JPH08186322A - Laser apparatus - Google Patents

Abstract

PURPOSE: To provide a laser apparatus by which the temperature rise of a laser diode is suppressed and which can effectively prevent the power and the wavelength of output light from the laser diode from being changed. CONSTITUTION: A PD 22 is installed, and, by using its detection signal, the power of an LD 20 is controlled. A part of a laser beam from the LD 20 is reflected by a beam splitter 24 so as to be guided to the PD 22. Reflected light from an objective lens does not reach the PD 22, and the PD 22 receives only a part of the laser beam emitted from the LD 20. The LD 20 is brought close to a cooling plate 26 for the LD and to an LD holder 21. The low-temperature side of a Peltier cooler 25 is brought close to the cooling plate 26 for the LD, and the high-temperature side is brought close to a heat-conducting plate 30 for the LD. A metal LD holder 21 and the cooling plate 26 for the LD are fitted and brought close to each other, and both are thermally integrated so as to become a nearly uniform temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates a laser medium from a laser diode which emits a laser beam for excitation to a laser medium, and resonates the laser beam emitted by the excited laser medium or a harmonic thereof to the outside. The present invention relates to a laser device for taking out.

[0002]

2. Description of the Related Art A laser device that excites a laser crystal by a laser diode (LD) to perform laser oscillation has features of small size, light weight, long life, high conversion efficiency and good operation stability. It is also known that blue or green laser light can be obtained by combining this laser device and a harmonic generating element to generate a harmonic of a fundamental wave. Such a laser device is described, for example, in JP-A-2-146784 and JP-A-6-69567.

FIG. 17 is a principle view showing a schematic structure of the laser device. This device mainly uses L for excitation.
D200, lens 202, laser crystal 204 which is a laser medium, harmonic generation element 208, output mirror 210
Consists of On the surface of the laser crystal 204 on the lens 202 side, a mirror that reflects light of a predetermined wavelength with high reflectance is formed.

In FIG. 17, the LD 200 is assumed to oscillate laser light in the absorption wavelength range of the laser crystal 204. The laser light is focused on the surface of the laser crystal 204 by the lens 202. The laser crystal 204 receives laser light and is excited to oscillate laser light of a predetermined wavelength. When this oscillating laser light passes through a KTP crystal that is a harmonic generating element, a second harmonic having a wavelength of ½ (or a third harmonic having a wavelength of ⅓) is generated. This harmonic is reflected by the output mirror 210, and
It is also reflected by the mirror 206. Ie mirror 2
The space between 06 and the output mirror 210 acts as a resonator, and the harmonic wave resonates by making several round trips between them and becomes high energy. This laser light is extracted from the output mirror 210 to the outside.

[0005]

By the way, when the LD is supplied with a current to cause the laser to emit light, the LD generates heat, and its power or wavelength changes due to the influence of the heat. Further, the temperature rise due to excessive heat generation causes destruction. When the power or wavelength of the laser light emitted from the LD changes, the laser crystal excited by this laser light is not properly excited and cannot emit laser light, or even if it emits laser light, its output laser The power and wavelength of light become unstable.

The present invention has been made in view of the above circumstances, and provides a laser device capable of effectively suppressing the temperature rise of the laser diode and effectively preventing the fluctuation of the power and wavelength of the output light of the laser diode. The purpose is.

[0007]

According to a first aspect of the invention for solving the above-mentioned problems, the laser medium is irradiated from a laser diode which emits a laser beam for excitation to the laser medium, and the excited laser medium. In a laser device that resonates the laser light emitted by the laser or its harmonics and takes it out to the outside, and a photodetection means for detecting the output of the laser light emitted by the laser diode, and a part of the laser light emitted by the laser diode. It is characterized by comprising optical means for guiding to the means, and laser diode control means for controlling the current supplied to the laser diode based on the detection signal from the light detection means.

According to a second aspect of the present invention, in the first aspect of the invention, the optical means includes a half mirror that reflects a part of the laser light substantially at a right angle. .

According to a third aspect of the present invention, in the first or second aspect of the present invention, a holding means for holding the laser diode and the light detecting means so that both are thermally integrated, and a current is supplied. By this, the cooling means that absorbs heat from the holding means and radiates heat to the outside, the temperature detecting means that detects the temperature of the holding means, and the supply current to the cooling means based on the detection signal from the temperature detecting means. And a cooling control means for controlling.

