JPH0736073A - Polarized light control solid-state laser - Google Patents

Abstract

PURPOSE:To provide a polarized control solid-state laser of a small size having an optical system which is simple in adjustment. CONSTITUTION:The central axis of the space distribution of an exciting laser beam 105 in the gain medium of the photoexcited solid-state laser 101, of which the central axis of the space distribution of a laser oscillated beam 106 in the gain medium is not aligned to the optical axis of the gain medium or the main axis of the refractive index ellipsoid of the gain medium, is aligned to the central axis of the space distribution of one polarized light of the laser oscillated beam 106 in the gain medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a second-order nonlinearity used, for example, in a compact solid-state green light laser based on semiconductor laser excitation second harmonic generation, an optical resonator for parametric amplification, a sum frequency wavelength conversion element, and the like. A polarization-controlled solid-state laser using a gain medium having

[0002]

2. Description of the Related Art FIG. 5 shows a conventional lithium niobate (Nd: Mg) doped with neodymium and magnesium oxide.
O: LiNbO ₃₎ is a block diagram showing the schematic configuration of the polarization control solid state laser having a second harmonic generation wavelength conversion function using.

In FIG. 5, reference numerals 2 and 5 allow the pump laser light (wavelength 813 nm) and the second harmonic (wavelength 546.5 nm) of the laser oscillation light to pass through, and the laser oscillation light (wavelength 109).
It is a dichroic mirror that reflects 3 nm). Three
Indicates that the a-axis coincides with the central axis of the spatial distribution of the laser oscillation light, and both ends are optically polished and have neodymium and magnesium oxide added lithium niobate (Nd: MgO: LiNbO ₃ ).
It is a single crystal.

Reference numeral 4 is a Brewster plate adjusted to completely transmit ordinary laser oscillation light.

Single crystal 3, dichroic mirror 2,
5 and the Brewster plate 4 together form an optical resonator. Further, 1 is a semiconductor laser having an oscillation wavelength of 813 nm, and 6 is a temperature adjuster for adjusting the temperature. Further, 7 is a pump laser light, 8 is a laser oscillation light, and 9
Is the second harmonic.

A lithium niobate (Nd: MgO: LiNbO ₃ ) single crystal to which neodymium and magnesium oxide are added serves as a gain medium of a laser, and has a second-order harmonic generation, a sum frequency generation, a parametric amplification, and the like. Is a single crystal that produces a nonlinear optical effect.

A lithium niobate (Nd: MgO: LiNbO ₃ ) single crystal containing neodymium and magnesium oxide is used as a gain medium in the conventional example shown in FIG. 5 and generates a second harmonic. .

The stimulated emission cross-section of this crystal has a polarization direction dependency, and the wavelength at which the stimulated emission cross-section shows the maximum value is 1093 nm for ordinary laser oscillation light, but extraordinary laser oscillation. It is 1084 nm for light.

The maximum value of the stimulated emission cross section is smaller in the case of the ordinary laser oscillation light than in the case of the extraordinary laser oscillation light. (TY Fan et al, “Nd: MgO: LiNbO ₃ spectr
oscopy and laser devices ", J. Opt. Soc. Am. B, vo
l.3 (1), P140 (1986)).

However, lithium niobate (Nd: MgO: LiNbO) containing neodymium and magnesium oxide is added.
₃ ) Due to the refractive index dispersion characteristics of the single crystal, when laser oscillation is performed with extraordinary laser oscillation light, phase matching cannot be achieved for the generation of the second harmonic with the laser oscillation light as the fundamental wave, and ordinary laser oscillation Phase matching can be achieved and highly efficient second harmonics can be generated only when laser oscillation is performed by light.

Therefore, in the conventional example shown in FIG. 5, in order to control the polarization and cause the laser oscillation with the ordinary laser oscillation light,
A method is used in which the Brewster plate 4 having the polarization dependency of the transmittance is inserted into the resonator.

As a result, in the semiconductor laser 1, lithium niobate (N
When d: MgO: LiNbO ₃ ) single crystal 3 is excited to emit light as a gain medium, only ordinary laser oscillation light having a wavelength of 1093 nm is amplified and laser oscillation occurs. Further, if phase matching is achieved by temperature adjustment by the temperature adjuster 6, the lithium niobate (Nd: MgO: LiNbO ₃ ) single crystal 3 to which neodymium and magnesium oxide are added efficiently generates the second harmonic of the laser oscillation wave. To do.

[0013]

However, in such a conventional polarization control solid-state laser, it is necessary to precisely adjust the angle of the Brewster plate, and it is necessary to place the Brewster plate in the resonator. However, there is a problem in that it cannot be applied to a laser that constitutes a resonator only by a crystal in which a reflecting mirror is directly formed on a crystal end face.

