Browse Prior Art Database

Superlattice Infrared Filters and Raman Scattering

IP.com Disclosure Number: IPCOM000077447D
Original Publication Date: 1972-Aug-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Tsu, R: AUTHOR

Abstract

This description relates to the use of semi-insulating and insulating polar materials to form a superlattice of a period 50-200 angstroms to achieve interference of phonons, infrared filters, and Raman scattering due to the interaction of photons with phonons.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Superlattice Infrared Filters and Raman Scattering

This description relates to the use of semi-insulating and insulating polar materials to form a superlattice of a period 50-200 angstroms to achieve interference of phonons, infrared filters, and Raman scattering due to the interaction of photons with phonons.

It is well known that the reflectivity is very high within the frequency band between the longitudinal and transverse optical phonons for polar solids. Filters utilizing this property are called residue-ray filters. It is possible to design man- made superlattice with alternate layers of polar solids with thicknesses ranging from 25 angstroms to 200 angstroms. The resultant omega-k dispersion curve is shown in the figure, calculated for alternate layers of AlAs and GaAs of thicknesses of approx. 100 angstroms in the [100] direction of the crystal.

In order to have interference filters for photons, the period of the structure must be comparable to the wavelengths of photons. The proposed filter is based on interference of phonons, and since phonons have lower phase velocity for a given frequency, their wavelength is shorter. Thus, the layers should be much thinner. In order to increase the interaction of photons with phonons, a periodic structure is made such that the period is of the phonon wavelength and the total thickness is of the photon wavelength. The coupled modes of photons and phonons are called polaritons. Note that, due to the periodic interaction, for n molecules per period, the number of optical branches has increased from one to n-1. Polaritons only involve long wavelengths or low k; the acoustic branch, is not shown in the figure because it has frequencies so close to zero in the range shown. For th...