1. Technical Field
This disclosure is related to microscopes adapted for use in charged-particle instruments, where the microscope provides multiple magnifications with a single objective lens.
2. Background
It is often desirable to optically monitor the processing of a sample inside the closed space of a charged-particle beam apparatus, such as a focused ion-beam microscope or scanning-electron microscope, or any other vacuum chamber lacking the capability to render an image with high magnification. The distance from the vacuum chamber wall to the sample imaging location, the limited space between the sample and the charged-particle beam pole piece, the limited number of ports available in the charged-particle beam apparatus and the necessity to keep the vacuum pressure unchanged make it difficult to find a reliable and simple solution to this problem.
In this disclosure, we solve these problems using a single-objective lens combined with a gradient index lens (also called a self-focusing rod lens) to provide images of a specimen with different magnifications to two or more cameras or imaging devices. We also disclose systems adaptable to existing nanomanipulators, so that the working distance from the specimen to the objective can be easily varied as the nanomanipulator moves the system toward or away from the specimen. Such a system would also preferably be integrated with light sources for illumination of the specimen The light delivered inside the vacuum chamber can be of any wavelength from the optical region of deep UV (starting from 190 nm) to far IR (up to 10 microns).
In this disclosure, the term “objective lens” should be understood to include simple lenses, as well as achromatic or other corrected lenses, and lenses having one or two principal planes. Suitable gradient-index lenses are manufactured by NGS America, Inc. of Somerset, N.J. and sold under the trademark SELFOC. The term “camera” refers to any sort of camera or imaging device, such as a charge-coupled device, or CCD. The “working distance” an objective lens is the distance from a specimen of interest to the first principal plane of the objective lens, or the one principal plane if there is only one.
In an alternative embodiment, a second lens (160) may be inserted in the second optical axis (210) between the beam splitter (130) and the second camera to obtain an image with a magnification equal to ______, when the focal length F2 of the second lens (160) is set to ______.
Given that the spacing relationships between the optical elements in the optical system (220) are preferably fixed, the first and second magnifications are obtained by moving the working distance (180) of the objective lens (100) from a specimen (115). In the usual application inside a vacuum instrument, this is easily done by moving the system (220) with a nanomanipulator probe, as next illustrated.
In the hardware embodiment, the gradient-index lens (120) is clasped in a sleeve (240), which sleeve (240) is sized to be gripped and moved axially by the nanomanipulator system (280).
The reader should understand that the optical system (220) can have more than one beam splitter (130), so as to create multiple optical axes and thus multiple images of the same area with different magnifications. For example, the first image obtained could be used to show a small part of the specimen (115) with high magnification, and the second and next order images could be used to show wider coverage of the area of interest on the specimen (115). The amount of light reflected and transmitted through each beam splitter (130) could be set at the most convenient ratio, such as 70/30, instead of 50/50. Also, a dichroic mirror could be used in place of a conventional beam splitter, for example, where a bright field image is used to investigate the fluorescence of different parts of the specimen (115) in different spectral bands. A colored region in a biological sample, for example, could be examined the optical image, and then this region could be imaged at higher magnification with an electron beam. The system (220) is not restricted to vacuum environments; it could also be used in variable pressure microscopes, such as the environmental scanning-electron microscope, or in the open air for areas not accessible by ordinary means.
None of the description in this application should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope; the scope of patented subject matter is defined only by the allowed claims. Moreover, none of these claims are intended to invoke paragraph six of 35 U.S.C. Section 112 unless the exact words “means for” are used, followed by a gerund. The claims as filed are intended to be as comprehensive as possible, and no subject matter is intentionally relinquished, dedicated, or abandoned.
This application claims the priority of U.S. Provisional Application Ser. No. 61/151,687, filed Feb. 11, 2009, which provisional application is incorporated by reference into the present application. This application is related to U.S. patent application Ser. No. 12/201,447, filed Aug. 29, 2008, titled “Single-channel optical processing system for energetic-beam microscopes.”
Number | Date | Country | |
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61151687 | Feb 2009 | US |