Vintage Lab Pics: The Laser System

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I already showed the vacuum system from my grad school days. This is the laser system that drove it. Slowing and trapping a thermal beam of atoms and then creating a new cold beam requires several lasers at different frequencies.

This first picture is a diode laser system, obviously home-built; this pre-dates any sort of commercially available system by several years, and perhaps a decade. On the far left are the electrical connections and the on/off switch. Power is needed for the laser, a piezoelectric transducer stack and the thermoelectic cooler, and a signal from a thermistor is fed back for coarse temperature tuning/stabilization of the wavelength. The diode is mounted in the thin rectangular block and has a collimating lens mounted in the thicker one; as I recall the lens position was adjusted with an external jig and then glued down.

osu-diode-laser

Light leaves the diode and hits the grating, reflecting off to the bottom, but the grating is blazed — the lines are angled, and in this position one of the diffraction orders is reflected back into the laser, which forces the laser to operate at that frequency. Thus, by changing the angle slightly, the wavelength can be tuned over some small range, perhaps a few nanometers. The grating is mounted on a small kinematic mount, and this obscures a gap between two parts of the mount. At the lower right you can see the gap where the piezo stack is, and at the upper left, near the screw, is the pivot point.

The entire block is mounted on a thermoelectric cooler to stabilize the temperature. Laser diodes are coarsely temperature-tunable, so the temperature is chosen to get you close to the desired wavelength (780.24 nm for Rb-85). When operating, this would be covered with a plexiglass housing to act as a thermal barrier and a baffle for air currents, and on later designs contained a tray for a desiccant to help prevent condensation on the cold laser.

Here is the table, with a couple of lasers in the foreground. Light goes out of the side of the boxes and hits the turning mirrors; some of the light is picked off and sent into the spectroscopy cells visible just past the lasers (the one on the left is closer) This ensured the lasers were on resonance.

osu-diode-laser-setup

This is the whole laser table, showing the vacuum system on the right. Much of the equipment is on shelves above the optical table, and this design ensured the attraction of shorter personnel to the lab, as might be predicted by Murphy’s law.

osu-laser-table

The blue boxes on the center-line of the table are fast photodiodes; we used a beat between lasers to generate a locking signal for those not locked to the spectroscopy signals, and could tune the other lasers several MHz away using this technique. This allowed us to tune the trapping laser beams such that the trap was not stationary in the lab frame. The atoms would feel a force to eject them from the atomic funnel, and the lasers would become equal due to the Doppler shift, once they atoms were moving at the right speed.

An Official Denial. Yeah, That'll Work

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Company Denies its Robots Feed on the Dead

In response to rumors circulating the internet on sites such as FoxNews.com, FastCompany.com and CNET News about a “flesh eating” robot project, Cyclone Power Technologies Inc. (Pink Sheets:CYPW) and Robotic Technology Inc. (RTI) would like to set the record straight: This robot is strictly vegetarian.

Sure, it’s vegetarian, now, because you programmed it that way. What happens when it becomes self-aware?

Goosing the Droplet

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Squirting Water without a Gun

Fluid jets are normally made by forcing liquid through a nozzle, such as in a squirt gun or a syringe. But in the 10 July Physical Review Letters, researchers report a way to induce a fluid jet to burst from an isolated droplet. The team placed a liquid droplet on a surface and blasted it with focused surface acoustic waves–nano-sized versions of the ground-shaking waves from earthquakes–causing the droplet to shoot upward in a narrow stream. The researchers believe the technique could be useful in drug delivery, biomedical research, and inkjet printing.

Apollo 11 landing on TV as it aired 40 years ago

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Kottke has set up a way to watch the Apollo 11 landing on TV as it aired 40 years ago

For a more authentic feel,

This is just like real TV…if you miss the appointed time, there’s no rewind or anything…the video is playing “live”. I have not done extensive browser testing so it may not work perfectly in your browser.

Yes, that’s right. In 1969 there was no Tivo, or even VHS/beta for the masses. And there may be technical difficulties.

Y?

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Cosmic Variance has a post linking to Why is Science Important (to which I linked back in February)

It’s worth revisiting, if for no other reason than to give this great quote from the video

“You’ve just seen me walk across red hot coals, at a temperature of over five hundred degrees Celsius. I could tell you that I’m an expert in an ancient form of meditation that lets me block out pain at will. I could then tell you that you could lead a happier life if you follow my teachings. For a small fee, of course.

