JPH07307513A - Solid laser device - Google Patents

Abstract

PURPOSE:To make it possible to direct a laser beam to an optical fiber of small diameter by a method wherein the distance between an output mirror and the main plane on the output side and the focal length of lense are in a specific relation in a large output solid laser device provided with a solid laser medium, an output mirror, a condensor lens and optical fiber to which the laser beam is directed. CONSTITUTION:In the formulas I and II, R1 is the radius of curvature of an output mirror 3, L1 is the distance from the output mirror 3 to the plane of the output side, RF is the core diameter of an optical fiber 8, NA is the numerical apertures of the optical fiber 8, RB is the radius of the laser beam to be made incident on a lense 7, RL is the radius of a solid laser medium 1, and (f) is the focal distance of the lense 7. Then, as the design procedure to determine each dimension, the focal length (f), the distance L1 from the main plane H' to the reflection surface 3A, an emission angle theta, the condition when RB=RL, the curvature radius R1 of a reflection surface 4A, the curvature radius R2 of the reflection surface 4A, and the distance L2 from the main plane H to the reflection surface 4A are computed. Accordingly, the angel of incidence of the laser beam which is made incident on the optical fiber 8 is smaller than the numerical aperture NA of the optical fiber 8, and its focused beam diameter becomes smaller than the core diameter RF.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser device. In particular, the present invention relates to a solid-state laser device that can make a laser beam incident on a small-diameter optical fiber even if it is configured to obtain a large output laser beam.

[0002]

2. Description of the Related Art FIG. 1 schematically shows a general structure of a solid-state laser device. In FIG. 1, a rod-shaped laser medium 1 made of YAG (yttrium-aluminum-garnet) or the like is a total reflection mirror 4 arranged coaxially with its central axis.
And the output mirror 3. An excitation lamp 2 as a pumping device is arranged on the side of the laser medium 1 in parallel with the laser medium. In addition,
Although illustration is omitted, the laser medium 1 and the excitation lamp 2 are covered with an inner mirror.

To oscillate the solid-state laser device having the above-described structure, first, power is applied to the excitation lamp 2 to apply excitation light to the laser medium 1. Then, the laser medium 1 is excited by the excitation light and oscillates the laser light. This laser light is amplified by reciprocating in the laser medium 1 while being reflected by both mirrors, and finally emitted from the output mirror 3.

In such a solid-state laser device, when the power supplied to the excitation lamp 2 is increased in order to obtain a high-power laser beam, a phenomenon called a thermal lens effect occurs in the solid-state laser medium. This is because the excitation light from the excitation lamp 2 diffuses in the laser medium 1 and is converted into heat, but is cooled only from the outer surface side. That is, a temperature distribution in which the temperature gradually decreases from the central axis of the laser medium toward the outer surface occurs. Since the refractive index of the laser medium increases as the temperature rises, the laser medium has a refractive index distribution substantially the same as that of the lens (convex lens).

Due to this thermal lens effect, the laser light 5 emitted from the laser device 1 has a divergence angle θ.
The thermal lens effect becomes stronger in proportion to the electric power supplied to the excitation lamp. Therefore, the divergence angle θ of the laser light 5 has a dependency on the input power. This is shown in FIG.

In a solid-state laser device intended for high output, a stable region (a region where the laser output simply increases as the input power increases) in the stability diagram (FIG. 13) even if a large input power is applied. This stability region was widened to maintain. That is, the reflecting surface 4a of the total reflection mirror 4 and the reflecting surface 3a of the output mirror 3 having a large curvature are used, and the distance between the total reflection side mirror 3 and the output side mirror 4 is made as short as possible.

A stability diagram of the solid-state laser device will be described with reference to FIG. Now, the g-parameter containing all the information of the solid-state laser device is defined as follows.

G ₁ = 1− (L ₁ + L ₂ ) / R ₁ −L ₂ / f · (1−L ₁ / R ₁ ) ... (1) g ₂ = 1− (L ₁ + L ₂ ) / R ₂₋ L ₁ / f · (1−L ₂ / R ₂ ) ... (2) where R ₁ is the radius of curvature of the reflecting surface 3 a of the output mirror 3 and R ₂ is the reflecting surface of the total reflection mirror 4. 4a is the radius of curvature, L ₁ is the distance between the output mirror side main plane of the laser medium 1 that is producing the thermal lens effect and the reflecting surface 3a of the output mirror 3, and L ₂ is the thermal lens effect. The distance between the main surface of the laser medium 1 facing the total reflection mirror and the reflection surface 4a of the total reflection mirror 4. At this time, the condition under which the resonator oscillates stably is 0 ≦ g ₁ g ₂ ≦ 1 (3), so that the region other than the hatched region on the g ₁ -g ₂ plane shown in FIG. It becomes a stable area. That is, when the input power is increased from the point of A ₀ at zero input power (f = ∞) to reach A ₂ , as shown in FIG. 14, the laser output simply increases in the stable region and in the unstable region. It will decrease. By shortening the mirror distance, the stable region described above can be expanded.

However, when the distance between the mirrors is shortened, the divergence angle θ of the laser light is determined in inverse proportion to the distance between the mirrors. Therefore, the divergence angle θ of the laser light oscillated from the high-power solid-state laser device is considerably large ( It was around 20 mrad).

