Transcript Slide 1
OPTICAL HOLOGRAPHY Muhammad Hasan Danish Khan University of Vaasa, Finland OUTLINE • Introduction • Principles • Optical holograms • Applications • References HOLOGRAPHY • Is a technique that allows the light scattered from an object to be recorded and later reconstructed so that when an imaging system (a camera or an eye) is placed in the reconstructed beam, an image of the object will be seen even when the object is no longer present. HOLOGRAPHY: PROPERTIES • • • • • Provide 3-Dimensional Realism Unlimited depth of sharp focus Provides depth perception and parallax Phase objects can be anaylzed with great precision Hologram Types: • • • Amplitude & Phase Modulation Holograms Thin(Plane) & Thick (Volume) Holograms Transmission & Reflection Holograms INTERFERENCE • What is it ? • • Combination of waves What is it exactly ? • Interference occurs when one or more wavefronts are superimposed. DIFFRACTION • What is it ? • • Bending / Spreading out of waves What is it exactly ? • Diffraction occurs whenever a wave-front encounters an object. HOLOGRAPHY PRINCIPLE • Recording • • Encoding phase and amplitude as interference pattern Two beams interfering • • • • Reference beam – known properties Object beam – recorded light field Complex diffraction grating is created – hologram Reconstructing • • • Hologram illuminated with reference beam Diffraction occurs Resulting light field contains original scene beam CREATING HOLOGRAMS RECONSTRUCTING THE IMAGE HOLOGRAM – IN-LINE • Recording • • • • Reference, object, hologram aligned in line Mostly transparent and planar objects Lower spatial frequency Reconstruction • Images disturbed by blurred counterparts Drawbacks • • Can be an out of focus second image There can be a strong coherent background HOLOGRAM – OFF-AXIS • Recording • • • • Non-zero angle between reference wave and object wave 3D opaque objects Higher spatial frequency Reconstruction • • Orders diffracted into different directions Clean original optical field Drawbacks • The depth of real image is inverted so image produced is called pseudo. HOLOGRAM – REFLECTION VS. TRANSMISSION • • Transmission hologram: reference and object waves traverse the film from the same side Reflection hologram: reference and object waves traverse the film from opposite sides View in Transmission View in reflection LENS & FOURIER HOLOGRAM • Lens • • • Different optical material: slowdown/diffraction of waves Use of thin lens: assumption on lack of diffraction Fourier Holograms • • • Recording through lens Reconstruction through lens Both virtual & real image in focus Drawbacks Positioning of Reference Beam Requirement of high spectral coherence OTHER HOLOGRAMS • Holographic Stereograms • • • Recording of multiple views through slit Reconstruction: only single focus depth Rainbow Hologram • 2 Stages of recording • • • • Record regular hologram Record rainbow hologram through slit Visible on white light: multiple color images Color Hologram • • Common hologram: rainbow due to diffraction Achromatic holograms: holographic stereograms • Overlapping/coplanar colors Applications • Supermarket Scanners read the bar codes on merchandise for the store's computer by using a holographic lens system to direct laser light onto the product labels during checkout • Holography is used to depict the shock wave made by air foils to locate the areas of highest stress. These holograms are used to improve the design of aircraft wings and turbine blades. • To better understand marine phytoplankton, researchers have developed an undersea holographic camera that generates in-line and off-axis holograms of the organisms. • An interferogram (a sort of hologram) is a technique providing a method of non-destructive analysis that determines structural deformations in objects. Applications • A holographic lens is used in an aircraft "heads-up display" to allow a fighter pilot to see critical cockpit instruments while looking straight ahead through the windscreen • Researchers are developing the sub- systems of a computerized holographic display. • Holography is ideal for archival recording of valuables or fragile museum artifacts. • Optical computers, which use holograms as storage material for data, could have a dramatic impact on the overall holography market. Conclusions • This presentation has briefly reviewed some of the concepts and applications . • It has been demonstrated how holographic methods have been used to creatively solve a variety of issues • These successful applications should pave the way for additional advances in this field. • One can safely anticipate that the list of technical applications of holography will expand significantly in the future . References 1. http://www.holo.com/holo/book/book1.html 2. http://www.hmt.com/holography/ 3. http://www.art-in-holography.org/ 4. http://assets.cambridge.org/