JP2002158387A - Laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser device capable of high-output operation at a high efficiency with a simple configuration. SOLUTION: The laser device comprises a pair of polarization selecting elements, a first optical path comprising an optical amplification part arranged between the pair of polarization selecting elements and a polarization rotator, and a second optical path in which the laser beam reflected on one polarization selecting element or transmitted is made incident on the other polarization selecting element by a plurality of total reflection mirrors, allowing it to round to the first optical path. Thus, the polarized/rotated laser beam rounds to the first optical path under the effect of double refraction at the optical amplification part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser device for generating a high-power linearly polarized laser beam.

[0002]

2. Description of the Related Art FIG. 4 is, for example, “Solid-
1 is a block diagram showing a conventional laser device shown in "State Laser Engineering" 5th edition, pp. 172-173.
In FIG. 4, reference numeral 1 denotes a laser beam generator for generating a linearly polarized laser beam 2a, 3 denotes a beam diameter correcting optical system, 5a,
5b, 5c, 5d are total reflection mirrors, 6 is a polarization selection element,
Reference numerals 7a, 7b, 7c and 7d denote a laser active medium such as Nd: YAG and an optical amplifying unit provided with a laser active medium exciting device such as a laser diode or a lamp.
Polarization direction rotating element, 10 is a vertical incidence total reflection mirror, 1
Reference numeral 1 denotes an isolator having a half-wave plate and a Faraday rotator, and 12 denotes a quarter-wave plate.

Next, the operation of the conventional laser device will be described with reference to FIGS. The beam diameter of the laser beam 2a generated from the laser beam generator 1 is changed by the beam diameter correction optical element 3, and the total reflection mirrors 5a, 5b,
The light enters the polarization selection element 6 through 5c and 5d. Since the laser beam 2a has the polarization direction 4a as shown in FIGS. 4 and 5, the laser beam 2a passes through the polarization selection element 6 and passes through the optical amplifiers 7a and 7b.
And is optically amplified to become a laser beam 2b.

The polarization direction of the laser beam 2b is rotated by 90 degrees by the 90-degree polarization direction rotating element 8 to form a laser beam 2c. The laser beam 2c is applied to the optical amplifiers 7c and 7c.
The light is amplified when passing through d, the beam direction is inverted by the total reflection mirror 10, and the polarization direction is rotated by 90 degrees by reciprocating the quarter-wave plate 12,
It becomes a laser beam 2d.

[0005] The laser beam 2d is optically amplified by passing through the optical amplifiers 7d and 7c, and the polarization direction is rotated by 90 degrees by the 90-degree polarization direction rotating element 8 to become the laser beam 2e. The laser beam 2e is applied to the optical amplifiers 7b and 7a.
Then, the light is amplified by passing through, and then enters the polarization selection element 6 again. Since the laser beam 2e has the polarization direction 4b, it is reflected by the polarization selection element 6 at 90 degrees,
Output to the outside of the laser device.

In the configuration of the conventional laser device, the optical amplifier 7
The polarization direction of the laser beam is rotated by the birefringence of the laser beams a to 7d, and the laser beam having the polarization direction 4a is partially mixed in the laser beam 2e, and the laser beam is transmitted as light to the polarization selection element 6. In some cases, the beam returned to the beam generator 1 side. In order to prevent such a problem, an isolator 11 is arranged as shown in FIG. 4 to prevent the laser beam from moving backward.

[0007]

In the conventional laser device shown in FIGS. 4 and 5, it is necessary to dispose an optical element such as the isolator 11 and the wave plate 12 which is more expensive than other optical elements on the optical path. As a result, the laser device is expensive.

Further, there is a problem that an optical loss occurs when the light passes through the optical element. Further, the optical amplifiers 7a to 7a
When the polarization direction is rotated by the birefringence generated by 7d and a polarization component other than the desired polarization direction is generated, there is a problem that an optical loss is caused and the output of the laser device is reduced.

