Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-08-25
2001-04-03
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S202100, C359S203100, C359S861000, C359S862000
Reexamination Certificate
active
06211988
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an optical configuration for scanning a beam in two, fundamentally perpendicular axes, particularly for use in confocal laser scanning microscopes, with two mirrors that can be rotated, each by a drive, around two axes that lie perpendicular to each other (x-axis, y-axis).
Basically what is involved here is a configuration for scanning a beam in two, fundamentally perpendicular axes, the significant feature in the present case being the rotation of the light beam in both axes around the pupil of the lens or a plane conjugated to the lens.
Technical practice is already acquainted with highly differing embodiments of an x-y scanner. Different scanners are known from the paper by J. Montagu: “Two-axis beam steering system, TABS”, Proceedings Reprint, SPIE—The International Society for Optical Engineering, Vol. 1920, 1993, pages 162-173 (reprinted from Smart Structures and Materials 1993: “Active and Adaptive Optical Components and Systems II”, 1-4 February 1993, Albuquerque, N. Mex.).
With the single mirror scanner, a single mirror is provided that rotates around an axis; the rotating axis of the mirror does not correspond to the optical axis. Single mirror scanners generally comprise a gimbal-mounted mirror for scanning in both the x and y directions.
Here, to be sure, the single mirror minimizes the loss of light that occurs when there is a plurality of mirrors; on the other hand, the x galvanometer must be continuously kept in motion, i.e., its mass must be accelerated and braked. This limits the image rate to about 10 images per second, specifically because of the otherwise excessive vibrational inputs into the microscope system. Furthermore, a resonant scanner cannot be employed due to its required installation.
In a two-mirror scanner, two mirrors positioned at a predetermined angle are provided that normally turn around rotating axes that are orthogonally positioned. This kind of arrangement is not absolutely necessary, however. The incident beam in any case runs parallel to the rotating axis of the last mirror in the beam path.
Furthermore, so-called “paddle” scanners and “golf club” scanners, as special embodiments of the two-mirror scanner, are known to the prior art. In these scanners, rotation of the beam around a virtual pivot point is achieved only approximately, which basically results in imaging errors.
According to A. F. Slomba: “A laser flying spot scanner for use in automated fluorescence antibody instrumentation”, Vol. 6, No. 3, May-June 1972, pages 230-234, mirror scanners are also known for use in fluorescence microscopy and in confocal microscopy. Reference is made thereto merely for supplementary purposes.
The known optical configurations discussed above for scanning a beam in two perpendicular axes are problematic in actual practice, and for a number reasons. Foremost among these reasons is certainly the large number of imaging errors, as well as the far-reaching problems associated with the fact that at least one of the drives must be continuously entrained, which results in a very considerable reduction in the image rate. In any case, the known two-mirror designs only approximately allow the beam to be rotated around a virtual pivot point, and a large number of imaging errors consequently arise in these scanners.
SUMMARY OF THE INVENTION
The invention is therefore based on the problem of specifying an optical configuration for scanning a beam in two, basically perpendicular axes, while avoiding serious imaging errors, a configuration that makes possible a high imaging rate for real time application, i.e., at conventional video speed, and in which the image can be easily adjusted or centered, particularly in confocal microscopy.
The configuration according to the invention for scanning a beam in two, basically perpendicular axes solves the above problem with the features described herein. The optical arrangement initially described—a two-mirror scanner—is accordingly supplemented and in such a way that one of the two mirrors is assigned in fixed, rotating fashion to yet another mirror and with a predetermined angular position, such that the assigned mirrors—the first and second mirrors—rotate jointly around the y-axis and thereby rotate the beam around a pivot point that lies on the rotating axis (x-axis) of the third mirror, which rotates in isolation.
According to the invention, further losses in light caused by unavoidable inadequacies in the mirror are tolerated by the third mirror; as with a gimbal-suspension scanning mirror, the arrangement of the three mirrors assures that the pivot point of the beam in the two scanning directions x and y meets in a single point. If this were not the case, the scanning process would result in uncorrectable errors and beam shadings, since a telecentric optical path would no longer be present. The design claimed here produces a slight, y-dependent relative line displacement of:
Δ
x
y
=
sin
β
2
tan
γ
with the y-scanning &bgr;-angle and the &agr;-beam angle between the rotational axis of the y-scanner and the beam that falls on the x-scanning mirror.
Given a typical scanning angle of 7°, the line displacement is less than 2% of the image width and is thus negligible for many applications. If necessary, it can be easily corrected, however, with an appropriate y-dependent offset on the x-drive. In special cases, care must also be taken to assure that the polarization on the upper and lower rim of the image is rotated a few degrees. Given the demand for high scanning rates, the disadvantage of using three mirrors instead of one, e.g., with a gimbal suspension, is easily offset, namely by the considerably smaller mass that must be accelerated here. In any case, drives with a higher frequency can also be used, since these are mounted statically in the design according to the invention.
According to the invention, it is in any case essential to minimize imaging errors, even at the price of losses of light, which in numerous applications are of secondary importance, at least in certain situations.
With regard to the concrete embodiment of the optical design that is claimed here, the two jointly rotating mirrors—the first and second mirrors—are positioned in front of the third mirror, which rotates in isolation. The incident beam falls on the first of the two correlated mirrors; more specifically, it advantageously falls along their common rotating axis (y-axis).
With respect to a compact realization of the optical design, it is advantageous if the two correlated mirrors are positioned on a turnable mount; here the angular positions of the mirrors relative to each other is nonadjustable, as is the distance between them. The entire mounting is able to rotate around the optical axis (y-axis) of the incident beam.
Instead of using a simple mount, it is also possible to arrange the two correlated mirrors in a housing, thus providing the mirrors with physical protection. As with the already mentioned mount, the housing would tun around the optical axis (y-axis) of the incoming beam.
The housing furthermore exhibits an entrance hole for the incident beam; here the beam on the rotating axis of the housing strikes, or falls upon, the first of the two associated mirrors, and is reflected to the second mirror. The third mirror can be positioned in rotating fashion outside the housing. In a particularly advantageous version, however, the housing exhibits a recessed area and is at least partially open vis-á-vis this recessed area. The third mirror, which rotates in isolation (x-rotating axis), rotates independent of the housing and is positioned within the housing recess.
In keeping with the position of the first two firmly positioned mirrors within the housing, the beam is reflected from the second mirror to the housing recess, where it falls on the third mirror positioned there and rotating in isolation. From there, the beam is conducted outside of the housing or back into the housing, to be conducted out of the housing throug
Engelhardt Johann
Ulrich Heinrich
Leica Microsystems Heidelberg GmbH
Schuberg Darren
Simpson, Simpson & Snyder, L.L.P.
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