Abstract

We present the results of studies of the femtosecond dynamics of C₆₀. This material forms a molecular crystal in the solid state, with relatively weak interactions between the covalently bound quasi-spherical C₆₀ molecules. Thin film samples are prepared 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 The Author(s)