[0010]

According to the invention described in claim 1, the laser diode detects the output light of the laser diode and controls the supplied current based on the signal of the laser diode. Therefore, if the output light becomes strong, If the supply current is reduced to lower the output and the output light becomes weaker, the supply current is increased to increase the output, so that the laser light emitted from the laser diode is always maintained at a substantially constant output.

According to a second aspect of the present invention, with the above configuration, the half mirror allows a part of the laser light emitted from the laser diode to be guided to the light detecting means, so that the half mirror is transmitted. It is possible to prevent the reflected light of the laser light from entering the light detecting means. Therefore, the control of the current supplied to the laser diode using the light detection means is performed with high accuracy.

According to the third aspect of the present invention, the laser diode generates heat in the operating state by the above-mentioned configuration, but it can be prevented from reaching a high temperature by cooling by the cooling means, and the output and wavelength of the laser light can be prevented. Fluctuations can be suppressed. Moreover, since the current supplied to the cooling means is also controlled, the temperature can be kept constant with higher accuracy.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a partially cutaway perspective view showing an overall configuration of a laser device according to the present invention, FIG. 2 is an enlarged partially cutaway perspective view of an excitation part of FIG. 1, and FIG.
It is a partially notched perspective view which expanded and showed the resonance part 12 of FIG. First, the overall configuration of the laser device 10 will be briefly described with reference to FIG. Laser device 1 shown in FIG.
When 0 is roughly divided, it is composed of an excitation unit 11 and a resonance unit 12. The pumping section 11 and the resonator section 12 can be independently assembled. In the final step, the resonator section 12 is inserted into the heat dissipation shell of the pumping section 11 along the optical axis and fixed at a predetermined position, so that the laser The device 10 is completed.

The pumping section 11 shown in FIGS. 1 and 2 mainly detects a laser diode (LD) 20 for generating a laser beam for pumping, an LD holder 21 for holding the LD 20, and a laser beam from the LD 20. A photodetector 22, a collimator lens 23 that converts the laser light from the LD 20 into parallel light, and a collimator lens 23.
A beam splitter 24 that transmits the laser beam that has passed through and guides a part of the laser beam to the photodetector 22;
Peltier cooler 25 that cools LD20 and LD20
LD that guides the heat from the Peltier cooler 25 for LD to the cooling surface
The cooling plate 26 for LD, the LD holder 21, the photodetector 22, the collimator lens 23, the beam splitter 24, and the ceramic sub-base 27 that defines the mutual positional relationship, and the LD Peltier cooler 25 are LD.
A spring 28 uniformly pressing against the cooling plate 26 for cooling, a holding piece 29 for fixing the spring 28 vertically to the ceramic sub-base 27, and the heat from the cooling surface of the LD Peltier cooler 25 is transferred to the heat dissipation shell 31. LD heat conduction plate 3
0 and LD that is a housing that includes all of them inside
The heat dissipation shell 31 also serves to dissipate the heat from the Peltier cooler 25.

The resonator 12 shown in FIG. 1 and FIG.
Objective lens 40 that converges the laser light from 0 on the surface of the laser crystal, objective lens holder 41 that holds this objective lens 40, and objective lens adjustment cam that adjusts the position of this objective lens holder 41 in the optical axis direction. 42,
A laser crystal 43 that is excited when it receives a laser beam from an objective lens and oscillates a laser beam having a predetermined wavelength, a harmonic generation element 44 that generates a harmonic of the laser beam emitted by the laser crystal 43, and a laser beam Output mirror 45 that emits a part to the outside and reflects into the resonance part 12
An output mirror holder 46 for holding the output mirror 45, two upper and lower mirror pitching adjustment cam followers 47 for adjusting the pitching inclination of the output mirror 45,
Two left and right mirror yawing adjustment cam followers 48 for adjusting the yawing inclination of the output mirror 45, and a cam surface 4
9a, a mirror pitching adjustment cam 49 that contacts the upper and lower mirror pitching adjustment cam followers 47, and a mirror yawing adjustment cam 50 that contacts the left and right mirror yawing adjustment cam followers 48 on the cam surface 50a.
An infrared filter 51 that blocks the transmission of infrared light in the light output from the output mirror 45, and a resonance length from the laser crystal 43 to the output mirror 45 are defined, and a cylindrical shape that plays various roles to be described later. It includes a ceramic base 52.

