JPH063511A - Optical thin film and laser device - Google Patents

Abstract

PURPOSE:To provide the optical thin film optimum as an output mirror of a laser device which make highly repetitive oscillation, an optical filter for shaping the intensity distribution of a laser beam, etc., and the laser device constituted by using this optical thin film. CONSTITUTION:This optical thin film is constituted by constituting one of the thin films, exclusive of the uppermost layer and the lowermost layer, of the plural thin films formed on a substrate, of a thin film having an optical film thickness distribution. The reflectivity distribution from the central part to the peripheral edge of the optical thin film is provided with a gaussian distribution by adequately selecting the optical film thicknesses of the other thin films. In addition, the min. reflectivity in the part corresponding to the skirt of the gaussian distribution is higher than the surface reflectivity of the substrate. The arbitrary setting of the reflectivity distribution is possible and the electric field intensity distribution within the thin films and at the boundaries of the thin films is easily decreased. The optical thin film usable as the laser device which can efficiently oscillate the laser beam of good mode patterns with high repetitions, the optical filter for shaping the intensity distribution of the laser beam, etc., and the laser device constituted by using this optical thin film are thus obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical thin film that can be used as a reflection mirror, a filter, etc., and a laser device using this optical thin film as a mirror for a resonator.

[0002]

2. Description of the Related Art Recently, attempts have been made to obtain laser light having a good mode pattern by using a so-called Gaussian mirror as an output mirror of a laser resonator. The Gaussian mirror has a reflectance distribution that follows a Gaussian function or a super Gaussian function with respect to the distance from the center of the mirror.

FIG. 13 shows the reflectance distribution characteristics of a conventional Gaussian mirror. In FIG. 13, the horizontal axis represents the distance (mm) from the center of the mirror, and the vertical axis represents the reflectance (%). As shown in FIG. 13, this Gaussian mirror has a peak reflectance of 55% at normal incidence.
And the minimum reflectance at the foot of the Gaussian distribution is 3%.

FIG. 14 is a view showing the film structure of this conventional Gaussian mirror. As shown in FIG. 14, the Gaussian mirror has a structure in which an I layer 101,
The second layer 102 and the third layer 103 are sequentially stacked. The I-th layer 101 and the III-th layer 103 are high refractive index layers (H layers) made of TiO ₂ thin films, and the II-layer 102 is made of SiO ₂ thin films and low refractive index layers (L layers).
Is. The substrate 100 is made of optical glass BSC7 (trade name of HOYA Co., Ltd.), and its refractive index n _s =
It is 1.51. Further, the refractive index n _{H of the} H layer (TiO ₂ )
= 2.15, refractive index of L layer (SiO ₂ ) n _L = 1.45
Is. Here, the III-th layer 103 (H layer) is an optical film thickness distribution layer. Optical film thickness, the first I layer 101 and the layer II 102 is lambda _0/4 with respect to the wavelength lambda ₀ = 1064 nm together, layer III 103 x · λ _0/4 (x
= 0 to 1.0). In such a film structure,
The reflectivity at each part of the mirror is the uppermost layer III
It depends on the optical thickness of the corresponding portion of the layer 103. FIG. 15 shows this relationship. 15, the horizontal axis is the film thickness of any portion of the mirror (expressed in optical thickness, expressed as a percentage relative to it when the lambda _0/4 and 1), the vertical axis the reflectance of the part ( %). Therefore, by setting the optical film thickness distribution of the third layer 103 to the distribution according to the Gaussian function as shown in FIG. 16, the reflectance distribution of the mirror becomes the super Gaussian distribution as shown in FIG. be able to. The film structure shown in FIG. 14 is expressed as follows.

Sub / (HL) ¹ x · H / Air FIG. 17 is a diagram showing the reflectance distribution of another example of the conventional Gaussian mirror. This example is an example in which the peak reflectance is 95% and the minimum reflectance in the foot of the Gaussian distribution is 4%. In this example, the film structure is Sub / (HL) ² x · H (LH) ² / Air. FIG. 18 shows this film structure.
The H and L thin films are alternately stacked on the substrate 100 to form the I layer 1
It is formed in nine layers from 11 to IX layer 119. In this case, the Vth layer 115 is an optical film thickness distribution layer. The material and the refractive index of the L and H thin films and the substrate 10
The material and the like of 0 are the same as in the above example. In this case, the reflectance of each part of the mirror depends on the optical film thickness of the corresponding part of the V-th layer 115. FIG. 19 shows this relationship. Here, the horizontal axis and the vertical axis in FIG. 19 are the same as those in FIG. Therefore, the V-th layer 1
By setting the optical film thickness distribution of 15 to a distribution according to the Gaussian function as shown in FIG. 16 described above, the reflectance distribution of the mirror can be made a super Gaussian distribution as shown in FIG. .