By the way, when the solid-state laser device is applied to metal processing or the like, as shown in FIG.
The laser light emitted while being diverged from is once made incident on the condenser lens 7 to be condensed and made incident on the optical fiber 8.
Then, the light that has passed through the optical fiber 8 is condensed at the processing point by the condenser lens system 9 and processed.

This processing performance depends on the energy density at the processing point when the total laser output emitted from the output mirror is constant. That is, the higher the energy density, the better the processing performance. The energy density at the processing point largely depends on the thickness of the optical fiber 8, and the smaller the energy density, the larger the energy density. This is because, if the total amount of energy to be transmitted is the same, the energy density increases as the fiber light 8 becomes thinner, and since the laser light is uniformly emitted from the entire core surface on the emission surface of the optical fiber 8, the core diameter is reduced. This is because the spot diameter depends on the core diameter of the optical fiber 8 because the light cannot be condensed smaller.

Therefore, the laser light is made thinner by the optical fiber 8
Need to be incident on. In the conventional solid-state laser device, the distance between the mirrors is increased to limit the divergence angle of the laser light incident on the condenser lens 7 to be small so that the laser light is incident on the thin fiber 8. .

[0013]

However, when the distance between the mirrors is increased, the stable region in the stability diagram is narrowed.

Further, in order to enter the thin fiber, the converging property of the laser light by the condenser lens 7 must be improved. In this case, the focus diameter of the laser light converged by the condenser lens 7 is proportional to the focal length of the condenser lens 7. Therefore, in order to form a laser light spot smaller than the core diameter of the thin optical fiber 8, the focal length of the condenser lens 7 must be shortened to some extent. Further, if the focal length is made too short, the angle of the light beam incident on the optical fiber 8 exceeds the numerical aperture of the optical fiber 8. Thus, the condition of the condenser lens cannot be ignored.

When the electric power applied to the laser medium exciting means is changed, the thermal lens effect also changes. Along with this, in the conventional solid-state laser device, the divergence angle θ of the laser light also changed as shown in FIG. 15 (FIG. 15A).
Shows the state where there is no thermal lens effect, and (c) shows the state where the thermal lens is maximum. ). Therefore, when the positions of the condenser lens 7 and the optical fiber 8 are fixed, the distance from the condenser lens 7 to the condensing point changes as shown in FIG. 15, and the spot diameter on the incident end surface of the optical fiber 8 changes. Changes. For this reason, conventionally, it has been necessary to use an optical fiber having a thickness capable of capturing the maximum spot diameter, assuming a case where the spot diameter becomes maximum in advance due to the change of the thermal lens effect.

As described above, in a solid-state laser device having a large output, it was very difficult to enter the thin fiber. The present invention has been made in order to solve the above problems, and it is a technical object of the present invention to provide a solid-state laser device capable of injecting laser light into a small-diameter optical fiber 8 in a solid-state laser device having a large output. To be an issue

[0017]

In order to solve the above-mentioned technical problems, the solid-state laser device according to the present invention has a radius R _L having a main plane on the output side and the total reflection side due to the thermal lens effect.
Solid laser medium, laser medium pumping means for pumping the solid laser medium, and total reflection of laser light oscillated from the solid laser medium pumped by the laser medium pumping means and returning to the solid laser medium. A total reflection mirror, and an output mirror for reflecting the laser light oscillated from the solid-state laser medium excited by the laser-medium excitation means and returning it to the solid-state laser medium, and transmitting the laser light toward the outside. It comprises a lens for condensing the laser light transmitted through the output mirror and an optical fiber on which the laser light condensed by the lens is incident. The radius of curvature of the output mirror is R ₁ and the core diameter of the optical fiber is R. _F, the numerical aperture of the optical fiber and NA, when the beam radius of the laser beam incident on the lens was R _B, the output-side mirror The distance L to the output side principal plane
₁ is R _B R _L / (R _F tan (sin ⁻¹ NA)) ≦ L ₁ ≦ R _1/2 (4), and the focal length f of the lens is L ₁ R _F / R _{L ≧ f ≧ R B / tan (} sin -1 NA) , characterized in that a ... (5) (corresponding to claim 1). Hereinafter, each constituent element will be described.

<Solid-State Laser Medium> The solid-state laser medium used in the present invention includes rare earth elements (La, C).
e, Pr, Nd, Pm, Sm, Eu, Gd, Tb, D
y, Ho, Er, Tm, Yb, Lu) to YAG (Y ₃
Garnet crystal such as Al ₅ 0 ₁₂ ) or GGG (Ga ₃ Gd ₅ O ₁₂ ) or glass, or YVO (YVO ₄ ) or YLF (Y
It may be doped with LiF ₄ ) or the like, or various stoichiometric crystals.

When the solid-state laser medium becomes equivalent to a lens due to the thermal lens effect, the principal planes on the total reflection mirror side and the output mirror side can be specified by the degree of refraction of incident light rays.

<Laser Medium Exciting Means> The laser medium exciting means can be an exciting light irradiation device such as a flash lamp, an arc lamp, a xenon discharge tube, or a semiconductor laser.

