JP2005024490A - Method and device for detecting displacement of object to be measured - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for detecting displacement of an object to be measured capable of highly sensitive detection in comparatively compact constitution. <P>SOLUTION: The method and device for detecting the displacement detect the displacement of the object to be measured of a cantilever 103 or the like by using an angle change of detection light emitted from the object to be measured, and amplify change accompanying angle change of incident detection light of a propagation angle for an incident face of the detection light incident on the crystal to detect the displacement of the object to be measured by using a deflection element consisting of a crystal periodically changing a refractive index. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method and an apparatus for detecting a displacement of an object to be measured by an angle change of detection light coming from the object to be measured.

  In recent years, since the development of scanning tunneling microscopes (STM) that can directly observe the electronic structure of conductors, probes with sharp tips such as atomic force microscopes (AFM), scanning capacitive microscopes (SCaM), and near-field microscopes (SNOM) Microscope apparatuses that obtain various information and distributions of a sample by scanning the sample with the use of are continuously developed. At present, these microscopes are collectively referred to as scanning probe microscopes (SPM), and are widely used as observation means for fine structures having atomic and molecular resolution.

  For example, the AFM uses a lever (cantilever) having a probe to detect a minute amount of bending of the lever caused by an atomic force acting between the probe tip and the sample surface. As one method of detecting this deflection, a method (optical lever method) is known in which laser light is irradiated to the tip of a cantilever and the displacement of the reflected light is measured.

On the other hand, a new artificial crystal called “photonic crystal” in which substances having different refractive indexes are periodically arranged at intervals of about a wavelength has been proposed and attracted attention (see Non-Patent Document 1). This artificial crystal has a light forbidden band (photonic band gap) due to a so-called photonic band structure similar to the band structure of a semiconductor, and also has a peculiar effect due to an apparent refractive index anomaly. Therefore, research and development as an optical element has been actively performed (see Patent Document 1). In this photonic crystal material, when light is incident on the photonic crystal from the outside, the transmitted wave induced by the light exists in the photonic band gap, and the diffracted wave exists outside the photonic band gap. In this configuration, only the diffracted wave whose propagation direction changes greatly propagates (this phenomenon is related to the apparent refractive index abnormality). This effect is called the super prism effect. When light is incident on the photonic crystal, the direction of light energy in the photonic crystal structure changes greatly with a slight difference in incident angle. (See Non-Patent Document 2).
E. Yablonovich, Phys. Rev. Lett. , 58 (1987) 2059-2062 Journal of the Physical Society of Japan, Volume 55 (2000), March issue 172-279 JP 2000-066002 JP

  In the optical lever system described above, in order to increase the detection sensitivity, for example, it is necessary to devise measures such as increasing the optical path of the detection light. However, when a sufficiently long optical path is used, a complicated optical system is required, and there is a problem that the apparatus is increased in size and cost. This problem is particularly noticeable when an extremely small angle change is to be detected by the optical lever method as in the AFM described above.

The displacement detection method of the present invention is a displacement detection method for detecting the displacement of an object to be measured such as a cantilever using a change in the angle of detection light coming from the object to be measured, and a crystal whose refractive index changes periodically. (Typically, a photonic crystal) is used to amplify a change in the propagation angle of the detection light incident on the crystal with respect to the incident surface, and detect the displacement of the object to be measured. It is characterized by that. The displacement detection device of the present invention is a displacement detection device that detects the displacement of the object to be measured by using the change in the angle of the detection light coming from the object to be measured, and the detection light coming from the object to be measured is incident thereon. And a photodetection means for measuring a change in the angle of detection light from the crystal, the refractive index of which is periodically changed. The propagation angle is an angle formed by the propagation direction of the propagation light in the crystal with respect to the normal line of the incident surface of the crystal on which the detection light is incident. The following modes are possible based on this basic configuration. The crystal has a propagation angle of detection light in the crystal and an emission angle of detection light emitted from the end face of the crystal (propagation of detection light emitted outside the crystal with respect to the normal of the exit surface of the crystal from which the detection light is emitted). It is possible to take a form in which the exit surface is processed so that the directions are equal. Further, the crystal can be provided in close contact with a light detection means for detecting a change in the angle of the detection light. The object to be measured may be a cantilever. In this case, the cantilever has an optical waveguide extending through the cantilever, and the detection light can propagate through the optical waveguide and be emitted to be incident on the crystal. Furthermore, the cantilever has a microlens optically coupled to the optical waveguide at its tip, and the detection light can be emitted through the lens and incident on the crystal. Alternatively, the detection light may be reflected by the reflecting surface of the cantilever and incident on the crystal. In consideration of the wavelength of the detection light, the polarization state, and the incident angle of the light to the crystal, the photonic crystal is refracted so that the propagation angle with respect to the incident surface is the above-mentioned refractive index anomaly of the photonic crystal. A rate modulation structure (period, refractive index change mode, etc.) is designed.

