JP6667824B2 - Q-switch solid-state laser device - Google Patents

Description

  The technology disclosed in the present specification relates to a solid-state laser device using a solid-state laser material that is in a population inversion state when excited by excitation light to cause a stimulated emission phenomenon. In particular, the present invention relates to a Q-switch solid-state laser device that emits a pulse laser by disposing a solid-state laser material and a Q-switch between a pair of resonant mirrors. Hereinafter, for the sake of simplicity, a Q-switch solid-state laser device may be abbreviated as a laser device.

  There is known a laser device in which a first resonance mirror, a solid-state laser material, a Q switch, and a second resonance mirror are arranged in that order. That is, there is known a laser device in which a solid-state laser material and a Q switch are arranged between a pair of resonance mirrors including a first resonance mirror and a second resonance mirror.

  Non-Patent Document 1 discloses a small laser device in which a solid state laser material and a Q switch are arranged between a pair of resonant mirrors. The Q switch is a passive Q switch using a saturable phenomenon, The Q switch cannot be actively controlled.

  Non-Patent Document 2 discloses a technique for actively controlling a Q switch using an electro-optic effect. The thickness of a solid-state laser material is 0.5 mm, whereas the thickness of a Q switch is 5 mm. Therefore, the Q switch is an obstacle to downsizing the laser device.

Non-Patent Document 3 discloses a technique of actively controlling a Q switch using an acousto-optic effect. However, the thickness of the Q switch is as large as 32 mm, and the Q switch is an obstacle to downsizing of a laser device. ing.
In the current technology, if the Q switch can be actively controlled, the Q switch becomes large, which is an obstacle to downsizing the laser device. With the current technology, it is impossible to achieve both miniaturization of the laser device and activation of the Q switch.

T.Taira, M.Tsunekane, K.Kanehara, S.Morishima, N.Taguchi and A. Sugiura: “7. Promise of Giant Pulse Micro-Laser for Engine Ignition”, Journal of Plasma and Fusion Research, Vol. 89, No.4, pp.238-241 (2013) T.Taira, and T.Kobayasdhi: “Q-Switching and Frequency Doubling of Solid-State Lasers by a Single Intracavity KTP Crystal”, IEEE Journal of Quantum Electronics of Vol. 30, No. 3, pp. 800-804 (1994 ) Gooch & Housego Co. Ltd., Product number 1-QS041-1, 8C10G-4-GH21http: //www.optoscience.com/maker/gooch/pdf/ao-qswuitch-air.pdf

  This specification discloses a technique for activating a Q-switch under the constraint that it does not hinder miniaturization of a laser device.

  In the laser device disclosed in this specification, the first resonance mirror, the solid-state laser material, the Q switch, and the second resonance mirror are arranged in that order. That is, a pair of resonance mirrors is constituted by the first resonance mirror and the second resonance mirror, and a solid-state laser material and a Q switch are arranged between the pair of resonance mirrors. The Q switch is composed of a combination of a film exhibiting a magneto-optical effect (hereinafter abbreviated as a magneto-optical film) and a magnetic flux generator. When the excitation light is incident on the solid-state laser material and a pulse is applied to the magnetic flux generator, the Q-switched solid-state laser device emits a pulsed laser.

  The magneto-optical film rotates a deflection surface of a laser transmitted through the magneto-optical film. The rotation angle (Faraday rotation angle) changes according to the magnitude of the magnetic flux generated by the magnetic flux generator. Depending on the magnitude of the Faraday rotation angle, the Q value can be adjusted to a low state or the Q value can be adjusted to a high state. An active Q-switch can be constituted by the magneto-optical film and the magnetic flux generator. When the magneto-optical film is used, a change in the Faraday rotation angle required for the Q switch can be secured by a thin magneto-optical film and a small magnetic flux generator. The Q switch can be activated without hindering downsizing of the laser device.

  As a result of research, it has been found that there is sensitivity between the Faraday rotation angle and the Q value, which can be said to be a threshold. That is, when the Faraday rotation angle corresponding to the threshold value is C °, the pulse laser does not emit at C-ΔC ° because the Q value is low, and the pulse laser emits light at C + ΔC ° because the Q value is high. ° was small and ΔC ° was about 0.5 °, indicating that the pulsed laser emitted light. That is, it was found that if the difference between C−ΔC ° and C + ΔC ° was 1 ° or more, the switch would be a Q switch. It is preferable that a film whose Faraday rotation angle changes by 1 ° or more due to a change in magnetic flux by a magnetic flux generator be a magneto-optical film.

