coA

*°*eM of * NBS TECHNICAL NOTE 954

U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards
NATIONAL BUREAU OF STANDARDS

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LIBRABY/

JUL 2 u ^77

tt>€> SPECTRAL RADIOMETRY: ^,

7^

A New Approach Based on Electro-Optics v

Jon Geist, Michael A. Lind, A. Russell Schaefer,

and Edward F. Zalewski

Optical Physics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D.C. 20234

*<

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued July 1977
National Bureau of Standards Technical Note 954

Nat. Bur. Stand. (U.S.), Tech. Note 954, 23 pages (July 1977) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.10

Stock No. 003-003-01805-8
TABLE OF CONTENTS

1. INTRODUCTION

2. FEASIBILITY EXPERIMENT

3. LASER-BASED CHARACTERIZATION FACILITY

m

Page

4. ELECTRICALLY CALIBRATED PYROELECTRIC RADIOMETER 10

5. CONCLUSION 13

6. REFERENCES 15

SPECTRAL RADIOMETRY:

A NEW APPROACH BASED ON ELECTRO-OPTICS*

Jon Geist, Michael A. Lind, A. Russell Schaefer and Edward F. Zalewski

Radiometric Physics Section

Optical Physics Division

Institute for Basic Standards

Progress in developing a new approach to radiometry based on electro-optical technology is discussed. A feasibility experiment

that demonstrates and motivates the new approach is described. The

laser-based, characterization facility that plays a central role in

the new approach, including the electrically calibrated pyroelectric

radiometer that provides the absolute radiant power measurements, and recent investigations of silicon photovoltaic detectors that were performed on the facility are all described. Alternatives for ex- tending the wavelength range of the new approach are also discussed.

Key Words: Absolute radiometry; detector; electrically calibrated

detectors; laser power measurements; pyroelectric detectors; radiometry; silicon cell; silicon detector; silicon photodetector

.

1. INTRODUCTION

The blackbody emerged as a standard source of the quantity and spectral distribution of

radiation following intense experimental and theoretical study during the late 19th and early

20th century [1] . The experimental studies of the total quantity of blackbody radiation

were carried out with electrically calibrated detectors [2]. Yet with the exception of these

experimental studies [3] , the starting point in measurement practice has been the blackbody

rather than the electrically calibrated detector [4].

Since 1960, however, this situation has begun to change. A number of new electrically

calibrated detectors have been built for laser radiation [5] , solar radiation [6] , and traditional radiometric and photometric applications in the national laboratories [7]. Recent remeasurements of the Stef an-Boltzmann constant have demonstrated that the long standing

inconsistencies [8] between blackbody and electrical calibration radiometry have been re- solved [9] . One laboratory has even based its spectral radiometry on an electrically calibrated detector; still using a blackbody, but determining its distribution temperature with

the detector and colored glass filters [10]

.

In this paper, we will discuss a new approach to spectral radiometry. It is based on electrically calibrated pyroelectric detectors [11] and other recent electro-optical devices,

but does not employ a blackbody. First, we will describe a previously reported [12] experiment that demonstrates the feasibility of the new approach and motivates our current efforts. Next we will describe the laser-based, characterization facility that replaces the blackbody

in the new approach, including a description of the electrically calibrated pyroelectric

detectors that provide absolute radiant power measurements for the facility. Then we will

turn our attention to recent studies [13] of silicon photovoltaic detectors that have been

carried out using the facility. These studies are also of interest outside the context of

the new approach to radiometry. We conclude by discussing alternatives for extending the

wavelength range of the new approach, including a discussion of the recent application of an electrically calibrated pyroelectric detector to pulsed laser measurements [14]

.

*This is an extended version of a paper presented at the 7th International Symposium of the IMEKO Technical Committee on Photon-Detectors, Braunschweig, West Germany, May 17-19, 1976.

•figures in brackets indicate the literature references at the end of this paper.