According to the displacement detection device or method for detecting the displacement of the object to be measured as the change in the angle of the detection light according to the present invention, by introducing an element that amplifies the angular displacement in the optical path of the detection light, it has been conventionally possible to detect with high sensitivity. High-sensitivity detection is possible without using a long optical path that is necessary. Further, there is an effect that a complicated optical system is not required and a simple apparatus configuration can be obtained. In addition, there is an effect that the device can be relatively compact and inexpensive.

A preferred embodiment of the present invention will be described with reference to FIG. In the present embodiment, as a displacement detection device, an application example to an atomic force microscope is shown, but the present invention is not limited to this, as long as the displacement of the object to be measured is detected as an angle change of detection light. Any device is acceptable.

  FIG. 1 is a diagram illustrating a configuration of a displacement detection device according to the present embodiment. The detection device of this embodiment includes a deflection element 101, a photodetector 102, a cantilever 103, and a light source 104. In particular, the cantilever 103 has a very fine probe 103a at the tip of the lever.

When the sample 105 and the tip of the probe 103a of the cantilever 103 are close to each other, the cantilever 103 is bent by a physical quantity (for example, atomic force) existing between the sample 105 and the tip of the probe 103a. The shape of the sample 105 can be observed by detecting the amount of bending. The deflection element 101, the photodetector 102, and the light source 104 are used for detecting the amount of deflection.

  A method for detecting the amount of deflection will be described. The light source 104 emits laser light having a desired wavelength as detection light. This detection light is applied to the tip of the cantilever 103, and the reflected light enters the deflection element 101. The deflection element 101 is made of a crystal called a photonic crystal whose refractive index inside the element changes periodically. Due to the refractive index anomaly characteristic (super prism effect) peculiar to the photonic crystal, the deflecting element 101 acts to amplify the propagation angle of the detection light incident on the crystal. By amplifying the propagation angle in this way, the angular displacement of the detection light accompanying the displacement of the cantilever 103 can be amplified. The photodetector 102 is composed of an element whose output changes depending on the incident position of light, such as a quadrant photodiode. By detecting the detection light whose propagation angle is amplified by the photodetector 102, even if the amount of bending of the cantilever 103 is very small, the amount of bending of the cantilever 103 can be detected as a large angular displacement.

  In this way, in a measurement system that detects the displacement of the object to be measured as the change in the angle of the detection light, by introducing an element that deflects light so as to amplify the propagation angle in the optical path of the detection light, a minute object to be measured is introduced. It is also possible to measure the displacement of with a simple configuration.

Further specific examples will be described below.
FIG. 2 shows the configuration of the first embodiment. In FIG. 2, the same reference numerals are used for the same parts as those described above. The exit surface of the deflection element 101 of this embodiment is processed so that the propagation angle of the amplified detection light and the exit angle of the detection light exiting from the end surface of the deflection element 101 are equal (typically, It has a spherical shape with the detection light incident position at the center. Therefore, the detection light whose propagation angle is amplified by the deflecting element 101 can be incident on the photodetector 102 while maintaining the amplified angle.

A quadrant photonic diode is used as the photodetector 102. As the light source 104, a laser having a wavelength of 660 nm is used. Then, the crystal structure of the deflecting element 101 is controlled so that a refractive index abnormality (super prism effect) occurs in this laser light band.

By scanning the sample 105 with the cantilever 103 using these elements, a minute displacement of the cantilever 103 can be observed with high accuracy and a simple configuration.

FIG. 3 shows the configuration of the second embodiment. In the figure, the same reference numerals are used for the same parts as those described above. The deflection element 101 of this embodiment is in close contact with the light detection surface of the photodetector 102. Therefore, the detection light whose propagation angle is amplified by the deflecting element 101 is directly incident on the photodetector 102 while maintaining the amplified angle.

  Again, a quadrant photonic diode is used as the photodetector 102. As the light source 104, a laser having a wavelength of 660 nm is used. And of course, the crystal structure of the deflecting element 101 is controlled so that the refractive index abnormality (super prism effect) occurs in the laser light band.

