Femtosecond time-resolved photodynamical study on Ag-O-Ba thin film

Summary form only given. The ultrafast relaxation of the Ag-O-Ba composite film was investigated by using a pump supercontinuum-probe technique (PSCP). The measurement was performed using a Ti:sapphire chirped-pulse amplification (CPA) laser system. Its output pulse was 800 nm, 120 fs, 10 mJ. The pulse was split into two beams. One beam, after passing a variable delay line, was used for optical pumping. The other beam was focused into distilled water to generate supercontinuum probe pulse wavelengths which ranged from 400 nm to 1000 nm. The Ag-O-Ba thin film consisted of silver nanoparticles embedded in a BaO semiconductor matrix which was considered as a new type of photoemissive material. When the Ag-O-Ba thin film was pumped by laser pulses of 800 nm wavelength, only free electron (intraband transition) absorption occurred through multiphoton absorption because the excitation wavelength is far from the surface plasma resonance (SPR) at 400 nm and the energy level of silver nanoparticles above the Fermi energy level is quasi-continuum. Meanwhile, the size of metal nanoparticles was around 40 nm in our experiment. It is convenient to describe the photodynamics in nanoparticles using a small solid approach. Thus the quantum confinement can not modify the band structure. So the maximal probability for electron transition should be the state gap energy between the occupied state density peak L/sub 2/ above the Fermi level and the unoccupied state density peak X/sub 4/ below the Fermi level according to Berglang´s (1994) energy structure of silver. The time-resolved transient transmissivity induced by multiphoton absorption were investigated at different probe wavelengths. The decay time of the Ag-O-Ba thin film changes from 0.67 ps to 4 ps. A typical result is shown at 700 nm probe wavelength. The transmission difference at zero delay caused by the pump was also measured. The maximal difference at 700 nm indicated that the unoccupied state density peak X/sub 4/ is 1- 47eV above the Fermi level.