  In particular, rare earth iron garnet is suitable for the magneto-optical film.

  The Faraday rotation angle of the magneto-optical film needs to be changed between a rotation angle equal to or less than C-ΔC ° and a rotation angle equal to or more than C + ΔC °. Even if the above-described relationship is realized by turning on and off a current having a value such that the Faraday rotation angle when the current flowing through the excitation coil is zero and the Faraday rotation angle when the excitation coil is energized becomes C + ΔC ° or more. Alternatively, a combination of a permanent magnet and a coil may be used. The Faraday rotation angle is adjusted to be close to C ° by a permanent magnet, and the Faraday rotation angle is changed between C-ΔC ° and C + ΔC ° by a magnetic field derived from a coil added thereto. Is also good. The exciting current can be kept low, and the exciting coil can be downsized.

  According to the Q-switch solid-state laser device disclosed in this specification, the emission timing of the pulse laser can be controlled by the active Q-switch, and the size can be reduced. With this technology, the Q-switch solid-state laser device can be mounted on an optical communication device or a laser processing device, or the display device can be reduced in size and output can be increased.

A configuration of the Q-switch solid-state laser device according to the first embodiment will be schematically described. The relation between the Faraday rotation angle and the peak output of the pulse laser is shown. A configuration of a Q-switch solid-state laser device according to a second embodiment will be schematically described. The relation between the Faraday rotation angle and the peak output of the pulse laser is shown. The relationship between the pulse current applied to the excitation coil and the pulse laser is shown. 4 shows the relationship between the energizing current and the Faraday rotation angle. The structure of the main part of the laser device of the third embodiment is schematically shown. The structure of the main part of the laser device of the fourth embodiment is schematically shown. The structure of the main part of the laser device of the fifth embodiment is schematically shown. 14 schematically shows a configuration of a main part of a laser device according to a sixth embodiment. 14 schematically shows a configuration of a main part of a laser device according to a seventh embodiment. The structure of the main part of the laser device of the eighth embodiment is schematically shown. The structure of the main part of the laser device of the ninth embodiment is schematically shown. 4 shows a relationship between a current and a Faraday rotation angle when a permanent magnet and a coil are used together.

Hereinafter, some of the technical features of the embodiments disclosed in this specification will be described. The items described below each have technical utility independently.
(Feature 1) A magneto-optical film is formed on an end face of a solid-state laser material.
(Feature 2) A magneto-optical film which exists independently of the solid-state laser material is used in combination with the solid-state laser material.
(Feature 3) An exciting coil is patterned on the surface of the magneto-optical film.
(Feature 4) An exciting coil is arranged near the magneto-optical film.
(Feature 5) A magneto-optical film is arranged between two exciting coils.

(First embodiment)
FIG. 1 schematically shows a configuration of a Q-switch solid-state laser device 22 that emits a pulse laser when excited by a semiconductor laser device 2. Reference numerals 4 and 6 are focusing lenses for the laser emitted by the semiconductor laser device 2. Reference numeral 8 denotes a solid-state laser material. When excited by a laser emitted from the semiconductor laser device 2, the semiconductor laser device 2 changes to a population inversion state and emits laser light by stimulated emission. In this embodiment, GdVO ₄ containing Nd ³⁺ ions is used. The composition of the solid-state laser material 8 is not particularly limited as long as it is a material that emits stimulated emission in a population inversion state. For example, a vanadate material such as Nd: YVO ₄ and Nd: LuVO ₄ or a garnet material such as Nd: YAG, Nd: LuAG, and Nd: GSGG may be used. The rare earth to be added is not limited to Nd, but may be Yb, Er, Tm, Ho, or the like.

