Drat. LEGO Robotics Summer Day Camp is in Palo Alto, California, and is almost full.
Category Archives: Video
Fields, Fields, Everywhere
And Now For Something Slightly Different
The previous MOT video showed the atoms squirting out of the side when the trapping field was turned off. In this video things are more balanced, and you can see the atoms remaining in the beam overlap region, and fluorescing quite brightly. The trap is cycled on and off and you can see the trap “grab” the atoms and pull them back to the center; when the trapping field is left off it takes several seconds for the cloud to dim as atoms diffuse out, and that’s a qualitative sign that the atoms in the molasses are pretty cold. Probably tens of microKelvin.
“Mr. Hands” is pointing out the trap axis at the beginning, as a cue to the person adjusting the trimming magnetic field. This kind of adjustment can be very laborious, as there are several parameters which need to be optimized, and they aren’t independent of each other. Beam alignment, magnetic field and beam intensity all need to be optimized, but all exert forces which can be offset by one of the the parameters, e.g. a slight imbalance in intensity can be offset by a small magnetic field, and the small amount of swirling of the atoms when the trap is turned off is likely an indication that this is the case.
However, at this level of adjustment, the atoms are the best indicators. An optical power meter or a magnetic field probe aren’t going to yield the precision necessary — they can only get you close. At this point you just have to wander around phase space, checking that you aren’t merely at a locally optimum signal. The true test comes when you can actually measure the temperature of the atoms, by imaging them in time-of-flight and seeing how much the cloud has expanded.
Luge + Skateboard =
Rollersuit
What's Opera, Doc?
Kill the wabbit goblet, kill the goblet!
Splendid Oscillation
Learn how to destroy expensive glassware with the power of sound
Cool video showing a resonantly-driven crystal goblet, with a strobe slightly off-resonance. Then it breaks. And in slo-mo (though not super slo-mo, which would be extra cool)
Notice the beautiful large wobbling standing waves in the video. The points in the glass which are oscillating the most are called the antinodes of the standing waves — where constructive interference is at a maximum. The locations that seem to be stationary are called nodes. They are experiencing continuous destructive interference. To shatter the glass, just turn up the volume until the amplitude of vibration exceeds the tensile strength of the glass. Most people don’t have the lung power to do this, so if you really want to break some crockery, either use an amplifier or hire an opera singer.
Boom De Yada
Photochrome
Photochrome
You give us those nice bright colors
You give us the greens of chemistry
Makes you think all the world’s a funky lab, oh yeah!
Zap the molecule with UV and it turns green. This is due (as I understand it) to the molecule changing to another state (isomer) — and not simply fluorescence — where it then has a different absorption spectrum, so in this example it looks green. When you remove the UV, it reverts to the original state and becomes clear again, and it’s doing this quite rapidly.
Gooooooaaaaaaaaaal!
via kottke
In celebration of Euro 2008, public prankster and more-than-fair soccer striker Rémi Gaillard made the following video of himself using the urban landscape as a soccer pitch. Gaillard scores goals into police vans, trash cans, open windows, etc. to the annoyance of his oblivious goalies.
I love the one where his first shot triggers the motion sensor and he “scores” on a rebound . . . at the police station.
Ghostly Visages
No, not of an alien at the window.
Here’s a little movie showing atoms being trapped and mistreated. What you’re seeing is a video of the monitor that’s hooked up to a little IR camera on the vacuum chamber. The really bright spot that’s squirming around a little are the atoms, or technically, the fluorescence from the atoms. There are probably more than a Sagan of them (i.e. biilliyuns) at about a milliKelvin or so in temperature (which is considered warm!) because it hasn’t been fine-tuned yet. The bluish circle is reflected light off of a flange, and there’s some other scattered light visible.
About 10 seconds in, the trap’s magnetic field is turned off, and the atoms squirt off to the side. A second or two later the field is turned on again, and the trap fills up. If the lasers were properly aligned and balanced, and the earth’s magnetic field were either shielded or zeroed out with trim coils, then what you would see is a nice uniform expansion into a much colder (microKelvin-ish) optical molasses, but the earth’s field is still present here, so that gives rise to an imbalanced residual force which is small compared to the trapping force, so you only really notice it when the trapping field is turned off. The molasses impedes the motion of the atoms, but doesn’t technically trap them, i.e. it doesn’t define a point where the atoms should be, so when only the lasers are there, the atoms would normally just drift through, very slowly. But here they’re being shoved a little bit.
The accelerations involved here are large — these atoms can scatter a million photons a second, give or take, depending on the exact laser frequency, so even though an individual scatter changes the atom’s speed by about 6 mm/sec, when you scatter them that rapidly you can get accelerations of hundreds of g’s. But in the situation here, where the atoms are almost at rest, that’s balanced by an equally large acceleration from an opposing laser.
I Can Geek Anything Up
Lady spinning on escalator handrails. Nominally the net force is zero, assuming each rail exerts the same magnitude of force, but there may be some differences depending on what part of her body is in contact, or the escalator speeds. They each exert a torque in the same direction, though, so she spins.
via Kottke