Ferrofluids behave superparamagnetically and can be manipulated by external magnetic fields, providing numerous applications in microfluidic systems. In this paper, an adaptive liquid microlens driven by a ferrofluidic actuator is presented. The microlens consists of a cylindrical well filled with a lens liquid connected to a microchannel containing a ferrofluid plug. When the ferrofluid plug is moved back and forth by an external magnetic field, the lens liquid is displaced, forming a liquid lens with an adaptive focus in the cylindrical well. The focal length of the lens can be changed from infinity to the scale of the radius of the cylindrical well, leading to a high optical power compared to conventional liquid lenses utilizing liquid crystals or electrowetting. The lens curvature is reversibly tunable without hysteresis when the ferrofluid plug moves with a speed below a specific threshold value. The lens can be acted on by a magnetic field of about 100 mT which can be generated by microcoils requiring much lower voltages than the electrowetting principle.
Materials having tunable optical properties are of great interest for photonic applications. Promising candidates in that context are transparent nanoporous media whose optical properties change after infiltration of a liquid into the pores. Herein we present an all-optical method to tune the light scattering properties of a nanoporous glass based on the light-induced phase change of the fluid filling the pores. The thermodynamic state of the gas inside the nanopores determines the light scattering, thereby the light transmission. The extent of capillary condensation inside the nanoscale pores is controlled by heat generated from light absorption inside the medium. The material can be configured in such a way that a laser beam of sufficient intensity either opens up or shuts down its own light path on a time scale of a few seconds. The scattering events inside the medium change the beam profile from Gaussian to super-Gaussian with a more homogeneous intensity distribution close to the beam axis. Our results demonstrate a new way of tuning the light transmission properties of nanoporous materials that could find various applications in integrated optical systems and optofluidic devices.
Ferrofluids are superparamagnetic suspensions of nanoparticles that can be used as transducers in microfluidic systems, among others. In corresponding setups a microscopic enclosure such as a microchannel is filled with a ferrofluid that is acted on by an external magnetic field. The induced motion of the ferrofluid is utilized to pump or manipulate minute amounts of liquids. Here the dynamic behavior of an adaptive liquid microlens driven by a ferrofluidic transducer is studied. Adaptive microlenses based on that principle promise a number of advantages over existing concepts, such as an increased tuning range of the focal length. It is shown that the delay time of the deformation of the lens surface to the displacement of the magnet producing the external field increases with increasing magnet speed. Dynamic leakage of the lens liquid around the ferrofluid plug, on the other hand, only occurs when the magnet speed exceeds a threshold value and further increases from that point onwards. When the viscosity of the lens liquid increases, both the delay time and the dynamic leakage increase.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.