As described above, the present invention treats the solid-state laser medium as a convex lens, so that it is desirable to obtain a uniform refractive index distribution over the entire circumference of the solid-state laser medium. For that purpose, it is necessary to irradiate the excitation light uniformly over the entire circumference of the solid-state laser medium. As the means, for example, the excitation light irradiation means is arranged around the entire circumference of the solid-state laser medium, or both the solid-state laser medium and the excitation light irradiation means are covered with an elliptic cylinder inner surface reflecting mirror and both are placed at respective focal positions of the ellipse. Means such as placement can be adopted.

<Total Reflection Mirror, Output Mirror> It is desirable that the positions of the reflection surfaces of the total reflection mirror and the output mirror and the radius of curvature are set so that the divergence angle of the laser light oscillated from the solid laser medium becomes small. If you do this,
This is because the beam radius R _B of the laser light that enters the condenser lens can be reduced. This is because when the incident beam radius R _B becomes smaller in this way, the lower limit of f in the equation (5) decreases and the range in which f can be taken becomes wider.

Further, in this case, it is desirable to set such that the change of the divergence angle is small regardless of the increase or decrease of the thermal lens effect. For example, the radius of curvature R of the reflecting surface of the output side mirror
_{If 1 is set} to 2L ₁ ≦ R ₁ ≦ 3L ₁ (6), the change in divergence angle can be suppressed (corresponding to claim 2).

Further, it is desirable to set the laser output so as to stably increase and decrease even when the input power is increased or decreased. For example, the distance L ₂ between the reflection surface of the total reflection side mirror and the main surface of the solid-state laser medium on the total reflection side is L ₁ (1−2L ₁ / (R ₁ + L ₁ )) ≦ L ₂ (7) Setting (corresponding to claim 3) or setting the radius of curvature R ₂ of the total reflection mirror to R ₂ = L ₂ ² R ₁ / (L ₁ ² + (L ₂ −L ₁ ) R ₁ ) ... (8) If set (corresponding to claim 4), the stable region of the laser output can be expanded.

<Optical fiber> The incident end face of the optical fiber is
It is desirable to place it at the converging point of the laser light by the condenser lens. This is because this position corresponds to the beam waist of the laser light and the beam diameter is the smallest.

Therefore, when the divergence angle of the laser light incident on the condenser lens is minimized and the laser light becomes parallel light, the incident end face of the optical fiber may be arranged at the focal position on the emission side of the condenser lens. desirable.

<Additional Constituent Requirements in the Present Invention> The present invention consists of the above essential constitutional requirements, but can also be realized by adding the following constitutions.

[Beam Diameter Limiting Member] A beam diameter limiting member may be used in combination to limit the divergence angle of the laser light emitted from the solid-state laser device. The beam diameter limiting member has a function as a diaphragm. The arrangement position may be between the solid-state laser medium and the output side mirror (corresponding to claim 5) or between the solid-state laser medium and total reflection mirror (corresponding to claim 6). By using such a beam diameter limiting member, even if the divergence angle of the laser light incident on the condenser lens is large, it is possible to suppress the expansion of the beam radius R _B of the laser light incident on the condenser lens.
For example, the incident beam diameter R _B can be made the same as the radius R _L of the solid-state laser medium. Further, this beam diameter limiting member can reduce the divergence angle of the laser light.

[0029]

When power is applied to the laser medium pumping means, the laser medium pumping means pumps the solid-state laser medium according to the power. When the solid laser medium is excited, laser light is oscillated. The oscillated laser light is multiply reflected by the total reflection mirror and the output mirror, amplified every time it passes through the solid-state laser medium, and finally emitted from the output mirror to the outside. At this time, the radius of curvature R _{1 of} the output mirror, the distance L ₁ between the output mirror and the output-side main plane, the core diameter R _{F of} the optical fiber, the numerical aperture NA of the optical fiber, and the laser light incident on the lens. Due to the relationship between the beam radius R _B and the radius R _L of the solid-state laser medium, the incident angle of the laser light incident on the optical fiber becomes smaller than the numerical aperture of the optical fiber,
The condensing diameter is smaller than the core diameter of the optical fiber. Therefore, the laser light can be incident on the optical fiber having a small diameter.

As a laser medium, N having a radius R _L = 5 mm
d: using a YAG rod, distance L ₁ = 408 mm from the reflecting surface of the output mirror to the output-side main plane of the solid-state laser medium
FIG. 11 shows changes in the divergence angle θ when other parameters are changed.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. Each of the following embodiments has a structure as shown in FIG. 1 on the assumption that it will be used in the laser processing apparatus shown in FIG. 2, but the present invention is not limited to this.

The dimensions of each part in FIG. 1 will be defined based on FIG. In FIG. 3, when excitation light is applied to the laser medium 1 by the excitation lamp 2, the laser medium 1 becomes equivalent to a convex lens due to the thermal lens effect. The position of the main plane at that time is indicated by H and H '. The principal planes H and H'move along with changes in the thermal lens effect. That is, the main planes H and H ′ are 1 / l from each end face of the laser medium 1.
It is formed at the position (2n). Here, 1 is the rod length of the laser medium 1, and n is the refractive index of the laser medium 1. Therefore, the positions of the principal planes H and H ′ slightly move as the value of n changes. However, since this amount of movement is negligible, there is no problem even if the positions of the principal planes H and H ′ are fixed.

