title: Nonlinear photoacoustic microscopy via a loss modulation technique: from detection to imaging.
abstract: In order to achieve high-resolution deep-tissue imaging, multi-photon fluorescence microscopy and photoacoustic tomography had been proposed in the past two decades. However, combining the advantages of these two imaging systems to achieve optical-spatial resolution with an ultrasonic-penetration depth is still a field with challenges. In this paper, we investigate the detection of the two-photon photoacoustic ultrasound, and first demonstrate background-free two-photon photoacoustic imaging in a phantom sample. To generate the background-free two-photon photoacoustic signals, we used a high-repetition rate femtosecond laser to induce narrowband excitation. Combining a loss modulation technique, we successfully created a beating on the light intensity, which not only provides pure sinusoidal modulation, but also ensures the spectrum sensitivity and frequency selectivity. By using the lock-in detection, the power dependency experiment validates our methodology to frequency-select the source of the nonlinearity. This ensures our capability of measuring the background-free two-photon photoacoustic waves by detecting the 2nd order beating signal directly. Furthermore, by mixing the nanoparticles and fluorescence dyes as contrast agents, the two-photon photoacoustic signal was found to be enhanced and detected. In the end, we demonstrate subsurface two-photon photoacoustic bio-imaging based on the optical scanning mechanism inside phantom samples.
authors: Yu-Hung
authors: YH
authors: Lai
authors: Szu-Yu
authors: SY
authors: Lee
authors: Chieh-Feng
authors: CF
authors: Chang
authors: Yu-Hsiang
authors: YH
authors: Cheng
authors: Chi-Kuang
authors: CK
authors: Sun
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007089:Image Enhancement / Q000295:instrumentation* / Q000379:methods*; D033401:Microscopy, Acoustic / Q000295:instrumentation* / Q000379:methods*; D036641:Microscopy, Fluorescence, Multiphoton / Q000295:instrumentation* / Q000379:methods*; D017711:Nonlinear Dynamics