Proceedings Volume 0499

Optical Radiation Measurements

Aaron A. Sanders
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Proceedings Volume 0499

Optical Radiation Measurements

Aaron A. Sanders
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Volume Details

Date Published: 8 February 1985
Contents: 1 Sessions, 17 Papers, 0 Presentations
Conference: 28th Annual Technical Symposium 1984
Volume Number: 0499

Table of Contents

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Table of Contents

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Design And Fabrication Of A Self-Calibrating Germanium Photodiode
R. J. Schwartz, D. L. Huang
The design of a self-calibrating germanium photo-diode with an internal quantum efficiency in excess of 980 in the wavelength range from .4 to 1.5 μm is described. The fabrication of these photodiodes by ion implantation is discussed.
Near-Infrared Limitations To Silicon Photodetector Self-Calibration
James M. Palmer
Recent improvements in silicon photodiode fabrication technology and our understanding of their properties have led to NBS development of a self-calibration technique yielding errors less than 0.1% in spectral responsivity over the spectral range 400-800nm. The wavelength range beyond 800nm has not been fully explored, most likely because of the lack of convenient laser sources in this region. We have successfully used conventional sources to study the response of silicon photodiodes in this region. Several types of photodiode (conventional, inversion layer and YAG) have been characterized to determine the longest wavelength feasible for self-calibration. Comparisons of empirical results were made with device theory. The limiting factors for metallurgical-junction diodes are the ability to deplete the bulk region with sufficient reverse bias prior to the onset of breakdown and absorption at the rear surface. The maximum wavelength appears to be about 920nm.
Intercomparison Between Independent Irradiance Scales Based On Silicon Photodiode Physics, Gold Point Blackbody Radiation, And Synchrotron Radiation
A. R. Schaefer, R. D. Saunders, L. R. Hughey
A radiometer composed of a silicon photodiode, interference filter, and integrating sphere was characterized and calibrated against an absolute silicon detector standard at 600 nm using a CW dye laser. This radiometer was then used to measure the irradiance at 600 nm from spectral irradiance lamps calibrated against a gold point blackbody, and also the irradiance from the NBS electron storage ring, SURF II. These results were intercompared with the independently calculated irradiances from these two sources, with overall agreement of better than one percent. Various aspects of the measurements are discussed.
The Use Of Field Radiometers In Reflectance Factor And Atmospheric Measurements
Che Nianzeng, R. D. Jackson, A. L. Phillips, et al.
This paper discusses field radiometer methods for measuring (1) the reflectance factor of a surface, (2) the ratio of atmospherically scattered to direct irradiance (s/d) at the ground, and (3) the atmospheric extinction coefficient. Calculations show that, under hazy or cloudy conditions, reflectance factor measurements of an unknown surface made in the field with reference to a white panel, both surfaces having nonlambertian characteristics, can differ by up to 6% from laboratory measurements of the unknown surface. This applies to surfaces having reflectance factors greater than 0.05. The error can be reduced to 0.4% if the direct solar component alone is used for the determination. Measurements of surfaces with reflectance factors from 0.09 to 0.4 showed errors of 10% and 2% respec-tively when the total radiance of the target was ratioed to that of the reference panel. These errors can be reduced to 4% and less than 1% respectively when the direct solar components are ratioed. The mid-infrared (mid-IR) bands of a commonly used field radiometer showed a high out-of-field response that gave rise to measurement errors on the order of 20%. The effect of the reflectance of other surfaces in the neighborhood of the target is demonstrated by determining the ratio of shaded to direct irradiances. Agricultural scenes can show changes of about 5% in the red and 20% in the near IR. A commonly available field radiometer, in conjunction with a reference panel, can be used reliably to determine the atmospheric extinction coefficients in broad wavelength intervals.
Detectors For Picosecond Optical Power Measurements
R. J. Phelan Jr., D. R. Larson, N. V. Frederick, et al.
There are many features in addition to time resolution that are desirable for a picosecond optical power measurement system. An interdigitated contact, Schottky barrier silicon photodiode coupled to an electro-optic sampler exhibits a rise time better than 22 picoseconds, a quantum efficiency greater than 30%, a uniform responsivity over its receiving aperture, and a usable spectral response to beyond 2 micrometers.
Radiometric Characterization Methods For Infrared Countermeasures Systems
John L. Grangaard, Charles Link, Gerald Spade, et al.
