Experiment 16Holography2019-02-15The Hungarian-British physicist Dennis Gabor was awarded the Nobel Prize in Physics in 1971 "forhis invention and development of the holographic method".His work, done in the late 1940s, was builton pioneering work in the field of X-ray microscopy.The discovery was an unexpected result ofresearch into improving electron microscopes in December1947.The techniqueas originally inventedis still used in electron microscopy,where it isknown as electron holography,but optical holographydid not really advance until the development of the laser in 1960The development ofthe laser enabled the first practical optical holograms that recorded 3D objectsto be made in 1962 by Yuri Denisyuk in the Soviet Union and by Emmett Leith and Juris Upatnieks atthe University of Michigan, USA. Several types of holograms can be made. Transmission holograms,are viewed by shining laser light through them and looking at the reconstructed imagefrom the side ofthe hologram opposite the source. Rainbow holograms are commonly used for security andauthentication, for example, on credit cards and product packaging. Another kind of common hologram,the reflection or Denisyuk hologram, can also be viewed using a white-light illumination source on thesame side of the hologram as the viewer and is the type of hologram normally seen in holographicdisplays. They are also capable of multicolour-image reproduction. Most holograms produced are ofstaticobjectsbut systemsfor displayingchangingscenes ona holographic volumetricdisplayare nowbeing developed. Holograms can also be used to store, retrieve, and process information optically[https://en.wikipedia.org/wiki/Holography]ExperimentalObjectives(1) Learn to master the basic principles and experimental techniques of holography(2)Initiallymaster themethod oftaking holograms and reproducing information(3) Understand the main features of holographic technology and compare them with ordinaryphotography(4)Understand the darkroom technology of photo development,fixing,andrinsingExperimental InstrumentsHe-Ne Laser: The He-Ne laser consists of a laser power supply and a laser emission tube. In general,helium lasers emit red light. Its wavelength is 632.8 nm. The main purpose of using lasers in thisexperiment istoensurethephaseofthe light source.Holographic Optical Experiment Platform: Since the interference fringes recorded by the hologramarevery fine,the platform is required to have good shock absorption performance.The platform isa flat large steel plate with shock absorbing material under the steel plate.Shutter: A shutter of variable speed is used to control exposure time of the filmOptical components: The main optical components required for this experiment include a BeamSplitter, two Plane Mirrors, two Beam Expanders, a White Screen, a Holographic Dry Plate and aSubject.Beam Splitter. It splits incident light into two coherent beams, by means of transmission andreflection.Plane Mirrors. The beam direction can be changed as neededBeam Expander: Enlarge the spot of the laser beam. The larger the magnification, the larger therange of the spot that is expanded, and the smaller the light intensity.Optical Component Mount: The optical component mount can be moved on the platform, and the
Experiment 16 Holography 2019-02-15 The Hungarian-British physicist Dennis Gabor was awarded the Nobel Prize in Physics in 1971 "for his invention and development of the holographic method". His work, done in the late 1940s, was built on pioneering work in the field of X-ray microscopy. The discovery was an unexpected result of research into improving electron microscopes in December 1947. The technique as originally invented is still used in electron microscopy, where it is known as electron holography, but optical holography did not really advance until the development of the laser in 1960. The development of the laser enabled the first practical optical holograms that recorded 3D objects to be made in 1962 by Yuri Denisyuk in the Soviet Union and by Emmett Leith and Juris Upatnieks at the University of Michigan, USA. Several types of holograms can be made. Transmission holograms, are viewed by shining laser light through them and looking at the reconstructed image from the side of the hologram opposite the source. Rainbow holograms are commonly used for security and authentication, for example, on credit cards and product packaging. Another kind of common hologram, the reflection or Denisyuk hologram, can also be viewed using a white-light illumination source on the same side of the hologram as the viewer and is the type of hologram normally seen in holographic displays. They are also capable of multicolour-image reproduction. Most holograms produced are of static objects but systems for displaying changing scenes on a holographic volumetric display are now being developed. Holograms can also be used to store, retrieve, and process information optically. [https://en.wikipedia.org/wiki/Holography] Experimental Objectives (1) Learn to master the basic principles and experimental techniques of holography. (2) Initially master the method of taking holograms and reproducing information. (3) Understand the main features of holographic technology and compare them with ordinary photography. (4) Understand the darkroom technology of photo development, fixing, and rinsing. Experimental Instruments He-Ne Laser: The He-Ne laser consists of a laser power supply and a laser emission tube. In general, helium lasers emit red light. Its wavelength is 632.8 nm. The main purpose of using lasers in this experiment is to ensure the phase of the light source. Holographic Optical Experiment Platform: Since the interference fringes recorded by the hologram are very fine, the platform is required to have good shock absorption performance. The platform is a flat large steel plate with shock absorbing material under the steel plate. Shutter: A shutter of variable speed is used to control exposure time of the film Optical components: The main optical components required for this experiment include a Beam Splitter, two Plane Mirrors, two Beam Expanders, a White Screen, a Holographic Dry Plate and a Subject. ◆ Beam Splitter. It splits incident light into two coherent beams, by means of transmission and reflection. ◆ Plane Mirrors. The beam direction can be changed as needed. ◆ Beam Expander: Enlarge the spot of the laser beam. The larger the magnification, the larger the range of the spot that is expanded, and the smaller the light intensity. ◆ Optical Component Mount: The optical component mount can be moved on the platform, and the
