JPH0980496A - Non-linear optical crystal element and laser light generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a maximum outgoing light output by providing an incident end side crystal surface cut so as to keep the Brewster's angle for the polarization direction of an incident light beam and an exciting end side crystal surface cut so as to keep the Brewster's angle for the polarization direction of an exiting light beam. SOLUTION: Although a non-linear optical element 1 is used as a wavelength conversion element making a wavelength of basic wave light L1 1/2 and outputting harmonic light L2 of a short wavelength, it outputs by changing the polarization directions of the basic wave light L1 and the harmonic light L2 by 90 deg.. The incident end side crystal surface 1a is cut so as to keep the Brewster's angle for the polarization direction of the basic wave light L1 of the wavelength 532nm being the incident light beam. Further, the exiting end side crystal surface 1b is cut so as to keep the Brewster's angle for the polarization direction of the harmonic light L2 of the wavelength 266nm being the exiting light beam. Thus, the occurrence of a reflection loss due to a Fresnel loss is prevented by both surfaces, and the maximum exiting light output is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear optical crystal element that changes the polarization direction of an incident light beam and outputs an outgoing light beam, and a laser light generator having this non-linear optical crystal element.

[0002]

2. Description of the Related Art A nonlinear optical crystal element is known as an element for changing the wavelength and polarization direction of incident light. For example, there is a wavelength conversion element that halves the wavelength of the incident fundamental wave light to generate the second harmonic, and a quarter wavelength plate that converts the incident linearly polarized light into circularly polarized light.

In such a nonlinear optical crystal element, the incident fundamental wave light is Fresnel-reflected by the incident end side crystal surface. Fresnel reflection is the reflection of part of incident light from the crystal surface, which causes Fresnel loss.

In order to prevent the Fresnel loss from occurring, an antireflection film is conventionally formed on the crystal plane on the incident end side. However, forming an optical thin film as an antireflection film is time-consuming and costly.

Therefore, the crystal plane on the incident end side is defined by Brewster's angle with respect to the polarization of the incident light.
Cutting has been done to keep e). As shown in FIG. 9, the Brewster angle refers to light reflected by a dielectric surface having a refractive index n ₁ and a reflectance R of light (p-polarized light) whose electric vector E is in the incident plane is 0 [%]. Is an incident angle θ (which is an angle between the angle and the normal).

In FIG. 10, the incident end side crystal face 30a is cut so as to maintain the Brewster angle, and the emitting end side crystal face 30a is cut.
The nonlinear optical crystal element 30 is shown by cutting b so as to be parallel to the crystal plane 30a on the incident end side. That is, the incident end side crystal surface 30a of the nonlinear optical crystal element 30 is cut at an angle θ _B that makes the reflectance R of the fundamental wave light L ₁ which is the incident light ray in the incident surface of the electric vector E 0 [%]. ing.
The nonlinear optical crystal element 30, the wavelength of the fundamental light L ₁ to 1/2, which is a wavelength conversion element for outputting harmonic light L ₂ having a short wavelength.

[0007]

By the way, in the above-mentioned nonlinear optical crystal element 30, the Fresnel loss of the harmonic light L ₂ which becomes the outgoing ray cannot be prevented only by preventing the Fresnel loss of the fundamental wave light L _{1 from} occurring. The output of the harmonic light L ₂ was lowered.

For example, β-Ba ₂ B ₂ O ₄ (hereinafter, BBO
Say. FIG. 11 shows the characteristics of the cutting angle and the reflectance with respect to the normal to the incident end side crystal face and the emitting end side crystal face when the phase) is type I phase-matched to form the nonlinear optical crystal element 30. That is, as shown in FIG. 11, in the nonlinear optical crystal element 30, the incident end side crystal plane 30a is formed.
Is an angle θ between the incident fundamental wave light L ₁ and the normal H is 6
When cut to about 0 °, the reflectance of the fundamental wave light L ₁ can be set to 0%.
The reflectance of the harmonic light L ₂ emitted from the emission end side crystal face 30b cut in parallel with 0a becomes 22.4%,
The above Fresnel loss occurs and the maximum output cannot be obtained.

