The conversion of light into mechanical energy is attracting increasing interest in the fields of chemistry, biology, photonics and material science. Manipulating strain waves on the time scale of coherent acoustic phonon beats the limits of thermodynamics, and opens new doorways to how matter can be controlled and monitored. This is particularly true at the nanometric scale where all the dynamics are generally fast, and the photo-induced stresses contained.
We use an ultrafast pump-probe photoacoustic technique that can excite and detect ultrasonic frequencies on the order of tens of GHz, i.e. ultrasonic wavelengths in a range of 100 nanometers, typical dimension of thin layer samples. Our findings, based on this novel background free signal recovery, lead to a characterization of nonlinear optical properties (NLO) of an organic pigment revealing a two-photon component followed by multi-photon reabsorption. The technique can in principle be applied to various systems, including those precluding usage of transmission or luminescence techniques often used in biology and microelectronics.
The work was carried out in collaboration between the teams of the Institute of Physics of Rennes, Wrocław University of Science and Technology, and the Massachusetts Institute of Technology. The technology transfer between MIT and IPR has been stimulated by the arrival at the Institute of Thomas Pezeril (DMV) and Ievgeniia Chaban (DML). Picosecond acoustics, as well as the generation of shock waves by an ultrashort laser, is a nascent collaborative project between DML and DMV.
Nonlinear Optical Absorption in Nanoscale Films Revealed through Ultrafast Acoustics
Ievgeniia Chaban, Radoslaw Deska, Gael Privault, Elzbieta Trzop, Maciej Lorenc*, Steven E. Kooi, Keith A. Nelson, Marek Samoc, Katarzyna Matczyszyn*, and Thomas Pezeril*