A method for calibrating the radiated power of a cryogenic blackbody source

Abstract

The application discloses a kind of low-temperature blackbody source radiation power calibration methods, comprising the following steps: building low-temperature test system, the radiation power of low-temperature blackbody source is calibrated;Change the bath temperature of superconducting dynamic inductance detector, test the response curve of superconducting dynamic inductance detector under different bath temperature, and extract response amplitude;The number of quasi-particles corresponding to the bath temperature of superconducting dynamic inductance detector is calculated;Response amplitude and quasi-particle number are fitted to obtain the function of quasi-particle number of superconducting dynamic inductance detector about response amplitude;The bath temperature of detector is reduced to below 100mK, the temperature of low-temperature blackbody source is reduced to below 4K, change the temperature of low-temperature blackbody source, test the curve of superconducting dynamic inductance detector under different blackbody source temperature, and extract amplitude;The corresponding quasi-particle number is calculated;The radiation power of low-temperature blackbody source is calculated from quasi-particle number;The radiation efficiency of low-temperature blackbody source is calculated.The application can solve the problem that blackbody source terahertz radiation power cannot be calibrated at extremely low temperature.

Description

Technical Field

[0001] This invention relates to the field of terahertz detection technology, and in particular to a method for calibrating the radiation power of a low-temperature blackbody source. Background Technology

[0002] In the electromagnetic spectrum, the terahertz band (frequency range of 0.1 THz to 10 THz) lies between the microwave and infrared bands. Due to its unique physical characteristics, it has broad application prospects in fields such as national defense and security, and astronomical detection. However, ultra-high sensitivity terahertz detectors typically need to operate in extremely low-temperature environments, which places stringent requirements on their calibration techniques.

[0003] In existing technologies, blackbody sources, as common terahertz radiation sources, can be used as calibration benchmarks for cryogenic terahertz detectors. Blackbody sources can emit broadband radiation at specific temperatures, thus providing calibration signals for detectors. However, when operating temperatures drop below 77K, there is still a lack of effective experimental methods to directly measure and calibrate the power of blackbody sources under cryogenic conditions. Existing calibration methods mainly rely on theoretical calculations, which have significant limitations because the deviation between theoretical calculations and actual radiation power is difficult to accurately predict. Furthermore, uncalibrated cryogenic blackbody sources cannot be used to accurately characterize terahertz detectors, while uncalibrated terahertz detectors cannot be used to calibrate cryogenic blackbody sources. This interdependence hinders the development of ultra-high sensitivity cryogenic terahertz detectors. There is an urgent need for a simple and easy-to-use experimental method to measure and calibrate the radiation power of blackbody sources under cryogenic conditions. Summary of the Invention

[0004] Purpose of the invention: This invention provides a calibration method for the radiation power of a low-temperature blackbody source, which can solve the problem of the inability to calibrate the terahertz radiation power of a blackbody source at extremely low temperatures.

[0005] Technical solution: The low-temperature blackbody source radiation power calibration method of the present invention includes the following steps:

[0006] Step 1: Set up a low-temperature testing system;

[0007] Step 2: Lower the blackbody source temperature to below 4K, change the detector bath temperature, and test the superconducting dynamic inductance detector S under different detector bath temperatures. 21 The curve is obtained, and the response amplitude is extracted.

[0008] Step 3: Calculate the number of quasiparticles at the corresponding detector bath temperature;

[0009] Step 4: Fit the response amplitude obtained in Step 2 with the quasi-particle number obtained in Step 3 to obtain the function of the quasi-particle number of the superconducting dynamic inductive detector with respect to the response amplitude;

[0010] Step 5: Lower the detector bath temperature to below 100 mK, change the blackbody source temperature, and test the Sk of the superconducting dynamic inductor detector at different blackbody source temperatures. 21 The curve is obtained, and its amplitude is extracted.

[0011] Step 6: Substitute the amplitude obtained in Step 5 into Step 4 to calculate the corresponding number of quasi-particles.

[0012] Step 7: Calculate the radiation power radiated from the low-temperature blackbody source to the detector based on the quasi-particle number obtained in Step 6.

[0013] Step 8: Calculate the radiation efficiency of the low-temperature blackbody source.

[0014] Furthermore, in step 1, the constructed test system includes: a low-temperature blackbody source, a terahertz filter, and a superconducting dynamic inductance detector; the low-temperature blackbody source is fixedly mounted on the 4K cold plate of the refrigerator, and the detector is fixed on the cold plate of the mixing chamber of the refrigerator; the low-temperature blackbody source is both the radiation source and the object to be calibrated, the terahertz filter is used to filter the electromagnetic waves radiated by the low-temperature blackbody source to obtain a narrower frequency band of electromagnetic waves, which is convenient for calculation; the superconducting dynamic inductance detector is used to detect the radiation of the low-temperature blackbody source.

[0015] Furthermore, in step 2, the blackbody source temperature should not exceed 4K, and the detector bath temperature should be gradually increased from the lowest temperature until the detector has a significant response.

