Optics: measuring and testing – By light interference
Reexamination Certificate
2001-02-27
2003-04-22
Hannaher, Constantine (Department: 2878)
Optics: measuring and testing
By light interference
C356S365000
Reexamination Certificate
active
06552795
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This invention claims priority of a German patent application DE 100 101 54.2 filed Mar. 3, 2000 which is incorporated by reference herein.
FIELD OF THE INVENTION
The present invention concerns a method for illuminating a transparent specimen, in particular for use in double confocal scanning microscopy, wherein for illumination of a point of the specimen, two light waves of a coherent light source focused from opposite directions onto the point interfere to form an illumination pattern.
BACKGROUND OF THE INVENTION
Methods of the generic type are used in particular in double confocal scanning microscopes such as those known, for example, from EP 0 491 289 A1. In double confocal microscopy, light from a light source is divided into two partial beams, each partial beam being focused by way of an objective onto a common specimen point. The two objectives are arranged on different sides of the specimen plane that is common to them. In the specimen point and at the detection aperture stop, this interferometric illumination results in the formation of an interference pattern that, in the context of constructive interference, exhibits a principal maximum and several secondary maxima. The secondary maxima are generally arranged along the optical axis. Because of the interferometric illumination, it is possible with a double confocal scanning microscope to achieve greater axial resolution as compared to a conventional scanning microscope.
An image of a specimen recorded with a double confocal scanning microscope has principally one contribution that results from the principal maximum of the illumination pattern. Also superimposed on the image, however, are components that result from the illumination of the specimen with the secondary maxima of the illumination pattern. These disruptive image components can be subsequently removed from the recorded image with suitable reconstruction methods. Most often used in this context are inverse filtering methods which are implemented in the form of program modules on a computer. The reconstruction methods can only be applied successfully, however, if the intensity of the secondary maxima is much less than 50% of the intensity of the principal maximum of the illumination pattern. If this precondition is not met, either the noise component of the reconstructed image is too great, or the contributions of the secondary maxima cannot be completely removed from the image, so that “ghost structures” of the recorded specimen structure remain in the image. This can make unequivocal specimen analysis or image interpretation difficult or even impossible.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to eliminate the causes of the problems of the reconstruction method.
The object is achieved by a method comprising the steps:
illuminating of a point of the specimen with two light waves of a coherent light source defining a first electromagnetic field strength,
focussing the light waves from opposite directions onto the point,
interfering the light waves at the point to form an illumination pattern and
superimposing of at least two additional coherent light waves defining a second electromagnetic field strength traveling toward one another with the illumination pattern in order to minimize a secondary maxima of the illumination pattern.
It is advantageous that with appropriate superimposition, the electromagnetic field distribution that interferes in this fashion to form an overall illumination pattern exhibits reduced intensities in the secondary maxima of the original illumination pattern; ideally, the secondary maxima are in fact extinguished. The consequence of this is that the resulting image advantageously allows unequivocal specimen analysis, and ideally it is even possible to dispense with the use of reconstruction methods.
Because of fundamental properties of electromagnetic waves, a prerequisite for minimizing the secondary maxima of the illumination pattern is that the additional light waves be coherent with respect to the light waves that generate the original illumination pattern. Furthermore, the additional light waves must each travel toward one another, so that the additional light waves of themselves also create an interference pattern which can be superimposed on the original illumination pattern. Only if the additional light waves can themselves interfere does the additional illumination pattern exhibit an illumination structure that has a resolution level comparable to the original illumination pattern.
In a particularly advantageous embodiment, the phase relationship between the illumination pattern and the additional light waves is adjustable. In this context, the phase relationship between the original illumination pattern and all additional superimposed light waves could be adjusted. The additional illumination pattern generated by the additional superimposed light waves can accordingly be modified in its entirety relative to the original illumination pattern. In addition, only the phase relationship among the additional light waves themselves could be adjusted, the result being that only the additional illumination pattern superimposed on the original illumination pattern changes. This would make it possible to achieve an alternative change in the overall illumination pattern.
If the electromagnetic field strength at the location of a secondary maximum of the original illumination pattern is opposite to the electromagnetic field strength of the additionally superimposed illumination pattern, the resulting illumination intensity can advantageously be reduced. Ideally, an effort will be made to achieve this condition for all the secondary maxima of the original illumination pattern. The illumination patterns superimposed in this fashion have different signs and can thus be reduced and, ideally, extinguished.
In particularly advantageous fashion, the secondary maxima of the original illumination pattern can be extinguished if the electromagnetic field strength of the illumination pattern at the location of the secondary maxima corresponds in terms of magnitude to the electromagnetic field strength of the superimposed light waves, provided the electromagnetic field strength of the original illumination pattern and the electromagnetic field strength of the additionally superimposed illumination pattern have different signs at the location of the secondary maxima. A considerable reduction in the intensity of the secondary maxima is accordingly already possible if the electromagnetic field strength of the illumination pattern at the location of the secondary maxima corresponds approximately, in terms of magnitude, to the electromagnetic field strength of the superimposed light waves. The electromagnetic field strengths of the superimposed light waves can be adjusted by appropriately selecting the intensity of the additionally superimposed light waves. For this purpose, the intensity of the additional light waves is generally selected to be less than or greater than the intensity of the light waves that provide illumination. It can, however, be very particularly advantageous if the intensity of the additional light waves is selected to be identical to that of the light waves that provide illumination.
An essential distinction may be made among several variants for minimizing the secondary maxima of the original illumination pattern. Common to all the variants, however, is the fact that the original illumination of a point of the specimen is accomplished from two opposite directions, the coherent light beams used for the purpose being focused onto a common point.
The first variant provides for the additional coherent light waves traveling toward one another to proceed in collimated fashion in the specimen region.
The second variant provides for the additionally coherently superimposed light waves to be focused to a point in the specimen region.
The third variant provides for modulation over time of the intensity of the light for generating the original illumination pattern
Gabor Otilia
Hannaher Constantine
Leica Microsystems Heidelberg GmbH
Simpson & Simpson PLLC
LandOfFree
Method and apparatus for illuminating a transparent specimen does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for illuminating a transparent specimen, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for illuminating a transparent specimen will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3037482