By using the above-mentioned Gaussian mirror as the output mirror, it is possible to construct a pulse oscillation YAG laser device capable of efficiently oscillating high-quality pulse laser light having a repetition rate of 1 to several + Hz, for example.

The optical thin film having the above structure can be used also as an optical filter whose transmittance distribution follows a Gaussian function, for example, as a filter for shaping a laser beam intensity distribution.

[0008]

By the way, in recent years, a high repetition pulse oscillation YAG having a repetition rate of 100 Hz or more.
Laser and pseudo CW oscillation (continuous pulse oscillation) YAG laser,
Further, since the CW oscillation YAG laser has been used for various purposes, demands for improvement of oscillation efficiency and improvement of durability have become stricter accordingly. This situation applies to glass lasers and titanium sapphire lasers as well as YAG lasers. Therefore, as a method for responding to such a demand, a method using the above-mentioned conventional Gaussian mirror has been studied.

However, if the above-mentioned conventional Gaussian mirror is applied as it is to a laser device of high repetition oscillation,
It was found that repeated oscillations were hindered or durability was problematic. Therefore, when the cause of this is investigated, when the above-mentioned conventional Gaussian mirror is used as an output mirror of a laser device with high repetition oscillation,
It has been found that the gain per pulse is too low, which tends to cause a shortage of energy stored inside the laser oscillator, and the oscillation energy per pulse is high, which accelerates damage to optical components. In particular, it has been found that the electric field strength becomes extremely high in the minimum reflectance portion corresponding to the foot of the Gaussian distribution, which lowers the laser damage threshold value.

Also, when used as an optical filter, the above-mentioned conventional optical thin film has a transmittance close to 100% at the foot of the Gaussian distribution.
For example, when used as a laser beam intensity distribution shaping filter for shaping the intensity distribution of a laser beam in a mode where there are ripples on both sides of the peak of the intensity distribution curve of the beam cross section, this ripple can be removed. No
There is a disadvantage that the intensity distribution cannot be made uniform.

The present invention has been made under the above-mentioned background, and an output mirror of a laser device capable of efficiently oscillating a laser beam having a good mode pattern with high repetition and an optical filter for shaping a laser beam intensity distribution. It is an object of the present invention to provide an optical thin film that can be used as a laser and a laser device using the optical thin film.

[0012]

In order to solve the above problems, an optical thin film according to the present invention is (1) an optical thin film formed by stacking a plurality of thin films made of substances having different refractive indexes on a substrate. And the reflectance distribution from the center to the periphery has a distribution represented by a Gaussian function or a super Gaussian function, and the minimum reflectance of the portion that is the skirt of the Gaussian function or the super Gaussian function is the surface reflection of the substrate. Higher than the rate,
An optical thin film in which at least one thin film excluding the uppermost layer and the lowermost layer of the plurality of thin films has an optical film thickness distribution represented by a Gaussian function or a super Gaussian function from the central portion toward the peripheral edge. Therefore, the film structure of the plurality of thin films has a structure represented by any of the following general expressions (1) to (4).

However, the meaning of the notation is as follows.

Arrangement rule of each symbol: Indicates that the constituent elements indicated by each symbol are arranged in the arrangement order as shown.

Sub: represents a substrate.

H: represents a thin film of a high refractive index material.

L: A thin film of a low refractive index material.

[0018] αH; with respect to the center wavelength _{λ 0, α × λ 0/} 4
3 represents a thin film of a high refractive index material having an optical thickness of

[0019] αL; with respect to the center wavelength _{λ 0, α × λ 0/} 4
3 represents a thin film of a low refractive index material having an optical thickness of

[0020] βH; with respect to the center wavelength _{λ 0, β × λ 0/} 4
3 represents a thin film of a high refractive index material having an optical thickness of

[0021] βL; with respect to the center wavelength _{λ 0, β × λ 0/} 4
3 represents a thin film of a low refractive index material having an optical thickness of

Air: Represents air or the outside.

(ΑHαL) ^m : A film structure in which a thin film of a low refractive index material is formed on a thin film of a high refractive index material is taken as one unit, and the unit film structure is formed m times. .

Sub / (αHαL) ^m ; on the substrate (α
It indicates that a thin film having a film structure of HαL) ^m is formed.

X · H: A thin film of a high refractive index substance having an optical film thickness distribution from the center to the periphery.

X.L: a thin film of a low refractive index substance having an optical film thickness distribution from the center to the periphery.

X = 0 to 1.0; the range of the optical thickness of a thin film having an optical thickness distribution represented by x · H or x · L is a predetermined thickness multiplied by a coefficient of 0 to 1. It means that it is a thing.

