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more power
Nov. 16th, 2008 08:07 pmOne of our current efforts at LIGO is to increase the laser power.
The sensitivity of our gravitational wave detector is ultimately limited by the granularity of light*. The light coming out of our detector, like any light, is packaged up in little bundles of energy, photons. In any given length of time, the number of photons coming out of the detector is an integer. We can't measure half a photon. It's the same problem as doing a survey where you don't survey enough people. If you ask only ten people who's going to win the election, your survey results can never be better than 10%. The solution is to survey more people. To measure more photons. As we put more laser power into our machine, the granularity of light matters less and less.
The noise caused by the granularity of light is called "shot noise." The name sticks because it makes us think of shot, like the light is a spray of BB's out of a shotgun. But it's really named after Walter Schottky.
We've replaced our ~ 8 Watt laser with a new 35 Watt one. But putting more light into the machine is not so simple as getting a more powerful laser, for at least two reasons.
* at frequencies above ~ 100 Hz
( 1. Things heat up )
( 2. Light pushes on things )
On Friday night we put 12 W into the machine for 12 minutes.
The sensitivity of our gravitational wave detector is ultimately limited by the granularity of light*. The light coming out of our detector, like any light, is packaged up in little bundles of energy, photons. In any given length of time, the number of photons coming out of the detector is an integer. We can't measure half a photon. It's the same problem as doing a survey where you don't survey enough people. If you ask only ten people who's going to win the election, your survey results can never be better than 10%. The solution is to survey more people. To measure more photons. As we put more laser power into our machine, the granularity of light matters less and less.
The noise caused by the granularity of light is called "shot noise." The name sticks because it makes us think of shot, like the light is a spray of BB's out of a shotgun. But it's really named after Walter Schottky.
We've replaced our ~ 8 Watt laser with a new 35 Watt one. But putting more light into the machine is not so simple as getting a more powerful laser, for at least two reasons.
* at frequencies above ~ 100 Hz
( 1. Things heat up )
( 2. Light pushes on things )
On Friday night we put 12 W into the machine for 12 minutes.
