JP3967918B2 - Near-field optical microscope probe - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a probe for a near-field optical microscope, and particularly to an improvement in background.
[0002]
[Prior art]
Near-field optical microscopes are used in various fields as optical microscopes capable of observing in a very small region exceeding the diffraction limit of light.
FIG. 1 schematically shows a near-field optical microscope. In the near-field optical microscope 10, incident light 14 from the light source 12 is guided to a probe manufactured by processing the tip 18 of the glass fiber 16 into a sharp shape. At this time, a surface wave 20 called evanescent light is generated in the vicinity of the opening from a minute opening having a diameter equal to or smaller than the light wavelength provided at the tip of the sharp part formed in the tip portion 18. This surface wave 20 is localized in a region within the distance of the light wavelength from the surface near the tip 18.
[0003]
The micro sample to be measured is arranged on the flat substrate 22 in advance. Then, the probe tip and the sample surface are gradually brought closer together, and when the field of the evanescent light 20 generated on the probe tip surface comes into contact with the sample surface, the evanescent light 20 is scattered. A part of the scattered light 24 enters the probe from the minute opening formed at the tip of the probe, passes through the fiber, passes through the beam splitter 26, passes through the spectrometer or filter 28, and is detected by the detector 30. Are guided and detected and processed by the computer 36.
[0004]
Then, the stage controller 34 moves the stage 32 and controls the distance in the vertical direction between the probe tip and the sample surface so that the intensity of the scattered light 24 detected by the detector 30 is constant. By scanning the measurement surface, the unevenness information on the surface of the sample is grasped, and on the other hand, by analyzing the fluorescence spectrum, Raman spectrum, etc. of the sample excited by the evanescent light 20, component analysis at a minute part in the sample is performed. Is called.
[0005]
The near-field optical microscope has several measurement modes. As described above, the sample is irradiated with the incident light guided through the probe to the tip as an evanescent light field (illumination). The (collection) measurement mode in which the scattered light having the above information is again guided through the probe through the microscopic aperture at the tip and detected (collection) is called an illumination-collection mode, and is one of typical measurement modes excellent in resolution and the like. One.
[0006]
As another measurement mode, measurement is performed in an illumination mode in which the sample is irradiated with incident light guided to the tip through the probe as an evanescent light field, and the scattered light is guided to the detector via a lens or the like. Has also been done.
[0007]
Further, it is generated by forming a field of evanescent light in advance on the surface to be measured of the sample by a method such as irradiating light on the substrate 22 from below with a total reflection condition, and bringing the probe tip into contact therewith. Measurement in a collection mode is also performed in which scattered light having sample information is guided and detected from a microscopic aperture formed at the tip of the probe into the probe.
[0008]
As a material for the probe for the near-field optical microscope, a general-purpose commercially available glass fiber is generally used, and a material obtained by processing its tip is used. For example, after the fiber tip is etched into a sharp shape, the sharp portion is covered with a metal or the like to form a light-shielding mask, and only the tip of the sharp portion is removed to provide a micro-optical aperture. Is done.
[0009]
Commercially available glass fibers are supplied in a form in which a protective coating is made with, for example, a UV curable resin or nylon in order to reinforce the strength against bending of the fibers. That is, as shown in the axial sectional view of the fiber shown in FIG. 2, the protective coating 46 is formed adjacent to the outer surface side of the cladding layer 44 of the glass fiber 40.
[0010]
[Problems to be solved by the invention]
In the near-field optical microscope, improving the background has been one problem. That is, there may be a large background depending on the measurement wavelength as shown in the background measurement in the illumination-collection mode shown in FIG. Then, a true spectrum must be obtained by subtracting this large background from the spectrum measured by placing the sample, which is an obstacle in obtaining good accuracy.
[0011]
As a main factor of this background, the contribution of the clad light component introduced into the detector through the clad layer can be considered. In other words, light emitted from the protective coating or the clad layer due to incident light leaking from the core layer, or external light mixed in the clad layer reaches the detector while remaining in the clad layer, and these are back. It is thought that it is detected as a ground component. Since the light component that has passed through the cladding layer and the light component that has passed through the core layer cannot be separated before being introduced into the detector, the background component is introduced into the detector together with the signal component and detected. .
[0012]
In particular, when the sample is excited using ultraviolet light as incident light and fluorescence in the visible light region is detected, the protective coating layer and the cladding layer also emit fluorescence in the visible light region due to ultraviolet light leaking from the core layer. Therefore, it is considered that this greatly contributes to the background.
[0013]
In the field of optical communication, for example, in a single mode fiber, as a method of removing cladding light or the like that becomes a noise source other than the single mode, a method of bending the fiber with a small curvature and scattering and removing components other than the single mode, or There is a method of transmitting a long fiber of about several kilometers and removing other components having poor transmission efficiency.
However, it is difficult to apply these methods to a probe for a near-field optical microscope, and no solution is provided for the background factors described above.