1
FEASIBILITY EXPERIMENT

MONITOR

SILICON CELL ELECTRICALLY CALIBRATED

PYROELECTRIC RAOIOMETER

WAVELENGTH TUNABLE CW DYE LASER BEAM

WEDGED BEAM

SPLITTER

TEST

SILICON CELL

The arrangement of the experiment to demonstrate the feasibility of a new approach to radiometry is shown in Fig. 1. The ratio of the monitor cell reading to the power in the

laser beam, as measured with the electrically

calibrated pyroelectric detector, was recorded

at 10 nm intervals from 570 nm to 630 nm (the

tuning range of rhodamine 6G) . The time constant of the pyroelectric and monitor

electronics were not matched, and the laser

beam power fluctuated significantly. Therefore, these measurements suffered significant

random noise, the standard deviation of a single measurement being ^±0.5 percent.

However, the time constants of the electronics

of both detectors were on the order of a few

seconds, so it was possible to repeat a wavelength scan in a few minutes, permitting a large quantity of data to be accumulated for

averaging. The 126 data points obtained in

this way were fit to a linear equation,

giving the monitor cell reading per unit

power in the test beam as a function of wavelength with an estimated [15] three standard

deviation interval of ±0.25% around 600 nm

and to somewhat greater uncertainty on the

wings of the wavelength interval.

APERTURE -m_ , •

-i -i The electrically calibrated pyroelectric

detector was replaced in the laser beam by a silicon cell fitted with a three cavity

interference filter of nominal 10 nm bandpass

at 600 nm. The ratio of the filtered cell

reading to the monitor cell reading was recorded over the 570 nm to 630 nm range. The sampling interval was varied over the

wavelength range so that the spectral response

was densely sampled in the center and on the

top edges of the bandpass, but less densely

in the wings. The bandwidth of the laser

radiation was less than 0.1 nm, but no channel

spectral interference effects [16], such as would be expected with a plane parallel piece of

glass [17], were observed. Since the monitor and test cell electronics had matched time

constants, the effect of laser power fluctuations were largely eliminated yielding a standard

deviation of a single measurement of 0.2%.

LAMP

Fig. 1: Experiment arrangement for

measuring the power per unit area per unit

wavelength from a lamp using a filtered silicon cell whose absolute spectral response has

been measured with respect to an electrically

pyroelectric radiometer using wavelength

tunable cw dye laser radiation.

A total of about 80 ratios of the test cell to monitor cell readings were recorded as described above. These ratios were multiplied, wavelength by wavelength, by the linear curve derived to represent the ratio of the monitor cell reading to the power in the test beam

(described above) to yield the spectral response of the filtered silicon cell. These data

are shown in Fig. 2. Notice that the abscissa was inadvertantly mislabeled in ref. 12 (Fig.

1) , and has been corrected here.

The linearity of the filtered silicon cell was verified by comparison with the electrically calibrated pyroelectric over the range of photocurrents encountered in the above

experiment and to be expected in the lamp measurements described next. Sensitivity to polarization and location on the filtered cell were also investigated, and uncertainties for these

effects were calculated.

The filtered silicon cell was now fitted with an aperture of known area and used to measure the radiant power per unit wavelength per unit area (spectral irradiance) emitted by

two different quartz halogen lamps at a wavelength of 602 nm and a distance of 50 cm from

each lamp. The detailed mathematical procedure is described in ref. 12. A spectrophotometer

was used to verify that the filter transmission was less than 0.01% outside of the 570 to
570 600 630

WAVELENGTH (nm)

Fig. 2: Measured spectral response of the

filtered silicon cell as a function of wavelength (from ref. 12). Note that the ordi- nate of this figure was inadvertantly

mislabeled in ref. 12 and has been corrected

here.

630 nm wavelength reg

irradiance curves [18

the lamp output outsi

region. In this way

tain a correction fac

of error for the resp

silicon cell to lamp

side of the dye laser

ion. Nominal spectral

] were used to represent

de of this wavelength

it was possible to obtor and an upper limit onse of the filtered

radiation falling out- measurement range.

The results of this procedure are shown in

Fig. 3. Also shown there are values obtained

by calibration of the lamp with respect to blackbody radiation characteristic of the

temperature of freezing gold. [19] Thus Fig.

