OPTICAL DEPHASING OF A NEAR-INFRARED DYE IN PMMA - PHOTON-ECHOES USING THE SUPERCONDUCTING ACCELERATOR PUMPED FREE-ELECTRON LASER

A superconducting accelerator pumped free electron laser is used to perform picosecond photon echo experiments on the near infrared dye 1,1′,3,3,3′,3′-hexamethylindotricarbocyanine iodide (HITCI) in poly(methyl methacrylate) (PMMA). The temperature dependence of the optical dephasing is measured from 1.5 to 10 K. At the lowest temperatures a temperature dependence, T-1.4, characteristic of two-level system glass dynamics is observed. Above 5 K, the optical dephasing is exponentially activated with an activation energy of 15 cm-1. This is the same activation energy reported for rhodamine B in PMMA, demonstrating that 15 cm-1 corresponds to an intrinsic glass mode. These are the first photon echo experiments, and to our knowledge, the first nonlinear optical coherence experiments, performed using a FEL as a source. © 1990.