Electric heating – Metal heating – By arc
Reexamination Certificate
2000-11-22
2002-10-01
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C372S006000, C385S032000
Reexamination Certificate
active
06459068
ABSTRACT:
BACKGROUND OF THE INVENTION
This Invention relates to a laser device, a laser machining device, and an optical amplifier each of which is for oscillating or amplifying a laser beam by supplying an excitation beam to a laser active material contained In a long-sized laser beam guide portion, such as an optical fiber, and, in particular, to a laser device, a laser machining device, and an optical amplifier of the type which are effectively applicable to the fields of optical communication, optical measurement, and laser machining.
In the fields of optical communication, optical measurement, and laser machining, it is desired to develop a laser device which is higher in output power or efficiency but is lower in cost. Presently, a fiber laser device is known as one of candidates which may possibly satisfy the above-mentioned demand.
The fiber laser device comprises an optical fiber as a laser beam guide portion (a so-called laser medium). The optical fiber comprises a core portion containing a laser active material and a cladding portion coaxially surrounding the core portion. By appropriately selecting the diameter of the core portion and the difference in optical refractive index between the core portion and the cladding portion, a single transverse mode of laser oscillation is relatively easily achieved.
In addition, by confining a light beam within the optical fiber at a high density, it is possible to enhance the interaction between the laser active material and the light beam. Since the length of interaction can be prolonged by increasing the length of the optical fiber, it is possible to generate a laser beam having a high quality in spatial characteristics at a high efficiency. Thus, the laser beam of an excellent quality can be obtained at a relatively low cost. In addition, optical amplification can be carried out at a high efficiency.
In order to achieve a higher output power and a higher efficiency of the laser beam, it is required to efficiently introduce an excitation beam to a laser active region (typically, the core portion) of the optical fiber so that the excitation beam is sufficiently absorbed in the laser active material, such as laser active ions, laser dyes, or any other emission center, added to the laser active region.
However, in order to satisfy a single-mode waveguide condition, the diameter of the core portion must be smaller than 20 &mgr;m. Generally, it is difficult to efficiently introduce the excitation beam to the core portion having such a small diameter.
In order to overcome the above-mentioned difficulty, proposal is made of a fiber laser device and a laser machining device in Japanese Unexamined Patent Publication (JP-A) No. H11-28425. The laser device comprises a laser fiber which has a core containing a laser active material and which is for producing a laser beam from its output end when the laser active material is excited. The laser fiber is, directly or indirectly through an optical medium, brought into contact with an beam guide structure adapted to confine an excitation beam for exciting the laser active material. The laser active material is excited by the excitation beam incident through a contact zone between the laser fiber and the beam guide structure.
Thus, the beam guide structure adapted to confine the excitation beam is used as an excitation beam guide portion. Through the excitation beam guide portion, the excitation beam is introduced from a side surface of the laser fiber as a laser beam guide portion. The excitation beam is introduced in a distributed state in which it is distributed along the length of the laser beam guide portion. By the excitation beam introduced into the laser beam guide portion in the distributed state, the laser active material contained in the laser beam guide portion is excited.
In this case, the introduction of the excitation beam into the excitation beam guide portion can be carried out through an incident prism portion formed at a desired position of the excitation beam guide portion. The excitation beam incident to the excitation beam guide portion is repeatedly reflected in the interior of the excitation beam guide portion to spread throughout the interior of the excitation beam guide portion. Then, the excitation beam is introduced into the laser beam guide portion through the contact portion where the excitation beam guide portion is directly or indirectly brought into contact with the side surface of the laser beam guide portion.
For example, the excitation beam guide portion comprises a hollow cylindrical structure or a flat disk-shaped structure. The excitation beam guide portion is supplied with the excitation beam from an excitation light source and transmits the excitation beam which is confined therein by internal reflection. The laser beam guide portion is brought into optical contact with the surface of the excitation beam guide portion over a predetermined length. For example, the laser beam guide portion in the form of a fiber is wound around the structure forming the excitation beam guide portion. Thus, the excitation beam confined within the excitation beam guide portion is incident into the laser beam guide portion through the contact zone.
With the laser device having the above-mentioned excitation structure, it is easy to introduce the excitation beam into the laser beam guide portion in the form of a fiber. In addition, the excitation beam can be introduced through a desired position on the structure forming the excitation beam guide portion. This facilitates the excitation by the use of a plurality of excitation light sources. In the past, the excitation beam could be introduced only through opposite end faces of the fiber.
In the above-mentioned conventional laser device, the excitation beam must be introduced at an efficiency as high as possible to the contact zone where the excitation beam guide portion is brought into contact with the laser beam guide portion in order to efficiently introduce the excitation beam from the excitation beam guide portion into the laser beam guide portion.
In order to efficiently excite the laser active material contained in the laser beam guide portion, it is required to extend the length of the contact zone where the excitation beam guide portion is brought into contact with the laser beam guide portion, i.e., to widen the area of distributed introduction of the excitation beam.
To this end, the excitation beam guide portion must have a surface area as large as possible. On the other hand, in order to increase the ratio of absorption of the excitation beam into the core portion, the excitation beam guide portion must have an internal volume as small as possible. If the internal volume of the excitation beam guide portion is large, an effective absorption coefficient becomes small so that an excitation efficiency is decreased due to an optical loss such as a scattering loss.
For example, the excitation beam guide portion is formed into a hollow cylindrical shape or a flat disk shape in order to have the large surface area. At any rate, the excitation beam guide portion must have a structure as thin as possible in order avoid the decrease in excitation efficiency. However, if such a thin structure is formed by molding or machining an optical material such as a glass, the production cost inevitably becomes high.
For example, in the above-referenced Japanese Unexamined Patent Publication (JP-A) No. H11-284255, a cylindrical glass tube is exemplified as the excitation beam guide portion. In order to avoid the decrease in excitation efficiency, the cylindrical glass tube must be reduced in thickness to about 0.5 mm or less. It is difficult to form such a thin structure by mechanical machining. This inevitably requires a high cost.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a laser device, a laser machining device, and an optical amplifier which are capable of increasing an efficiency of exciting a laser active material through an excitation beam guide portion to thereby achieve an increase in output power a
Sekiguchi Hiroshi
Yamaura Hitoshi
Evans Geoffrey S.
Hoya Corporation
Sughrue & Mion, PLLC
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