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Modification of coherent acoustic phonon lifetimes in thin gold films by self-assembled molecular monolayers

We report on the modification of coherent acoustic phonon lifetimes in thin gold films induced by insertion of self-assembled monolayers as interface layers between gold films and substrates. The lifetimes of coherent acoustic phonons are investigated by asynchronous optical sampling (ASOPS) [1], a high speed pump-probe method which utilizes two Ti:sapphire lasers of ∼1 GHz repetition rate. The time delay between pump and probe pulse is obtained by a repetition rate offset of 5 kHz. The absence of moving mechanical parts allows for fast scanning times and high signal to noise ratios which are hard to achieve by conventional pump-probe methods [2].