The present invention has been made to solve the above-mentioned problems, and provides a laser device which can generate a high-efficiency and high-output laser beam, has a simpler structure, and is inexpensive. The purpose is to do so.

[0010]

According to the present invention, there is provided a laser apparatus comprising: a laser active medium for optically amplifying an incident laser beam; an optical amplifier having a laser active medium exciting device; and a polarization unit for rotating the polarization direction of the laser beam. A rotation element, a first optical path composed of a pair of polarization selection elements disposed before and after so as to sandwich the optical amplification unit and the polarization rotation element, and a laser beam reflected or transmitted by one of the pair of polarization selection elements And a second optical path which is made to circulate around the first optical path by causing the laser beam to enter the other of the pair of polarization selecting elements by a plurality of laser beam reflecting means.

Further, the laser device according to the present invention is arranged so as to include a pair of polarization selecting elements inside the optical path, and includes a partial transmission mirror and a total reflection mirror.

Further, in the laser device according to the present invention, the optical amplifying section is constituted by at least two or more.

Further, in the laser device according to the present invention, a beam diameter correcting optical element is disposed in the second optical path.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a schematic diagram for explaining a laser device according to a first embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a laser beam generator for emitting a linearly polarized beam 2a, 3a and 3b denote beam diameter correcting optical systems for correcting the beam diameter of the laser beam, and 5a, 5b, 5c and 5d denote total reflection of the laser beam. Mirrors, 6a and 6b are a pair of polarization selection elements, and 7a and 7b are optical amplification units including a laser activation medium such as Nd: YAG and a laser activation medium excitation device provided between the pair of polarization selection elements 6a and 6b. Numeral 8 denotes a 90-degree polarization direction rotating element provided between the optical amplifiers 7a and 7b.

The operation of the laser device configured as shown in FIG. 1 will be described. A linearly polarized laser beam 2a generated by a laser beam generator 1 that generates a linearly polarized laser beam
Has a polarization direction 4a parallel to the plane of the drawing and perpendicular to the direction of travel of the laser beam. The beam diameter is first changed by the beam diameter correction optical element 3a. Total reflection mirror 5
The laser beam 2a having passed through the first and second polarization selection elements 6a and 5b enters the first polarization selection element 6a. The first and second polarization selection elements 6a and 6b are totally reflected with respect to a laser beam having a polarization direction perpendicular to the plane of the drawing and totally transmitted with respect to a laser beam having a polarization direction parallel to the plane of the drawing. Therefore, the laser beam 2a emitted from the laser beam generator 1 passes through the first polarization selection element 6a and travels in the direction of the optical amplifiers 7a and 7b.

The laser beam 2a is optically amplified by passing through the optical amplifiers 7a and 7b, and the polarization direction is changed to 4b by the action of the 90-degree polarization direction rotating element 8, so that the second polarization selecting element 6b Incident on. Above, the first
From the polarization selection element 6a to the optical amplification units 7a, 7b and 90
The optical path reaching the second polarization selecting element 6b via the polarization direction rotating element 8 is referred to as a first optical path. Second polarization selection element 6b
Since the polarization direction 4b of the laser beam incident on the second polarization selection element 6b is perpendicular to the paper surface,
The laser beam 2b is reflected by changing the degree direction. The laser beam 2b passes through a second optical path composed of total reflection mirrors 5c and 5d, and passes through a first polarization selection element 6
The light is guided to a. The laser beam 2b is corrected in beam diameter by the beam diameter correction optical system 3b while passing through the second optical path, and enters the first polarization selection element 6a while having a polarization direction 4d.

