JP2792437B2 - Ring type solid laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring-type solid-state laser device, and more particularly to a reduction in noise.

[0002]

2. Description of the Related Art A laser diode-pumped solid-state laser has high efficiency and is compact, and is attracting attention as a replacement for the conventional lamp-pumped solid-state laser and gas laser.

FIG. 3 shows a conventional ring-type laser wavelength converter using a wavelength conversion technique disclosed in Japanese Patent Application Laid-Open No. 4-335586. A first condenser lens 215a and a second condenser lens 215b for condensing the fundamental wave 213 emitted from the laser diode 214;
It is provided with glass 270 having a plurality of reflection surfaces (reflection surface 270a, reflection surface 270b, reflection surface 270c), a part of which is formed by wavelength conversion element 210. Next, the operation will be described.

[0004] The fundamental wave 13 enters from the reflection surface 270a and is reflected by the other two reflection surfaces (reflection surface b and reflection surface a) to form a ring resonator. Since a part of the glass 270 is formed by the wavelength conversion element 210, the fundamental wave 213 is wavelength-converted into the second harmonic 242. And
The laser beam passes through the reflection surface 270b and obtains a predetermined laser beam.

[0005]

This conventional ring resonator type wavelength converter increases or decreases the optical noise of the second harmonic 242 obtained by the polarization characteristics of the laser diode 214. For example, when the polarization ratio indicating the polarization characteristics of the laser diode 214 is low, noise increases when the wavelength conversion method of the wavelength conversion element 210 is the second type phase matching. The reasons are considered as follows. (1) In the wavelength conversion method based on the second type phase matching , two polarized photons of the fundamental wave 213 become orthogonal ordinary light and extraordinary light, respectively, and are added in the same phase. Therefore, if the polarization characteristic is low, it hardly contributes to the wavelength polarization. Photons stay in the ring resonator and these photons disturb the phase. (2) Since the wavelength conversion element 210 has a birefringent characteristic in which the speed of light varies depending on the polarization direction, light may be separated to such an extent that it does not diverge from the ring resonator optical axis and may return to the ring resonator optical axis again. for disturbing the advance <br/> traveling wave phase of the fundamental wave 213 in the ring resonator.

Generally, the polarization ratio of a Fabry-Perot type laser diode is about 1: 100, which is lower than that of a gas laser (for example, the polarization ratio of an internal mirror type 10 mW He-Ne laser is 1: 1000 or more).
When the laser beam is output by a laser diode, the polarization state must be carefully considered for the reasons (1) and (2) described above.

As described above, the ring resonator type wavelength converter using the conventional laser diode has a problem that optical noise is large.

[0008]

The ring-type solid-state laser device according to the present invention comprises a laser diode 1, a condensing lens 2 for condensing the output light of the laser diode 1, a uniaxial solid-state laser medium 6, and a ring-shaped solid-state laser medium. It has three mirrors (incident mirror 3, output mirror 4, and reflecting mirror 5) constituting a resonator, and a wavelength conversion element 7, and the uniaxial solid
The laser light incident surface of the laser medium is opposite to the normal of the incident surface.
The optical axis has a certain angle, and the laser beam
Not perpendicular to the surface .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a ring resonator type wavelength converter according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

The configuration includes a laser diode 1, a condenser lens 2, an entrance mirror 3, an output mirror 4, a reflection mirror 5, a uniaxial solid laser medium 6, and a wavelength conversion element 7.
, A fundamental wave 8, a second harmonic 9, and a unidirectional device 10.

