A Cell Lens Model for Transverse Modes in Optofluidic Intracavity Spectroscopy

Optofluidic intracavity spectroscopy of individual cells from canine hemangiosarcoma (HSA) and canine lymphoma cancer cell lines exhibit relatively uniformly spaced multiple transverse modes repeated in each free spectral range of a microfluidic Fabry-Pérot cavity, while similar spectra of healthy canine monocytes and lymphocytes have minimal or no transverse-mode peaks. Modeling of the cells as thin lenses allows paraxial Gaussian beam resonator analysis that produces spectral features that quantitatively match the frequencies of transverse modes and qualitatively agree with the trends in maximum transmission of the modes when aperture losses are included. Cell focal lengths of 600 and 300 μm, respectively, are extracted for canine HSA and lymphoma cells from the ratio of transverse to longitudinal frequency spacing, while the spectra of canine monocytes indicate that they have a focal length ≥ 580 μm. Under an assumption of constant refractive index, the focal lengths imply a radius of curvature for the top surface of the cells that is much greater than their lateral radius.