The present invention has been made to solve the problems of the conventional example, and an object of the present invention is to enable a small-sized polarization control solid-state laser having an optical system which can be easily adjusted. To provide the technology.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0016]

In order to achieve the above object, according to the present invention, the central axis of the spatial distribution of the laser oscillation light in the gain medium is the optical axis of the gain medium or the ellipsoid of the refractive index of the gain medium. In the optically pumped solid-state laser that does not coincide with the main axis of the body, the central axis of the spatial distribution of the pump laser light in the gain medium coincides with the central axis of the spatial distribution of one polarization of the laser oscillation light in the gain medium. Characterized by

[0017]

According to the above-mentioned means, in a laser which uses a gain medium having a polarization direction in which laser oscillation is performed and a polarization direction in which the stimulated emission cross-section is maximum, the spatial distribution of the laser oscillation light in the optical resonator is It is possible to increase the overlap of the pump laser light only with the polarized light that causes the laser oscillation, and to simplify the adjustment of the optical system and to reduce the size, and to form a reflecting mirror directly on the end face. A polarization-controlled solid-state laser capable of forming a resonator only with a gain medium becomes possible.

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings.

[0019]

[Embodiment 1] FIG. 1 is a block diagram showing a schematic configuration of a polarization control solid state laser which is Embodiment 1 of the present invention.

In FIG. 1, reference numeral 102 denotes a niobium doped with neodymium and magnesium oxide, which has a crystal axis tilted at a predetermined angle with respect to the central axis of the resonator as shown in the figure, and whose both ends are optically polished. Lithium acid (Nd: MgO:
LiNbO ₃ ) single crystal, one end of which is flat-polished, and the other end of which is polished into a spherical surface having a radius of curvature slightly longer than the crystal length.

Reference numerals 103 and 104 denote excitation laser light (wavelength 80
9 nm) and laser oscillation light (wavelength 1093 nm)
It is a dichroic mirror that reflects light.

Dichroic mirrors 103, 104
Are formed by vapor deposition or the like.

The single crystal 102 and the dichroic
The mirrors 103 and 104 together form an optical resonator. Further, 101 is a semiconductor laser having an oscillation wavelength of 813 nm, and 105 is an excitation laser beam.

Reference numeral 106 shows the spatial distribution of the ordinary laser oscillation light, and 107 shows the spatial distribution of the extraordinary laser oscillation light.

Next, the operation of the polarization controlled solid state laser of the first embodiment will be described.

In FIG. 1, light emitted from one end face of the semiconductor laser 101 is transmitted through a dichroic mirror 103, and a lithium niobate (Nd: MgO: LiNbO ₃ ) single crystal 10 to which neodymium and magnesium oxide are added.
It is absorbed by 2.

The excited laser oscillation light from the single crystal 102 induces a standing wave mode in the resonator, leading to laser oscillation. Therefore, the polarization of the standing wave mode induced in the resonator is considered.

The stimulated emission cross section of a lithium niobate (Nd: MgO: LiNbO ₃ ) single crystal doped with neodymium and magnesium oxide has a plurality of values corresponding to a plurality of wavelengths, but laser oscillation is the most effective. It has a low threshold wavelength.

The laser threshold Pth is calculated by the following mathematical formula 1.
It is represented by.

[0030]

[Equation 1] Pth∝1 / (η · J) η: Stimulated emission cross section J = ∫cavity r (x, y, z) s (x, y, z) dv r (x, y, z): Excitation Ion number distribution s (x, y, z): oscillation photon number distribution J: volume integral of product of excited ion number distribution and oscillation photon number distribution in the resonator. Hereinafter, it will be referred to as overlap integral.

Here, the wavelength at which the stimulated emission cross-section (η) is maximized by the extraordinary laser oscillation light is 1.084 μm.
= 1.8 × E-19cm ² (E-19 is 10-19
The wavelength at which the stimulated emission cross-section (η) is maximum with ordinary laser oscillation light is 1.093 μm, and η =
It is 0.6 × E-19 cm ² (E-19 represents 10 −19 power). (TY Fan et al, “Nd: MgO: LiNbO ₃
spectroscopy and laser devices ", J. Opt. Soc. Am.
B, vol.3 (1), P140 (1986)).

In the first embodiment, in order to oscillate with the ordinary laser oscillation light whose maximum value of the stimulated emission cross-section (η) is smaller than the extraordinary laser oscillation light, the overlap integral with the oscillation mode of the ordinary laser oscillation light is used. The excitation laser light is focused such that (J) is sufficiently larger than the overlap integral (J) of the abnormal light with respect to the laser oscillation light.