Since the polarization direction 4d of the laser beam 2b in the second optical path is perpendicular to the plane of the paper, the laser beam 2b is reflected by the first polarization selection element 6a by changing its direction by 90 degrees.
The laser beam goes around the first optical path and becomes a laser beam 2c. The laser beam 2c is optically amplified again when passing through the optical amplifiers 7a and 7b inside the first optical path, and further, the polarization direction is rotated 90 degrees by the action of the 90-degree polarization direction rotating element 8,
A laser beam having the polarization direction 4c is obtained. Since the second polarization selecting element 6b has a function of transmitting a laser beam having a polarization direction 4c parallel to the paper surface, the laser beam 2c
Is output outside the laser device.

If the optical amplifiers 7a and 7b are made of a solid laser active medium such as Nd: YAG, the laser active medium may have birefringence due to heat generated by optical excitation. As a countermeasure, a 90-degree polarization direction rotating element 8 is disposed between substantially the same optical amplifiers 7a and 7b to reduce the rotation of the polarization direction of the laser beam due to the above-described birefringence effect. The laser beam having a polarization component generated by the rotation of the polarization of the laser beam is transmitted to the total reflection mirror 5.
c, by guiding the light inside the second optical path composed of the total reflection mirror 5d, the laser beam component that has been polarized and rotated by the birefringence generated in the optical amplifiers 7a and 7b does not become an optical loss. I have to. Therefore, according to the configuration of the present apparatus, optical loss of the entire laser apparatus can be minimized.

In the first embodiment, the optical amplifier 7a,
Although the case where the 90-degree polarization direction rotating element 8 is arranged between 7b has been described, a similar laser device may be configured by disposing one single optical amplification unit and the 90-degree polarization direction rotating element. .

Further, the laser beam generated from the laser beam generator 1 may be a pulse beam or a continuous wave beam.

In the above description, a case has been described in which a 45-degree incident type element is used as the pair of polarization selecting elements 6a and 6b. Needless to say, the same effect can be obtained.

Further, if the optical path is set so that the first laser beam 2b passing through the optical amplifier and the laser beam 2c passing through the second optical amplifier accurately overlap with each other, the rotation of the polarization direction when passing through the optical amplifier can be achieved. Even when the laser beam circulates the second optical path two or more times, a laser beam having the same characteristics is emitted to the extent that there is no practical problem, so that the effects of the present invention can be more exerted. As a method of realizing this, for example, an optical path inside a resonator in the laser beam generator 1 and a light guide path to an optical amplifier, a circuit light path constituting a laser device,
By arranging each optical element so as to form a so-called cascade-type optical path in which the beam diameter converges and diverges in the same manner, the above object can be achieved more easily.

Embodiment 2 FIG. FIG. 2 is a configuration diagram showing another embodiment of the present invention. 1 are denoted by the same reference numerals. 2, reference numeral 9 denotes a partially transmitting mirror having a predetermined reflectance, and reference numeral 10 denotes a total reflection mirror.

The configuration and operation of the embodiment according to the present invention shown in FIG. 2 will be described. The laser beam 2a having the polarization direction 4a at the position of the total reflection mirror 10 is incident on the first polarization selection element 6a. Since the first polarization selection element 6a has a property of transmitting the laser beam having the polarization direction 4a, the laser beam 2a is transmitted to the optical amplifiers 7a and 7b.
Pass through. The polarization direction is rotated by 90 degrees by the action of the 90-degree polarization direction rotation element 8a, and the laser beam having the polarization direction 4b is incident on the second polarization selection element 6b.

Since the second polarization selecting element 6b has a property of reflecting a laser beam having the polarization direction 4b, the laser beam 2a is changed to the laser beam 2 having the polarization direction 4d.
b, and the light is guided to the second optical path including the total reflection mirrors 5c and 5d. The beam diameter of the laser beam 2b is changed by the beam diameter changing optical element 3b.
The light again enters the first polarization selection element 6a. Since the first polarization selection element 6a has a property of totally reflecting the laser beam having the polarization direction 4d, the laser beam 2b is guided as a laser beam 2c toward the optical amplifiers 7a and 7b. The laser beam 2c is amplified by the optical amplifiers 7a and 7b, and the polarization direction is rotated as shown by 4c by the action of the polarization direction rotation element 8a, and is incident on the second polarization selection element 6b. Since the second polarization selection element 6b has a property of transmitting a laser beam having the polarization direction 4c, the laser beam 2c is guided to the partial reflection mirror 9. A part of the laser beam 2c incident on the partially transmitting mirror 9 is extracted as an output laser beam to the outside of the resonator by the action of the partially transmitting mirror 9.

