Near-field optical microscope

Details Near-field optical microscope Near-field optical microscope

1999-06-02

2002-08-13

Le, Que T. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

C250S306000, C250S201300

Reexamination Certificate

active

06433327

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microscope which utilizes near-field optics.
2. Related Background Art
The probe of a near-field optical microscope is mainly constructed of a probe wherein the distal end of an optical fiber is sharpened into a tip, which is covered with a metal film by vapor deposition or the like and then formed with a micro-opening. The optical fiber probe is caused to guide illuminating light, thereby to generate an evanescent wave at the tip micro-opening. When the evanescent wave is brought near to a sample, it is converted into scattered light by the interaction thereof with the sample. The microscopic configuration or structure of the sample, or the material distribution of a microscopic region can be observed by detecting the intensity profile of the scattered light.
The simplest scheme of the probe is a scheme wherein the optical fiber probe for guiding the illuminating light functions also as an optical fiber probe for detecting the scattered light. Herein, the intensity of the scattered light can be detected in such a way that the scattered light picked up at the micro-opening is guided by the optical fiber probe and then split from the entered illuminating light by a semitransparent mirror.
It is known, however, that since the near-field optical microscope in the prior art illuminates the sample and detects the scattered light through the micro-opening, it exhibits low conversion and coupling efficiencies, resulting in feeble light detection, which makes the signal-to-noise ratio (hereinbelow, expressed as “SNR”) of the detected light very inferior.
In view of the drawback, there has been proposed a system wherein a sample is placed on the totally reflective surface of a total reflection prism, and wherein scattered light based on the interaction between the sample and an evanescent wave on the totally reflective surface is picked up by the optical fiber probe. It has also been studied to heighten the intensity of the scattered light by raising the intensity of illuminating light for the total reflection prism.
Disadvantageously, however, this system is applicable only to samples each of which can be arranged on the total reflection prism. That is, it has a very narrow range of applications to configurations and materials.
Moreover, the prior-art system cannot distinguish the configuration or structure of the sample from the difference of the materials. In a case, for example, where a minute ruggedness coexists with a minute material difference on a flat surface, the same outputs are produced, and the ruggedness and the material difference cannot be identified.
In this manner, the prior-art examples have had the problems that the SNR is inferior on account of the feeble light detection, that measuring conditions and subjects to-be-measured are limited, and that subjects to-be-measured are further limited because the configuration or structure of the sample cannot be discriminated from the difference of the materials.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the problems of the prior art as stated above, and to provide a near-field optical microscope with which samples to-be-analyzed are not limited, which is less expensive and which is capable of detection of good SNR.
A near-field optical microscope for accomplishing the above object of the present invention comprises an optical probe which is arranged in opposition to a sample, and which irradiates the sample with an evanescent wave; a plurality of photodetectors which detect respective components of light scattered in different directions, among components of the scattered light generated by scattering of the evanescent wave by said sample; and a processor which analyzes characteristics of said sample on the basis of respective detection signals of said plurality of photodetectors.


REFERENCES:
patent: 5294790 (1994-03-01), Ohta et al.
patent: 5450376 (1995-09-01), Matsumura et al.
patent: 5610897 (1997-03-01), Yamamoto et al.
patent: 5739527 (1998-04-01), Hecht et al.
patent: 5789742 (1998-08-01), Wolff
patent: 3210407 (1991-09-01), None

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