In this embodiment, a semiconductor laser having a wavelength of 809 nm is used as the pumping LD 20, and a laser crystal 4 is used.
As N3, a known Nd-doped YVO ₄ is used. Further, as the harmonic generation element 44, a well-known KTP is used.
Use crystals. A mirror is formed on the surface of the laser crystal 43 on the objective lens 40 side by mirror surface coating. The laser crystal 43 excited by the LD 20 generates infrared light having a wavelength of 1064 nm, and resonates by repeating reflection between the mirror of the laser crystal 43 and the output mirror 45. The reflectance of both mirrors is wavelength 1
Since it is set high for 064 nm, infrared light does not go out and is confined between both mirrors with high intensity. Therefore, the laser light generated by the laser crystal 43 is converted into the second harmonic having a half wavelength with high efficiency by the harmonic generating element 44, and the visible output light having the wavelength of 532 nm is obtained.

By the way, in order to generate the second harmonic wave having a wavelength of 532 nm with high efficiency, the laser light having the fundamental wave of 1064 nm travels back and forth between the mirror of the laser crystal 43 and the output mirror 45 many times. Is required, and for that purpose, it is premised that the inclinations of both mirrors satisfy a predetermined condition. In this embodiment, the mirror of the laser crystal 43 is flat. On the other hand, the output mirror 45 is a concave spherical mirror so that even if the laser light spreads due to the diffracting action while traveling inside the resonator, the output mirror 45 converges again to the original beam diameter. Further, the laser crystal 43 is fixed and the inclination of the output mirror 45 is variable. Therefore, the output mirror 45
Accurate adjustment of the inclination of is an important condition for obtaining high-power laser light.

Next, the tilt adjusting mechanism of the output mirror 45 will be described with reference to FIGS. Here, FIG.
(A) is an output mirror holder 46 of FIGS. 1 and 3,
A perspective view showing a mirror pitching adjustment cam follower 47 and a mirror yawing adjustment cam follower 48 provided in this holder. FIG. 2B shows an optical axis defined corresponding to the output mirror holder 46 in FIG. 5 is a schematic horizontal cross-sectional view of the resonator section 12, and FIG. 6 is a schematic view of the output mirror holder 46 seen from the front side of the optical axis.

As shown in FIGS. 4A and 4B, the optical axis passing through the output mirror 45 is the z axis, the central axis of the mirror pitching adjustment cam follower 47 is the x axis, and the central axis of the mirror yawing adjustment cam follower 48 is the y axis. And As shown in FIG. 4B, in this embodiment, the z-axis and the x-axis and the z-axis and the y-axis are orthogonal to each other at points O ₁ and O ₂ , respectively. The points O ₁ and O ₂ are offset by about ₁ to ₂ mm, and therefore the x-axis and the y-axis are in a twisted position, but when viewed from the z-axis direction,
The x-axis and the y-axis are in a perpendicular positional relationship. However, the point O ₁ and the point O ₂ are shifted in this way because, as will be described later, the mechanism of pitching adjustment and yawing adjustment can be simplified, and even in this case, pitching and yawing can be made substantially independent. This is because it can be adjusted and does not relate to the essence of the present invention.

As shown in FIGS. 5 and 6, four cam follower guide grooves 61 are provided around the ceramic base 52.
~ 64 are provided at angular intervals of 90 °. Each cam follower guide groove is an elongated hole whose major axis is parallel to the optical axis.
Of these, mirror pitching adjustment cam followers 47 are inserted in the upper and lower cam follower guide grooves 61 and 63, and mirror yawing adjustment cam followers 48 are inserted in the left and right cam follower guide grooves 62 and 64. As a result, the output mirror holder 46 is constrained at a position where the central axis of the output mirror 45 provided at the center coincides with the optical axis, but each cam follower moves in the optical axis direction along the respective cam follower guide groove. It is possible.

