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PUBLICATIONS

NATL INST. OF STAND & TECH

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NBS TECHNICAL NOTE 1216

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U.S. DEPARTMENT OF COMMERCE/National Bureau of Standards

100

Radiometric Calibration

Procedures Using the

NBS MARBLE Electronics

Package

QC

101

.U5753

No. 1216

1985

c- 2

M.E. Mickelson, L.E. Larson, and Joel Fowler
Tm he National Bureau of Standards' was established by an act of Congress on March 3, 1901. The

m Bureau's overall goal is to strengthen and advance the nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a

basis for the nation's physical measurement system, (2) scientific and technological services for industry and

government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety.

The Bureau's technical work is performed by the National Measurement Laboratory, the National

Engineering Laboratory, the Institute for Computer Sciences and Technology, and the Institute for Materials

Science and Engineering

.

The National Measurement Laboratory

Provides the national system of physical and chemical measurement;

coordinates the system with measurement systems of other nations and

furnishes essential services leading to accurate and uniform physical and

chemical measurement throughout the Nation's scientific community, in- dustry, and commerce; provides advisory and research services to other Government agencies; conducts physical and chemical research; develops,

produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

• Basic Standards2

• Radiation Research

• Chemical Physics

• Analytical Chemistry

The National Engineering Laboratory

Provides technology and technical services to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement

capabilities; provides engineering measurement traceability services; develops

test methods and proposes engineering standards and code changes; develops

and proposes new engineering practices; and develops and improves

mechanisms to transfer results of its research to the ultimate user. The

Laboratory consists of the following centers:

• Applied Mathematics

• Electronics and Electrical Engineering2 • Manufacturing Engineering

• Building Technology

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Chemical Engineering

The Institute for Computer Sciences and Technology

Conducts research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and economy in Government

operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing

the Federal Information Processing Standards Program, developing Federal ADP standards guidelines, and managing Federal participation in ADP

voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and provides the technical foundation for computer-related policies of the Federal Government. The Institute consists of the following centers:

• Programming Science and

Technology

• Computer Systems

Engineering

The Institute for Materials Science and Engineering

Conducts research and provides measurements, data, standards, reference

materials, quantitative understanding and other technical information fundamental to the processing, structure, properties and performance of materials; addresses the scientific basis for new advanced materials technologies; plans

research around cross-country scientific themes such as nondestructive

evaluation and phase diagram development; oversees Bureau-wide technical programs in nuclear reactor radiation research and nondestructive evaluation; and broadly disseminates generic technical information resulting from

its programs. The Institute consists of the following Divisions:

Inorganic Materials Fracture and Deformation3 Polymers

Metallurgy Reactor Radiation

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address

Gaithersburg, MI) 20899. Some divisions within the center are located at Boulder, CO 80303.

led ai Boulder, CO, with some elements at Gaithersburg, MD.
ITATIONAL BUREAU

Of STANDARDS

Radiometric Calibration Procedures ^7^

Using the NBS MARBLE Electronics

racKage

M.E. Mickelson and L.E. Larson

Denison University

Granville, OH 43023

Joel Fowler

Center for Radiation Research

National Measurement Laboratory

National Bureau of Standards

Gaithersburg, MD 20899

.<*

*** of e

M?>5 koAMAAthJ tvok

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldnge, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued September 1985
National Bureau of Standards Technical Note 1216

Natl. Bur. Stand. (U.S.), Tech Note 1216, 20 pages (Sept. 1985)

CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1985

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402
RADIOMETRIC CALIBRATION PROCEDURES USING

THE NBS MARBLE ELECTRONICS PACKAGE

PREPARED BY

M. E. Mickelson and L. E. Larson

Department of Physics and Astronomy

Denison University

Granville, Ohio 43023

and

Joel Fowler

National Bureau of Standards

Gaithersburg, Maryland 20899

I. THE MARBLE ELECTRONICS PACKAGE

The NBS MARBLE electronics package provides the means for conditioning

electrical signals from optical light detectors for radiometric measurement

and calibration purposes. In particular, the DC electrical currents from

silicon photodiodes may be fed directly into the MARBLE inputs. In some

cases, signals from detectors which have their own electronics packages may

also be accommodated. This document describes the procedures to be followed

in using the MARBLE with single photodiodes such as the UV-444B which have

been self-calibrated and the UV-100 configured in an absolute ref lectrometer

and with the QED-100 light trapping detector array. Both the UV-100 and the

QED-100 detectors are manufactured by United Detector Technology, Inc. and the

UV-444B is manufactaured by EG&G. The QED-100 light trapping detector

consists of four of the UV-100 inversion layer photodiodes arranged so that

nearly all of the incident light is absorbed by the array of diodes. A series

of five papers relating to radiometry using silicon photodiodes is referenced

in this document. 1_5

The MARBLE electronics package provides the following functions. (See

figure 1 for the front panel layout and figure 2a for the circuit diagram).

1. Two channels of high accuracy DC current to voltage conversion and

conditioning for silicon photodiodes without integral electronics

packages. The input for these two channels are labeled A and B.

The output from channel B can be inverted.

2. One channel for any detector with its own electronics package

which produces an output voltage less than 12 volts. The input for

this channel is accessed through the input adjacent to input A and

is labeled ALT. This input is active whenever the switch between

input A and the ALT input is positioned to the right as indicated

by the arrow. When ALT is activated, the A input cannot be used.

3. Two adjustable 0-60 VDC power supplies for biasing of silicon photodiodes. Reverse biasing of silicon diodes is accomplished by
connecting two cables with BNC connectors from the plus and minus

outputs of one of the power supplies to the pair of inputs immediately under the amplifier controls. Polarity is determined by a simple procedure described in a following section.

4. Digital voltmeter and output BNC connectors. The MARBLE contains a low accuracy integral DVM which can be switched to monitor the

output of each channel as well as the ratio of channel A to channel

B. For high accuracy applications, the output voltages of channels

A and B and their ratio can be measured by connecting an external

digital voltmeter to the appropriate BNC connector located below

the DVM on the front panel.

II. SET-UP PROCEDURE

Two types of silicon photodiodes may be used with the MARBLE electronics package. Typical of these two types are the EG&G UV-444B p on n type

silicon photodiodes and the UDT UV-100 and the QED-100 inversion layer photodiodes. Note that the UDT QED-100 device is merely a combination of four (4)

UDT UV-100 diodes arranged optically in series to collect nearly all of the

incident light (see figure 3b and reference 3). The four photodiodes are electrically wired in parallel. QED-100 devices obtained directly from UDT

sometimes have a non-optical diode wired in series with the UV-lOOs for protection. This diode will adversely affect the calibration process and

should be shorted out. The diode can be readily seen by removing the cover

with the UDT label. The diode is connected between the center terminal of the

BNC connector and the first photodiode. The effect of the diode can be eliminated by soldering a shorting wire across the diode.

1. ELECTRICAL CONNECTIONS .

AMPLIFIERS . In most applications, the complete system will consist of a source, three detectors, the MARBLE electronics package and possibly a data

acquisition system. For calibration work, the detectors will include the

standards, the test detector (device to be calibrated) and the monitor

detectors. The standard and test detectors should be connected to channel A and the monitor detector to channel B. Measurements should be made as ratios

of channel A signals to channel B signals in order to reduce the effects of

varying source intensity and electrical noise. If the standard detectors used

required biasing, then correct polarity and proper bias level must be

determined. In these measurements, dark currents must be taken into account.

As mentioned above, there are two independent electrical channels for

amplifying signals. (Refer to the electrical schematic in figure 2a.) Channel A can be used for photodiodes without integral amplifiers by connecting

their outputs to the lower input labeled A. The correct photodiode electrical

polarity is indicated in figures 2a, 3a, 3c, and 3d. It should be noted that

the amplifier design assumes the input of negative currents. Also note that

the output voltage of channel B must always be positive. The ratio or divider

circuit requires a positive divisor voltage. If for some reason the output of

channel B is negative, invert the voltage by throwing the invert switch to the

INV. B position.
If the photodiode has its own current to voltage converting amplifier,

then it should be connected to the input labeled ALT. The switch between the

inputs labeled A and ALT should be set toward the input being used as indicated by the arrow. The ALT input bypasses the amplifier in the A channel.

