ultra-fast, ultra-intense laser part of this year’s Nobel prize a couple of days ago, but of course, there’s another half I didn’t cover. This was awarded to Arthur Ashkin, for the development of “optical tweezers,” which let you manipulate small objects with laser light, a very different subject that’s prizeworthy in its own right.

This is a prize that many would’ve guessed had been foreclosed by the 1997 Nobel Prize in Physics to Steve Chu, Claude Cohen-Tannoudji, and Bill Phillips (full disclosure: Bill was my Ph.D. thesis advisor). Chu had worked with Ashkin at Bell Labs, and his citation included mention of optical tweezers. The Nobel folks don’t like to repeat themselves, so a lot of people in the field expected Ashkin would never win. It’s nice to be wrong sometimes.

So, what are “optical tweezers,” and how do they work? The key idea, as with the 1997 prize for laser cooling of atoms, is that light carries momentum. In laser cooling, the momentum of a single photon is used to slow the motion of a single atom, which when repeated billions of times a second can slow an atoms from the speed of sound to speeds of a few centimeters per second. In optical tweezers, the momentum of a beam of light containing huge numbers of photons is used to push around a solid object.

Ray optics diagrams showing the origin of the trapping force for optical tweezers, using a refractive sphere.Chad Orzel

The easiest way to understand this is by considering a small transparent object, which being a physicist I will represent as a sphere in the figure above. This will act like a tiny lens, bending the path of a light beam coming in, which leads to a force pulling the sphere into the center of a focused laser beam.

The force is basically a reaction force based on the change in momentum that comes from redirecting the light beam. In the case of the transverse force (perpendicular to the laser direction), shown in the left half of the figure above, the light starts out headed straight down, with its momentum directed the same way, but is bent to the left or right. After passing through the sphere, the light has acquired some leftward or rightward momentum, but the total momentum of the universe as a whole isn’t allowed to change, so the sphere must have gotten a push in the opposite direction. If the light bends right, the sphere is pushed left, and vice versa.

If the sphere is centered in the beam, these forces cancel out, but if the intensity varies, the force will be larger on the side where the light is more intense. This leads to a force that pulls the sphere toward the brightest point available.

A similar process will work along in the longitudinal direction, if the beam is brought to a tight focus, as shown in the right half of the above figure. If the bead is centered in the beam near but slightly below the focus, the bending leads to forces that go up-and-right and up-and-left as drawn in the figure. The and-right and and-left portions cancel each other out, leading to a vertical force. The net effect is to pull the object into the focus of the light beam.

Simple optical tweezer apparatus at Union College. Photo by Casey Lee ’20.Casey Lee

The cartoons above draw the object as a refractive sphere, but the result is much more general than that. We usually demonstrate this with small beads, but it can work with basically anything refractive. I’ve had a series of undergraduate research students work on optical tweezers at Union (a photo of the apparatus is above), and a staple activity when a given student gets the trap up and working is to go out to the creek and get some water with algae in it, and hunt for microscopic critters to trap in the tweezers. It’s great fun.

You can also extend this basic idea to things that aren’t floating in water, and even objects that are opaque. In some of these cases, you need to use two counter-propagating beams to balance out the push that comes from the light that reflects off the object, but the basic idea is similar.

What’s this good for? Well, it’s a system for pushing around microscopic objects using forces from light. Since the force depends on the intensity of the light, this offers an excellent method for measuring the tiny forces between biological objects– people have attached motor proteins to little glass beads, and measured the force exerted as the proteins drag the bead along. The Block lab at Stanford pioneered a lot of these biophysics applications, and they’ve got some cool pictures and explanations.

The force also depends on the scattering of light, which depends on the position of the trapped object relative to the focus, so by measuring the beam after the trap, you can get information about how the trapped object is moving. The Raizen group at Texas has used this to do some really cool work on Brownian motion of little trapped beads, which is a much more physics-y angle on the use of optical tweezers.

Like the chirped-pulse amplification process described in the previous post, this prize is mostly for the development of a tool that’s become widely used. There are dozens of biophysics labs around the world making use of optical tweezers to manipulate organisms, genes, and even single molecules, and all of that research traces back to Ashkin’s original ideas about how to take advantage of the momentum of light.

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I wrote the ultra-fast, ultra-intense laser part of this year’s Nobel reward a number of days back, however obviously, there’s another half I didn’t cover. This was granted to Arthur Ashkin, for the advancement of “optical tweezers,” which let you control little items with laser light, a really various topic that’s prizeworthy in its own right.

