JPH11103115A - Wavelength conversion laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high beam characteristic and output stability even when using optical components having internal defects by providing a member in a resonator for blocking an optical path at specified distance outside from the optical axis of a specified-order mode light; the distance is specified times the beam waist radius. SOLUTION: A laser diode-excited solid state laser comprises a semiconductor laser 11 emitting an exciting laser beam 10, laser medium of Nd:YVO4 crystal 13 and resonator mirror 14 with an etalon holder 35 having a hole 35a for passing a solid state laser beam 18 with which the hole 35a is aligned center to center. The holder 35 surely cuts higher-order modes having optical paths outside a position distant from the resonator optical axis 1.5-7 times the beam waist radius of the O-order mode light, thereby suppressing the higher-order modes originating from optical components having internal defects.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser having a wavelength conversion function, and more particularly, to a method for obtaining high-quality beam characteristics and output stability even when an optical component having an internal defect is used. The present invention relates to a wavelength conversion laser described above.

[0002]

2. Description of the Related Art As shown in, for example, JP-A-62-189783, a solid-state laser in which a solid-state laser crystal doped with neodymium (Nd) is pumped by light emitted from a semiconductor laser or the like is known. . In this type of solid-state laser, in order to obtain a laser beam with a shorter wavelength, an optical wavelength conversion element made of a crystal of a nonlinear optical material (nonlinear optical crystal) is arranged in the resonator, and the solid-state laser beam is emitted. Wavelength conversion to a second harmonic or the like is also widely performed.

As the above-mentioned optical wavelength conversion element, for example, as shown in JP-A-5-5920, a region in which the spontaneous polarization (domain) of a nonlinear optical crystal made of a ferroelectric material is periodically inverted is used. What is provided is known. In the case of using such an optical wavelength conversion element, the period ド メ イ ン of the domain inversion unit is represented by: {c = 2π / {β (2ω) -2β (ω)} (1) where β (2ω) is the second harmonic By setting the propagation constant β (ω) to be an integral multiple of the coherent length Λc given by the propagation constant of the fundamental wave, phase matching between the fundamental wave and the second harmonic can be achieved.

[0004]

However, in the conventional wavelength conversion laser using the nonlinear optical crystal having the periodic domain inversion structure, there has been a problem that the beam quality and output stability tend to be low. I have.

[0005] This problem is due to the fact that the nonlinear optical crystal having the periodic domain inversion structure has a refractive index distribution on the light transmitting surface and inside for some reason.
In other words, if the nonlinear optical crystal has a refractive index distribution, higher-order transverse modes are more likely to oscillate, so that beam quality deteriorates.
In addition, a scramble for gain occurs between the higher-order mode and the zero-order mode, and output fluctuation is likely to occur due to disturbance or the like.

The present invention has been made in view of the above circumstances, and even when an optical component having an internal defect such as a nonlinear optical crystal having a refractive index distribution is used, high-quality beam characteristics and output stability can be obtained. It is an object of the present invention to provide a wavelength conversion laser capable of obtaining the following.

[0007]

According to the wavelength conversion laser of the present invention, as described above, a laser crystal is excited by light, and a solid-state laser beam emitted by the laser is converted by a nonlinear optical crystal arranged in a resonator. In the wavelength conversion laser, the beam waist radius of the 0th-order mode light from the optical axis (1 / e ² diameter) is set in the resonator.
A member that blocks an optical path in a range outside the position that is 5 to 7 times is provided.

More specifically, as the member for blocking the optical path, more specifically, a holder having a light passage hole for passing a solid-state laser beam and holding an optical member for transmitting the beam can be suitably used. it can. That is, in this case, the radius of the light passage hole of the holder may be set to 1.5 to 7 times the beam waist radius of the 0th-order mode light.

Further, as the member for interrupting the optical path, a member having an optical path interrupting portion extending from at least one radially outer side of the solid-state laser beam toward the center may be used.

[0010]

The high-order transverse mode is generated outside the zero-order mode light. Therefore, in the wavelength conversion laser according to the present invention, if a member that blocks the optical path is provided, the oscillation of the higher-order transverse mode is suppressed. If so, it is possible to prevent the beam quality from deteriorating due to the higher-order transverse mode and prevent the output from fluctuating, thereby realizing high-quality beam characteristics and output stability.

If the range in which the optical path is cut off is set too far from the optical axis, the effect of suppressing the oscillation of the higher-order transverse mode is impaired. If this range is set to a range outside seven times or less of the beam waist radius of the 0th-order mode light as in the present invention, the effect of suppressing the oscillation of the higher-order transverse mode can be clearly obtained.