Even if these elements are used, by scanning the sample 105 with the cantilever 103, a minute displacement of the cantilever 103 can be accurately observed with a simple configuration.

  FIG. 4 shows the configuration of the third embodiment. In the figure, the same reference numerals are used for the same parts as those described above. The cantilever 103 of the present embodiment has an optical waveguide inside. This waveguide section is coupled to a waveguide 402 outside the cantilever 103, and guides light from the light source 104 into the cantilever 103. Further, a microlens 403 is in close contact with the end face of the cantilever 103, and the guided light is condensed and output to the outside.

  The exit surface of the deflection element 101 of this embodiment is processed so that the propagation angle of the amplified detection light and the exit angle of the detection light exiting from the end face of the deflection element 101 are equal. Therefore, the detection light whose propagation angle is amplified by the deflecting element 101 can be incident on the photodetector 102 while maintaining the amplified angle.

  Again, a quadrant photonic diode is used as the photodetector 102. As the light source 104, a laser having a wavelength of 660 nm is used. Of course, the crystal structure of the deflecting element 101 is controlled so that the refractive index abnormality (super prism effect) occurs in this laser light band.

In this embodiment, the detection light from the light source 104 is emitted from the microlens 403 at the tip of the cantilever 103 and enters the deflection element 101. Therefore, the emission direction from the microlens 403 is displaced with the displacement of the cantilever 103, and this displacement is amplified by the deflection element 101. Even if these elements are used, by scanning the sample 105 with the cantilever 103, a minute displacement of the cantilever 103 can be accurately observed with a simple configuration.

  FIG. 5 shows the configuration of the fourth embodiment. In the figure, the same reference numerals are used for the same parts as those described above. The cantilever 103 of the present embodiment is the same as that of the third embodiment. The deflection element 101 of this embodiment is in close contact with the light detection surface of the photodetector 102. Therefore, the detection light whose propagation angle is amplified by the deflecting element 101 is directly incident on the photodetector 102 while maintaining the amplified angle.

  Again, a quadrant photonic diode is used as the photodetector 102. As the light source 104, a laser having a wavelength of 660 nm is used. Of course, the crystal structure of the deflecting element 101 is controlled so that the refractive index abnormality (super prism effect) occurs in this laser light band.

Even if these elements are used, by scanning the sample 105 with the cantilever 103, a minute displacement of the cantilever 103 can be accurately observed with a simple configuration.

It is a figure which shows embodiment of this invention. It is a figure explaining Example 1 of the present invention. It is a figure explaining Example 2 of this invention. It is a figure explaining Example 3 of this invention. It is a figure explaining Example 4 of this invention.

Explanation of symbols

101 deflection element
102 Photo detector
103 Cantilever
103a probe
104 Light source
105 samples
402 waveguide
403 lens

Claims (9)

A displacement detection method for detecting a displacement of an object to be measured using an angular change of detection light coming from the object to be measured, using a crystal whose refractive index changes periodically, and detecting light incident on the crystal A displacement detection method for detecting a displacement of an object to be measured by amplifying a change of the propagation angle with respect to an incident surface accompanying an angle change of the detection light. The displacement detection method according to claim 1, wherein the crystal is processed so that a propagation angle of detection light in the crystal is equal to an emission angle of detection light emitted from an end face of the crystal. The displacement detection method according to claim 1, wherein the crystal is provided in close contact with a light detection unit that detects a change in angle of detection light. The displacement detection method according to claim 1, wherein the crystal is a photonic crystal. A displacement detection device that detects the displacement of an object to be measured using the change in angle of the detection light coming from the object to be measured, and the refractive index arranged so that the detection light coming from the object to be measured is periodic A displacement detection device comprising: a crystal that changes to a light angle; and a light detection means that measures an angle change of detection light from the crystal. The displacement detection device according to claim 5, wherein the crystal is configured to amplify a change in a propagation angle of the detection light incident on the crystal with respect to an incident surface accompanying an angle change of the detection light. The displacement according to claim 5 or 6, wherein an exit surface of the crystal is processed so that a propagation angle of detection light in the crystal is equal to an emission angle of detection light emitted from an end face of the crystal. Detection device. The displacement detection device according to claim 5, wherein the crystal is provided in close contact with a light detection unit that detects an angle change of the detection light. The displacement detection device according to claim 5, wherein the crystal is a photonic crystal.

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