Measurement of the nonlinear refractive index of air
Abstract
All materials exhibit nonlinear refraction, which means that their index of refraction may change as the irradiance of laser light increases. In this project, we will measure the nonlinear refraction of the atmosphere in the mid infrared wavelength range and will identify and characterize the contributing mechanisms, including bound-electronic, rotational, vibrational, and possibly plasma, along with any possible unanticipated contributions. Our methods allow clear delineation of the temporal dependence of the various contributions to the nonlinear response. We will primary use our recently developed beam-deflection method that has been shown to allow separation of different nonlinear response mechanisms in solvents, gases and semiconductors including air at STP and to give the temporal dependencies of each mechanism. This method has sensitivity to induced phase changes as small as one twenty thousandth of a wavelength in the near IR, and allows measurement at multiple irradiances. By systematically measuring the nonlinear refraction using femtosecond excitation pulses, we will develop a comprehensive theory for the nonlinear response function that will allow prediction of the nonlinear response of air for different pulse widths. We have already successfully applied this methodology to a multitude of different materials in various phases from solid to liquid to gas. In this project, one of the initial challenges will be to adapt the quad cell detectors used for the beam-deflection method to the mid infrared. Once we determine the best detection scheme, we will use our 100 femtosecond mid infrared source to measure nonlinear refraction in air. We will also attempt to measure nonlinear refraction of nitrogen and oxygen separately in confined gas chambers. We will perform measurements using different polarization combinations that will allow us to separate the bound-electronic response of the molecules from their nuclear responses. This will allow predictions of the nonlinear response at other pulse widths. The results of these experiments will be compared to measurements in the visible/near-IR that have already been performed in our labs, and to theory.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 17, 2017
- Source ID
- HR00111710003
Entities
People
- Eric Van Stryland
Organizations
- Defense Advanced Research Projects Agency
- University of Central Florida Board of Trustees