upper part is used to fix the optical component. The fixed optical element can be adjusted in sixdirections of up, down, left and right and pitch, and the lower part can be fixed on the platformsteel plateSoft Ruler: Measure the optical pathdifference. White Screen: Receiving screen.Subject. The object to be photographed.Recording Medium: The transmittance after sheet processing is linear with the amount of exposureto meet the requirements of recording and reproduction. Often used domestic I, I, II Holographicdry plate.?Darkroom Rinsing Equipment: Developer, Fixer, Rinsing Equipment and Materials.Experimental Principle1.The main difference between holography and ordinary photographyThelightemitted orreflectedbyeachpointontheobject(referredtoastheobject lightwave)isanelectromagnetic wave. According to the frequencies, amplitudes and phases, people can distinguish thecolor, shape and distance of an object. Ordinary photography uses the principle of lens imaging ingeometric optics to image the object on a photographicfilm. After rinsing,a planar image ofthe surfaceintensity (square of the amplitude of the light vibration) is recorded. The brightness and darknesscorrespond exactly to the intensity of the reflected light from the surface of the object. Ordinaryphotography has no three-dimensional effect. The hologram adopts a lensless imaging method, andusestheprincipleofinterferencetorecordalltheinformation(mainlyamplitudeandphase)oftheobject light. The information is completely displayed when observed, so that the image of thereproduced object has a stereoscopic effect.2.Recording of Hologram -Interference of LightHolography is an interference technique.In order to clearly record interference fringes, the light sourcerequired must be a laser source with good coherence. A laser source with good dry performance.Figure16-1 is a light path diagram of a holography.Beam SpliterPlane MirrorlHe-Ne LaserCBeamiBeamExpanderlShutterBeamllBeamExpanderllObjectBeamPlane Mirror IlReference BeamRecordingMediumObject(HolographicDryPlate）Figure 16-1 Light Path Diagram of a HolographyThe laser beam emitted by the He-Ne laser is split into two coherent beams by a beam splitter(transmittedandreflected).Thenthetwobeamsarereflectedbytwoplanemirrors(PlaneMirrorIanoIl)separatelytochangetheirtransmittingdirections.Andthentheyareall expandedbytwodifferentbeam expanders. One expanded beam (Beam I) illuminates the object, and the reflected light (namedObject Light) then projects on the Recording Medium (Dry Plate). The other expanded beam directlyilluminatestheRecordingMedium(DryPlate),and isnamedasReferenceLight.Sincethetwobeamssplit by the same laser have high time coherence and spatial coherence, interference occurs and
upper part is used to fix the optical component. The fixed optical element can be adjusted in six directions of up, down, left and right and pitch, and the lower part can be fixed on the platform steel plate ◆ Soft Ruler: Measure the optical path difference. ◆ White Screen: Receiving screen. ◆ Subject. The object to be photographed. ◆ Recording Medium: The transmittance after sheet processing is linear with the amount of exposure to meet the requirements of recording and reproduction. Often used domestic I, II, III Holographic dry plate. ◆ Darkroom Rinsing Equipment: Developer, Fixer, Rinsing Equipment and Materials. Experimental Principle 1. The main difference between holography and ordinary photography The light emitted or reflected by each point on the object (referred to as the object light wave) is an electromagnetic wave. According to the frequencies, amplitudes and phases, people can distinguish the color, shape and distance of an object. Ordinary photography uses the principle of lens imaging in geometric optics to image the object on a photographic film. After rinsing, a planar image of the surface intensity (square of the amplitude of the light vibration) is recorded. The brightness and darkness correspond exactly to the intensity of the reflected light from the surface of the object. Ordinary photography has no three-dimensional effect. The hologram adopts a lensless imaging method, and uses the principle of interference to record all the information (mainly amplitude and phase) of the object light. The information is completely displayed when observed, so that the image of the reproduced object has a stereoscopic effect. 2. Recording of Hologram - Interference of Light Holography is an interference technique. In order to clearly record interference fringes, the light source required must be a laser source with good coherence. A laser source with good dry performance. Figure 16-1 is a light path diagram of a holography. Figure 16-1 Light Path Diagram of a Holography The laser beam emitted by the He-Ne laser is split into two coherent beams by a beam splitter (transmitted and reflected). Then the two beams are reflected by two plane mirrors (Plane Mirror I and II) separately to change their transmitting directions. And then they are all expanded by two different beam expanders. One expanded beam (Beam I) illuminates the object, and the reflected light (named Object Light) then projects on the Recording Medium (Dry Plate). The other expanded beam directly illuminates the Recording Medium (Dry Plate), and is named as Reference Light. Since the two beams split by the same laser have high time coherence and spatial coherence, interference occurs and