[0014]
In addition, when a glass fiber is used as a probe for a near-field optical microscope, it is not always necessary to provide strength by applying a coating as in the case of the commercially available fiber in FIG. 2, so that, for example, the fiber is immersed in an organic solvent. By peeling off the protective coating layer 46 such as UV curable resin or nylon, the background due to light emission of the protective coating layer 46 due to incident light leaked from the core layer can be reduced.
However, this method cannot reduce the light emission caused by the cladding layer and the background based on stray light mixed in the cladding layer.
[0015]
The present invention has been made in view of the above prior art, and an object thereof is to provide a probe for a near-field optical microscope having a reduced background.
[0016]
[Means for Solving the Problems]
In order to solve the above problems, the near-field optical microscope probe of the present invention is a near-field optical microscope probe using a glass fiber,
Adjacent to the outer surface side of the cladding layer of the glass fiber, comprising a scattering layer having a refractive index substantially the same as the refractive index of the cladding layer ,
The scattering layer is formed at least at the incident light introduction side end of the glass fiber, and incident light is introduced into the glass fiber from the incident light introduction side end where the scattering layer is formed, and passes through the glass fiber. Then, the sample is irradiated with incident light guided to the end portion on the sample side as a field of evanescent light .
[0017]
Further, the probe illumination - when used in the collection mode, the scattering layer is preferably formed on the incident light introduction side end portion of the glass fiber.
Further, when the probe is used in the collection mode, it is preferable that the scattering layer is formed at an incident light introduction side end of the glass fiber.
Further, in the probe, the scattering layer, it is also preferable that formed over the entire length of the glass fiber.
In the probe, it is preferable that a thin tubular protective layer is provided outside the scattering layer.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 4 shows an axial sectional view of a probe according to one embodiment of the present invention. The probe 140 shown in the figure includes a glass fiber 146 composed of a core layer 142 and a cladding layer 144, and a scattering layer 150 adjacent to the outer surface side of the cladding layer 144.
Note that the scattering layer 150 has substantially the same refractive index as that of the cladding layer 144.
[0019]
In the present invention, by providing the scattering layer 150 in this way, the background is remarkably reduced as compared with the conventional case. This effect is considered to be obtained for the following reason. That is, the refractive index n ₁ of the clad layer 144, so it was decided to almost the same refractive index n ₂ of the scattering layer, the light emitting and generated in the protective coating layer and a cladding layer described above by the incident light leaking from the core, Alternatively, the background component 160 due to the external light mixed in the cladding layer is refracted without being reflected at the interface between the cladding layer 144 and the scattering layer 150 and easily exits to the scattering layer 150 side.
[0020]
On the other hand, for example, when a commercially available fiber is used as in the prior art, the refractive index (about 1.4) of the protective coating layer is smaller than the refractive index (about 1.5) of the cladding layer of the fiber. Reflection is likely to occur at the interface between the layer and the protective coating layer. Therefore, it is considered that the background component repeats reflection at the interface between the cladding layer and the protective coating layer and the interface between the cladding layer and the core layer, propagates while remaining in the cladding layer, and reaches the detector.
[0021]
Here, the refractive index _{n 1} of the clad layer 144, the refractive index _{n 2} of the scattering layer 150, depending on if _n 1 / _{n 2} is approximately 0.9 to 1.1, more preferably 0.95. In the range of 05, the background reduction effect is exhibited as compared with the conventional case, and in particular, the refractive index n _{2 of the} scattering layer is preferably higher than the refractive index n _{1 of the} cladding layer in view of the refractive angle of the cladding light. .
[0022]
Examples of the structure of the scattering layer 150 include resins such as optical adhesives (preferably those that do not contain a light emitting component), plastics, glass, water glass, glycerin, quartz, silicon, ZnSe, diamond, and the like. A mode in which a plastic solid or a highly viscous liquid is attached to the surface of the clad layer can be mentioned. In the case of a solid, even if it does not have plasticity at room temperature but exhibits plasticity at high temperature, it can be heated and attached to the surface of the clad layer in a state of increasing fluidity, and then the scattering layer can be formed by cooling.
[0023]
In addition, in some cases, the scattering layer may be formed by exposing a gas such as Ar gas to the surface of the cladding layer. In this case, for example, the gas scattering layer can be formed by filling the sample chamber 38 of FIG. 1 with a gas for the scattering layer or supplying the gas in a flow, or by previously providing a gas sealing layer outside the cladding layer.
Moreover, you may make it adjoin to the clad layer surface by immersing a glass fiber in this liquid as a scattering layer.
[0024]
The scattering layer is most preferably coated on the circumference of the glass fiber without a gap, but is not particularly limited.
[0025]
It is also possible to adjust the refractive index of the scattering layer by adjusting the composition of the cladding layer with an additive component other than quartz, etc., thereby reducing the refractive index of the cladding layer.
Next, the mode at the time of using the probe of this invention for each measurement mode of a near field optical microscope is illustrated.
[0026]
Illumination-collection mode or collection mode FIG. 5 shows a schematic view when the probe of the present invention is used in the illumination-collection mode or the collection mode. As shown in FIG. 2A, the scattering layer 150, which is an essential requirement of the present invention, is formed on the incident light introducing side end 170 of the glass fiber.
