RU2696364C1 - Method of measuring absolute spectral sensitivity of ir mpdd - Google Patents

Abstract

FIELD: measurement technology.

SUBSTANCE: invention relates to methods of measuring absolute spectral sensitivity of multielement or matrix infrared photodetectors (IR MPDD). Said technical result is achieved by the fact that N measurements of integral signals of the photosensitive elements (PSE) of the IR MPDD are performed at different stationary temperatures of the black body model (BBM). BBM has small size of radiating platform, its radiation is modulated and K measurements of integral signal at each stationary temperature of BBM are measured. Thus, for each PSE a data array is accumulated, including K⋅N measurements. Then, for each BBM fixed temperature, the mean-square deviation from the average PSE signal value is automatically calculated, which will be equal to the value of the light modulated signal from the BBM radiation. Obtained signal value is automatically substituted into the left part of integral equations, including convolution of Planck function and corresponding photoelectric characteristic: current S_I(λ),volt S_u(λ) sensitivity or quantum efficiency η(λ). By converting integral equations, three systems of linear equations for which unknowns will be spectral components of said characteristics are obtained for each PSE. Solving systems, obtained dependencies S_I(λ), S_u(λ) and η(λ).

EFFECT: method enables one-dimensional determination of absolute spectral sensitivity of all photosensitive elements of the IR MPDD.

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Description

The spectral sensitivity of the infrared system is one of the most important characteristics of photodetectors. It is determined by the characteristics of all its components, optical and optoelectronic, namely: spectral transmission, absorption, reflection and radiation of the materials used, spectral transmission of filters that can be applied, and the spectral sensitivity of the radiation receiver itself.

The measurement of the absolute sensitivity spectra of photodetectors is still, in fact, based on two methods. The first one is based on measuring their signals during sequential exposure to narrow-spectrum radiation generated by an optical monochromator, normalizing signals by measuring the same spectrum with a calibrated photodetector, then recalculating and plotting, for example, a graph of the absolute sensitivity S (λ) versus the irradiation wavelength [1]. The second one is to record the interferogram of the optical signal generated by the Michelson interferometer, followed by its mathematical processing by the Fourier transform method, obtaining the relative photosensitivity spectrum [2], which then must also be calibrated using an exemplary photodetector and then converted to the absolute photosensitivity spectrum.

The first drawback of these methods is their cost, because their implementation requires expensive IR spectrophotometers or Fourier spectrometers. Their other disadvantage is the impossibility of directly measuring the absolute spectral curve of the volt or current sensitivity. The third drawback is the impossibility of measuring even the relative spectral photosensitivity curve on all the photosensitive elements (PSE) of the IR MFP sensor.

For these reasons, an interesting method for measuring the spectral sensitivity of IR devices without the use of expensive spectrophotometers, but only using the Black Body Model (MCT) and the corresponding software in a computer connected to the MCT control unit that controls the operation of the IR MFP [3].

от МФЧЭ с размером по диагонали равным 2⋅d, окруженной холодным экраном с диафрагмой радиуса 2⋅r, отстоящей от плоскости МФЧЭ на расстоянии

включение МЧТ в рабочий режим, установку первой температуры МЧТ, регистрацию первого сигнала каждого ФЧЭ ИК МФПУ, последовательное пошаговое повышение температуры на заданную величину и измерение соответствующего ей сигнала, составление для каждого ФЧЭ системы N линейных уравнений, в правой части которых стоят измеренные сигналы ИК МФПУ, а в левой части - ряды, представляющие собой разложение интегралов, выражающих выходной сигнал ФЧЭ, в ряд Тейлора с N линейными компонентами абсолютной спектральной чувствительности при соответствующих длинах волн с необходимыми коэффициентами, получение численного решения данной системы уравнений для каждого ФЧЭ с определением значений компонент относительной чувствительности.A known method of measuring the absolute spectral sensitivity, including the installation of an extended MRI with a radius of 2⋅R at a distance of not more than

from MFES with a diagonal size of 2⋅d surrounded by a cold screen with a diaphragm of radius 2⋅r spaced apart from the MFES plane at a distance

turning the MCB into operation, setting the first temperature of the MCB, registering the first signal of each PSE IR MFP, sequential stepwise increase in temperature by a predetermined value and measuring the corresponding signal, compiling a system of N linear equations for each PSI, the right part of which contains the measured signals of the IR MPU , and on the left side are the series representing the expansion of the integrals expressing the output signal of the PSE into a Taylor series with N linear components of absolute spectral sensitivity for the corresponding wavelengths with the necessary coefficients, obtaining a numerical solution of this system of equations for each PSE with determining the values of the components of relative sensitivity.

