OPTICAL INSTRUMENTATION AND TECHNOLOGY

Ways to improve the industry-wide system for metrological assurance of infraredoptoelectronic devices

V. A. Baloev and V. I. Kurt

NPO State Institute of Applied Optics, Kazan

A. N. Shchipunov

State Scientific Research Institute, Mytishchi, Moscow Oblast�Submitted September 6, 2006�Opticheski� Zhurnal 74, 5–12 �March 2007�

This paper discusses problems of the metrological assurance of the production, testing, and op-eration of IR optoelectronic devices and proposes ways to improve systems for the metrologicalassurance of IR optoelectronic devices. © 2007 Optical Society of America.

The main activity of the metrological service of NPOState Institute of Applied Optics �NPO GIPO� is the metro-logical assurance of the development, production, testing,and operation of optoelectronic devices �OEDs� that operatein the IR region. The main types of OEDs that operate in theIR are scanning and array thermal-vision and radiometricdevices. From the viewpoint of metrological assurance, theindicated devices combine the need to normalize their pa-rameters in the values of the radiation-temperature difference�RTD� and the radiance difference �RD� with the need tomonitor their spectral responses.

The metrological-assurance system that is active atGIPO for OEDs with respect to the spectroenergetic param-eters of optical radiation �Fig. 1� consists of secondary stan-dards of the physical units of continuous optical radiation inthe spectral range 0.25–15 �m and working standards �ref-erence measurement complexes� that are multipurpose infunctional possibilities, intended for checking and calibratingvarious types of OEDs. It should be pointed out that this iscurrently the most fully equipped metrological-assurancesystem for OEDs in the industry from a technical standpoint.

The main principles that govern the metrological serviceof GIPO when constructing metrological-assurance systemsfor OEDs can be formulated as follows:

• Regardless of the class and type of OED, test-and-measurement complexes or test stands that most accuratelysimulate the spectral content and energy of the radiation ofthe objects for the investigation of which the devices areintended must be used when they are rated with respect tothe energy, spectral, and spatial characteristics of opticalradiation.

• Metrological-assurance systems for OEDs, depending ontheir class and type, need to be developed by means ofinstrumental-methodological complexes that differ in theprinciples of the reproduction, measurement, and transmis-sion of the magnitudes of the physical quantities of opticalradiation in accordance with the verification schemes thathave been legislated at the state, industry, or plant level.

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The metrological requirements on the test-and-measurement facilities are directly determined by the re-quirements on the devices to be monitored. An analysis ofthe requirements imposed on prospective samples of OEDswith respect to the allowable RTD and noise-equivalent RTD�RTDnoise� shows that one of the main problems from theviewpoint of metrological assurance of the development andtesting of OEDs is the lack of facilities in this country formeasuring RTD values less than 50 mK.

Taking into account the current requirements on themeasurement facilities even today it is necessary to developand when possible to modernize the test facilities available atplants in order to ensure correct measurements of the re-quired RTDnoise values.

An analysis of the status of the metrological assurance ofthe production, testing, and operation of OEDs showed that,in the industry,

• There was a significant reduction in the 1990s of thescientific-technical potential in the technology for measur-ing the parameters of optical radiation as a whole.

• There is a lack of standardized facilities and methods ratedin accordance with metrological rules and norms for cali-brating and graduating differential facilities for measuring,testing, and monitoring OEDs �measurement stands, tech-nological IR collimators, test-and-checking apparatus�.1

• The routine metrological procedure of circular comparisonthat ensures efficient monitoring of the “industry-widepipeline of accuracy” and provides information on the cali-bration characteristics of differential measurement facili-ties up to the “allowable scatter of the measurement re-sults” is carried out only within separate plants, and thisproduces, for example, different results of the measure-ment of the temperature-frequency response of the sameOED on test stands at different plants.

• The facilities used for checking have a high degree of wearand are often obsolete.

• The current State Standards in the industry, GOST 8.195-89, 8.106-2001, and 8.023-2003, which regulate the sys-tem for ensuring the uniqueness and accuracy of measure-

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ments of the absolute magnitudes of spectral, spectrozonal,and overall optical radiation, do not provide the requiredaccuracy of the calibration of IR measurement apparatusthat differs in type.