3 shows a comparison of the new approach to spectral radiometry with the traditional

approach based on a blackbody. The difference

of 1.0% ±0.3% shown there is well within the

combined estimated uncertainties of the two approaches. These are ±1.0% for the calibration of the filtered silicon cell with re- spect to the electrically calibrated pyroelectric detector, ±1.0% for the calibration

of the lamp and ±0.4% for the alignment,

drift etc. of the lamp. A more detailed

error analysis is presented in Fig. 4. It is

of some interest that the uncertainties

associated with the aperture area and the

variations in response over the pyroelectric

receiver have already been reduced significantly below the values listed in the figure.

Having demonstrated the comparability of

the two approaches to spectral radiometry at the one percent level, we anticipate the

replacement of the interference filter with

an electronically tunable filter such as the

acoustically tuned optical filters (AT0F)

that have been the subject of much interest

recently [20].

LASER-BASED CHARACTERIZATION FACILITY

This facility plays a major role in our study of the new approach to radiometry. For most radiometric purposes, cw lasers approximate delta functions in wavelength, position,

direction, and polarization. This greatly simplifies precise characterization of optical

instruments with respect to variations of these parameters. Computer control assists these

characterizations as well as those with respect to time, temperature, power level and power

density. The power in the laser beam is measured with respect to electrical standards using

an electrically calibrated pyroelectric radiometer. The combination of laser facility and

the radiometer is synergistic, since the facility is used to determine the equivalence of the

radiometer's response to radiant and electrical power.

Our facility is modular, providing flexibility for growth, as well as for a variety of

characterization activities. This flexibility has also proven useful in support of other

activities that require accurately known quantities of monochromatic power. These include

studies of photoelasticity [21], chemical actinometry [22], and photorheology of blood [23].

Figure 5 is a schematic diagram of the present facility. It is set up on a 4' x 18' rigidhoneycomb, optical table made from three 4' x 6' sections. The top of the table is 1/4"

thick magnetic steel with tapped 1/4-20 mounting holes on 1" centers.

The numbered circles in Fig. 5 represent kinematically mounted mirrors that permit

removal and simple realignment. The alignment apertures have proven useful for preliminary

3
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Fig. 3: Comparison of the values of the spectral radiant power

density (spectral irradiance) at 50 cm from two quartz-halogen

projection lamps as measured by a filtered silicon cell whose

absolute response was measured with reference to an electrically

calibrated pyroelectric detector using a dye laser (A) , and

measured with reference to the radiation from a blackbody at the freezing point of gold (•) as a function of the burning time

on the lamps. The work necessary to obtain these latter values

was not complete in time for the publication of ref. 12, which

included only the preliminary values (o) available to us at that

time.

SILICON PH0T0DI0DE/

INTERFERENCE FILTER. BASED ON PYROELECTRIC

NBS LAMP STANDARD OF SPECTRAL

IRRADIANCE BASED ON A BLACKBODY AND TEMPERATURE

Primary Area uniformity 0.5

Reference Power equivalence 0.2

Power measurement 0.5

Duty cycle 0.0

Transfer to Area uniformity 0.4

Secondary Spectral integration 0.6

Standard Polarization

Measurement Linearity 0.1

Against Aperture area 0.6

Secondary

Standard

Au melting point 0.5

Measurement of IPTS 0.5

temperature and quality

of the blackbodies

Spectral radiance 0.7

and irradiance

transfers

Alignment 0.4

X interpolation 0.2

Drift 0.5

Fig. 4: Comparison of uncertainties in the measurement of the

spectral power density (spectral irradiance) from a lamp at a wavelength of 602 nm using two different approaches.
ARGON ION LASER

ELECTROOPTICAL MODULATOR

MONO- Iy7\_ CHROMATOR"vJ/

%/1 LASER V*

ALIGNMENT

APERTURES V£ HELIUM (O- NEON

LASER

BEAM

OPTICS MONITOR

DETECTOR

TEST LOCATION

SPATIAL FILTER. BEAM EXPANDING

TELESCOPE AND

VARIABLE APERTURE

COMPUTER

CONTROLLED TRANSLATION

STAGES AND

TEMPERATURE

CONTROLLED

DETECTOR

HOLDER

alignment of the test beam from the different

radiation sources. By suitable placement of

the appropriate mirrors it is possible to direct the argon-ion laser radiation into

either the test beam, the spectrometer for

wavelength calibration, or the dye laser

where it pumps a jet of fluorescent dye

which in turn lases. The dye laser beam can be directed into the test beam or into the

spectrometer for calibration of the dye

laser wavelength scale. Similarly, it is

possible to direct the HeNe laser beam into

the test beam or into the spectrometer.

