Intracavity Optical Trapping preprint on ArXiv

Intracavity Optical Trapping

Intracavity Optical Trapping
Fatemeh Kalantarifard, Parviz Elahi, Ghaith Makey, Onofrio M. Maragò, F. Ömer Ilday & Giovanni Volpe
arXiv: 1808.07831

Standard optical tweezers rely on optical forces that arise when a focused laser beam interacts with a microscopic particle: scattering forces, which push the particle along the beam direction, and gradient forces, which attract it towards the high-intensity focal spot. Importantly, the incoming laser beam is not affected by the particle position because the particle is outside the laser cavity. Here, we demonstrate that intracavity nonlinear feedback forces emerge when the particle is placed inside the optical cavity, resulting in orders-of-magnitude higher confinement along the three axes per unit laser intensity on the sample. We present a toy model that intuitively explains how the microparticle position and the laser power become nonlinearly coupled: The loss of the laser cavity depends on the particle position due to scattering, so the laser intensity grows whenever the particle tries to escape. This scheme allows trapping at very low numerical apertures and reduces the laser intensity to which the particle is exposed by two orders of magnitude compared to a standard 3D optical tweezers. We experimentally realize this concept by optically trapping microscopic polystyrene and silica particles inside the ring cavity of a fiber laser. These results are highly relevant for many applications requiring manipulation of samples that are subject to photodamage, such as in biological systems and nanosciences.

Microscopic Crowd Control published in Nature Commun.

Disorder-mediated crowd control in an active matter system

Disorder-mediated crowd control in an active matter system
Erçağ Pinçe, Sabareesh K. P. Velu, Agnese Callegari, Parviz Elahi, Sylvain Gigan, Giovanni Volpe & Giorgio Volpe
Nature Communications 7, 10907 (2016)
DOI: 10.1038/ncomms10907

Living active matter systems such as bacterial colonies, schools of fish and human crowds, display a wealth of emerging collective and dynamic behaviours as a result of far-from- equilibrium interactions. The dynamics of these systems are better understood and controlled considering their interaction with the environment, which for realistic systems is often highly heterogeneous and disordered. Here, we demonstrate that the presence of spatial disorder can alter the long-term dynamics in a colloidal active matter system, making it switch between gathering and dispersal of individuals. At equilibrium, colloidal particles always gather at the bottom of any attractive potential; however, under non-equilibrium driving forces in a bacterial bath, the colloids disperse if disorder is added to the potential. The depth of the local roughness in the environment regulates the transition between gathering and dispersal of individuals in the active matter system, thus inspiring novel routes for controlling emerging behaviours far from equilibrium.

 

Featured in:
Understanding the dynamics of crowd behaviororg
Physics Explains Group Dynamics: When There’s Chaos, Individuals Disperse”, Medical Daily
Ученые выяснили, как меняющаяся окружающая среда влияет на движение толпы”, Gazeta.ru
Understanding the dynamics of crowd behaviour”, Nano
Understanding the dynamics of crowd behaviour”, Noodls
Understanding the dynamics of crowd behavior”, EurekAlert!
Understanding the dynamics of crowd behavior”, Informs
Understanding the dynamics of crowd behavior”, Nanowerk