On the other hand, as shown in FIG. 12, the emitting end side crystal face 40b is cut so as to maintain the Brewster angle, and the incident end side crystal face 40a is cut out.
Consider a nonlinear optical crystal element 40 that is cut so as to be parallel to.

As the nonlinear optical crystal element 40, type I
FIG. 13 shows the characteristics of the cutting angle and the reflectance with respect to the normal line of the incident end side crystal face and the emission end side crystal face when the BBO phase-matched with is used. That is, as shown in FIG. 13, in the nonlinear optical crystal element 40, the emitting end side crystal face 40b is cut so that the angle θ formed by the emitted harmonic light L ₂ and the normal line H is about 60 °. Then, the reflectance of the harmonic light L ₂ can be set to 0%, but the reflectance of the fundamental wave light L ₁ incident on the incident end side crystal face 40a cut parallel to the emitting end side crystal face 40b is 22. It becomes 4% and the above Fresnel loss occurs. Therefore, the fundamental wave light L ₁ suffers a loss, and the harmonic light L ₂ is
You cannot get the maximum output.

The present invention has been made in view of the above-mentioned circumstances, and in both the incident end side crystal face and the emitting end side crystal face,
(EN) Provided are a nonlinear optical crystal element capable of preventing the occurrence of reflection loss due to Fresnel loss and obtaining the maximum output light output, and a laser light generator capable of obtaining the maximum laser light output using the nonlinear optical crystal element. With the goal.

[0012]

In order to solve the above-mentioned problems, a nonlinear optical crystal element according to the present invention has an incident-end-side crystal plane cut so as to maintain a Brewster angle with respect to a polarization direction of an incident light beam. And a crystal plane at the emission end side cut so as to maintain the Brewster angle with respect to the polarization direction of the emitted light beam.

Further, the laser light generator according to the present invention is
In order to solve the above problems, the incident end side crystal plane cut so as to keep the Brewster angle to the polarization direction of the fundamental wave light from the fundamental wave light generation light source, and the polarization direction of the generated laser light A non-linear optical crystal element having an emission end side crystal plane cut so as to maintain the Brewster angle.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a nonlinear optical crystal element according to the present invention will be described below with reference to the drawings.

First, in the first embodiment, for example, β-
A nonlinear optical crystal device 1 as shown in FIG. 1 in which Ba ₂ B ₂ O ₄ (hereinafter referred to as BBO) is phase-matched with type I.

This nonlinear optical crystal element 1 is composed of a fundamental wave light L
_It is used as a wavelength conversion element that outputs the short wavelength harmonic light L ₂ by halving the wavelength of 1 and outputs the fundamental wave light L ₁ and the higher harmonic light L ₂ with different polarization directions by 90 °.

The crystal plane 1a on the incident end side is cut so as to maintain the Brewster angle with respect to the polarization direction of the fundamental wave light L ₁ having a wavelength of 532 nm which is an incident light ray. Also, the crystal plane 1b on the emission end side is cut so as to maintain the Brewster angle with respect to the polarization direction of the harmonic light L ₂ having a wavelength of 266 nm which is an emission light beam.

That is, as shown in FIG. 2, the incident end side crystal plane 1a of the nonlinear optical crystal element 1 has a reflectance R of 0 [%] for the fundamental wave light L _{1 having} the electric vector E in the incident plane. It is cut at an angle θ ₁ . In addition, the crystal plane 1 on the output end side
b is cut at an angle θ ₅ at which the electric vector E makes the reflectance R of the harmonic light L _{2 in} the exit surface 0 [%].

Let the refractive index of ordinary light of the nonlinear optical crystal element 1 be n.
_o and the refractive index of extraordinary light when the type I phase matching angle is 47.6 °, n _e , the angles θ ₁ and θ ₂ shown in FIGS. 2A and 2B, The following relational expressions hold for θ ₃ , θ ₄ , θ ₅ and θ ₆ .

[0020] _{sinθ 1 / sinθ 2 = n o} tanθ 1 = n o / 1 θ 2 + θ 3 = 90 ° _{sinθ 4 / sinθ 5 = 1 /} n e tanθ 4 = 1 / n e θ4 + θ6 = 90 °, however, n _o = N _e = 1.6742.