[0027]
In this case, as shown in FIG. 2B, the background-caused clad light 160 accumulated from the glass fiber sample-side end part goes out to the scattering layer 150 side formed at the end part 170, Since the clad light is reduced and then introduced into the detector, the background is greatly reduced.
Thus, for example, after the protective coating layer of a commercially available glass fiber is peeled only at the end portion, the background reduction is achieved by a relatively simple operation such as forming a scattering layer there.
[0028]
Illumination mode Fig. 6 shows a schematic diagram when the probe of the present invention is used in the illumination mode. As shown in FIG. 2A, the scattering layer 150, which is an essential requirement of the present invention, is formed at the sample side end 172 of the glass fiber.
[0029]
In this case, the background factor clad light 160 accumulated from the incident light introduction side end 170 of the glass fiber is emitted to the scattering layer 150 side formed at the end 172, as shown in FIG. Then, after the cladding light is reduced, irradiation from the probe tip is performed, and the background is greatly reduced.
[0030]
In this case, the installation location of the scattering layer 150 may be selected as appropriate, for example, when the distance between the probe tip and the sample surface is determined by measuring the frequency of the probe vibration, on either side of the exciter connection. The
[0031]
In addition to the above, the scattering layer may be formed over the entire length of the glass fiber. In addition, when it is necessary to reinforce the strength against bending of the probe, it is preferable to provide a thin tubular protective layer 180 as shown in FIG. As the protective layer 180, for example, a metal thin tube, a resin thin tube or the like is used.
[0032]
【Example】
Using the probe of the present invention and a conventional probe, the background was measured in the illumination-collection mode. As a probe of the present invention, a glycerin (refractive index 1.52) is used as a scattering layer on the outer surface side of the cladding layer (refractive index 1.5) of the glass fiber in the 5 mm portion of the incident light introduction side end of the glass fiber. As a comparative example, a commercially available probe in which a UV curable resin (refractive index: 1.4) is adjacent as a protective coating layer is attached to a near-field optical microscope. It was measured. The results are shown in FIGS. 8A and 8B.
[0033]
As apparent from FIGS. 8A and 8B, it can be seen that the background is remarkably reduced when the probe of the present invention is used.
[0034]
【The invention's effect】
As described above, according to the near-field optical microscope probe of the present invention, the scattering layer having the refractive index substantially the same as the refractive index of the cladding layer is provided adjacent to the outer surface side of the cladding layer of the glass fiber. Therefore, the background is significantly reduced.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory diagram of a near-field optical microscope.
FIG. 2 is an axial sectional view of a commercially available glass fiber.
FIG. 3 is a background measured in an illumination-collection mode using a conventional probe.
FIG. 4 is a schematic explanatory view of a probe of the present invention.
FIG. 5 is a schematic explanatory view according to one embodiment of the probe of the present invention.
FIG. 6 is a schematic explanatory view according to one embodiment of the probe of the present invention.
FIG. 7 is a schematic explanatory view of a probe of the present invention provided with a thin tubular protective layer.
FIG. 8 is a background measured using the present invention and a conventional probe.
[Explanation of symbols]
10: near-field optical microscope, 12: light source, 14: incident light, 16: glass fiber, 18: tip, 20: evanescent light, 22: substrate, 24: scattered light, 26: beam splitter, 28: spectrometer or Filter: 30: Detector, 32: Stage, 34: Stage controller, 36: Computer, 38: Sample chamber, 40: Glass fiber, 44: Clad layer, 46: Protective coating layer, 140: Probe, 142: Core layer, 144: Cladding layer, 146: Glass fiber, 150: Scattering layer, 160: Clad light, 170: End portion on the incident light introduction side, 172: End portion on the sample side, 180: Protective layer on the tubular tube

Claims (5)

In a near-field optical microscope probe using glass fiber,
Adjacent to the outer surface side of the cladding layer of the glass fiber, comprising a scattering layer having a refractive index substantially the same as the refractive index of the cladding layer ,
The scattering layer is formed at least at the incident light introduction side end of the glass fiber, and incident light is introduced into the glass fiber from the incident light introduction side end where the scattering layer is formed, and passes through the glass fiber. A near-field optical microscope probe characterized by irradiating the sample with incident light guided to the sample side end as an evanescent light field . The probe according to claim 1, wherein
The scattering layer, the formed on the incident light introduction side end portion of the glass fiber, Illumination - near-field optical microscope probe, characterized by being used in the collection mode. In a near-field optical microscope probe using glass fiber,
Adjacent to the outer surface side of the cladding layer of the glass fiber, comprising a scattering layer having a refractive index substantially the same as the refractive index of the cladding layer,
The scattering layer is formed on the incident light introduction side end portion of the glass fiber, near-field optical microscope probe, characterized by being used in the collection mode. The probe according to any one of claims 1 to 3 ,
The scattering layer, the near-field optical microscope probe, characterized in that it is formed over the entire length of the glass fiber. The probe according to any one of claims 1 to 4,
A near-field optical microscope probe comprising a thin tubular protective layer outside the scattering layer.

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