The distance from the principal plane H'on the optical axis C of the laser medium 1 to the reflecting surface 3a of the emitting mirror 3 is L.
_Set to ₁ . Similarly, the distance from the principal plane H on the optical axis C of the laser medium to the reflecting surface 4a of the total reflection mirror 4 is L ₂
And Further, the radius of the laser medium 1 is _RL . The radius of curvature of the reflecting surface 3a is R ₁ and the radius of curvature of the reflecting surface 4a is R ₂ .

Next, a design procedure for determining each dimension defined as above will be described.

[Focal Length f] Now, assuming that substantially parallel laser light is emitted from the laser medium 1 and refraction at the output mirror 3 can be ignored, the beam radius R _B of the laser light at the incident side surface of the condenser lens 7 is , the _{R B = R L ...... (9} ).

[0036] To enter the laser light to the optical fiber 8 which places the end surface at the focal position of the condenser lens 7, needs to be ^{tan (sin -1 NA) ≧ R} B / f ...... (10) is there. Here, NA is the numerical aperture of the optical fiber 8 and f is the focal length of the condenser lens. By modifying this equation (10), the lower limit of f can be defined as f ≧ R _B / tan (sin ⁻¹ NA) (11).

When the divergence angle of the laser beam 5 is θ,
In the range in which θ is small, the diameter of light condensed by the lens 7 is approximately represented by f · θ. Therefore, in order to enter the optical fiber having the radius R _F , it is necessary to satisfy f · θ ≦ R _F (12).

As for the divergence angle θ of the laser beam 5, as a result of intensive studies by the present inventor, it became clear that it has the relationship shown in the following formula (13). _{θ = R L / L 1 ......} (13) Therefore, to be defined from this equation (12) and (13), the upper limit of _{f f ≦ L 1 R F /} R L ...... (14) it can.

From the equations (11) and (14), the following equation (15) can be obtained as a range in which f can be taken. L ₁ R _F / R _L ≧ f ≧ R _B / tan (sin ⁻¹ NA) …… (15)

[Distance L from the main plane H'to the reflecting surface 3a]
₁ ] From the equation (15), if the term of f is deleted, then L ₁ R _F / R _L ≧ R _B / tan (sin ⁻¹ NA) (16) Transferring this equation (16), the following equation (17)
Can be obtained.

R _L R _B / (R _F tan (sin ⁻¹ NA)) ≦ L ₁ (17) In this way, the lower limit of L ₁ can be defined.
On the other hand, the upper limit of L ₁ can be defined by the relationship with R ₁ . That is, as shown in FIG. 4, if the relationship of 2L ₁ = R ₁ (18) is satisfied, the divergence angle θ becomes constant (θ ₀ ) regardless of the input power. However, if L ₁ is made larger than the relation of the equation (18) and 2L ₁ > R ₁ (19), the divergence angle θ becomes larger than θ ₀ , and further, it changes depending on the input power. become. Therefore, the relationship of the following expression (20) can be obtained from the expressions (17) to (19).

R _L R _B / (R _F tan (sin ⁻¹ NA)) ≦ L ₁ ≦ R _1/2 (20) If both conditions of these formulas (15) and (20) are satisfied,
While making the maximum angle of the light beam incident on the optical fiber 8 smaller than the numerical aperture of the optical fiber 8, the converging diameter by the condenser lens 7 is made smaller than the core diameter of the optical fiber 8, thus making the optical fiber 8 of a small diameter. Laser light can be incident.

[Divergence angle θ] By substituting the equation (12) into the equation (11), the condition for the divergence angle θ of the laser beam is as follows:
1).

Θ ≦ (R _F tan (sin ⁻¹ NA)) / R _B (21)

[Conditions for R _B = R _L ] In FIG.
The aperture S ₁ as a beam diameter limiting member is arranged between the end face of the solid-state laser medium 1 and the total reflection mirror 4. On the other hand, the aperture S as a beam diameter limiting member
₂ is arranged between the end face of the solid-state laser medium 1 and the output mirror 3. These apertures S ₁ and S ₂ shape the shape of the beam emitted from the output mirror 3 into a circular shape, and adjust the beam diameter so that the incident beam radius R _B to the condenser lens 7 can be controlled by the solid laser medium 1. R _B = for radius R _L
RL .

The above equations (10), (15), (20),
And (21), on the assumption that R _B = R _L , respectively, tan (sin ⁻¹ NA) ≧ _RL / f (22) L ₁ R _F / R _L ≧ f ≧ _RL / tan ( ^{sin -1 NA) ...... (23)} R L 2 / (R F tan (sin -1 NA)) ≦ L 1 ≦ R 1/2 ...... (24) θ ≦ (R F tan (sin -1 NA) ) / _RL …… (25)

[Curve Radius R ₁ of Reflecting Surface 3a] When L ₁ is made smaller than the relation of the expression (18) and 3L ₁ = R ₁ (26), the divergence angle θ becomes θ. ₀ half will be (θ _0/2),
Moreover, it changes depending on the input power (in the middle of this, it gradually changes as shown in FIG. 11). Therefore, equations (18), (19), and (26)
From this, the following equation (27) can be obtained.

2L ₁ ≦ R ₁ ≦ 3L ₁ (27) If the condition of this expression (27) is satisfied, the solid-state laser device is designed so that the divergence angle θ is limited to the necessary minimum and does not depend on the input power. Can be configured.

Next, conditions for stable laser oscillation will be described.

