JPH07135361A - Fiber transmission pumped laser - Google Patents

Abstract

PURPOSE:To provide a highly efficient high output fiber transmission pumped laser conveniently at low cost in which fiber transmission is realized using a high output laser without requiring conventional intricate transmission optical system. CONSTITUTION:In the fiber transmission pumped laser where a pumping laser beam 3 transmitted on an optical fiber 5 impinges on a laser medium 9 to cause laser oscillation, the optical fiber 5 is tapered 15 toward its outlet at the end part where the pumped laser beam 3 enters.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber transmission pumping laser device, and more particularly to irradiating a laser medium for pumping transmitted by an optical fiber to a laser medium such as liquid, solid or gas to cause laser oscillation. The present invention relates to a fiber transmission pump type laser device.

[0002]

2. Description of the Related Art Conventionally, most laser devices for exciting a laser medium by another exciting laser beam to obtain laser oscillation use an optical system combining a lens and a mirror to produce an exciting laser beam for a liquid, a solid, a gas, etc. Is transmitted to the laser medium. However, this method has a drawback in that the positional relationship between the pumping laser and the pumped laser is limited and the transmission optical system becomes complicated. Further, if the optical system becomes complicated, the beam transmission efficiency will also decrease.

On the other hand, there is a method of using an optical fiber 20 for transmitting a laser beam for excitation, as shown in FIG. 3, without using such an optical system. This system has the advantages that the transmission optical system is very simple, the transmission efficiency can be increased, and the positional relationship between the pumping laser and the pumping laser is not limited.

[0004]

However, there is a limit to the power of the excitation laser beam that can pass through the optical fiber 20 without damaging it. For this reason, high power laser fiber transmission has not been realized so far.

The limited power of the transmitted laser beam can be improved by increasing the fiber diameter. However, increasing the fiber diameter makes it difficult to handle, such as bending,
The positional relationship between the pumping laser and the pumped laser is limited. Further, when the aperture on the emission side becomes large, the diameter after being condensed by the condenser lens also becomes large, and the excitation efficiency of the laser medium also decreases. Therefore, in order not to reduce the excitation efficiency, it is necessary to make the diameter of the fiber, in particular, the diameter on the exit side as small as possible. Therefore, after all, there is a problem that the diameter on the emission side cannot be increased and the fiber cannot be used for transmission of the excitation laser beam for a high-power laser.

Therefore, an object of the present invention is to solve the problems of the prior art described above, to enable fiber transmission even with high power lasers, which was not possible with conventional high power lasers, and to use conventional complicated transmission optical systems. It is an object of the present invention to provide a simple, inexpensive, high-efficiency, high-power and high-power fiber transmission pump laser device. [Constitution of Invention]

[0007]

In order to achieve the above object, a fiber transmission pump type laser device according to the present invention comprises:
In a fiber transmission pumping laser device for irradiating a laser medium with a laser beam for excitation transmitted by an optical fiber to excite and oscillate, a diameter of the optical fiber is provided at an incident side end of the optical fiber on which the laser beam for excitation is incident. Is formed with a taper portion that decreases toward the emission side of the optical fiber.

Further, it is preferable that the diameter of the fiber on the incident side is made larger than that on the emitting side and the tapered portion is provided in the middle thereof.

Further, it is preferable that at least one of the incident side end face and the emitting side end face of the optical fiber is non-reflection coated with respect to the wavelength of the excitation laser beam.

[0010]

Since the tapered portion is formed at the incident side end of the optical fiber on which the excitation laser beam is incident, the diameter of the optical fiber decreases toward the emission side of the optical fiber. It is possible to reduce the power density of the laser beam for excitation in, and it is possible to prevent damage that is likely to occur at the incident end of the optical fiber.

Further, since the taper portion is formed,
By concentrating the excitation laser beam according to the taper shape of the taper part, the excitation laser beam is not condensed at the incident side end face of the optical fiber, and the focal plane position of the condensing lens is set at the incident side end face of the optical fiber. It is possible to shift it from the position. This makes it possible to smooth the intensity distribution on the incident side end face of the optical fiber,
It is possible to prevent damage that is likely to occur at the incident end of the optical fiber.

The largest reason why a high power laser beam cannot pass through when the fiber diameter is small lies in the entrance portion of the fiber. The reason will be described below.