(ΑHαL) ^m x · H; (αHαL) ^m
It means that a thin film of x · H is formed on the thin film of.

(ΒLβH) ^{m ′} ; a film structure in which a thin film of a high refractive index substance is formed on a thin film of a low refractive index substance as one unit, and the unit film constitution is formed m ′ times. Represents

(ΒLβH) ^{m '} / Air; (βLβH)
^{m '} indicates that the uppermost layer of the membrane is in contact with air or the outside.

(1) Sub / (αHαL) ^m x · H
(ΒLβH) ^{m '} / Air where α ≠ 1.00 and β ≠ 1.00 or α ≠ 1.00 and β = 1.00 or α = 1.00 and β ≠ 1.00 and m and m ′ is an integer of 1 or more, and x = 0 to 1.0.

[0032] (2) Sub / (αHαL) m x · L
(ΒLβH) ^{m '} / Air where α ≠ 1.00 and β ≠ 1.00 or α ≠ 1.00 and β = 1.00 or α = 1.00 and β ≠ 1.00 and m and m ′ is an integer of 1 or more, and x = 0 to 1.0.

(3) Sub / (αLαH) ^m x · H
(ΒHβL) ^{m '} / Air where α ≠ 1.00 and β ≠ 1.00 or α ≠ 1.00 and β = 1.00 or α = 1.00 and β ≠ 1.00 and m and m ′ is an integer of 1 or more, and x = 0 to 1.0.

[0034] (4) Sub / (αLαH) m x · L
(ΒHβL) ^{m '} / Air where α ≠ 1.00 and β ≠ 1.00 or α ≠ 1.00 and β = 1.00 or α = 1.00 and β ≠ 1.00 and m and m ′ is an integer of 1 or more, and x = 0 to 1.0.

Further, the laser apparatus according to the present invention comprises (2) a laser medium, a light source for exciting the laser medium, and a plurality of mirrors for reflecting at least a part of the laser light generated by the laser medium. In a laser device having a laser resonator, at least one of the mirrors forming the resonator is formed of the optical thin film described in the structure 1.

[0036]

According to the film structure 1 described above, an output mirror of a laser device capable of efficiently and repeatedly oscillating a laser beam having a good mode pattern and an optical thin film that can be used as an optical filter for shaping a laser beam intensity distribution. Obtainable. In this case, by appropriately selecting the values of α and β, the reflectance distribution can be arbitrarily set, so that the design flexibility can be remarkably widened and the electric field strength distribution in the thin film and the thin film interface can be reduced. It is also possible easily. Further, according to Configuration 2, it is possible to obtain a laser device that can efficiently and repeatedly oscillate laser light having a good mode pattern.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical thin film and a laser device according to embodiments of the present invention will be described below with reference to the drawings. In the following description, first, an embodiment of an optical thin film will be described, and then an embodiment of a laser device using this optical thin film will be described.

(Example of Optical Thin Film) Example 1 In this example, the reflectance distribution from the center to the periphery has a distribution represented by a Gaussian function, and the peak reflectance is 94.
%, An optical thin film having a minimum reflectance of 26% in the skirt portion of the Gaussian distribution and a radius of the film thickness distribution of 1.5 mm, and an example of forming a circular Gaussian mirror that can be used as an output mirror of a laser device. Is. In addition,
The reflectance in this case is for vertical incidence of light having a wavelength λ = 1064 nm, and the same applies to the following examples.
FIG. 1 is a diagram showing the reflectance distribution characteristics of the optical thin film according to this embodiment. In FIG. 1, the horizontal axis represents the distance (mm) from the center of the mirror, and the vertical axis represents the reflectance (%).

FIG. 2 is a view showing the film structure of the optical thin film of this embodiment. The film structure shown in FIG. 2 is expressed by the general notation: Sub / (αHαL) ^m x · H (βLβH) ^{m '} /
Air (α ≠ 1.00 and β ≠ 1.00, or α ≠ 1.0
0 and β = 1.00, or α = 1.00 and β ≠
1.00, m and m ′ are integers of 1 or more, and x
= 0 to 1.0. ), In the film structure represented by
= 2, m ′ = 2, α = 1.06, β = 1.00, the total number of layers is 9, and the fifth layer (Vth layer) is an optical film thickness distribution layer. .

However, the meanings of the notations are as follows, and the same applies to the following examples.

Arrangement rule of each symbol: Indicates that the constituent elements indicated by each symbol are arranged in the arrangement order as shown.

Sub: represents a substrate.

H: A thin film of a high refractive index material.

L: represents a thin film of a low refractive index material.

