Radiant energy – Invisible radiant energy responsive electric signalling – Ultraviolet light responsive means
Reexamination Certificate
1999-06-25
2002-06-11
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Ultraviolet light responsive means
C250S373000
Reexamination Certificate
active
06403966
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P10 187774 filed Jul. 2, 1998, which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for measuring the structure of an object by heterodyne detection or homodyne detection employing the laser light.
2. Description of the Related Art
For measuring the structure of an object, an optical microscope has so far been used extensively. In an ordinary optical microscope, the observing light is illuminated on the object for measurement, and observation is made of the intensity distribution of the observing light transmitted through the object or that of the light reflected from the object for measurement. The limit of resolution of the optical microscope is determined by the limit of optical diffraction. That is, if the wavelength of the light for observation is &lgr; and the numerical aperture of the object lens is NA, the spatial wavelength of the limit of resolution in an optical microscope adapted for observing only the light intensity distribution is expressed by &lgr;/2×NA. In such optical microscope, the light for observation is extremely weak in the vicinity of the limit of resolution to render the observation difficult.
On the other hand, there is proposed a technique of measuring the structure of the object by heterodyne or homodyne detection as a technique which enables the measurement of a fine textured structure even with the weak light. With the heterodyne or homodyne detection, it becomes possible to measure the fine textured structure with the weak light by employing the laser light superior in coherence as the light for observation and by exploiting the phase information of the laser light.
The principle of the technique of exploiting the phase information of light is disclosed in, for example, The Antenna Properties of Optical Heterodyne Receivers, Appl. Oct., vol.5 (1966) 1588 to 1594. There is also disclosed in Probing of Acoustic Perturbations by Coherent Light Appl. Output terminal, vol.8 (1969) 1572 to 1573 a technique of measuring the intensity and the phase of the reflected light from the object under measurement by exploiting wavelength shift by an acousto-optical element of a carrier signal f
1
and by synchronously detecting beat signals of the frequency f
1
.
There is disclosed in U.S. Pat. No. 3,796,495 entitled:“Apparatus and Method for Scanning Phase Profilometry” a technique of differential heterodyne detection of two transversely shifted beams. There is disclosed in U.S. Pat. No. 4,171,159 entitled: “Optical Homodyne Microscope” a technique of effecting homodyne detection with mechanical phase modulation by a piezoelectric element. There is disclosed in U.S. Pat. No. 4,353,650 entitled: “Laser Heterodyne Surface Profiler” a technique of illuminating both the reference light and the detection light on the object for measurement and causing rotation of the object about the reference light as center of rotation to effect phase measurement. In the U.S. Pat. Nos. 4,627,730 and 4,848,908, there is disclosed a technique of illuminating both the reference light and the detection light on the object for measurement and employing a common optical path to improve resistance against oscillations. There is disclosed in Japanese Laying-Open Patent H-7-248203 a laser scanning microscope exploiting the heterodyne detection.
There is further disclosed the result of observation of a pseudo-living body sample by heterodyne detection in the visible light range in a thesis entitled: “Measurement of Spectroscopic Transmission Characteristics in the Visible Range to the Near-Infrared Range of a Pseudo-Living Body Sample Employing Optical Heterodyne Detection Method” in Optics Vol.27.1 (1998) 40 to 47.
By exploiting heterodyne or homodyne detection, it becomes possible to measure the fine textured structure with weak light. Of course, it would be meritorious if measurement can be made of a micro-sized structure. It would be more meritorious if measurement can be made not only of the planar direction but also of the depth-wise direction of the object for measurement.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and apparatus for measuring the structure of an object for measurement by exploiting heterodyne or homodyne detection, whereby measurement can be made of a micro-sized structure of the object for measurement.
It is another object of the present invention to provide a method and apparatus for measuring the structure of an object for measurement by exploiting heterodyne or homodyne detection, whereby measurement can be made of a structure along the depth-wise direction of the object.
In one aspect, the present invention provides a measurement device including ultraviolet laser light generating means for generating ultraviolet laser light by wavelength conversion of laser light from a solid-state laser light source, and measurement means for measuring the structure of an object for measurement by heterodyne detection or homodyne detection employing the ultraviolet laser light. Specifically, the ultraviolet laser light means the laser light having the wavelength of the order of 180 to 360 nm.
Preferably, the solid-state laser light source is oscillated in a single longitudinal mode.
Preferably, the solid-state laser light source is a diode laser pumped solid state laser pumped by the laser light from a semiconductor laser to radiate laser light. The diode laser pumped solid state laser preferably includes a monolithic ring type optical resonator. The laser light from a semiconductor laser falls on the monolithic ring type optical resonator to excite the laser medium to radiate the laser light. The diode laser pumped solid state laser is preferably configured so that the optical path in the monolithic ring type optical resonator is non-coplanar.
Preferably, the solid-state laser light source includes semiconductor laser and a wavelength selecting element and the laser light from the semiconductor laser is radiated via the wavelength selecting element to radiate the laser light of a single frequency.
The ultraviolet laser light generating means preferably generates the ultraviolet laser light by wavelength conversion by multiple stages.
As the wavelength converting means, a nonlinear optical element, formed as a ring type resonator, is desirable. The laser light from the solid-state laser light source is resonant in the nonlinear optical element, and the nonlinear optical element generates harmonics or the sum frequency to effect the wavelength conversion.
The wavelength converting means preferably includes an optical resonator made up of multiple mirrors and a nonlinear optical element arranged in the optical resonator. The laser light from the solid-state laser light source is resonant in the optical resonator, with the nonlinear optical element generating harmonics or the sum frequency to effect the wavelength conversion. Preferably, the position control means precisely controls the position of the mirrors making up the optical resonator.
Preferably, the measurement means includes movement means for causing movement of an object for measurement. The movement means causes movement of the object for measurement so that a light spot of the ultraviolet laser light scans the object for measurement at the time of measuring the structure of the object for measurement.
Preferably, the measurement means includes deflection means for deflecting the ultraviolet laser light to control the proceeding direction of the ultraviolet laser light. The deflection means causes deflection of the ultraviolet laser light so that the ultraviolet laser light will be incident on a pre-set position of the object for measurement at the time of measuring the structure of the object for measurement. Alternatively, the deflection means causes deflection of the ultraviolet laser light so that a light spot of the ultraviolet
Hannaher Constantine
Lee Shun
Sonnenschein Nath & Rosenthal
Sony Corporation
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