The maximum power that can be passed through a fiber is ideally determined under the condition that the laser power divided by the fiber cross-sectional area (power density) does not exceed the limit of the fiber material. In the fiber, the intensity distribution of light is almost uniform, and the maximum power is determined under this condition. The intensity distribution becomes non-uniform. FIG. 4 shows an example of the intensity distribution of the laser beam on the incident end face. With this distribution,
The fiber strength is limited by the value at the highest strength, and only a fraction of the ideal maximum power or less of laser power can be passed. Furthermore, the proof stress of the peripheral part of the fiber is lower than that of the central part,
The beam must be focused so that it is much smaller than the fiber diameter, and as a result, the power of the beam that can pass through is
It will be further reduced to about 1/10 of the ideal value.

Therefore, according to the present invention, the maximum power of the laser beam at the incident portion is increased by increasing the diameter of the incident side of the fiber, and then the fiber is tapered to eliminate the transmission loss. The fiber diameter is made thin. Since light propagates randomly within the fiber, the intensity distribution is uniform, which allows the fiber diameter to be reduced to an ideal value, facilitating the handling of the fiber, reducing the cost, and emitting the light. The diameter on the side becomes smaller, the power density at the time of converging and irradiating the laser medium can be increased, the excitation efficiency of the laser medium is increased, and the oscillation efficiency is also increased.

Further, by applying antireflection coating to the end faces of the fiber entrance portion and the exit portion, the transmission efficiency can be further enhanced.

[0016]

Embodiments of the fiber transmission pump type laser device according to the present invention will now be described with reference to the drawings. Figure 1
The first of the fiber transmission pumped laser devices of the present invention
An example is shown. Here, a case where a dye solution is used as the laser medium will be taken as an example. The fiber transmission pump type laser device according to this embodiment comprises a dye laser oscillator 1 and a dye laser amplifier 2. A laser beam 3 emitted from, for example, a metal vapor laser (not shown) as an exciting laser is condensed by an incident condenser lens 4 in the vicinity of an incident side end face 6 of an optical fiber 5. The excitation laser beam 3 is transmitted by the optical fiber 5, emitted from the emission-side end face 7 of the optical fiber 5, and laterally focused by the focusing lens 8 on the laser medium 9.

The dye laser oscillator 1 includes an output mirror 1
0 and the grating 11 form a laser resonator in a direction perpendicular to the direction in which the laser medium 9 is excited. An etalon plate 12 and a beam expander 12 are provided in this laser resonator. By the etalon plate 12, the oscillation wavelength is further finely selected from the oscillation wavelength width roughly selected by the grating 11. In addition, the beam expander 12 enhances the wavelength selectivity of the grating 11 and the laser medium 9
The efficiency of excitation can be improved. The laser beam emitted from the output mirror 10 passes through the excited laser medium 9 in the dye laser amplifier 2.

At the incident side end of the optical fiber 5, there is formed a tapered portion 15 from which the diameter of the optical fiber 5 decreases from the incident side end face 6 toward the emitting side end face 7. The portion of the optical fiber 5 following the taper portion 15 continues to the exit side end surface 7 with the small diameter at the exit side end portion of the taper portion 15, and the exit side end surface 7 of the optical fiber has a smaller diameter than the entrance side end surface 6. Has become.

The position of the focal plane of the condenser lens 4 for incidence is deviated from the position of the end face 6 on the incident side for the following reason.
As the condensing diameter of the condensing lens 4 for incidence is reduced, the influence of the spherical aberration of the lens becomes greater, and the light intensity distribution on the end face 6 is as shown in (a) or (b) of FIG. The distribution has a locally strong intensity. On the other hand, when the position of the focal plane of the lens 4 is slightly displaced from the position of the incident-side end face 6 to increase the condensing diameter on the incident-side end face 6, the light intensity distribution on the incident-side end face 6 is shown in FIG. Becomes smooth. Therefore, the position of the focal plane of the condensing lens 4 for incidence is shifted to the inside of the optical fiber 5 from the position of the end face 6 on the incident side to reduce the peak intensity on the end face 6 on the incident side. The method of reducing the peak intensity by smoothing the light intensity distribution on the incident-side end face 6 is more effective than reducing the peak intensity by increasing the focused diameter.

According to the configuration of this embodiment, the optical fiber 5
Since the tapered portion 15 is formed at the incident side end of
Even when the optical fiber 5 having a small diameter is used as an optical fiber for transmitting the excitation laser beam 3,
The optical fiber 5 on the incident-side end face 6 does not cause a transmission loss at the incident-side end of the optical fiber 5.
Can be prevented from causing damage.

