Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1991-11-29
1993-09-21
Turner, Samuel A.
Optics: measuring and testing
By particle light scattering
With photocell detection
356358, G01B 902
Patent
active
052473422
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a light wavelength measuring apparatus for electrically measuring the wavelength of target light on the basis of the count value of interference fringes, supplied from an interference spectroscopic portion, and, more particularly, to a light wavelength measuring apparatus for measuring the wavelength of target light with high precision by using an interference spectroscopic unit such as a Michelson interferometer.
DESCRIPTION OF THE RELATED ART
There have recently been demands for easy measurement of the wavelength of target light, e.g., a laser beam with high precision and high resolution.
For this reason, a light wavelength measuring apparatus using an interference spectroscopic unit 1 such as a Michelson interferometer shown in FIG. 3 has been put into practice as an apparatus for electrically measuring the wavelength of target light with high precision without using an optical device such as a diffraction grating.
In this light wavelength measuring apparatus, coherent reference light r having a known reference wavelength .lambda..sub.0, output from a reference light source 2, is incident on a half mirror 4 in a beam splitter 3. The half mirror 4 is arranged at an inclination angle of 45.degree. with respect to the incidence angle of the reference light. Part of the reference light r is reflected at a point A on the half mirror 4 at a right angle, and its propagation direction is reversed through 180.degree. by a stationary mirror 5. The light is then transmitted through a point B on the half mirror 4 to be incident on a reference light receiver 6. Part of the reference light r output from the reference light source 2 is transmitted through the point A on the half mirror 4, and its propagation direction is reversed through 180.degree. by a movable mirror 7. The light is then reflected at the point B on the half mirror 4 to be incident on the reference light receiver 6.
Meanwhile, target light a having an unknown wavelength .lambda. is transmitted through the point B on the half mirror 4, and its propagation direction is reversed through 180.degree. by the movable mirror 7. The light is then reflected at the point A on the half mirror 4 to be incident on a target light receiver 8. In addition, part of the target light a is reflected at a right angle at the point B on the half mirror 4, and its propagation direction is reversed through 180.degree. by the stationary mirror 5. The light is then transmitted through the point A on the half mirror 4 to be incident on the target light receiver 8. The movable mirror 7 is arranged to be movable parallel to the optical path, as shown in FIG. 3.
The reference light r and the target light a, which are respectively incident on the light receivers 6 and 8, respectively cause interference with the light components reflected by the stationary mirror 5 and the movable mirror 7. If the movable mirror 7 is moved in directions indicated by arrows, repetitive waveforms (interference fringes: fringes) formed by the interference are periodically formed in light intensity signals r.sub.1 and a.sub.1 corresponding to the light intensities of the interference light components output from the light receivers 6 and 8, as shown in FIG. 4. A pitch length P of each of these repetitive waveforms (interference fringes) corresponds to the wavelength of the corresponding light. Therefore, the wavelength .lambda. of the target light a can be obtained according to the following equation (1) by counting numbers Nr and Na of repetitive waveforms (interference fringes) in a case wherein the movable mirror 7 is moved by a predetermined distance L (corresponding to D.sub.S =2L where D.sub.S is the change amount of the optical path length in FIG. 3) from a position indicated by solid lines in FIG. 3 to a position indicated by dotted lines:
In the light wavelength measuring apparatus using the interference spectroscopic unit 1 such as a Michelson interferometer shown in FIG. 3, in order to measure the wavelength .lambda. of the target lig
REFERENCES:
patent: 4165183 (1979-08-01), Hall et al.
patent: 4413908 (1983-11-01), Abrams
patent: 4847878 (1989-07-01), Badeau
"A Digital Interferomter for Wavelength Measurement", Bennett et al, J. Phys. E: Sci. Instrum., Feb. 1980, pp. 174-177.
"Accurate Laser Wavelength Measurement with a Precision Two-Beam Scanning Michelson Interferometer", J. P. Monchalin et al, Applied Optics, vol. 20, No. 5, Mar. 1, 1981, pp. 736-757.
Applied Physics Letters, vol. 29, Sep. 15, 1976, No. 6 pp. 367-369.
Goto Hiroshi
Ichihashi Yasutaka
Imai Takamasa
Tamura Youichi
Tsukamoto Takeshi
Anritsu Corporation
Nippon Telegraph & Telephone Corporation
Turner Samuel A.
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