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What is a Tandem Scanner?

Technology of SP8 confocal microscope

A Tandem Scanner [1] is an assembly of two different types of scanning together in one system for true confocal point scanning. The Tandem Scanner consists of a three-mirror scanning base with the x-scanner exchangeable with a motorized device. This combination allows scanning of large areas with high scan-resolution by a FOV-scanner and of very fast processes by a resonant scanner, both within the same instrument.

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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 (gimbal/cardanic mounts) offers homogeneous illumination, but is restricted to very low scanning speeds.

The x2y scanner illuminates the full field of view homogeneously and allows high scanning speed. This scanning concept also allows the x-mirror to be exchanged by moving the alternative mirror (either conventional or resonant) into the proper position.

Fig. 1: Animated schematic to illustrate the x2y principle when used in combination with a tandem x-scanning option. Light from the illumination laser, L, is deflected by the galvo mirrors Y1, Y2, and X to generate scanning in both the vertical and horizontal directions. Galvo mirror Y1 controls vertical scanning and galvo mirror X FOV horizontal scanning. Galvo mirror Y2 adjusts its angle (with respect to Y1) to always deflect the beam into the center of X FOV, while causing at the same time a vertical deflection. The light finally reaches the sample, S, which is optically illuminated in the expected way. The dots indicate points of measurement (simplified representation). By exchanging the standard scanner, X FOV, with a resonant scanner, X RES, the same instrument can operate at very high speed and achieve the desired optical illumination of the sample.
Fig. 2: The Tandem Scanner unifies resonant and non-resonant versions of galvanometric mirrors (scan mirrors for x-direction). Switching is performed by sliding the x-galvanometers back and forth. Using the resonant galvanometer frame rates up to 428 fps are possible, while the non-resonant mirror optimizes the field of view and provides adjustable speed in steps of 1 Hz.

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  1. Be careful not confuse it with the spinning-disc-type tandem scanner developed in the 1960s by Petran et al.: M. PETRÁŇ; M. HADRAVSKÝ; M.D. EGGER; R. GALAMBOS (1968), "Tandem-Scanning Reflected-Light Microscope", Journal of the Optical Society of America (JOSA), 58 (5): 661–664, DOI: 10.1364/JOSA.58.000661.