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NASA SP-5973 (03)January 1976

TECHNOLOGY UTILIZATION

OPTICS AND LASERS

A COMPILATION

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

https://ntrs.nasa.gov/search.jsp?R=19760013377 2020-03-14T17:01:13+00:00Z

Foreword

The National Aeronautics and Space Administration has established a TechnologyUtilization Program for the dissemination of information on technological developmentswhich have potential utility outside the aerospace community. By encouraging multipleapplication of the results of its research and development, NASA earns for the public anincreased return on the investment in aerospace research and development programs.

This document is one in a series intended to furnish such technological information.Divided into three sections, this Compilation presents a number of innovative devicesand techniques in optics and related fields. Section 1 covers advances in laser andholography technology. Section 2 contains several articles on spectroscopy and generaloptics, and Section 3 includes aew information in the area of photography.

Additional technical information on the innovations described herein can berequested by circling the appropriate number on the Reader Service Card included in thisCompilation,

The latest patent information available at the final preparation of this Compilationis presented on the page following the last article in the text. For those innovations onwhich NASA has decided not to apply for a patent, a Patent Statement is not included.Potential users of items described herein should consult the cognizant organization forupdated patent information at that time.

We appreciate comment by readers and welcome hearing about the relevance andutility of the information in this Compilation.

Technology Utilization OfficeNational Aeronautics and Space Administration

NOTICE •This document was prepared under the sponsorship of the National Aeronautics and SpaceAdministration. Neither the United States Government nor any person acting on behalf of the UnitedStates Government assumes any liability resulting from the use of the information contained in thisdocument, or warrants that such use will be free from privately owned rights.

For sale by the National Technical Information Service, Springfield, Virginia 22161

Contents

PageSECTION 1. LASER TECHNOLOGY

Reference-Beam Control of Holographic InterferometryFringe Patterns 1

Broadband Modulation-Index Meter 2Measurement of Relative Depth in Holographic Images 4Development of a Three-Dimensional Laser-Doppler System . . . 6Double Film-Plate Holography .'..'. . 7A Holographic Viewing System for Large Audiences 8Laser Beam Deflection Control: A Concept 9Sensitive Holographic Detection of Small Aerodynamic

Perturbations 10Three-Dimensional,Gas Turbulence Measurement With a

Laser-Doppler Velocimeter System 11Holographic Testing With a Double Reference Beam . . 12Alignment Microscope for Rotating Laser Scanner ' . - . . ' ' 13A Laser Head for Simultaneous Optical Pumping of

Several Dye Lasers 14Laser System Detects Air Turbulence ' . . ' . ' 15Coplanarity Measurement Tool 16

SECTION 2. SPECTROSCOPY AND GENERAL OPTICS :

Improved Photographic-Film Recording by MultipleElectron Exposures 17

Transmission of Optical Frequencies With Minimal Losses 18Membrane Light-Valve Computer Memory . . . 19Solid-State Television Camera Has No Imaging Tube 20Advances in High-Resolution X-Ray Photography 20Pinhole Collimator for Radiography ' 21Operation of AlkaH Vapor Lamps in Nonyacuum Environments 21Microscope Eyepiece for Concentricity Inspection 22Spectral Matching of Alkali-Metal Vapor Lamps Using

Total Fluorescence Measurements . . . . ' . ' . . . 23

SECTIONS. PHOTOGRAPHY AND FILM .,Rotary Solenoid Shutter 24Rotary-Inertia Damper and Stop-Plate Assembly 24Film-Calibration System for Cameras 25Automatic Focus Control for Facsimile Camera 26

PATENT INFORMATION 27

Section 1. Laser Technology

REFERENCE-BEAM CONTROL OF HOLOGRAPHIC INTERFEROMETRYFRINGE PATTERNS

Fringe-ControlMirror

LaserAdjustable

Fringe-Control

Lens

Laser-Beam Fringe-Control System

Fringe-pattern for a holographic interferometer isusually attained by manipulation of the illuminationbeam. In a new technique, the reference beam is usedto regulate the fringe, by means of mirrors andadjustable lenses.

The figure shows a typical table setup utilizing thereference beam for fringe control. The fringe-controlmirror is used to position the bull's-eye in the fringepattern, and the fringe-control lens is adjusted tocontrol the width of the fringes. The adjustments can bemade without affecting the critical-illumination setting

made in the object beam. Improved and more rapidadjustment is possible, because interaction is eliminatedfrom the object beam.

Source: F. H. Stuckenberg ofRockwell International Corp.

under contract toJohnson Space Center

(MSC-17788)

No further documentation is available.

OPTICS AND LASERS

BROADBAND MODULATION-INDEX METER

An automatic metering system supplies a real-timeindication of the modulation index associated withlaser beams. The technique is shown in the blockdiagram (Figure 1). The input for the meter is thesignal from the anode of a photomultiplier tube. Thedc and video-channel amplifiers separate and amplifythe ac and dc components. The video signal is appliedto the sampling gate, which is opened by short pulsesfrom the pulse generator. The repetition rate of thesampling pulses is determined by the voltage-controlledmultivibrator, with its frequency controlled by theintegrated low-frequency multivibrator output. Thesample amplifier amplifies the short-term, sample-and-hold output of the sampling gate.

The positive and negative peak levels of the splitsignal are derived separately by the two peak detectors.

A difference amplifier compares the two peak levelsand generates a bias feedback, which is used to keep thesampling bridge balanced. The peak-to-peak value of thevideo signal is derived at the output of the sumamplifier, which adds the outputs of the peak detectors.This signal is inverted and is applied to one input of theanalog divider. The other input is from the dc channelamplifier.

The output, of the de-channel amplifier is a voltageproportional to the output power of the laser; thisoutput is also used to drive a meter and/or a recorder.The output of the analog divider is a voltage proportionalto the modulation index; it also drives a meter and/ora recorder.

To Power-Level Indicator

FromPhotomult

TubeO <

To Modulation-Index Indicator

Zero Adjust .

> >

1 — »•

— »

DCAmplifier

tBackground

Null

VideoAmplifier

Low-Frequency

Multivibrator

AnalogP uivider

PulseGenerator

EP PInverter

I 1

SamplingBridgeGate

InternalNoise Null

SumAmplifier

tExternal

Noise Null

DifferenceAmplifier

SampleAmplifier

PositivePeak

Detector

PositivePeak

Detector

-^_

Bridge Bias Balance

Multivibrator

Figure 1. System Block Diagram

LASER TECHNOLOGY

P-P

avg

Figure 2. Amplitude Modulation

0 Volts DC

avg

P-P

Figure 3. Demodulated Signal

Figure 2 illustrates an amplitude-modulated signal.The modulation index (m) can be found from therelationship: m = E /2E . Figure 3 shows thedetected signal at the photomuftiplier anode. This is theinput to the system, from which the modulation indexis computed. The index meter allows unattended, real-time measurements for a wide range of modulationfrequencies and for wide variations in signal-power levels.