Infrared countermeasures systems used to protect aircraft must produce a powerful infrared radiation pattern spread over a wide range of angles, and with a complicated modulation in time. The measurement of this radiation with respect to the parameters of time, angle, and wavelength is described. The radiometer measurement equation is examined to see what approximations are necessary for a solution in the terms desired. The measurement apparatus is described along with how it satisfies the measurement equation approximations. A two-step procedure was required for measurement of the spectral radiant intensity. First, the relative spectral output was determined using a monochromator, and then a scaling factor is determined for converting this to absolute units. An electrically activated shutter was used for the radiometer reference rather than the usual chopper. The detector was used in the DC coupled mode and a digital oscilloscope was used under computer control to acquire data. The results obtained were intended mainly for setting parameters for simulation studies of the effectiveness of these countermeasures systems. The manu-facturers of these systems also have measurement facilities in their own plants. A comparison is made between these different techniques, discussing the different approximations required and the advantages or disadvantages of these different methods.
Beam Profiling In Gigawatt 1064-Nm Lasers Used In Research On Optical Materials At Livermore
D. Milan, S. E. Peluso
Laser pulses with intensities ranging from 109-1011 watts/cm? are routinely used at Livermore to measure nonlinear properties of optical materials. The energy in each of these pulses is measured with an absorbing glass calorimeter. Both vidicon cameras and photographic emulsions are used to record the fluence distribution in laser beams. Pulse waveforms are recorded by a streak camera, or by a combination of a photodiode and an oscilloscope. This paper describes our procedures for using this data to determine the fluence and intensity for short duration laser pulses.
Beam Profile Measurements For Target Designators
J. D. Frank
I.A review of automated systems for far field measurements There have been several efforts at Hughes Aircraft Company to improve on the tedious, slow manual methods of measuring pulsed lasers for rangefinders particularly beam divergence which is done by varying aperture sizes and positions in the laser beam path. The manual method of measuring divergence is somewhat easier to perform if the shot to shot laser energy and wander changes are minimized using a ratiometer. Three instruments have been developed and are being used. They are referred to by the acronyms ALIMS, LIPS, and ALTS.
Beam And Spot Profile Measurement Methods For Optical Storage Systems
Scott D. Wilson, Timothy Reed
Convenient measurements of the spatial dimensions of propagating laser beams and submicron focused spots are described, applicable to optical storage systems. Methods for determining accuracy are discussed, together with error analyses. Examples of typical beam and focused spot measurements are presented including Gaussian, non-Gaussian and aberrated spots.
Using Optical Processing To Find The Beam Profile Of A Laser Pulse (Theory)
Eric G. Johnson Jr.
This paper looks at a particular form of optical processing, namely a form of cross-correlation, and demonstrates how the method measures certain beam profile features of a laser pulse. Beam profile is defined to mean a description of the electromagnetic field of a laser pulse in space and time. In this paper, I represent the laser pulse as a complete set of orthogonal modes and show that an appropriate spatial filter and a measurement system can provide information about the beam profile of the laser in terms of the individual eigenfunctions of this representation. First I trace what happens when a laser pulse is modified by the spatial filter. I then do a specific example which looks at the TEMOO laser beam pulse with beam tilt, beam curvature, beam width, and beam shift to show that these effects produce higher order Hermite modes in the measurement system. The spatial filter modifies the electric field distribution in the focal plane such that at known spatial locations, the magnitude of the intensity is proportional to the pulse power or energy in particular Hermite modes. Since the size of these locations is infinitesimal (without getting errors from the electromagnetic fields from other modes), I demonstrate the effect and errors associated with using finite size detectors for measuring the magnitude of the intensity at these locations. The purpose of this paper is to demonstrate the concept of using optical processing to measure laser beam profile. Hermite modes are used because they are similar to many actual laser beam profiles and because they can be simply expressed in analytical form which is convenient for a theoretical presentation. In practice it is probably desirable to choose a set of modes for a basis which more closely represents the actual characteristics of the laser beam. This choice of course determines the properties of the spatial filter. Subject to reasonable assumptions shown in the paper, it is possible to use the optical unit with nine detectors to measure the beam profile properties of a laser beam. The detectors, each with high speed electronics can be chosen to provide measurement speeds in the nanosecond range. Two of the detectors for each axis provide primary information about beam tilt and beam shift, two detectors for each axis give secondary information about beam shift and beam width, and one detector gives the power in the primary mode (the TEMOO mode for the example in this paper). Five detectors are located at selected points in the focal plane of the lens and four are located just before the spatial filter. Detectors of five micrometer diameter give a 23 percent ratio of desired to undesired signal and implies a lower limit in beam control of +/- 30 microradians. Some discussion is presented about reducing these values. The use of nine detectors applies to a single mode. More detectors are required if the measurement is to apply to multimode lasers. Also one must be careful to choose the most efficient basis for the particular measurement of interest. The optimum basis would be sensitive to the key features of interest and suppress the features of no interest.