Or, I could tell you the truth; that walking on hot coals doesn’t require any kind of magical powers. It’s just the case that the coals are a poor conductor of heat, and I walk so quickly that there’s hardly any time for heat transfer to take place.

Separating truth from fraudulent mumbo-jumbo is just one reason why science is important.”

On the Case

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Cocktail Party Physics: NEW VOICES: georgie boy

Dr. Cheadle has never heard of vitamins. Their discovery is decades in the future. But he understands that diet is the issue here, although many colleagues disagree. Dr. Cheadle argues in his 1878 paper against the various other theories about scurvy, including that it is caused by humid and/or cold climates, excess salt in the diet, lack of exercise, and ptomaine poisoning. “There is, however, an invariable factor, without the presence of which all other casual and irregular factors are powerless to set up the disease. This essential factor, it has been proved over and over again, is the absence of certain elements in food. If the body is deprived of these elements, [scurvy] is produced. What these elements are has not yet been absolutely settled with scientific precision, but we know positively that they exist in fresh vegetables, in lime-juice, in milk, and in less considerable degree, perhaps, in some other fresh animal foods.”

Only 5? You Just Made the List, Buddy.

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5 Atrocious Science Clichés to Throw Down a Black Hole

After careful consideration and consultation with members of the local science writing community (only some of them were drunk), we have selected the five most annoying and ubiquitous clichés we think should be sucked into a black hole, forever banished from all future descriptions of science.

Funny — I just saw “shedding light” in several headlines on my RSS feed before getting to this, and “shedding light on black holes” (ouch!) got me ~41k Google hits.

I’m surprised “quantum leap’ isn’t on the list. Quantum means discrete, not big, i.e. the opposite of quantum is continuum.

I’d also add “all heat and no light” because visible light from a blackbody is heat, and it can certainly be used to warm things up. Radiant energy is radiant energy. The problem here is that out experience is with “hot” things is at around 400K or so, where most of the blackbody radiation is in the infrared. So we equate infrared radiation with heat, and they just aren’t synonymous. You can be burned with focused visible light (ask an ant if you don’t believe me — oh, wait, you can’t: they’ve all been burned up). A microwave oven is another example of radiant energy transfer which doesn’t involve the infrared as the source.

Doctor Obvious, Come Here … Slowly

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Higher Speed Limits Cost Lives, Researchers Find

“This is a failed policy because it was, in essence, an experiment over 10 years. People assumed that increasing the speed limit would not have an impact,” said Friedman. “We’ve shown that something has happened and it’s quite dramatic.”

Umm, really? People assumed that if you drive faster, with its associated reduction in response times and increase in collision energy, that there would be no effect? I think people wanted the higher speed limit despite the higher risk it entailed, in part because of other safety advances.

Friedman uses the example of the 3,000 people who died in the September 11th terrorist attacks.

“That tragic event has led to a whole foreign policy,” he said. “We estimate that approximately 12,500 people died as a result of a policy to deregulate speed enforcement — four times what happened on September 11th — and yet changing the policy to reduce speed limits may be very difficult.”

What they don’t say is that despite the extra ~1250 deaths per year from the higher speed, overall deaths have fallen, and the rate per vehicle-mile has dropped dramatically over the years. Per mile traveled, you’re about half as likely to die as compared to 1980.

trafficstats

From this NHTSA PDF

The problem with simply presenting a number is that there is no basis for a valid comparison. The apples-to-oranges 9/11 fatalities number is given instead. The graph shows about 15,000 fatalities per year, currently, making this a 9% increase, which discounts the possibility of other influences such as more cars on the road and more miles being traveled, which the fatality rate statistic indicates. (Though that can be influenced by many things as well)

A more meaningful analysis might go something like this. My upcoming vacation will entail me driving perhaps 1,000 miles. I can drive slower if I choose, but I have to consider if saving a half-hour of travel is worth it. Since being on the road for ~8 hours means fatigue comes into play, it might actually be safer to cut down on the travel time. If the fatality rate is 2 per 100 million miles, this means a statistical chance of 0.002%, which is quite small. And we’re talking about increasing this by 10%, to 0.0022%. The sin-by-omission in the article has you focusing on the dramatic large number rather than the overall picture.