JPH0714666U - Solid-state laser device - Google Patents

Abstract

(57) [Summary] [Object] To obtain efficient operation in a semiconductor laser pumped solid-state laser and obtain the polarization direction of the second harmonic in a direction according to vertical or horizontal use. [Structure] On the optical axis of the excitation light emitted from the semiconductor laser 1, from the side of the semiconductor laser 1, a half-wave plate 4 that functions at the wavelength of the semiconductor laser 1, a condenser lens 2, and a solid-state laser medium. Nd: YVO ₄ crystal 5 and a wavelength conversion element
The KTP crystal 6 and the resonator mirror 3 are arranged in this order, and N
A resonator mirror 5a is formed on the end surface of the d: YVO ₄ crystal 5 on the excitation side by coating. The polarization direction of the semiconductor laser 1 is made horizontal, the half-wave plate 4 is made its fast axis direction 22.5 ° with respect to the horizontal direction, and the Nd: YVO ₄ crystal 5 is made the axis direction of which the absorption coefficient is large. The KTP crystal 6 is arranged at 45 ° with respect to the horizontal, and the extraordinary optical axis direction is arranged vertically. The polarization direction of the second harmonic is obtained in a direction depending on vertical or horizontal use.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a solid-state laser device, and more particularly to a solid-state laser device in which light from a semiconductor laser is directly guided by an optical fiber or the like, and the solid-state laser medium is end-pumped by using this as excitation light.

[0002]

[Prior art]

 Conventionally, a solid-state laser of the type in which a solid-state laser medium such as Nd: YAG is placed between a pair of mirrors that face each other is excited by irradiating the emitted light from a semiconductor laser from one end face of the resonator. There is a device, which is known as a laser light source that is easier than a solid-state laser device that uses a rare gas lamp or the like. The second harmonic light of solid-state laser light is highly useful as a light source for optical recording and optical measurement.

A nonlinear optical crystal such as KTP (KTiOPO ₄ ) is used to generate the second harmonic light. The polarization of the second harmonic light generated there is linearly polarized light parallel to the extraordinary optical axis direction of the KTP crystal. Becomes For this reason, the polarization of the second harmonic light extracted depends on how the KTP crystal is placed. On the other hand, in various applications, it is often convenient that the polarization of laser light is vertical or horizontal.

For example, in a magneto-optical disk device, the polarization rotation by the disk is used as information, but this requires a reference, and the reference polarization direction can be the vertical direction or the horizontal direction according to the designer's preference. Normally, the disc is rotated in the horizontal plane, and the light from the laser light source is emitted in the horizontal direction, and up to the disc, it is guided in a light path bent at a right angle by a mirror made of a cubic glass with good productivity. It Therefore, in order to improve the light guiding efficiency from the laser light source through the disc to the photodetector, it is necessary to set the polarization direction of the laser light source to the vertical direction or the horizontal direction. It is very important because it leads to saving power consumption.

From this point of view, looking at the second harmonic light of a semiconductor laser pumped solid-state laser, the arrangement of the KTP crystal, which is a wavelength conversion element, is first determined, and then the laser oscillation is determined by the physical law. It turns out that the components of the laser must be arranged for efficient realization.

[0006]

[Problems to be solved by the device]

 In view of the above problems of the prior art, the main object of the present invention is a solid-state laser device capable of obtaining efficient operation and obtaining the polarization direction of the extracted second harmonic light in a direction convenient for use. To provide.

[0007]

[Means for Solving the Problems]

According to the present invention, such an object is to provide a semiconductor laser, an anisotropic solid-state laser medium end-pumped by pumping light from the semiconductor laser, a resonator including a pair of mirrors, and a resonator from the resonator. A non-linear optical crystal for generating second harmonic light as emitted light, and a half-wavelength for rotating the excitation light by polarization to match it in the axial direction where the absorption coefficient of the anisotropic solid-state laser medium is large. A plate, the semiconductor laser is arranged so that its polarization direction is horizontal, and the half-wave plate is arranged so that its fast axis direction is 22.5 ° with respect to the horizontal plane. The anisotropic solid-state laser medium is arranged such that the axial direction having the large absorption coefficient is 45 ° with respect to the horizontal, and the nonlinear optical crystal is arranged so that the extraordinary optical axis direction is vertical. Providing a solid-state laser device characterized by It is achieved by. Especially, it is advisable to rotate the whole body 90 degrees with respect to the horizontal. The solid laser medium is preferably Nd: YVO ₄ crystal.

