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)
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