Therefore, in the first embodiment of FIG. 1, (1)
The polarization of the pump laser light 105 is adjusted so as to be ordinary light in the gain medium, and (2) the central axis of the pump laser light 105 is aligned with the central axis of the ordinary laser oscillation light 106.

For example, the curvature of the spherical mirror is 3.65 mm, the resonator length is 3.02 mm, and the angle 7 from the C axis of the central axis of the resonator is 7
At 0.8 °, the beam diameter of the fundamental mode of the laser oscillation light at the plane end face is 15 μm, and the ordinary laser oscillation light 1
The central axis of the laser oscillation light 107 of 06 and the extraordinary light is 67 μm
Since they are separated, if the excitation laser light is focused as described above,
The threshold of the ordinary laser oscillation light 106 can be made smaller than the threshold of the extraordinary laser oscillation light 107.
Therefore, it becomes possible to oscillate with the laser oscillation light of ordinary light.

As described above, according to the first embodiment, it becomes possible to oscillate with the ordinary laser oscillation light by the method capable of miniaturizing,
The Brewster plate in the conventional example becomes unnecessary, and the angle adjustment for that is also unnecessary.

[0036]

[Embodiment 2] FIG. 2 is a block diagram showing a schematic configuration of a polarization-controlled solid-state laser for generating a second harmonic, which is Embodiment 2 of the present invention.

In FIG. 2, reference numeral 202 denotes a surface-polished one end and a spherically-polished other end, which is lithium niobate (Nd: MgO: LiN) added with neodymium and magnesium oxide.
bO ₃ ) single crystal.

Reference numerals 203 and 204 denote laser oscillation light (wavelength 10
(93 nm) and the pump laser light wavelength and the second harmonic 2
It is a dichroic mirror that transmits 08 (wavelength 546.5 nm).

Dichroic mirrors 203 and 204
Are formed by vapor deposition or the like.

Reference numeral 201 denotes an excitation laser beam 205 (wavelength 809
nm) is emitted from the semiconductor laser.

Reference numeral 206 shows the spatial distribution of the ordinary laser oscillation light, and 207 shows the spatial distribution of the extraordinary laser oscillation light. Further, 208 is the second harmonic of the laser oscillation light (wavelength 5
46.5 nm).

In the lithium niobate (Nd: MgO: LiNbO ₃ ) single crystal to which neodymium and magnesium oxide are added, it is possible to generate the second harmonic wave with high efficiency only in the case of ordinary laser oscillation light.

In the second embodiment, it is possible to oscillate with the ordinary laser oscillation light, and it is possible to generate the highly efficient second harmonic.

[0044]

Third Embodiment FIG. 3 is a block diagram showing a schematic configuration of a polarization control solid-state laser having an independent mirror and a gain medium, which is a third embodiment of the present invention.

In FIG. 3, reference numeral 303 denotes a lithium niobate (Nd: Mg) having a crystal axis as shown in the figure and having both ends flat-polished and neodymium and magnesium oxide added.
O: LiNbO ₃ ) single crystal.

Reference numeral 302 denotes an excitation laser beam (wavelength 809 nm)
Is a flat dichroic mirror that transmits laser light and reflects laser oscillation light (wavelength 1093 nm).
It is a concave dichroic mirror with the same reflection and transmission characteristics as 2.

The single crystal 303 and the dichroic mirrors 302 and 304 integrally form an optical resonator. Further, 301 is a semiconductor laser having an oscillation wavelength of 813 nm, and 305 is an excitation laser beam.

Reference numeral 306 shows the spatial distribution of the ordinary laser oscillation light, and 307 shows the spatial distribution of the extraordinary laser oscillation light.

The laser of FIG. 3 has the same effect as that of FIG.

[0050]

Fourth Embodiment FIG. 4 is a block diagram showing a schematic configuration of a polarization control solid-state laser having a ring resonator which is a fourth embodiment of the present invention and generating a sum frequency laser beam.

In FIG. 4, 401 has a crystal axis as shown in the figure and has three end faces optically polished, and lithium niobate (N) containing neodymium and magnesium oxide is added.
d: MgO: LiNbO ₃ ) single crystal.

The single crystal 401 has one end polished flat to totally reflect the laser oscillation light, and the other two ends polished to a spherical surface, and one end has a laser oscillation light (wavelength 1093n).
m) is formed, and a dichroic mirror 403 that transmits the excitation laser light (wavelength 809 nm) is formed, and a dichroic mirror 404 that has the function of 403 at the other end and that transmits the sum frequency laser light (wavelength 590 nm) is formed. Has been done.

The dichroic mirrors 403 and 404 are
It is formed by a method such as vapor deposition.