In any case, the output voltage of the detector package connected to the ATL

input must be limited to less than 10 volts in order to prevent saturation of

the operational amplifiers used as buffers in this channel. It should be

noted that the output voltages of channels A and B must be maintained at

values less than 1U volts and greater than U.b volts at all times in order to

prevent saturation of operational amplifiers and nonlinear effects in the

ratioing circuit. Channel B is similar to channel A with the following

exception. Channel B does not have a switch allowing the stage of amplification to be bypassed. It does, however, allow the output of the amplifier in

channel B to be inverted as mentioned above.

BIAS SUPPLIES . The MARBLE contains two adjustable power supplies which

can provide up to approximately 60 volts of DC bias for the detectors. As

indicated in figure 2a, the positive and negative connections to the bias

supplies are to the center terminals of the BNC connectors, thus floating the

supplies. Bias voltage is applied to a diode in channel A by connecting two

coaxial cables from the +A and -A BNC connectors to the A and OP A BNC con- nectors located just below the gain control for the channel. If no bias is

required, the A and OP A BNC inputs must be connected together by a short

coaxial cable. The same holds true for the B channel. A detector connected

to the ALT input cannot be biased.

Great care should be exercised in biasing a photodiode. The correct

polarity must be determined for each detector. Since the saturation reverse

bias is wavelength and power density dependent, it should be determined for

the wavelength of operation and the power level being used. See references 4

and b.

The correct polarity can be checked in two ways. Figures 3c and 3d show

the usual connections for photodiodes which require a reverse bias. Whether

it is a single photodiode such as the UV-100 or a multiple array like the QED100, the anode should be connected to the shell of the BNC connector. This

can be determined with an ohmmeter in the same manner that any diode is checked for forward current flow. (The arrow in the diode symbol indicated the

direction of positive current flow). If the anode of the photodiode is connected to the shell of its BNC then the bias supply connections described

below will be correct. The following method used the MARBLE and essentially

amounts to the same procedure. This method serves as a check on the ohmmeter

approach. With the MARBLE turned off, connect a photodiode to the A input at

the bottom of the MARBLE and position the switch to the left. Connect the A

bias supply outputs as follows. The +A output to the amplifier "bias" A input

and the -A output to the amplifier "bias" OP A input. The amplifier bias inputs are located immediately below the GAIN and ROLLOFF controls. This should

be the correct arrangement if the photodiode is wired as shown in figures 2b,

3c, and 3d. MAKE SURE that the bias voltage control is turned all the way

counter clockwise. The bias supply meter should read ZERO volts. Set the

output control to the A output position. The output DVM is read for this

procedure. With no light impinging on the photodiode, turn on the MARBLE and

slowly turn up the bias voltage. If the photodiode is in the circuit correctly, there will be very little indication on the meter as the bias voltage

is increased. If the photodiode is in the circuit incorrectly, the indication
on the output meter will rise rapidly. STOP immediately! This situation is

corrected by interchanging the +A and -A connections at the bias supply. A

rapid increase in the output voltage as the photodiode is biased would indicate that it was forward biased. Continued increase of the bias voltage

may destroy the device. The polarity of a photodiode connected to channel B can be checked in an analogous way.

The proper level of bias must be determined for each wavelength at which

the photodiode is to be used. The correct bias level is found by plotting the

output of the photodiode with light on its active surface minus the output of

the photodiode with its surface covered (dark current output) as a function of

reverse bias voltage. The voltage at or slightly greater than the saturation

voltage is the correct setting. The optical set up is shown in figure 3a and

will be discussed later in more detail. In order to obtain precise measurements with an unstable radiation source, the output of channel A should be

ratioed with the output of a stable monitor detector placed in a reference

beam as shown in figure 3a and fed through channel B. The output control

should be set in the A/B position. The best way to make the series of mea- surements is to take several at each bias voltage and plot their average. A

specific example will be shown later.