[0045] αH; with respect to the center wavelength _{λ 0, α × λ 0/} 4
3 represents a thin film of a high refractive index material having an optical thickness of

[0046] αL; with respect to the center wavelength _{λ 0, α × λ 0/} 4
3 represents a thin film of a low refractive index material having an optical thickness of

[0047] βH; with respect to the center wavelength _{λ 0, β × λ 0/} 4
3 represents a thin film of a high refractive index material having an optical thickness of

[0048] βL; with respect to the center wavelength _{λ 0, β × λ 0/} 4
3 represents a thin film of a low refractive index material having an optical thickness of

Air: Represents air or the outside.

(ΑHαL) ^m : A film structure in which a thin film of a low refractive index material is formed on a thin film of a high refractive index material is taken as one unit, and the unit film structure is formed m times. .

Sub / (αHαL) ^m ; on the substrate (α
It indicates that a thin film having a film structure of HαL) ^m is formed.

X · H: A thin film of a high refractive index substance having an optical film thickness distribution from the center to the periphery.

X.L: a thin film of a low refractive index substance having an optical film thickness distribution from the central portion toward the peripheral edge.

X = 0 to 1.0; the range of the optical thickness of a thin film having an optical thickness distribution represented by x · H or x · L is a predetermined thickness multiplied by a coefficient of 0 to 1. It means that it is a thing.

(ΑHαL) ^m x · H; (αHαL) ^m
It means that a thin film of x · H is formed on the thin film of.

(ΒLβH) ^{m ′} ; a film structure in which a film structure in which a thin film of a high refractive index material is formed on a thin film of a low refractive index material is taken as one unit, and the unit film structure is formed m ′ times. Represents

(ΒLβH) ^{m '} / Air; (βLβH)
^{m '} indicates that the uppermost layer of the membrane is in contact with air or the outside.

As shown in FIG. 2, this optical thin film
On the substrate 10, the I layer 11, the II layer 12, the III layer 13, the IV layer 14, the V layer 15, the VI layer 16, and the V layer
The II layer 17, the VIII layer 18, and the IX layer 19 are sequentially stacked to form a nine layer. Layer I 11, Layer II
I layer 13, V layer 15, VII layer 17, and IX layer 1
9 is a high refractive index layer (H layer) made of a TiO ₂ thin film, and the II layer 12, the IV layer 14, the VI layer 16 and the VIII layer 18 are made of a SiO ₂ thin film to a low refractive index layer (L layer).
Layer).

The substrate 10 is a borosilicate optical glass BSC7.
(Trade name of HOYA Co., Ltd.), and its refractive index n _s = 1.51 and surface reflectance R _s = 4.1%. Further, the refractive index n _H = 2.15 of the H layer (TiO ₂ ),
The refractive index n _{L of the} L layer (SiO ₂ ) is 1.45. Here, the V-th layer 15 (H layer) is an optical film thickness distribution layer.

[0060] Optical film thickness, with respect to the wavelength lambda ₀ = 1064 nm, the I layer 11, layer II 12, III, layer 13 and layer IV 14 is 1.06 × λ _0/4, the VI layer 16, VII layer 17, VIII layer 18, and IX layer 1
9 with a 1.00 × λ _0/4, the V layer 15 is x · λ ₀ /4(x=0~1.0).

In such a film structure, the reflectance of each part of the mirror is determined depending on the optical film thickness of the corresponding part of the V-th layer 15. FIG. 3 shows this relationship. 3, the horizontal axis (as shown in case of a lambda _0/4 to 1 as a ratio to it) an optical film thickness of any portion of the mirror, the reflectance of the vertical axis portion thereof (%). Therefore, by setting the optical film thickness distribution of the V-th layer 15 to the distribution according to the Gaussian function as shown in FIG. 16, the reflectance distribution of the mirror becomes the super Gaussian distribution as shown in FIG. be able to. To form such a thin film, a well-known thin film forming technique such as vacuum deposition or sputtering can be used. Also,
To obtain the optical film thickness distribution, there are a method of changing the physical film thickness by using an optically uniform thin film and a method of providing a distribution in the refractive index while keeping the physical film thickness constant. . To implement the former method, it is possible to apply a method of covering the front surface of the substrate with a mask having appropriate small holes at the center during vacuum vapor deposition and depositing fine particles scattered from the evaporation source through the small holes on the substrate. (For details, refer to the specification of Japanese Patent Application No. 2-294736). In addition, the latter method is a diffusion method,
It can be carried out by diffusing substances having different refractive indexes into a thin film having a predetermined refractive index. In that case, for example, the refractive index distribution with respect to the distance X from the center to the periphery is
A Gaussian distribution represented by the following formula may be used.