The single crystal 401 and the dichroic mirrors 403 and 404 together form an optical resonator.

Reference numeral 402 denotes a signal laser beam (wavelength 1.3).
It is a dichroic mirror that reflects the excitation laser light (wavelength 809 nm).

Reference numeral 406 is a signal laser beam, and 405 is an excitation laser beam, which is multiplexed by the dichroic mirror 402. Reference numeral 407 denotes an optical path of ordinary laser oscillation light.
Reference numeral 08 denotes an optical path of extraordinary light oscillation light.

The signal laser light 406 (ordinary light) incident on the lithium niobate (Nd: MgO: LiNbO ₃ ) single crystal doped with neodymium and magnesium oxide is second-order nonlinear together with the laser light 407 (ordinary light) in the resonator. An optical effect is generated, and the sum frequency laser light 409 (abnormal light) is generated.

In the laser of FIG. 4 as well, by adjusting the optical path of the excitation light, it is possible to oscillate the ordinary laser light, as in the above example.

As described above, according to this embodiment,
In a laser that uses a gain medium in which the polarization direction to cause laser oscillation and the polarization direction that maximizes the stimulated emission cross-section, the spatial distribution of the laser oscillation light in the optical resonator is
A difference due to the difference in polarization is generated, and the overlap of the pump laser light can be increased only in the polarization for laser oscillation, so that the optical system can be easily adjusted, and the size can be reduced.
A polarization-controlled solid-state laser capable of forming a resonator only with a gain medium in which a reflecting mirror is directly formed on an end face is possible.

As the gain medium, lithium niobate containing only neodymium, lithium niobate containing neodymium and zinc oxide (ZnO), lithium niobate containing neodymium and scandium oxide (Sc ₂ O ₃ ) and erbium are used. Added lithium niobate, lithium added niobate containing thulium, neodymium yttrium aluminum borate (NdxY1-xAl
_The present invention is also applicable to a wavelength conversion laser using ₃ (BO ₃ ) ₄ : NYAB) or the like.

The present invention can be applied not only to the second harmonic generation and the sum frequency generation but also to the parametric conversion as the second-order nonlinear optical effect requiring polarization control.

As described above, the invention made by the present inventor is
Although the specific description has been given based on the above-described embodiments, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the scope of the invention.

[0063]

As described above, according to the present invention,
In a laser that uses a gain medium in which the polarization direction to cause laser oscillation and the polarization direction that maximizes the stimulated emission cross-section, the spatial distribution of the laser oscillation light in the optical resonator is
A difference due to the difference in polarization is generated, and the overlap of the pump laser light can be increased only in the polarization for laser oscillation, so that the optical system can be easily adjusted, and the size can be reduced.
A polarization-controlled solid-state laser capable of forming a resonator only with a gain medium in which a reflecting mirror is directly formed on an end face is possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a polarization control solid-state laser which is an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a polarization-controlled solid-state laser that generates a second harmonic, which is an embodiment of the present invention.

FIG. 3 is a block diagram showing a schematic configuration of a polarization control solid-state laser having an independent mirror and a gain medium that is an embodiment of the present invention.

FIG. 4 has a ring resonator which is an embodiment of the present invention,
It is a block diagram which shows the schematic structure of the polarization control solid-state laser which produces | generates a sum frequency laser beam.

FIG. 5 is a block diagram showing a schematic configuration of a polarization-controlled solid-state laser using a conventional Brewster plate.

[Explanation of symbols]

101, 201, 301, 1 ... Semiconductor laser, 103,
104, 203, 204, 302, 304, 403, 4
04, 2, 5 ... Dichroic mirror, 102, 20
2, 303, 401, 3 ... Single crystal, 402 ... Combined dichroic mirror, 4 ... Brewster plate, 6 ... Temperature controller, 105, 205, 305, 405, 7 ... Excitation laser light, 106, 206, 306 , 407, 8 ... Ordinary laser oscillation light, 107, 207, 307, 408 ... Abnormal light laser oscillation light, 208, 9 ... Second harmonic wave, 406 ... Signal laser light, 409 ... Sum frequency laser light.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01S 3/108 8934-4M 3/109 8934-4M 3/16 8934-4M

Claims (1)

[Claims] 1. A photoexcited solid-state laser in which the central axis of the spatial distribution of laser oscillation light in the gain medium does not coincide with the optical axis of the gain medium or the principal axis of the index ellipsoid of the gain medium. A polarization-controlled solid-state laser, wherein the central axis of the spatial distribution of the pump laser light in the medium is made to coincide with the central axis of the spatial distribution of one polarization of the laser oscillation light in the gain medium.