Method for remotely measuring fluctuations in the optical index of refraction of a medium
Inventors
Estes, Lee E. • Hendricks, Peter J. • Jilling, Adam
Assignees
US Department of Navy • Government of the United States of America
Publication Number
US-8711344-B1
Publication Date
2014-04-29
Expiration Date
2031-11-09
Interested in licensing this patent?
MTEC can help explore whether this patent might be available for licensing for your application.
Abstract
A method is provided for remotely measuring index of refraction fluctuations. From a first location, an optical beam is focused at a focal plane located at a second location in a medium of interest. As a result, a beam of energy is backscattered towards the first location. At the first location, a size of the backscattered beam is determined where the size is indicative of strength of fluctuations in the medium's index of refraction.
Core Innovation
The invention provides a method for remotely measuring fluctuations in a medium's index of refraction by focusing an optical beam from a first location to a focal plane located at a second location within the medium. This focused beam results in a backscattered beam that returns toward the first location, and the size of this backscattered beam is determined as an indication of the strength of the index of refraction fluctuations in the medium.
The method capitalizes on the effect that index of refraction variations within a medium have on a laser beam, such as steering the beam and increasing its size at the focal point beyond the diffraction limited spot size. By imaging the backscattered light at the source, which has passed through the fluctuations twice, the change in beam size provides a measure of these fluctuations.
The problem addressed by this invention is the lack of prior methods or instruments capable of remotely sensing index of refraction fluctuations. Existing approaches rely on sampling the medium directly or inferring index of refraction from measurements such as temperature and salinity. While methods like shadowgraphs and wavefront sensors indicate the presence of fluctuations, they do not provide the capability to remotely measure these fluctuations.
Claims Coverage
The claims include three independent claims covering methods and systems for remotely measuring index of refraction fluctuations through analysis of backscattered optical beams. These claims focus on optical beam focusing, detection of backscattered beam size, and processing to determine the strength of fluctuations.
Method of remote measurement of index of refraction fluctuations
Focusing a first beam of optical energy from a first location at a focal plane in a medium of interest, causing a backscattered second beam to return; receiving the second beam at the first location; determining a change in size of the second beam as an indirect measure of the strength of fluctuations in the medium's index of refraction.
Method employing a pulsed laser beam with controlled length and mode
Using a laser beam pulse whose length is less than the distance between the first and second locations, preferably having a TEM00 transverse mode, to focus the beam and isolate the scattering region.
System for remotely measuring fluctuations using focused optical beam and backscattered image detection
A light source to focus a beam at a focal plane in a medium, a detector to generate an image of a backscattered beam, and a processor to determine irradiance indicative of beam size and thereby measure strength of index of refraction fluctuations.
System with optical elements including laser, beam splitter, lens, waveplate, shutter, and detector
A system comprising a laser emitting pulses of beam length shorter than the distance to the focal plane, a beam splitter to separate forward and backscattered beams, a lens to focus and collect beams, a quarter waveplate for polarization manipulation, a shutter controlled to time gate backscatter detection, and a processor to measure fluctuations based on detected beam size.
The independent claims collectively cover the novel method and system configurations that enable remote measurement of index of refraction fluctuations through focusing an optical beam, capturing backscattered light, measuring its size, and interpreting this data to determine the fluctuation strength.
Stated Advantages
Enables remote measurement of index of refraction fluctuations without requiring physical sampling of the medium.
Provides an indirect method to quantify fluctuation strength by analyzing backscattered beam size changes resulting from propagation through fluctuating media.
Permits spatial and range-resolved measurement of fluctuations using pulsed laser beams with precise control and timing.
Documented Applications
Remote sensing and measurement of index of refraction fluctuations in media such as air and water.
Use in optical systems where fluctuation characterization over various ranges and focal planes is required, potentially including multiple simultaneous or sequential range measurements.
Interested in licensing this patent?