Speckle Reduction Using Multi-Color Illumination,
Abstract
The occurrence and the smoothing of speckle are studied as a function of the linewidth of an illuminating source. A general theory is presented for speckling in the image of a partially diffuse, phase-type of object which has a variable number of random scattering centers per resolution element. Then, an expression is derived for the wavelength spacing which is required to decouple the speckle patterns arising from two monochromatic tones in an imaging system, thereby establishing that it is feasible to smooth speckle using multi-color illumination. This theory is verified in a series of experiments using both laser illumination and band-limited light from a carbon-arc. For an imaged diffuser, it is shown that speckle appears laser-like for highly collimated sources even up to line-widths of 5A. Then, smoothing of speckle is demonstrated in the imaging both of a diffuser and for a section of an optic nerve when the illumination is provided by six monochromatic tones each spaced by 300A. Since with panchromatic viewing the speckle smooths, a direct extension of this method to holographic microscopy, using a multi-tone laser, should permit one to record and reconstruct holograms of diffraction limited resolution which are essentially speckle-free. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1972
- Accession Number
- AD0752240
Entities
People
- Atul Jain
- Nicholas George
Organizations
- California Institute of Technology