As shown in FIG. 5, the ceramic base 52
A mirror pitching adjustment cam 49 and a mirror yawing adjustment cam 50 are provided on the periphery of the, and are "clearance fit" rotatably around the ceramic base.
Further, a preload spring 65 that urges the mirror pitching adjustment cam 49 in the extending direction is provided around the mirror pitching adjustment cam 49. Figure 5
At the left end of the preload spring 65,
The second end surface 52a is in contact with the right end, and the right end is in contact with the back side of the cam surface 49a. Therefore, the mirror pitching adjustment cam 4
9 is urged in the direction toward the tip (right side in FIG. 5) along the optical axis. This biasing force is applied to the cam surface 49a, the mirror pitching adjustment cam follower 47, the output mirror holder 4
6, mirror yawing adjustment cam follower 48, cam surface 5
It is transmitted to the mirror yawing adjustment cam 50 via 0a and is received by the lid member 66 at the tip of the ceramic base 52. The mirror pitching adjustment cam followers 47 are in contact with the cam surface 49a of the mirror pitching adjustment cam 49 by two upper and lower sides, and the mirror yawing adjustment cam followers 48 are two left and right sides by the mirror yawing adjustment cam 50.
Since it abuts against the cam surface 50a, there is no play at the abutting portion.

As shown in FIG. 5, the cam surface 49a of the mirror pitching adjustment cam 49 is a part of an inclined plane obtained by obliquely cutting a cylinder. Mirror yawing adjustment cam 5
The zero cam surface 50a is also formed by a similar inclined plane. Therefore, when the mirror pitching adjustment cam 49 is rotated, the normal line of the output mirror 45 is rotated around the y-axis via the two upper and lower mirror pitching adjustment cam followers 47 that come into contact with the cam surface 49a. Also, the mirror yawing adjustment cam 5
When 0 is turned, the normal line of the output mirror 45 is rotated around the x-axis via the two mirror yawing adjustment cam followers 48 that are in contact with the cam surface 50a. Therefore, the tilt of the output mirror 45 can be adjusted by rotating the mirror pitching adjustment cam 49 and the mirror yawing adjustment cam 50.

As shown in FIG. 4B, since the point O ₁ and the point O ₂ are displaced, the mirror pitching adjustment cam 4
The cam surface 49a of 9 and the cam surface 50a of the mirror yawing adjustment cam 50 do not collide. Further, by shifting the point O ₁ and the point O ₂ , the mirror pitch adjusting cam 49 and the mirror yawing adjusting cam 50 can be formed into a cylinder having the same radius, and the cam surfaces 49a and 50a can be arranged so as to face each other. The mechanism can be simplified and downsized, and the tilt adjustment work is facilitated.

As can be seen from the above description, the cam surface 49
The magnitude of the inclination of a and 50a and the change of the inclination of the output mirror 45 due to the rotation of each cam are closely related. Therefore, if the inclination of the cam surfaces 49a and 50a is made smaller, the angular range in which the mirror pitching adjustment cam follower 47 and the mirror pitching adjustment cam follower 48 rotate becomes smaller, and thus the fine adjustment of the inclination of the output mirror 45 becomes possible. . Further, since the upper and lower mirror pitching adjustment cam followers 47 and the left and right mirror yawing adjustment cam followers 48 each have a sufficient stroke, this also contributes to enabling fine adjustment.

Moreover, in such a configuration, the output mirror 45
The tilt adjustment around the x-axis and the y-axis can be independently performed. That is, first, the tilt of the output mirror is adjusted around the x-axis (y-axis) so that the output of the obtained laser light is maximized, and then the tilt around the y-axis (x-axis) is adjusted. Even if the output is maximized,
Since the adjusted state around the already adjusted x-axis (y-axis) is not affected, the maximum output laser light is obtained. Therefore, it is possible to easily and efficiently adjust the inclination. Incidentally, as shown in FIG. 4B, since the points O ₁ and O ₂ are slightly displaced, strictly speaking, when one is adjusted, the other is slightly affected. However, the results of experiments conducted by the present inventor confirmed that such an influence was negligibly small.

