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Observation of three-photon enhanced four-photon absorption
Fumiyo Yoshino1, Sergey Polyakov, Mingguo Liu
1School of Optics and Center for Research and Education in Optics and Lasers, University of Central Florida, 4000 Central Florida Boulevard, Orlando, Florida 32816-2700, USA.
Physical Review Letters
|August 26, 2003
Summary
We measured resonant four-photon absorption in polydiacetylene-PTS polymer, an effect enhanced by specific energy level alignments. This allows observation of a previously unmeasurable nonlinear optical phenomenon.
Area of Science:
- Nonlinear Optics
- Materials Science
- Condensed Matter Physics
Background:
- Polydiacetylenes (PDAs) exhibit significant nonlinear optical properties.
- Four-photon absorption is typically a very weak nonlinear optical process.
- Resonant enhancement can dramatically increase the observability of weak nonlinear phenomena.
Purpose of the Study:
- To measure instantaneous resonant four-photon absorption in polydiacetylene-PTS.
- To investigate the influence of energy level degeneracy on nonlinear absorption.
- To characterize other nonlinear optical properties of polydiacetylene-PTS.
Main Methods:
- Femtosecond spectroscopy was employed for measurements.
- Wavelength-dependent measurements were conducted from 1200 to 2200 nm.
- The four-photon absorption coefficient was determined under resonant conditions.
Main Results:
- Instantaneous resonant four-photon absorption was successfully measured in polydiacetylene-PTS.
- A peak absorption was observed at 1900 nm with a coefficient alpha(4)=0.01 cm(5)/GW(3).
- Two-photon absorption, three-photon absorption, and nonlinear refractive index were also characterized.
Conclusions:
- Exact degeneracy between three- and four-photon absorption states significantly enhances four-photon absorption.
- Polydiacetylene-PTS demonstrates potential for applications requiring strong nonlinear optical responses.
- The study provides a comprehensive nonlinear optical characterization of polydiacetylene-PTS.