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Optical Tweezers

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Re: Optical Tweezers

#21

Post by dekhn »

arctux wrote: post #18
dekhn wrote: post #14

This isn't the first Nobel for optical tweezers. Steve Chu used them in atom trapping experiments at Bell Labs, although the award is for the atom trap results, not for the tweezers themselves.

Chu's prize was for laser cooling, which uses a magneto-optical trap. Magneto-optical traps confine atoms by exploiting the Zeeman effect, a spatially-varying magnetic field, and a laser with a precisely-controlled wavelength tuned to be slightly red of an electronic transition. Optical traps, on the other hand, rely on the refraction of a much larger, but still microscopic, object. Some of Chu's work uses an optical…

Thanks for that clarification.

Re: Optical Tweezers

#22

Post by arctux »

crispyambulance wrote: post #20
arctux wrote: post #15

Earlier quoted context omitted.

Our strongest trap is powered by 1.5 W 1064 nm laser beam. (For comparison, laser pointers are usually under 0.005 W.) Unlike most other light sources, laser power measures the output power rather than electrical input power. The beam will instantly ignite paper, and will cause damage to the most common type of laboratory laser beam blocks, which are made out of stainless steel. We don't take the air out the system.…

> specializes in using optical tweezers for single-molecule biophysics research. ... > The beam will instantly ignite paper, and will cause damage to... Curious, it appears that you guys use a highly focused beam on small particles, like 1 W focused into a diffraction limited spot, right? How come the bio-molecules that you're manipulating with this light don't just "burn up"? Is it because they're mostly transparent…

> Curious, it appears that you guys use a highly focused beam on small particles, like 1 W focused into a diffraction limited spot, right?

That's correct.

> How come the bio-molecules that you're manipulating with this light don't just "burn up"? Is it because they're mostly transparent at that wavelength? Or you're only exciting a marker molecule that is stuck to them?

We trap and manipulate a micron-sized polystyrene sphere that the proteins are attached to, not the proteins themselves. The microspheres don't burn up because they don't strongly absorb (i.e., they're mostly transparent) at the laser's frequency. Paper, on the other hand, absorbs strongly and ignites.

Optical traps rely on the momentum of light and the fact that a microsphere displaced from the diffraction-limited spot refracts light in direction of the displacement. Since momentum is conserved, the light directed away from the center of the trap creates a force that pushes the sphere toward the trap. If the light were mostly absorbed or scattered, this force would be along the axis of the beam.

Re: Optical Tweezers

#23

Post by dr_coffee »

dmead wrote: post #8
arctux wrote: post #5

I'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?

Depends who you ask... I saw David Grier (http://physics.nyu.edu/grierlab/) give a talk in which he said that this kind of optical tweezers doesn't really count as a a tractor beam. He went on to define the characteristics of a tractor beam and how he realized such a device in a laboratory setting.

He does use optical trapping forces, but is able to create exotic traps such as vortexes with the help of spatial light modulators. My understanding of the physics is not very good but here are some links to his papers (the second one has a cool visualization of a solenoidal tractor beam)

http://physics.nyu.edu/grierlab/conveyor7c/

http://physics.nyu.edu/grierlab/photobessel14c/

Re: Optical Tweezers

#24

Post by rrock »

crispyambulance wrote: post #20
arctux wrote: post #15

Earlier quoted context omitted.

Our strongest trap is powered by 1.5 W 1064 nm laser beam. (For comparison, laser pointers are usually under 0.005 W.) Unlike most other light sources, laser power measures the output power rather than electrical input power. The beam will instantly ignite paper, and will cause damage to the most common type of laboratory laser beam blocks, which are made out of stainless steel. We don't take the air out the system.…

> specializes in using optical tweezers for single-molecule biophysics research. ... > The beam will instantly ignite paper, and will cause damage to... Curious, it appears that you guys use a highly focused beam on small particles, like 1 W focused into a diffraction limited spot, right? How come the bio-molecules that you're manipulating with this light don't just "burn up"? Is it because they're mostly transparent…

I also work with tweezers.

Back in my postdoc, we got a sample of purified melanosomes to work with. Melanosomes are small vesicles that hold pigment in your skin. Well, when we tried to trap them, we found that they absorbed the trap light, and turned it into heat. Enough to boil the sample.