The laser beam guided inside the resonator from the total reflection mirror 10 to the partial reflection mirror 9 in the above order passes through the optical path in the reverse direction with the rotation of the polarization direction in the reverse direction, and is partially transmitted. The light is guided from the mirror 9 to the total reflection mirror 10. As described above, the beam is amplified until it has a constant beam intensity distribution and intensity by repeating reciprocation in the optical path in the resonator, and becomes a standing wave beam inside the resonator.

In the laser device configured as shown in FIG.
Even when the polarization of the laser beams 2a and 2c passing therethrough is rotated by the birefringence generated in the optical amplifiers 7a and 7b also serving as the light source, the rotational polarization component is a pair of the polarization selecting element 6
Since the optical path is confined inside the first and second optical resonators by the action of the first optical path formed by using the first and second optical paths 6a and 6b, the optical rotation is caused by the rotation of the polarization direction caused by the birefringence, as in the first embodiment. Loss can be kept small.

Further, in addition to the optical resonator configuration shown in FIG. 2, a resonator Q value modulation element such as a Q switch element may be provided inside the optical resonator.

In the embodiment shown in FIG. 2, two optical amplifiers 7a and 7b and a 90-degree polarization direction rotating element 8 are used.
Is shown inside the first optical path, but it goes without saying that the same effect can be obtained even if a similar device is configured using only one optical amplifying unit and a polarization direction 90 ° rotation element.

Embodiment 3 FIG. 3 is a configuration diagram for explaining a laser device according to another embodiment for carrying out the present invention. 1 are denoted by the same reference numerals.

The operation of the laser device configured as shown in FIG. 3 will be described. The linearly polarized laser beam 2a generated by the laser beam generator 1 has a polarization direction 4b parallel to the paper and perpendicular to the beam traveling direction, and the beam diameter is first changed by the beam diameter correction optical element 3a.
The laser beam 2a that has passed through the total reflection mirror 5a enters the first polarization selection element 6a. A pair of polarization selection elements 6
Since a and 6b have characteristics of being totally reflected with respect to a laser beam having a polarization direction perpendicular to the paper surface and being totally transmitted with respect to a laser beam having a polarization direction parallel to the paper surface,
Laser beam 2a incident from laser beam generator 1
Proceeds toward the optical amplifier 7a.

The laser beam 2a is optically amplified by passing through the optical amplifiers 7a and 7b, is further changed to the polarization direction 4c by the action of the 90-degree polarization direction rotating element 8, and is incident on the second polarization selecting element 6b. I do. Polarization direction 4c of laser beam 2b incident on second polarization selection element 6b
Is parallel to the plane of the paper, the second polarization selection element 6
b, the light is guided to the second optical path including the total reflection mirrors 5b, 5c, 5d, and 5e. The beam diameter of the laser beam is corrected by the beam diameter correction optical system 3b,
4c while maintaining the polarization direction of the first polarization selection element 6c.
orbit to a.

Since the polarization direction 4c of the laser beam 2b is parallel to the plane of the drawing, the laser beam 2b passes through the first optical path, that is, passes through the first polarization selection element 6a, becomes the laser beam 2c, and becomes the optical amplifier 7a again. , 7b. Optical amplifier 7
The laser beam 2c is again optically amplified by passing through a and 7b, and the polarization direction is rotated by 90 degrees by the action of the 90-degree polarization direction rotating element 8, thereby becoming a laser beam having a polarization direction 4d. Since the second polarization selection element 6b transmits a laser beam having a polarization direction parallel to the paper surface,
The laser beam 2c is output from the laser device via the total reflection mirror 5f.