Reference numeral 8a denotes a film coated on the end face of the solid-state laser material 8, which has a high transmittance to a laser emitted from the semiconductor laser device 2 and a high transmittance to a laser emitted from the solid-state laser material 8 by induction. It is a film having a reflectance. This corresponds to a first resonance mirror described in the claims.
In the present embodiment, the semiconductor laser device 2 outputs a laser of 808 nm, and the Q-switch solid-state laser device 22 outputs a laser of 1064 nm. The coating film 8a has a transmittance of 99.8% or more for 808 nm and a reflectance of 98% or more for 1064 nm.
Reference numeral 8b is also a film coated on the end face of the solid-state laser material 8 and has a reflectance of 99.8% or more for 808 nm and a transmittance of 98% or more for 1064 nm. . No mirror effect is provided for 1064 nm.

  Reference numeral 16 denotes a reflection film having a reflectance of 99.8% or more for 808 nm and a reflectance of 95% or more for 1064 nm. The reflection film 16 corresponds to a second resonance mirror described in the claims.

The reflection surfaces of the first resonance mirror 8a and the second resonance mirror 16 are parallel to each other, and confine the laser stimulated emission of the solid-state laser material 8 between the two. The first resonance mirror 8a and the second resonance mirror 16 constitute a resonance device. The second resonance mirror 16 has an appropriate reflectivity to the laser emitted from the solid-state laser material 8, and when the Q value of the magneto-optical film 10 described later increases, a part of the resonated laser is It passes through a two-resonant mirror 16. A pulse laser is obtained from the second resonance mirror 16.
The first resonance mirror 8a and the second resonance mirror 16 are obtained by an existing technology, and a detailed description thereof will be omitted. The reflection surface of the second resonance mirror 16 may be a concave surface. If the optical axis of the reflection surface of the first resonance mirror 8a and the optical axis of the reflection surface of the second resonance mirror 16 are aligned, the laser emitted by the solid-state laser material 8 can be confined between the two.
Reference numeral 18 denotes a measuring instrument for measuring the power of the laser light emitted from the second resonance mirror 16.

Reference numeral 10 denotes a film exhibiting a magneto-optical phenomenon. In this embodiment, rare-earth iron garnet ([BiTb] ₃ [FeGa] ₅ O ₁₂ ) was used. The magneto-optical film 10 may be a film exhibiting a magneto-optical phenomenon that changes between a Faraday angle for realizing a high Q value and a Faraday angle for realizing a low Q value, and is not limited to rare earth iron garnet. The thickness of the magneto-optical film 10 is 190 μm, which is extremely thin. The magneto-optical film 10 does not hinder the downsizing of the laser device 22.

Reference numeral 12 denotes an excitation coil, which makes a circuit along the outer periphery of the magneto-optical film 10, and a Faraday rotation phenomenon can be obtained by applying a magnetic field to a central portion (a portion where a laser passes) of the magneto-optical film 10. To do. In this embodiment, the excitation coil 12 is not energized during the period in which the pulse laser is not emitted, and the Faraday rotation angle of the magneto-optical film 10 is reduced to zero. While the Faraday rotation angle is zero, the Q value is low, and a pulse laser cannot be obtained. During the period in which the pulse laser emits light, the excitation coil 12 is energized to increase the Faraday rotation angle of the magneto-optical film 10. As the Faraday rotation angle increases, the Q value increases, and a pulsed laser can be obtained.
Although the magneto-optical film 10 and the exciting coil 12 are illustrated separately in the drawing, they are actually arranged close to each other.

  FIG. 2 shows the relationship between the Faraday rotation angle (which is substantially proportional to the value of the current supplied to the exciting coil 12) and the peak output (W) of the pulse laser. The peak output of the pulse laser changes sharply when the Faraday rotation angle is around 44.5 °. When the Faraday rotation angle is 44 °, the Q value is low, and a pulse laser cannot be obtained. When the Faraday rotation angle becomes 45 °, the Q value increases, and a pulse laser is obtained. That is, the Faraday rotation angle of the magneto-optical film 10 changes only once between 44 ° and 45 °, and changes between a state in which the pulse laser does not emit light and a state in which the pulse laser emits light. Experiments have shown that if the Faraday rotation angle changes by 1 ° or more across the threshold, the magneto-optical film 10 becomes a Q-switch.