Next, the operation will be described. Excitation light is emitted from the laser diode 1, and the condensing lens 2 condenses the excitation light to form a uniaxial solid laser medium (for example, Nd: YVO4 or Er: Y having a high light absorption characteristic and high excitation efficiency).
VO4) is excited. The solid-state laser resonator is formed by three mirrors (incident mirror 3, output mirror 4, and reflection mirror 5). The unidirectional device 10 is a device for advancing light in a specific direction by the Faraday effect for rotating the polarization direction, and is used for a linearly polarized laser. Oscillated fundamental wave 8
Only passes in the direction of the arrow (counterclockwise) shown in FIG. On the other hand, the uniaxial solid-state laser medium 6 splits into a normal light and an extraordinary light with respect to a polarization plane in a specific direction as shown in FIG.
Therefore, the light is not split into ordinary light and extraordinary light, that is, polarized in the direction of the optical axis where the speeds of the ordinary light and the extraordinary light coincide.

As described above, the clockwise light shown in FIG. 1 causes the unidirectional device 10 to shift the plane of polarization from the optical axis of the uniaxial solid-state laser medium 6 due to the Faraday effect. As a result, no oscillation occurs.

[0014]

The fundamental wave 8 oscillated by the above operation is wavelength-converted by the wavelength conversion element 7 and a predetermined output can be obtained from the output mirror 4, but optical noise is large. The main causes of the optical noise are as follows (a) and (b). (A) Disturbance of the fundamental wave 8 due to optical axis shift and phase shift due to the birefringence characteristics and polarization characteristics of the uniaxial solid-state laser medium 6 and the wavelength conversion element 7. (B) Disturbance of the fundamental wave 8 due to reflected light of the fundamental wave 8 at the end face of the uniaxial solid-state laser medium 6 and the wavelength conversion element 7.

In order to solve this problem, the uniaxial solid laser medium 6 and the wavelength conversion element 7 in the uniaxial solid laser medium 6 and the wavelength conversion element 7 of the ring type solid laser device are used.
Was rotated about the optical axis, and was installed so as to have an angle of 5 mrad to 20 mrad with respect to the optical axis of the fundamental wave 8 with respect to the normal of the incident surface of the uniaxial solid laser medium 6 and the normal of the incident end surface of the wavelength conversion element 7.

Since the resonator length is in the range of 50 to 200 mm from the practical design dimensions, the angle is set with the diverging angle.

For example, when the resonator length is 50 mm and the beam diameter is 0.5 mm, an angle shift of 5 mrad is 0.25 mm.
The optical axis shifts and diverges. As a result, the noise is reduced since it does not affect the fundamental wave 8 even if it becomes a noise source. On the other hand, if the optical axis of the fundamental wave 8 is unnecessarily shifted from the optical axes of the uniaxial solid-state laser medium 6 and the wavelength conversion element 7, alignment of laser oscillation becomes difficult. Therefore, it is necessary to determine a necessary and sufficient amount of angle.

As described above, a ring resonator type wavelength converter having constant noise and easy alignment has been completed.

Incidentally, the above-mentioned uniaxial solid laser medium 6
May be selected as Nd: YVO4 (neodymium-added yttrium vanadium oxide crystal) or Er: YVO4 (erbium-added yttrium vanadium oxide crystal). The reason for this will be additionally described.

[0021] (i) Nd: YVO4 because it is uniaxial crystal for, direction (axial velocity of light matches the ordinary and extraordinary light) the optical axis fried light loss low, the polarization in the optical axis direction, easily Linearly polarized light can be obtained.

Furthermore, as compared with Nd: YAG, which is widely used as a solid-state laser crystal, the absorption efficiency is about three times larger, so that the excitation efficiency is improved.

(Ii) Er: YVO4 Since the crystal is a uniaxial crystal, the optical axis (the axis at which the speed of the ordinary light and the speed of the extraordinary light coincide) has a low light loss, so that it is polarized in the direction of the optical axis and easily. Linearly polarized light can be obtained.

Further, since it has a tendency of blue-green in a wavelength band of 450 nm to 550 nm, it may oscillate as an up-conversion laser. Oscillation threshold is high due to the optical loss of the crystal itself, and oscillation does not occur with pumping of about 1 W. However, in recent years, the output of laser diodes for solid-state laser pumping has been high, and up to 100 W is available in commercially available laser diodes. ing. In the future, if the price decreases, it will be more advantageous for commercialization. A blue-green laser is not attractive because it is easily output by a water-cooled Ar laser, but its attractiveness arises when a UV laser is intended due to wavelength conversion. As a wavelength conversion element, BBO (β-BaB 2 O 4) or LBO (LiB 3
O4) A wavelength conversion element is desirable.