Next, the position adjusting mechanism of the objective lens 40 shown in FIGS. 1 and 3 will be described with reference to FIGS. FIG. 7 shows the objective lens 40 and the objective lens holder 4.
FIG. 8A is a side view of the cylindrical objective lens adjusting cam 42 provided around the ceramic base, and FIG. 8B is the same. It is a development view showing a state where the objective lens adjustment cam 42 of FIG.

As shown in FIGS. 3 and 7, the disc-shaped objective lens holder 41 is provided with three notches 70a to 70c extending over an angular range of about 100 °. Further, in this embodiment, the objective lens holder 41 is made of aluminum, but other metals or engineering plastics can be used. Therefore, in the objective lens holder 41, the portions outside the notches 70a to 70c become cantilever springs 71a to 71c utilizing the elasticity of metal, and the inner surface of the ceramic base 52 is radiused at the protrusions 72a to 72c at the tip. Press evenly outward in the direction. This allows the central axis of the objective lens 41 to coincide with the optical axis. Moreover, since the pressure is applied at three points, this consistent state can be stably maintained even if there is an environmental change such as a temperature change.

Further, the objective lens holder 41 is provided with three objective lens adjusting cam followers 73a to 73c. The cam followers 73a to 73c have cantilevered springs 71 so that their respective central axes pass through the center of the objective lens.
It is provided on the fixed side of a to 71c. Ceramic base 5
2 around the cam follower guide groove 6 shown in FIG.
Cam follower guide groove 7 consisting of an elongated hole similar to 1 to 64
4a to 74c are provided. The long axes of the cam follower guide grooves 74a to 74c are parallel to the optical axis. Therefore, the objective lens adjusting cam followers 73a to 73c inserted in the respective cam follower guide grooves can move parallel to the optical axis.

An objective lens adjusting cam 42 is provided around the ceramic base 52 so that the central axis thereof coincides with the central axis of the ceramic base 52. The objective lens adjustment cam 42 is rotatably fitted around the ceramic base 52 in the same manner as the pitching cam 49 and the mirror yawing adjustment cam 50 described with reference to FIG. As shown in FIG. 7, the objective lens adjusting cam 42 is provided with three cam grooves 42a to 42c, and the corresponding objective lens adjusting cam followers 73a to 73c are inserted into the respective cam grooves 42a to 42c.

As shown in FIGS. 1 and 3, an objective lens preload spring 75 is provided in front of the objective lens holder 41. The objective lens preload spring 75 biases the crystal holder 77 holding the harmonic generating element 44 forward through the front cap 76, and moves the objective lens holder 41 rearward through the rear cap 78. Urge to. Due to this rearward biasing force, the objective lens adjusting cam followers 73a to 73c come into contact with the objective lens adjusting cam 42 on the rear side surface (left side in FIGS. 8A and 8B) of each cam groove. At this time, since the three points of the objective lens adjusting cam followers 73a to 73c contact the rear side surface of each cam groove, the plane defined by these three points is uniquely defined.

As shown in FIG. 8, the cam grooves 42a to 42c are provided parallel to each other and obliquely. Therefore, when the objective lens adjustment cam 42 rotates around the ceramic base 52, the objective lens holder 41 continuously moves in translation along the optical axis.

Therefore, the position of the objective lens 40 in the optical axis direction can be adjusted based on the direction in which the objective lens adjusting cam 42 is rotated and the rotational position thereof.
When the objective lens adjusting cam 42 is rotated, the cantilever spring 71
The protrusions 72a to 72c at the tips of the a to 71c slide on the inner surface of the ceramic base 52. For this reason, it is necessary to set the elasticity of the cantilever springs 71a to 71c within an appropriate range so that unnecessary friction does not occur and such sliding is performed smoothly.

As will be described later, the forward biasing force of the objective lens preload spring 75 causes the crystal holder 77, which holds the laser crystal 43 and the harmonic generating element 44, to firmly abut the ceramic base 52. Play a role. The length of the resonator portion 12, that is, the laser crystal 43
The distance between the output mirror 45 and the output mirror 45 is mainly the crystal holder 7.
7 and the size of the ceramic base 52, the crystal holder 77 is controlled by the objective lens preload spring 75.
By securely contacting the ceramic base 52 with the ceramic base 52, the distance between the laser crystal 43 and the output mirror 45 can be kept constant.