This is a reward that lots of would’ve thought had actually been foreclosed by the 1997 Nobel Reward in Physics to Steve Chu, Claude Cohen-Tannoudji, and Expense Phillips (complete disclosure: Expense was my Ph.D. thesis consultant). Chu had actually dealt with Ashkin at Bell Labs, and his citation consisted of reference of optical tweezers. The Nobel folks do not like to duplicate themselves, so a great deal of individuals in the field anticipated Ashkin would never ever win. It’s great to be incorrect in some cases.

So, what are “optical tweezers,” and how do they work? The crucial concept, just like the 1997 reward for laser cooling of atoms, is that light brings momentum. In laser cooling, the momentum of a single photon is utilized to slow the movement of a single atom, which when duplicated billions of times a second can slow an atoms from the speed of noise to speeds of a couple of centimeters per second. In optical tweezers, the momentum of a beam consisting of big varieties of photons is utilized to boss around a strong item.

Ray optics diagrams revealing the origin of the trapping force for optical tweezers, utilizing a refractive sphere. Chad Orzel

The most convenient method to comprehend this is by thinking about a little transparent item, which being a physicist I will represent as a sphere in the figure above. This will imitate a small lens, flexing the course of a beam being available in, which causes a force pulling the sphere into the center of a concentrated laser beam.

The force is generally a response force based upon the modification in momentum that originates from rerouting the beam. When it comes to the transverse force (perpendicular to the laser instructions), displayed in the left half of the figure above, the light starts headed directly down, with its momentum directed the very same method, however is bent to the left or right. After going through the sphere, the light has actually obtained some leftward or rightward momentum, however the overall momentum of deep space as a whole isn’t enabled to alter, so the sphere should have gotten a push in the opposite instructions. If the light bends right, the sphere is pressed left, and vice versa.

(****************** )(********** )(* )If the sphere is focused in the beam, these forces counteract, however if the strength differs, the force will be bigger on the side where the light is more extreme. This causes a force that pulls the sphere towards the brightest point offered.

A comparable procedure will work along in the longitudinal instructions, if the beam is given a tight focus, as displayed in the best half of the above figure. If the bead is focused in the beam near however somewhat listed below the focus, the flexing causes forces that go up-and-right and up-and-left as attracted the figure. The and-right and and-left parts cancel each other out, causing a vertical force. The net result is to pull the item into the focus of the beam.

Basic optical tweezer device at Union College. Image by Casey Lee’20 Casey Lee

The animations above draw the item as a refractive sphere, however the outcome is far more basic than that. We generally show this with little beads, however it can deal with generally anything refractive. I have actually had a series of undergraduate research study trainees deal with optical tweezers at Union (a picture of the device is above), and a staple activity when a provided trainee gets the trap up and working is to head out to the creek and get some water with algae in it, and hunt for tiny animals to trap in the tweezers. It’s terrific enjoyable.

You can likewise extend this standard concept to things that aren’t drifting in water, and even items that are nontransparent. In a few of these cases, you require to utilize 2 counter-propagating beams to cancel the push that originates from the light that shows off the item, however the standard concept is comparable.

What’s this helpful for? Well, it’s a system for bossing around tiny items utilizing forces from light. Considering that the force depends upon the strength of the light, this uses an outstanding technique for determining the small forces in between biological items– individuals have actually connected motor proteins to little glass beads, and determined the force put in as the proteins drag the bead along. The Block laboratory at Stanford originated a great deal of these biophysics applications, and they have actually got some cool images and descriptions.

The force likewise depends upon the scattering of light, which depends upon the position of the caught item relative to the focus, so by determining the beam after the trap, you can get details about how the caught item is moving. The Raizen group at Texas has actually utilized this to do some actually cool deal with Brownian movement of little trapped beads, which is a a lot more physics-y angle on making use of optical tweezers.

Like the chirped-pulse amplification procedure explained in the previous post, this reward is mainly for the advancement of a tool that’s ended up being extensively utilized. There are lots of biophysics laboratories around the globe using optical tweezers to control organisms, genes, and even single particles, and all of that research study traces back to Ashkin’s initial concepts about how to benefit from the momentum of light.

