What is Optical tweezers: Definition and 18 Discussions

Optical tweezers (originally called single-beam gradient force trap) are scientific instruments that use a highly focused laser beam to hold and move microscopic and sub-microscopic objects like atoms, nanoparticles and droplets, in a manner similar to tweezers. If the object is held in air or vacuum without additional support, it can be called optical levitation.
The laser light provides an attractive or repulsive force (typically on the order of piconewtons), depending on the relative refractive index between particle and surrounding medium. Levitation is possible if the force of the light counters the force of gravity. The trapped particles are usually micron-sized, or smaller. Dielectric and absorbing particles can be trapped, too.
Optical tweezers are used in biology and medicine (for example to grab and hold a single bacterium or cell like a sperm cell, blood cell or DNA), nanoengineering and nanochemistry (to study and build materials from single molecules), quantum optics and quantum optomechanics (to study the interaction of single particles with light). The development of optical tweezing by Arthur Ashkin was lauded with the 2018 Nobel Prize in Physics.

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  1. wheatie

    I Optical Tweezer Laser Focus/Alignment Troubleshooting

    Currently we have an optical tweezer setup that has a beam expander + dichroic mirror that fills the aperture of the objective, and a microscope that is able to look into the aperture and see a diameter of about 30 microns. We have been stuck for a couple weeks now, as we do not know if our...
  2. S

    What Causes Molecules to Aggregate Over a Fiber in Optical Trapping?

    I poured a droplet that has 1.55 refractive index (RF) over a fiber that has core and cladding with (RI) 1.45 and 1.4 respectively, and I the molecules aggregated over the fiber, known that because the refractive index of the liquid is higher than of than of the core or the cladding a leakage of...
  3. S

    Trapping stiffness of optical tweezers

    I read in some articles that the force in optical tweezers can be written as: F=kx, with no minus because the force will increase as the distance increased and the particle moves to the source..., This I can understand, but what I can not understand if I make integral (it is conservative force)...
  4. C

    Optical Tweezers and 3D Printing

    I am trying to assemble an optical tweezers setup and was thinking if it is realistic to assemble an optical tweezers setup using 3D printed parts? Also can DMD (Digital Micromirror Device) be used instead of SLM to manipulate the beam and generate multiple traps?
  5. J

    Optical Tweezers in the Ray Optics Regime

    Homework Statement Consider an optical tweezer operated in the ray optics regime as shown in Figure. Net reflection angle of the ray shown in Figure is θ = 10◦ (See Figure). Since more photons take the thick ray than the thin ray, a net force of F = 1 pN is exerted on the sphere toward the...
  6. henil

    Optical Tweezers: Preparing Samples for RBC Trapping

    I am currently working on project for trapping RBC's using optical tweezers but i think i am making a mistake in preparing the sample. Can anyone provide an appropriate sample preparing method ?
  7. S

    Optical tweezers for manipulating atoms together to form new structure

    I am trying to figure out a method for using optical tweezers to manipulate individual atoms into new meta-material structures. I understand this would require a very complicated process. I thought of some general steps this process might use. This is roughly what I think it might require...
  8. BiGyElLoWhAt

    Optical Tweezers experiment =]

    I'm an undergrad at IPFW and I just got on this project setting up an optical trap. Our (my professors) main goal is to find out at what intensity (he keeps saying temperature) of light the objects behave as free particles. I see where this could be of interest, but aren't there bigger things...
  9. P

    Description of optical tweezers: Ponderomotive force?

    It is mentioned that in optical tweezers the dielectric particles are attracted to the gradient of the laser's electric field. Is this mechanism the same as the ponderomotive force? If so, why is this connection not made directly? Thanks
  10. D

    Optical tweezers, QPD back focal plane interferometry vs imaging

    Hello, I use a 10x infinity objective as a condenser in a optical trap setup. The collimated forward scattered light is then focused with a 40mm lens onto a QPD. This is the imaging techqnique. There is also BFPI, and I am not clear on this method. My understanding is that I need to image the...
  11. F

    Optical tweezers that not always atract but also repel

    Hi! I have the following problem: the optical tweezers attract beads but when the beads get to the trap, they are repelled. Furthermore, when once in a while a bead gets trapped, it goes out of focus. The tweezers are coupled to an inverted optical microscope. They are made with an IR laser...
  12. M

    Laser power in optical tweezers

    Hi, I'm currently recalibrating an optical tweezer for my undergraduate thesis. The alignment did turn out well so far but I'm a little bit concerned about the power loss within the microscope (here's a picture of the relevant part, without prisms). I read in a paper that 20 to 100mW are...
  13. C

    Understanding the Mechanism of Linear Optical Tweezers for Cell Stretching"

    Hi, I work with a diode laser, astigmatic Gaussian beam (elliptic), that has two foci positions. One is for to focus the width of the beam and the other one to focus the length of the beam. I trap particles using the first focus. The two parts of the beam act as two orthogonal beams. So, the...
  14. K

    Optimizing Focal Plane Alignment for Optical Tweezers: A Guide for Researchers

    I have a question concerning optical tweezers. How do you make sure that the focal plane of the beam and the laser are the same..? In other words, I can see the laser on my CCD image when it is reflected off the cover slide, but if I see the reflection of the laser then the beads that are...
  15. J

    Optical Tweezers: Intuitive Explanation

    Can someone give an intuitive explanation for this effect? I didn't go through the derivation carefully, but I know that the upshot of the math is that the dipole feels a force in the direction of the intensity gradient, so it goes to the focus of the laser. But I feel like there must be some...
  16. Pythagorean

    Best Schools for Optical Tweezers Engineering & Application in Neurology

    I'm near graduating with a Bachelor's in Physics in the US. What schools would be the best for application and engineering of optical tweezers? I'm mostly interested in its applications to neurology.
  17. N

    Info in nanotechnology, optical tweezers

    hi do anyone of you know optical tweezers... these are used in manipulating nanoparticles... any of u if ur working or familiar in nanotechnology or optical tweezers.. it would greatly help me... please reply thanks in advance
  18. O

    Can Optical Tweezers Still Challenge Mathematicians and Physicists?

    Help Wanted: Lone maths freak seeks aid from physicists for research into optical trapping/optical tweezers Ok just for the benefit of those who may not be aware, Optical tweezers or optical traps are a relatively recent experimental technique in which focused lasers are used to trap...
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