The disadvantage of this method is the presence of stationary irradiation from a large-area MWD, the signal of which, during subsequent calculation, must be isolated from the sum of several stationary signals, including signals caused by radiation from the input window of the MFP, the dark current of the PSE and the multiplexer at zero input signal, which impairs the correctness of the method . The second disadvantage is the lack of accuracy of the method, due to the limitation in the maximum distance from the MCT to the MFCE, associated with the need to cover the radiating platform of the MCHT aperture of the MFCE. Hence, there is a limitation of the maximum temperature and the number of set values of the temperature of the MCT at which the integrated signals of the MFP are measured.

The aim of the present invention is to improve the correctness and accuracy of the measurement of the absolute sensitivity spectra of the PSE IR MFPU, in the form of the dependence of the current, voltage sensitivity or quantum efficiency of the PSE on the wavelength, by eliminating the influence of spurious signals on the measured parameter of the MFCE and limiting the distance from the MCH to MFCE and the maximum temperature of the MRI.

This goal is achieved by the fact that the known method of measuring the absolute spectral sensitivity of an IR MFP, including sequentially setting N stationary values of the temperature of the MRI, recording the integral signal of all PSEs at each stationary temperature value of the MRI, automatically compiling for each PSE three systems of N integral equations corresponding to stationary the values of the temperature of the MCT, the solution of each system of N integral equations with respect to the N values of the spectral characteristics of the PSE p about wavelengths, the construction of the absolute spectral characteristics of the PSE from the calculated components, characterized in that they establish the characteristic size of the radiating area of the MChT smaller than the size of the MPHE, the radiation of the MChT is modulated at a constant frequency, the signal of each PSH is automatically measured at a stationary temperature of the MCT K times, the average signal of each PSE according to the measured signals, calculate the standard deviation of the signals of each PSE from the average value and substitute the obtained value of the mean square deviation to the left side of the integral equation corresponding to a given temperature.

The goal is achieved by the fact that a stationary temperature regime MCHT continued for a time of at least t = K⋅τ _{landline frame,} wherein _{the frame} τ - MFP time frame.

This goal is also achieved by the fact that the signal of each PSE is automatically measured at a stationary temperature of the MCT of at least K = 256 times.

To confirm the achievement of the goal, we consider the work of the IR MFP The registration of the integrated signals of all PSE IR MFPU in automatic mode is carried out at a fixed temperature of the MCT and the signal accumulation time.

The integral signal of each PSE can be represented as the sum of the five main signals.

where V _mcht - modulated light signal from the MChT [1];

V _background - unmodulated light signal generated by the radiation of the surrounding background [4];

V _in - unmodulated signal generated by the radiation of the input window of the MFP [4];

V _{is dark} - non-modulated signal generated by the dark current of the PSE [4];

V ₀ is the unmodulated signal of the MFP multiplexer at zero irradiation [4].

A small radiating area of the MCT is in the field of view of each PSE MFPU. With such dimensions of the site, the radiation of the MChT is easy to modulate with a conventional modulator.

If at each fixed level of irradiation, the integrated PSE signal is recorded K times, its average value and standard deviation from the average signal are calculated, then we automatically obtain the value of the modulated light signal V _mcht . In this case, the error in determining the magnitude of the signal, proportional to 1 / √K, will be the smaller, the greater the number of measurements of each integral signal will be performed, or the greater the value K. The time spent on such a number of measurements in automatic mode will approximately equal to the _frame . It was found that in order to obtain a signal measurement accuracy of several percent, it is necessary to perform at least K = 256 signal measurements at each fixed temperature of the MCT.

In the prototype, this extraction of the useful MFP signal is difficult because it measures the stationary integral signal due to the dark current of the PSE, the radiation of the MST, the radiation of the input window, a light filter, a cold screen and the constant output signal of the MFP multiplexer at zero exposure. For this reason, the true signal will be overestimated, and calculations can lead to a measurement error of approximately (50-80)%.

If we measure the output signals of the IR MFP at N temperatures of the MRI, then we get N values of the output modulated signal of each PSE of the MFP. The time spent on these measurements will be _edited t ≈ N⋅K⋅t _frame + N⋅t _landline. At N = 50, K = 256, t _frame ≤ 5 ms and t _stat = 5 sec, the value of t _ISM will not exceed six minutes (6 minutes). The measured data array will correspond to fifty points on the spectral curve for each PSE. Thus, in the indicated time in the automatic mode, three types of photosensitivity spectra of all PSE MFPUs will be recorded.