N = N ₀ · exp [−2 (X / w) ⁿ ] where N: Refractive index X; Distance from center to peripheral edge N ₀ = 2.15 w = 1.50 n = 2.00 To do.

Example 2 In this example, the film structure is expressed in general terms as follows: Sub / (αHαL) ^m x L (βLβH) ^{m '} /
Air (α ≠ 1.00 and β ≠ 1.00, or α ≠ 1.0
0 and β = 1.00, or α = 1.00 and β ≠
1.00, m and m ′ are integers of 1 or more, and x
= 0 to 1.0. ), In the film structure represented by
= 4, m ′ = 3, α = 1.00, β = 1.02, the total number of layers is 15, and the ninth low-refractive index material layer (L layer) is counted from the substrate side. The film thickness distribution layer is used. This gives a peak reflectance of 99% and a minimum reflectance of 40.
This is an example in which an optical thin film having a reflectance distribution of%, which can be used as a mirror similar to the case of Example 1, is configured. In addition,
The material, the refractive index, the optical film thickness, the substrate material, and the like of each of the L and H thin films are the same as those in the first embodiment.

In such a film structure, the reflectance of each part of the mirror is determined depending on the optical film thickness of the corresponding part of the thin film of the ninth layer. FIG. 4 shows this relationship. In FIG. 4, the relationship between the horizontal axis and the vertical axis is the same as in FIG. Therefore, by setting the optical film thickness distribution of the ninth layer to a distribution according to the Gaussian function as shown in FIG. 16, the reflectivity distribution of the mirror is changed to the peak reflectivity 99.
%, The minimum reflectance is 40%, and a super Gaussian distribution as shown in FIG. 5 can be used. The relationship between the horizontal axis and the vertical axis in FIG. 5 is the same as in FIG.

Example 3 In this example, the film structure is expressed in the general notation: Sub / (αLαH) ^m x · H (βHβL) ^{m '} /
Air (α ≠ 1.00 and β ≠ 1.00, or α ≠ 1.0
0 and β = 1.00, or α = 1.00 and β ≠
1.00, m and m ′ are integers of 1 or more, and x
= 0 to 1.0. ), In the film structure represented by
= 4, m ′ = 5, α = 1.03, β = 1.02, the total number of layers is 19, and the ninth high refractive index layer (H layer) counted from the substrate side is an optical film. It is a thickness distribution layer. This is an example in which an optical thin film having a reflectance distribution with a peak reflectance of 99% and a minimum reflectance of 82%, which can be used as a mirror similar to the case of the first embodiment, is configured. In addition, L, H
The material of each thin film, the refractive index, the optical film thickness, the material of the substrate, and the like are the same as in the first embodiment.

In such a film structure, the reflectance of each part of the mirror is determined depending on the optical film thickness of the corresponding part of the thin film of the ninth layer. FIG. 6 shows this relationship. In FIG. 6, the relationship between the horizontal axis and the vertical axis is the same as in FIG. Therefore, by setting the optical film thickness distribution of the third layer to the distribution according to the Gaussian function as shown in FIG.
%, And the minimum reflectance is 82%, which can be a super Gaussian distribution as shown in FIG. The relationship between the horizontal axis and the vertical axis in FIG. 7 is the same as in FIG.

[0067] This Example Example 4, the general notation film ^{structure, Sub / (αLαH) m x} · L (βHβL) m '/
Air (α ≠ 1.00 and β ≠ 1.00, or α ≠ 1.0
0 and β = 1.00, or α = 1.00 and β ≠
1.00, m and m ′ are integers of 1 or more, and x
= 0 to 1.0. ), In the film structure represented by
= 3, m ′ = 4, α = 0.97, β = 1.11, the total number of layers is 15, and the seventh low refractive index layer (L layer) is the optical thickness when counted from the substrate side. It is a distribution layer. This is an example in which an optical thin film having a reflectance distribution with a peak reflectance of 97% and a minimum reflectance of 66%, which can be used as a mirror similar to the case of the first embodiment, is configured. The materials of the L and H thin films, the refractive index, the optical film thickness, the material of the substrate and the like are the same as those in the first embodiment.

In such a film structure, the reflectance of each part of the mirror is determined depending on the optical film thickness of the corresponding part of the thin film of the seventh layer. FIG. 8 shows this relationship. In FIG. 8, the relationship between the horizontal axis and the vertical axis is the same as in FIG. Therefore, by setting the optical film thickness distribution of the seventh layer to the distribution according to the Gaussian function as shown in FIG.
%, The minimum reflectance is 66%, and a super Gaussian distribution as shown in FIG. 9 can be used. The relationship between the horizontal axis and the vertical axis in FIG. 9 is the same as in FIG.

