Laser App- Holography Lecture [Compatibility Mode]

7/28/2019 Laser App- Holography Lecture [Compatibility Mode]

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Subject of the Nobel prize in

Physics to Gabor in 1971

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Exposure of holographic film



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This is known as the linear response regime. Thus, after the film is exposed to

the fringe pattern and developed, the film acquires a spatially varying

transmission function according to



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Holographic Wavefront Reconstruction ھ ھ ی

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Holographic

reconstruction of

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diffraction fromfringes

on film

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I. TYPES OF HOLOGRAMS-- Reflection holograms

- Transmission holograms.



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n Hologram:¨ ی ھی ی

¨ (in-phase - maximum amplitude, out-of-phase –

minimum amplitude)

¨ Interfere wavefront of light from a scene with a

reference wave

¨ The hologram is a complex interference pattern of

microscopically spaced fringes

¨ “holos” – Greek for whole message



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Hologram :

Direct, object and conjugate wavesn Direct wave: corresponds to zeroth order grating

diffraction pattern

n Object wave: gives virtual image of the object

(reconstructs object wavefront) – first order diffraction

n Conjugate wave: conjugate point, real image(not useful since image is inside-out due tonegative phase angle) – first order diffraction

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In general, we wish to view only the object wave – the other waves just confuse the issue



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Off-axis- Direct, object and conjugate waves

Virtual imageReal image

Direct wave

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Conjugate

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Reference wave

Use an off-axis system to record the hologram, ensuring separation of the three waves on reconstruction



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n Transmission hologram: reference and object waves

traverse the film from the same side

n Reflection hologram: reference and object waves

traverse the emulsion from opposite sides

Hologram – Reflection vs. Transmission

View in Transmission View in reflection



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Hologram: Wavelength

n With a different color, the virtual image willappear at a different angle – (i.e. as a grating,the hologram disperses light of differentwavelengths at different angles)

n Volume hologram: emulsion thickness >> fringespacing¨Can be used to reporduce images in their original

color when illuminated by white light.

¨Use multiple exposures of scene in three primary

colors (R,G,B)



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Hologram: Some Applications

n Microscopy M = λr /λs¨ Increase magnification by viewing hologram with longer

wavelength

¨ Produce hologram with x-ray laser, when viewed with visiblelight M ~ 106

¨ 3-d images of microscopic objects – DNA, viruses

n Interferometry¨ Small changes in OPL can be measured by viewing the direct

image of the object and the holographic image (interferencepattern produce finges ∝ Δl)

¨ E.g. stress points, wings of fruit fly in motion, compression waves

around a speeding bullet, convection currents around a hotfilament



Color Holography:Holography with Multiple Lasers



Holographic One-Way Window

n Large hologram of a window display

masks the interior



Virtual Forces



Virtual Camouflage

Camouflage



Virtual Doors, Walls and Windows

n Indoor environments have controllable optical environments

n Holography may provide a way to disguise or misleadintruders

Door With Edge

Illuminated Hologram



Infrared Holography

n Infrared holography is appealing because viewing devices are mucless sophisticated than the human eye

n Color fidelity is much less importantn no such holograms exist nor do the materials to make them



Exampleholography

Laser App- Holography Lecture [Compatibility Mode]

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