JP3720173B2 - Evaluation device for micro-aperture probe - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for evaluating the performance of a minute aperture probe used in a near-field optical microscope or the like.
[0002]
[Prior art]
In a near-field optical microscope such as a photon scanning tunneling microscope, in order to generate evanescent light, a micro-aperture probe having a light passage opening with a diameter shorter than the wavelength of light at the tip is used. This micro-aperture probe is often formed by sharpening the tip of an optical fiber by etching, then depositing a metal film thereon, and then removing the metal film at the tip to form an opening.
[0003]
In such a micro-aperture probe, the propagation loss of light varies depending on the shape of the aperture, and the intensity distribution pattern of near-field light that is an evanescent wave emitted from the aperture changes accordingly. Conventionally, in order to inspect the probe performance, a technique of observing the opening shape with an electron microscope has been used.
[0004]
The intensity distribution pattern of the evanescent light also corresponds to the polarization state of the light incident on the probe. Therefore, when using the probe, it is required to know this correspondence in advance and select the optimum polarization state. In order to do so, it is necessary to actually detect the intensity distribution pattern of near-field light. Conventionally, a method of detecting this pattern by scanning with another probe has been used.
[0005]
[Problems to be solved by the invention]
However, since the inspection method using the electron microscope is a destructive inspection, there is a problem that it cannot be used for inspection of a minute aperture probe that is actually used.
[0006]
In addition, the above-described method of scanning another probe requires skill and takes time, so that the yield is poor and is not suitable for practical use. In this method, since the measurement probe affects the intensity distribution pattern of the near-field light emitted from the probe to be measured, there is a problem that the reliability of the evaluation is low.
[0007]
Therefore, the present invention provides an apparatus that can accurately and easily evaluate the performance of a micro-aperture probe (more specifically, the intensity distribution pattern of near-field light emitted therefrom) and the optimal polarization state of incident light. For the purpose.
[0008]
[Means for Solving the Problems]
An evaluation apparatus for a microscopic aperture probe according to the present invention includes:
In an apparatus for evaluating the intensity distribution pattern of near-field light emitted from a micro-aperture probe having a light passage opening having a diameter shorter than the wavelength of light at the tip,
A light source that emits light for evaluation having a wavelength longer than the diameter of the light passage opening;
An incident optical system that makes this light incident from the base end of the micro-aperture probe, that is, the end opposite to the tip having the aperture,
Imaging means for receiving propagation light emitted from the tip of the microscopic aperture probe and imaging an in-plane intensity distribution pattern intersecting the traveling direction of the propagation light;
It is characterized by comprising display means for displaying the imaged intensity distribution pattern.
[0009]
In the above configuration, more preferably, a collimating optical system is provided that collimates the propagating light emitted from the tip of the minute aperture probe and makes it incident on the imaging means.
[0010]
In addition, the collimating optical system is combined with an imaging optical system that branches a part of the collimated propagation light and converges the branched propagation light to form an image of the tip of the minute aperture probe. Is desirable.
[0011]
In the above configuration, more preferably, a polarization control means for controlling the polarization state of the light incident on the microscopic aperture probe or a means for detecting the polarization state of the propagating light emitted from the tip of the microscopic aperture probe is provided.
[0012]
Note that the propagation light emitted from the tip of the minute aperture probe has a very low intensity, so it is desirable to use a particularly high-sensitivity image sensor, for example, a cooled CCD image sensor.
[0013]
【The invention's effect】
It is known that there is a correlation of intensity distribution patterns between propagating light emitted from the tip of the minute aperture probe and near-field light. This correlation can be obtained by electromagnetic analysis such as Bethe's formula. Moreover, since it is possible to directly observe the intensity distribution pattern of near-field light with a near-field optical microscope, the observation pattern and the intensity distribution pattern of propagation light can be correlated in advance.
[0014]
Therefore, in the microaperture probe evaluation apparatus of the present invention having the above-described configuration, if the intensity distribution pattern of propagating light emitted from the tip of the microaperture probe can be imaged and displayed, the display pattern and the above-described correlation can be obtained. Based on this, it is possible to know the intensity distribution pattern of near-field light and evaluate the performance of the probe.
[0015]
As described above, if the propagating light emitted from the tip of the microscopic aperture probe is collimated by the collimating optical system and incident on the imaging means, the intensity distribution pattern of the propagating light can be directly observed.
[0016]
In addition, if the collimating optical system is combined with an imaging optical system that branches a part of the collimated propagation light and converges the branched propagation light to form an image of the tip of the minute aperture probe. By adjusting the focus while observing the image formed there, the propagation light can be collimated with high accuracy.
[0017]
On the other hand, if a polarization control means for controlling the polarization state of light incident on the microscopic aperture probe or a means for detecting the polarization state of propagating light emitted from the tip of the microscopic aperture probe is provided, It is also possible to know the polarization state at which an optimum intensity distribution pattern (for near-field light) is obtained.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a micro-aperture probe evaluation apparatus according to a first embodiment of the present invention.
