Fixing method for narrow bandwidth volume holograms in photorefractive materials
AssigneeAccuwave Corporation
InventorsVictor Leyva, George A. Rakuljic
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Abstract
An improved method for storing permanent holographic gratings in photorefractive materials for use in narrow band filters such as the H.sub.60 filter, as well as the filters themselves. The invention also provides an improved method of controlling the electric field and the nature of the photorefraction to minimize wavelength shifts and band broadening at a minimal reduction of diffraction efficiency.
Claims33
The method of developing a uniform electron distribution in a photorefractive crystal having a fixed grating formed by displaced electron patterns compensated locally by equalizing ionic displacements, comprising the steps of:
- applying a thin transparent conductive coating to the crystal;
- coupling an electrical potential to the coating to dissipate potential electrical fields in the crystal;
- and
- illuminating the crystal with a distributed beam having multiple wavelength components to migrate the electrons to a uniform disposition due to the photorefractive effect.
The method of developing a fixed hologram of narrow bandwidth in a photorefractive medium, comprising the steps of:
- illuminating the medium with coherent electromagnetic wave energy while maintaining the medium short circuited to establish a diffraction pattern therein;
- thermally fixing the diffraction pattern in the medium while the medium is short-circuited;
- and
- developing the diffraction pattern by illuminating the medium while minimizing the generation of non-AC electrical potential therewithin.
The method of generating a high diffraction efficiency hologram image of sub-Angstrom bandwidth at half height in a photorefractive element having a thickness of the order of millimeters in the c-axis direction, comprising the steps of:
- writing a diffraction grating in the element with the planes of the grating being substantially transverse to the element's c-axis,
- the grating being written with a wavelength stabilized beam and with the element being shorted;
- fixing the diffraction grating thermally while the element is shorted;
- and
- developing the grating while the element is shorted.
A narrow band optical filter for reflecting only a sub-Angstrom band of energy from a wide band illuminating source, comprising a crystal having a thickness in its c-axis direction in excess of about 2mm, more than about 0.05% dopant, and a holographic grating image fixed therein of less than about 0.5 Angstrom bandwidth at half height.
The method of developing a permanent ionic grating of sub-Angstrom bandwidth at half height from compensating an electronic grating with an ionic distribution in a photorefractive crystal, comprising the steps of:
- inhibiting the internal buildup of photovoltaic and pyroelectric fields in the crystal;
- and
- erasing the electronic grating by redistributing the electrons uniformly within the crystal.
A narrow bandwidth filter system for imaging incoming light beams at a specified wavelength, comprising:
- a volume holographic grating generating reflected output beams from the incoming light beams, wherein the reflected output beams have wavelengths matching the specified wavelength;
- and
- beam traps comprised of neutral density filters oriented at Brewster's angle to absorb stray reflections, thereby improving contrast.
Dependencies are inferred from the claim text.