Femtosecond time-resolved transmissivity of laser heated thin copper films

The phenomenon of inequality between electron and lattice temperatures in metals subjected to ultrafast heating (laser pulse width ≤ electron-phonon energy relaxation time) was postulated some time ago. However, very few experimental observations of such inequality have been accomplished. In a previous experimental observation of picosecond (≅5-ps FWHM) time-resolved reflectivity or copper during laser heating of up to a few degrees, a fast transient was observed. This observation was interpreted to be due to rapid electronic heating which subsequently thermalizes with the lattice. In another thermally enhanced multiphoton photoemission in tungsten heated by amplified 75-fs laser pulses has provided evidence of nonequilibrium heating. The authors report results on thermomodulation transmissivity of thin copper films heated by amplified 150-fs laser pulses, which were sufficient to time resolve the initial fast transient