Further, by focusing the excitation laser beam in accordance with the taper shape of the taper portion 15, the position of the focal plane of the focusing lens 4 is shifted from the position of the incident side end face 6 of the optical fiber 5 and focused. be able to. As a result, the intensity distribution on the incident side end surface 6 of the optical fiber 5 can be made smooth, and damage that is likely to occur at the incident side end portion of the optical fiber can be prevented. This allows
By making the diameter of the incident side end face 6 larger than the diameter of the emitting side end face 7 and changing the aperture ratio, the power density per unit area at the incident side end face 6 is reduced and the intensity distribution at the incident side end face 6 is made smooth. The allowable range of available power can be expanded.

Since the tapered portion 15 is formed at the incident end of the optical fiber 5, the optical fiber 5 having a small diameter is used as an optical fiber for transmitting the excitation laser beam 3.
Can be used, and as a result, the optical fiber 5 can be easily handled and an optical system can be constructed at low cost.

Further, since the optical fiber 5 having a small diameter can be used, the diameter on the emitting side can be reduced.
As a result, the laser beam emitted from the emission side end face 8 of the optical fiber 5 and condensed by the emission condensing lens 8 can be applied to the laser medium 9 with a high power density, and the excitation effect of the laser medium is enhanced, The oscillation efficiency can also be increased.

Next, a second embodiment of the present invention will be described with reference to FIG. Here, a plurality of excitation lasers 3
An example in which a, 3b, and 3c are incident on one optical fiber 5 is shown. A taper portion 15 is provided at the incident end.
Are formed. A plurality of laser beams are respectively incident on the incident side end face 6 by the condenser lenses 4a, 4b, 4c.
The light is focused and emitted upward, and is guided to the optical fiber 5 along the shape of the tapered portion 15. The subsequent operation is similar to that of the first embodiment.

According to the structure of this embodiment, since the taper portion 15 is formed at the incident side end portion, the plurality of exciting lasers 3a, 3b, 3c can be easily made into optical fibers by the condenser lenses 4a, 4b, 4c. You can lead into 5. As a result, it is possible to irradiate the laser medium 9 with the excitation laser beam at a high power density.

Although the metal vapor laser and the dye laser have been described as examples in the above embodiments, any semiconductor laser, gas laser, solid laser or the like may be used as the exciting laser.

Further, the laser medium is not limited to the dye solution, but a solid for a solid laser such as titanium sapphire,
Alternatively, a gas may be used.

In the above embodiments, the transmission efficiency of the excitation laser beam can be increased by coating the end face of the optical fiber with a non-reflective coating. Further, the tapered portion 15 may be provided on a part of the optical fiber 5, or may be provided over the entire length of the optical fiber 5.

[0029]

As described above, according to the present invention,
Since a taper is formed at the incident side end of the optical fiber, even when using an optical fiber with a small diameter as the optical fiber for transmitting the excitation laser beam, it is possible to cause transmission loss at the incident side end of the optical fiber. Therefore, it is possible to prevent the optical fiber from being damaged on the incident side end face.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of a fiber transmission pumping laser device according to the present invention.

FIG. 2 is a diagram showing a part of a schematic configuration of a second embodiment of a fiber transmission pumping laser device according to the present invention.

FIG. 3 is a diagram showing a schematic configuration of a conventional fiber transmission pump type laser device.

FIG. 4 is a diagram showing an example of a light intensity distribution when an excitation laser beam is condensed on an incident end face of a fiber by a condenser lens.

FIG. 5 is a diagram showing an example of a light intensity distribution when a laser beam for excitation is condensed with a large condensing diameter by removing a focal plane on an incident end face of a fiber with a condensing lens.

[Explanation of symbols]

 1 Dye laser oscillator 2 Dye laser amplifier 3 Excitation laser beam 4 Incident condenser lens 5 Optical fiber 6 Incident side end face 7 Beam expander 8 Emission condenser lens 9 Laser medium 10 Output mirror 11 Grating 12 Etalon 13 Beam expander

Claims (1)

[Claims] 1. A fiber transmission pumping laser device for irradiating a laser medium with a laser beam for excitation transmitted by an optical fiber to excite the laser medium to oscillate the laser beam, and at the incident side end of the optical fiber where the laser beam for excitation is incident. A fiber transmission pump type laser device, characterized in that a tapered portion is formed in which the diameter of the optical fiber decreases toward the emission side of the optical fiber.