Power Controls (r4.1)

The POWER CONTROLS panel pertains to the (optional) control of a voltage-controlled light modulator (typically a Pockels cell) supported by ScanImage, allowing the power level used during image acquisition to be controlled.

The POWER CONTROLS panel only appears on ScanImage startup if pmtModuleControl is enabled and at least one beamChanID is specified in the

.

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This menu selects among the (up to 3) Beams that have been configured (and named) in the

. The

level and

value displayed and controlled in this panel pertain to the selected Beam. Actions initiated via the Calibration menu items also pertain to the selected Beam.

Calibration Menu

Many light modulators, including Pockels Cells, do not follow a linear relationship between the control voltage and output power. ScanImage thus allows Beam Calibration, where the power transmitted as a function of control voltage is measured, using a light meter (typically a photodiode). Calibration data stored for each Beam determines voltage signal output to generate a specified percentage of the maximum power.

To allow calibration of a particular Beam, its beamCalInputDeviceID and beamCalInputChanID must be specified in the

.
At ScanImage startup, all Beams with specified Beam Calibration input channels are automatically calibrated

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  : Causes Beam Calibration for currently selected
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  to be remeasured

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  : Displays Matlab figure showing result of most recent Beam Calibration obtained for currently selected
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  : Used to measure voltage offset on Beam Calibration input channel when no laser is present, i.e. offset of light meter and input A/D channel combined. User is prompted to block laser beam for the Beam Calibration offset measurement. All exiting and subsequent calibration curves are adjusted to reflect this input offset.

KEY POINTS:

• Ratio of the maximum to the minimum signal level measured during Beam Calibration determines the dynamic range of the Beam. The minimum value allowed for the
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  level is clamped accordingly, e.g. 0.1% implies a 1000:1 dynamic range, 0.5% implies a 200:1 dynamic range, etc.
• Maximum voltage range used during the Beam Calibration process is specified, for each Beam, by the beamVoltageRanges values in the
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  .
• For some light modulators (e.g. Pockels Cells), the calibration relationship between voltage and percent-power depends on the laser wavelength. In such cases, the calibration should be updated when the laser is significantly re-tuned.
• Calibration curve is not displayed on successful calibrations - use Calibration >> Show Calibration to see calibration results for a particular
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• If calibration curve appears noisy, non-monotonic, or otherwise suspicious, the calibration curve or raw calibration data is shown.
• For Beams without a calibration input (or if no acceptable calibration was maintained), a naive calibration is used where power is specified as a percentage of the beamVoltageRange entered in the
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• Beam Calibration input channel offsets are stored in the
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  after being measured and automatically reapplied on subsequent use of ScanImage. Offsets are not expected to change significantly from day to day. The
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  operation should be done/checked only periodically to ensure there are no significant fluctuations.

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The value displayed and controlled, either by direct numeric input or with the slider control, represents the power level ScanImage should use during subsequently initiated image acquisitions.

Power level is specified as

of the maximum power determined during Beam Calibration. Specifying power in

is not currently supported.

The

level is stored/loaded as part of the ScanImage Configuration (.CFG) file

KEY POINTS:

• Power is adjusted to specified level immediately upon each trigger initiating an acquisition.
  • Triggers in ScanImage arrive at start of FOCUS or GRAB acquisitions, each LOOP Repeat, or each Slice within a standard (stepping) Image Stack.

• Between acquisitions (i.e. between triggers), the Beam power level output is adjusted to minimum power measured during Beam Calibration – i.e. the Beam is 'OFF'

• If Blank Flyback is enabled in the CONFIGURATION window, then command signal generated by ScanImage for selected Beam will alternate between the specified
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  level and the minimum power (during scanner flyback or turnaround)

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(Always On in ScanImage 4.1)
In ScanImage 4.1, slider adjustments to power can be made during FOCUS acquisitions. Acquisition will be briefly stopped and restarted with each adjustment.

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Normally, changes to

have no immediate effect when not acquiring. For optical measurement & testing purposes, the

option can be selected. This causes changes to the

level to take immediate effect, i.e. Beam has specified power even though no scanning/imaging is being done. This mode applies to all Beams.

Note that following any image acquisition (including with

enabled), the power for each Beam is set to minimum value measured during its last Beam Calibration. The

level must be changed, with slider or text entry, to re-enable transmission with a non-scanning Beam.

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The

value simply determines the maximum value to allow for the

level setting, for the specified

. This is useful for preventing the value from accidentally being set too high.

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and

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