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Optical Microscopy Using Second-Harmonic Generation

IP.com Disclosure Number: IPCOM000039341D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Heinz, TF: AUTHOR [+2]

Abstract

Recent scientific advances in the area of nonlinear optics have shown the process of second-harmonic generation (SHG) to be an exceedingly sensitive probe of the top atomic layer of a surface or of the two atomic layers of an interface provided the materials involved are centrosymmetric. This surface sensitivity, unique to second-order nonlinear optical effects, arises from the fact that the process of harmonic generation is (electric-dipole) forbidden with the bulk of a centrosymmetric medium, but is allowed on the surface or at an interface where the symmetry is lowered. A reference describing this effect is the following: T. F. Heinz, M. M. T. Loy, and W. A. Thompson, Phys. Rev. Lett. 54 63 (1985).

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Optical Microscopy Using Second-Harmonic Generation

Recent scientific advances in the area of nonlinear optics have shown the process of second-harmonic generation (SHG) to be an exceedingly sensitive probe of the top atomic layer of a surface or of the two atomic layers of an interface provided the materials involved are centrosymmetric. This surface sensitivity, unique to second-order nonlinear optical effects, arises from the fact that the process of harmonic generation is (electric-dipole) forbidden with the bulk of a centrosymmetric medium, but is allowed on the surface or at an interface where the symmetry is lowered. A reference describing this effect is the following: T. F. Heinz, M. M. T. Loy, and W. A. Thompson, Phys. Rev. Lett. 54 63 (1985). Surface second-harmonic generation can be utilized for microscopy of surfaces and interfaces with monolayer sensitivity, as shown schematically in the figure. Laser radiation from a pulsed source impinges on the surface of the interface of interest. A typical source is a Q-switched Nd:YAlG laser yielding pulses of 10 nsec duration and energies of a fraction of a Joule. The second- harmonic radiation in the reflected (or transmitted) direction is imaged with standard optics onto the face of a multichannel plate (MCP). The intensified image from the multichannel plate is recorded by a vidicon or a SIT camera interfaced with a computer for image storage. The scattered light from the pump laser is removed by color filter CF1 (low-pass); color filter CF2 (high-pass) and interference filters IF (band-pass) are used to reduce the intensity of all light at frequencies other than the second-harmonic. Lens L1, L2 are collimating and focusing lens. Two critical features of the design are parallel image processing and gated detection. The first feature re...