Coherent Generation of Photo-Thermo-Acoustic Wave from Graphene Sheets
Yichao Tian1He Tian2Yanling Wu1Leilei Zhu1Lu-Qi Tao2Wei Zhang1Yi Shu2Dan Xie2Yi Yang2Zhiyi Wei1Xinghua Lu1Tian-Ling Ren2Chih-Kang Shih3Jimin Zhao1
摘要：Many remarkable properties of graphene are derived from its large energy window for Dirac-like electronic states and have been explored for applications in electronics and photonics. The interplay of graphene’s unique electronic structures and lattice vibrations under photo-excitation（strong electron-phonon interaction） has led to efficient photo-thermo energy conversions, which has been harnessed for energy applications. Here we introduce another innovative application: coherent generation of acoustic waves in a multi-layer graphene（MLG） sheet at ambient environment. Various ultrafast laser pulses with temporal durations ranging from fs-ps-ns were used to examine the underlining physics mechanism of the sound generation, verifying the photo-thermal-acoustic mechanism. Multiple ultrafast laser systems with different repetition rates were used to further control the acoustic waves generated in a coherent way. This employs anharmonic sound generation. Our investigation combined the wavelength independent absorption property and the efficient photo-thermo energy conversion. Unambiguous sound generation was realized by shining ultrafast laser pulses onto a MLG sheet sample. The sound wave generation was experimentally demonstrated to be of photo-thermo-acoustic（PTA） mechanism. Significantly, we demonstrate the ability to control the phase of sound waves coherently by tuning the repetition rates of the ultrafast laser pulses. An optical speaker based on a graphene material has been realized for the first time, which has non-contact and remote control capability. The physics mechanism（PTA） has been experimentally revealed for the first time. Anharmonic sound waves facilitated the realization of coherent control of the sound. Our investigation paves the way to energy harvesting far from the Fermi surface. Our investigation can be easily extended to electrical interference control and other sound generation applications, such as optical switching of acoustic sound generation.
The 6th International Conference on Nanoscience & Technology, China 2015