Abstract

Metal surfaces have been excited with high-intensity, ultrafast optical pulses in order to understand the relaxation dynamics of the transient nonequilibrium between the electron and lattice temperatures, the temperature-dependent collisionality of the material¹ and the radiation of soft x-rays from a high-temperature, solid-density plasma². Pulsewidths on the order of 100 fs offer the bonus of depositing large amounts of energy within a skin depth of the surface, creating transient, high electron temperatures. The electrons thermalize rapidly via electron-electron scattering while electron-phonon scattering is expected to take more than 100 fs. Experimental techniques used to study the electron cooling dynamics include thermally assisted photoemission³, thermal modulation of the optical constants⁴ and multishot optical damage⁵. The critical issues in the measurement of the electron-lattice coupling constant include the trade-off between diffusion of the electron gas and electron-lattice energy exchange, the energy distribution of the hot electrons and the thickness of the sample⁶. These same dynamics are important to the realization of a short-pulse, soft x-ray source since the tail of the x-ray pulse will follow the cooling of the electron energy distribution. We report the direct measurement of the time-resolved electron energy distribution from a Ag(111) surface under ultrafast optical excitation.

© 1990 Optical Society of America