In each of the above embodiments, the optical glass BSC7 is used as the substrate, but it may be a transparent material such as another optical glass. In addition to TiO ₂ , high refractive index substances such as ZrO ₂ , Ta ₂ O ₅ , Z
It may be rTiO ₄ , ZnSe, ZnS or the like, and the low refractive index substance may be, for example, MgF ₂ or the like in addition to SiO ₂ .

Further, an overcoat or an undercoat may be formed on the front and back portions of the multilayer film in order to enhance resistance to laser damage, environmental resistance, or adhesion to the substrate. The overcoat is formed on the uppermost layer of the multilayer film, that is, at a portion in contact with the outside (Air), and the undercoat is formed under the lowermost layer of the multilayer film, that is, at a portion in contact with the substrate. These are usually λ / 2 films (half-wavelength films) so as not to affect the optical characteristics of the entire multilayer film. In addition, as the material for the coat, a low-refractive index substance is often used in the sense of increasing resistance to laser damage, but in the case of an undercoat for the purpose of enhancing adhesion to a substrate, a substance other than the low-refractive index substance is used Sometimes. In this way, the film structure when the overcoat and the undercoat are added is represented by the following general notation.

Sub / 2L (αHαL) ^m x · H
(ΒLβH) ^{m '} 2L / Air In this notation, both the overcoat and the undercoat are made of a low refractive index material, and the optical film thickness is λ /
2 (indicated by 2L).

(Embodiment of Laser Device) Embodiment 5 FIG. 10 is a diagram showing a main configuration of a laser device according to an embodiment of the present invention. This embodiment is a CW oscillation YAG laser device using the optical thin film according to the present invention as an output mirror.

As shown in FIG. 10, in this laser device, a mirror 2 having a highly reflective film formed on a concave glass surface is provided on both sides of the Nd: YAG laser rod 1 in the laser optical path, and a reflecting surface is emitted with a convex surface. An output mirror 3 having a meniscus lens shape as a whole and a concave surface complementary to this convex surface is arranged.

The output mirror 3 has the same structure as that of the optical thin film shown in each of the above-described embodiments, and has a multi-layered film formed on the surface of the convex portion of the optical glass substrate having a meniscus lens shape. An AR coat 3a for antireflection is formed on the concave portion. The output mirror 3 has a distribution in which the reflectance of the convex surface follows the Super Gaussian function represented by the following equation.

R (X) = R ₀ · exp [−2 (X / w) ⁿ ] + Rmin where X: distance from substrate center R ₀ ; R _p −R _min R _p ; peak reflectance = 95% R _min ; minimum reflectance = 50% n; super Gaussian factor = 3.5 w; spot diameter = 1.1 mm. FIG. 11 shows the reflectance distribution curve expressed by the above equation, where the horizontal axis of the figure is the distance (X) from the substrate,
The vertical axis represents the reflectance (R (X)).

Further, FIG. 12 shows the oscillation characteristics of the CW oscillation YAG laser device of this embodiment in which a Gaussian mirror is used as an output mirror and a normal mirror (Nor having no reflectance distribution only for the output mirror.
The conventional C is the same as the present embodiment except that a hard aperture having a hole diameter of 1.5 mmφ is inserted between the output mirror and the laser rod instead of the mal mirror.
It is the figure which compared and showed the oscillation characteristic of a W oscillation YAG laser apparatus. In FIG. 12, the horizontal axis represents the input power (KW) of pumping light and the vertical axis represents the power (W) of output laser light. The three-dimensional view of FIG. 12 shows the Near f of the output beam.
shows the field pattern, and ηslope shows the slope of the straight line in the input / output characteristic diagram.

It can be seen from FIG. 12 that the oscillation characteristics of this embodiment are extremely excellent, although they are all single mode oscillations. For example, comparing the case where the input power is 1.4 KW, 2.6 in the present embodiment (Gaussian mirror).
6W (M ² = 1.4, B = 120 MW / cm ² · Sr)
Output power of 1.04 W (M ² = 1.3, B = 54 MW) in the conventional example (normal mirror).
/ Cm ² · Sr) output power can only be obtained. In addition,
Here, M ² is a so-called M ² factor, B is flatness (luminance), and B = Power / (πθW
₀ ) ² = Power / (M ² λ) ² (however, Power
r: laser output [W], θ: beam divergence angle [rad],
W ₀ : Spot radius [cm] at the beam waist,
λ; wavelength [cm]). And in this case,
In this example, CW oscillation was performed smoothly, no laser damage was observed, and the durability was extremely excellent.