From this, θ ₁ = 59.15 °, θ ₂ = 3
0.85 °, θ ₃ = 59.15 °, θ ₄ = 59.15 °,
θ ₅ = 30.85 ° and θ ₆ = 59.15 °.

Crystal surface 1 on the incident end side of the nonlinear optical crystal element 1
FIG. 3 shows the reflectance characteristics of the fundamental wave light L ₁ on the incident end side crystal face 1a when the cutting angle θ _{1 of a} is changed, and when the cutting angle θ ₅ of the emission end side crystal face 1b is changed. FIG. 4 shows the reflectance characteristic of the higher harmonic light L ₂ on the crystal plane 1b on the emitting end side. From these, when θ ₁ = 59.15 °, the fundamental wave light L
_The reflectance for ₁ is 0%, and when θ ₅ = 59.15 °, the reflectance for the harmonic light L ₂ is also 0%.

As described above, in the nonlinear optical crystal device 1, the crystal plane 1a on the incident end side is cut at the Brewster angle at which the electric vector E makes the reflectance R of the fundamental wave light L _{1 in} the incident plane 0%. , The emitting end side crystal face 1b is cut at the Brewster angle which makes the reflectance R of the harmonic light L _{2 in} the emitting face E 0%, so that the incident end side crystal face 1a and the emitting face 1a It is possible to prevent the occurrence of reflection loss due to Fresnel loss on both of the end-side crystal faces 1b, and obtain the maximum output light output.

Next, in the second embodiment, for example, BB
A nonlinear optical crystal element 10 as shown in FIG. 5 in which O is phase-matched by type II.

This nonlinear optical crystal element 10 is also the fundamental wave light L.
_It is used as a wavelength conversion element that outputs the short wavelength harmonic light L ₂ by halving the wavelength of 1 and outputs the fundamental wave light L ₁ and the harmonic light L ₂ with different polarization directions by 45 °.

The crystal plane 10a on the incident end side is cut so as to maintain the Brewster angle with respect to the polarization of the fundamental wave light L ₁ . Since the nonlinear optical crystal element 10 has the type II phase matching as described above, the incident fundamental wave light L ₁
Is the direction of polarization as shown in FIG. 6 (A) an electric vector as viewed from the arrow S _a side.

Further, the crystal plane 10b on the emitting end side is cut so as to maintain the Brewster angle with respect to the polarization of the harmonic light L ₂ . The emitted harmonic light L ₂ is polarized light whose electric vector is as shown in FIG. _{6B when} viewed from the arrow S _b side.

A side view of the nonlinear optical crystal element 10 shown in FIG. 5 is shown in FIG. 7A, and a bottom view thereof is shown in FIG. 7B.

Even in such a nonlinear optical crystal element 10,
The incident end side crystal face 10a is cut so as to maintain the Brewster angle with respect to the polarization direction of the fundamental wave light L ₁ , and the emission end side crystal face 10b is maintained with respect to the polarization direction of the harmonic light L _{2 at} the Brewster angle. Since it is cut into two, the occurrence of reflection loss due to Fresnel loss can be prevented on both the incident end side crystal face 10a and the emission end side crystal face 10b, and the maximum output light output can be obtained.

Next, an embodiment of the laser light generator according to the present invention will be described with reference to the drawings.

[0031] In this embodiment, as shown in the bottom in FIG. 8, a pulse laser oscillator 30 for generating a fundamental wave light L ₁ of the pulsed, Brewster to the polarization direction of the fundamental wave light L ₁ of the pulse-like Non-linear optics having an incident end side crystal face 1a cut so as to maintain an angle and an emitting end side crystal face 1b cut so as to maintain a Brewster's angle with respect to the polarization direction of the harmonic light L ₂ which is emitted light. A harmonic light generating device 25 including the crystal element 1.

In the nonlinear optical crystal device 1, as described above, the crystal plane 1a on the incident end side has the Brewster angle at which the electric vector E makes the reflectance R of the fundamental wave light L _{1 in} the incident plane 0%. By cutting the crystal plane 1b on the emission end side, the reflectance R of the harmonic light L ₂ whose electric vector E is in the emission plane is 0.
Since it is cut at Brewster's angle to [%],
It is possible to prevent the occurrence of reflection loss due to Fresnel loss on both the incident end side crystal face 1a and the emission end side crystal face 1b, and obtain the maximum output light output.

