Optical Tweezers
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Optical Tweezers
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Re: Optical Tweezers
#2I was surprised by this explanation describing how the beam is focused:
Optical tweezers are capable of manipulating nanometer and micron-sized dielectric particles by exerting extremely small forces via a highly focused laser beam. The beam is typically focused by sending it through a microscope objective. ...
I imagined something more complex, although what exactly I'm not sure.
Are there any other ways of doing it? Are off-the-shelf microscope lenses used routinely, or are custom lenses the norm?
Re: Optical Tweezers
#3It is worth noting for those who don't know yet, the findings of Optical Tweezers has made Arthur Ashkin a laureate of the 2018 Physics Nobel prize, on par with Donna Strickland and Gérard Mourou for their work on generating high-intensity, ultra-short optical pulses.
Re: Optical Tweezers
#4I was surprised by this explanation describing how the beam is focused: Optical tweezers are capable of manipulating nanometer and micron-sized dielectric particles by exerting extremely small forces via a highly focused laser beam. The beam is typically focused by sending it through a microscope objective. ... I imagined something more complex, although what exactly I'm not sure. Are there any other ways of doing it…
Usually optical traps use 1064 nm NdYAG lasers, which is in the infrared. Most objectives aren't designed for infrared light, so the objectives used for optical trapping are usually customized.
Re: Optical Tweezers
#5I'm a grad student in a lab that specializes in using optical tweezers for single-molecule biophysics research. I'm out sick today with nothing better to do, so feel free to ask me anything.
Re: Optical Tweezers
#6As an undergrad I worked in a lab where they built an iPad app to control optical tweezers [1, 2]. It's a cool example of the possibilities of this technique - allowing you to manipulate nanoscopic particles suspended in fluid.
[1] https://www.youtube.com/watch?v=qgDMcP9e5G0
[2] http://iopscience.iop.org/article/10.1088/2040-8978/13/4/044...
Re: Optical Tweezers
#7I was surprised by this explanation describing how the beam is focused: Optical tweezers are capable of manipulating nanometer and micron-sized dielectric particles by exerting extremely small forces via a highly focused laser beam. The beam is typically focused by sending it through a microscope objective. ... I imagined something more complex, although what exactly I'm not sure. Are there any other ways of doing it…
Note that usually you are also using the microscope to observe what you are trapping, so it' super convenient (but not easy), to use the same objective that the one you observe to send a laser through (in the opposite direction) and trap your sample. If you send your laser-beam quasi parallel it will focus and trap particula quasi-where your are observing.
(source: did my PhD with optical traps: http://matthiasphd.herokuapp.com/html/parts/part1.html#optic..., picture of trapped beed as viewd through microscope: http://matthiasphd.herokuapp.com/html/parts/part3.html#exper...)
Re: Optical Tweezers
#8I'm a grad student in a lab that specializes in using optical tweezers for single-molecule biophysics research. I'm out sick today with nothing better to do, so feel free to ask me anything.
this is tractor beam yes?
Re: Optical Tweezers
#9As an undergrad I worked in a lab where they built an iPad app to control optical tweezers [1, 2]. It's a cool example of the possibilities of this technique - allowing you to manipulate nanoscopic particles suspended in fluid. [1] https://www.youtube.com/watch?v=qgDMcP9e5G0 [2] http://iopscience.iop.org/article/10.1088/2040-8978/13/4/044...
Pardon my language yet that is so fucking cool. Do you know how the app interfaced with the microscope and optical tweezers? I just love the idea of a simple api that controls this crazy complicated lab equipment.
Re: Optical Tweezers
#10I'm a grad student in a lab that specializes in using optical tweezers for single-molecule biophysics research. I'm out sick today with nothing better to do, so feel free to ask me anything.
this is tractor beam yes?
Kind of? It's the only way that I know of for a laser to move a particle towards the laser's source. But it has some severe limitations: the force is extremely weak, on the order of 0.1 pN/(nm W); the particles have to refract, rather than absorb or scatter, the light; particles larger than 10 microns in diameter tend to be melted or vaporized since they can't dissipate the energy quickly enough.
I want to emphasize how incredibly weak these traps are. In order to apply a maximum force of 200 pN orthogonally to the path of the laser to a 1 micron polystyrene sphere requires approximately 1 W of laser power. Further, it takes about five times more laser power to apply the same amount of force axially (i.e., along the path of the beam) compared to transversely (i.e., in the plane orthogonal to the beam).