Coherent light generators – Particular beam control device – Tuning
Patent
1988-01-29
1990-05-15
Scott, Jr., Leon
Coherent light generators
Particular beam control device
Tuning
372 24, 372 76, H01S 310
Patent
active
049264281
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method and apparatus for sensing the wavelength of a laser beam oscillated by a laser oscillator, and more particularly such method and apparatus which uses a laser optogalvanic system (hereinafter referred to as the LOG system) as a sensing system.
BACKGROUND ART
Conventionally, in order to know the wavelength of a laser beam, the laser beam irradiated from a laser beam source 1 is processed by a preprocessing system 2 including a lens and a filter so as to be suitable for a spectroscope 3, as shown in FIG. 8. The processed beam is then guided into an incident slit 3a in the spectroscope 3 and introduced in the direction determined by diffraction gratings 4b and 3c (or prisms) and a rotary stage in the spectroscope 3. The beam exiting the output slit 3d is then sensed to a signal processing system 4 to sense the wavelength of he laser beam from the angle of the rotary stage (the relationship between the angle of the rotary stage and the wavelength is known in advance).
Therefore, where the wavelength of the laser beam is controlled to a predetermined value, the angle of the rotary stage is adjusted in advance such that when a laser beam having a predetermined wavelength is entered, the beam is irradiated from the outlet slit 3d, and the wavelength of the laser beam is identified by a wavelength selective means (for example, an adjustable etalon) such that the laser beam is irradiated from the outlet slit 3d.
The identification of the wavelength using the spectroscope is, however, necessarily accompanied by troublesome alignment. In addition, in order to obtain a good result of analysis, a large-sized spectroscope is needed to thereby increase the entire size and cost of the system.
This invention derives from the contemplation of these situations. The object of this invention is to provide an apparatus which is capable of sensing and controlling the wavelength of a laser beam without using a spectroscope and a method of controlling the wavelength of the laser beam.
DISCLOSURE OF THE INVENTION
This invention senses the wavelength of an input laser beam using an LOG system.
The LOG system utilizes an optogalvano effect in which the electrical property of plasma is changed when it is irradiated with light resonant with the optical transition of the atoms and particles in the plasma. The wavelength of the resonant light which creates the reaction corresponds to the wavelength inherent to the atoms and particles in the plasma, so that the LOG system is used in quantitative analysis, the analysis of a molecular structure, etc.
If the plasma A between electrode plates 10a and 10b of a discharge tube 10 used in the LOG system which is charged and discharged in advance as shown in FIG. 2(a) is irradiated with a laser beam, ions will increase in number as shown in FIG. 2(b). Therefore, the impedance of the plasma is decreased and this change can be extracted as a voltage (current) signal from the discharge tube 10. For example, when an iron hollow cathode lamp is used as the discharge tube 10, iron plasma exists between the electrode plates, so that a signal such as is shown by a graph in FIG. 2 is obtained in accordance with the wavelength of the irradiated laser beam.
Therefore, a specific pattern produced by substances present in the discharge tube when the substances are irradiated with a laser beam and corresponding to the wavelength of the irradiated laser beam, is measured and determined in advance using the characteristic of the LOG system. An electrical signal produced by the irradiation of the laser beam and the pattern are compared to sense the wavelength of the laser beam which is being produced at present.
According to this invention, predetermined atoms or molecules in plasma are irradiated with a laser beam as an object to be sensed, the impedance of the plasma at that time is sensed, and the sensed impedance is compared with an impedance pattern measured in advance to thereby sense the wavelength of the laser beam as the object to be sensed.
This in
REFERENCES:
patent: 4450565 (1984-05-01), Copeland
patent: 4451766 (1984-05-01), Angle et al.
Analytical Chemistry, Aug., 1982, pp. 1006A-1018A.
Applied Physics, vol. 53, No. 7, 1984, pp. 590-599.
Handbook of Applied Spectroscopy, pp. 828-836 by Asakura Shoten of Nov. 25, 1978.
SPIE 1986, Microlithography.
Optics Communications, vol. 30, No. 2, Aug. 1979.
IEEE Journal of Quantum Electronics, vol. QE-15, No. 3, Mar. 1979.
Itakura Yasuo
Kajiyama Koichi
Kowaka Masahiko
Saito Kaoru
Wakabayashi Osamu
Jr. Leon Scott
Kabushiki Kaisha Komatsu Seisakucho
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