[Radius of curvature R ₂ of reflecting surface 4a] In FIG. 13, the condition of R ₂ for the most stable laser oscillation is obtained from the condition that A ₁ passes through the origin. In the formula (1), when g ₁ = 0 is set and transformed, D = (1- (L ₁ + L ₂ ) / R ₁ ) / (L ₂ (1-L ₁ / R ₁ )) (28) However, D = 1 / f. Substituting this equation (28) into equation (2), g ₂ =
Putting 0, g ₂ = 1- (L ₁ + L ₂ ) / R ₂ -L ₁ (1- (L ₁ + L ₂ ) / R ₁ ) (1-L ₂ / R ₂ ) / (L ₂ (1 -L ₁ / R ₁ )) (29). From this, when the condition of R ₂ = L ₂ ² R ₁ / (L ₁ ² + (L ₂ −L ₁ ) R ₁ ) ... (30) is satisfied, the unstable region in the middle of increasing the input power is I know what I can lose.

[Distance L ₂ from Principal Plane H to Reflecting Surface 4a] On the other hand, first, in equations (1) and (2), if the input power is zero (f = ∞), then g ₁ = 1 - a _{(L 1 + L 2) /} R 1 ...... (31) g 2 = 1- (L 1 + L 2) / R 2 ...... (32). Applying these expressions (31) and (32) to the condition of the expression (3), (1- (L ₁ + L ₂ ) / R ₁ ) (1- (L ₁ + L ₂ ) / R ₂ ) ≦ 1 ... (33) When this equation (33) is modified, ((L ₁ + L ₂ ) − (R ₁ −R ₂ )) / R ₁ R ₂ ≦ 0 (34) By substituting the equation (30) into the equation (34), (L ₁ −R ₁ ) ((L ₁ + R ₁ ) L ₂ + (L ₁ −R ₁ ) L ₁ ) ≦ 0 (35) When deformed, the condition of L ₂ can be obtained.
That is, the condition of L ₂ ≧ (R ₁ −L ₁ ) L ₁ / (R ₁ + L ₁ ) ≧ L ₁ (1−2L ₁ / (R ₁ + L ₁ )) (36) can be satisfied. It turns out that this is desirable for laser oscillation.

[0052]

Example 1 Formulas (22) to (25) shown above,
The following numerical values were substituted for each parameter determined by (27), (30) and (36).

That is, the laser medium 1 has a length of 195 m.
An Nd: YAG rod with m and radius R _L = 5 mm was used.
Then, it is configured such that it can be incident on the optical fiber 8 having a radius R _F = 0.3 mm and NA = 0.2. In this case, the formula (2
From 5), it is necessary to satisfy θ ≤ 12.2 mrad (37).

At this time, the distance L ₁ from the reflecting surface 3a of the output mirror 3 to the output side main plane H'of the YAG rod is 408 mm ≤ L ₁ ≤ 500 mm (38) according to the equation (24). Become. Therefore, 410 mm is adopted as a specific value of L ₁ .

Since L ₁ = 410 mm is determined, the radius of curvature R ₁ of the reflecting surface 3a of the output mirror 3 is 820 mm ≤ R ₁ ≤ 1230 mm (39) according to the equation (27). Therefore, 1000 mm is adopted as a specific value of R ₁ .

Since R ₁ is set to 1000 mm, the distance L ₂ from the reflection surface 4a of the total reflection mirror 4 to the main surface H of the YAG rod on the total reflection side is 171.56 mm ≤ L ₂ from the equation (36). … (40) Therefore, 282 mm is adopted as a specific value of L ₂ .

Since L ₂ = 282 mm is determined, the radius of curvature R ₂ of the reflecting surface 4a of the total reflection mirror 4 is R ₂ = 1983 mm (41) according to the equation (30). Therefore, 2000 mm is adopted as a specific value of R ₂ .

On the other hand, since L ₁ = 410 mm is determined, the focal length f of the condenser lens 7 is 24.6 mm ≧ f ≧ 24.49 mm (42) according to the equation (23). Therefore, 24.5 mm is adopted as a specific value of f.

When the solid-state laser device of which the dimensions are determined as described above is excited by a flash lamp, the dependency of the divergence angle θ on the power supplied to the lamp is as shown in FIG. 5, and the supplied power stably oscillates from 0 to 30 kW. . At this time, the divergence angle θ changes only from 9.8 to 12.1 mrad.
Laser power is 0 to 90 when input power is 0 to 30 kW
Obtained up to 0 W, radius R _F = 0.3 mm, NA = 0.2
Was able to enter the optical fiber of

[0060]

[Embodiment 2] Equations (22) to (25) shown above,
The following numerical values were substituted for each parameter determined by (27), (30) and (36).

That is, the laser medium 1 has a length of 195 m.
An Nd: YAG rod with m and radius R _L = 5 mm was used.
Then, it is configured such that it can be incident on the optical fiber 8 having a radius R _F = 0.3 mm and NA = 0.2. In this case, the formula (2
From 5), it is necessary to set θ ≤ 12.2 mrad (43).

At this time, the distance L ₁ from the reflecting surface 3a of the output mirror 3 to the output side main plane H'of the YAG rod is 408 mm ≤ L ₁ ≤ 500 mm (44) according to the equation (24). Become. Therefore, 410 mm is adopted as a specific value of L ₁ .