A CAUTION . In order to bias the detectors, it is necessary to apply the

bias voltage to the shield of the coax connecting the photodiode to the

MARBLE. .It is therefore possible to come into contact with as much as plus or

minus 60 VDC relative to ground potential! This is not a health hazard as would be the case with the same AC voltage, unless it causes some accident

because of the response to the unexpected very mild shock. One should test

his or her reaction to the shock so as to eliminate the surprise.

2. OPTICAL ARRANGEMENT .

A typical optical arrangement using a laser is shown in figure 3a. Light

from a helium-neon laser is spatially filtered to remove optical noise and

then split into two beams. One beam goes to a monitor detector connected to

channel B and the other to the standard or test detector which is connected to

channel A. In this arrangement, the standard and test detectors are alternately placed in the second beam. The output signals of the standard or test

detectors are ratioed with the monitor detector. This approach helps to eliminate source drift and electronic noise. The optical set up in figure 3a

using the QED-100 is practical only in cases employing an optical beam which

is well collimated and of small diameter. This is the result of the way in

which the four detectors used in the QED-100 are arranged. The geometry is

such that the device will not accept a beam having angular dimension greater

than 4.2 by 5.9 degrees. As pointed out in reference 3, the QED-100 is nearly

100% quantum efficient. (A photon-to-electron conversion efficiency of 0.999

plus or minus 0.002 over the 400 to 700 nm wavelength region has been demonstrated.) The QED-100 requires careful optical alignment and proper biasing

to achieve this level of accuracy.

For uncoil imated beams from monochromators or optical systems utilizing

narrow band pass filters, the refelectometer using a UV-100 described in ref- erence b provides good results. Refer to figure 4. Use of this detector

again requires proper biasing and a self-calibration procedure to achieve

comparable results. The self-calibration procedure consists in determining
the reflectance of the front surface of the photodiode as a function of wavelength.

III. EXAMPLES

In this section, examples of the use of the MARBLE will be described.

Data taken and the results of their analysis will be presented. The following

applications are discussed.

1. The quantum efficiency of a QED-100 is compared with that of a selfcalibrated UV-4448 using the radiation from a 632.82 nm HeNe laser.

2. Self-calibration of a windowless UV-100 inversion layer photodiode

with 632.82 nm radiation from a HeNe laser and from a low resolution

monochromator.

3. The self-calibrated UV-100 radiometer above is compared with the

self-calibrated UV-444B used in the first example.

1. INTERCOMPARISON OF A QED-100 WITH A SELF -CALIBRATED UV-444B .

The QED-100 and the UV-444B with its integral amplifier are set up as shown in figure 3a. The monitor detector is another UV-444B without an integral amplifier. All windows have been removed from the photodiodes. The

"RATIO OUT" BNC connector of the MARBLE was connected to the input of a HP3456A DVM. On the order of 100 readings were taken automatically and then

sent to an HP9836 computer. The average and standard deviation were than

determined by the HP9836 computer.

The response of the previously self-calibrated UV-444B detector is

R(632.99 nm) = 0.46060 A/W with a standard deviation of 0.00099 A/W. (Note

that the wavelength has been converted to its vacuum value). The absolute

spectral response R(X) for the UV-444B silicon photodiode is given in equation

(1 ). See reference 1.

R(X) = [l-p(X)][R

N (X)/R

+(X)]e(X)-X/K (1)

X = 0.63299 ym (in this example)

K = 1.23985 ym.W/A

Since the photodiode is used with its own amplifier, a correction needs

to be made to the voltage measurements for the current to voltage conversion

factor, G. In this case G = 10,012.6 V/A with a standard deviation of

0.2 V/A. A properly reversed biased QED-100 (see reference 3) has an external

quantum efficiency of 0.999 with an uncertainty of 0.002 over the visible

spectrum from 400 to 700 nm. The external quantum efficiency of such a photodetector is defined by equation (2).

