luminous flux standard detector that can be used for measuring the absolute quantity of luminous radiation flux, completing the standard transfer from the low temperature absolute radiometer shown in Figure 1 to the Trap standard detector.

The multi-band filter type radiance meter of the present invention is shown in FIG. 3 . Among them, 1. Stray light removal diaphragm, 2. Precision temperature sensor, 3. Field diaphragm, 4. Aperture diaphragm, 5. Narrow band interference filter, 6. VFD fluorescent digital display screen, 7. Front panel keys , 8. RS232-C serial interface, 9. Trap detector with optical trap structure.

According to the definition, radiance L refers to the radiant flux dΩ leaving, reaching or passing through a certain surface unit solid angle dΩ and unit projected area dS cosθ, which is:

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; d\&Phi;</span>}}{\mathrm{<span\; class="notranslate">\; d\&Omega;</span>}\mathrm{<span\; class="notranslate">\; wxya</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}$

According to the above definition, to accurately measure the radiance reaching the entrance pupil of the Trap detector, it is necessary to know the radiant flux dΦ entering the entrance pupil of the Trap detector, the solid angle dΩ and the projected area dS cosθ. Since the Trap detector has been calibrated for absolute radiation relative to the cryogenic absolute radiometer, its absolute spectral responsivity is known. After measuring the output voltage signal of the Trap detector, it can be calculated according to its absolute spectral responsivity. The radiation flux dΦ at the entrance pupil of the detector. The solid angle dΩ and the projected area dS cosθ in this design are finally jointly determined by geometric factors such as the field diaphragm, the aperture diaphragm, and the distance between the two. After the phalanx and the distance between the two, the solid angle dΩ and the projected area dS cosθ can be calculated. In this way, after knowing dΦ, dΩ and dS cosθ, the radiance value at the entrance pupil of the Trap detector can be accurately calculated according to the above definition of radiance.

The above formula gives the definition of radiance in the whole band without any constraints on the band, but in practical applications, it is often necessary to know the spectral radiance of a specific wavelength within a certain bandwidth, so it is also necessary to consider the wavelength and bandwidth factors.

In the present invention, a narrow-band interference filter is used as the light-splitting element of the optical system to limit the wavelength position and bandwidth. In this way, after the spectral transmittance and bandwidth of the optical filter are accurately measured, the spectral radiance of a specific wavelength can be calculated by combining the radiance values obtained above. The multi-band radiance meter becomes a radiance detection benchmark that can be used for accurate measurement of spectral radiance.

So far, the standard transfer process from the Trap standard detector to the multi-band radiance meter shown in Figure 1 has been realized. The essence is to realize the transfer and conversion from the optical radiation flux reference to the spectral radiance reference, and establish a new The radiance detection benchmark based on standard detectors.

The invention adopts the radiance detection standard realized by the multi-band radiance meter, has high absolute precision, and the uncertainty is better than 1%. The performance of the standard is very stable and is convenient for preservation. The structure of the multi-band filter type radiance meter of the present invention is shown in Fig. 3, and consists of three parts: a cylindrical aperture tube part, a Trap detector part and a circuit acquisition control part. A field of view diaphragm 3, a stray light removal diaphragm 1, an aperture diaphragm 4 and a narrow-band interference filter 5 are sequentially installed in the cylindrical diaphragm tube, and then the diaphragm tube is installed on a box, and the box A polyhedral Trap framework 9 is installed on the side close to the narrow-band interference filter, and a circular light entrance hole 14 is left on the surface of the Trap framework close to the diaphragm tube, and each of the remaining three surfaces is respectively Fixed with a silicon photodiode. The plane where the light incident hole 14 is located is perpendicular to the bottom surface 15, the right side 16 is at a 45-degree angle to the plane where the light incident hole 14 is located, and the right side 16 is perpendicular to the bottom surface 15, and the left side 17 is at a 45-degree angle to the bottom surface 15. Angle, the left side 17 is perpendicular to the plane where the light entrance hole 14 is located, and the three silicon photodiodes fixed on the Trap polyhedron skeleton adopt a parallel connection mode on the circuit, and the photocurrent signals output by the three parallel photodiodes are passed through the pre-amplifier. The circuit performs I-V change and amplification, transforms it into a voltage signal, and then sends it to the A/D conversion and signal processing unit controlled by the single-chip microcomputer system after preprocessing by the signal conditioning circuit, and then completes signal collection, radiance absolute value calculation, Storage and real-time display of measurement results and other functions. The multi-band filter-type radiance meter of the present invention is designed with front panel buttons and a VFD high-brightness fluorescent digital display screen for inputting user-set parameters and displaying measurement results in real time. In the local automatic measurement mode, the system can store the measurement results in the power-down non-volatile memory. After the measurement, it can be uploaded to the PC through the RS232C serial port for statistical analysis and processing of the later data.

The multi-band filter type radiance meter of the present invention is equipped with a narrow-band interference filter. Experimental research shows that the performance parameters of the filter will change greatly with the fluctuation of the ambient temperature, which is the key factor affecting the absolute accuracy of the multi-band filter type radiance meter. Considering that when the multi-band filter type radiance meter is used as a daily radiance detection standard in different ambient temperatures, its accuracy should not be affected by the ambient temperature. The present invention designs a precision temperature control system to keep the temperature of the filter constant. Control, so that the temperature of the optical filter is always controlled at the temperature when it is calibrated for absolute response relative to the cryogenic absolute radiometer. The precision temperature control system of the present invention is as shown in Figure 4, comprises: multi-band filter type radiance meter 10, the digital temperature sensor DS18B20 11 that is fixed on the filter type radiance meter, and the filter type radiance meter The semiconductor thermoelectric cooler Peltier 12 connected to the meter, the radiator 13, the intelligent temperature control circuit connected to the output terminal of the digital temperature sensor and the human-machine interface circuit.

