Please enter your username below and press the send button.A password reset link will be sent to you.
If you are unable to access the email address originally associated with your Delicious account, we recommend creating a new account.
This link recently saved by orzelc on June 15, 2012
if they had actually been used as spy satellites, what would these super telescopes have been able to see on the ground? It’s a fascinating question, and leads into a nice basic discussion of the optical resolution of imaging systems. In other words, what is the smallest detail that could be picked up by one of these telescopes in orbit?
This link recently saved by orzelc on May 21, 2012
Purcell had the insight that in a cavity, the number of states available for photons is not quadratic in frequency anymore. Instead, a cavity on resonance has a photon density of states that is proportional to the "quality factor", Q, of the cavity, and inversely proportional to the size of the cavity. The better the cavity and the smaller the cavity, the higher the density of states at the cavity resonance frequency, and off-resonance the photon density of states approaches zero. This means that the spontaneous emission rate of atoms, a property that seems like it should be fundamental, can actually be tuned by the local environment of the radiating system. The Purcell factor is the ratio of the spontaneous emission rate with the cavity to that in free space.
While I was doing some writing today, I decided to look up the original citation for this idea. Remarkably, the "paper" turned out to be just an abstract!
This link recently saved by orzelc on May 11, 2012
A new method for measuring distance based on an optical frequency comb has been unveiled by physicists in the Netherlands. The main benefit of the technique, which involves passing the light from an optical comb through a Michelson interferometer and analysing the resulting interference patterns, is that it allows distances to be measured accurately without already knowing the value to within half a wavelength of the light used. The technique could be used to measure the distance between satellites or to make very precise measurements of the dispersion of light in optical materials.
This link recently saved by orzelc on April 16, 2012
" “The beauty of it is that we have the people who can come up with this low-risk, high-reward experiment,” says Fermilab's Raymond Tomlin. “It's one shot, and if you discover something you go to Stockholm [to collect a Nobel Prize]. And if you don't see anything, you set a limit.”
Not everyone cheers the effort, however. In fact, Leonard Susskind, a theorist at Stanford University in Palo Alto, California, and co-inventor of the holographic principle, says the experiment has nothing to do with his brainchild. “The idea that this tests anything of interest is silly,” he says, before refusing to elaborate and abruptly hanging up the phone. Others say they worry that the experiment will give quantum-gravity research a bad name."
This link recently saved by orzelc on February 09, 2012
A physical phenomenon that is widely used to slow and store pulses of light in clouds of atoms has been seen for the first time in a system of nuclear-energy levels. The breakthrough has been made by a team of physicists in Germany that has seen evidence for the phenomenon, known as electromagnetically induced transparency (EIT), as X-rays pass through nanometre-scale layers of iron. The researchers think their method, which is also the first to achieve EIT using just two energy levels rather than the usual three, could lead to the development of devices for controlling X-rays, which is currently very tricky to do.
This link recently saved by orzelc on February 03, 2012
Physicists in the US have created an optical frequency comb that operates in the extreme ultraviolet (XUV). Touted as the first practical comb to work in this region of the spectrum, the device could be used to look for tiny variations in the fine-structure constant and other physical constants that could point to new physics. An XUV comb could also be used to create better atomic clocks and new techniques for atomic spectroscopy.
This link recently saved by orzelc on August 19, 2011
"I guess I should state the full question:
Why do mirrors reverse left and right, but they don’t reverse up and down?
Answer: Mirrors don’t reverse left and right and they don’t reverse up and down. Wouldn’t that be kind of funny if I just stopped here? But you know I can’t."
This link recently saved by orzelc on July 25, 2011
"Recently, in the course of other writing I've been doing, I again came to the topic of what are called Einstein A and B coefficients, and it struck me again that this has to be one of the most elegant, clever physics arguments ever made. It's also conceptually simple enough that I think it can be explained to nonexperts, so I'm going to give it a shot."
This link recently saved by orzelc on June 05, 2011
"Over the past few years, in conditions of strict secrecy, a multinational team of scientists has been making a mighty effort to change the light bulb. The prototype they’ve developed is four inches tall, with a familiar tapered shape, and unlighted, it resembles a neon yellow mushroom. Screw it in and switch it on, though, and it blazes with a voluptuous radiance. It represents what people within the lighting industry often call their holy grail, an invention that reproduces the soft luminance of the incandescent bulb — Thomas Edison’s century-old technology — but conforms to much higher standards of energy efficiency and durability. The prototype is supposed to last for more than 22 years, maybe as long as you own your house, so you won’t need to stock up at the supermarket. And that’s fortunate, because one day very soon, traditional incandescent bulbs won’t be available in stores anymore. They’re about to be effectively outlawed."
This link recently saved by orzelc on June 01, 2011
"One thing that fascinates me in physics is that the Second Law of Thermodynamics can be used to derive some important results in physics. Some of them are rather technical (e.g. the relationship between the Einstein A and B coefficients, the Abbe Sine condition), but one is quite simple: The impossibility of a one-way mirror. (Explained below) What fascinates me about all of these results is that thermodynamics and optics rest on completely different logical foundations. There is, on the surface, absolutely nothing that connects optics and thermodynamics. There certainly is a relationship between thermodynamics and photons, but the other phenomena (image focusing and mirrors) have, on the surface, almost nothing to do with thermodynamics."