Conversely, if the range for blocking the optical path is set too close to the optical axis, the bottom of the zero-order mode light is cut off, and the originally used zero-order mode light loses. If this range is set to a range outside 1.5 times or more the beam waist radius of the 0th-order mode light as in the present invention, the loss due to vignetting at the foot of the 0th-order mode light can be practically ignored. (Generally 1% or less).

If the loss exceeds 1%, the power of the fundamental wave stored in the resonator becomes 以下 or less, and the output of the wavelength-converted wave becomes １ ／ or less. The wavelength conversion laser becomes unsuitable for practical use.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a side view of a laser diode-pumped solid-state laser according to one embodiment of the present invention.

This laser diode pumped solid-state laser has a semiconductor laser 11 for emitting a laser beam 10 as excitation light, a condensing lens 12 for condensing a laser beam 10 as divergent light, and neodymium (Nd) doped. YVO ₄ crystal (Nd: YV) which is a solid laser medium
And O ₄ crystal) 13, the Nd: YVO ₄ crystal 13 front side (the semiconductor laser 11 and the opposite side) arranged resonators mirrors
14 and has.

Nd: YVO ₄ crystal 13 and resonator mirror
The Brewster plate 17, a MgO: LiNbO ₃ (MgO-doped LiNbO ₃ ) crystal 15 which is a nonlinear optical material having a periodic domain inversion structure, and an etalon 16 are arranged in this order from the Nd: YVO ₄ crystal 13 side. Are arranged. Nd: YVO ₄ crystal 13, MgO: LiNbO ₃ crystal
15, etalon 16, Brewster plate 17, and resonator mirror
14 is adhesively fixed to a copper holder 21 and is fixed to a package base 32 via a plate-shaped base plate 30 and a Peltier element 31.

The temperature in the resonator is detected by a thermistor 33 attached to the resonator, and the current of the Peltier element 31 is controlled by a temperature control circuit (not shown) so that the detected temperature becomes a predetermined temperature. Adjusted to maintain the temperature in the resonator at a predetermined temperature.

The semiconductor laser 11 emits a laser beam 10 having a center wavelength of 809 nm, and is press-fitted and fixed in a holder 20. The etalon 16 is formed of a quartz plate having a thickness of 0.3 mm, and one light transmitting surface thereof is adhesively fixed to an etalon holder 35 made of copper, and is arranged at an angle of 45 'with respect to the optical axis. The Brewster plate 17 is made of a quartz plate having a thickness of 0.385 mm.

The Nd: YVO ₄ crystal 13 emits light having a wavelength of 1064 nm when neodymium ions are excited by the incident laser beam 10. On the incident end face 13a of the Nd: YVO ₄ crystal 13, light having a wavelength of 1064 nm is reflected well (reflectance of 99.9% or more), while the excitation laser beam 10 having a wavelength of 809 nm is transmitted well (transmittance of 93%).
Above) coating is applied. This Nd: Y
The other end face of the VO ₄ crystal 13 is provided with a coating that allows good transmission of light having a wavelength of 1064 nm.

On the other hand, on the mirror surface 14a of the resonator mirror 14,
Light having a wavelength of 1064 nm is well reflected (reflectance is 99.9% or more), and light having a wavelength of 532 nm is transmitted (the transmittance is 90%).
%) Coating is applied.

Therefore, the above-mentioned light having a wavelength of 1064 nm is a highly reflecting surface of the Nd: YVO ₄ crystal end face.
The laser beam is confined between the mirror 13a and the mirror surface 14a to cause laser oscillation, and a laser beam 18 having a wavelength of 1064 nm is generated. This laser beam 18 is MgO: LiNbO ₃
The crystal 15 performs type I phase matching, and is converted into a second harmonic 19 having a wavelength of 1/2, that is, 532 nm. The second harmonic 19 is mainly emitted from the resonator mirror 14. I do.

In this example, the Nd: YVO ₄ crystal 13
Has a thickness of 1 mm. MgO: LiNbO ₃ crystal
The length of 15 2 mm, the radius of curvature of the resonator mirror 14 is a concave mirror 50 mm, Nd forming a resonator: distance between the YVO ₄ crystal end face 13a and the mirror surface 14a is about 11 mm.

The MgO: LiNbO ₃ crystal 15 may have a refractive index distribution for the above-described reason, and in that case, a higher-order transverse mode is likely to oscillate. Hereinafter, the point of suppressing the oscillation of the higher-order mode will be described.

As shown in FIG. 2 in an enlarged manner, the etalon holder 35 has a light passing hole 35a for passing the laser beam 18, and the center of the light passing hole 35a coincides with the beam center of the laser beam 18. It is arranged in.

