What is a Field-of-View Scanner?

Borlinghaus, Rolf T.

March 06, 2019

What is a Field-of-View Scanner?

Technology of SP8 confocal microscope

A field-of-view scanner is an assembly of galvanometric scanning mirrors used in single-point confocal microscopes that offer the correct optical recording of large field sizes. The field-of-view scanner employs a three-mirror concept that offers superior homogeneity in illumination compared to classical two-mirror scanners, without compromising high scanning speed. The galvanometric scanners are controllable in speed and position, allowing zoom and pan functions as well as tuning the scan frequency. They also allow resting point illumination as is required for, e.g., FCS-measurements.

X2Y scanner design

The tree-mirror concept is known as the “x2y scanner”. This approach solves the general problem of scanner systems with two mirrors which cannot be placed in the correct position (the back focal plane) at the same time without additional relay optics. Usually, deviations are accepted by compromising the homogeneity of illumination (with negative effects on uniformity of brightness and resolution). A single mirror solution (cardanic) offers homogeneous illumination, but is restricted to very low scanning speeds.

The x2y scanner illuminates the full field of view (FOV) homogeneously and allows high scanning speed.

Fig 1: Animated schematic that illustrates the principle of the x2y scanner concept. The x2y design ensures always correct filling of the entrance pupil of the objective lens and still allows high scan speeds.

Control zoom & pan

The field-of-view scanner is composed of two y-scanning mirrors in combination with a position-programmable galvanometric scanner for the x-direction. Such a combination allows the position of the beam to be known and actively controlled at any time. It also enables an electronic control of the scan speed, offset (panning), and amplitude (zooming) which are restricted only by the mechanical properties of the scanner.

Fig 2: Pan and zoom function in a single point laser scanner microscope is controlled by scan amplitude and scan offset. This allows to scan arbitrary rectangles within the entire field of view.

Extremely high scanning speed is achieved with a resonant scanner. A tandem scanner is a device that combines both field of view and resonant scanning for alternative uses.