Linear Scanning

A galvanometric scanner is a scanning device whose angular deflection of the beam can be controlled directly with a linear relation to an analog command signal. A linear scanner is a Galvo-Galvo scanhead with a galvo to control the deflection in the X and Y axes. Frame scanning ROIs scanned with a linear scanner automatically has raster waveforms calculated based on the size, location, and rotation of the ROI.

Performance

The ability of a galvo to follow a command signal can be called its performance. Its performance is heavily dependent on the moment of inertia of the mirror, which varies with aperture sizes. No galvo mirror exists which can perfectly follow the command signal, and so a command signal should be altered (i.e. exaggerated) to ensure the angular deflection of the beam follows the intended path precisely spatially and temporally. ScanImage® is able to do this through a premium feature, Command Waveform Optimization.

The limitation on the frame rate of an acquisition with a linear scanner is based on the sampling speed of the acquisition DAQ, pixel binning, and size of the ROI. ScanImage® sets a slew rate limit for the derivative of the command signal, but it is up to the user to scan at frame rates which are not harmful to the galvo scanners - particularly the X (fast axis) scanner. The frame rates achievable with a linear scanner are typically lower than that achieved with a resonant scanner.


Compatible Premium Features

Arbitrary Line Scanning

A linear scanner does not necessarily have to follow a raster pattern to scan ROIs. If the fluorescence of only certain pixel-sized locations of the scanfield are desired, the linear scanner can be used for Arbitrary Line Scanning.

Photostimulation

With the ability to arbitrarily control the deflection position of the beam comes the ability to expose specific ROI to a specific beam power. ScanImage® Premium has a Photostimulation module where users can do just this. Microscopes built with separate RG(G) and GG scan paths are able image and apply photostimulation simultaneously.

When operating ScanImage® to acquire multiple regions of interest, a linear scanning imaging system can be used to capture ROIs that are offset from the center of the scanfield.


Striping Display

Because of the limited velocity of galvanometric mirrors, high resolution LinScan frames refresh at relatively slow rates (0.5-2Hz). To provide faster visual feedback of the specimen, the linear scanning imaging system allows to subdivide a frame into multiple stripes. As soon as the scan of a stripe is finished, it is displayed in the Channel Display windows. The striping display feature is activated by default, but the ScanImage’s standard settings can be changed in the Machine Data File:

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%% LinScan

% add the following lines to the LinScan section to overwrite ScanImage's defaults
stripingEnable = true; % enables/disables striping display
stripingMaxRate = 5; % [Hz] determines the maximum display update rate for striping

Note

Striping display is unavailable if Multiple Region of Interest (MROI) mode is enabled.