Abstract

This study focusses on the fast dynamics of solid C₆₀ following photoexcitation. Thin film samples are preparated by thermal sublimation of purifed C₆₀ powder. The samples are excited with optical pulses of ~ 12 fs duration in both the red and blue-green regions of the spectrum. Optical pulses centered at 620 nm are generated with a femtosecond laser system consisting of a colliding-pulse modelocked (CPM) dye laser with a copper vapor laser pumped dye amplifier that produces 50 fs pulses at an 8 kHz repetition rate. These pulses are chirped in an optical fiber and compressed using a sequence of diffraction gratings and prisms.^[1] To increase the energy of the compressed pulses, an additional copper vapor pumped dye amplifier is introduced prior to compression of the chirped pulse. Optical pulses at blue-green wavelengths (450-550 nm) are generated by using amplified CPM pulses to generate a femtosecond continuum in an ethylene glycol jet. The blue-green portion of the continuum is then re-amplified in an excimer laser pumped dye amplifier operating at a 400 Hz repetition rate, and is directly compressed using diffraction gratings and prisms.^[2] Time-resolved measurements of the differential transmittance are made using a pump-probe technique, and wavelength resolution is achieved by filtering the probe beam after transmission through the sample.

© 1992 IQEC