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Descriptions of Selected Subsystems
FIU
The Fiber Injection Unit splits the light using dichroics in to theee parts:
The blue wavelengths which are injected to a fiber and sent to the Ca HK spectrograph inthe K1 AO electronics room.
The bulk of the visible wavelengths are sent via fiber to the main science spectrograph in the basement.
The long wavelengths (850-1200 nm) are sent to the CRED2 guide camera located in the FIU itself.
The FIU also contains two Fiber Viewing Cameras (FVCs) which can be used to image the science or Ca HK fiber tip. This is not used in normal operation.
Agitator
The See the KPF Web Page section on the FIU.
Agitator
See also the KPF Web Page section on the Agitator.
The agitator is located in the crypt beneath the K1 azimuth axis. The crypt has been designated a “Permit Required Enclosed Space” while there is LN2 in the basement (anytime KPF is cold). This means we can not access this area without substantial safety precautions.
The agitator simply agitates the fibers to help with mode scrambling. The observing scripts turn the agitator on and off as appropriate. For normal readout mode, the agitator it turned on and off for every exposure. For the fast readout mode, the agitator is turned on once for each set of exposures (i.e. for each “observing sequence” in the OB).
Exposure Meter
The exposure meter receives a small fraction (a few percent) of the light from the science fiber and is used to determine the flux weighted exposure midpoint time for accurate barycentric correction. It can also be used to terminate exposures once a target flux level has been reached in an exposure.
The exposure meter is fed by two extra slices in the “reformatter” (an image slicer). These slices are illuminated by only the very edge of the image of the fiber and so receive only a small fraction of the light.
Cal Bench
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Exposure Meter
See the KPF Web Page section on the Exposure Meter.
Cal Bench
See the KPF Web Page section on the Cal Bench.
Scripts
KPF is operated using “Observing Blocks” (OBs). Observers build an OB which describes their observation an then the OB is executed using a script. There are currently two types of OBs: Science and Calibration.
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If a trigger file is taken while kpfguide.TRIGCUBE is set to Active, then the system will store and write out an image cube containing the subframe of the image (set by kpfguide.WINDOW) which is used in the tip tilt calculation. This goes in to the third FITS extension of the trigger output file as described above.
Please note: full image cube output is extremely costly in computer resources and is not recommended for use except in engineering contexts. Taking a full image cube of duration longer than about 10 seconds can crash software and hang the server depending on conditions.
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