[0025]

As described above, according to the present invention, in the uniaxial solid laser medium 6 and the wavelength conversion element 7 of the ring type solid laser device, the uniaxial solid laser medium 6 and the wavelength conversion element 7 are arranged around the optical axis. By rotating and installing so as to have an angle of 5 mrad to 20 mrad with respect to the optical axis of the fundamental wave 8 with respect to the end face of the uniaxial solid laser medium 6 and the normal to the wavelength conversion element 7, (a) the uniaxial solid laser Disturbance of fundamental wave 8 due to optical axis shift and phase shift due to birefringence characteristic and polarization characteristic of medium 6 and wavelength conversion element 7 (b) Uniaxial solid-state laser medium 6 and fundamental wave 8 reflected light at end face of wavelength conversion element 7 The disturbance of the fundamental wave 8 was eliminated, and low noise was realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 shows a conventional ring-type solid-state laser device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser diode 2 Condensing lens 3 Incident mirror 4 Output mirror 5 Reflecting mirror 6 Uniaxial solid laser medium 7 Wavelength conversion element 8 Fundamental wave 9 Second harmonic 10 Unidirectional device 210 Wavelength conversion element 211 Optical axis 213 Fundamental wave 214 Laser Diode 215a First condenser lens 215b Second condenser lens 242 Second harmonic 270 Glass 270a Reflective surface 270b Reflective surface 270c Reflective surface

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/094 H01S 3/083 H01S 3/16 H01S 3/17 JICST file (JOIS)

Claims (7)

(57) [Claims] 1. A ring resonator comprising a laser diode, a solid-state laser medium excited by the laser diode, three or more reflection mirrors, and a wavelength conversion element disposed in an optical axis of the ring resonator. In a ring-type solid-state laser device, the solid-state laser medium is a uniaxial solid-state laser medium, and the laser light incident surface of the uniaxial solid-state laser medium has a predetermined angle with respect to a normal to the incident surface. A ring-type solid-state laser device, wherein the laser light does not perpendicularly enter the incident surface. 2. A ring resonator comprising a laser diode, a solid-state laser medium excited by the laser diode, three or more reflection mirrors, and a wavelength conversion element arranged in an optical axis of the ring resonator. In the ring-type solid-state laser device, the solid-state laser medium is a uniaxial solid-state laser medium, and a laser beam incident surface of the uniaxial solid-state laser medium has an optical axis of 5 m with respect to a normal line of the incident surface.
A ring-type solid-state laser device having an angle of rad to 20 mrad. 3. The method according to claim 1, wherein the uniaxial laser medium is Nd: YVO.
3. The ring-type solid-state laser device according to claim 1, wherein the ring-type solid-state laser device is ₄ or Er: YVO ₄ . 4. The fixed angle is 5 mrad to 20 mr.
ring solid-state laser apparatus according to claim 1, characterized in that the angle of the ad. 5. A laser beam incident end face of the wavelength conversion element, wherein the optical axis has a certain angle with respect to a normal line of the incident face, and laser light is not perpendicularly incident on the incident end face. The ring-type solid-state laser device according to claim 1. 6. A laser beam incident end face of the wavelength conversion element.
Definitive said predetermined angle is a ring-type solid-state laser apparatus according to claim 5, characterized in that the angle of 5Mrad～20mrad. 7. The method according to claim 1, wherein the uniaxial solid laser medium is Er: YV.
A O _4, wherein the wavelength conversion element BBO (β-BaB2
0 ₄₎ or a ring-type solid-state laser apparatus according to claim 1 or 2, wherein the a LBO (LiB ₃ 0 _4).