Source: G. B. Shelton and W. A. Hurd ofSperry Rand Corp.

under contract toMarshall Space Flight Center

(MFS-22740)

Circle 1 on Reader Service Card.

OPTICS AND LASERS

MEASUREMENT OF RELATIVE DEPTH IN HOLOGRAPHIC IMAGES

A double reference beam can be used to create adouble holographic image, from which relative depthmay be determined by taking measurements betweenthe identical points of the twin images. When thehologram is illuminated with light from two separatesources, with a known angle between the sources andone known distance in the recorded holographic image,it is possible to determine the distance of other pointsgeometrically, once their lateral translation is known.This method, as illustrated in Figure 1, is more accuratethan conventional stereoptic techniques.

The double image is recorded on a film plate, andthe depth analysis is made as described in Figures 2 and3. Two initial reference points such as 1 and 2 arechosen (!' and 2' are the same points in the secondimage). If these points are chosen so that the relativedepth (AL) of each is known, then a quantitative ratiomay be found for calculating other depth as follows:Distances Dj and D2 (Figure 2) are measured on thefilm. For a small angle a in a triange with side a oppositea and the two other sides b =c,

^ a (Xb — — esc —

2 2

Mirror

Virtual DoubleImage Created

at Positionof Original Test

Object

Film Holder

Figure 1. Double Reference Illumination

LASER TECHNOLOGY

In Figure 3, L, corresponds to b and a correspondsto the distance between spatial points 1 and 1', which isproportional to Dt on the film. Thus, when thisproportionality constant is known, the AL for any pointmay be calculated from measurements on the film.The proportionality constant may be found from aknown AL as follows:

D, aL! °c— esc—; and likewise

2 2 •

D2 aL2 oc — esc—; and

2 2

1 a(Li-L2) = AL12

a-(D,-D2) esc- or

ALr2 =C (D!-D2), where C is a constant.

Since ALi2 is known, C may be calculated, and therelative depth of other points may be found fromlateral measurements on the film plate.

ilm /FilmPlate

Figure 2. Measurement of Offset of Typical Points onDouble Virtual Image on the Film

lane of Film i 1

I

£

(

L

1

I I

,L

2

H-^

s

_•-

1

iI 2'

'*"" "**

«

-~.

.

L-

"*~

i

k

-a

AL and LDimensions ArePerpendicular tothe X-Y (Film)Plate

Figure 3. Spatial Relationship Showing How At Varies WithOffset of Double Images

If no reference AL is known, a series of offsetmeasurements, Dj, D2, D3, ..., may be made. Fromthese, relative depth. AL may be established fromratios such as:

AL12 D,-D2

AL.23 D,-D,

Source: F.'H. Stuckenberg ofRockwell International Corp.


(MSC-17632)


6 OPTICS AND LASERS

DEVELOPMENT OF A THREE-DIMENSIONAL LASER-DOPPLER SYSTEM

1 t*Transmitter/Receiver

Transmitter/Receiver

3-D Coaxial System (A bistatic system would have a separate transmitterand receiver at each station, thus requiring three additional components.)

A report is available on a system for measuringatmospheric-wind velocity and aircraft-trailing vortices,using a three-dimensional laser-doppler system. Three-dimensional measurements are an advance over the one-dimensional coaxial heterodyne system, that lacks thespecified resolution characteristics. Several such systemsare described and evaluated in the report.

A system using a CO2 laser as the source of illumina-tion measures the doppler shift of illuminated movingobjects. The scattering targets are the aerosols, con-tained in the atmosphere, that are excited and then arerelaxed to atmospheric velocity. This scattered energyis collected, heterodyned (combined with a portion ofthe incident radiation), and detected. The frequency ofthe detector output signal gives a measure of a com-ponent of the atmospheric velocity.

Another method described is fringe ahemometry, inwhich a laser generates a fringe pattern in the atmos-phere. Aerosols travel through the pattern and scatteran intensity-modulated signal. An analysis of the in-tensity modulation gives a measurement of the trans-verse wind velocity.

Doppler systems (see figure) are constructed in acoaxial configuration with common transmitting andreceiving optics as opposed to bistatic systems that usea separate transmitter and a separate receiver. Anotherapproach, using radar wavelengths to obtain threevelocity components from a single system by a conicalscan, has also been evaluated.

The evaluation of these and other systems indicatesthat the best methods are (A) electronic beam-sharpening

LASER TECHNOLOGY

coaxial heterodyne system and (B) the bistatic het-erodyne system. The only drawback in A is the possi-bility of a velocity error in certain rare circumstances.In system B, there are problems with signal/noise ratios,alignment, scanning,, cavity isolation, and probabilityof detection. When the two systems are compared,spatial resolution and velocity accuracy are better in Bbut angular alignment is worse. The signal/noise ratiosare similar for both. Average detection probability andfalse-alarm rate are 96.5 percent and 10"6, respectively,for A, while in B the detection probability is a functionof the misalignment between the transmitter and thereceiver. Also, there is a lag-angle problem with scanningin A.

The report includes design details on the laser, theinterferometer, the frequency translator, telescope, out-put mirror, and detector. There is also a block diagramof the equipment and the computer system.

Source: F. Campbell, W. Keene,A. Jelalian, and C. Sonnenschein of

Raytheon Companyunder contract to

Marshall Space Flight Center(MFS-22669)


DOUBLE FILM-PLATE HOLOGRAPHY

Time and cost may be reduced with a new techniquefor obtaining high-quality double-exposure hologramsthat record real-time visual displays- of interferometricfringe patterns. A commercial double-width film-plateholder is used to hold two film plates. Guides or pinsmay be added to. permit precise removal and replace-ment of either plate. The two film plates are placedemultion-to-emulsion in the holder for the initial ex-posure. This forms a basic hologram of the illuminatedtest object in each film plate. Both exposed plates arethen removed, and the front plate is developed. Theback plate is stored in a light-tight container for laterdouble exposure.

Next, a clear plate (without emulsion) is placed backon the developed hologram, and the assembly is reloadedinto the holder. The test object is stressed, and thefringe pattern is observed through the clear back plate,or with a. television monitor. The laser is adjusted toprovide the optimum fringe patterns needed to investi-gate the strain distribution. Following this, the clear

back plate is replaced, in darkness, by the undevelopedhologram. The two holograms must be matched exactlyto their original positions. This unchanged stressedsetup is used to make a double exposure of the fringe,pattern in the back plate. The added fringe pattern isrecorded in exact relation to the original hologram.

After removal of the test setup, the developeddouble exposure can be laser illuminated while beingheld in a single holder. The resulting holographicprojection displays the test object with the fringepattern showing on its surface.