[0019]
This probe evaluation apparatus is for evaluating the performance of a micro-aperture probe 10 used in a near-field optical microscope and the like. A laser 12 that emits evaluation light (laser beam) 11 and a laser that is divergent light. A collimator lens 13 for collimating the beam 11; a condensing lens 14 for converging the laser beam 11 that has become collimated light on the proximal end of the micro-aperture probe 10, that is, the left end in the figure; and these lenses 13 and 14 And a λ / 2 plate 15 as a polarization control element disposed between the two.
[0020]
The micro-aperture probe 10 is made of, for example, an optical fiber, and has a light passage opening having a diameter shorter than the wavelength of light at a sharpened tip (right end in the drawing). The laser beam 11 converged on the proximal end of the minute aperture probe 10 as described above enters the probe from the proximal end, propagates there, and exits from the aperture in a divergent light state.
[0021]
At this time, near-field light is emitted from the opening together with the laser beam 11 which is normal propagation light. In a near-field optical microscope or the like, this near-field light is used for observation, analysis, processing, etc. of a sample, but this near-field light is not directly used for probe evaluation.
[0022]
A collimator lens 16 for collimating the laser beam 11 is disposed at a position where a laser beam (propagating light) 11 emitted in a divergent light state from the probe opening is incident. A cooled CCD image pickup device 17 is disposed at a position where the laser beam 11 having become parallel light is incident. An analyzer 18 is disposed between the cooled CCD image sensor 17 and the collimator lens 16. The image signal S output from the cooling CCD image sensor 17 is input to the image display means 19 made of, for example, a CRT.
[0023]
When the minute aperture probe 10 is evaluated, the laser beam 11 is incident on the probe 10 as described above, and the laser beam (propagating light) 11 emitted from the minute aperture of the probe 10 is then cooled by CCD imaging. Light is received by the element 17. Since the laser beam 11 is incident on the cooled CCD image sensor 17 in a parallel light state with the beam axis perpendicular to the light receiving surface, the cooled CCD image sensor 17 changes the intensity distribution pattern in the beam cross section of the laser beam 11. Large image is taken. The image signal S indicating this intensity distribution pattern is input to the image display means 19, where this pattern is displayed.
[0024]
Note that the laser beam 11 that is the propagating light emitted from the probe aperture is very weak. However, in this example, an extremely sensitive cooled CCD image sensor 17 is used as the imaging means. The intensity distribution pattern can be clearly imaged.
[0025]
As described above, there is an intensity distribution pattern correlation between the propagation light emitted from the tip of the microscopic aperture probe 10 and the near-field light. Therefore, based on this correlation obtained in advance, the intensity distribution pattern of the near-field light is known from the intensity distribution pattern of the laser beam (propagation light) 11 displayed on the image display means 19, and the performance of the probe 10 is evaluated. can do.
[0026]
In this embodiment, by rotating the λ / 2 plate 15, the direction of linearly polarized light of the laser beam 11 before entering the minute aperture probe 10 is changed, and the direction of the polarized light is confirmed by the analyzer 18. Meanwhile, the intensity distribution pattern of the laser beam 11 emitted from the minute aperture can be confirmed. Thereby, it is also possible to know the polarization state in which the optimum intensity distribution pattern of the propagation light (that is, the near-field light) can be obtained.
[0027]
Next, a second embodiment of the present invention will be described with reference to FIG. The apparatus according to the second embodiment is basically different from the one shown in FIG. 1 in the collimating optical system. Therefore, only the part after the collimating optical system is shown in FIG. . In FIG. 2, the same elements as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted unless otherwise necessary (the same applies hereinafter).
[0028]
In this embodiment, the collimating optical system includes a beam splitter 21 that branches a part of the laser beam 11 emitted from the tip of the minute aperture probe 10 and collimated by the collimator lens 16, and the branched laser beam. An image forming lens 22 for converging 11 and forming an image of the tip of the minute aperture probe 10 is combined.
[0029]
The collimator lens 16, the beam splitter 21, the imaging lens 22, the analyzer 18, and the part of the lens barrel 20 holding the cooled CCD image pickup device 17 are driven by a driving means (not shown) by an optical axis direction Z and a direction X perpendicular thereto. Y is movable. The imaging lens 22 forms an image of the tip of the microscopic aperture probe 10 when the laser beam 11 is incident thereon in a parallel light state.
[0030]
Therefore, the apparatus operator moves the lens barrel 20 three-dimensionally while observing the image formed by the imaging lens 22, and holds the lens barrel 20 at a position where the image of the tip of the minute aperture probe 10 can be clearly observed. As a result, the laser beam 11 as the propagating light can be incident on the cooled CCD image pickup device 17 in a parallel light state.
[0031]
Also in the second embodiment, as in the first embodiment, the laser beam (propagating light) 11 displayed on the image display means 19 based on the image signal S output from the cooled CCD image pickup device 17 is used. By knowing the intensity distribution pattern of the near-field light from the intensity distribution pattern, the performance of the probe 10 can be evaluated.
[0032]
In the present embodiment, the image signal S output from the cooled CCD image pickup device 17 is input to the image processing device 23, and is subjected to predetermined image processing there before being input to the image display means 19.