Fig. 5: Block diagram of the laser-based

radiometric characterization facility.

The power in the test beam is stabilized

using an electro-optic modulator (EOM) in a feedback loop [24]. Part of the radiation

in the test beam is split off via a reflection

from a wedged quartz beamsplitter. This

radiation is directed onto a diffuser covering

the active area of a uv-stable silicon

photodiode. The 1 cm

2 diode used in our system is a UV444B manufactured by EG&G. [25] Both

the beamsplitter and the diode are mounted in a temperature controlled housing shown in Fig.

6. The temperature of the housing is maintained at a few degrees above ambient to within

±0.1 C using the simple thermistor controlled DC power amplifier shown schematically in Fig.

7.

The output from the silicon photodiode is amplified in a high gain DC servo amplifier

illustrated in Fig. 8. An AD52K manufactured by Analog Devices is used as the current to voltage converter on the input stage of the amplifier. The output of this amplifier is fed onto an adjustable laglead compensation network and also to a buffer amplifier which can be

used to monitor the silicon detector. The output of the compensation amplifier feeds one junction of a X100 summing amplifier. The other junctions allow for the injection of both

an offset bias which is used to control the DC power level of the test beam and an external

auxiliary signal. The auxiliary input is needed for such functions as stable sinusoidal

modulation, etc. The X100 amplifier feeds another X1000 amplifier for additional DC gain.

This signal is then used to drive a X10 high voltage amplifier which in turn provides the

necessary 240 volt P-P half wave voltage for the EOM. This high slew rate, high voltage,

low drift amplifier is an AM302B manufactured by Datel Systems.

The modulator itself is a 45° X cut ADP crystal mounted in an index matching fluid

enclosed in an aluminum housing for thermal stability. The Model 28 modulator, supplied by

Coherent Associates, is capable of handling optical powers up to 6 watts in the 300 to 800 nm spectral range. In practice we have used the device to stabilize lines from 257 nm to 1.09 um.

Depending upon the source and wavelength of the laser radiation, beam power stabilities

of 0.1% to 0.01% have been obtained within a dc to 5 kHz bandwidth with the system described

above. By using faster amplifiers it is possible to extend the bandwidth to several MHz with only a small degradation of performance.

The spatial filter, beam expanding telescope and variable aperture in Fig. 5 are used

to "clean up" the laser beam, and to select the uniform central region of gaussian and/or

diffraction limited beam patterns (with consequent reduction of beam power) for applications

requiring a relatively uniform beam. The computer controlled translation stages are used to investigate the angular and spatial sensitivity of detectors, optical elements and instru- ments of moderate size. A temperature-controlled detector holder attached to the trans- lation stages allows the investigation of the sensitivity of various parameters to small

temperature variations above ambient. The present wavelength coverage of the facility is

shown in Fig. 9. Also shown there is the wavelength range to which we hope to expand the

facility in the near future.
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ELECTRICALLY CALIBRATED PYROELECTRIC RADIOMETER

Figure 10 presents a cross-sectional view of an electrically calibrated pyroelectric

detector with isolated heater and transducer circuits. [26] The isolation is obtained by

grounding the vacuum deposited gold on the back surface of the plastic film. Figures 11 and

12 show the electrical circuitry for waveform independent [27], null radiometer based on

this type of detector. Such a system responds

to the difference in the areas under the

pulses of radiant and electrical power,

rather than to the first harmonic of the

waveform. Thus modulators such as choppers,

whose output waveform depends upon the

distribution of the incident radiation in

the entrance aperture of the modulator can be used. However, it is necessary that the

energy content of the modulator's output

pulses be independent of the distribution of

the incident radiation. Furthermore, the

transducer and signal processing electronics

must preserve the area under the pulses

within the gating time of the synchronous

demodulator. Thus wideband electronics must

be used.