In the above embodiments, the case where the optical thin film of one embodiment is used as the output mirror of the laser device has been described, but it can also be used as an optical filter whose transmittance distribution follows the Gaussian function. As such an optical filter, for example, there is a laser beam intensity distribution shaping filter for uniformizing the electric field intensity of each spatial mode when a plurality of spatial modes occur in the laser light. When the optical filter of one embodiment is applied to this laser beam intensity distribution shaping filter, for example, even in a laser beam in a mode where there are ripples on both sides of the peak of the intensity distribution curve of the beam cross section, the ripple is removed. It is possible to obtain laser light having a uniform distribution.

Further, the substrate may be made of borosilicate glass such as BSC7, or may be made of quartz glass or other glass or other material.

[0080]

As described above in detail, according to the present invention, at least one of the thin films excluding the uppermost layer and the lowermost layer of a plurality of thin films made of substances having different refractive indexes, which are formed by being stacked on the substrate, is optically used. A distribution in which the reflectance distribution from the central portion to the peripheral edge is represented by a Gaussian function or a super Gaussian function by being configured with a film thickness distribution and by appropriately selecting the optical film thickness of another thin film. And the minimum reflectance of the portion corresponding to the skirt of the function is higher than the surface reflectance of the substrate, the reflectance distribution can be set arbitrarily and the degree of freedom in design is excellent. An output mirror of a laser device that can easily reduce the electric field intensity distribution at the interface and efficiently oscillate a laser beam having a good mode pattern with high repetition, and an optical filter for shaping the laser beam intensity distribution. To obtain a laser apparatus using the optical thin film and optical films can be used as such.

[Brief description of drawings]

FIG. 1 is a diagram showing a reflectance distribution of an optical thin film of Example 1 of the present invention.

FIG. 2 is a diagram showing a film configuration of an optical thin film of Example 1.

FIG. 3 is a diagram showing the relationship between the film thickness of the film thickness distribution layer and the reflectance of the optical thin film of Example 1.

FIG. 4 is a diagram showing the relationship between the film thickness of a film thickness distribution layer and the reflectance of an optical thin film of Example 2.

5 is a diagram showing a reflectance distribution of the optical thin film of Example 2. FIG.

FIG. 6 is a diagram showing the relationship between the film thickness of the film thickness distribution layer and the reflectance of the optical thin film of Example 3.

7 is a diagram showing a reflectance distribution of the optical thin film of Example 3. FIG.

FIG. 8 is a diagram showing the relationship between the film thickness of the film thickness distribution layer and the reflectance of the optical thin film of Example 4.

9 is a diagram showing a reflectance distribution of the optical thin film of Example 4. FIG.

FIG. 10 is a diagram showing a configuration of a laser device according to an example (Example 5) of the present invention.

FIG. 11 is a diagram showing a reflectance distribution of an output mirror of Example 5;

FIG. 12 is a diagram comparing the oscillation characteristics of the laser device of Example 5 and a conventional laser device.

FIG. 13 is a diagram showing a reflectance distribution of a conventional Gaussian mirror.

14 is a diagram showing a film configuration of the Gaussian mirror shown in FIG.

FIG. 15 is a diagram showing the relationship between the film thickness of a film thickness distribution layer and the reflectance of an optical thin film in a conventional example.

FIG. 16 is a diagram showing a film thickness distribution of a film thickness distribution layer.

FIG. 17 is a diagram showing a reflectance distribution of another conventional Gaussian mirror.

FIG. 18 is a diagram showing a film structure of another conventional example.

FIG. 19 is a diagram showing the relationship between the film thickness of the film thickness distribution layer and the reflectance of the optical thin film in another conventional example.

[Explanation of symbols]

1 ... YAG laser rod, 2 ... Total reflection mirror, 3 ... Output mirror, 10, 100 ... Substrate, 11, 111, 101 ...
Layer I, 12, 102, 112 ... Layer II, 13, 10
3, 113 ... Layer III, 14, 114 ... Layer IV, 1
5, 115 ... V layer, 16, 116 ... VI layer, 17,
117 ... VIIth layer, 18, 118 ... VIIIth layer, 1
9, 119 ... Layer IX.

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[Procedure amendment]

[Submission date] July 8, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0077

[Correction method] Change

[Correction content]

It can be seen from FIG. 12 that the oscillation characteristics of this embodiment are extremely excellent, although they are all single mode oscillations. For example, comparing the case where the input power is 1.4 KW, 2.6 in the present embodiment (Gaussian mirror).
6W (M ² = 1.4, B = 120 MW / cm ² · Sr)
Output power of 1.04 W (M ² = 1.3, B = 54 MW) in the conventional example (normal mirror).
/ Cm ² · Sr) output power can only be obtained. In addition,
Here, M ² is a so-called M ² factor, B is brightness (luminance), and B = Power / (πθW
₀ ) ² = Power / (M ² λ) ² (however, Power
r: laser output [W], θ: beam divergence angle [rad],
W ₀ : Spot radius [cm] at the beam waist,
λ; wavelength [cm]). And in this case,
In this example, CW oscillation was performed smoothly, no laser damage was observed, and the durability was extremely excellent.