Q = I«h«c/U'X-e«n»(X)] (2)

where h, c and e are the usual fundamental physical constants. n(X) is the

index of refraction as a function of wavelength, <j> is the light intensity in

watts and I is the net photocurrent. The relationship between absolute spec-
tral response and the external quantum efficiency of a photodetector is given

below.

R(X) = A-Q/K (3)

The two detectors, QEO-100 and UV-444B were alternately placed in the laser

beam which had an intensity of less than 1 mW. The gain of channel A was

adjusted to be comparable to the gain of the amplifier in the UV-444B package

(10,000 V/A). The ratioed outputs (with the monitor in channel B) of the two

detectors are given below with their respective dark currents in Table I.

TABLE I

Voltage response of QED-100 and UV-444B

photodiodes with constant light intensity.

QEO (QED-100) TEST (UV-4448)

Voltage (A/B) -1.4122 -1.2682

Voltage (A/B) (dark) 0.0016 -0.0014

V(QED) = -1.4106 V(TEST) = -1.2696

V(TEST) = -1.2680 (corr.)

V(TEST) must be divided by 1.00126 since the gain of the amplifier used with

the UV-444B is not exactly 10,000. The external quantum efficiency of the

UV-444B is determined by direct comparison with the known external quantum

efficiency of the QED-100. The ratios of the external quantum efficiencies of

the two photodiodes are in direct proportion to the measured voltage responses

when subjected to the same amount of radiation. Solving equation (4) below

and substituting into (3) above yields equation (5).

Q(QED)/Q(TEST) = V (QED) /V(TEST) (6)

R(TEST) = A.Q(TEST)/K = A-Q(QED) [V(TEST) /V(QED) ]/K (5)

= 0.63299 ym • A *0. 999*1 .2680V/ (1 .23985 ym.W*l .4106V)

= 0.4685 A/W

The value obtained from self-calibration on the UV-444B is 0.4606 A/W.

Comparison with the value obtained above yields a difference of 0.46%. The

standard deviations for the voltage measurements were of the order of

0.002 V.

2. SELF -CALIBRATION OF THE UV-100 WITH THE NBS REFLECTOMETER .

The self-calibration of the UV-100 induced junction (inversion layer)

photodiode based on in-situ reflectance measurements is completely described

in reference 5. All that is required for self-calibration of a proper reversed biased inversion layer photodiode is the determination of the reflectance

of the photodiode's front surface as function of wavelength. In this example,
an UV-100 is self-calibrated with 632.82 nm radiation from a HeNe laser and

from a low resolution (2 nm bandwidth) monochromator. Figures 4 and 5 show

the optical layout. The voltage response of the photodiode in the three

positions shown for the reflectometer are given below in equaiton (6-8)

respectively. The constant C takes into account amplifier current to voltage

agai n.

V(l) = C.(1-pW, (6)

V(2) = 0(l-p).(Hpp M

).<j>, (7)

V(3) = CpM .(l-p)i, (8)

where 4> is the incident light intensity, p is the reflectance of the surface

of the photodiode and p^ is the reflectance of the mirror M. The reflectance

of the photodiode's front surface is found by combining the three equations

above. The resulting expression is given in equation (9).

P = (V(2)-V(l))/V(3) (9)

The details of the calibration procedure consist in the following steps.

The correct bias voltage was determined for the level of light intensity i n- dicient on the detector. The response of the photodiode was measured as a function of reverse bias over the range from to 14 volts. The table below

shows a typical set of measurements for this procedure.

TABLE II

Response of a UV-100 verses applied reverse bias voltage.

V(BIAS) V(SIG) V(DARK) R (V(SIG)-V(DARK) )

-1.6731 -0.01171 -1.6624

4 -1.9646 -0.2643 -1.7003

8 -2.1520 -0.4413 -1.7107

10 -2.2689 -0.5612 -1.7077

12, -2.3846 -0.6741 -1.7105

14 -2.4301 -0.7200 -1.7101

From Table II, the photodiode appears to be saturated at 8 volts. With

the photodiode biased at 8 volts, measurements of the voltage response was

made for the reflectometer in each of the three positions shown in figures 4

and 5. The voltage measurements are shown in Table III below. Since in these

measurements, the light was not incident normally on the detector, a correction factor must be determined. It is clear that this factor is the ratio of

the response at normal incidence to the response at the angle used in measurement of V(l). These data are also given below. Note, in order to use these

detectors correctly in radiometric applications, they should always be set up

with the light incident normal to the surface of the photodiode.
TABLE III

Voltage response of UV-100 for incident light

from a 632.82 nm HeNe laser and from an H-20

monochromator with 0.5 mm slits set at 632.82 nm.