GOLD FILM

SILVER FILLED EPOXY (TYPICAL)

PYROELECTRIC TRANSDUCER

EPOXY

PLASTIC FILM

The operation of the radiometer is as follows. The gain of the variable amplifier

in Fig. 11 is varied until the output of the

low pass filter is null. The gain can be

controlled manually or by feedback from the

low pass filter. Once the null is achieved,

the unmodulated radiant power is given by

Fig. 10: A cut-away view of an electrically

calibrated pyroelectric detector with isolated heater and transducer circuits.

PR

- P

E WF ' (1)

where Pg is the electrical power computed by

the circuitry of Fig. 12, Dg and Dr are the

duty cycles of the electrical and radiant modulation waveforms, and F is a correction factor

that accounts for incomplete equivalence between the detector's response to electrical and

radiant heating. The measurements of Dg and DR

are routine, but the measurements that

determine F are less straightforward. They are similar in principal to the measurements

described in ref. 7 (J. Geist, 1971) and they have been discussed briefly in other papers

cited in ref. 7. Such a system appears capable of better than one percent accuracy from

around 200 nm to beyond 20 pm.

It is also possible to build a null radiometer based on electrically calibrated pyroelectric detector in which the heater and transducer circuits are coupled. [28] The absence

of the ground plane, insulating plastic film and epoxy joint simplifies the construction of

the detector, but requires somewhat more sophisticated signal generation and processing

electronics. A commercial system employing this type of detector is currently available. [29]

The principal reason for the choice of the latter design for commercialization was a supposed

problem in obtaining uniform response over the detector surface due to the epoxy joint.

However, the problem turned out to be caused in fact by imperfections in the transducer

crystals, so either configuration can be used.

Similarly it is possible to base the circuitry on narrow band (tuned) electronics. [30] In this case the radiometer responds to the first harmonic of the waveform, so the angular

aperture of the chopper must be suitably limited. It will be some time, if ever, before the

optimum system design is unequivocally established.

5. SILICON PH0T0DETECT0R STUDIES

The increasingly stringent requirements on silicon photovoltaic detectors in modern

radiometric measurements require a thorough understanding of the basic characteristics of

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Fig. 12: Electrical power computation electronics.

these devices. Several instances of anomalous behavior with resulting degradation of performance illustrate the importance of careful characterization of these detectors.

One such recently observed problem [31] is the enhancement of spectral response of

certain types of silicon pn photodiodes by exposure to near ultraviolet radiation. In this

study, a 2 mm diameter area of the detector surface was irradiated by a reasonably uniform

laser beam at 364 nm with an average incident power density of 4 mW/cm . The responsibity

of this area increased about 25% during the course of one hour. When beams of other wavelengths were scanned across the detector surface, the enhancement of the response at the

"burned in" spot was very evident, even at 633 nm. Figure 13 is a plot of the relative

responsibity of a "burned in" detector as a function of position on the detector surface for

various incident wavelengths of radiation. This enhanced responsibity decreased back to normal over a period of several days.

It was also observed that the uniformity of response as a function of position across

some silicon photodiodes begins to degrade in the blue region of the spectrum. One type of

detector, uniform within .5% over the 500 to 700 nm wavelength region, exhibits non-uniformities

larger than several percent at wavelengths below 460 nm. An improved type of detector was

found to be more uniform in the blue region, but also degrades at shorter wavelengths.

Furthermore, this type of detector shows no UV enhancement effect.

Additional studies of silicon detectors, done by irradiating a 2 mm area with 6 mW/cm2 radiation at 313 nm from a mercury arc, produced similar results. The responsibility enhancement was exponential with time, reaching a saturation level of about 25% relative increase

in three hours. No enhancement effect was seen when using 405 nm radiation.

Several possible explanations of the enhancement effect have been investigated experimentally. The results, presented in detail elsewhere [32], will be discussed briefly here. A possible explanation of the effect lies in the presence of extra available energy states

due to crystalline discontinuities and impurities trapped near the surface of the detector.

One simple model that was considered postulates an impurity material near the detector sur- face which possesses an intermediate metastable state that can only be populated by incident

ultraviolet photons. Electrons in this intermediate state could then be further excited

into the conduction band by absorption of other ultraviolet or visible photons. These

additional carriers would result in an enhanced responsivity until the intermediate levels were depleted.