(MSC-17787)


OPTICS AND LASERS

A HOLOGRAPHIC VIEWING SYSTEM FOR LARGE AUDIENCES

Virtual ImageMotion

Dispensing Reelfor 70-mm

Holographic Film

S~~\ /OrFilm Travel

f?

1

^Film Trave

A

"\\

/AO O

Opaque Wall

O

D^

yAo

/Ao

\\\ /Ao

/Ao

/A\\

/Ao o

Audience

/A */Ao o

Audience

^\yAo

-

\ /A0

Beam Splitter(one of several)

/ vrA Ao. o *

i<.

/ 7\A AO O

L

1-Cj Laser | '

•

j— ' Laser 1

— >.

O^Multiple-Viewing System

For the first time, it is possible for a very largeaudience to view simultaneously a three-dimensionalholographic motion picture. The virtual image of a70-mm filmstrip is used without either the limitationsof the film size or the use of a two-dimensional screen.Because a hologram is reconstructed by reproducing theincidence of the reference beam at the same angle atwhich the hologram was made, many such beams mustbe supplied for multiple viewers.

The illustration shows how several lasers and m beamsplitters (B/S) are used to allow multiple viewers. Theactual size of the audience determines how many beamsplitters must be used. The 70-mm filmstrip is allowedto pass in front of each viewer and then on to the nextone, until it is finally rewound on a takeup spool orreturned to the original reel. Each viewer in his ownviewing section can see five to seven separate hologramsfrom the total movie at one time. Each hologram on thefilmstrip measures about 70 by 70 mm; they arerecorded successively on the entire length of thefilmstrip at the rate of 20 to 30 exposures per second.This is necessary in order to allow the reconstructionof real-time motion.

In a very large audience, the last observer sees agiven scene considerably after the first observer saw

that scene, due to the travel speed of the filmstrip.The sound has to be synchronized with the passage ofthe frames past the respective viewing section. Thismethod allows the size of the effective hologram to beas large as desired, simply by displaying the long film-strip in front of the viewers, rather than having theviewers look through a single section separately as hasbeen done up to now; the size of the hologram per selimits the audience size.

The filmstrip may be displayed above or in front ofthe viewer or reflected by spherical mirrors to becomeenlarged. In any case, the observer must look throughseveral frames of the film at once. As the entire strippasses -by, the viewer receives the total informationpresent in the holographic filmstrip. This new techniquewill be useful in visual instruction and communications,although the necessity of audio synchronization forthe individual viewer limits its use for entertainmentpurposes.

Source: R. L. KurtzMarshall Space Flight Center

(MFS-22723)


LASER TECHNOLOGY

LASER BEAM DEFLECTION CONTROL: A CONCEPT

Side Deflection*Coil

ReflectedLaser Beam

IncidentLaser Beam

Front and RearDeflection Coils

Liquid-Filled Cell

Side DeflectionCoil

UltrasonicWave Source

Laser Deflection Device

Improved control of laser beam deflection angles mayresult from a new conceptual device. Reflectively coatedmagnetized particles are suspended in a liquid-filled cellsurrounded by two pairs of crossed electromagneticcoils and are selectively aligned by controlling themagnetic fields.

The cell contains a low-viscosity fluid to minimizefrictional losses, and low-inertia particles to permitrapid deflection of the incident beam. Each particleconsists of a magnetized core located normally to thereflective surface. This assures particle alignment in auniform direction when a magnetic field is applied. Anultrasonic energy source keeps the particles suspendedin the fluid.

One process for making the particle is to chemicallydeposit a thin layer of silver on a flat base, deposit a

magnetized powder in the presence of a normal magneticfield, and deposit another layer of silver. The base isthen dissolved and the sandwich plate broken to the

" desired particle size.This concept should be of interest to designers and

manufacturers of electro-optical devices, systems andsupport equipment. It has potential applications inlaser TV and display systems, optical signal processingand optical memories.

Source: C. L. Garvie ofLockheed Electronics Co.


(MSC-13814)


10 OPTICS AND LASERS

SENSITIVE HOLOGRAPHIC DETECTION OF SMALL AERODYNAMIC PERTURBATIONS

A method has been developed to enhance the sensi-tivity of holographic techniques for detecting the verysmall aerodynamic disturbances which are caused byvariations in gas density of the order of 1/10 wavelengthor less. Ordinarily, the minute optical phase retardationscaused by such disturbances are too small to detect.

In a more sensitive technique, the disturbance isdetected on the hologram plate in the form of phasemodulation of a basic, moderate spatial frequency

Laser

. Subject

Hologram

Reference Beam

180" Phase Shifter .

Optical Diagram for Phase-Modulation Hologram

grating; the first exposure is made of the unperturbedgas, and the second of the gas in the perturbed state.Since the system responds only to changes in thesubject between exposures, perfect optics are notrequired. The readout resembles that from a doubleexposure, subfringe, holographic interferogram. Thesubject perturbations show up as brightenings on a darkbackground.

To produce the phase modulations, the subject andreference beams in the holographic apparatus are eachseparated into two component beams. The angle be-tween the components is small and is the same' forboth the subject and the reference beams. As shown inthe figure, mirrors A, B, C, and D form two beams at asmall angle; beamsplitter E divides these into subjectand reference beam pairs.

In the first exposure, the two components of thesubject beam interfere with each other at the holo-gram, producing effectively a single wave with anamplitude that varies sinusoidally as the hologram istraversed; the same is true for the reference wave.

The interference between the subject and referencebeams thus has an intensity which varies like a sin2

function for the relatively slow variations correspond-ing to the fringes produced by the narrow angle be-tween components. Superimposed on these slow varia-tions are the fine holographic fringes correspondingto the large angle between the subject and referencebeams.

For the second exposure, a phase shift of 180° isintroduced into one component of the subject beamand the corresponding component in the referencebeam. The phase shift causes a displacement of theslow variation of the intensity at the hologram so thatthe intensity varies like a cos2 function; the fine fringe.holographic component is not changed. In view of thefact that sin2+cos2 = 1, the sum of the two envelopeintensities is constant. Thus, a hologram produced inthe absence of a change in the subject is simply auniform grating of fine fringes which diffracts only aplane wave upon reconstruction. However, if the objectintroduces a small differential phase shift between

LASER TECHNOLOGY 11

the two exposures, the phase (position) of the finefringes for the second exposure with the cos2 envelopewill be shifted accordingly. Upon reconstruction, theoutput wave, instead of being plane, will have a smallphase wrinkle on it with the amplitude of the phasewrinkle set by the small phase shift caused by thesubject. This phase wrinkle diffracts light at the smallangle from the primary reconstruction, and the intensity

of this diffracted light reveals the magnitude of theoriginal, small optical perturbation made by the subject.