Good steel thermal contact must be maintained between the filter-type radiance meter and the DS18B20 temperature sensor and between the filter-type radiance meter and the Peltier in this implementation, so as to achieve an ideal temperature control effect. In the actual connection, thermal silica gel bonding or clamp connection can be used. When the bonding method is used, the radiometer, the temperature sensor and the Peltier can be bonded with thermally conductive epoxy resin or soldered with low-temperature solder; when the fixture is used for connection, the radiometer, the temperature sensor and the Peltier need to be evenly spread. Silicone to reduce the thermal resistance of the contact surface.

The device used for heating or cooling operation in the present invention adopts semiconductor thermoelectric cooler Peltier, which is composed of multiple pairs of thermoelectric coolers based on Peltier effect, which are electrically connected in series and thermally conducted in parallel. Cooling can be changed to heating by changing the polarity of the direct current applied to the device, and the heat absorption or heat release rate is proportional to the magnitude of the applied direct current. Because Peltier can realize both heating and cooling, and is small in size, easy to use, it is especially suitable for temperature control of small heat and precision instruments limited by space.

The method and device for realizing the high-precision radiance detection standard based on the standard detector of the present invention have advantages that cannot be compared with the traditional method based on the radiation source in terms of key performance indicators such as absolute accuracy and long-term stability, and are a new set of Ideas and methods for establishing radiometric benchmarks.

Claims (2)

1. A method for realizing a high-precision radiance reference based on a standard detector, comprising the following steps: (1), designing a multi-band filter type radiance meter, which actually consists of three Part composition: cylindrical diaphragm tube part, Trap detector part and circuit acquisition control part, (2), field diaphragm, stray light removal diaphragm, aperture light are installed sequentially in the cylindrical diaphragm tube Diaphragm and narrow-band interference filter, and then the diaphragm tube is installed on a box body, and a polyhedral Trap frame is installed on the side of the box close to the narrow-band interference filter, and the surface of the Trap frame is close to the diaphragm tube A circular light incident hole is left on the top, and a silicon photodiode is respectively fixed on each of the remaining three surfaces. These three surfaces are respectively set as the bottom surface, the left side, and the right side. The positional relationship is: the plane where the light entrance hole is located is perpendicular to the bottom surface, the right side is at a 45-degree angle to the plane where the light entrance hole is located, and the right side is perpendicular to the bottom surface, the left side is at a 45-degree angle to the bottom surface, and the left side is Vertical to the plane where the light incident hole is located, the three silicon photodiodes fixed on the Trap polyhedral skeleton are connected in parallel on the circuit, and the photocurrent signal output by the three parallel photodiodes is changed and amplified by the pre-amplifier circuit for I-V. It is converted into a voltage signal, and then sent to the A/D conversion and signal processing unit part controlled by the single-chip microcomputer system after being preprocessed by the signal conditioning circuit, (3), in the radiance meter described in (1), (2) The polyhedral structure Trap skeleton and the back-end operational amplifier circuit together constitute a Trap detector with an optical trap structure; several wavelengths of lasers are selected in the visible light range, and at each wavelength point, the cryogenic absolute radiometer and HP34970A are used to The 6.5-digit digital voltmeter respectively measures the incident laser radiation flux and the output voltage signal of the Trap detector entering the optical trap structure Trap detector, and establishes the input optical radiation flux and output of the optical trap structure Trap detector at each wavelength point The one-to-one correspondence between the voltages, through internal difference and extrapolation, calculates the absolute spectral responsivity of the Trap detector in the entire visible light band; after the absolute calibration of the above-mentioned cryogenic absolute radiometer, the Trap detector becomes a light Radiant power standard detector; (4), according to the definition of radiant power and radiant brightness, radiant power or radiant flux φ refers to the radiant energy dQ of a certain space position per unit time dt, has: φ=dQ/dt; radiant brightness L It refers to the radiant flux dΦ on the unit solid angle dΩ and the unit projected area dScosθ leaving, arriving at or passing through a certain surface, which has: $L=\frac{\mathrm{d\&Phi;}}{\mathrm{d\&Omega;}\mathrm{wxya}\cos \mathrm{\&theta;}};$ Comparing the difference between the definition formulas of radiant flux and radiance, it can be seen that, compared with radiant flux, there is only one more geometric factor dΩ·dS·cosθ in the definition formula of radiance, and this geometric factor is actually determined by the entrance aperture It is determined jointly with the solid angle; that is, the measurement of radiance relative to the measurement of radiant flux has only one more accurate determination of the geometric factor determined by the entrance aperture and the solid angle; therefore, the incident light path of the Trap optical power standard detector A cylindrical diaphragm tube that can limit the incident aperture and solid angle is introduced in the front, and after the precise measurement of the incident aperture and solid angle, the Trap light radiation power standard detector can be transformed into a radiation power standard detector through strict calculation by the formula. Luminance standard detector; (5), when measuring a certain Lambertian target, through the temperature control system, the temperature of the radiance standard detector is controlled at the absolute power of the Trap optical power standard detector in (3) relative to the cryogenic radiometer The temperature during calibration, so far, the radiance standard based on the standard detector has been established. 2. The method according to claim 1, characterized in that the radiance detection benchmarks of different central wavelengths can be formed by freely replacing narrowband interference filters with different central wavelengths.

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