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[Sensitivity Home | Online Curve Generator | Tool Version History] Other Resources:[LISA Home | LISA Science Team | LISA Simulator]
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INTRODUCTIONSo you've found the Sensitivity Curve Generator, and now you are wondering how to use it, and what all the choices are. This short document should help get you started.The online sensitivity curve generator is a basic tool designed to provide the end user with a numerical representation of the sensitivity curve for a space based gravitational wave interferometer, such as LISA. The tool takes a series of inputs from the user which describe the observatory configuration, and computes the expected sensitivity curve averaged over all polarization states and all sky locations. The choices the user makes for the observatory parameters affect the performance in a variety of ways; how the tool uses each of these numbers is described in detail below. The curves generated are for an equal arm, Michelson configuration, and conform to the standard LISA curves which may be found in the literature (a list of starting points is given at the bottom of this page). The LISA Project has produced a white paper which describes the baseline sensitivity curve for the LISA mission: Sensitivity Curve White Paper |
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CHOICES USER CAN MAKEIn addition to making choices about the raw numbers describing the observatory, the tool is currently configured to let the user make two choices regarding how the curves are computed.
(1) Type of Output Curve
(2) Setting for Noise Floor If the user chooses position noise budget, the limting noise on the floor will be set using the value the user inputs for one way position noise (default value of 20 pm per root Hz). If the user chooses shot noise, the limting noise on the floor will be computed using observatory parameters (telescope diameter, laser power, etc) from the rest of the page. In a future upgrade to this page, we will break all the contributing noise sources out so they may be individually specified.
CURVE GENERATOR INPUT FIELDSMost of the choices for observatory parameters are fed into algorithms which compute a variety of instrumental noise spectra which ultimately limit the performance of the observatory. By altering the parameters, you can explore how different design choices in the construction of an observatory affects the sensitivity performance, which feeds directly into what kind of science can be done with the instrument.
Default Value: 1.0 Impacts: Overall level of curve This specifies the SNR value for a threshold detection at the level of the plotted sensitivity curve. The default value is 1.0, but some LISA literature (e.g. the LISA Pre-Phase A Report) uses SNR = 5.
Default Value: 5.0e9 meters Impacts: Location of "corners" on curve This specifies the armlength in the observatory (assumed to be equal for all arms). The choice of armlength affects the sensitivity in a variety of ways: (1) The transfer frequency, f* = c/(2 pi L), is defined by the right-hand corner of a stanard sensitivty curve, where the sensitivity begins to drop off. It scales inversely with the armlength, shifting to higher frequencies as the arms get shorter. (2) The acceleration wall (limiting noise at low frequencies) shifts to higher frequencies.
Default Value: 0.3 meters Impacts: Shot noise level (mid-frequency sensitivity) This specifies the diameter of the telescope which transmits and receives laser light. The telescope diameter does not affect the performance of the instrument except as it directly relates to the computation of shot noise. If the user specifies that the floor should be set by the position noise budget, then this value is not used in the current version of the tool.
Default Value: 1064 nanometers Impacts: Shot noise level (mid-frequency sensitivity) This specifies the wavelength of the interferometer laser light (currently, this is for Nd:YAG lasers). The laser wavelength does not affect the performance of the instrument except as it directly relates to the computation of shot noise. If the user specifies that the floor should be set by the position noise budget, then this value is not used in the current version of the tool.
Default Value: 1.0 Watt Impacts: Shot noise level (mid-frequency sensitivity) This specifies the transmitted power of the interferometer lasers. The laser power does not affect the performance of the instrument except as it directly relates to the computation of shot noise. If the user specifies that the floor should be set by the position noise budget, then this value is not used in the current version of the tool.
Default Value: 3.0e-15 m/[s^2 rt Hz] Impacts: Low frequency loss in sensitivity This specifies the acceptable level of acceleration noise in the instrument, which is the limiting factor on performance at low frequencies. Acceleration noise has a 1/f^2 dependence, so the sensitivity decreases at lower frequencies.
Default Value: 2.0e-11 m/[rt Hz] Impacts: Mid-frequency sensitivity level This specifies the total contribution of position type noises (including laser shot noise) in the instrument. This value is used for the noise spectrum (instead of a computation of laser shot noise from the above quantities) if the user chooses Floor Set by Position Noise Budget.
If you have Problems with the GeneratorThis page is currently a beta test! Please email suggestions and bug reports about this page to shane@srl.caltech.edu. Be sure it include a complete list of parameters for the observatory you were designing -- it will greatly aid me in debugging your problem on this end.
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Sensitivity and LISA Literature (A Small Sample)Mission Documents
Basis for Online Tool
Time Delay Interferometry
Other Sensitivity Calculations
White Dwarf Background |
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