Whispering gallery mode laser: towards the deep and turbid tissue optical sensing

This study explores the application of whispering gallery mode (WGM) lasers for deep optical sensing in turbid media. Experimental results demonstrate that WGM lasers achieve accurate detection of the resonator diameter when it is deep in a highly scattering medium. Specifically, a resonator diameter of 261 μm is detectable with low intra-sample variation (<±2%), even when the resonator is placed at 5 mm deep in a scattering medium with a reduced scattering coefficient of 6.3 mm⁻¹ , a value comparable to the reduced scattering coefficient of skin tissues in visible range. In other words, the sample depth exceeds 30 times the transport length while the resolution maintains in micrometer range. As a comparison, the conventional method of optical coherence tomography can only achieve the penetration depth of one transport length.