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authorUser <>2009-10-13 02:52:09 +0000
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+LIGO: Laser Interferometer Gravitational Observatory
+.. warning:: This is a rough work in progress!! Likely to be factual errors, poor grammar, etc.
+.. note:: Most of this content is based on a 2002 Caltech course taught by
+ Kip Thorn [PH237]_
+Noise Sources
+For initial LIGO, seismic noise dominates below about 60Hz, suspension thermal
+noise between 60 and 180Hz, and radiation pressure shot noise above 180Hz.
+Advanced LIGO will use 40kg sapphire test masses with sensitivity of about 10e-19 meters: 1/10000 of an atomic nucleus, 10e-13 of a wavelength, and half of the entire mirror's wave function.
+5e6 km separations between three spacecraft, 1 (astronomical unit, ~1.5e8 from the sun. 1 watt lasers.
+The heterodyne detection is of the beat frequencies at each spacecraft of the
+two incoming beams. Doppler shifts of spacecraft must be taken into account,
+due not only to sun radiation pressure etc, but varying gravitational fields
+from planetary orbits.
+The test masses inside LISA should be free falling and have relative
+separations stable to 10e-9 cm (10e-5 wavelength of light).
+LISA's sensitivity is in the milihertz regime.
+.. note: (insert LISA noise curve?)
+Data Analysis
+Using matched filtering (eg, take cross correlation between two waveforms,
+integrating their product), frequency sensitivity will be around the inverse
+of the number of cycles of waveform (for LIGO, around 20,000 cycles, for LISA
+around 200,000 cycles).
+This technique requires known, theoretically derived waveforms (within
+phase/amplitude). There are other methods when we don't have good guesses
+about the waveform we are looking for...