Since L ₁ = 410 mm is determined, the radius of curvature R ₁ of the reflecting surface 3 a of the output mirror 3 is 820 mm ≦ R ₁ ≦ 1230 mm (45) according to the equation (27). Therefore, 1000 mm is adopted as a specific value of R ₁ .

Since R ₁ is set to 1000 mm, the distance L ₂ from the reflection surface 4a of the total reflection mirror 4 to the main surface H of the YAG rod on the total reflection side is 171.56 mm ≤ L ₂ from the equation (36). (46) Therefore, 218 mm is adopted as a specific value of L ₂ .

Since L ₂ = 218 mm is determined, the radius of curvature R ₂ of the reflecting surface 4 a of the total reflection mirror 4 is R ₂ = −1988 mm (convex mirror) (47) from the equation (30). . Therefore, as a specific value of R ₂ , -2000 mm
It was adopted.

On the other hand, since L ₁ = 410 mm is determined, the focal length f of the condenser lens 7 is 24.6 mm ≧ f ≧ 24.49 mm (48) from the formula (23). Therefore, 24.5 mm is adopted as a specific value of f.

When the solid-state laser device having the dimensions as described above is excited by a flash lamp, the dependence of the divergence angle θ on the input power is as shown in FIG. 6, and the divergence angle θ is from 9.3 to 12.1 mrad. It has only changed. When the applied power was 0 to 30 kW, the laser output was obtained from 0 to 900 W, and the laser could be incident on the optical fiber with radius R _F = 0.3 mm and NA = 0.2 without loss.

[0068]

[Third Embodiment] Equations (22) to (25) shown above,
The following numerical values were substituted for each parameter determined by (27), (30) and (36).

That is, the laser medium 1 has a length of 195 m.
An Nd: YAG rod with m and radius R _L = 5 mm was used.
Then, it is configured such that it can be incident on the optical fiber 8 having a radius R _F = 0.3 mm and NA = 0.2. Further, an aperture S ₂ having a radius of 4.5 mm is arranged in the vicinity of the reflecting surface 3 a of the output mirror 3.

In this case, from the equation (25), it is necessary to satisfy θ ≦ 12.2 mrad (49).

At this time, the distance L ₁ from the reflecting surface 3a of the output mirror 3 to the output side main plane H'of the YAG rod is 408 mm ≤ L ₁ ≤ 500 mm (50) according to the equation (24). Become. Therefore, 410 mm is adopted as a specific value of L ₁ .

Since L ₁ = 410 mm is determined, the radius of curvature R ₁ of the reflecting surface 3a of the output mirror 3 is 820 mm ≤ R ₁ ≤ 1230 mm (51) according to the equation (27). Therefore, 1000 mm is adopted as a specific value of R ₁ .

Since R ₁ is set to 1000 mm, the distance L ₂ from the reflection surface 4a of the total reflection mirror 4 to the total reflection side main plane H of the YAG rod is 171.56 mm ≤ L ₂ from the equation (36). ... (52). Therefore, 282 mm is adopted as a specific value of L ₂ .

Since L ₂ = 282 mm is determined, the radius of curvature R ₂ of the reflecting surface 4a of the total reflection mirror 4 is R ₂ = 1983 mm (53) according to equation (30). Therefore, 2000 mm is adopted as a specific value of R ₂ .

On the other hand, since L ₁ = 410 mm is determined, the focal length f of the condenser lens 7 is 24.6 mm ≧ f ≧ 24.49 mm (54) from the formula (23). Therefore, 24.5 mm is adopted as a specific value of f.

When the solid-state laser device whose dimensions are determined as described above is excited by a flash lamp, the dependence of the divergence angle θ on the applied power is as shown in FIG.
It oscillated stably up to kW. At this time, the divergence angle θ changes only from 6 to 12.1 mrad. In particular, the divergence angle could be reduced by arranging the aperture in a relatively low output region (power input of 20 kW or less).
Laser power is 0 to 90 when input power is 0 to 30 kW
Obtained up to 0 W, radius R _F = 0.3 mm, NA = 0.2
Was able to enter the optical fiber of

[0077]

Comparative Example 1 Equations (22) to (25) shown above,
The following numerical values were substituted for each parameter determined by (27), (30) and (36).

That is, the laser medium 1 has a length of 195 m.
An Nd: YAG rod with m and radius R _L = 5 mm was used, and an optical fiber 8 with radius R _F = 0.3 mm and NA = 0.2 was used. Then, in comparison with the condition of 408 mm ≤ L ₁ ≤ 500 mm (55) obtained in Examples 1 and 2, 210 mm was adopted as a specific value of L ₁ .

Since L ₁ = 210 mm is determined, the radius of curvature R ₁ of the reflecting surface 3a of the output mirror 3 is 420 mm ≤ R ₁ ≤ 630 mm (56) according to the equation (27). However, as a specific value of R ₁ , ∞ mm (plane mirror) was adopted.

Since R ₁ = ∞ mm is determined, the distance L ₂ from the reflection surface 4a of the total reflection mirror 4 to the main plane H of the YAG rod on the total reflection side is 210 mm ≤ L ₂ ... (57) Therefore, 210 mm is adopted as a specific value of L ₂ .

