Showing papers by "David McGloin published in 2010"

Optical tweezers : methods and applications

Abstract: The technical development of optical tweezers, along with their application in the biological and physical sciences, has progressed significantly since the demonstration of an optical trap for micron-sized particles based on a single, tightly focused laser beam was first reported more than twenty years ago. Bringing together many landmark papers on

Forty Years of Optical Manipulation

Abstract: This year, as the laser celebrates its 50th anniversary, a field that was made possible through laser technology reaches an important milestone as well. Over the past 40 years, optical manipulation research has deepened our understanding of physics and biology, and it has yielded the optical-tweezer technique that is used across all the sciences.

Observation of bistability of trapping position in aerosol optical tweezers

Abstract: Bistability in the axial trapping position of aqueous aerosol droplets has been observed for the first time, to our knowledge, in optical tweezers. The behavior has been observed for two distinct trapping configurations, with the trapping beam oriented either along the vertical or horizontal axis. This represents the first report of the optical tweezing of aerosol droplets with a horizontally propagating laser beam. Side imaging was used in conjunction with imaging in the plane of the optical trap. Droplet sizing was performed using cavity-enhanced Raman spectroscopy or by applying a circular regression routine to the acquired images. Predictions from a theoretical model of optical forces are shown to be in good agreement with the experimental observations of bistability in the trapping position. These studies have significance both for the rigorous interpretation of data obtained using aerosol optical tweezers and for the modeling of aerosol optical traps.

Observation of bistability of trapping position in aerosol optical tweezers

Abstract: Bistability in the axial trapping position of aqueous aerosol droplets has been observed for the first time, to our knowledge, in optical tweezers. The behavior has been observed for two distinct trapping configurations, with the trapping beam oriented either along the vertical or horizontal axis. This represents the first report of the optical tweezing of aerosol droplets with a horizontally propagating laser beam. Side imaging was used in conjunction with imaging in the plane of the optical trap. Droplet sizing was performed using cavity-enhanced Raman spectroscopy or by applying a circular regression routine to the acquired images. Predictions from a theoretical model of optical forces are shown to be in good agreement with the experimental observations of bistability in the trapping position. These studies have significance both for the rigorous interpretation of data obtained using aerosol optical tweezers and for the modeling of aerosol optical traps.

Parameter exploration of optically trapped liquid aerosols.

Abstract: When studying the motion of optically trapped particles on the microsecond time scale, in low-viscosity media such as air, inertia cannot be neglected. Resolution of unusual and interesting behavior not seen in colloidal trapping experiments is possible. In an attempt to explain the phenomena we use power-spectral methods to perform a parameter study of the Brownian motion of optically trapped liquid aerosol droplets concentrated around the critically damped regime. We present evidence that the system is suitably described by a simple harmonic oscillator model which must include a description of Faxen's correction, but not necessarily frequency dependent hydrodynamic corrections to Stokes' law. We also provide results describing how the system behaves under several variables and discuss the difficulty in decoupling the parameters responsible for the observed behavior. We show that due to the relatively low dynamic viscosity and high trap stiffness, it is easy to transfer between over- and underdamped motion by experimentally altering either trap stiffness or damping. Our results suggest stable aerosol trapping may be achieved in underdamped conditions, but the onset of deleterious optical forces at high trapping powers prevents the probing of the upper stability limits due to Brownian motion.

Generation of optofluidic microchannels in ice

Abstract: We demonstrate that light can be used to create microchannels in ice. We make use of free space and fiber coupled infrared laser light to produce microchannels with diameters down to 100 microns in diameter. We demonstrate that the channels can be created in a timescale of seconds and that by controlling the input power that they can be stabilized over a timescale of several minutes using powers as low as 30mW. We compare the fiber coupled geometry, using both single mode and multimode fiber and free space coupling and show that fiber coupling produces optimal results. We demonstrate that liquid samples can be inserted into the channels and particle movement is observed using a combination of optical and thermally induced forces. We also present data looking at droplet freezing within the microchannels. We present preliminary results looking at dual beam coupling into such optofluidic channels and examine prospects for using such channels as rapid microfluidic prototypes. We further discuss the possibility of using optically shaped ice channels as a means to study aerosol nucleation processes and the ability of ice to act as a template for microfluidic devices.

Optical Tweezers: The Early Years

Abstract: An optical tweezers apparatus uses a tightly focused laser to generate a trapping force that can capture and move small particles under a microscope. Because it can precisely and nondestructively manipulate objects such as individual cells and their internal components, the optical tweezers is extremely useful in biological physics research. In this experiment you will use optical tweezers to trap small silica spheres immersed in water. You will learn how to measure and analyze the frequency spectrum of their Brownian motion and their response to hydrodynamic drag in order to characterize the physical parameters of the optical trap with high precision. The apparatus can then be used to measure a microscopic biological force, such as the force that propels a swimming bacterium or the force generated by a transport motor operating inside a plant cell.