A consequence of this is that each plant must act inde-pendently in developing measurement facilities and methodsin the absence of centralized metrological supervision, aswell as the extremely high likelihood of making a wrongdecision from the results of measurements carried out usingthe OEDs.

For the majority of metrological services of plants, theonly available way to calibrate the measurement stands andcontrol-and-checking apparatus �CCA� for OEDs is thecalculational-experimental method �Fig. 2�, based on the fol-lowing measurements and calculations of functional quanti-ties:

FIG. 1. Metrological-assuranc

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• on the legislated �MTSh-90, GOST 8.558� system for mea-suring the thermodynamic temperatures between the work-ing surfaces of a differential radiator—the test object of themeasurement stands and the CCA of the OED;

• on the measurement and calculation of the effective emis-sivities of the working surfaces of the test object;

• on the measurement of the spectral transmission and cal-culation of the spectrozonal transmission of the opticalsystem of the measurement stands and the CCA in theregion of spectral sensitivity of the OEDs �the measure-ments are carried out over flat control specimens withoutintroducing corrections into the actual geometry of the sur-faces of the optical elements and the radiation flux�;

• on engineering calculations of the reproduction of the RTDand the RD values �numerous versions of the calculationaltechniques are not certified, approximations and allow-ances in the calculations have no basis�.

tem for OEDs at NPO GIPO.

e sys

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In practice, one very often uses an expression that makesit possible to estimate the RTD but not to calculate its accu-rate value:

�Tm = ����T , �1�

where �� is the transmittance of the optical system of themeasurement stand, � is the emissivity of the radiator and thetarget �it is assumed that they are equal�, and �T is the dif-ference of the thermodynamic temperatures between the ra-diator and the target.

The calculation of the RTD from Eq. �1�, first, neglectsthe mutual thermal influence of the background radiator andthe target, as well as the influence of the ambient tempera-ture, and, second, it is hard to obtain equality of the emis-sivities of the background radiation and the test-object target,because they are usually fabricated from different materials.

FIG. 2. Metrological-assurance set

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It should also be taken into account that the radiator-target-slot system is a cavity radiator with an effective emissivitythat differs from that of a flat surface.

Based on an analysis of many years of experimentalstudies and calibrations of blackbody models, a techniquehas been developed at GIPO for calibrating measurementstands and CCA, by means of which the RTD is also deter-mined by an experimental-calculational method, but with therequisite referencing of the results of the measurements toradiance units according to GOST 8.106-2001. Based on thistechnique, a local checking setup has been developed forRTD and RD measurement facilities �Fig. 3�.

The measurement stands and CCA are calibrated bymeans of a measurement stand based on the K-100 steady-state radiometer-comparator. The optical layout of the mea-surement stand is shown in Fig. 4. The calibration techniqueconsists of successively comparing the radiances created atthe output of the measurement stand or the CCA separately

r OEDs actually used in industry.

up fo

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FIG. 3. Local checking setup for measurement facilities of the units of the physical quantities RTD and RD.

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with a bar target and separately with a source of backgroundradiation with the radiances, normalized according to GOST8.106, of the working standards, which are absolute black-bodies �ABBs� consisting of model ABB 213–343/20 Kradiators,2 followed by a calculation using the Stephan-Boltzmann law to find the radiation temperature �RT� and theRTD.3,4

The parallel radiation flux from the radiating bar of thetarget or of a background radiator �through the target slot� ofmeasurement stand 1 being calibrated is transformed by asystem of interchangeable mirrors 2 and 3 of the couplingoptics into a convergent beam, and the target is sharply fo-cused in focal plane 4 of aspheric mirror objective 5, 6. Theradiations from the measurement stand and from referenceradiator ABB 213–343/20 K 8 are switched by reflectivesector modulator 7. The aspheric mirror objective 5, 6 fo-cuses the image of the target and the stop of the ABB in theplane of exit stop 10, behind which are mounted interchange-able photodetectors 11. Detector-recorder system �DRS� 12amplifies and processes the difference signal from the radia-tion detector.

Before the measurement stand is calibrated, the calibra-tion response of the DRS is checked with respect to sensitiv-ity S0. To do this, the signal difference �U of the two ABB213–343/20 K units 8 and 9, calibrated in radiance, is mea-sured:

�Us = �1�Le,1 − Le,2�S0, �2�

where �1 is the transmittance of the optics of the K-100, andLe,1 and Le,2 are the radiances of the radiators given in thetest certificates.