Method For Monitoring The Change In Relative Transmittance Of Small-Spot Laser-Damaged Optics At 10.6 pm
J. B. Franck, J. O. Porteus, S. C. Seitel, et al.
We report the results of an effort to correlate visible small-spot laser damage with changes in the transmittance of optical components at 10.6 pm. The test source used was a pulsed CO2 TEA laser, operating in the lowest order spatial mode and producing plane-polarized, gain-switched pulses of 0.1 is nominal length.
Pyroelectric Matrix Arrays For Laser Beam Imaging
Carlos B. Roundy
This paper gives an overview of why beam profile measurements are important in laser research. We also describe new pyroelectric matrix detector arrays, their outputs and displays, and how they make beam profile measurements easy. Pyroelectric detector fabrication, assembly, and performance are also explained.
An Enclosed Laser Calibration Standard
Thomas E. Adams, M. L. Fecteau
We have designed, evaluated and calibrated an enclosed, safety-interlocked laser calibration standard for use in US Army Secondary Reference Calibration Laboratories. This Laser Test Set Calibrator (LTSC) represents the Army's first-generation field laser calibration standard. Twelve LTSC's are now being fielded world-wide. The main requirement on the LTSC is to provide calibration support for the Test Set (TS3620) which, in turn, is a GO/NO GO tester of the Hand-Held Laser Rangefinder (AN/GVS-5). However, we believe it's design is flexible enough to accommodate the calibration of other laser test, measurement and diagnostic equipment (TMDE) provided that single-shot capability is adequate to perform the task. In this paper we describe the salient aspects and calibration requirements of the AN/GVS-5 Rangefinder and the Test Set which drove the basic LTSC design. Also, we detail our evaluation and calibration of the LTSC, in particular, the LTSC system standards. We conclude with a review of our error analysis from which uncertainties were assigned to the LTSC calibration functions.
Infrared Calibration: Very Low Signals May Have Very Large Errors
Frederick O. Bartell
While infrared signals at the levels of watts per square centimeter and milliwatts per square centimeter are commonly measured and calibrated with accuracies of a few percent and less, the measurement and calibration of infrared signals with values of nanowatts per square centimeter, picowatts per square centimeter and lower values may have errors of 100% or more. These large errors for low signals involve such problems as chopper blades, baffle systems, stay radiation, detector optics, attenuators, spectral mismatch, experiment planning and blunders.
Spectrophotometric Measurement Of Thin Film Thickness In The 90 To 10,000 Nanometer Region
Fred Alan Wolf
We report here a new measurement technique (patents pending), using a modified, commercially available spectroradiometer and software program which instantly and directly measures thin film thicknesses in the range from 90 nm (3.5 microinches) up to as much as 10,000 nm (394 pin). This measurement technique is applicable to "flying height" determination and other thin film applications. The computer software algorithm determines the thin film thickness directly (within seconds) from the broadband whitelight interference spectra. The algorithm uses the theoretical physics formula for thin film interference and uses the measured intensities and wavelengths to solve for the thickness directly. Because of the "closeness to theory" it is not necessary to absolute spectral-radiance-calibrate the spectroradiometer. Since the algorithm predicts the theoretical (perfect) energy spectrum, it compares its distance estimate to the theoretical spectrum, thus providing an estimate of "goodness of fit" of the thickness measurement.
A Calorimeter For Measuring 1-15 KJ Laser Pulses
P. A. Simpson, Eric G. Johnson Jr.
Two calorimeters for measuring high peak power laser pulses have been constructed by the NBS and delivered to the Newark Air Force Station, Newark, Ohio. These calorimeters are designed to measure pulses having intensities great enough to damage the volume absorbing material in normal calorimeters. In these new calorimeters the volume absorbing material is already fragmented and flowing dry N2 gas is used to extract the temperature rise information. Pulse energy can be in the range 1 to 15 kJ. Wavelength range is from the it to uv by employing various volume absorbing materials.
Results Of Optical Radiation Measurements Requirements Session
Richard G. Miller, Aaron A. Sanders, Robert L. Hinebaugh, et al.
This paper reviews the results of the Electro-Optics Measurements Requirements Study of the National Conference of Standards Laboratories (NCSL). It shows that the results were mostly inconclusive and was due to dissemination of the questionaires. It also reports the results of the panel discussion on Standards Requirements for Radiation Measurements conducted at session 4 of the Optical Radiation Measurements Conference of the SPIE Sympo-sium, San Diego, August 1984. I. Results of National Conference of Standards Laboratories (NCSL) Electro-Optics Measurement Requirements Study