In this embodiment, the radius of the light passing hole 35a is
350 μm. On the other hand, since the beam waist radius of the zero-order mode light of the laser beam 18 is 80 μm, the radius of the light passage hole 35a is equivalent to 4.4 times the beam waist radius. Therefore, a higher-order mode having an optical path outside the position of 4.4 times the beam waist radius of the 0th-order mode light from the resonator optical axis can be reliably cut by the etalon holder 35.

As a result, the dispersion of the divergence angle of the laser beam between the individual solid-state laser modules is generally about 15% pp in the conventional apparatus, but is reduced to 3% pp in the present apparatus. 10-
The output fluctuation when a temperature change of 45 ° C is given is generally about 50% pp in the conventional device,
It decreased to 10% pp.

In this embodiment, since the etalon holder 35 having the light passage hole 35a is used as an optical path blocking member, it differs from the case where an optical path blocking member such as a pinhole plate is inserted into the resonator after oscillation. This eliminates the need for adjusting the position of the light path blocking member.

The etalon holder 35 is not limited to the etalon holder 35. It is also possible to use a holder having a light passage hole for fixing other optical members as an optical path blocking member.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 3 shows an optical path blocking member that can be used in the apparatus of FIG. The optical path blocking member 40 is a U-shaped member having an optical path blocking section 40a extending toward the center from the outside of one radial (vertical direction in the drawing) of the laser beam 18, MgO: LiNbO ₃ crystal
It is arranged to cover 15.

Further, the light path blocking member 40 includes a light path blocking section 40.
The inner edge of a is 350 μm from the center of the laser beam 18.
It is arranged to be located at a distance. Also in this case, since the beam waist radius of the zero-order mode light of the laser beam 18 is 80 μm,
Higher-order modes having an optical path outside the position of 4.4 times are reliably cut by the optical path blocking member 40. As described above, the light path blocking member 4 is provided above the MgO: LiNbO ₃ crystal 15.
When 0 is arranged, the adjustment is unnecessary or facilitated.

MgO: L having periodic domain inversion structure
In the iNbO ₃ crystal 15, the beam characteristics particularly in the direction corresponding to the c-axis direction are deteriorated. In the conventional device, the beam when the resonator temperature is changed between ± 5 ° C. with respect to the drive resonator temperature is used. The divergence angle change was generally about 10% pp. On the other hand, in the present apparatus, the change in the beam divergence angle was suppressed to 3% pp.

In the structure shown in FIG. 3, the depth of the vignetting prevention groove 21a provided in the holder 21 is made shallower than the ordinary depth of about 500 μm, and the holder 21 at the lower portion of the groove 21a is It can also function as a similar light path blocking unit. If so, the light path blocking member
You can omit 40.

The present invention is not limited to a nonlinear optical crystal having a periodic domain inversion structure, but also has an effect of suppressing a higher-order mode caused by using another optical component having an internal defect.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing a wavelength conversion laser according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing an optical path blocking member used in the wavelength conversion laser.

FIG. 3 is a perspective view showing an optical path blocking member used in a second embodiment of the present invention.

[Explanation of symbols]

10 Laser beam (pumping light) 11 Semiconductor laser 12 Condensing lens 13 Nd: YVO ₄ crystal 14 Resonator mirror 15 MgO: LiNbO ₃ crystal 16 Etalon 17 Brewster plate 18 Solid-state laser beam (fundamental wave) 19 Second harmonic 20 Holder 21 Block 30 Base plate 31 Peltier element 33 Thermistor 35 Etalon holder 35a Light passage hole of etalon holder 40 Optical path blocking member 40a Optical path blocking section

Claims (5)

[Claims] 1. A wavelength conversion laser that excites a laser crystal with light and converts the wavelength of a solid-state laser beam emitted from the laser crystal by a nonlinear optical crystal disposed in a resonator. A wavelength conversion laser provided with a member for blocking an optical path in a range outside a position 1.5 to 7 times a beam waist radius of mode light. 2. The wavelength conversion laser according to claim 1, wherein said nonlinear optical crystal has a periodic domain inversion structure. 3. The holder for blocking an optical path has a light passing hole through which a solid-state laser beam passes and holds an optical member through which the beam passes, wherein the radius of the light passing hole is 3. The wavelength conversion laser according to claim 1, wherein the wavelength is 1.5 to 7 times the beam waist radius of the zero-order mode light. 4. The solid-state laser beam as claimed in claim 1, wherein the member for blocking the optical path has a light-path blocking portion extending from at least one radial outside of the solid-state laser beam to the center side. Wavelength conversion laser. 5. The wavelength conversion laser according to claim 1, wherein the nonlinear optical crystal having the periodic domain inversion structure is a MgO: LiNbO ₃ crystal.