JPH0347754B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a nonlinear optical crystal and a container enclosing the crystal, which are integrally formed, and a laser beam incident on the nonlinear optical crystal, an optical axis, and a The present invention relates to a wavelength tunable laser device that changes the wavelength of emitted laser light by changing the angle formed by the optical axis of a nonlinear optical crystal.

[Prior Art] Conventionally, an optical parametric oscillator as a wavelength tunable laser device of this type has been constructed as shown in FIG. In this figure, 1 is a nonlinear optical crystal (hereinafter simply referred to as a crystal) such as a urea single crystal that is deliquescent in air, and this crystal 1 is sealed together with matching oil 2 in a container 3 having a rectangular parallelepiped outer surface. , protected. In addition, in order to avoid problems such as sealing of the rotation axis that would occur when only the crystal 1 is rotated independently with the container 3 fixed, the crystal 1 and the container 3 are rotated around the rotation axis 4 perpendicular to the plane of the paper. are configured to rotate together in the direction of the arrow. Third harmonic laser light (wavelength 355 nm) 5 from an Nd-YAG laser (not shown) passes through the first mirror 6 as excitation light, and is generated by entering the crystal 1 through the window 7 of the container 3. The light that
The first and second mirrors 6 and 8 resonate, causing parametric oscillation. At this time, the wavelength of the laser beam 5a emitted via the second mirror 8 can be changed, for example, from the visible region to the near-infrared region by rotating the crystal 1 and the container 3 in the direction of the arrow around the rotation axis 4. The area can be changed continuously. 9 is a window of the container 3.

[Problems to be Solved by the Invention] However, in the conventional example shown in FIG. 4, the container 3 is formed in the shape of a rectangular parallelepiped outer surface. , since the incident laser beam 5 obliquely enters the outer surface of the window 7 of the container 3 and is refracted, the output laser beam 5a
is moved parallel to the optical axis 10 of the incident laser beam 5 by a distance d corresponding to the rotation angle. Therefore, when using this type of wavelength tunable laser device for measurements etc.,
The problem is that the position of the emitted laser beam 5a cannot be kept constant unless the moving distance d corresponding to the rotation angle of the container 3 is corrected each time the wavelength of the emitted laser beam 5a is changed, so a correction mechanism or the like is required. The dot was hot.

The present invention was made in view of the above-mentioned problems.
By changing the angle between the laser beam, the optical axis, and the optical axis of the crystal (for example, by rotating the container)
The purpose of this is to prevent the position of the emitted laser beam from moving.

[Means for Solving the Problems] A crystal enclosure according to the present invention integrally forms a nonlinear optical crystal and a container for enclosing the nonlinear optical crystal, and the optical axis of the laser beam incident on the nonlinear optical crystal is aligned with the optical axis of the incident laser beam. In the wavelength tunable laser device in which the wavelength of the emitted laser light is changed by changing the angle formed between the nonlinear optical crystal and the optical axis, a medium having a refractive index substantially equal to that of the nonlinear optical crystal is provided in the container. The outer surface of the window through which the laser beam enters and exits the container is formed into a curved shape including an arc centered at the intersection of the optical axis of the nonlinear optical crystal and the optical axis of the laser beam. This is a characteristic feature.

[Function] When the angle between the optical axis of the nonlinear optical crystal, the laser beam, and the optical axis is changed in order to change the wavelength of the emitted laser beam (for example, when the nonlinear optical crystal and the container are rotated together), The outer surface of the window through which the laser beam enters and exits is made of a nonlinear optical crystal, such as a cylindrical surface centered on the rotation axis of the container or a spherical surface centered on the intersection of the container rotation axis and the laser beam and optical axis. Since it is formed into a curved shape that includes an arc centered on the intersection of the optical axis, the laser beam, and the optical axis, the angle between the optical axis of the nonlinear optical crystal, the laser beam, and the optical axis (for example, the rotation angle of the container) ), the laser light always enters and exits the container window perpendicularly to the outer surface and is not refracted by the window outer surface.
Moreover, since the container is filled with a medium whose refractive index is approximately equal to that of the nonlinear optical crystal, the entire container in which the nonlinear optical crystal and the medium are sealed can be regarded as a medium with a uniform refractive index. Therefore, the position of the emitted laser beam is not moved by changing the angle between the optical axis of the nonlinear optical crystal and the optical axis of the laser beam (for example, by rotating the container).

