The active force spectrum of a microswimmer - modeling and experiments

Chlamydomonas reinhardtii are a widely-studied microswimmer that propel themselves by converting chemical energy to mechanical motion of their flagellum in a breast stroke motion. Fluid dynamics approaches have revealed much about the importance of hydrodynamics at the micron-scale and its role in microswimmer transport. However, the stochastic dynamics which are dominated by active non-thermal fluctuations are not well understood. We use optical tweezers and the photon momentum method to directly measure the stochastic forces generated by a trapped Chlamydomonas microswimmer. We model the microswimmer using the generalized Langevin equation approach with active stochastic forcing. Our combined experimental and theoretical approach, based on microrheological techniques, isolates the active force spectrum generated by Chlamydomonas to quantify their nonequilibrium dynamics. We seek to use this framework to test recent developments in stochastic thermodynamics.