There's a new laser in town. It's produced in a completely different way from other lasers, using 'phased arrays' which can make it 1,000 times as stable as other lasers and a million times weaker than other lasers. At last, a laser that you can settle down with.
So far conventional lasers have created their beams a certain way. They get photons shooting back and forth in a mirrored chamber. The photons are being emitted by identical atoms, all at the same frequency, and so as they bounce back and forth between the mirrors, their wavelengths all sync up. One of the mirrors allows a certain percentage of the photons to spill out of the chamber, and those synced up photons go forward in a beam of focused laser light.
Or, almost. Photons hitting one mirror and the other, or outside disturbances, will cause the mirrors themselves to wobble. Oh, not much. If you were the proud owner of one of these lasers, you could even tell yourself that it wasn't wobbling at all. But it is, and since the mirrors are what get the photons to stay in phase with each other, this throws off the frequency, or color, of the laser beam, causing it, too, to wobble back and forth. Other people will notice this wobble. And they will laugh at you. Not to your face, but behind your back. All the time.
How to stop this dreadful embarrassment? Physicists at JILA have found a technique, called 'phased arrays.' Phased arrays stop relying on the mirrors and just create photons that are in phase with each other from the beginning. They start with a million rubidium atoms and put them in an ordinary mirror-lined chamber. Instead of getting the atoms to create a laser in the chamber, they shoot laser light into the chamber and get that going between the mirrors. Then they use a second laser to hop the electrons in the rubidium atoms into and out of an excited state. When the electrons fall back down out of the more energetic state, they emit photons perfectly in phase with each other. Those photons bust out of the chamber at such a high rate that they don't reflect in the chamber. This keeps the rubidium atoms all in phase, all the time, producing a laser that wobbles a thousand times less than any other laser out there. There's a trade-off, though.
This new laser is dim. It's roughly a million times weaker than a laser pointer. But it's reliable, and in a world where we use lasers to regulate atomic clocks and keep satellites running how and where we want them, the more reliable the laser the better off we are.
Top Image of Laser: NASA
Image of Superradiant Laser: JILA