Therefore, this harmonic light generating device 25
Can produce maximum laser light output.

The nonlinear optical crystal element according to the present invention is not limited to the above wavelength conversion element,
For example, it can be applied to a wave plate whose main purpose is to make the polarization directions of incident light and emitted light different.

[0035]

The nonlinear optical crystal element according to the present invention has a crystal plane on the incident end side which is cut so as to maintain a Brewster angle with respect to the polarization direction of an incident light beam, and a Brewster with respect to the polarization direction of an outgoing light beam. Since the output end side crystal face cut so as to keep the angle is provided, the occurrence of reflection loss due to Fresnel loss is prevented on both the input end side crystal face and the output end side crystal face, and the maximum output light output is obtained. Obtainable.

Further, the laser light generator according to the present invention is
Incident end side crystal plane cut so as to maintain the Brewster angle with respect to the polarization direction of the fundamental wave light from the fundamental wave light generation source, and so as to maintain the Brewster angle with respect to the polarization direction of the generated laser light Since the crystal plane is on the emitting end side, the maximum laser light output can be generated.

[Brief description of drawings]

FIG. 1 is an external perspective view of a first embodiment of a nonlinear optical crystal element according to the present invention.

FIG. 2 is a side view and a bottom view of the first embodiment.

FIG. 3 is a characteristic diagram showing reflectance characteristics of a fundamental wave light on a crystal plane of the incident end side when the cutting angle of the crystal plane of the incident end side is changed in the first embodiment.

FIG. 4 is a characteristic diagram showing a reflectance characteristic of higher harmonic light on the emitting end side crystal face when the cutting angle of the emitting end side crystal face is changed.

FIG. 5 is an external perspective view of a second embodiment of a nonlinear optical crystal element according to the present invention.

FIG. 6 is a schematic diagram showing polarization directions of incident light and emitted light according to the second embodiment.

7A and 7B are a side view and a bottom view of the second embodiment.

FIG. 8 is an external view of a harmonic light generation device that is an embodiment of a laser light generation device according to the present invention.

FIG. 9 is a schematic diagram for explaining a Brewster angle.

FIG. 10 is a side view of a conventional nonlinear optical crystal element in which a crystal plane on the incident end side is cut at a Brewster's angle.

11 is a characteristic diagram showing the relationship between the cutting angle and the reflectance at the incident end side crystal face and the emitting end side crystal face of the conventional nonlinear optical crystal device shown in FIG.

FIG. 12 is a side view of a conventional nonlinear optical crystal element in which a crystal plane on the output end side is cut at a Brewster's angle.

13 is a characteristic diagram showing the relationship between the cutting angle and the reflectance at the incident end side crystal face and the emission end side crystal face of the conventional nonlinear optical crystal element shown in FIG.

[Explanation of symbols]

 1 Non-Linear Optical Crystal Element 1a Crystal Face of Incident End Face 1b Crystal Face of Emitting End Face

Claims (5)

[Claims] 1. A non-linear optical crystal device that makes the polarization directions of an incident light beam and an outgoing light beam different from each other, and an incident end-side crystal plane cut so as to maintain a Brewster angle with respect to the polarization direction of the incident light beam, and the emission light. A non-linear optical crystal element, comprising: a crystal plane that is cut so as to maintain a Brewster angle with respect to a polarization direction of a light beam. 2. The nonlinear optical crystal element according to claim 1, wherein the incident light and the outgoing light have different polarization directions by 90 °. 3. The nonlinear optical crystal element according to claim 1, wherein the incident light and the outgoing light have different polarization directions by 45 °. 4. The nonlinear optical crystal element according to claim 1, wherein the incident light beam is a fundamental wave and the emitted light beam is a harmonic light. 5. A laser beam generator for generating a laser beam having a polarization direction different from the polarization direction of the irradiated fundamental wave light, wherein a fundamental wave light generating light source for generating the fundamental wave light and a polarization direction for the fundamental wave light are provided. Non-linear optical crystal element having an incident end side crystal plane cut so as to keep the Brewster angle and an emitting end side crystal plane cut so as to keep the Brewster angle with respect to the polarization direction of the generated laser light A laser light generator comprising: