Observation of three-photon enhanced four-photon absorption.
We report the measurement of instantaneous resonant four-photon absorption in the polydiacetylene-PTS [polymer poly(bis para-toluene sulfonate) of 2,4-hexadyine-1,6 diol]. Although normally too weak to be observable, an exact degeneracy between three- and four-photon absorption into the dominant exciton and two-photon states, respectively, resonantly enhances this effect so that it can be measured (four-photon coefficient alpha(4)=0.01 cm(5)/GW(3)) at its peak wavelength of 1900 nm. Femtosecond measurements from 1200 to 2200 nm of two- and three-photon absorption, and the nonlinear refractive index coefficient are also reported.
Yoshino
Fumiyo
F
School 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.
Polyakov
Sergey
S
Liu
Mingguo
M
Stegeman
George
G