In a mechanism of this type, one should be able to depopulate the metastable state by

irradiating the enhanced area with visible light. Experiments were performed in which the

relative response of an enhanced detector was recorded as a function of time. This was done

first with the detector in the dark, except for brief responsibity measurements, and then

with the detector irradiated with visible light. These measurements were performed at a 12
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variety of wavelengths from 405 nm to 633 nm. In no case was the enhancement seen to de- crease with a time constant different from

the approximate three hour time constant observed in the dark. This results rules

out this simple model.

Another possibility considered was that,

due to some physical phenomenon in the

detector surface, the reflectance of the

ultraviolet irradiated area would decrease,

resulting in an increased number of photons

absorbed and an apparent increased responsivity. To check this hypothesis, one of

the new type of ultraviolet stable detectors was employed. This stable detector was irradiated with ultraviolet radiation to ascertain that it did indeed show no enhancement effect. The stable detector was then

used to measure the reflectance of the test detector as a function of time while it was being irradiated with 3 mW/cm of 334 nm

radiation, and again using 0.4 mW/cm of

254 nm radiation. Although a response

enhancement of 25% was observed, no change

in the reflectance of the detector surface

was observed.

Other possible models have been proposed

to explain this effect. In one such mechanism, surface or impurity states between

the conduction and valence bands are affecting the apparent quantum efficiency by

trapping photon generated carriers. Electrons trapped in these extra states, together

with the positive ions left behind, alter

the potential barrier in the surface region,

as well as other parameters such as conductivity and recombination rate. The spectral

response of the detector is thus directly

related to surface state availability and

population. More detailed experimentation

would be required to isolate the specific

mechanism involved in the enhancement effect.

Perhaps the ultraviolet photons ionize a sufficient number of impurity atoms to result in a significant depopulation of the

surface states, causing an increased detector

efficiency due to the reduced surface energy barrier. The response could then be observed

to slowly decrease again in the dark, as the impurity induced states once again trap electrons

and the detector returns to its former condition.

" °°XvJ \ 514 run "

i ± ji -5.0 0.0 +5.0

DISTANCE FROM CENTER (mm)

Fig.

as a

13: Relative response of a silicon cell

function of wavelength and position

through a 2 mm diameter region of the cell

that was irradiated by 364 nm wavelength,

4 mW/cm2 nominal power density radiation for one hour.

6. CONCLUSION

We have reviewed current progress in developing a new approach to radiometry. In this

approach wavelength tunable, cw lasers replace traditional blackbody sources, and electrically

calibrated pyroelectric detectors provide the absolute power scale. Since laser radiation

is highly concentrated with respect to wavelength, position, direction, and polarization,

the new approach facilitates the detailed characterization of radiometric instrumentation.

Finally, we observe that the principal impediment to the full utilization of the new approach

at any arbitrary wavelength is the lack of wavelength tunable, cw lasers in certain regions.

There are two promising alternatives for expanding the wavelength range. The first is

to wait for the development of new wavelength tunable, cw lasers in those regions where they

13
presently do not exist. Wavelength tunable, pulsed lasers, in conjunction with frequency

doublers, mixers and parametric amplifiers, already provide continuous coverage from 220 nm

to 30 ym, and the cw capability has rapidly followed the pulsed capability in the past.

The second alternative is to extend the techniques discussed above to pulsed lasers.

As a first step in this direction, we have recently shown that pyroelectric radiometers are compatible with high accuracy measurements of pulsed laser radiation. [33] We demonstrated

that the piezoelectric response (of the pyroelectric detector) to the acoustic pulses

generated during the absorption of impulsive energy was on the order of one percent of the

pyroelectric response to the thermalized absorbed energy, and is capable of correction. An oscilloscope trace illustrating this result is shown in Fig. 14. The temporal resolution of

the thermally and acoustically derived pulses that is shown in the figure is due to the

presence of a thin plastic film between the absorbing layer and the pyroelectric transducer,

as was shown in Fig. 10. Acoustic waves propagate across this film in something of the

order of twenty picoseconds, while the thermal pulses require milliseconds to diffuse across

it. To complete the extension, silicon photodiodes or other stable solid state detectors

with linear response at the high photon current densities existing in pulsed laser radiation

must be obtained and accurately characterized.