interference fringes are formed in the emulsion on the Dry Plate.Theamplitudeandphaseinformationoftheobjectlightarerecorded intheformsof contrastandshadingintheinterferencefringes.Thedirection of theobject light is recordedbythepitchand thedirection of the stripe. Therefore, all the information of the object light wave is recorded in the form ofinterference fringes. In order to obtain a hologram, the hologram film has to subjected some process,such as exposure, development, fixing, etc.3.ReproductionofHologram-Diffractionof Light-If directly observe a hologram, there are only dense interference fringes on it, the density, orientation,strength and contrast of the interference fringes are irregular, and the image of the object beingphotographed previously is not visible. A hologram indeed is a complex"diffraction grating", and theReproduction of Hologram is a process of light diffraction. Generally, the same laser that used in therecording progress is also as the reproducing light source. The hologram is irradiated with the samelaser light in the original reference light direction, and a series of zero-order diffracted light wave andtwo first-order diffracted light waves can be obtained after the hologram.00ScreenVirtual ImageReal ImageFigure 16-2 Reproduction of HologramZero-order diffracted light has a similar phase characteristic and in the same direction as thereproducing light source.+1st order diffracted light is divergent, and has all the characteristics of the original object lightwave. A virtual image can be observed toward the coming direction and the virtual image has thesame appearance as the original object.-lst order diffracted light is convergent. It will converge into a real image on the opposite side ofthe virtual image.4.MainFeatures of Holography(1) Strong sense of three-dimensionality.The hologram records all the information of the object'slight waves. Therefore, the virtual image seen through the hologram is a realistic three-dimensionalobject.Ifyoulookatthehologramfromdifferentangles,youcanseedifferentsidesoftheobject.with parallax effects and depth of field. This feature makes holography widely used in stereoscopicdisplay.(2) Separable. Because every point on the hologram is likely to receive the scattered light from eachpoint of the object, the information of light wave from each point of the object is recordedConversely, the scattered light at every point on the object can illuminate the various points of theholographic film, so the hologram can reproduce the entire object even if it has been divided intomany small pieces. That means that the fragments still can reproduce the complete object imageThis feature has enabled holography to open up applications in information storage
interference fringes are formed in the emulsion on the Dry Plate. The amplitude and phase information of the object light are recorded in the forms of contrast and shading in the interference fringes. The direction of the object light is recorded by the pitch and the direction of the stripe. Therefore, all the information of the object light wave is recorded in the form of interference fringes. In order to obtain a hologram, the hologram film has to subjected some process, such as exposure, development, fixing, etc. 3. Reproduction of Hologram - Diffraction of Light - If directly observe a hologram, there are only dense interference fringes on it, the density, orientation, strength and contrast of the interference fringes are irregular, and the image of the object being photographed previously is not visible. A hologram indeed is a complex "diffraction grating", and the Reproduction of Hologram is a process of light diffraction. Generally, the same laser that used in the recording progress is also as the reproducing light source. The hologram is irradiated with the same laser light in the original reference light direction, and a series of zero-order diffracted light wave and two first-order diffracted light waves can be obtained after the hologram. Figure 16-2 Reproduction of Hologram Zero-order diffracted light has a similar phase characteristic and in the same direction as the reproducing light source. +1st order diffracted light is divergent, and has all the characteristics of the original object light wave. A virtual image can be observed toward the coming direction and the virtual image has the same appearance as the original object. -1st order diffracted light is convergent. It will converge into a real image on the opposite side of the virtual image. 4. Main Features of Holography (1) Strong sense of three-dimensionality. The hologram records all the information of the object's light waves. Therefore, the virtual image seen through the hologram is a realistic three-dimensional object. If you look at the hologram from different angles, you can see different sides of the object, with parallax effects and depth of field. This feature makes holography widely used in stereoscopic display. (2) Separable. Because every point on the hologram is likely to receive the scattered light from each point of the object, the information of light wave from each point of the object is recorded. Conversely, the scattered light at every point on the object can illuminate the various points of the holographic film, so the hologram can reproduce the entire object even if it has been divided into many small pieces. That means that the fragments still can reproduce the complete object image. This feature has enabled holography to open up applications in information storage