This method of measuring the MFP signal will be correct, because only the modulated light signal will be measured, and will be more accurate since only the useful signal due to the MRI will appear in the calculations.

In calculating a PC, only the true value of the irradiation from the MCT will be used, and not its sum with several additional irradiations, which in any case would have to be eliminated, which would introduce a noticeable error in the values of the spectral components of the quantum efficiency, current or volt sensitivity of all PSEs of the MFP. These spectral components were previously generally inaccessible when measuring MPPU on standard spectrophotometers and Fourier spectrometers. On these instruments, it was possible to measure only the relative spectral sensitivity of single test PSEs, and then calibrate them using a certified photodetector to obtain the absolute value of the spectral characteristic. The inventive method allows you to immediately get the absolute spectral sensitivity (current S _I (λ), volt S _u (λ) or quantum efficiency η (λ)) of all PSE MFPU.

When measuring a modulated light signal, in accordance with [1], in the calculations it is necessary to take into account the effective value of the luminous flux Ф _е , which is expressed by the formula

where Ф ₀ is the value of the unmodulated light flux from the MRI, W ,cm ^-2 or photon⋅cm ^-2 ⋅s ^-1 ;

β is the coefficient of the modulation form [1].

The modulated luminous flux incident from the MFT at the PSE will be described by the following expression:

- коэффициент пропускания диафрагмы МЧТ [5] (коэффициент излучения МЧТ [6]);Where

- transmittance of the diaphragm of the MCT [5] (emissivity of the MCT [6]);

To _in (λ) is the transmittance of the input window of the MFP;

To _sf (λ) is the transmittance of the cold filter in the spectral range [λ ₁ , λ ₂ ];

ε is the blackness of the MRI;

- функции Планка, p - Вт⋅см^-2⋅мкм^-1; n - квант⋅см^-2⋅с^-1⋅мкм^-1 [7];

- Planck functions, p - W⋅cm ^-2 ⋅mkm ^-1 ; n - quantum ⋅ cm ^-2 ⋅ s ^-1 ⋅ μm ^-1 [7];

x, y - coordinates in the plane of MFPE, cm;

- расстояние от МЧТ до МФЧЭ, см.

- distance from MChT to MFCHE, see

The modulated output signal V _{sv of} each PSE IR MFP will be described by the following integral equations in which S _I (λ), S _u (λ) and η (λ) participate, which will be automatically recorded in the memory of the control computer:

where τ is the accumulation time of MFPU, s;

A _S is the area of PSE, cm ² ;

q is the electron charge, K electron ^-1 ;

With _n - the value of the accumulation capacity in the cell MFPU, F;

To ₀ is the transfer coefficient of the multiplexer circuit;

S _I (λ) - current sensitivity of the PSE, А⋅W ^-1 ;

S _u (λ) is the volt sensitivity of the PSE, V⋅W ^-1 ;

η (λ) is the quantum efficiency of the PSE, electron-quantum ^-1 .

Заметим, что в выражениях (3), (4), (5) и (6) все параметры, стоящие перед знаком интеграла известны и не зависят от Т_МЧТ и λ. Обозначим их буквой W. В каждой подинтегральной функции содержатся три известных параметра К_во(λ), К_сф(λ) и

значения которых нам известны при любой длине волны облучения, и лишь один неизвестный линейный параметр S_I(λ), S_u(λ) или η(λ). Тогда, если решить систему интегральных уравнений относительно N неизвестных, каждое из которых будет соответствовать значению S_I(λ_i), S_u(λ_i) или η(λ_i), то получим спектральную зависимость токовой, вольтовой чувствительности или квантовой эффективности для каждого ФЧЭ.In the expressions there is a transmittance of the diaphragm of the MCT [5] (emissivity of the MCT [6])

Note that in expressions (3), (4), (5), and (6), all parameters facing the integral sign are known and do not depend on T of the _MRT and λ. Denote them by the letter W. Each subintegral function contains three known parameters K _in (λ), K _sf (λ), and

the values of which are known to us at any irradiation wavelength, and there is only one unknown linear parameter S _I (λ), S _u (λ) or η (λ). Then, if we solve the system of integral equations for N unknowns, each of which will correspond to the value of S _I (λ _i ), S _u (λ _i ) or η (λ _i ), then we obtain the spectral dependence of the current, volt sensitivity, or quantum efficiency for each PSE.

There are many methods for solving such systems. For example, conversion to a system of linear equations, so we will not dwell on them. The solution of the obtained systems of equations will give us the numerical values of the spectral components S _I (λ _i ), S _u (λ _i ) or η (λ _i ), which will allow us to construct the necessary spectral characteristics of the dependences of the current and voltage sensitivity, as well as the quantum efficiency of any PSE matrix on irradiation wavelengths. The method also allows constructing a 2D dependence of the red sensitivity border or maximum sensitivity along the MFES plane.