[0033]
Next, a third embodiment of the present invention will be described with reference to FIG. The probe evaluation apparatus according to the third embodiment is incorporated in a near-field optical microscope and has a microscopic aperture probe 30 made of a long optical fiber. The micro aperture probe 30 is configured to be handled in the same manner as a general optical fiber having flexibility, and the basic configuration and operation are the same as those of the micro aperture probe 10 described above.
[0034]
A beam splitter 33 is disposed in the optical path of the laser beam 11 that has passed through the analyzer 18, and the laser beam 11, which is propagating light, is reflected here and guided to the cooled CCD image sensor 17.
[0035]
From the tip of the probe 30 (lower end in the drawing), near-field light that is an evanescent wave is emitted together with the laser beam 11 that is propagating light. When the sample 31 is placed in the near-field light, scattered light 11S is generated. The scattered light 11S is collected by a condenser lens 34 and guided to a photodetector 35. The light detection signal S1 output from the light detector 35 is input to the controller 36.
[0036]
The sample 31 is held on a sample table 38. The sample table 38 is movable in the X, Y, and Z directions by a sample table driving means 37 made of, for example, a piezo element. Thus, if the probe 30 is scanned in the X and Y directions with respect to the probe 30, and the light detection signal S1 indicating the intensity of the scattered light 11S at that time is taken as a function of the sample stage position, the function is the evanescent field. Since the distribution is shown, information indicating the shape and structure of the sample 31 can be obtained from this function.
[0037]
The operation of the driving means 37 is controlled by the controller 36. Further, the position of the probe 30 in the optical axis direction is detected by the position detection device 32, and the position detection signal S2 output therefrom is input to the controller 36. Based on the position detection signal S2, the controller 36 controls the operation of the driving means 37 so as to set the Z direction position of the sample stage 38 (that is, the sample 31) to a desired position.
[0038]
Also in the third embodiment, as in the first and second embodiments, the laser beam (propagating light) displayed on the image display means 19 based on the image signal S output from the cooled CCD image pickup device 17. ) The intensity distribution pattern of near-field light can be known from the 11 intensity distribution patterns, and the performance of the probe 30 can be evaluated.
[0039]
In the present embodiment, the image signal S output from the cooled CCD image sensor 17 is input to the controller 36, subjected to predetermined image processing by an image processing device included in the controller 36, and then input to the image display means 19. Is done.
[0040]
In this case as well, the apparatus operator moves the lens barrel 20 three-dimensionally while observing the image formed by the imaging lens 22 so that the image of the tip of the minute aperture probe 30 can be clearly observed. By holding 20, the laser beam 11 as propagating light can be incident on the cooled CCD image pickup device 17 in a parallel light state.
[Brief description of the drawings]
FIG. 1 is a side view showing a micro-aperture probe evaluation apparatus according to a first embodiment of the present invention. FIG. 2 is a partial side view showing a micro-aperture probe evaluation apparatus according to a second embodiment of the present invention. FIG. 3 is a side view showing a micro-aperture probe evaluation apparatus according to a third embodiment of the present invention.
10, 30 Micro-aperture probe
11 Laser beam
12 laser
13, 16 Collimator lens
14, 34 Condensing lens
15 λ / 2 plate
17 Cooling CCD image sensor
18 Analyzer
19 Image display means
20 Lens tube
21, 33 Beam splitter
22 Imaging lens
23 Image processing device
31 samples
32 Position detector
35 photodetectors
36 controller
37 Sample stage drive means
38 Sample stage

Claims (6)

In an apparatus for evaluating the intensity distribution pattern of near-field light emitted from a micro-aperture probe having a light passage opening having a diameter shorter than the wavelength of light at the tip,
A light source that emits light for evaluation having a wavelength longer than the diameter of the light passage opening;
An incident optical system for making this light incident from the base end of the microscopic aperture probe;
Imaging means for receiving propagation light emitted from the tip of the microscopic aperture probe and imaging an in-plane intensity distribution pattern intersecting the traveling direction of the propagation light;
A micro-aperture probe evaluation apparatus comprising display means for displaying the imaged intensity distribution pattern.   2. The micro-aperture probe evaluation apparatus according to claim 1, further comprising a collimating optical system that collimates the propagating light emitted from the tip of the micro-aperture probe so as to enter the imaging unit. The collimating optical system is combined with an imaging optical system that branches a part of the collimated propagation light and converges the branched propagation light to form an image of the tip of the microscopic aperture probe. The apparatus for evaluating a microscopic aperture probe according to claim 2,   4. The micro-aperture probe evaluation apparatus according to claim 1, further comprising a polarization control unit that controls a polarization state of the light incident on the micro-aperture probe. 5.   5. The micro-aperture probe evaluation apparatus according to claim 1, further comprising a means for detecting a polarization state of propagating light emitted from a tip of the micro-aperture probe. 6.   6. A micro-aperture probe evaluation apparatus according to claim 1, wherein a cooling CCD imaging device is used as the imaging means.

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