[0008]

[Action]

The anisotropic solid-state laser medium is different from the well-known isotropic laser crystal such as Nd: YAG, and has the property of lasing with linearly polarized light in one direction determined by the crystal axis. Nd: YVO _4, which is one of the anisotropic solid-state laser media, has a large absorption coefficient at the oscillation wavelength of the semiconductor laser and is attracting attention as a solid-state laser medium suitable for pumping the semiconductor laser. Nd: Y VO ₄ is a uniaxial crystal and has different absorption coefficients in the c-axis direction and the a-axis direction of the crystal. The size ratio is about 4 to 1 near 809 nm, which corresponds to the oscillation wavelength of the GaAs semiconductor laser, and the absorption coefficient in the c-axis direction is large.

On the other hand, generally, the polarized light of a semiconductor laser is linearly polarized light in a direction substantially parallel to its active layer. Therefore, in order to operate the Nd: YVO ₄ laser efficiently, it is desirable to match the polarization of the semiconductor laser with the c-axis direction of the Nd: YVO ₄ crystal (for example, see Japanese Patent Laid-Open No. 4-177775). . From the viewpoint of efficient operation, in general, when an anisotropic crystal is used as a solid-state laser medium, it is necessary to match the polarization of the semiconductor laser light, which is the excitation light, with the direction in which the absorption coefficient of the solid-state laser medium is large. There is.

However, since the active layer, which is the light emitting portion of the semiconductor laser, is very small, it is actually not easy to exactly match the polarization of the semiconductor laser with the c-axis direction of the Nd: YVO ₄ crystal. . Therefore, in the present invention, a half-wave plate for rotating the polarization of the semiconductor laser light that is the excitation light is used, and it is arranged between the semiconductor laser and the Nd: YVO ₄ crystal.

The half-wave plate is made of a transparent anisotropic crystal such as quartz. However, when light propagates in the anisotropic crystal, the difference in the refractive index depending on the axial direction causes each axis to move. There is a phase velocity difference in the direction. Since the fast axis in the direction of fast light and the slow axis in the direction of slow light are orthogonal to each other, and the phase difference between the fast and slow axes is exactly π in the half-wave plate, the incidence The phase of the component that oscillates in the slow axis direction of light is delayed by π compared to the fast axis direction. For example, if the polarization of the incident light is 45 ° with respect to the fast axis of ½ wavelength, the polarization of the emitted light will rotate exactly 90 °. Generally, when the angle formed by the polarization direction of the incident light and the fast axis direction of the half-wave plate is θ, the polarization of the emitted light is rotated by 2θ.

For example, if the Nd: YVO ₄ crystal has an a-axis cut and the polarization direction of the semiconductor laser and the c-axis of the Nd: YVO ₄ crystal form 45 °, the polarization direction of the semiconductor laser is 1 The polarization of the semiconductor laser can be rotated by 45 ° by setting the fast axis of the / 2 wave plate to 22.5 °, and the polarization of the semiconductor laser can be perfectly aligned with the c-axis direction of the Nd: YVO ₄ crystal. be able to.

The polarization is important for efficient operation also in the case of the second harmonic light generation, and in order to efficiently generate the second harmonic light, for example, when using a KTP crystal, solid It is desirable that the polarization of the laser light be linearly polarized at 45 ° with respect to the extraordinary optical axis of KTP. The generated second-harmonic polarization is linearly polarized in the direction of the extraordinary optical axis of the KTP crystal. As described above, in the case of the second harmonic light, the polarization of the output light is determined by the arrangement of the nonlinear optical crystal such as KTP. Therefore, considering the efficiency, the anisotropic solid-state laser medium at the previous stage is set horizontally. It is necessary to incline it by 45 °.

From the above two requirements, for example, when using a Nd: YVO ₄ crystal as the solid-state laser medium, it is desirable that the polarization of the semiconductor laser light is linear polarization of 45 ° with respect to the horizontal. Therefore, it is necessary to arrange the Nd: YVO ₄ crystal so that its c-axis is oriented at 45 ° with respect to the horizontal. If the polarization direction of the semiconductor laser is horizontal, the polarization of the semiconductor laser can be rotated 45 degrees by setting the fast axis of the half-wave plate to 22.5 ° with respect to the horizontal. , the polarization of the semiconductor laser Nd: Y VO ₄ can perfectly match with the c-axis direction of the crystal. In the anisotropic solid-state laser medium, the axis having the large absorption coefficient and the axis having the large stimulated emission cross section coincide with each other, and thus the above arrangement provides the most efficient operation.

With this configuration, efficient operation can be obtained, and the polarization direction of the extracted second harmonic light can be obtained in a direction convenient for use.

[0016]

【Example】

 Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic perspective view showing the configuration of a solid-state laser device in an embodiment to which the present invention is applied. In the present embodiment, as shown in FIG. 1, a half-wave plate 4 that functions at the wavelength of the semiconductor laser 1 from the semiconductor laser 1 side on the optical axis of the excitation light emitted from the semiconductor laser 1. A condenser lens 2, a Nd: YVO ₄ crystal 5 as a solid-state laser medium, a KTP crystal 6 as a wavelength conversion element, and a resonator mirror 3 are arranged in this order. A resonator mirror 5a formed by coating is provided on the end surface of the Nd: YVO ₄ crystal 5 on the excitation side.