Inside the resonance part 12, as shown in FIGS. 1 and 3, a hollow, cylindrical activated carbon filter 140 is provided. As shown in FIG. 9, this activated carbon filter 140 is held at a predetermined position in the resonance part 12 by a holder 141, and a lid member 142 having several holes is provided on both sides of the holder 141. It is covered. The hollow portion of the active end filter 140 serves as a passage path for laser light.

In the conventional laser device, it is known that silica gel is enclosed in order to absorb the moisture in the inside. However, the laser device uses an adhesive agent described later and other polymer materials, and these generate a slight amount of gas. Such gas causes contamination of the surface of the optical element. Therefore, by enclosing the activated carbon filter 140 inside the resonance portion 12 as in this embodiment, such a gas can be absorbed,
Impurities can be effectively removed from the inside of the resonance section 12, and contamination of the optical element can be prevented. Further, in the laser device of the present embodiment, complete sealing is avoided so that a pressure difference between the inside and the outside does not occur, and therefore,
Moisture may enter from the outside. Such water can also be removed by an activated carbon filter.

Next, the temperature control of the LD and the power control of the LD to which the temperature control mechanism of the optical device according to the present invention is applied will be described with reference to FIGS. here,
10 is a schematic vertical cross-sectional view in which the configuration of the excitation unit 11 shown in FIGS. 1 and 2 is partially omitted, and FIG. 11 is a schematic vertical cross-sectional view of the excitation unit in which the configuration of FIG. 10 is partially changed. is there. The LD 20 shown in FIG. 10 generates heat when a current is supplied to emit light,
Power and wavelength change due to the influence. Further, the temperature rise due to excessive heat generation causes destruction. Therefore, L
In order for the D20 to operate properly, it is desirable to control its power and temperature.

First, the power control of the LD 20 in this embodiment will be described. Some conventional LDs have a minute light receiving portion provided behind the light emitting portion and a terminal for taking out an output signal from the light receiving portion to the outside. When such an LD is used, the light leaking backward from the light emitting unit is detected by the light receiving unit, and the output current thereof is used as a power detection signal to feed back the current supplied to the LD, whereby the power control of the LD can be performed. . However, a part of the laser light emitted from the LD is slightly reflected by, for example, an objective lens in the front, and L
Return to D. The sensitivity of the light receiving portion of the LD is generally very high, and weak reflected light is inevitably detected. Further, the amount of reflected light from the objective lens changes depending on the position of the objective lens on the optical axis. Therefore, in a device of the type as in the present embodiment, which moves on the optical axis by the focus adjustment mechanism, the reflected light from the objective lens or the like becomes noise, which affects the detection current of the light receiving unit, and the power control of the LD. It causes a decrease in accuracy.

Therefore, in this embodiment, the photodetector (PD) 22 is provided in the arrangement shown in FIG. 10, and the LD is detected by using the detection signal from the PD 22 without using the light receiving portion of the LD 20.
20 power control is performed. Most of the laser light emitted from the LD 20 passes through the beam splitter 24, reaches the objective lens 40 in the resonator 12, and the other part is reflected by the beam splitter 24 and guided to the PD 22. On the other hand, part of the reflected light from the objective lens 40 passes through the beam splitter 24 as it is and returns to the LD 20, and the remaining part is reflected upward by the beam splitter 24 in FIG. 10. However, the reflected light from the objective lens is
It never reaches 2. That is, the PD 22 purely receives only a part of the laser light emitted from the LD 20. Therefore, if the output current of the PD 22 is used as the power detection signal of the LD 20 and this is fed back to the supply current of the LD 20 via the gain adjusting unit 80 and the power control unit 81, the power control of the LD 20 can be accurately performed.

