• Created by Unknown User (iyerv), last modified on Oct 09, 2013
This page contains macros or features from a plugin which requires a valid license.

You will need to contact your administrator.


POWER CONTROLS Panel

 

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.

(info) The POWER CONTROLS panel only appears on ScanImage startup if pmtModuleControl is enabled and at least one beamChanIDis specified in the Machine Data File.

This menu selects among the (up to 3) Beamsthat have been configured (and named) in the Machine Data File. 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.

(info) To allow calibration of a particular Beam, its beamCalInputDeviceID and beamCalInputChanIDmust be specified in the Machine Data File.

(tick) At ScanImage startup, all Beams with specified Beam Calibration input channels are automatically calibrated

  • : Causes Beam Calibration for currently selected to be remeasured
  • : Displays Matlab figure showing result of most recent Beam Calibration obtained for currently selected
  • : 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 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 beamVoltageRangesvalues in the Machine Data File.

  • 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
  • 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 beamVoltageRangeentered in the Machine Data File.

     

  • Beam Calibration input channel offsets are stored in the Machine Data File after being measured and automatically reapplied on subsequent use of ScanImage. Offsets are not expected to change significantly from day to day. The operation should be done/checked only periodically to ensure there are no significant fluctuations.

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.

(tick) 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 level and the minimum power (during scanner flyback or turnaround)

(Always On in ScanImage 4.2)
In ScanImage 4.2, slider adjustments to power can be made during FOCUS acquisitions. Acquisition will be briefly stopped and restarted with each adjustment.

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.

(info) 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.

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.

and

When collecting Image Stacks, step-wise or sweeping (i.e.Volume Imaging), in scattering tissue, the power level required at each slice in the stack generally increases with depth in order to maintain a fixed signal. ScanImage can adjust the power automatically during stacks.

: Checkbox enables/disables automatic 'P vs z' adjustment feature for currently selected
: Specifies exponential length constant for currently selected . Power is increased with depth according to P = P0 * exp^((z-z0)/Lz).
(tick) A value of Inf implies no power adjustment should occur for the selected .
(info) Value of Lz must be positive

  • In general, the user will experiment to identify the value suited for their preparation, which is typically fairly constant from acquisition to acquisition.
  • Note the power level only adjusts in integer increments of the percentage value.
  • The and controls are User Settings, i.e saved/loaded to User (.USR) files. Thus, once value is determined/entered by user for each Beam, these values are typically loaded on ScanImage startup and apply to all stack configurations/acquisitions during that ScanImage session.
 

Measure Lz

ScanImage provides a facility to interactively measure, rather than enter, the value for the current specimen/stack. See MOTOR CONTROLS for more information.

 

 

  • No labels