WFS acquisition | cacao documentation

WFS acquisition: processing raw WFS input to computCACAO_FPSPROC_ACQUWFSe the WFS signal

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1. ACQWFS compute unit

The raw WFS image is processed to compute a WFS signal. This is performed by compute unit ACQWSF. This step is optional if no pre-processing of the WFS input is required.

The ACQWFS CU performs the following steps.

1.1. Dark subtraction and multiplication -> imWFS0

Subtract stream aolX_wfsdark to input, amd multiply by aolX_wfsmult. Result is written to stream aolX_imWFS0.

This step is enabled by (set to OFF to disable):

cacao-fpsctrl setval milt comp.darksub ON

Note: If stream aolX_wfsdark does not exist, it will be created and set to zero. If stream aolX_wfsmult does not exist, it will be created and set to 1.0.

Note: If skipping this step (comp.darksub set to OFF), the WFS input will be copied to aolX_imWFS0 without any change, other than type conversion to ensure aolX_imWFS0 is in float32.

1.2. Flux Normalization -> imWFS1

Multiply stream aolX_imWFS0 by aolX_wfsmask, normalize the result and write it to aolX_imWFS1.

This step is enabled by (set to OFF to disable) :

cacao-fpsctrl setval milt comp.WFSnormalize ON

Note: If stream aolX_wfsmask does not exist, it will be created and set to 1.0.

Warning: Flux normalization is WFS-specific. For example, if the WFS input is a centroid vector (SH type WFS), or a curvature signal, disable this step.

Note: If skipping this step (comp.WFSnormalize set to OFF), aolX_imWFS0 will be copied to aolX_imWFS1.

1.3. Reference subtraction -> imWFS2

Subatract stream aolX_wfsrefc to aolX_imWFS1, write result to aolX_imWFS2.

This step is enabled by (set to OFF to disable) :

cacao-fpsctrl setval milt comp.WFSrefsub ON

Note: If stream aolX_wfsrefc does not exist, it will be created and set to 0.0.

Note: If skipping this step (comp.WFSnormalize set to OFF), aolX_imWFS1 will be copied to aolX_imWFS2.

1.4. Time averaging -> imWFS3

Important: By default, stream aolX_imWFS2 is the input to the wavefront reconstruction matrix-vector-multiply, so this time averaging is not applied to the real-time AO loop input, and will not slow down the loop.

The WFS signal imWFS2 may be time-averaged. This feature is enabled by :

cacao-fpsctrl setval milt comp.WFSsigav ON

The time aveaged output is useful for monitoring, and used by optional advanced AO loop contorl techniques, such as ensuring that the time-averaged AO correction is unbiased (zero mean).

2. Scripts

2.1. Taking the WFS dark

If the WFS input has a bias and/or dark, acquire the “dark”, which is the WFS input when no signal is present:

# -n option: number of frames averaged
cacao-aorun-005-takedark -n 2000

Make sure to turn off or block light source before running the cacao-aorun-005-takedark command, and remember to turn on / unblock after done.

2.2. Starting WFS acquisition

cacao-aorun-025-acqWFS -w start

2.3. Acquiring the WFS reference

This is the WFS response to a flat (unaberrated) input wavefront, and defines the convergence point for the AO loop. This step can be skipped is the WFS input is already referenced to zero for a flat wavefront.

cacao-aorun-026-takeref -n 2000

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