Observation and application of optical interference and diffraction effects in reflection from photochemically fabricated Gaussian interfaces

Citation
L. Koker et Kw. Kolasinski, Observation and application of optical interference and diffraction effects in reflection from photochemically fabricated Gaussian interfaces, J APPL PHYS, 86(4), 1999, pp. 1800-1807
Citations number
42
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
JOURNAL OF APPLIED PHYSICS
ISSN journal
00218979 → ACNP
Volume
86
Issue
4
Year of publication
1999
Pages
1800 - 1807
Database
ISI
SICI code
0021-8979(19990815)86:4<1800:OAAOOI>2.0.ZU;2-U
Abstract
A HeNe laser has been used to fabricate photochemically a photoluminescent porous Si thin film on top of crystalline Si. The porous Si film has Gaussi an shaped upper and lower interfaces. When the reflection of a laser beam f rom this film during, or after, the photochemical process is observed, two distinct, concentric circular interference patterns are observed. A pattern of thick rings is superimposed upon a pattern of fine rings. The reflected beam is far more divergent than the incident beam. The formation of the ou ter rings is a coherent phenomenon. Analysis of the patterns indicates that reflection from the upper interface is not involved in the ring formation process but that optical interference and Fresnel diffraction of the light reflected from the bottom interface cause the pattern formation. It is show n that the radius of the pattern is linearly proportional to the optical pa th length through the film. Therefore, measurements of pattern sizes yield information about the depth and index of refraction of the porous Si film. This observation provides us with a novel, in situ technique for measuring the kinetics of formation of the photoluminescent silicon thin films and mi ght be exploited for applications in chemical sensing. (C) 1999 American In stitute of Physics. [S0021-8979(99)05316-5].