The size of the Nd: YVO ₄ crystal 5 of this embodiment is 3 × 3 × 1 ^t mm, and is cut by the ac plane. The semiconductor laser 1 is arranged so that its polarization is in the horizontal direction shown by the arrow A in the figure, and the polarization direction of the semiconductor laser 1 and the c-axis of the Nd: YVO ₄ crystal 5 form 45 °. , Nd: YVO ₄ crystal 5 is arranged. The polarized light of the semiconductor laser 1 is rotated by using the half-wave plate 4 arranged between the semiconductor laser 1 and the lens 2, and coincides with the c-axis which has a large absorption coefficient of the Nd: YVO ₄ crystal 5. I am letting you. The arrangement of the 1/2 wavelength plate 4 can be adjusted so that the output becomes maximum while observing the magnitude of the Nd: YVO ₄ laser output. The KTP crystal 6, which is a wavelength conversion element, is arranged in the resonators 5a and 3 such that the extraordinary optical axis is in the vertical direction.

The excitation light (809 nm) emitted from the semiconductor laser 1 first passes through the half-wave plate 4, is polarized and rotated, and is then collected by the condenser lens 2 to be irradiated on the Nd: YVO ₄ crystal 5. , Nd: YVO ₄ crystal 5 is excited to generate spontaneous emission light (1064 nm) at the fundamental laser light wavelength. The spontaneous emission light radiated from the Nd: YVO ₄ crystal 5 is reflected by the resonator mirror 3 and returns to the Nd: YVO ₄ crystal 5 through the original optical path in the opposite direction, where it is amplified by stimulated emission. At the same time, the Nd: YVO ₄ crystal 5 is reflected by the resonator mirror coating 5 a provided on the end face on the excitation side and reciprocates in the resonator. In this way, if the resonator mirrors 5a and 3 satisfy the conditions for laser oscillation, laser oscillation occurs. In the case of the Nd: YVO ₄ crystal 5, since the emission intensity in the c-axis direction is strong, it oscillates with polarized light in the c-axis direction. The oscillated basic laser light is incident on the KTP crystal 6, which is a wavelength conversion element, at 45 ° to the extraordinary optical axis, and the wavelength is converted in the KTP crystal 6, and as shown by the arrow B in the figure, it is vertical. It becomes the second harmonic light having the linearly polarized light in the direction and is emitted from the output mirror 3.

Further, by rotating the entire body by 90 ° with respect to the horizontal, the second harmonic light having horizontal linear polarization can be emitted from the output mirror 3, and thus the polarization direction of the second harmonic can be Can be obtained in a suitable direction depending on the use.

In this embodiment, the Nd: YVO ₄ crystal is used as the anisotropic solid-state laser medium, but other anisotropic crystals may be used. The half-wave plate may be inserted anywhere between the semiconductor laser 1 and the Nd: YVO ₄ crystal 5.

[0022]

[Effect of device]

 As described above, according to the solid-state laser device of the present invention, efficient operation can be obtained, and the polarization direction of the extracted second harmonic light can be easily adjusted to a direction convenient for use.

[Brief description of drawings]

FIG. 1 is a perspective schematic view showing a configuration of a solid-state laser device in an embodiment to which the present invention is applied.

[Explanation of symbols]

1 semiconductor laser 2 condenser lens 3 resonator mirror 4 1/2 wave plate 5 Nd: YVO ₄ crystal 5a resonator mirror 6 KTP crystal

Claims (3)

[Scope of utility model registration request] 1. A semiconductor laser, and an anisotropic solid-state laser medium that is end-pumped by pumping light from the semiconductor laser,
A resonator including a pair of mirrors, a non-linear optical crystal for generating second harmonic light as light emitted from the resonator, and polarization conversion of the excitation light to cause absorption coefficient of the anisotropic solid-state laser medium. 1 to match the direction of the larger axis
1/2 wavelength plate, the semiconductor laser is arranged so that its polarization direction is horizontal, and the 1/2 wavelength plate is so arranged that its fast axis direction is 22.5 ° with respect to horizontal. The axial direction of the anisotropic solid laser medium having a large absorption coefficient is 4 with respect to the horizontal.
A solid-state laser device, wherein the solid-state laser device is arranged at an angle of 5 °, and the nonlinear optical crystal is arranged so that its extraordinary optical axis direction is vertical. 2. The solid-state laser device according to claim 1, wherein the whole is rotated by 90 ° with respect to the horizontal. 3. The solid-state laser device according to claim 1, wherein the solid-state laser medium is an Nd: YVO ₄ crystal.