Since L ₂ = 210 mm is determined, the radius of curvature R ₂ of the reflecting surface 4a of the total reflection mirror 4 is R ₂ = 1000 mm (58) according to the equation (30). However, as a specific value of R ₂ , ∞ mm (plane mirror) was adopted.

On the other hand, since L ₁ = 210 mm is determined, the focal length f of the condenser lens 7 is 12.6 mm ≧ f ≧ 24.49 mm (59) from the formula (23), and the formula (59) 23) will not hold. However, 24.5 mm was adopted as the specific value of f.

When the solid-state laser device having the dimensions as described above was excited by the flash lamp, the dependence of the divergence angle θ on the power applied to the lamp was as shown in FIG. 8, and the power oscillated stably from 0 to 40 kW. . At this time, the divergence angle θ is 0
To 21.4 mrad. Thus, a strong dependence of the divergence angle θ on the input power is recognized. The maximum laser output was 1000 W,
Since the divergence angle θ is large, the radius of the optical fiber R _F
Was 0.5 mm (NA = 0.2).

[0084]

Comparative Example 2 Formulas (22) to (25) shown above,
The following numerical values were substituted for each parameter determined by (27), (30) and (36).

That is, the laser medium 1 has a length of 195 m.
An Nd: YAG rod with m and radius R _L = 5 mm was used.
Then, it is configured such that it can be incident on the optical fiber 8 having a radius R _F = 0.3 mm and NA = 0.2. Then, in comparison with the condition of 408 mm ≤ L ₁ ≤ 500 mm (60) obtained in the cases of Examples 1 and 2, 346 mm was adopted as the specific value of L ₁ .

Since L ₁ = 346 mm is determined, the radius of curvature R ₁ of the reflecting surface 3a of the output mirror 3 is 692 mm ≤ R ₁ ≤ 1038 mm (61) according to the equation (27). However, as a specific value of R ₁ , ∞ mm (plane mirror) was adopted.

Since R ₁ = ∞ mm is determined, the distance L ₂ from the reflection surface 4a of the total reflection mirror 4 to the total reflection side principal plane H of the YAG rod is 346 mm ≤ L ₂ ... (62) Therefore, 346 mm is adopted as a specific value of L ₂ .

Since L ₂ = 346 mm is determined, the radius of curvature R ₂ of the reflecting surface 4a of the total reflection mirror 4 is R ₂ = 1000 mm (63) according to the equation (30). However, as a specific value of R ₂ , ∞ mm (plane mirror) was adopted.

On the other hand, since it is determined that L ₁ = 346 mm, the focal length f of the condenser lens 7 is 20.75 mm ≧ f ≧ 24.49 mm (64) from the expression (23), and the expression (64) 23) will not hold. However, 24.5 mm was adopted as the specific value of f.

When the solid-state laser device of which the dimensions are determined as described above is excited by the flash lamp, the dependence of the divergence angle θ on the applied power is as shown in FIG. 9, and the applied power to the lamp is 0.
Oscillated stably up to 30 kW. However, the divergence angle θ at this time changed from 0 to 14.4 mrad. Thus, a strong dependence of the divergence angle θ on the input power is recognized. Further, the laser output was obtained up to 900 W, but the radius R _F = 0.3 m only in the range of input power 0 to 20 kW, that is, in the range of laser output 0 to 580 W.
m could be incident on the optical fiber of NA = 0.2 without loss.

[0091]

COMPARATIVE EXAMPLE 3 Expressions (22) to (25),
The following numerical values were substituted for each parameter determined by (27), (30) and (36).

That is, the laser medium 1 has a length of 195 m.
An Nd: YAG rod with m and radius R _L = 5 mm was used.
Then, it is configured such that it can be incident on the optical fiber 8 having a radius R _F = 0.5 mm and NA = 0.2. In this case, the formula (2
According to 5), θ ≦ 20.4 mrad (65) must be satisfied.

At this time, the distance L ₁ from the reflecting surface 3a of the output mirror 3 to the output side main plane H ′ of the YAG rod is 245 mm ≦ L ₁ ≦ 2500 mm (66) according to the equation (24). Become. However, 210 mm was adopted as a specific value of L ₁ .

Since L ₁ = 210 mm is determined, the radius of curvature R ₁ of the reflecting surface 3a of the output mirror 3 is 420 mm ≤ R ₁ ≤ 630 mm (67) according to the equation (27). However, 5000 mm was adopted as a specific value of R ₁ .

Since R ₁ = 5000 mm is determined, the distance L ₂ from the reflecting surface 4 a of the total reflection mirror 4 to the total reflection-side main plane H of the YAG rod is 193 mm ≦ L _{2 according to} equation (36). (68) However, 210 mm was adopted as a specific value of L ₂ .

Since L ₂ = 210 mm is determined, the radius of curvature R ₂ of the reflecting surface 4a of the total reflection mirror 4 is R ₂ = 5000 mm (69) according to the equation (30). Therefore, 5000 mm is adopted as a specific value of R ₂ .

On the other hand, since L ₁ = 210 mm is determined, the focal length f of the condenser lens 7 is 21.0 mm ≧ f ≧ 24.49 mm (70) from the formula (23), and the formula (70) 23) will not hold. However, 24.5 mm was adopted as the specific value of f.