Source: Lee 0. Heflinger ofTRW Systems Group, TRW, Inc.

under contract toAmes Research Center

(ARC-10422)


THREE-DIMENSIONAL GAS TURBULENCE MEASUREMENT WITHA LASER-DOPPLER VELOCIMETER SYSTEM

Conventional gas-velocity measurement devices, suchas a Pitot tube or a hot-wire anemometer, are limited indynamic range and sensitivity to velocity direction. Inaddition, they require a physical probe which in manycases disturbs the flow field. In contrast, the laser-Doppler system records gas-velocity data over a widedynamic range in three-dimensional space without aphysical probe.

The system detects the Doppler-frequency shift in alaser beam scattered by flowing particles and uses thisfrequency to calculate the particle velocities. . Thetechnique is based on the principle that a laser beamscattered by flowing particles is shifted in frequency byan amount proportional to the laser frequency. Thevelocities of the particles cause this shift and fromthe geometrical angle at which the scattered light isobserved.

In use, a focused laser beam is directed into a flowfield containing submicron particles. A laser-Dopplervelocimeter (LDV), placed on the opposite side of theflow, field, collects the forward-scattered laser lightfrom three different directions and homodynes thislight with reference, or unscattered laser light, to

produce a Doppler-frequency output on three photo-detectors. The three Doppler frequencies are then fedinto a frequency-tracking unit which locks onto andtracks the Doppler signal. The frequency trackersprovide a dc voltage output, corresponding to the meanDoppler frequency or flow velocity, and an ac voltageoutput, corresponding to the fluctuating Doppler fre-quency or flow turbulence. The three dc componentsare then passed through an analog network whichtransforms the components into three outputs, corre-sponding to a Cartesian coordinate system.

With a knowledge of the frequency-tracker calibrationcurves and the geometry of the LDV relative to theflow field, the three-dimensional levels of the particlescausing the shift can be computed.

Source: C. E. Fuller ofRemtech, Inc.

• under contract toMarshall Space Flight Center

(MFS-22713)



HOLOGRAPHIC TESTING WITH A DOUBLE REFERENCE BEAM

TestObject

Fringe Control

Mirror (3) Mirror (2)

Mirror (4)

2 SuperimposedReference Beams

BeamsplitterI (2)

Laser

SpatialFilter

V—u — nL

Film Plate

Beamsplitter(1)

THE FOLLOWING BEAM LENGTHS ARE EQUAL1. Beamsplitter (1)—^-Mirror (4) > Test Object—^-Film Plate2. Beamsplitter (1)—+- Beamsplitter (2) ^-Mirror (1)—*-Beamsplitter (3)-3. Beamsplitter (1)—+- Mirror (2)—^-Mirror (3)—*-Film Plate

Mirror (5)

-Film Plate

Holograms are images made on a photographic plateby the interference patterns of laser beams. They can bethree-dimensional images and are used in areas as diverseas magazine covers and optical memory devices forcomputers. One industrial application involves "taking apicture" of a mechanical object, placing the object understress, and taking another "double-exposure-picture" ofthe same object. This results in a pattern of lines aroundthe stressed object called interferometric fringes whichmay be analyzed to discover the presence of flaws inthe tested object. Unfortunately, this technique, asusually done, results in multiple images which interferewith analysis of the fringe pattern.

Multiple images in the object focal plane can beeliminated by the use of two reference beams instead ofthe usual one.

A hologram requires two beams; one is reflected offthe test object to be "photographed", and the other,the reference beam, intersects the beam reflected fromthe test object to provide an interference pattern oflight waves on the photographic plate. The image maybe reconstituted by placing the plate in its original

position with respect to the reference beam and illumina-ting it with light from the reference beam.

The figure shows how two superimposed referencebeams are used to make a double exposure hologram.An image of the unstressed object is taken with thereflected beam and one of the reference beams. Theobject is then stressed, and a second (double) exposureis made. The developed film plate provides a doubleexposure hologram that can be projected by simul-taneous illumination with both of the reference beams.Because the two reference beams may be adjustedseparately, the appearance of multiple images may beeliminated while manipulating the fringe patterns. Thisis not possible in a single reference beam system.



(MSC-17959)


LASER TECHNOLOGY 13

ALIGNMENT MICROSCOPE FOR ROTATING LASER SCANNER

Curved Platen

RotatingMirror

EyepieceHandle forMicroscope

BearingsMotor forRotatingMirror

In rotary laser scanners, the alignment of the scanline relative to the points of interest on the film beingscanned has been observed by one of the two methods.The first method, subject to translation errors, requireslocation of a film area outside the scanner. This area isthen positioned in the scanner by use of an arbitraryreference point chosen on the film which will stillremain outside the scanner. In the second technique, thescan line is observed at an angle through the rear ofthe glass platen. This method introduces distortions andmakes the film backlighting somewhat difficult.

An alignment microscope assembly has been develop-ed which allows observation' of the exact position of thescan line relative to the points of interest on the filmbeing scanned. This assembly does not interfere with thesystem operation.

The microscope assembly, as shown in the figure, isoptically designed to focus on a small area of the filmalong the laser scan line at an oblique angle, withoutsignificant keystoning effects. By suitable choice of angleand location of the optical components clear of the laserfocusing cone, alignment of the laser scan line on thefilm is observed with the system in full operation. Underthese conditions, the laser-beam line becomes the

X-coordinate reticle. A single horizontal reticle line isincluded in the microscope to facilitate the Y-coordinateposition indexing.

The entire assembly may be rotated about the center-line of the laser-scanner mirror which is coincident withthe center of the radius of curvature of the film. Thefocusing eyepiece is placed in close proximity to therotational axis of the assembly to minimize head trans-lation during viewing of the full 72° scanned arc. Inaddition, a scale and index mark affixed to the rotatingmirror support and microscope carrier, respectively,serve as a coarse viewing position locator. Variable back-lighting of the film, accomplished in another assembly(not shown), further facilitates the microscope assembly.

Source: A.Maciel, Jr., and J. C. Beck ofSinger Link Division of

Singer-General Precision, Inc.under contract to

Johnson Space Center(MSC-14118)



A LASER HEAD FOR SIMULTANEOUS OPTICAL PUMPINGOF SEVERAL DYE LASERS

Copper Tube forFlashlamp Support

Dye-SolutionExit Ports

Dye-SolutionExit Ports

Laser Head WithFour Elliptical Cylindrical

Cavities

Dye-SolutionInlet Ports

Holders

Dye-SolutionInlet Ports

FlashlampPower-SupplyConnection

CommonFocal Axis

Laser Head for Simultaneous Optical Pumping of Several Dye Lasers

A multielliptical-cavity laser head has been developedwhich provides simultaneous optical pumping of severaldye lasers in a compact, efficient, and reliable manner.This device accomplishes such optical pumping using asingle flashlamp and an electrical driver. This is possiblebecause dye lasers require relatively low energy tooperate (low-threshold pumping requirement) and pro-vide a new simple method for producing simultaneousindependent laser output at a number of differentwavelengths.

In this design (see illustration), the lamp is placed onthe common focal axis, and the dye cells occupy thefour remaining focal axes. The dye cells share theradiation output of the lamp equally.

This laser head consists of a number of ellipticalcylinders with a common focal axis and the remainingaxes equally spaced about it. The number of cylindersused can range from one to more than eight, dependingon the number of laser systems to be pumped, theavailable flashlamp energy, and the dye-laser mediumused.

The multielliptical-cylinder cavity can be machinedfrom a single block or made in sections and assembled.

The cavity must be polished for maximum uniformreflectivity. The dye cells and the lamp are held in placeby stainless steel end plates, which hold mirrors for eachlaser cavity, permit dye solution to flow through thecells, and reflect light from polished surfaces to increasepumping efficiency. Stainless steel is used as it is non-reactive to solvents used with the dyes. Copper tubes,mounted on the end plates, act mechanically to supportthe flashlamp and complete the electrical circuit asground return. Optics holders, also mounted on the endplates, are used to support and adjust the laser mirrors.Windows are used instead of mirrors, if externallymounted mirrors are required. A standard capacitiveelectrical driver system is used to supply electricalenergy to the flashlamp. The lamp used in this deviceis water cooled and rated at 100 joules input.

Source: Peter B. Mumola andBelton T. McAlexander

Langley Research Center(LAR-11341)


LASER TECHNOLOGY

LASER SYSTEM DETECTS AIR TURBULENCE

15

Laser Amplifier

Master Laser

CO.

fSrf:D-.

N D..I

/

.+_ =r=»

Telescope

Pulse Gate

IR - Detector

Laser-Doppler System

A prototype laser-Doppler system can remotelymeasure atmospheric wind velocity and detect airturbulence. .The system employs a laser beam that isemitted from a pod on the side of the aircraft. The beamis aimed ahead of the aircraft. All along its path thebeam is scattered by airborne particles (e.g., dust, waterdroplets, ice crystals, smog, etc.). Some of this scatteredlight returns to the aircraft, but at a shifted frequencycaused by the Doppler effect from local air speeds.

A beam from the CC>2 master laser (see figure) issplit into two parts. One part is pulsed and laseramplified to increase the range and is aimed by atelescope. The second part serves as a reference beamThe scattered and frequency-shifted light is recombinedwith the reference beam causing a beat frequency in the

detector. This signal is processed in the receiver anddisplayed for on-board evaluation.

The system can detect a change in air velocityindicating the presence of a wind shear up to about 9nautical miles (16.67 kilometers) ahead. Current workfocuses on extending this range, including investigationsof the effects of particle density, focusing, back scatterefficiency, absorption, and other factors.

Source: W. K. Dahm, J. A. Dunkin, andE. A. Weaver




COPLANARITY MEASUREMENT TOOL

MonochromaticLaser

BeamExpanderTelescope

Collimator 1_l

AttenuatorMirror

Field Lens

Object BeingTested for

Coplanarity

With a new technique, the plane parallelism of theopposite surfaces of transparent objects can be measuredprecisely. A laser-beam generator produces a beam ofmonochromatic light. The beam is collimated by anappropriate beam-expanding telescope and is focused ona front-surface mirror through an attenuator, which maybe a neutral density filter (see figure). The reflectedbeam is directed from the mirror to the material beingtested for uniformity of thickness, plane parallelism, orcoplanarity. A reflection of the beam from the near andfar surfaces of the material being tested is viewed by anobserver through a field lens.

The interference patterns, produced by representativedeviations from the conditions of plane parallelism, areobserved as they are produced; and no adjustment ofthe equipment is required once it is set up.

Source: A. R. JohnstonNASA Pasadena Office

(NPO-10666)


17

Section 2. Spectroscopy and General Optics

IMPROVED PHOTOGRAPHIC-FILM RECORDING BYMULTIPLE ELECTRON EXPOSURES

When an image is exposed on a photographic film incertain types of electron-beam recorders, the signal/noiseratio in electron-beam-recorder (EBR) image qualitymay be improved, along with its radiometric, geometric,and resolution measurements. The underlying idea is tomake the input electron signal add repetitive exposureslinearly while the noise adds randomly. The resultingsignal/noise improvement is proportional to the squareroot of the number of correlated images scanned on thefilm before development. The images scanned should beidentical to each other so that they superimpose. Withtwo identical images scanned over each other, animprovement In the signal/noise ratio by the \A2 canbe expected.

This technique also makes it possible to average rmscurrent variation, due to electron gun noise, by themultiple-exposure method. Thus, density variation onthe film, caused by electron-gun noise or by otherelectron noise, will be added randomly while the signalwill be added linearly. An additional improvement insignal/noise, which is proportional to the square root ofthe number of exposures, can therefore be expected.

Reducing or averaging the nonlinearity of the EBRscanning position also can be effected by using multipleexposures, with a probable error of 1 part in 5000 due

to sweep nonlinearities. Two EBR images of the samescene may be in good registration but actually may bedistorted due to sweep nonlinearities. The latter can beaveraged by using different portions of the EBR scanningcycle to produce specific portions of the duplicateimages.

For example, one line of the image can be writtenfrom left to right on the first image, and this same linecan be fed into a delay line and can be read in reversefor the second image. Thus, the two images will beidentical in registration except for the sweep non-linearities, which actually will be averaged by producinga multiple-image master more accurate than a singleone. Other possible methods include reversing theimages from right to left or up and down. The signal/noise ratio is expected to improve by a factor of atleast 1.4, when two duplicate images are formed toproduce one master image.

Source: A. R. ShulmanGoddard Space Flight Center

(GSC-11524)



TRANSMISSION OF OPTICAL FREQUENCIES WITH MINIMAL LOSSES

^\

Laser

Beam

n

1 -

•v^

X

... '* ^•J^ ^\

Dielectric NMedium

/

ID\

•. |

"Tube" of Materials withIncreased Dielectric Constant

Receiver

v Divergent Beams Reflected atDielectric Interface and Retained inWaveguide "Tube"

Diffractionless-dielectric transfer media have beenused to reduce power loss during power transmission atoptical frequencies. An optical beam of sufficient poweris transmitted through a dielectric medium of a nonlinearrefractive index. This transmitting medium may be solid,liquid, or gas with a uniform dielectric constant in theabsence of an electrical field; however, gases show thebest results. A beam of sufficient power incident on thismedium increases its dielectric constant and, thus, self-generates a waveguide through the dielectric of thesame diameter and shape as the beam. This effect issimilar, to that in fiber optics in that all the beam com-ponents are self trapped by the total internal reflection.Thus, power loss due to beam spreading between thesource and receiver is minimized. The general systemdiagram is shown in the figure.

