Trapping Laser Power Research Articles

Laser microfabrication and rotation of ship-in-a-bottle optical rotators

We have fabricated optical rotators inside a silica substrate and rotated them by a laser trapping technique. The fabrication method used was femtosecond laser-assisted etching, i.e., modification of the host material by irradiation with femtosecond laser pulses along a predesigned pattern, followed by selective chemical etching. The rotators, which consist of the same material as the substrate, can move inside the microcavity but cannot get out. The rotation speed was proportional to the trapping laser power, and the maximum achieved was about 100rpm. Such rotators will be applicable to micro-total-analysis systems and microfluidics.

The µPIVOT: an integrated particle image velocimeter and optical tweezers instrument for microenvironment investigations

A novel instrument to manipulate and characterize the mechanical environment in and around microscale objects in a fluidic environment has been developed by integrating two laser-based techniques: micron-resolution particle image velocimetry (µPIV) and optical tweezers (OT). This instrument, the µPIVOT, enables a new realm of microscale studies, yet still maintains the individual capabilities of each optical technique. This was demonstrated with individual measurements of optical trap stiffness (∼70 pN µm−1 for a 20 µm polystyrene sphere and a linear relationship between trap stiffness and laser power) and fluid velocities within 436 nm of a microchannel wall. The integrated device was validated by comparing computational flow predictions to the measured velocity profile around a trapped particle in either a uniform flow or an imposed, gravity-driven microchannel flow (R2 = 0.988, RMS error = 13.04 µm s−1). Interaction between both techniques is shown to be negligible for 15 µm to 35 µm diameter trapped particles subjected to fluid velocities from 50 µm s−1 to 500 µm s−1 even at the highest laser power (1.45 W). The integrated techniques will provide a unique perspective toward understanding microscale phenomena including single-cell biomechanics, non-Newtonian fluid mechanics and single particle or particle–particle hydrodynamics.

Photon Force-Induced Phase Transition Dynamics of Single Hydrogel Nanoparticles in Water

--isopropylacrylamide) gel particles labeled with a polarity-sensitive °uores-cent probe monomer were optically trapped by a focused laser beam and its°uorescence dynamics was analyzed. The °uorescence intensity of trappedsingle gel particles was increased with the trapping laser power, while the °u-orescence peak wavelength was not changed. Temperature-induced changesof °uorescence properties of the single particle were conflrmed to be simi-lar to those of the bulk solution. These behaviors are well interpreted byconsidering that the °uorescence intensity and °uorescence peak re°ect lo-cal interactions between the °uorescent probe and attaching (bound) watermolecules and efiective polarity determined by (free) water content in theparticle, respectively. A change in the °uorescence peak wavelength afterlaser trapping was followed and its blue-shift was conflrmed to occur withina few hundreds seconds, indicating that a single gel particle gradually attainsto a globular state on this timescale, expelling initially free water moleculesand then bound ones.PACS numbers: 87.80.Cc, 33.50.Dq, 61.25.Hq, 87.64.{t

The combination of optical tweezers and microwell array for cells physical manipulation and localization in microfluidic device

A microfluidic device combined with the microwell array and optical tweezers was set up for cell manipulation, localization and cultivation. Yeast cells were manipulated by a 1,064 nm laser and transferred to microwell array as a demonstration. The flow velocities at which the yeast cell can be confined in microwells of different sizes are characterized. The simulation of the cell's flow trace in the microwell at different flow velocities is consisting with our experiment result. And we also proved a trapping laser power of 0.30 W is harmless for yeast cell cultivation. As a simple approach, this method can push forward the cell cultivation, cell interaction and other cell biology or biomedical studies in microfluidic system.

Trapping and tracking a local probe with a photonic force microscope

An improved type of scanning probe microscope system able to measure soft interactions between an optically trapped probe and local environment is presented. Such a system that traps and tracks thermally fluctuating probes to measure local interactions is called a photonic force microscope (PFM). The instrument can be used to study two-dimensional and three-dimensional surface forces, molecular binding forces, entropic and viscoelastic forces of single molecules, and small variations in particle flow, local diffusion, and viscosities. We introduce and characterize a PFM, and demonstrate its outstanding stability and very low noise. The probe’s position can be measured within a precision of 0.2–0.5 nm in three dimensions at a 1 MHz sampling rate. The trapping system facilitates stable trapping of latex spheres with diameter D=λ0/2 at laser powers as low as 0.6 mW in the focal plane. The ratio between the trapping stiffness and laser power was able to be optimized for various trapping conditions. The measured trap stiffnesses coincide well with the calculated stiffnesses obtained from electromagnetic theory. The design and the features of the novel PFM setup are discussed. The optical and thermodynamical principles as well as signal analysis are explained. Applications for three-dimensional, hard-clipping interaction potentials are shown. The technique discussed in this article and the results presented should be of great interest also to people working in the fields of classical optical tweezing, particle tracking, interferometry, surface inspection, nanotechnology, and scanning probe microscopy.

Optimized single-beam dark optical trap

We propose a new scheme for constructing a single-beam dark optical trap that minimizes light-induced perturbations of the trapped atoms. The proposed scheme optimizes the trap depth for given trapping laser power and detuning by creating a light envelope with (a) an almost minimal surface area for a given volume and (b) the minimal wall thickness that is allowed by diffraction. The stiffness of the trap’s walls, combined with the large detuning allowed by the efficient distribution of light intensity, yields a low spontaneous photon scattering rate for the trapped atoms. Our trap also optimizes the loading efficiency by maximizing the geometrical overlap between a magneto-optical trap and the dipole trap. We demonstrate this new scheme by generating the proposed light distribution of a single-beam dark trap with a trap depth that is ∼33 times larger than that of existing blue-detuned traps and ∼13 times larger than that of a red-detuned trap with the same diameter, detuning, and laser power. Trapped atoms are predicted to have a decoherence rate that is >200 times smaller than in existing single-beam dark traps and ∼1800 times smaller than in a red-detuned trap with the same diameter, depth, and laser power.

Optical trapping of small particles using a 13-μm compact InGaAsP diode laser

We describe the noncontact optical trapping of small particles by a single-beam gradient force using a near-infrared InGaAsP diode laser operating at 1.33 microm. The feasibility and reliability of diode-laser trapping was confirmed with polystyrene latex and glass spheres as well as with yeast cells. By moving small particles vertically to the laser beam axis, we measured the horizontal component of the trapping force based on the Stokes law. Thus a linear relationship between the trapping laser power and the horizontal trapping force is demonstrated and compared quantitatively with that for the Ar laser.