” readability =”114
766219239″ >

I wrote the ultra-fast, ultra-intense laser part of this year’s Nobel reward a number of days back, however obviously, there’s another half I didn’t cover. This was granted to Arthur Ashkin, for the advancement of “optical tweezers,” which let you control little items with laser light, a really various topic that’s prizeworthy in its own right.

This is a reward that lots of would’ve thought had actually been foreclosed by the 1997 Nobel Reward in Physics to Steve Chu, Claude Cohen-Tannoudji, and Expense Phillips (complete disclosure: Expense was my Ph.D. thesis consultant). Chu had actually dealt with Ashkin at Bell Labs, and his citation consisted of reference of optical tweezers. The Nobel folks do not like to duplicate themselves, so a great deal of individuals in the field anticipated Ashkin would never ever win. It’s great to be incorrect in some cases.

So, what are “optical tweezers,” and how do they work? The crucial concept, just like the 1997 reward for laser cooling of atoms, is that light brings momentum. In laser cooling, the momentum of a single photon is utilized to slow the movement of a single atom, which when duplicated billions of times a second can slow an atoms from the speed of noise to speeds of a couple of centimeters per second. In optical tweezers, the momentum of a beam consisting of big varieties of photons is utilized to boss around a strong item.

.

.

Ray optics diagrams revealing the origin of the trapping force for optical tweezers, utilizing a refractive sphere. Chad Orzel

.

.

The most convenient method to comprehend this is by thinking about a little transparent item, which being a physicist I will represent as a sphere in the figure above. This will imitate a small lens, flexing the course of a beam being available in, which causes a force pulling the sphere into the center of a concentrated laser beam.

The force is generally a response force based upon the modification in momentum that originates from rerouting the beam. When it comes to the transverse force (perpendicular to the laser instructions), displayed in the left half of the figure above, the light starts headed directly down, with its momentum directed the very same method, however is bent to the left or right. After going through the sphere, the light has actually obtained some leftward or rightward momentum, however the overall momentum of deep space as a whole isn’t enabled to alter, so the sphere should have gotten a push in the opposite instructions. If the light bends right, the sphere is pressed left, and vice versa.

If the sphere is focused in the beam, these forces counteract, however if the strength differs, the force will be bigger on the side where the light is more extreme. This causes a force that pulls the sphere towards the brightest point offered.

A comparable procedure will work along in the longitudinal instructions, if the beam is given a tight focus, as displayed in the best half of the above figure. If the bead is focused in the beam near however somewhat listed below the focus, the flexing causes forces that go up-and-right and up-and-left as attracted the figure. The and-right and and-left parts cancel each other out, causing a vertical force. The net result is to pull the item into the focus of the beam.

.

.

Basic optical tweezer device at Union College. Image by Casey Lee’20 Casey Lee

.

.

The animations above draw the item as a refractive sphere, however the outcome is far more basic than that. We generally show this with little beads, however it can deal with generally anything refractive. I have actually had a series of undergraduate research study trainees deal with optical tweezers at Union (a picture of the device is above), and a staple activity when a provided trainee gets the trap up and working is to head out to the creek and get some water with algae in it, and hunt for tiny animals to trap in the tweezers. It’s terrific enjoyable.

You can likewise extend this standard concept to things that aren’t drifting in water, and even items that are nontransparent. In a few of these cases, you require to utilize 2 counter-propagating beams to cancel the push that originates from the light that shows off the item, however the standard concept is comparable.

What’s this helpful for? Well, it’s a system for bossing around tiny items utilizing forces from light. Considering that the force depends upon the strength of the light, this uses an outstanding technique for determining the small forces in between biological items– individuals have actually connected motor proteins to little glass beads, and determined the force put in as the proteins drag the bead along. The Block laboratory at Stanford originated a great deal of these biophysics applications, and they have actually got some cool images and descriptions.

The force likewise depends upon the scattering of light, which depends upon the position of the caught item relative to the focus, so by determining the beam after the trap, you can get details about how the caught item is moving. The Raizen group at Texas has actually utilized this to do some actually cool deal with Brownian movement of little trapped beads, which is a a lot more physics-y angle on making use of optical tweezers.

Like the chirped-pulse amplification procedure explained in the previous post, this reward is mainly for the advancement of a tool that’s ended up being extensively utilized. There are lots of biophysics laboratories around the globe using optical tweezers to control organisms, genes, and even single particles, and all of that research study traces back to Ashkin’s initial concepts about how to benefit from the momentum of light.

.