The method operates as follows: Consider the IR MFP installed on the signal measurement bench. The stand should include the following blocks:

- MCHT with a radiating area, the characteristic size of which is smaller than the size of the MFCE, with a temperature adjustment source;

- standard modulator of light flux MCT;

- sample holder IR MFPU, coaxial with MCT;

- a unit for interfacing (BS) with constant power sources, which generates and supplies constant voltage power, clock pulse power supply voltage and pulse control voltage to the MFP, as well as receiving, primary processing, generating its output signals and transmitting them to the subsequent stand unit;

- A block of analog-to-digital signal processing (BACO);

- A PC that digitally processes the signals of the MPPU, controls the temperature of the MPP and controls the operation of the MPP and MPPU.

Install the MFP in the holder, connect it to the BS. We turn on all the devices of the stand in the operating mode. We launch the program for measuring the sensitivity spectrum of the MFP. We enter into the program the number of the sample, the design and operational parameters of the MPPU [4], including the experimentally measured dependences K _in (λ) and K _sf (λ), the first specified temperature of the MCT, the interval and step of its change, or the number of measured points of the spectral curve . We turn on the measurement program. The installation, under the control of a computer program, carries out a change in the temperature of the MCB by a given step, monitors the degree of stationarity of temperature according to the derivative of the signal from the temperature sensor of the MCB, and measures the signals of all PSE MFPs at a stationary temperature. At the end of the measurements, we turn on the calculation of the spectral characteristics of the MFP, enter the numbers of the PSE and the type of spectral characteristics that need to be shown. The computer calculates, stores, displays on the display screen and prints, if necessary, the spectral dependences of individual PSEs, or 2D arrays of red borders or sensitivity maxima of all PSEs.

Literature

1 GOST 17772-88, Radiation receivers. Semiconductor photoelectric and photodetector devices. Methods for measuring photoelectric parameters and determining characteristics, M., USSR State Committee for Standards, Ed. Standards, 1988, p. 34, Appendix 4.

2 Bell R. J., Introduction to Fourier spectroscopy, M. Mir, 1975, 382 S.

3 A.I. Patrashin, G.A. Ivanov, Testing Unit for Measuring Photoelectric Characteristics of IR Arrays, Proceedings of SPIE, 1998, V. 3379, p. 555-560.

4 A.I. Patrashin, I.D. Burlakov, et al., An analytical model for calculating the parameters of matrix photodetector devices, Applied Physics, No. 1, 2014, P. 38.

5 A.I. Patrashin, A.V. Nikonov, B.C. Kovshov, A Generalized Method for Calculating Irradiation from a Blackbody, Advances in Applied Physics, vol. 6, No. 2, 2018, p. 157.

6 A.I. Patrashin, K.V. Kozlov, B.C. Kovshov, A.V. Nikonov, V.A. Streltsov, Method for setting a predetermined irradiation from an MRI, Advances in Applied Physics, vol. 6, No. 4, 2018, P. 349.

7 Rogalski, Infrared Detectors, CRC Press, 2011, p. 10.

Claims (3)

1. A method for measuring the absolute spectral sensitivity of an IR MFP, including the sequential installation of N stationary temperatures of the blackbody model (MCT), registration of the integral signal of all photosensitive elements (PSE) at each stationary value of the temperature of the MCI, automated compilation of three systems of N integral for each PSE equations corresponding to stationary values of the temperature of the MRI, the solution of each system of N intetral equations with respect to N values of spectral characteristics PSE by wavelength, construction of absolute spectral characteristics of PSE by calculated components, characterized in that the characteristic size of the emitting area of the MCT is smaller than the size of the MPE, the radiation of the MCT is modulated with a constant frequency, the signal of each PSE is automatically measured at a stationary temperature of the MCT K times, the average value is calculated the signal of each PSE according to the measured signals, calculate the standard deviation of the signals of each PSE from the average value and substitute the obtained value adratichnogo deviation to the left side of the integral equation corresponding to a predetermined temperature. 2. A method for measuring absolute spectral sensitivity IR FPA according to claim 1, characterized in that a stationary temperature regime MCHT continued for a time of at least t = K⋅τ _{landline frame,} wherein _{the frame} τ -. FPA time frame. 3. A method for measuring the absolute spectral sensitivity of an IR MFP according to claim 1 or 2, characterized in that the signal of each PSE is automatically measured at a stationary temperature of the MCT of at least K = 256 times.