To establish internal reflection, the optical beam mustexceed a certain critical power PC expressed in MKSunits as:

Pc = (1.22X)2C/64n

where X is the wavelength, C is the energy flow per unitarea, and n is the index of refraction due to electro-striction. Power levels produced in most laser applica-tions are substantially above the critical levels. However,in communications, beam power may be just above thecritical levels and may therefore require corrections toachieve self trapping.

Self trapping of the beam is easily induced in steelgas-filled pipes using CO2. To produce this effect, gaspressure is set as a function of beam power: when beampower is high the pressure should be low and viceversa.

These pipes provide negligible power losses as a resultof gas even at high pressures compared to those of liquidor solid dielectrics. Such gas-filled systems are selfrepairing in that, if gas overheats or ionizes within thebeam, it is quickly replaced by the remaining gas in thesystem.

The developed system can be applied in power trans-mission, communication, bloodless surgery, machinery,etc. With this concept the laser can be placed remotelyfrom the target area and still provide high power andsmall beam width.

Source: C. H. Townes, R. Y. Chiao, andE. M. Garmire of

Massachusetts Institute of Technologyunder contract to

NASA Headquarters(HQN-10541)


SPECTROSCOPY AND GENERAL OPTICS

MEMBRANE LIGHT-VALVE COMPUTER MEMORY

19

From OpticalMemory for ReadFrom Light Source

for WriteLight

TransparentMembrane

SupportStructure

N Substrate(Cathode of Photodiode)

X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X XX X

SemitransparentMetallization

P+ Region IsElectrode ofLight Valveand Anode ofPhotodiode

Membrane Light-Valve Element

A new membrane light valve has been developed forelectrically and optically accessible computer memories.These memories combine the functions of a page-composer and photodetector. They consist of semi-conductor substrates, with memory drivers (e.g., flip-flops) and photodiodes that provide an optical responsewhich determines the state of the transistor memory. Inaddition, light valves (operated by the flip-flops toassume optically different states) determine the state ofa bit in a page of optical memory.

The original liquid-crystal light valve used in thesesystems may be replaced with a membrane light valve(MLV) which operates in microseconds as compared tomilliseconds for the liquid crystal. The MLV has alonger lifetime, no contamination problems, and is moreeasily fabricated. The MLV is an electrostatically de-formable mirror, which can reflect light specularly or,in its deformed state, scatter it over a wide area.Furthermore, the MLV can be made compatible withsemiconductor voltages and fabrication techniques.

The integrated assembly is shown in the figure. Asingle n substrate serves as the photodiode cathode formany elements. Each element is characterized by a p+region that is both the electrode of the light valve andthe anode of its photodiode. The rest of the valveconsists of the gap (airspace) in the opaque support

structure (to allow light to reach the photodiode) andthe semitransparent, metallized membrane.

The membrane can be made to assume two states:When a.voltage is applied, (1) it deforms to scatterlight and (2) it is semireflective when unenergized. Inthe reflective state, the semitransparent membranereflects about one half the incident light and transmitsthe remainder to the photodiode.

To write into an optical memory or act as a pagecomposer, the state of the MLV is controlled by thetransistor memories. To write a "1" the membrane isunenergized and light is reflected to the optical memory.To write a "0", voltage is applied to the membrane andlight is scattered randomly.

To read an optical memory signal, the elements actas photo detectors. All elements are in the "clear"unenergized state, and the presence or absence of lightis determined from the photodiode outputs.

Source: L. S. Cosentino ofRCA Corp.


(MFS-22433)



SOLID-STATE TELEVISION CAMERA HAS NO IMAGING TUBE

Important advances have been made in recent yearsin the area of image sensors, particularly in areas of solid-state image converters, and peripheral video and digital-data-handling circuits using large scale integration. Amosaic produced only a few years ago contained 2500photo-transistors on a single wafer of silicon 1.25 cm(0.5 in.) on a side and arranged in a 50 by 50 squarearray spaced on 0.25 mm (.001 in.) centers. Since then,three other generations of mosaic arrays have beenproduced, with the final one containing 200,000 photo-transistors on a single silicon wafer approximately2.5 cm (1 in.) on a side.

A solid-state television camera that has no imagingtube and has characteristics of a vidicon camera and aresolution greater than the home TV receiver has beendeveloped using a mosaic of photo-transistors. Thecamera is rectangular in shape, approximately 5 cm(2 in.) by 25 cm (10 in.) by 31 cm (12 in.) and hasa 50-mm lens in the center of the large side. The camerahas a resolution of 500 lines horizontal and 400 linesvertical, and, due to the completely solid-state construc-tion, it has the usual advantages offered by integratedcircuit systems, i.e., reduced weight, volume, and powerconsumption plus greatly increased reliability and en-vironmental immunity. In addition, the photo-transistor

mosaic performs the functions of a vidicon without thenecessity for high voltages, magnetic fields, vacuumenvelopes, filament power, and protection against me-chanical shock. The elimination of the high-voltagerequirement is a particularly salient advantage for spaceenvironments. The fact that the image plane of thesensor consists of discrete sensor elements, geometricallyprecise in position, eliminates tube beam deflectionerrors. These errors are important in optical processingsystems such as stereo imaging, motion detection, andscene correlation, where it is important to return to anexactly known segment of the image over relativelylong periods of time. The electrical accessing of theimage area could also facilitate random scanning in theseapplications.

Because of its low power and small size, the cameramay have a large number of applications. The mosaicscan be utilized as cathode-ray tubes and analog-to-digitalconverters, for the assessment of nuclear blasts.

Source: C. T. HugginsMarshall Space Flight Center

(MFS-21553)


ADVANCES IN HIGH-RESOLUTION X-RAY PHOTOGRAPHY

X-ray photography is frequently used in the non-destructive testing (NDT) of metallurgical specimens.Several new techniques have been devised to allowimproved resolution and magnification with this tech-nique.

One improvement involves the substitution of ametallurgical metallograph for a conventional enlarger.With the metallograph, magnification up to 1000X ispossible as compared to a limit of 25X with the con-ventional enlarger.

In another improvement, high-speed fine-grain micro-film is used in place of conventional X-ray film. Micro-film has not been used previously for X-ray workbecause it is somewhat slow; however, the increasedresolution of the microfilm more than compensates forthe modest loss in film speed.

Another new high-resolution X-ray photography tech-nique has been developed for testing solder joints. The

process has been compared with 23 other NDT processes,and it is the only one that is successful with conformalcoated joints, both during fabrication and after use.With this process, cracks 0.007 to 0.017 cm (5 to 7 mil)in depth can be detected, even though they are notvisible from the surface of the joint. The methodrequires a small X-ray target source (0.7 mm or smaller),high-resolution film, and magnification of from 10X to75X.

Source: W. R. Hutchinson ofMartin Marietta Corp.


