Nonlinear photoacoustic microscopy via a loss modulation technique: from detection to imaging

Abstract

Abstract:In order to achieve high-resolution deep-tissue imaging, multiphoton 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 frequencyselect 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.

Lock-in detection of photoacoustic feedback signal for focusing through scattering media using wave-front shaping

“…However pulsed excitation generates much stronger PA signals while posing detection challenges. For instance, a demodulation scheme using a high repetition rate Ti-Sapphire femtosecond laser, and a lock-in amplifier was applied for nonlinear two-photon absorption PA measurements [28,29]. There, relatively low energy pulses for PA, of a few nJ, at high (80MHz) repetition rate, were used, causing suppression of the transient response of the material.…”

Photophysical and Photoacoustic Properties of π‐Extended Curcumin Dyes. Effects of the Terminal Dimethylamino Electron‐donor and the Bridging Aryl Ring

“…It should be appreciated that high laser fluence nonlinear optical methods are not applicable to in vivo imaging, due to the American National Standards Institute (ANSI) laser fluence thresholds (46). However, in vitro high-resolution photoacoustic microscopy (PAM) is not restricted by ANSI limitations (47)(48)(49)(50)(51)(52)(53)(54)(55)(56).…”

Quantitative photoacoustic imaging of two-photon absorption

“…We study here two-photon photoacoustic tomography (TP-PAT) [12,32,33,34,52,67,69,75,77,78,79,81], a variant of PAT that is used to image two-photon absorption properties of tissue-like heterogeneous media. Here by "two-photon absorption" we mean the absorption event where an electron transfers to an excited state after simultaneously absorbing two photons whose total energy exceed the electronic energy band gap [37,55,63].…”