(3)Multiplehologramscanoverlaponthesamephotographicfilm.Afterthefirstexposure,iftheorientationoftheHolographicDryPlate(orthedirectionoftheobjectlightorreferencelight)isslightlychanged,thesecondandthirdexposurescanbeperformedtorecorddifferentshots.Whenreproducing, as long as the plate is rotated properly, a series of images that do not interfere witheach other can be obtained.This multiple-exposure method is widely used in holographicinterferometry.ExperimentalContentandProcedure1.Recording ofHologram(1) According to the schematic diagram shown in Figure 16-1, arrange the optical path, and make thelaser beam parallel align the center of each optical element. Adjust the angle of the beam splitterand the position of the two mirrors, so that the optical path difference between the Object Beam(S-M1-E1-O-H) and Reference Beam (S-M2-E2-H) is approximately equal. Further, the angle betweentheopticalpath1andtheopticalpath2ispreferablyintherangeof30to45degreesM1He-Ne LaserObjectBealERefetenceBeamE2M2OFigure16-3LightPathSchematicDiagramforHolography(2) After the light path is arranged, exposure is performed to the Holographic Dry Plate in darkconditions.(3) After exposure, the darkroom operation is performed, mainly including development and fixingAfter each process, the dry plate should be washed with water, and finally dried with a hair dryer2.Reproduction ofHologram(1) Place the hologram in the original light path, and move away the object light.Illuminate theholographic dry plate with the reference light.(2) Observe the image of the original object from the hologram against (virtual image) and along (realimage) the light path, and record the observed phenomenon.BeamSplitterHe-NeLaserReferenceLightViewerPlane MirrorVirtual ImageFigure16-4:ReproductionofHolograminanExperimental LightPath
(3) Multiple holograms can overlap on the same photographic film. After the first exposure, if the orientation of the Holographic Dry Plate (or the direction of the object light or reference light) is slightly changed, the second and third exposures can be performed to record different shots. When reproducing, as long as the plate is rotated properly, a series of images that do not interfere with each other can be obtained. This multiple-exposure method is widely used in holographic interferometry. Experimental Content and Procedure 1. Recording of Hologram (1) According to the schematic diagram shown in Figure 16-1, arrange the optical path, and make the laser beam parallel align the center of each optical element. Adjust the angle of the beam splitter and the position of the two mirrors, so that the optical path difference between the Object Beam (S-M1-E1-O-H) and Reference Beam (S-M2-E2-H) is approximately equal. Further, the angle θ between the optical path 1 and the optical path 2 is preferably in the range of 30 to 45 degrees. Figure 16-3 Light Path Schematic Diagram for Holography (2) After the light path is arranged, exposure is performed to the Holographic Dry Plate in dark conditions. (3) After exposure, the darkroom operation is performed, mainly including development and fixing. After each process, the dry plate should be washed with water, and finally dried with a hair dryer. 2. Reproduction of Hologram (1) Place the hologram in the original light path, and move away the object light. Illuminate the holographic dry plate with the reference light. (2) Observe the image of the original object from the hologram against (virtual image) and along (real image) the light path, and record the observed phenomenon. Figure 16-4: Reproduction of Hologram in an Experimental Light Path
Questions(1) What are the characteristics of holography? Briefly explain the fundamental difference betweenholography and ordinary photography.(2) Briefly describe the shooting conditions of holograms. How to arrange the light path beforeshooting? What conditions should be pay attention to when arranging the light path?(3) What are the requirements for the illuminating light to reproduce a hologram?(4)Holographicrecordingtheoreticallyrequiresthatthereferencelight shouldbe strongerthantheobject light, but in experiment, the strong beam split by the beam splitter always is taken as objectlight.Is thetwo contradictory?(5) After the light path is basically set, which component can be moved to change the light intensityratio between object light and reference light, and has no affect to their angular separation andoptical pathdifference?(6)Howcaneachfragment ofa hologramreproducean imageof an entireobject?
Questions (1) What are the characteristics of holography? Briefly explain the fundamental difference between holography and ordinary photography. (2) Briefly describe the shooting conditions of holograms. How to arrange the light path before shooting? What conditions should be pay attention to when arranging the light path? (3) What are the requirements for the illuminating light to reproduce a hologram? (4) Holographic recording theoretically requires that the reference light should be stronger than the object light, but in experiment, the strong beam split by the beam splitter always is taken as object light. Is the two contradictory? (5) After the light path is basically set, which component can be moved to change the light intensity ratio between object light and reference light, and has no affect to their angular separation and optical path difference? (6) How can each fragment of a hologram reproduce an image of an entire object?