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Narrow Band Optical Filters Produced by Photochemical Bleaching

IP.com Disclosure Number: IPCOM000051449D
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Macfarlane, R: AUTHOR [+2]

Abstract

A very narrow band absorption filter is made by photochemically etching away part of an inhomogeneously broadened absorption band of a suitable material. In this way, absorption filters as narrow as ~1 MHz can be constructed. This filter process has about three orders of magnitude better selectivity than other filter processes.

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Narrow Band Optical Filters Produced by Photochemical Bleaching

A very narrow band absorption filter is made by photochemically etching away part of an inhomogeneously broadened absorption band of a suitable material. In this way, absorption filters as narrow as ~1 MHz can be constructed. This filter process has about three orders of magnitude better selectivity than other filter processes.

The filter is made by taking a slab of a suitable material 12, such as dimethyltetrazine doped into durene which has an inhomogeneously broadened absorption band B of width gamma(B) which is photochemically bleachable. This absorption band B is then etched" away by scanning a tunable narrow band laser 14 (width gamma(L)) through the absorption band B, but omitting a region 16 between omega(1) and omega(2), as shown in the drawing. Th produces an absorption band C with a width of the order of (omega(1) - omega(2)) The laser and the material is chosen so that the gamma and the homogeneous linewidth of the band B are much less than (omega(1) - omega(2)).

The peak absorption of the band C, that is the filter, is selected by adjusting the thickness of the medium or by "etching" its optical density with the laser. In order to achieve the full potential of the narrow band width, the filter should be made and used at liquid helium temperatures. The filter is also most suited to low light applications, as high intensity light will bleach out the filter in time and necessitate reprocess...