Energy enhancement in time-reversed ultrasonically encoded optical focusing using a photorefractive polymer

Time-reversed ultrasonically encoded (TRUE) optical focusing achieves light focusing into scattering media beyond one transport mean free path, which is desirable in biomedical optics. However, the focused optical energy needs to be increased for broad applications. Here, we report the use of a photorefractive polymer (PRP) as the phase conjugate mirror in TRUE optical focusing. The PRP boosted the focused optical energy by ~40 times in comparison to the previously used photorefractive Bi12SiO20 crystal. As a result, we successfully imaged absorbing objects embedded in the middle plane of a tissue-mimicking phantom having an optical thickness of 120 scattering mean free paths.