Experimental Holography

Traditional Setup:

Requirements:

• Monochromaticity : Laser
• Stability : Vibration Isolation Table
• Coherence Length : Keep length of Object Beam and length of Reference Beam measured from Beam Splitter to Holographic Plate equal to each other within the coherence length of the laser (usually a few inches)
• Polarization : Both beams must have same polarization
• Resolution : Special Holographic emulsions (optimized for wavelength and resolution)
• Beam Strength : Set ratio of Reference to Object beam at about 6~8 to 1. This places hologram exposure in linear region of HD curve (light intensity vs film darkening) for emulsion. If interested in interferometric fringes, set ratio at about 1~2:1.
• Depth of Field : Keep depth of object within half the coherence length of laser

Advantages:

• Full-field image
• Non-contact
• Three-dimensional image

Disadvantages:

• Viewable only with laser in dark room (white light viewable holograms are possible)
• Monochromatic (Multi-Spectral Holograms can be made)
• Speckled appearance (noisy - much of the speckle is removed if white-light viewable)
• Dark Room Procedures are time-consuming and messy
• Delicate Alignment (some freedom can be obtained by using Fiber Optics)

Uses:

Industry hasn't shown much interest in straight holography, and is more interested in holographic interferometry, which gives quantitative measurement of deflections and deformations. Artists and advertisers are interested in Display Holography, but are generally involved with white light holograms. Because of the information density of a hologram, futurists talk of holographic data bank elements with huge information storage capabilities.

Simplification of Holographic Process

• Rigid requirements for setup can be relaxed by using optical fibers, either monomode or multimode.
• Repositioning difficulties can be eased by developing film in situ, or by using electronic imaging techniques.
• Multicolor holograms can be obtained by using lasers with multiple wavelengths.
• Some types of holograms are viewable in white light - some reflection holograms, image plane holograms, Benton (rainbow) holograms.

Reference Texts:

• Collier, R, Burckhardt, C, and Lin, L.: Optical Holography, Academic Press. A classic work in the field.
• Unterseher, F., Hansen, J., and Schlesinger, B.: Holography Handbook, Making Holograms the Easy Way, Ross Books. A simple practical manual on making holograms.

Send Mail or Comments: matthysd@vms.csd.mu.edu

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