[0016] Furthermore, in step 3, the calculation of the number of quasi-particles at the corresponding detector bath temperature is specifically as follows:

[0017]

[0018] N0 is the electron single-spin state density at the Fermi level of the superconductor in the superconducting dynamic inductance detector absorber, V is the volume of the superconducting dynamic inductance detector absorber, and k is the electron single-spin state density at the Fermi level. B It is the Boltzmann constant, T bath Δ0 is the detector bath temperature, and Δ0 is the superconductor band gap of the superconducting dynamic inductive detector absorber.

[0019] Furthermore, in step 5, the ambient temperature should not exceed 1 / 10 of the superconducting critical temperature of the absorber portion of the superconducting dynamic inductance detector, and the blackbody source temperature should be gradually increased from the lowest until the detector has a significant response.

[0020] Furthermore, in step 7, the calculation of the low-temperature blackbody source radiation power is specifically as follows:

[0021] N qp =η pb η opt Pτ qp Δ0

[0022] N qpThe number of quasi-particles, η, is calculated in step 6. pb The Cooper pair splitting efficiency of the absorber section of the superconducting dynamic inductor detector, η opt P is the optical efficiency, and P is the radiation power of the low-temperature blackbody source.

[0023] Furthermore, in step 8, the radiation efficiency of the low-temperature blackbody source is calculated as follows:

[0024]

[0025] P is the radiated power from the low-temperature blackbody source to the detector calculated in step 7, ∈ is the radiation efficiency of the low-temperature blackbody source, Ω is the solid angle of the superconducting dynamic inductor detector relative to the low-temperature blackbody source, A is the radiation window area of ​​the low-temperature blackbody source, and ν l ν is the lower limit of frequency integration. h Here, T is the upper limit of the frequency integral, T is the transmittance of the filter bank, and I is the radiative exitance of the low-temperature blackbody source.

[0026] Furthermore, in step 8, the radiation power of the low-temperature blackbody source conforms to Planck's blackbody radiation law. Multiplying the radiation efficiency by the ideal blackbody radiation power gives the actual blackbody source radiation power, thereby achieving the calibration of the low-temperature blackbody source radiation power.

[0027] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: It can directly calibrate the radiation power of a low-temperature blackbody source under extremely low temperature conditions, without the need for testing at room temperature and extending to low temperature, thus reducing the complexity of operation; It can directly utilize the low-temperature terahertz detector characterization system to achieve calibration, without the need to build an additional test system; It can achieve radiation calibration at extremely low power, without the need to calibrate the detector, thus avoiding expensive equipment and testing costs. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the test system structure of the present invention.

[0029] Figure 2 This is a schematic diagram of the method flow of the present invention.

[0030] Figure 3 The graph shows the calibration and fitting data of the low-temperature blackbody source in this invention.

[0031] Among them, 1. 4K cold plate; 2. distillation cold plate; 3. 300mK cold plate; 4. mixing chamber cold plate; 5. low temperature blackbody source; 6. terahertz filter; 7. superconducting dynamic inductive detector. Detailed Implementation

[0032] like Figure 2 As shown, a method for calibrating the radiation power of a low-temperature blackbody source includes the following steps:

[0033] Step 1, press Figure 1 The test system shown is a composite of a cryogenic blackbody source, a terahertz filter, and a superconducting dynamic inductance detector. The cryogenic blackbody source is fixedly mounted on a 4K cold plate of the refrigerator, and the detector is fixed on a cold plate in the mixing chamber of the refrigerator. The cryogenic blackbody source serves as both the radiation source and the calibration target. The terahertz filter is used to filter the electromagnetic waves radiated by the cryogenic blackbody source to obtain a narrower frequency band. The superconducting dynamic inductance detector is used to detect the radiation from the cryogenic blackbody source. The center frequency of the filter in the diagram is 1.6 THz, and the superconducting dynamic inductance detector is located 315 mm from the cryogenic blackbody source with a solid angle of 2.3 × 10⁻⁶. -7 sr;

[0034] Step 2: Lower the temperature of the low-temperature blackbody source to 4K, change the ambient temperature range to 60mK-120mK, test the curves of the superconducting dynamic inductor detector under different ambient temperatures, and extract the amplitude.

[0035] Step 3: According to the formula Calculate the number of quasi-particles at the corresponding ambient temperature; N0 is the electron single-spin state density at the Fermi level of the superconductor inductor of the superconducting dynamic inductor detector absorber, V is the volume of the superconducting dynamic inductor detector absorber, and k is the electron spin density at the Fermi level of the superconducting dynamic inductor detector absorber. B It is the Boltzmann constant, T bath Δ0 is the detector bath temperature, and Δ0 is the superconductor band gap of the superconducting dynamic inductive detector absorber.

[0036] Step 4: Interpolate the response amplitude obtained in Step 2 with the quasi-particle number obtained in Step 3 to obtain the function of the quasi-particle number of the superconducting dynamic inductive detector with respect to the response amplitude;

[0037] Step 5: Lower the ambient temperature to 60mK, change the temperature range of the low-temperature blackbody source to 4K-30K, test the curves of the superconducting dynamic inductor detector at different low-temperature blackbody source temperatures, and extract the amplitude.

