Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
2000-07-28
2002-08-27
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C250S235000, C359S215100, C359S385000
Reexamination Certificate
active
06441356
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to confocal scanning microscopy and optical coherence microscopy. More specifically, it relates to fiber-based optical coherence microscopy systems incorporating a novel, fiber-coupled, angled-dual-axis confocal scanning microscope.
BACKGROUND ART
The advent of fiber optics and laser technology has brought a renewed life to many areas of conventional optics. Confocal microscopes, for example, have enjoyed higher resolution, more integrated structure, and enhanced imaging capability. Consequently, confocal microscopes have become increasingly powerful tools in a variety of applications, including biological and medical imaging, optical data storage and semiconductor applications. The original idea of confocal microscopy traces back to the work of Marvin Minsky. Described in his seminal U.S. Pat. No. 3,013,467 is a system in which an illumination beam passes through a pinhole, traverses a beamsplitter, and is focused by an objective to a focal volume within an object. An observation beam that emanates from the local volume is in turn converged by the same objective lens, reflected by its second encounter with the beamsplitter, and passes through a second pinhole to a photo detector. The geometry of this confocal arrangement is such that only the light beam originating from the focal volume is able to pass through the second pinhole and reach the photo detector, thus effectively discriminating all other out-of-focus signals.
Contemporary confocal microscopes tend to adopt one of two basic confocal geometries. In the transmission arrangement using two objectives, one objective focuses an illumination beam from a point source onto a focal volume within an object and another objective collects an observation beam that emanates from a confocal overlapping volume (within the focal volume). Whereas in the so-called “reciprocal” reflection arrangement, a single objective plays a dual role of focusing light on the object and collecting the light emanated from the object. In either case, the confocal arrangement enables the confocal microscope to attain a higher resolution and sharper definition than a conventional microscope, because out-of-focus signals are rejected. This unique ability has made confocal microscopes particularly useful tools in the examination of biological specimens, since they can view a specific layer within a sample and avoid seeing other layers, the so-called “optical sectioning”. Confocal microscopy techniques are also exploited to provide a spatial filter in many applications.
The transmission confocal microscope typically employs two separate lenses: one serves as the illumination objective and the other as the observation objective. The single objective in the “reciprocal” arrangement can also be a single lens, in either simple or compound form. In order to image a thin layer about a few micrometers thick within a sample, however, the numerical aperture (NA) of the objective lenses must be large, so as to provide adequate resolution particularly in the axial direction. This generally results in a short working distance, which is undesirable in practice.
A great deal of ingenuity has accordingly been devoted to improving the axial resolution of confocal microscopes without using high NA lenses. A particularly interesting approach is to spatially arrange two separate illumination and observation objective -lenses, or the illumination and observation beam paths, in such a way that the illumination beam and the observation beam intersect at an angle theta (&thgr;) at the focal points, so that the overall point-spread function for the microscope, i.e., the overlapping volume of the illumination and observation point-spread functions results in a substantial reduction in the axial direction. A confocal microscope with such an angled, dual-axis design is termed a confocal theta microscope, or an angled-dual-axis confocal microscope, hereinafter. The underlying principle as well as the advantages of confocal theta microscopy are described in US Patent Application, “Fiber-coupled, High-speed, Integrated, Angled-Dual-Axis Confocal Scanning Microscopes Employing. Vertical Cross-Section Scanning” of Michael J. Mandella, Mark H. Garrett, and Gordon S. Kino, Ser. No. 09/628,118, filed on Jul. 8, 2000, incorporated herein by reference for all purposes.
More specifically, Ser. No. 09/628,118 discloses an angled-dual-axis confocal scanning microscope comprising an angled-dual-axis confocal scanning head mechanically coupled to a vertical scanning unit. The angled-dual-axis confocal scanning head is configured such that the illumination and observation beams intersect optimally at an angle &thgr; within an object and the scanning is achieved by pivoting the illumination and observation beams jointly using a single scanning element, thereby producing an arc-line scan. The vertical scanning unit further causes the angled-dual-axis confocal scanning head to move towards or away from the object, whereby a succession of arc-line scans that progressively deepen into the object is produced, providing a two-dimensional vertical cross-section scan of the object. The vertical scanning unit also comprises a compensation means, for keeping the optical path lengths of the illumination and observation beams unchanged so to ensure the optimal intersection of the illumination and observation beams in the course of vertical scanning. This novel scanning mechanism, along with the integrated structure of the angled-dual-axis confocal scanning head and the coupling of optical fibers, enables this angled-dual-axis confocal scanning microscope to perform fast and high resolution scanning over a large transverse field of view, while maintaining a workable working distance. The integration of optical fibers and silicon fabrication technology further renders this angled-dual-axis confocal scanning microscope integrity, flexibility, scalability, and maneuverability, as desired in many applications.
For example, one of the applications the aforementioned angled-dual-axis confocal scanning microscope is particularly suited for is optical coherence microscopy (OCM), which effectively filters out multiple-scattered photon noise, thus providing high sensitivity and large dynamic range of detection when imaging in a scattering medium. Although great stride has been made in improving the sensitivity and imaging capabilities of optical coherence microscopy, as exemplified by U.S. Pat. No. 6,201,608 B1, commonly assigned to the same inventors as the current application, optical coherence microscopy has yet to reach its full potential of high resolution and fast scanning, as required in biological and medical applications, particularly in vivo imaging of live tissue which is constantly in motion. Two of the prior art methods of obtaining high axial resolution in an OCM apparatus involve the use of either a large NA objective lens, or the use of a femto-second pulsed laser with a very short coherence length. These methods are described by Wang et al. in “High Speed, full field optical coherence microscopy”, Proceedings of The SPIE Conference on Coherence Domain Optical Methods in Biomedical Science and Clinical Applications III, San Jose, Calif., January 1999, pp. 204-212, and by Drexler et al. in “In vivo ultrahigh-resolution optical coherence tomography”, Optics Letters, 21(17), pp. 1221-1223, 1999, all incorporated herein by reference. The primary disadvantage of using a high NA is the limited field of view in which diffraction-limited performance is obtained during high speed transverse scanning. High cost and intricacy of femto-second lasers make the second approach undesirable for a practical instrument.
Hence, there is a need in the art for a new way of applying the techniques of optical coherence microscopy that overcomes the limitations of the prior art methods.
OBJECTS AND ADVANTAGES
Accordingly it is a principal object of the present invention to provide an angled-dual-axis optical coherence scanning microscope that achieves
a) high axial resolutio
Garrett Mark H.
Kino Gordon S.
Mandella Michael J.
Kao Chih Cheng G
Kim Robert H.
Lumen Intellectual Property Services
Optical Biopsy Technologies
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