US 2003/0197112 A1 · Autofocus z stage

Abstract

The present invention provides for very rapid autofocusing of optical scanning systems. If a sample is sufficiently out of focus, the focal error signal used to focus a conventional half-blocked system can become saturated. Multiple steps toward the focus position then typically are required to bring the system into the operational range. To minimize this, a light adjustment system is provided to reduce the amount of light impinging on the half-blocked system when the focal error signal is at or near saturation. The half-blocked system then becomes primary controller again, and can move the system into a position generally close to the correct focal point. The light adjustment system then can be deactivated, but since the system now is much closer to focus, the half-blocked system can quickly bring the system into final focus. Alternatively, the photodetectors used to generate the focal error signal are segmented. The approximate distance to the correct focal point then is determined by comparing the amount of light detected by segments at different radial positions.

Drawings

Claims2

Dependent claims

A focusing system for an optical system for imaging light from a sample, the system comprising:

a) a photodetector for receiving and detecting a light beam from the sample along an optical path, the photodetector having at least four parts positioned at at least two different radial distances from a center of the photodetector, each part independently detecting the intensity of the light falling upon it and generating a light intensity signal indicative thereof;
b) at least one lens in the optical path between the sample and the photodetector for focusing the light beam coming from the sample;
c) a knife edge positioned in the optical path between the sample and the photodetector for blocking at least one, but not all, of the parts of the photodetector from receiving the light beam from the sample;
d) a stage for holding the sample;
e) a focus mechanism for controllably moving at least one lens or the stage along the optical path in response to a focus signal to adjust the focus of the system;
and
f) a controller for generating the focus signal in response to the light intensity signals, by:
i) subtracting light intensity signals from substantially opposite parts of the photodetector to generate a focal error signal indicative of a direction in which the image of the sample is out of focus;
ii) comparing light intensity signals from parts of the photodetector at different radial positions to determine an amount by which the image of the sample is out of focus;
iii) generating a focus signal in response to which the focus mechanism will adjust the focus of the system in the direction and by an amount sufficient to bring the focal error signal closer to zero;
and
iv) repeating steps (i) through (iii) until the focal error signal is within a predetermined acceptable range.

9 more elements

Dependencies are inferred from the claim text.

Description3,613 words

Summary2,212 words

#1. Technical Field

#The present invention relates to automated focusing systems, in particular to extremely rapid automatic focusing of optical scanning systems.

#2. Description of the Related Art

Brief description of the drawings7 figures

#The invention will be described with reference to the drawings, in which:

#FIG. 1 is a schematic representation of a typical prior art optical scanning system.

#FIG. 2 is a schematic representation of the scanning portion of the optical scanning system of FIG. 1.

Detailed description1,237 words

#Simply put, the inventors have recognized that the problem with the prior half-blocked systems arises because the FES is saturated. The present invention therefore provides a mechanism to reduce the area of the light incident on the photodetectors, and thereby extend the capture region in which the system will operate properly. Alternatively, the present invention provides a mechanism to measure the distance by which sample is out of focus by determining the radial extent of the light beam incident on the photodetectors.

#A first embodiment of the present invention is shown in FIGS. 5a, b. In FIGS. 5a, b, the elements analogous to those shown in FIGS. 3a, b, c have been shown with the same numbers with a prime (′).

#According to this embodiment of the invention, an iris 52 is added between lens 26′ and knife edge 44′, preferably closer to lens 46′ than to the beam splitter 40 to avoid interfering with the light going to the main optics 18. When iris 52 is dilated fully, as shown in FIG. 5a, all of light 47′ that previously would have reached photodetector 48 in FIGS. 3a, b, c, still reaches photodetector 48′. As has been recognized by the inventors, if sample 16′ is too far out of focus, the absolute value of FES 50′ will be above some predetermined value that indicates that FES 50′ is saturated or nearly saturated. When this happens, computer 22′ generates a light reduction signal (either digital or analog) to contract iris 52 to reduce the amount of light reaching photodetector 48′, as shown in FIG. 5b.

Autofocus z stage

Life of this patent

Autofocus z stage

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims2

Description3,613 words

Drawings

Classification3 codes

Life of this patent

Description3,613 words