(Second embodiment)
FIG. 3 schematically shows the configuration of the laser device of the second embodiment. In the following, the same reference numerals will be used for the already described events, and duplicate description will be omitted. Only the differences will be described. In the laser device 22a of the second embodiment, a ring-shaped permanent magnet 14 is added at a position close to the magneto-optical film 10. The laser passes through the central opening of the permanent magnet 14.
FIG. 4 shows a relationship between a Faraday rotation angle and a peak output when a magnetic flux is generated by using a permanent magnet and a coil together. The Faraday rotation angle of the magneto-optical film 10 is adjusted to 44 ° immediately below the threshold value by the permanent magnet 14. In this embodiment, the Faraday rotation angle is changed from 44 ° by energizing the excitation coil 12. Also in the present embodiment, when the value of the current supplied to the exciting coil 12 is changed, the Q value changes, and the peak output changes. Although the reason is unknown, a comparison between FIG. 2 and FIG. 4 shows that the peak output changes sensitively to the change in the Faraday angle in FIG. 2, whereas the sensitivity can be reduced in FIG. According to the second embodiment, since the permanent magnet 14 is used in combination, the change in the exciting current required to change the Q value can be small, and the size of the exciting coil 12 can be reduced.

  FIG. 5 shows the relationship between the pulse current that electrically charges the coil 12 and the laser output obtained from the Q-switch solid-state laser device. (A) shows the case where the rising speed of the pulse current is steep, and (c) shows the case where the rising speed is slow. The changing speed of the pulse laser output is affected by the rising speed of the pulse current, and the faster the rising speed of the pulse current, the more rapidly the pulse laser output increases (see (b)).

  When the magneto-optical film 10 is used for a Q switch, the changing speed of the Faraday angle can be increased, the changing speed of the pulse laser output can be increased, the time width of the pulse laser can be shortened, and the peak output of the pulse laser can be increased. can do. Experiments have confirmed that the half width of the pulse laser can be reduced to 45 ns. When the magneto-optical film 10 is used for a Q switch, the repetition frequency of the pulse laser can be increased.

  FIG. 6 shows the relationship between the magnetic field applied to the magneto-optical film 10 and the Faraday rotation angle. It can be seen that the Faraday rotation angle is substantially proportional to the flowing current value although there is a slight hysteresis. The Faraday rotation angle has a saturation value, and the saturation value is higher than the threshold (C °). Furthermore, the Q value does not decrease even when the saturation value is reached, and the pulse laser oscillates even when the saturation value is reached.

  FIG. 7 schematically shows the configuration of the laser device of the third embodiment. In this embodiment, the exciting coil 12 is patterned on the surface of the magneto-optical film 10. Since the winding of the exciting coil 12 is sufficient, the exciting coil 12 can be easily patterned on the surface of the magneto-optical film 10 by a technique of a printed circuit board.

  FIG. 8 schematically shows the configuration of the laser device of the fourth embodiment. The path of the current that generates the magnetic flux applied to the magneto-optical film 10 may be a straight line instead of a coil. When a pulse voltage is applied to one end of the metal pattern 12b on the straight line, currents in opposite directions flow at the time of rising and falling. The Faraday rotation angle of the magneto-optical film 10 may be changed using this current.

FIG. 9 schematically shows the configuration of the laser device of the fifth embodiment. The excitation coil 12c may surround the outer periphery of the magneto-optical film 10.
FIG. 10 schematically shows the configuration of the laser apparatus according to the sixth embodiment. The two exciting coils 12c and 12d may be arranged in parallel, and the magneto-optical film 10 may be arranged between them. The excitation coils 12c, 12d, etc., may make a circuit around the outer circumference of the magneto-optical film 10, or may be patterned in a region along the outer circumference of the end face of the magneto-optical film 10.

FIG. 11 schematically shows the configuration of the laser device of the seventh embodiment. The permanent magnet 14 may go around the outer periphery of the magneto-optical film 10.
FIG. 12 schematically shows the configuration of the laser apparatus according to the eighth embodiment. A polarizer 20 may be inserted between the magneto-optical film 10 and the second resonance mirror 16.
FIG. 13 schematically shows the configuration of the laser apparatus according to the ninth embodiment. The semiconductor laser device 2, the first resonance mirror 8a, the solid-state laser material 8, the magneto-optical film 10, and the excitation coil 12a are integrated and integrated. This is advantageous for miniaturization. By coating the end surface of the magneto-optical film 10, it is also possible to integrate the second resonance mirror 16.

