Femtosecond-tunable measurement of electron thermalization in gold

Femtosecond cubic optical nonlinearity of thin nickel films

Transient pump-probe measurements of circular anisotropy in nickel films induced by 38-fs optical pulses show an instantaneous response that is related to the optical orientation of the spins of free electrons. Measurements in a sample of variable thickness, performed in both transmission and reflection, revealed that the surface significantly influences the degenerate cubic optical nonlinearity of the nickel films to a depth of approximately 4-5 nm into the bulk.

Probing nonequilibrium electron distributions in gold by use of second-harmonic generation

Second-harmonic radiation is generated at a gold surface by use of a laser pulse that is varied in duration from 14 to 29 fs and in intensity from 10(9) to 10(11)W/cm(2) . At laser intensities below 10(10)W/cm(2) , the second-harmonic signal has the expected quadratic dependence on pump-laser intensity; however, at higher intensities, the dependence is supraquadratic. This difference arises because the leading edge of the laser pulse interacts significantly with the gold electrons to create a nonequilibrium, photoexcited distribution. The second-harmonic generation process occurs before electron-electron or electron-phonon collisions can equilibrate the distribution and therefore serves as a probe of the nonequilibrium distribution.