In the laser device configured as shown in FIG.
As in the first embodiment, the laser beams 2a, 2a, 2b,
Even when the polarized light of c is rotated, the rotated polarized light component is confined inside the first and second optical resonators by the action of the first optical path formed by using the pair of polarization selecting elements 6a and 6b. Optical loss due to rotation of the polarization direction due to birefringence can be kept small.

[0035]

According to the laser apparatus of the present invention, a laser active medium for optically amplifying an incident laser beam, an optical amplifying unit having a laser active medium exciting device, a polarization rotating element for rotating the polarization direction of the laser beam, A first optical path composed of a pair of polarization selection elements disposed before and after so as to sandwich the optical amplification unit and the polarization rotation element, and a laser beam reflected or transmitted by one of the polarization selection elements, And a second optical path that circulates around the first optical path by being incident on the other of the pair of polarization selecting elements by the beam reflecting means, so that the laser beam component that has been polarized and rotated by the birefringence generated in the optical amplification unit is also provided. Since optical loss does not occur, optical loss can be minimized as a whole laser device, resulting in a simple device configuration,
In addition, a highly efficient laser device can be obtained.

Further, the laser device according to the present invention includes the partial transmission mirror and the total reflection mirror arranged so as to include the pair of polarization selecting elements inside the optical path, so that the laser device can be operated with a simple configuration and high output operation. Laser device can be obtained.

Further, in the laser device according to the present invention, since the optical amplifier is constituted by at least two or more, a high-power laser beam can be obtained with a simple structure.

In the laser device according to the present invention, the second
Since the beam diameter correcting optical element is arranged in the optical path, the optical loss in the optical path can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a laser device according to a first embodiment.

FIG. 2 is a diagram illustrating a configuration of a laser device according to a second embodiment.

FIG. 3 is a diagram illustrating a configuration of a laser device according to a third embodiment;

FIG. 4 is a diagram illustrating a configuration of a conventional laser device.

FIG. 5 is a diagram for explaining the operation of the conventional laser device shown in FIG.

[Explanation of symbols]

1 laser beam generator, 2 laser beam, 3
Beam diameter correcting optics, 4 symbol for polarization direction,
5 a total reflection mirror, 6 a polarization selector, 7 an optical amplifier including a laser active medium and a laser active medium pumping device,
8 90 degree polarization direction rotating element, 9 partial transmission mirror,
10 vertical incidence total reflection mirror, 11 isolator, 12 quarter wave plate.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01S 3/081 H01S 3/081 3/23 3/23 (72) Inventor Shuichi Fujikawa Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 2-3, Mitsubishi Electric Corporation 2H042 CA10 CA14 CA17 DB01 DD04 DE07 2H049 BA05 BA08 BA42 BA43 BC21 5F072 AB02 JJ04 KK05 KK30 LL09 PP01 PP07

Claims (4)

[Claims] 1. An optical amplification unit comprising a laser active medium for optically amplifying an incident laser beam and a laser active medium excitation device, a polarization rotating element for rotating the polarization direction of the laser beam, the optical amplification unit and the polarization A first optical path composed of a pair of polarization selection elements arranged before and after so as to sandwich the rotation element, and a plurality of laser beam reflection means for reflecting the laser beam reflected or transmitted by one of the pair of polarization selection elements. And a second optical path which is made to enter the other of the pair of polarization selecting elements and thereby circulates around the first optical path. 2. The laser device according to claim 1, further comprising a partial transmission mirror and a total reflection mirror arranged so as to include said pair of polarization selecting elements inside an optical path. 3. The laser device according to claim 1, wherein the optical amplification unit includes at least two or more. 4. The laser device according to claim 1, wherein a beam diameter correcting optical element is arranged in the second optical path.