We report that silicon surfaces develop an array of sharp conical spikes when irradiated with 500 laser pulses of 100-fs duration, 10-kJ/m2 fluence in 500-Torr SF6 or Cl2. The spikes are up to 40-μm tall, and taper to about 1-μm diam at the tip. Irradiation of silicon surfaces in N2, Ne, or vacuum creates structured surfaces, but does not create sharp conical spikes.

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Laser induced formation of CO2 and desorption of 02 e initiated with femtosecond and picosecond laser excitation of a Pt(1 1 1) surface prepared with coadsorbed CO and 02 at 90 K. The nonlinear fluence dependent reaction yields were measured for 267, 400, and 800 nm wavelengths, and for pulse durations from 80 fs to 3.6 ps. Two-pulse correlation experiments measuring total 02 desorption yield versus time delay between 80 fs pulses show a 0.9 Ps HWHM central peak and a slower 0. 1 ns timescale. At 267 nm the relative yields of 02 and CO2 are found to depend on fluence. Comparison of results at different wavelengths and pulsewidths shows that nonthermalized surface electrons play a role in the laser-induced surface chemistry.

Time-resolved coherent anti-Stokes Raman spectroscopy is used to obtain the rovibrational energy distributions in polyatomic molecules following infrared multiphoton excitation. In addition to presenting new results on SF 6 , we review previously obtained data on S02 and OCS. The data yield new details about infrared muItiphoton excitation and intramolecular vibrational energy relaxation. In particular they show the significance of collisions in redistributing vibrational energy following excitation. The results also clearly show stronger intermode coupling and higher excitation in systems with increasing numbers of atoms per molecule.