[0038] Step 6: Substitute the amplitude obtained in Step 5 into Step 4 to calculate the corresponding number of quasi-particles;

[0039] Step 7: According to formula N qp =η pb Pτ qp Δ, the radiation power of the low-temperature blackbody source is calculated from the number of quasi-particles in step 6, such as... Figure 3 As shown in the figure, the test data represents the radiation power received by the detector from the low-temperature blackbody source; N qp The number of quasi-particles, η, is calculated in step 6. pb It is the Cooper pair splitting efficiency of the superconducting dynamic inductance detector absorber, η opt P is the optical efficiency, and P is the radiation power of the low-temperature blackbody source.

[0040] Step 8: According to the formula Calculate the radiation efficiency of the low-temperature blackbody source. Figure 3 The value is the radiation power of the low-temperature blackbody source received by the detector. The fitting result is the result of Planck blackbody radiation fitting on the radiation power of the low-temperature blackbody source. The fitting yields a radiation efficiency of ∈ = 0.9 for the low-temperature blackbody source, thus achieving calibration of the radiation power of the low-temperature blackbody source.

[0041] This invention enables extremely low-power radiation calibration at extremely low temperatures, eliminating the need for detector calibration and avoiding expensive equipment and testing costs.

Claims

1. A method of calibrating the radiant power of a cryogenic blackbody source, the method comprising: Comprise the following steps: Step 1, build a low-temperature test system; Step 2, change the bath temperature of the probe, test the superconducting dynamic inductance probe S at different bath temperatures of the probe 21 The curve is drawn and the response amplitude is extracted; Step 3, calculate the number of quasi-particles corresponding to the bath temperature of the detector; Specifically: ， is the single-spin electron density of states at the Fermi surface of the superconductor of the superconducting dynamic inductance probe absorber, V is the volume of the superconducting dynamic inductance probe absorber, k B is the Boltzmann constant, T bath is the bath temperature of the probe, Δ0is the superconductor energy gap of the superconducting dynamic inductance probe absorber; Step 4, the response amplitude obtained in step 2 is fitted with the quasi-particle number obtained in step 3 to obtain the function of the quasi-particle number of the superconducting dynamic inductance detector with respect to the response amplitude; Step 5: Lower the detector bath temperature to below 100 mK, change the blackbody source temperature, and test the Sk of the superconducting dynamic inductor detector at different blackbody source temperatures. 21 The curve is obtained, and its amplitude is extracted. Step 6, the amplitude obtained in step 5 is brought into the function of the quasi-particle number of the superconducting dynamic inductance detector with respect to the response amplitude in step 4, and the corresponding quasi-particle number is calculated; Step 7, calculate the radiation power of the low-temperature blackbody source radiated to the detector from the quasi-particle number in step 6; Specifically: ， N qp is the calculated number of quasi-particles in step 6, η pb is the superconducting dynamic inductance detector absorber section Cooper pair unpairing efficiency, η opt is the optical efficiency, P is the low temperature blackbody source radiant power; Step 8, calculate the radiation efficiency of the low-temperature blackbody source.

2. The cryogenic blackbody source radiometric power calibration method of claim 1, wherein, In step 1, the test system includes: a low-temperature blackbody source, a terahertz filter and a superconducting dynamic inductance detector; The low-temperature blackbody source is fixed on the 4K cold plate of the refrigerator, and the detector is fixed on the cold plate of the refrigerator mixing chamber; The low-temperature blackbody source is a radiation source and also an object to be calibrated, the terahertz filter is used to filter the electromagnetic waves radiated by the low-temperature blackbody source to obtain electromagnetic waves with a narrower frequency band, which is convenient for calculation; The superconducting dynamic inductance detector is used to detect the low-temperature blackbody source radiation.

3. The cryogenic blackbody source radiometric power calibration method of claim 1, wherein, In step 2, the blackbody source temperature should not exceed 4K, and the detector residual temperature should be increased from the lowest temperature until the detector has a significant response.

4. The cryogenic blackbody source radiometric power calibration method of claim 1, wherein, In step 5, the detector bath temperature should not exceed 1 / 10 of the superconducting critical temperature of the superconducting dynamic inductance detector absorber, and the temperature should be increased from 4K until the detector has a significant response.

5. The cryogenic blackbody source radiometric power calibration method of claim 1, wherein, In step 8, the radiation efficiency of the low-temperature blackbody source is calculated as follows: ， P is the power calculated in step 7 of the low temperature blackbody source radiation onto the detector, is the low temperature blackbody source radiation efficiency, Ω is the solid angle of the superconducting dynamic inductance detector relative to the low temperature blackbody source, A is the low temperature blackbody source radiation window area, v l is the lower frequency integration limit, v h is the upper frequency integration limit, T is the transmissivity of the filter set, I is the low temperature blackbody source radiance.

6. The cryogenic blackbody source radiometric power calibration method of claim 1, wherein, In step 8, the low-temperature blackbody source radiation power conforms to the Planck blackbody radiation law, and the radiation efficiency is multiplied by the ideal blackbody radiation power to obtain the actual blackbody radiation power, thereby realizing the calibration of the low-temperature blackbody source radiation power.

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