Abstract
Optical tweezers based on optical radiation pressure are widely used to manipulate nanoscale to microscale particles. This study demonstrates direct measurement of the optical force gradient distribution acting on a polystyrene (PS) microsphere using a carbon nanotube (CNT) mechanical resonator, where a PS microsphere with 3 μm diameter is welded at the CNT tip using laser heating. With the CNT mechanical resonator with PS microsphere, we measured the distribution of optical force gradient with resolution near the thermal noise limit of 0.02 pN/μm in vacuum, in which condition enables us to high accuracy measurement using the CNT mechanical resonator because of reduced mechanical damping from surrounding fluid. The obtained force gradient and the force gradient distribution agree well with theoretical values calculated using Lorenz–Mie theory.
Highlights
Photon radiation pressure acting toward the center of the tightly focused laser beam has been used for trapping and manipulation of nanoscale to microscale particles, with a technique known as “optical tweezers”[1,2,3,4,5]
Carbon nanotube (CNT) cantilevers[19,20,21,22,23,24,25,26,27] are a promising component for use in nanomechanical resonators because of their minute mass and high aspect ratio. These mechanical properties result in a small spring constant on the order of 100 pN/μm, which is 2–3 orders of magnitude smaller than that of commercially available Si cantilevers used for atomic force microscopy (AFM)
We demonstrate direct measurements of the spatial distribution of optical radiation force acting on a PS microsphere using a CNT mechanical resonator in vacuum, for which we propose easy attachment process of an individual PS microsphere on the CNT mechanical cantilever
Summary
One can estimate the optical spring constant kOPT from the resonance frequency shift Δf of the CNT-PS resonator induced. A spring constant of the CNT cantilever, kCNT, was estimated as 194 pN/μm from the resonance frequency of 364 kHz before attachment of the PS sphere. The estimated added mass corresponds to the mass of PS sphere with diameter of 2.9 μm, which is close to the average diameter (3 μm) of PS spheres used in this experiment These indicate that the spring constant of the CNT cantilever was maintained after the attachment of the PS sphere through the welding process in air and the attached PS sphere induces no significant mechanical dumping to the resonance properties
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
