title: Single laser pulse generates dual photoacoustic signals for differential contrast photoacoustic imaging.
abstract: Photoacoustic sensing and imaging techniques have been studied widely to explore optical absorption contrast based on nanosecond laser illumination. In this paper, we report a long laser pulse induced dual photoacoustic (LDPA) nonlinear effect, which originates from unsatisfied stress and thermal confinements. Being different from conventional short laser pulse illumination, the proposed method utilizes a long square-profile laser pulse to induce dual photoacoustic signals. Without satisfying the stress confinement, the dual photoacoustic signals are generated following the positive and negative edges of the long laser pulse. More interestingly, the first expansion-induced photoacoustic signal exhibits positive waveform due to the initial sharp rising of temperature. On the contrary, the second contraction-induced photoacoustic signal exhibits exactly negative waveform due to the falling of temperature, as well as pulse-width-dependent signal amplitude. An analytical model is derived to describe the generation of the dual photoacoustic pulses, incorporating Gruneisen saturation and thermal diffusion effect, which is experimentally proved. Lastly, an alternate of LDPA technique using quasi-CW laser excitation is also introduced and demonstrated for both super-contrast in vitro and in vivo imaging. Compared with existing nonlinear PA techniques, the proposed LDPA nonlinear effect could enable a much broader range of potential applications.
authors.affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.|School of Information Science and Technology, ShanghaiTech University, Shanghai, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Gao
authors.affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Feng
authors.affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
authors.forename: Ruochong
authors.initials: R
authors.lastname: Zhang
authors.affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
authors.forename: Siyu
authors.initials: S
authors.lastname: Liu
authors.affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
authors.forename: Ran
authors.initials: R
authors.lastname: Ding
authors.affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
authors.forename: Rahul
authors.initials: R
authors.lastname: Kishor
authors.affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore. yjzheng@ntu.edu.sg.
authors.forename: Yuanjin
authors.initials: Y
authors.lastname: Zheng