(MFS-21067)


SPECTROSCOPY AND GENERAL OPTICS 21

PINHOLE COLLIMATOR FOR RADIOGRAPHY

A new pinhole collimator may be used to detectnearby sources of radiation. The high-resolution col-limator is used to scan an area for an energy source.Radiation incident on the collimator is focused at asingle point. With modification the collimator could beused with high -energy electromagnetic radiation as well.

The collimator consists of several plates with ran-domly placed apertures. The apertures on a given plateare of the same size; the aperture sizes and spacingschange from plate to plate, but the relative orientationremains the same. This arrangement produces radiationchannels that converge to a single point.

The first plate contains a random distribution ofholes of diameter d1; covering an area aj • bt. Thesecond plate contains the same random distribution butcontains holes of size d2 , covering a smaller area, a? ' b2 .Each plate has successively smaller holes, covering corre-spondingly smaller areaa. The holes are sized so that

d, a, b!

pinholes will all converge to a single point. Thespacings are found from the following proportionality:

where sn is the distance between the nth and the(n+l)th plate.

The holes in each plate can be photoetched from asingle master plate. The master plate is put into aphotographic enlarger, and the image is focused on theplates to be photoetched. The hole size is determinedby the enlargement, and the relative orientation of theholes is kept the same for each plate.

Source: R. B. Hoover and J. H. UnderwoodMarshall Space Flight Center

(MFS-20932)

These ratios determine the spacings required, to insurethat lines drawn through the centers of corresponding


OPERATION OF ALKALI VAPOR LAMPS IN NONVACUUM ENVIRONMENTS

Alkali vapor pump lamps for lasers normally areoperated in a vacuum environment. However, it has beenfound that the lamps also can operate in an inertatmosphere such as argon without affecting laser outputpower. The argon gas surrounding the lamps preventsoxidation of the refractory metals used in the lampassemblies.

To achieve high laser outputs, it is frequentlynecessary to operate the lamps at powers higher thantheir vacuum ratings. This results in increased tempera-tures that drastically reduce the strength of the sapphireenvelopes. The use of argon also acts as a coolant, pro-viding conductive heat transfer that keeps these tempera-tures within reasonable limits.

In addition, since most of the long-wavelength black-body emission from a system stems from the hotalumina envelope, the reduction of the wall temperature(by about 200° C) reduces the blackbody-radiatedcontribution by a factor of two.

Source: K. Ward ofHolobeam, Inc.

under contract toGoddard Space Flight Center

(GSC-11755)



MICROSCOPE EYEPIECE FOR CONCENTRICITY INSPECTION

Field of View .

Size "0" Centering Ring

Size "0" Clip Inspection Ring

Size "4" Centering Ring

SpecialEyepieceReticle

Size "4" Clip Inspection Ring

Tine

Figure 1. Etched Eyepiece

Size "0" Clip

Clip Inspection Ring

InspectionRing

Tines

Size "0" Application

Figure 2. Eyepiece Used to Inspect Tines and Clips

A newly designed eyepiece allows microscopic in-spection for concentricity without physically touchingthe object with gauging tools. To check the position oftines and retention clips, a standard microscope eyepieceis etched precisely with lines that define the physicaldimensions of the parts (see Figure 1). As the parts areviewed under the microscope, they are aligned with thesuperimposed image produced by the etched eyepiece(see Figure 2). Any divergence of the part from theoptical limits is definitely established.

Source: J. M. Beekman andE.G. Brunskow of

Rockwell International Corp.under contract to



SPECTROSCOPY AND GENERAL OPTICS 23

SPECTRAL MATCHING OF ALKALI-METAL VAPOR LAMPSUSING TOTAL FLUORESCENCE MEASUREMENTS

The optimum-fill ratio has been determined forpotassium/rubidium (K/Rb) lamps [used to excite aneodymium/YAG (Nd/YAG) laser]. The individual com-ponents of the K/Rb mixture have been analyzedspectroscopically at varying vapor pressures. From this,the contribution of each component to the total'fluorescence of the laser output is found. To find theoptimum spectral match, a lamp with a rubidium fill isoperated in an integrating sphere. The total fluorescence

.is recorded with a scanning spectrometer through thezero order (i.e., all radiation entering the collectingoptics of the spectrometer is transmitted into thefluorescence cell). Filters exclude most radiation beyond8600 A, thus limiting the total fluorescence to thecontributions from the Nd/YAG 7300 through 8300 A.The integrated total fluorescence and the total fluo-rescence measurement agree to within 20 percent,which is adequate for optimization tests.

. Instead of repeating the measurements with a purepotassium lamp, an empirical method of varying theweight ratios and the mole fractions of the Rb and K

components was developed and used (with experimentalverification) to determine the optimum fill. The opti-mum calculated K/Rb pressure ratios are as follows:

Tube Diameter(mm)

234 .56.

Ratio

5/12.2/1.1.25/10.8/10.55/1

It can quickly be appreciated from the above tablethat the pressure ratios vary as the square of the tubediameter. This means that discharges in different-sizeenvelopes still maintain similar arc properties (i.e.,temperature and radiation), if the product of thediameter (or radius) squared and .the vapor pressure(or pressure ratio) is a constant.

'. Source: K. Ward ofHolobeam, Inc.

under contract .toGoddard Space Flight Center

(GSC-11753)


24

Section 3. Photography and Film

ROTARY SOLENOID SHUTTER

A rotary solenoid is used to drive the shutter in ahighly-precise shutter assembly. It provides 4- to 16-millisecond exposure times, with less than 5 percentvariation in aperture size and exposure time. Theassembly consists of a Tee-shaped frame which mountstwo rails, each bearing a rotary .solenoid. The framealso mounts a set of gibs which guide the two shutterblades. The solenoid-drive arms move the blades througha single-link system, using bushings at the pivot pointsof the link.

The shutter allows uniform exposure across theaperture and repeatable exposure times, over a tempera-ture range of 0° to 50° C (32° to 122° F). Thisperformance is consistent for a life of one millioncycles in a vacuum of 10~s torr. Only a simpleadjustment of the inputs to the direct and delaysolenoids is required to maintain this accuracy. Thedirect blade of the shutter exposes the aperture,

while the delay blade follows to close the aperture;thus, a moving slit travels across the aperture. Longerexposure, times are obtained by increasing the timedelay between the instants of applying power to thedirect solenoid and to the delay solenoid.

Another practical application is the possibility of therapid insertion and retraction of lens filters on cameras.The filters merely replace the shutter blades and areheld and driven on command through the rotarysolenoids,

iSource: W. L. Cable and H. B. Dougherty of

RCA Corp.under contract to

Goddard Space Flight Center(GSC-11561)


ROTARY-INERTIA DAMPER AND STOP-PLATE ASSEMBLY

A new rotary damper reduces the stroke reboundeffect (bounce) of a camera shutter. It is specificallydesigned for use with the shutter described in theprevious article, but may also be used with othersystems.