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 18

[Correction method] Change

[Correction content]

FIG. 18

Claims (2)

[Claims] 1. An optical thin film formed by stacking a plurality of thin films made of substances having different refractive indexes on a substrate, wherein a reflectance distribution from a central portion to a peripheral portion is expressed by a Gaussian function or a super Gaussian function. And a minimum reflectance of a portion corresponding to the skirt of the Gaussian function or the super Gaussian function is higher than the surface reflectance of the substrate, and at least one of the thin films excluding the uppermost layer and the lowermost layer of the plurality of thin films. The thin film is an optical thin film having an optical film thickness distribution represented by a Gaussian function or a super Gaussian function from the central portion toward the periphery, the film configuration of the plurality of thin films is the following (1) ~ ( An optical thin film having a structure represented by any one of 4). However, the meaning of the notation is as follows. Arrangement rule of each symbol: Indicates that the constituent elements indicated by each symbol are arranged in the arrangement order as shown. Sub: represents a substrate. H: represents a thin film of a high refractive index substance. L: represents a thin film of a low refractive index material. .alpha.H; with respect to the center wavelength lambda _0, represents a thin film of high refractive index material having an optical film thickness of the α × λ _0/4. .alpha.L; with respect to the center wavelength lambda _0, represents a thin film of low refractive index material having an optical film thickness of the α × λ _0/4. BetaH; with respect to the center wavelength lambda _0, represents a thin film of high refractive index material having an optical film thickness of the β × λ _0/4. .beta.L; with respect to the center wavelength lambda _0, represents a thin film of low refractive index material having an optical film thickness of the β × λ _0/4. Air; represents air or the outside. (ΑHαL) ^m ; A film structure in which a thin film of a low refractive index substance is formed on a thin film of a high refractive index substance is taken as one unit, and the unit film structure is formed m times. Sub / (αHαL) ^m ; indicates that a thin film having a film structure of (αHαL) ^m is formed on the substrate. x · H: A thin film of a high refractive index substance having an optical film thickness distribution from the central portion toward the peripheral edge. x · L: a thin film of a low refractive index substance having an optical film thickness distribution from the central portion toward the peripheral edge. x = 0 to 1.0; the range of the optical thickness of the thin film having the optical thickness distribution represented by x · H or x · L is a predetermined thickness multiplied by a coefficient of 0 to 1. Indicates that there is. (ΑHαL) ^m x · H; represents that a thin film of x · H is formed on the thin film of (αHαL) ^m . (ΒLβH) ^{m ′} : A film structure in which a thin film of a high refractive index material is formed on a thin film of a low refractive index material is taken as one unit, and the unit film structure is formed m ′ times. (ΒLβH) ^{m '} / Air; (βLβH) ^m' represents that the uppermost layer of the film is in contact with air or the outside. (1) Sub / (αHαL) ^m x · H (βLβH)
^{m ′} / Air where α ≠ 1.00 and β ≠ 1.00 or α ≠ 1.00 and β = 1.00 or α = 1.00 and β ≠ 1.00 and m and m ′ are It is an integer of 1 or more and x = 0 to 1.0. (2) Sub / (αHαL) ^m x · L (βLβH)
^{m ′} / Air where α ≠ 1.00 and β ≠ 1.00 or α ≠ 1.00 and β = 1.00 or α = 1.00 and β ≠ 1.00 and m and m ′ are It is an integer of 1 or more and x = 0 to 1.0. (3) Sub / (αLαH) ^m x · H (βHβL)
^{m ′} / Air where α ≠ 1.00 and β ≠ 1.00 or α ≠ 1.00 and β = 1.00 or α = 1.00 and β ≠ 1.00 and m and m ′ are It is an integer of 1 or more and x = 0 to 1.0. (4) Sub / (αLαH) ^m x · L (βHβL)
^{m ′} / Air where α ≠ 1.00 and β ≠ 1.00 or α ≠ 1.00 and β = 1.00 or α = 1.00 and β ≠ 1.00 and m and m ′ are It is an integer of 1 or more and x = 0 to 1.0. 2. A laser device having a laser medium, a light source for exciting the laser medium, and a laser resonator having a plurality of mirrors for reflecting at least a part of laser light generated in the laser medium, At least one of the mirrors which comprises a resonator was comprised with the optical thin film of Claim 1, The laser apparatus characterized by the above-mentioned.