MEASUREMENTS LASER MONOCHROMATOR

V(l) (light)

V(l) (dark)

-1.3397

-0.0161

(0.00018)

(0.00002)

-2.1350 1 -0.43b5 ( 0.0048)

0.0027)

V(l) -1.3236 -1.6995

V(2) (light)

V(2) (dark)

-1.5290

-0.0160

(0.00026)

(0.00002)

-2.3753

-0.4388 (

;o.ooo9)

0.0009)

V(2) -1.5130 -1.9364

V(3) (light)

V(3) (dark)

-1.2110

-0.0160

(0.00015)

(0.00001)

-1.9652

-0.4392 (

;o.ooo8)

0.0011)

V(3) -1.1950 -1.5260

V(normal) (light)

V(normal) (dark)

-1.3566

-0.0177

(0.00009)

(0.00002)

-2.1621

-0.4517 ( ;0.0019)

0.0010)

V(normal

)

-1.3389 -1.7104

V(10 degrees)

V(10 degrees)

(light)

(dark)

-1.3465

-0.0175

(0.00019)

(0.00001).

-2.1357

-0.4377 1;o.ooi5)

,0.0020)

V ( 1 degrees) -1.3290 -1.6980

V(normal)/V(10 de grees) 1.0074 1.0073

Having determined the reflectance at the wavelength of interest, the

external quantum efficiency is given by equation (10).

q(X) = (l-p(X)) = (l-[V(2)-V(l)]/V(3))(V(normal)/V(angle)) (10)

The values for the laser and monochromator respectively are 0.8478 and

0.8510. The difference between the two determinations of is 0.38%. In

order to use the UV-100 at other wavelengths, either measurements of the re- flectance at those wavelengths must be carried out or some method of

theoretically predicting the reflectance must be used. Several additional

interpolation scheme such as described in reference 2 can be used. An alternative method suggested by Geist, makes use of a computer program which

predicts the reflectance based on the complex index of refraction of silicon

and the results of a single measurement of the reflectance at some wavelength

within the spectrum of interest.
3. INTERCQMPARISQN OF A UV-lOO WITH A SELF-CALIBRATED UV-444B .

In this example, the absolute spectral response of the UV-444B which was

i ntercompared with the QED-100 in example 1 is now determined again by intercomparing with the UV-100 in example 2. Both devices were alternately placed

into the focused beam of the monochromator so that the optical axis of the

optical system was normal to the surface of the photodiodes. See figure 6.

Voltage response readings were taken both with the light impinging on the

photodiodes and with the beam blocked. TABLE IV displays the data for these

measurements.

TABLE IV

Voltage response of UV-444B and UV-100 with

incident light from an H-20 monochromator

with 0.5 mm slits set to 632.82 nm.

MEASUREMENT UV-444B UV-100

V(light)

V(dark)

V(device)

1.6167

0.2003

1.8170*

(0.00012)

(0.00009)

-2.3054

-0.5976

-1.7078

(0.00067)

(0.00090)

*This voltage must be divided by the amplifier gain factor discussed in

example 1. The corrected value for V(device) is 1.8147

The external quantum efficiency of the UV-100 from example 2 is 0.8510

and the absolute spectral response of the UV-444B is 0.4606 A/W determined by

an independent measurement. The external quantum efficiency of the UV-444B is

determined using equation (4) and the above data. The absolute spectral re- sponse is calculated using equation (5). The absolute spectral response thus

determined is 0.4617 A/W. The difference between this value and the one

previously determined is 0.23%. This is an impressive result considering that

both values were determined completely independently by different methods and

using light sources with quite different bandwidths.
APPENDIX

This appendix provides more detail about the electronics aspects of the

MARBLE for the interested and knowledgeable user. A familiarity with analog

electronics, especially operational amplifiers and analog dividers, is

assumed.