- 10 H

COo

Q_CO

LJJ cc

Fig. 14: An oscilloscope trace showing the relative piezoelectric (area of first pulse) and pyroelectric (area of

second pulse) responses to the absorption of impulsive radiant

power. The circles show the result of a calculation of the

expected pyroelectric response for a diffusive heat flow.

****************

We gratefully acknowledge the contributions of B. Steiner to the new approach to radiometry, A. Crigler to the construction of apparatus and application of gold black coatings, J. Fowler to the design and construction of automation instrumentation, R. Keller for arranging

to loan us the lasers for the feasibility experiment, H. Beerman, W. Blevin, R. Brusa, G. Day, W. M. Doyle, C. Frohlich, C. Hamilton, B. Mcintosh, and R. Phelan to the concepts and

development of our electrically calibrated pyroelectric radiometers, and to the Army Metrology

Lab, Huntsville, Alabama, the NASA Johnson Space Flight Center, Houston, Texas, the Bureau

of Radiological Health, Rockville, Maryland, and the NASA Lewis Research Center, Cleveland,

Ohio, for providing partial support to this program.

14
7. References

1. M. Planck, The Theory of Heat Radiation , (P. Blakiston's Sons, Philadelphia, 1914) 10,

42-43, 63-64.

E. Whittaker, A History of the Theories of Aether and Electricity, the Classical Theories , (Thomas Nelson & Sons, London, 1951) 370-372.

E. Whittaker, A History of the Theories of Aether and Electricity, Vol. 2 , (Harper & Bros., N.Y., 1960), 78-81.

2. W. W. Coblentz, Bull. Bur. Stand. 12_, 553 (1916) reviews earlier measurements.

C. Mifller, Zeits f . Physik 82_, 1 (1933) reviews earlier measurements. No new measurements were reported between 1934 and 1957.

3. There are three other exceptions to this statement. J. Guild, Proc. Roy. Soc. (London)

A161, 1 (1937), G. A. W. Rutgers, Physica 17_, 1291 (1951), and M. Eppley and A. R. Karoli, J. Opt. Soc. Am. 47 , 748 (1957). The latter two can be considered part of the

post 1960 trends described in the text.

4. G. Bauer, Measurement of Optical Radiations, (Focal Press, London, 1965), 94.

5. G. Birnbaum and M. Birnbaum, Proc. IEEE 55_, 1026 (1967) reviews earlier work.

J. W. Stearn, J. Sci. Inst. 44_, 218 (1967).

R. Nowicki, Inf. Phys. 8, 223 (1968).

M. M. Birky, Appl. Opt. 10, 132 (1971).

E. D. West, et. al. , J. Res. Nat. Bur. Stand. 76A , 13 (1972).

6. R. Kruger, Appl. Opt. 8, 1716 (1969).

J. M. Kendall and C. M. Berdahl, Appl. Opt. 9_, 1082 (1970).

R. W. Brusa and C. Frohlich, Tech. Note 1, World Radiation Center (Davos, Switzerland,

1972).