The following condition must be met during the mea-surements: Le,1�Le,rad�Le,2, where Le,rad is the radiance ofthe background radiator of the measurement stand being cali-brated.

The signal from the DRS, proportional to the RD fromthe radiator of the measurement stand and standard radiator8, can be written similarly to Eq. �2� as �Urad=�1�Le,1

−�2Le,rad�S0, where �2 is the total transmittance of mirrors 2and 3, and Le,rad is the radiance of the radiator of the mea-surement stand.

Since the measurements are made virtually simulta-neously, it can be assumed that the sensitivity S does not

FIG. 4. Optical layout of the K-100M radiometer-comparator. See text forexplanation.

0

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change, and hence �Urad=�Us�Le,1−�2Le,rad� / �Le,1−Le,2�and Le,rad= �1/�2��Le,1− �Le,1−Le,2��Urad /�Us�.

Similarly, the radiance of the target of the measurementstand can be written as Le,tar= �1/�2��Le,1− �Le,1

−Le,2��Utar /�Us�, where �Utar is the DRS signal, propor-tional to the RD of the target of the measurement stand andstandard radiator 8.

The RT of the radiating bar of the target, Tm,tar, and ofthe source of background radiation, Tm,rad, of the measure-ment stand are calculated from the Stephan-Boltzmann for-mula, and the target-background RTD at the output of themeasurement stand is calculated from the expression �Tm

=Tm,rad−Tm,tar.The calibration response of the K-100 and the stability

of the working levels of the RT of the standard radiators �theworking standards of the radiance according to GOST 8.106�are periodically checked from radiators based on phasetransitions—the triple points of water and gallium �the sec-ondary standards of radiance according to GOST 8.106 andthe reference points of MTSh-90, in SI units and kelvin�.

The calibration errors of the measurement stand in theRTD values �with confidence level P=0.95, for example, forthe most accurate measurement stand, model NSI-K� liewithin the limits ±0.02 K in the range from 0.05 to 2.0 K,±0.05 K in the range from 2.0 to 5.0 K, and ±0.2 K in therange from 5.0 to 20 K.

The technique considered here is also valid for the spec-tral range from 3 to 5 �m. It is only necessary to replace thephotodetector unit �PDU�, as well as to carry out calibrationand comparison between its reference radiators in the regionfrom 3 to 5 �m.

The advantages of the given technique are as follows:The possibility of separately determining the stability of theradiation characteristics of the radiator and the target of themeasurement stand, a quantitative estimate of their mutualthermal influence on each other, as well as the influence ofthe background radiation on the variation of the RTD; thepossibility of eliminating the operation of measuring thetransmittances of the optical system and the emissivities ofthe target and the radiator of the measurement stand.

At the same time, the developed technique has certainlimitations: It is necessary to measure the transmittances ofthe matching optics and to match the optics of comparatorK-100 and the matching optics in their relative apertures,while the minimum measurable radiance values are limitedby the sensitivity of the DRS of the comparator and by theerror of the electronic thermal stabilization system of thereference radiator.

The local verification system considered here uses theprinciple of normalization of the RTD and the RD, based ona measurement of the difference of the radiation fluxes be-tween the stabilized level of the homogeneous radiation fromABB 213–343/20 K and the radiation from the elements ofthe test object of the measurement stand; i.e., the referencestandard of the RTD and the RD as physical magnitudes isabsent, and the only available quantity is their reading level,which is normalized with respect to the radiation-stabilization error. In the final analysis, the normalization

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FIG. 5. Prospective metrological-assurance setup for IR OEDs.

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error of the RTD and RD values is determined by the stabi-lization error of the working levels of the radiation, by theerror, and by the limiting sensitivity of the measurements ofthe difference of the radiations from the ABB and the mea-surement stand being calibrated, i.e., by the technical possi-bilities of the radiometry. There are thus purely technologicallimitations �the quality of the set of components, the systemsolutions� with respect to normalization of the minimumRTD and RD levels that can be reproduced by the measure-ment stand being checked.