The assembly consists of a stop plate, which isriveted to a heavy metal ring containing a bushing. Theplate is a limit stop for the solenoid armature stroke.In principle, the inertia of the damper is matched withthat of the rest of the armature/linkage/blade system, inan approximate ratio of 1 to 2. Peripheral rotation ofthe shutter beyond the point of initial impact islimited to approximately 0.051 cm (0.020 in.).

The matched inertias and the controlled overtravelregulate the multiple-collision reaction of the armature/blade system against the stop plate. In this way, thecoefficient of restitution in the system, and thus thebounce at the end of a stroke, are reduced, and doubleexposure is eliminated.

Source: W. L. Cable ofRCA Corp.

under contract toGoddard Space Flight Center

(GSC-11560)


PHOTOGRAPHY AND FILM

FILM-CALIBRATION SYSTEM FOR CAMERAS

25

Space Allocatedto PowerSupply

B

Adapterfor

Camera

BayonetAttachment

Connection Ring

Sensitometric /Calibration '

Target

For TargetIllumination

A-ABlower

Air Intake Ports

B-B

Film-Calibration System

Compact size, stability, and a highly refined sensi-tometer are the advantages of a new film-calibrationmethod. A light source with a stable output is used toexpose a frame of film that can be compared with filmexposed in the machine at other times.

The film-calibration system is a semiportable unitabout 36.8 cm (14.5 in.) long and 10.16 cm (4 in.) indiameter, which must be positioned in a camera loadedwith the film to be calibrated. The illustration showsthe lens system, a calibration target, a target-illuminationsystem, and a regulated power supply. The lens of thecalibration system is connected directly to the lens ofthe camera via a connection-ring adapter.

With the camera lens focused at infinity, the calibra-tion system provides a full-frame projection of thetarget on the film plane. This projected image is

recorded on the film through the normal camera-exposure sequence. The camera-shutter speed and thef-number settings must be set according to the originalcalibrations. These settings are used as standard inmeasuring and correcting any changes (degradation).Corrections can be made on the second-generationfilm.

Source: L.P.OldhamofMartin Marietta Corp.


(MFS-21272)

Circle 19 on Reader Service Card. ' •


AUTOMATIC FOCUS CONTROL FOR FACSIMILE CAMERA

Object Encoder

Lens

MovableStage

\VideoDetector

"•• Basic Components of the Atomic Focus System

This automatic focus control performs the functionof automatically focusing a facsimile camera throughoutan object field being scanned. It does this by determiningthe correct focus point for objects, as they are scanned,and adjusting the focus of the imaging sensor accord-ingly. Since the facsimile camera images a scene byscanning discrete strips, it is possible to have the entirethree-dimensional scene in perfect focus at the point ofimaging by use of this automatic focus control.

The basic components of the automatic focus systemare schematically shown in the illustration. They con-sist of a movable stage, containing two photodetectorsfor sensing and one or more imaging sensors, which isconnected to an electromagnetic linear actuator and theelectronics equipment. The two focus detection sensorsare placed with one closer to the lens than the imagingsensor, which produces the video data in the fashionstandard to facsimile cameras, and the other fartheraway. The actuator is similar to a common speakervoice coil; and the primary actuator is driven by anerror signal, which•• is the difference in focus sensoroutputs. The electronics equipment consists of balancedac amplifiers, two square-law function generators, adifferential amplifier, and a power drive.

The two facsimile-camera focus sensors scan a line ofa three-dimensional scene, with the first slightly beforeand second slightly behind the imaging sensor, and havea field of view equal to that of the imaging sensor. As

the focus sensors scan, they receive varying lightintensities and produce signals which may be equal ornormally different. The fail-safe circuit is includedbecause of the equal signals which would be produced bythe focus sensors looking at a blank wall or shadow; byuse of the secondary actuator, this circuit preventsexcessive excursions in the primary actuator servo whentrue video is reacquired. When the scan produces thenormally different signals, the signal from the detectorin best focus will show the most ac components. Thesignals are passed through the ac amplifiers to driveseparate function modules, which square the individualsignals. Each signal is then filtered and applied toinverting and noninverting inputs of the differentialamplifier. The output (signal difference) drives theinput of the power driver and primary linear actuator.The servo drives the actuator until there is equal signalfrom each focus sensor. The imaging sensor, mountedon the movable stage at the calculated focus pointbetween the focus sensors, is then in focus.

Source: A. R. Sinclair, S. J. Katzberg, andE. E. Burcher

Langley Research Center(LAR-11213)


27

Patent Information

The following innovations, described in this Compilation, have been patented orare being considered for patent action as indicated below.

Inquiries concerning rights for the commercial use of the inventions describedbelow should be addressed to:

Patent Counsel " •• Marshall Space Flight Center' • • .

CodeCCOl . 'Marshall Space Flight Center, Alabama 35812

Broadband Modulation-Index Meter (Page 2) MFS-22740

Development of a Three-Dimensional Laser-Doppler System (Page 6) MFS-22669

A Holographic Viewing System for Large Audiences (Page 8) MFS-22723

Three-Dimensional Gas Turbulence Measurement With a Laser-Doppler VelocimeterSystem (Page 11) MFS-22713

Membrane Light-Value Page-Composer/Photodetector (Page 19)MFS-22433

Solid-State Television Camera Has No Imaging Tube (Page 20) MFS-21553

Pinhole Collimator for Radiography (Page 21) MFS-20932

Microscope Eyepiece (Page 22) MFS-24060

The inventions described below are owned by NASA, and patent applications havebeen filed. Inquiries concerning nonexclusive or exclusive license for their developmentshould be addressed to:

Patent CounselLangley Research CenterCode 456Hampton, Virginia 23665

A Laser Head for Simultaneous Optical Pumping of Several Dye Lasers(Page 14) LAR-11341

Automatic Focus Control for Facsimile Camera (Page 26) LAR-11213

28 Patent Information

Laser System Detects Air Turbulence (Page 15) MFS-21244This invention is owned by NASA, and a patent application has been filed. Inquiries

concerning nonexclusive or exclusive license for its commercial use should be directed to:Patent CounselMarshall Space Flight CenterCodeCCO1Marshall Space Flight Center, Alabama 35812

Transmission of Optical Frequencies With Minimal Losses (Page 18) HQN-10541This invention has been patented by NASA (U.S. Patent Nos. 3,556,634;

3,571,555; 3,575,602; and 3,606,522). Inquiries concerning nonexclusive or exclusivelicense for its commercial development should be addressed to:

Patent CounselNASA HeadquartersCodeGP .Washington, D.C. 20546

NASA-Langley, 1976

Download - OPTICS AND LASERS - NASA · OPTICS AND LASERS BROADBAND MODULATION-INDEX METER An automatic metering system supplies a real-time indication of the modulation index associated with

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