[Example] Figures 1 and 2 show an example of the present invention. In these figures, 11 is a nonlinear optical crystal (hereinafter simply a crystal) such as a urea single crystal that is deliquescent in air. ). Reference numeral 12 denotes a cylindrical body 14 made of quartz material and rotatable about a rotation shaft 13;
It is a container consisting of disks 15 and 16 that close both end faces of the container. The crystal 11 is sealed in the container 12, and a matching oil 17 as a medium whose refractive index is approximately equal to that of the crystal 11 is sealed, and the crystal 11 and the matching oil 17 are sealed in the container 12.
The entire container 12 in which is sealed can be regarded as a medium with a uniform refractive index. The crystal 11 is connected to the center portions of the disks 15 and 16 by the rotation shaft 13, and is integrated with the container 12 so that the rotation shaft 1
3 in the direction of the arrow. 18 and 19 are the first for parametric oscillation;
This is the second mirror. A portion of the container 12 has a first
A first window 21 is formed on the mirror 18 side, and a second window 22 is formed on the second mirror 19 side.

Next, the operation of the above embodiment will be explained.

Third harmonic laser light (wavelength = 355 nm) 25 from an Nd-YAG laser (not shown) passes through the first mirror 18 as excitation light and enters the crystal 11 through the first window 21 of the container 12. The generated light resonates with the first and second mirrors 18 and 19, causing parametric oscillation. And the second
By rotating the crystal 11 and the container 12 together in the direction of the arrow around the rotation axis 13, the wavelength of the laser beam 25a emitted via the mirror 19 can be changed continuously from the visible region to the near-infrared region, for example. It can be changed as before.

However, when the crystal 11 and the container 12 are rotated together around the rotation axis 13 in order to change the wavelength of the emitted laser beam 25a, the first and second The outer surfaces of the windows 21 and 22 are perpendicular to the optical axis 26 of the laser beam 25.
Therefore, the laser beam 25 always enters and exits perpendicularly to the outer surfaces of the first and second windows 21 and 22 of the container 12, and
It is not refracted by the outer surfaces of the second windows 21 and 22. Therefore, the position of the emitted laser beam 25a does not move due to rotation of the container 12. Furthermore, the first of the container 12,
The outer surface of the second windows 21 and 22 is connected to the rotation axis 13 of the container 12.
Since it is formed into a cylindrical surface with the central axis at
The interval between the two does not change. Therefore, the distance between the container 12 and the first and second mirrors 18 and 19 can be set as short as possible.

In the above embodiment, the container is formed of a cylinder and a disc, and a part of the cylinder is formed into a window through which the laser beam enters and exits. However, the present invention is not limited to this, and the laser beam of the container is The outer surface of the window through which the laser beam enters and exits is formed into a curved shape including an arc centered at the intersection of the rotation axis of the container and the laser beam and the optical axis, so that when the container is rotated, the optical axis of the laser beam is always aligned. It suffices if it is perpendicular to . For example, as shown in FIG. 3, first and second windows 21a whose surfaces are partially cylindrical surfaces with the rotation axis 13 as the central axis are formed on the left and right side walls of a cylinder 14a whose upper and lower side walls are flattened. Alternatively, the container may be formed into a spherical shape centered on the intersection of the rotation axis and the optical axis, and a portion thereof may be used as the first and second windows through which the laser beam enters and exits. good.

