A theoretical framework for acoustically produced luminescence: From thermometry to ultrasound pressure field mapping

Acoustically produced luminescence (APL) can be used for fast and easy mapping of ultrasound pressure fields, allowing quantitative investigation of these fields for a wide range of acoustic frequencies and pressures. APL offers a fast and inexpensive alternative for the conventional point-by-point hydrophone scanning. This can benefit industrial and medical ultrasound applications that experience stringent certification and safety requirements on pressure field characterization. APL was shown to originate from absorption-mediated heating by ultrasound irradiation of a membrane material, which consists of a polymer binder and a luminescent material (or phosphor). This heating induces local thermoluminescence emission, which is proportional to the ultrasound pressure. However, a precise framework describing the physics of the APL process, allowing the retrieval of acoustic field information from the measured light emission has been lacking. Here, we present a full theoretical model of the APL phenomenon, allowing the reconstruction of both the pressure and temperature fields from the measured luminescence. The developed theoretical model is verified using finite-element modeling and experimental validation. We then demonstrate how APL can be used to obtain a 3D reconstruction of an ultrasound pressure field, in a fast and easy way. Finally, the general model demonstrated here can also prove useful for other applications, e.g. in luminescence-based thermometry using persistent phosphors.