We couldn’t do the experiment, obviously, but we did have a fun day playing Death Star, shooting every melanosome we could find.

Re: Optical Tweezers

#25

Post by ufo »

arctux wrote: post #19
mikey_p wrote: post #17

Earlier quoted context omitted.

Spent alot of time working with low to medium power lasers in the entertainment industry, and I'm happy to say that was also a joke in that industry as well.

Powerful lasers can be scary, especially if they're in the infrared. The first warning you receive that it's reflecting into your eye is blood seeping into the vitreous humor from your retina's capillaries.

Has someone you personally know ever suffered a laser injury?

Re: Optical Tweezers

#26

Post by rrock »

arctux wrote: post #19
mikey_p wrote: post #17

Earlier quoted context omitted.

Spent alot of time working with low to medium power lasers in the entertainment industry, and I'm happy to say that was also a joke in that industry as well.

Powerful lasers can be scary, especially if they're in the infrared. The first warning you receive that it's reflecting into your eye is blood seeping into the vitreous humor from your retina's capillaries.

And you’ll hear the popping noise when the tissue is vaporized.

Re: Optical Tweezers

#27

Post by rrock »

ufo wrote: post #25
arctux wrote: post #19

Earlier quoted context omitted.

Powerful lasers can be scary, especially if they're in the infrared. The first warning you receive that it's reflecting into your eye is blood seeping into the vitreous humor from your retina's capillaries.

Has someone you personally know ever suffered a laser injury?

I met one person who took a hit from a pulsed laser (the -other- Nobel from today). Pulsed lasers can be even worse. Fortunately, it was in his peripheral vision. But he described hearing and feeling the pop.

Re: Optical Tweezers

#28

Post by chimere »

scrumbledober wrote: post #11
matthberg wrote: post #9

Earlier quoted context omitted.

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.

I remember as a child watching an episode of some version of battlebots, where a competitor had an articulated grabbing arm on top of his robot. The arm had, I believe, two articulating joints and then an articulating grabber/jaw at the end. To control the arm he had made a small 2d model of it and could simply move that around on a clipboard like backing, and it would map those movements to the servos in the arm. I…

Perhaps you're thinking of Snake, built by Mark Setrakian? One of the most iconic battlebots ever. I could only find one video of him using the skeuomorphic controller [1], and a picture of him holding it [2]

[1] https://www.youtube.com/watch?v=NVyMzo-D97A

[2] http://www.teamdelta.com/ax/markwwac.jpg

Re: Optical Tweezers

#29

Post by arctux »

ufo wrote: post #25
arctux wrote: post #19

Earlier quoted context omitted.

Powerful lasers can be scary, especially if they're in the infrared. The first warning you receive that it's reflecting into your eye is blood seeping into the vitreous humor from your retina's capillaries.

Has someone you personally know ever suffered a laser injury?

My undergraduate advisor had a small hole in his retina due to a high-power laser. The injury would have been far worse if it weren't a visible laser, since his blink reflex greatly reduced the damage.

Re: Optical Tweezers

#30

Post by ssl232 »

matthberg wrote: post #9
sleavey wrote: post #6

As 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.

The paper I linked describes it a bit more, but it's unfortunately behind a paywall. I'll summarise it here.

They used a camera connected to a LabVIEW interface to view the trapped particles, but they control it using a laser and a spatial light modulator (SLM), which is able to imprint a spatial pattern onto the laser beam, which is ultimately what creates the optical traps. The paper says "The trap coordinates [on the iPad] are synchronized over the wireless network with a desktop computer, which controls the SLM using our freely available LabVIEW software" (square brackets mine), i.e. they control the traps using a separate computer interfaced using LabVIEW to the SLM. The iPad is used to show the video stream and allow the user to set and manipulate the position of the traps. The camera is also connected via LabVIEW: "Using the JPEG compression available in the National Instruments Vision library, we can stream around ten frames per second from the control PC to the iPad over a wireless network (limited by available CPU power on the iPad). Up to 11 optical traps can be simultaneously dragged around, and they can be created and removed with a double tap on the screen. Double tapping with multiple fingers creates multiple optical traps simultaneously, which is very useful when trapping non-spherical objects."

I guess a more up-to-date iPad would manage more traps. The one they used (circa 2011) was probably 1st generation.

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