Introduction to the various LPF noise models


As with the system models, the various noise models also come in different versions. You can build these noise models individually and inspect their responses. Let's look at a couple of examples.

Capacitive actuation Noise Model

For example, let's build the noise model used for generating force and torque noise of the GRS actuation. The model is called DIST_CAPACT.
We start by inspecting the model to see what versions are available, and, within each version, the parameters available for setting. Start with opening the model documentation:

      help ssm_model_DIST_CAPACT
and click on the 'Model Information' link. As we can see, there are 5 versions available. All of them allow the user to choose a parameter for the dimension of the model, so to operate only along x (1D), along x, y and phi (2D), or along all degrees of freedom (3D). In addition, you can scroll to the details section for a particular model version and see what configuration parameters are available to you. For instance, in this case we have different pole-zero models that characterize the noise shaping filters that color unit-variance white noise to mimick the force and torque noise associated with the electrostatic actuation provided bt the GRS and the FEE. After deciding the version we want to build, and the values of the parameters we want to set, we can build it by doing:
      % Build the default version of the GRS CAPactive ACTuation noise model      
      GRScapactNoise = ssm(plist('built-in', 'DIST_CAPACT'));
Now that we've built the object, we can use the ssm/viewDetails method to inspect the various inputs and outputs of this model:
      GRScapactNoise.viewDetails
so to understand how the input blocks are called, how many and which ports we have for each input, and how many and which outputs are available.

IFO readout Noise Models

As another example, let's build the noise model used for generating readout noise of the interferometer. The model is called DIST_IFO_READOUT.
Again, start by inspecting the model to see what versions are available, and, within each version, the parameters available for setting. As before, open the model documentation with:

      help ssm_model_DIST_IFO_READOUT
As we can see, there are 4 versions available. All of them allow the user to choose a parameter for the dimensions of the model, so to operate only with the longitudinal degrees of freedom (1D), or also with angular ones (2D and 3D). In addition, you can scroll to the details section for a particular model version and see what configuration parameters are available to you. For instance, in this case we have different pole-zero models that characterize the noise shaping filters that color unit-variance white noise to mimick the readout noise for the different IFO components. After deciding the version we want to build, and the values of the parameters we want to set, we can build it by doing:
      % Build the default version of the IFO Readout noise model      
      IFOreadoutNoise = ssm(plist('built-in', 'DIST_IFO_READOUT'));
Now that we built the object, we can use the ssm/viewDetails method to inspect the various inputs and outputs of this model:
      IFOreadoutNoise.viewDetails
so to understand how the input blocks are called, how many and which ports we have for each input, and how many and which outputs are available.

This noise source is added after the modelling of the actual conversion of the TMs position into an IFO reading, so it represents noise sources such as shot noise in the beams, electronics noise (additive, digitization, ...).

Other noise sources that act 'common mode' on all IFO channels, such as laser frequency fluctuations, are modelled by the DIST_IFO_POSITION noise model, that can be built by doing:

      % Build the default version of the IFO so-called position noise model      
      IFOfrequencyNoise = ssm(plist('built-in', 'DIST_IFO_POSITION'));
Now that we built the object, we can use the ssm/viewDetails method to inspect the various inputs and outputs of this model:
      IFOfrequencyNoise.viewDetails
so to understand how the input blocks are called, how many and which ports we have for each input, and how many and which outputs are available.



©LTP Team