The condition for creating a metrological-assurance sys-tem for prospective OEDs that record physical RTD and RDquantities dependent on MTSh-90 is the advanced develop-ment of the principles of high-accuracy reproduction andnormalization of the indicated quantities, followed by thedevelopment and introduction into metrological practice ofthe reference standard and an instrumental-methodologicalcomplex of facilities for transferring the RTD and RD valuesaccording to the indicated verification scheme.

In order to create a unified high-accuracy metrological-assurance system for OEDs in this country, it is extremelycrucial to solve the following problems:5,6

1. The development and creation of a unified referencestandard of the reproduction and transfer of the units of thephysical quantities called RTD and RD, which must ensurestable reproduction of the RTD and the RD values in therange from 0.005 �±0.001� to 70 �±0.05� K and from 0.01�±0.002� to 40 �±0.1� W/ �sr m2�, respectively.

2. The development and creation of a high-accuracystandard transferring agent �a scanning radiometer-comparator� for direct measurements of RTD values in therange from 0.01 �±0.005� to 70 �±1.0� K and of RD valuesfrom 0.02 �±0.01� to 140 �±2.0� W/ �sr m2�, and the transfer-ence of these measurements from the reference standard tothe working standards.

3. The development and creation of a fundamentally newtest-stand and test-and-checking apparatus for monitoring thecharacteristics of OEDs characterized by a noise-equivalenttemperature difference between 0.02 and 0.025 K.

Our theoretical investigations showed that reproductionand accurate normalization of the RTD levels correspondingto the indicated requirements cannot be provided by known

158 J. Opt. Technol. 74 �3�, March 2007

optical systems of test-and-measurement stands with classi-cal bar targets and with electronic regulation of the thermo-dynamic temperature.

The fundamentally new layout of the test-and-measurement stand for measuring the characteristics ofOEDs, developed from the results of theoretical and experi-mental studies, makes it possible to reproduce a temperaturedifference at the 0.005 K level to within at most 0.001 K.

Building on many years of experience in the checkingand calibration of OEDs, a metrological-assurance setup forprospective IR engineering �Fig. 5� has been developed atNPO GIPO. The development, in accordance with the pro-posed metrological-assurance setup for OEDs, of a referencemeasure �standard� of the units of the physical quantities“radiation-temperature difference” and “radiance difference,”and of a secondary standard—a high-accuracy radiometer-comparator for transferring the RTD and RD values to theworking measurement facilities- and a working standard—atest stand for measuring the characteristics of the OEDs—makes it possible to solve the problem of metrological assur-ance of the production, testing, and operation of high-accuracy IR engineering.

1V. I. Kurt, “Methods of calibrating with respect to the radiation-temperature difference of test stands and CCA of thermal viewers,” inAbstracts and Program of the International Conference on Applied Optics-98, St. Petersburg, 16–18 December 1998, St. Petersburg, 1998, p. 103.

2A. F. Grigor’eva, V. I. Kurt, Z. V. Kiatrova, and V. A. Novoselov, “Low-temperature IR radiators,” Opt. Mekh. Prom. No. 4, 20 �1985� �Sov. J.Opt. Technol. 52, 210 �1985��.

3V. I. Kurt, A. G. Bugaenko, and E. K. Pavlyukov, “Calibration of theNSI-K test stand with respect to the radiation-temperature difference,” inAbstracts of the Twelfth Scientific-Technical Conference on Photometryand Its Metrological Assurance, Moscow, 1999, p. 11.

4V. I. Kurt, G. K. Kholopov, and V. A. Novoselov, “Analysis of the meth-ods for calibrating IR radiators in radiation temperature,” in Abstracts ofthe Twelfth Scientific-Technical Conference on Photometry and Its Metro-logical Assurance, Moscow, 1999, p. 9.

5G. K. Kholopov, V. A. Novoselov, V. I. Kurt, A. K. Pavlyukov, and V. I.Sapritski�, “General physicomathematical model of an optical system forreproducing the values of the physical quantities ‘radiance difference’ and‘radiation-temperature difference’,” Izmer. Tekhnika No. 1, 10 �2000�.

6V. A. Novoselov, G. K. Kholopov, V. I. Kurt, and A. K. Pavlyukov, “Ver-sions of the optical systems of test stands with Fresnel attenuators for thereproduction of the radiance difference and the radiation-temperature dif-ference,” Izmer. Tekhnika No. 1, 17 �2000�.

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