Sensing non-light-absorbing media via thermally modulated photoacoustic measurements

In conventional photoacoustic (PA) imaging, the imaging contrast is largely determined by the difference in optical absorption of the targets. Therefore, to distinguish non-light-absorbing media using these optical methods presents practical difficulties. It has been shown that the difference in thermodynamic properties is more obvious in certain situations. Further, it has been found experimentally that the PA response of a probe is significantly different due to the thermodynamic action of the surrounding medium, for example, there is a reverse trend for lipid and collagen. In this Letter, an optical method using a PA-responsive external probe to sense the difference in thermodynamic properties of non-light-absorbing media is proposed. The experimental results demonstrate that the proposed method provides a scheme to solve the challenges encountered by traditional PA technologies and has significant potential in biomedical applications.