Demo request 4/8 Monday Physics 471 C285 ESC, 2 pm Hess call 2-2108 to confirm. Holography demo kit...
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Transcript of Demo request 4/8 Monday Physics 471 C285 ESC, 2 pm Hess call 2-2108 to confirm. Holography demo kit...
Demo request 4/8 MondayPhysics 471 C285 ESC, 2 pm Hess call 2-2108 to confirm. Holography demo kit with laser, chess, cannon holograms in cylindrical plastic holders, and some flat holograms Horses blue/green reflection framed hologram (about 18” x 12”) that used to hang on the far west door of the demo area before remodeling. Hope you can find it…ask Clark
Bring: green laser
Hologram of a point light source
Another simple example
Look familiar?
2 2
22 2
2 2 2 2
22O R O R
ik ikR R
O R O R
I z R E E E E kR
E E E E e e
( ) cos
Announcements
Why does 3D look 3-D?O
Holography
Coherence lengths required for reference beam?
Hologram recording
Simple exampleObject wave can be made up by summing plane waves. Imagine one of these coming at angle qob vs the z axis. Put film at z = 0. Illuminate also with reference beam along z.
ref ob obE E E ik y exp sin
Spacing of fringes on screen:when changes by 2p
yob
h
sin
obk ysin
I(y) depends on phase and amplitude of Eob . Expose a film
The film becomes a grating of spacing . Send a reconstruction beam along z: What diffraction angles do we get out?
yh
Hologram reconstruction
222ob ref ob ref objI y A E E E E k y
cos sin
For the first order, we get out exactly ! ob
A zone plate is a crude hologram of a point source of light!
I(y) for two object waves (and reference)
Imagine infinite number of gratings superposed from all object angles...The reconstruction diffraction creates all the object angles again.
When we shine the reference beam on the film, we get 1) undeflected part of the reconstruction beam, with no image information (m = 0)2) reconstructed object beam (m = 1)3) “conjugate” reconstruction beams that form a real “image” that is inside out! (m = -1)
Hologram reconstruction
What coherence lengths are needed for the reconstruction beam?
Film requirements
Resolution: 1000-2000 fringes/mm (almost down to l)
Need a special nonlinear transparency of film:
Normal (linear) film: so film exposureT IexposuretransmittedE I
Holography needs exposuretransmittedE I
2 4film exposure exposureT I E
so
Reflection holography
Object and reference beam come from opposite sides of holographic plate.
Reconstructing beam from same side as viewer: reflection
Reflection holography
White-light hologramsRecorded with coherent light. Reconstructed with incoherent light
15-20mm thick (“volume” hologram). Use “Bragg-plane” interference to give constructive interference for only a narrow band of wavelengths (like photonic crystal)
2d sin
Rainbow thin reflecting holograms for white light exposure
Slit near object. 3-D appearance only along one axis. Rainbow in other direction.
K-space Under-sampling
Jorge Jimenez
Fully sampled k-space
Low frequencies
High Frequencies
Vertical Image resolution
Horizontal Image resolution