  14A shows a Faraday rotation angle by the permanent magnet 14, FIG. 14B shows a pulse-like excitation current, and FIG. 14C shows a Faraday rotation angle by the permanent magnet 14 and the excitation coil 12. The exciting current in FIG. 14B is much smaller than the exciting current in the first embodiment.

  14D to 14F may be obtained by a combination of the permanent magnet 14 and the exciting coil 12. FIG. 14D shows that the Faraday rotation angle is adjusted to C + ΔC by the permanent magnet. FIG. 14E shows that the excitation coil applies a current having a Faraday rotation angle of −2 × ΔC at times other than the emission timing of the pulse laser. At the light emission timing of the pulse laser, the exciting current is set to zero.

The phenomena of FIGS. 14 (g) to (i) may be used. FIG. 14G shows that the Faraday rotation angle is adjusted to C by a permanent magnet. FIG. 14H shows that, except for the light emission timing of the pulse laser, a current having a Faraday rotation angle of −ΔC is applied by the excitation coil, and a current having a Faraday rotation angle of + ΔC is applied by the excitation coil at the light emission timing of the pulse laser. .
In any case, as shown in (c), (f) and (i), the Faraday rotation angle can be changed between C + ΔC of C−ΔC with a small excitation current, and the light emission timing of the pulse laser can be changed with a small excitation current. Can be controlled.

  The laser light emitted by the semiconductor laser device 2 may be a continuous laser or a pulsed laser. In the latter case, a relationship can be obtained in which the half-width of the pulse laser from the fixed laser device 22 is shorter than the half-width of the pulse laser from the semiconductor laser device 2.

In the above embodiment, the first resonance mirror 8a is formed on the end face of the solid-state laser material 8, but a mirror existing separately from the solid-state laser material 8 may be used as the first resonance mirror. In the above embodiment, the magneto-optical film 10 and the second resonance mirror 16 are separately provided, but the second resonance mirror 16 may be formed on the end surface of the magneto-optical film 10. The same applies to the excitation coil and the permanent magnet, and may be integrated with the magneto-optical film or may be combined with the magneto-optical film.
Also, the light source of the excitation light is not limited to the semiconductor laser device, and may be another light source. However, since the semiconductor laser device is small, the entire device combining the semiconductor laser device and the Q-switch solid-state laser device is small. Can be

The film referred to in the present specification may be a film attached to a substrate or a plate existing independently of the substrate. Garnet crystals manufactured separately from the laser material are also referred to herein as films. The same applies to the mirror, and a film attached to the substrate may serve as a mirror, or a plate independent of the substrate may serve as a mirror.
Both the mirror and the magneto-optical film can be realized by a multilayer film (a so-called one-dimensional photonic crystal). The mirror and the magneto-optical film are a metal mirror, a multilayer mirror, a photonic crystal, or the like, and can be formed of a film or a plate whose reflectance and transmittance are controlled.

As described above, the specific examples of the present invention have been described in detail. However, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples illustrated above.
The technical elements described in the present specification or the drawings exert technical utility singly or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Further, the technology exemplified in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

2: Semiconductor laser device 4: First condenser lens for excitation light 6: Second condenser lens for excitation light 8a: First resonance mirror 8: Solid laser material 8b: Coating film 10: Magneto-optical film 12: Excitation coil 14 : Permanent magnet 16: second resonance mirror 18: detector
20: Polarizer 22: Solid Q switch laser device

Claims (3)

A first resonance mirror, a solid-state laser material, a Q switch, and a second resonance mirror are arranged in that order;
The Q-switch is formed by a combination of a film exhibiting a magneto-optical effect having the saturation value of the Faraday rotation angle, and a magnetic flux generator the Faraday rotation angle varying once before and after around a certain threshold by the magnetic flux change And
A Q-switched solid-state laser device that emits a pulsed laser when excitation light is incident on the solid-state laser material and a pulse is applied to the magnetic flux generator. 2. The Q-switched solid-state laser device according to claim 1, wherein the film exhibiting the magneto-optical effect is a rare earth iron garnet. 2. The Q-switch solid-state laser device according to claim 1, wherein the magnetic flux generator includes a combination of a permanent magnet and an exciting coil.