Both input channels to the MARBLE are identical with the exception of the

inverter stage in channel B. The input stage consists of an Analog Devices

52K precison FET input operational amplifier operated in the transimpedance

mode (current to voltage conversion). The 52K was chosen for its overall

excellent operational characteristics and specifications. The feedback

network consists of a Caddock Electronics 1776-6-1 divider network. This is a laser-trimmed, thick film component that is custom-made to NBS specifications

for very high accuracy and low temperature coefficient. The feedback network

includes the appropriate parallel capacitors to set the R C time constant to a value which will limit the bandwidth to less than 10 kHz for each range.

The output of the two 52K amplifiers are each buffered by high impedance

buffer amplifiers in a follower configuration in order to minimize the effects

of errors due to the load arising from reduction of open loop again.

There is a relative error in the current-to-voltage conversion-ratio of

the op-amp that is given by Rf/(A»Rd), where Rf is the feedback resistance, Rd

is the dynamic impedence of the detector at the bias voltage established by

the operational amplifier input offset voltage, and A is the open loop gain of

the op-amp. With a high impedance detector this error is usually negligible.

But the fact that the open loop gain is not infinite allows the input to

depart from virtual ground. With low impedance detectors or intermediate

impedance detectors mounted in such a way that the op-amp offsets voltage

forward biases them, non-negligible errors can be encountered.

It has been observed when using silicon cells in the configuration

described in this manual, that connecting the diffusion to the active

(inverting) input and the bulk to the ground (non-inverting) input causes a reduction in electrical noise pickup by the detector.

The analog divider is a Burr-Brown 4291k. It was chosen for its high

accuracy and wide dynamic range (as analogy divider circuits go). Still it is

not really satisfactory for this application, because it provides barely

enough accuracy when properly nulled, and it loses accuracy as the null drifts

during usage. Unfortunately, there were no better divide circuits available

at the time that the MARBLE was designed, and the newer devices may not offer

enough improved performance to warrent redesign. Probably the best approach

to improved performance and reliability would be to replace the analog divide

circuit by a digital divide circuit including the associated A to D converters.

The two buffer amplifiers feeding the divider circuit maintain a constant

source impedance to the divide circuit as required for highest accuracy by the

manufacturer. The purpose of the filter on the output of the divider is to remove artifacts created by slightly varying outputs of the divider caused by

small periodical variations in the inputs.

10
REFERENCES

1. Silicon photodiode absolute spectral response self-calibration, E. F.

Zalewski and J. Geist, Appl. Opt. 19, 1214 (1980).

2. Spectral response self-calibration and interpolation of silicon photodiodes, J. Geist, E. F. Zalewski and A. R. Schaefer, Appl. Opt. 19, 3795

(1980).

3. Silicon photodiode device with 100% external quantum efficiency Edward F.

Zalewski and C. Richard Duda, Appl. Opt. 22, 2867 (1983).

4. Silicon detector nonlinearity and related effects, A. R. Schaefer, E. F.

Zalewski and Jon Geist, Appl. Opt. 22, 1232 (1983).

5. Induced junction (inversion layer) photodiodes self-calibration , R. L.

Booker and J. Geist, Appl. Opt. 23, 1940 (1984)

6. The mention of specific commercial products does not imply endorsement

by NBS or by Denison University, nor that the products mentioned are

necessarily the best ones suited for the applications described.