In the above embodiment, the present invention is applied to a wavelength tunable laser device in which the angle between the optical axis of the laser beam and the optical axis of the crystal is changed by rotating the nonlinear optical crystal and the container integrated therewith. However, the present invention is not limited to this, and the nonlinear optical crystal and the container integrated therewith are fixed, and the laser beam can be changed by changing the input and output of the laser beam to the nonlinear optical crystal. It is also possible to use a wavelength tunable laser device in which the angle between the axis and the optical axis of the crystal is changed. For example, a rotatable reflecting mirror is provided between the laser oscillator and the first mirror to change the traveling direction of the laser beam, and the reflected light from the reflecting mirror is transmitted to the nonlinear optical crystal in the container via the first mirror. It can also be used for a wavelength tunable laser device which is provided with a concave mirror for incidence, and by rotating the rotatable reflecting mirror, the angle formed between the optical axis of the laser beam and the optical axis of the crystal is changed. can.

[Effects of the Invention] As described above, the crystal enclosing container of the wavelength tunable laser device according to the present invention can be used even if the angle between the optical axis of the crystal and the optical axis of the laser beam is changed in order to change the wavelength of the emitted laser beam. (For example, even if the container is rotated), the outer surface of the window through which the laser beam enters and exits the container is always formed into a curved shape that is perpendicular to the optical axis of the laser beam, regardless of the angle (for example, the rotation angle). Therefore, the laser light is not refracted at the outer surface of the container window. Moreover, since the container is filled with a medium whose refractive index is approximately equal to that of the nonlinear optical crystal, the entire container in which the nonlinear optical crystal and the medium are sealed can be regarded as a medium with a uniform refractive index. Therefore, the position of the emitted laser beam does not shift due to rotation of the container or change of the incident angle of the laser beam. Therefore, there is no need for a correction mechanism for correcting the position of the emitted laser beam, which was required in the past. In addition, a wavelength tunable laser device is formed by a parametric oscillator that encloses a nonlinear optical crystal and a medium and has first and second mirrors for resonance on both sides of a container that rotates together with the nonlinear optical crystal. In the case where the space between the outer surface of the container window and the first and second mirrors does not change due to the rotation of the container, the distance between the container and the first and second mirrors can be adjusted. It can be set as short as possible.

[Brief explanation of drawings]

1 and 2 show an embodiment of the crystal enclosure container of the wavelength tunable laser device according to the present invention, in which FIG. 1 is a partially sectional plan view, and FIG.
The figure is a partially cutaway perspective view showing the main parts of Figure 1;
FIG. 3 is a plan view of a main part of another embodiment, partially shown in cross section, and FIG. 4 is a plan view, partially shown in cross section, of a conventional example. 11...Nonlinear optical crystal, 12...Container, 13
... Rotation axis, 21 ... Window, 25 ... Incident laser light, 25a ... Output laser light, 26 ... Optical axis.

Claims (1)

[Claims] 1. A nonlinear optical crystal and a container enclosing the nonlinear optical crystal are integrally formed, and an angle between a laser optical axis incident on the nonlinear optical crystal and an optical axis of the nonlinear optical crystal is changed. In a wavelength tunable laser device configured to change the wavelength of emitted laser light, the container is filled with a medium having a refractive index substantially equal to that of the nonlinear optical crystal, and a window through which the laser light of the container enters and exits. A crystal enclosing container for a wavelength tunable laser device, characterized in that an outer surface of the nonlinear optical crystal is formed into a curved shape including an arc centered at the intersection of the optical axis of the nonlinear optical crystal and the optical axis of the laser beam. 2. A wavelength tunable laser device rotates a nonlinear optical crystal and a container enclosing the nonlinear optical crystal together to change the angle between the optical axis of the laser beam and the optical axis of the nonlinear optical crystal, and emit a laser beam. A crystal enclosing container for a wavelength tunable laser device according to claim 1, which is configured to change the wavelength of light. 3. The crystal-enclosed container for a wavelength tunable laser device according to claim 2, wherein the outer surface of the window through which the laser beam enters and exits the container is a cylindrical surface having the rotational axis of the container as the central axis. 4. The wavelength tunable laser device according to claim 2, wherein the outer surface of the window through which the laser beam of the container enters and exits is a spherical surface centered on the intersection of the rotational axis of the container and the optical axis of the laser beam. crystal enclosure.