R. C. Willson, Appl. Opt. 12, 810 (1973).

D. Crommelynck, I. R. M. Belgique, Publ. Ser. A, No. 81 (1973).

7. E. J. Gillham, Proc. Roy. Soc. (London) A269 , 249 (1962).

W. R. Blevin and W. J. Brown, Aust. J. Phys. 20, 567 (1967).

N. Ooba, Res. Electrotech. Lab. No. 675 (December 1967).

K. Bishoff, Optik 28, 183 (1968).

J. Geist, NBS Tech. Note 594-1, June 1971.

J. Geist, L. B. Schmidt and W. E. Case, Appl. Opt. 12, 2773 (1973).

8. R. T. Birge, Rev. Mod. Phys. 13, 233 (1941).

9. J. M. Kendall and C. M. Berdahl, Appl. Opt. 9_, 1082 (1970).

W. R. Blevin and W. J. Brown, Metrologia 7_> 15 (1971).

10. F. J. Wilkinson, Metrologia 11, 105 (1975).

11. R. J. Phelan and A. R. Cook, Appl. Opt. 12_, 2494 (1973).

J. Geist and W. R. Blevin, Appl. Opt. 12, 2532 (1973).

12. J. Geist, et. al. , Appl. Phys. Lett. 2_6, 309 (1975).

13. M. Lind and E. Zalewski, Appl. Opt. 15_, 1377 (1976).

A. R. Schaefer, to be published in Appl. Opt. 16^, (1977).

14. J. Geist, H. J. Dewey and M. Lind, Appl. Phys. Lett. 2_8, 171 (1976).

15. This estimate does not include the uncertainty associated with the absolute accuracy of

the radiant power measurements made by the pyroelectric detector. This is discussed

later.

16. M. Born and E. Wolf, Principals of Optics , (Pergamon Press, N.Y. , 1965), 265.

17. Such effects would have significantly complicated our experimental procedure.

15
18. W. E. Schneider, R. Stair and J. K. Jackson, Appl. Opt. 6, 1479 (1967).

19. D. McSparron, personal communication.

20. S. Harris, S. Nieh and D. Winslow, Appl. Phys. Lett. 17, 223 (1970).

I. Chang, Appl. Phys. Lett. 25, 323 (1974).

21. R. A. Forman, B. A. Weinstein and G. Piermarini, Proceedings of Colloque International

du C. N. R. S., Lyon, 1976, paper 51.

22. D. G. Taylor, J. N. Demas, W. D. Bowman, E. W. Harris and R. P. McBride, Proceedings

of the 12th Informal Conference on Photochemistry, June 28-July 1, 1976,. page A4-4.

23. A. Tamoush, in preparation.

24. R. L. Barger, M. S. Sorem and J. L. Hall, Appl. Phys. Lett. 22^ 573 (1973) and R. L. Barger, J. B. West and T. C. English, Appl. Phys. Lett. 27, 31 (1975).

25. At times, certain commercial materials and equipment will be identified in this report

in order to adequately specify the experimental procedure. In no case does such identification imply recommendation or endorsement by NBS, nor does it imply that that which

is identified is the best available for the purpose.

26. J. Geist and W. R. Blevin, Appl. Opt. 12, 2532 (1973).

27. J. Geist, Rev. Sci. Inst. .43, 1704 (1972).

28. R. J. Phelan and A. R. Cook, Appl. Opt. 12_, 2494 (1973).

C. A. Hamilton, G. W. Day and R. J. Phelan, NBS Technical Note 678, March 1976.

29. W. M. Doyle, B. C. Mcintosh and J. Geist, Opt. Eng. 15, 541 (1976).

30. C. A. Hamilton, G. W. Day and R. J. Phelan, NBS Tech. Note 678, March 1976.

31. M. Lind and E. Zalewski, Appl. Opt. 15, 1377 (1976).

32. A. R. Schaefer, to be published in Appl. Opt. 16, (1977).

33. J. Geist, H. J. Dewey and M. A. Lind, Appl. Phys. Lett. 28, 171 (1976).

16
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN 954

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE 5. Publication Date

SPECTRAL RADIOMETRY; A New Approach Based on

Electro-Optic s

July 1977

6. Performing Organization Code

7. author(S) Jon Geist, Michael A. Lind, A. Russell Schaefer and

Edward F. Zalewski

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

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15. supplementary notes Tnis j_ s an extended version of a paper presented at the

7th International Symposium of the IMEKO Technical Committee on Photon-Detectors,

Braunschweig, W. German, 5/17-I9/1976.

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Progress in developing a new approach to radiometry based on electro-optical

technology is discussed. A feasibility experiment that demonstrates and motivates

the new approach is described. The laser-based, characterization facility that

plays a central role in the new approach, including the electrically calibrated

pyroelectric radiometer that provides the absolute radiant power measurements, and

recent investigations of silicon photovoltaic detectors that were performed on the

facility are all described. Alternatives for extending the wavelength range of the new approach are also discussed.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Absolute radiometry; detector; electrically calibrated

detectors; laser power measurements; pyroelectric detectors; radiometry; silicon

cell; silicon detector; silicon photodetector.

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