11
Gain Rolloff A A

o o

A OP

A

0_®_O

A " **ALT

Gain Rolloff B B

o o

B OP

B

B ® INV B

O

B

Output

o

SUPPLY A 0-60V °

N

SUPPLY B 0-60V

|

60

A

+ A -A

o

MARBLE

60

B

i + B -B

B

A Qa,B

o

RATIO OUT

O O

\ OUT B OU1

Key

Q BNC Connector

Control

<g> Swith

Fig. 1. MARBLE Front Panel Layout

12
2a

2b

BNC

I 1 A

Gain

Network

tr t^> ©—©—r~t^

BNC BNC -=l OP A

ALT

A OP A

A

BNC

A ALTr

Gain

Network

B

©

6 0-

BNC BNC =L OP B

B OP

B

T>

o A/B OUT

Supply A Supply B

B OUT

0-60VDC 0-60VDC SGhrQ

Fig. 2a. Simplified schematic diagram for the MARBLE

Fig. 2b. Schematic diagram of detector

13
HeNe

Laser

3a

^

L 1 , L 2 —OiO— -7^

Marble

Front Panel

6 6 £~& Ratio Out

A OP B OP O

A B AOUTBOUT+A.. ,,-A +B -B

A ? ?ALT?B • • * * ° •

MON

DET

1

QED-100

EZZF

v T

Test Detector

3c

i « i

» i -J BNC

3d —vw^—

^Ir^^ K - -4=

Fig. 3a. Optical arrangement and electrical connections used for intercomparison

of a test detector with a QED-100

Fig. 3b. Optical layout inside a QED-100

Fig. 3c. Electrical configuration for a QED-100

Fig. 3d. Typical bias connection to a UV-100 or QED-100 photodiode

14
4a *<S>-

Monochromator

4b

Monochromator

4c *<3D>

Monochromator

UV-444B

Monitor

Mirror

\

Beam Splitter

juf-IOOPHOTODIODE,

NBS Reflectometer

Monitor

NBS Reflectometer

Mirror

jUy-JOOPHOJODIODE

Beam Splitter

NBS Reflectometer

uv-loo photodiooe"!

Beam Splitter

Fig. 4a. NBS Reflectometer in position 1

Fig. 4b. NBS Reflectometer in position 2

Fig. 4c. NBS Reflectometer in position 3

15
Laser

(a)

fl>T_

To Channel B

of Marble

e

UV-444B

Monitor

*

Beam Splitter

NBS Reflectometer

Mirror

tj

UV-100 Photodiode

to Channel A of Marble

Laser

^

Monitor

*

NBS Reflectometer

I

| Mirror

I

s tzz^J

UV-100 Photodiode

(b) Beam Splitter

Laser

(c)

^

Monitor

^

NBS Reflectometer

I 1 UV-100

Beam Splitter

Fig. 5a. NBS Reflectometer in position 1

Fig. 5b. NBS Reflectometer in position 2

Fig. 5c. NBS Reflectometer in position 3

16
Monitor

Detector

Source Order

Blocking

Filter

Off-Axis

Parabolic

Mirror

Monochromator Beam

Splitter

Photodiode

Position

Fig. 6. Optical arrangement for intercomparison of UV-100

and UV-444 B photodiodes

17
NBS-114A (REV. 2-8C) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS/TN-1216

2. Performing Organ. Report No. 3. Publication Date

Sept. 1985

4. TITLE AND SUBTITLE

Radiometric Calibration Procedures Using the NBS MARBLE Electronics Package

5. AUTHOR(S)

M.E. Mickelson, L.E. Larson, and Joel Fowler

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

Denison University National Bureau of Standards

Granville, OH 43023 U.S. Department of Commerce

Gaithersburg, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

National Bureau of Standards

U.S. Department of Commerce

Gaithersburg, MD 20899

10. SUPPLEMENTARY NOTES

"2 Document describes a computer program; SF-185, FIPS Software Summary, is attached.

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

bibliography or literature survey, mention it here)

The NBS MARBLE Electronics Package, which is designed to support calibration

of radiometric detectors, including self-calibration of Si photodiodes, is

described.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Current-to-voltage converters; detectors, MARBLE; photodiodes; radiometry;

self-calibration' transimpedence amplifiers.

13. AVAILABILITY

[~xl Unlimited

| | For Official Distribution. Do Not Release to NTIS

f x] Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C

20402.

J Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

20

15. Price

USCOMM-DC 6043-P80
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