When the solid-state laser device having the dimensions as described above is excited by a flash lamp, the dependence of the divergence angle θ on the power supplied to the lamp is as shown in FIG.
From 40 kW to 40 kW. At this time, the divergence angle θ changed from 6.8 to 21.3 mrad. Thus, a strong dependence of the divergence angle θ on the input power is recognized. The laser output was obtained up to 1000 W, but since the divergence angle θ was large, the radius R _F of the optical fiber that could be incident was 0.5 mm (NA = 0.2).

[0099]

According to the present invention configured as described above, in a solid-state laser device having a large output, it becomes possible to make a laser beam enter an optical fiber having a small diameter through a condenser lens.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a general configuration of a solid-state laser device.

FIG. 2 is a diagram showing a configuration in which a solid-state laser device is used as a processing device.

FIG. 3 is a diagram illustrating dimensions of a laser medium and a mirror in FIG.

FIG. 4 is a graph showing a condition for eliminating the dependence of the divergence angle on the input power.

FIG. 5 is a graph showing input power-divergence angle characteristics in the first embodiment.

FIG. 6 is a graph showing input power-divergence angle characteristics in the second embodiment.

FIG. 7 is a graph showing input power-divergence angle characteristics in the third embodiment.

FIG. 8 is a graph showing input power-divergence angle characteristics in the first comparative example.

FIG. 9 is a graph showing input power-divergence angle characteristics in the second comparative example.

FIG. 10 is a graph showing input power-divergence angle characteristics in a third comparative example.

FIG. 11 is a graph showing the action of the present invention.

FIG. 12 is a graph showing input power-divergence angle characteristics in a conventional example.

FIG. 13 is a stability diagram showing the stability of a solid-state laser device.

FIG. 14 is a diagram showing a laser output characteristic when the input power is increased from A _{0 in} FIG.

FIG. 15 is a diagram showing changes in divergence angle.

[Explanation of symbols]

 1 Laser Medium 2 Excitation Lamp 3 Output Mirror 3a Reflecting Surface 4 Total Reflecting Mirror 4a Reflecting Surface 5 Laser Light 7 Condensing Lens 8 Optical Fiber 9 Condensing Lens System 10 Workpiece

Claims (7)

[Claims] 1. A solid-state laser medium, a laser medium pumping means for pumping the solid-state laser medium, and a laser light oscillated from the solid-state laser medium pumped by the laser-medium pumping means to totally reflect the solid-state laser medium. A total reflection mirror for returning the laser light oscillated from the solid-state laser medium excited by the laser-medium excitation means to return to the solid-state laser medium and to transmit the laser light to the outside. Of the output mirror, a lens for condensing the laser light transmitted through the output mirror, and an optical fiber on which the laser light condensed by the lens is incident, the radius of curvature of the output mirror is R ₁ , and the solid-state laser is the laser radius of the medium R _L, the core diameter of the optical fiber R _F, the numerical aperture of the optical fiber and NA, enters the lens When the beam radius was R _B, the distance L ₁ between the output side principal plane by thermal lens effect of the solid-state laser medium to said output-side _{mirror, R B R L / (R} F tan (sin -1 NA) ) ≤ L ₁ ≤ R
_The solid-state laser device having an optical system, wherein the focal length f of the lens is L ₁ R _F / R _L ≧ f ≧ R _B / tan (sin ⁻¹ NA). 2. The solid-state laser device according to claim ₁ , wherein the radius of curvature R ₁ of the output-side mirror reflection surface is 2L ₁ ≦ R ₁ ≦ 3L ₁ . 3. The distance L ₂ between the total reflection side mirror reflection surface and the total reflection side main plane of the solid-state laser medium is L ₁ (1-2L ₁ / (R ₁ + L ₁ )) ≦ L ₂ The solid-state laser device according to claim 1 or 2, characterized in that: 4. The radius of curvature R ₂ of the total reflection mirror is R ₂ = L ₂ ² R ₁ / (L ₁ ² + (L ₂ −L ₁ ) R ₁ ). 4. The solid-state laser device according to any one of 4 above. 5. The solid-state laser device according to claim 1, further comprising a member for limiting a beam diameter of laser light provided between the output-side mirror and the solid-state laser medium. 6. The solid-state laser device according to claim 1, further comprising a member for limiting a beam diameter of a laser beam provided between the total reflection side mirror and the solid-state laser medium. . 7. A solid laser medium, a laser medium pumping means for pumping the solid laser medium, and a laser light oscillated from the solid laser medium pumped by the laser medium pumping means for totally reflecting the solid laser medium to obtain the solid laser medium. A total reflection mirror for returning the laser light oscillated from the solid-state laser medium excited by the laser-medium excitation means to return to the solid-state laser medium and to transmit the laser light to the outside. Of the output mirror, a lens for condensing the laser light transmitted through the output mirror, and an optical fiber on which the laser light condensed by the lens is incident, the radius of curvature of the output mirror is R ₁ , and the solid-state laser is the radius of the medium R _L, when the core diameter of the optical fiber and R _F, the numerical aperture of the optical fiber and NA, Netsure of the solid-state laser medium Distance L ₁ between the output side principal plane by's effect to the output side ^{_{mirror, R L 2 / (R F}} tan (sin -1 NA)) ≦ L 1 ≦ R 1
/ 2, the focal length of the lens, the solid-state laser apparatus having an optical system, which is a _{L 1 R F / R L ≦} f ≦ R L / tan (sin -1 NA).