[time-nuts] LIGO detects gravitational waves

Magnus Danielson magnus at rubidium.dyndns.org
Mon Feb 15 02:23:19 EST 2016


I was thinking the same thing, the circulated energy isn't all that 
great and each arm is feed with 10 W (it's a 20 W laser split in two).

The fact that it is a vacuum chamber of sizeable volume would make me 
avoid punching a hole in it for starters.

Considerining that they seemed to have a sample rate of 16384 Hz, they 
where keeping this operating this in relatively continuous mode or very 
high pulse-rate.


On 02/14/2016 09:26 PM, Paul Boven wrote:
> Hi PHK, everyone,
> On 2016-02-14 0:30:22, Poul-Henning Kamp wrote:
>> --------
>> In message <1E75A9592178425ABD11390EB725D060 at pc52>, "Tom Van Baak"
>> writes:
>>> Yes, the interferometer is 4 km in length but they bounce the beam back
>>> and forth 400 times so the effective length is more like 1600 km. They
>>> keep the mirrors stationary to "picometers". They use hundreds of clever
>>> tricks to pull this off.
>> It's actually more amazing than that, each arm is a resonant cavity,
>> so while the actual laser is only about 10W, they have about 20 kW of
>> photons inflight at any one time.
>> With 20 kiloWatt of light safety-glasses are not _that_ important any
>> more.
> This number keeps getting repeated, but I have some doubts there.
> The 'finesse' of the cavity is about 1000. The view that the photons
> keep bouncing back and forth seems a bit simplistic, wouldn't it be more
> like a standing wave?
> The cavity acts as a resonator, and although the instantaneous power
> would indeed be 20kW, as soon as you load that cavity, its stored energy
> would be dissipated in whoever was unlucky enough to end up in the beam.
> Given a length of 4km, it would take no more than 13 us to empty the
> cavity. And 13us times 20kW gives an energy of only 0.27 J.
> The part that I am still having trouble understanding is why the two
> cavities in the arms of the interferometer help increase the
> sensitivity. Are they modulating the reflectivity of the mirrors on the
> inner testmasses so they can 'dump' both beams at the same time back
> into the half-silvered mirror?
> Cheers, Paul - 73 de PEaNUT.
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