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Laser Scanning Using Nonlinear Crystals

IP.com Disclosure Number: IPCOM000092454D
Original Publication Date: 1966-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Myers, RA: AUTHOR

Abstract

In this device, large optical nonlinearities can be used as a highly selective spatial filter in scanning lasers. This device, in addition to being one in which second harmonic light is scanned directly, can be employed as a spatial filter which can have a selectivity in an order of magnitude better than the much-discussed Kerr-Babinet filter.

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Laser Scanning Using Nonlinear Crystals

In this device, large optical nonlinearities can be used as a highly selective spatial filter in scanning lasers. This device, in addition to being one in which second harmonic light is scanned directly, can be employed as a spatial filter which can have a selectivity in an order of magnitude better than the much- discussed Kerr-Babinet filter.

When an intense monochromatic optical field, such as that found within a laser cavity, is incident upon certain piezoelectric crystals, the second harmonic frequency of the optical radiation is generated. In general, the magnitude of this second harmonic generation SHG depends on the polarization of the fundamental and of the harmonic, on the indices of refraction for the fundamental and the harmonic, and on the direction of propagation of the fundamental.

There is a particular combination of these parameters which sharply maximizes the SHG, known as the matching conditions. The propagation direction of the fundamental is known as the matching direction.

Should the crystal be birefringent and thus doubly refracting, the maximum length of the crystal over which it is possible to maintain the matching conditions is limited. This is because the fundamental and the harmonic have different Poynting vectors, i.e., they propagate in different directions. However, there are certain crystals, such as lithium niobate LiNbO(3), in which it is possible to avoid double refraction and thus maintain matching conditions for distances of tens of centimeters. This material, which has a large electro-optic effect, is one in which the matching direction is strongly dependent on temperature and also on an applied electric field. Furthermore, the nonlinear coefficient in this material is about ten times greater than that of KDP.

This device is a directionally-degenerate cavity, such as the flat-field conjugate cavity FFC, in which such a nonlinear crystal is placed. The matching direction in the crystal can be controlled, either thermally or electrically. The cavity is made to be res...