Next, the temperature control of the LD 20 will be described. In the control of this embodiment, the wavelength of the LD 20 changes depending on the temperature.
This is done to match the wavelength of D20. This control is mainly performed by the well-known Peltier cooler 25 and the temperature control unit 84. When supplying current, the Peltier cooler 25 forcibly absorbs the heat of the object to be cooled on its cooling surface and releases the absorbed heat to the outside on its heat dissipation surface. As shown in FIG. 10, the LD 20 is in close contact with the LD cooling plate 26 and the LD holder 21. The cooling surface of the Peltier cooler 25 is attached to the LD cooling plate 26, and the heat radiation surface thereof is attached to the LD heat conduction plate 30, respectively. The close contact between them is ensured by fixing the rod-shaped spring 28 to the ceramic sub-base 27 by the upper and lower rod-shaped spring holding pieces 29 and pressing the central portion of the LD heat conduction plate 30 to the front Peltier cooler 25. To be taken. LD holder 2 made of metal
1. The LD cooling plate 26 is fitted and closely attached to each other. Therefore, the LD holder 21 and the LD cooling plate 26
Are thermally integrated and have a substantially uniform temperature.

As shown in FIGS. 2 and 10, the LD holder 21 is also in contact with the ceramic sub-base 27, but the ceramic used in this embodiment has a sufficient heat insulating action as described later. Therefore, the heat inflow and outflow with the outside through this is effectively blocked. In addition to the LD 20, the PD 22 is also attached to the LD holder 21. Therefore, the LD 20 and the PD 22 have substantially uniform temperatures.
Since the characteristics of the PD 22 also change depending on the temperature, if the temperature of the LD 20 is controlled with the above configuration, the temperature of the PD 22 is also controlled at the same time and the characteristics can be kept constant. Further, in this case, it is not necessary to separately provide the Peltier cooler for the LD 20 and the PD 22, which is economical.

As shown in FIG. 10, a thermistor 82 for temperature detection is embedded in the LD cooling plate 26.
The temperature detection signal of the thermistor 82 is supplied to the gain adjusting section 83 by the lead drawn to the outside, where the gain is adjusted, and then sent to the temperature control section 84. The temperature controller 84 controls the current supplied to the Peltier cooler 25 based on the temperature detection signal from the thermistor 82. As a result, the LD cooling plate 26, the LD holder 21, and the LD, which are in contact with the cooling surface of the Peltier cooler 25,
20 and PD22 are maintained at a constant temperature.

On the other hand, the LD heat conduction plate 30 which is in close contact with the heat radiation surface of the Peltier cooler 25 is further shown in FIGS.
As shown in, the reference shell pressing spring 90 and the spring pressing screw 91 are closely fixed to the heat radiating shell 31. Since the heat dissipation shell 31 has a sufficiently large surface area, the LD 20 absorbed by the Peltier cooler 25 is absorbed.
This heat is radiated from the heat dissipation shell 31 to the outside.
Therefore, the temperature controller 84 and the Peltier cooler 25
The efficiency of the temperature control of the LD 20 performed by the method is significantly improved, and the fluctuation of the thermal characteristics of the LD 20 and the PD 22 can be effectively prevented. By this, the LD20 by the PD22
The power control accuracy is improved, the output wavelength of the LD 20 can be kept substantially constant, and the mode change of the laser light resonating in the resonator 12 can be prevented.

In the embodiment shown in FIG. 11, the PD 22 is an LD
It is attached to the cooling plate 26. Therefore, a total reflection mirror 85 is provided in order to guide the light from the beam splitter 24 to the PD 22. In this way, PD22
When attached to the LD cooling plate 26, LD20 and PD2
It is possible to bring the distance of 2 closer, and the Peltier cooler 25
This has the advantage that the volume of the member to be cooled can be reduced and the heat capacity can be reduced. In this way, even if a thermal disturbance occurs, it can be followed in a short time and returned to the predetermined temperature. Therefore, it is possible to suppress the error due to the temperature variation to be smaller and improve the accuracy of the power control of the LD 20. Further, the accuracy of temperature control is also improved.

By the way, when the Peltier cooler 25 is used, it is generally desirable to firmly screw a heat conduction plate to the heat radiation surface thereof. But,
When fixing with a plurality of screws, when some screw loosens, the heat-conducting plate often hits one side and the other side floats, which makes it difficult to always maintain a close contact. Particularly, in mass production, it becomes more difficult to reliably prevent loosening of individual screws. Also, in the assembly process, to quickly tighten multiple screws,
It takes a considerable amount of time and causes a drop in workability.

However, as in this embodiment, the rod-shaped spring 28 is used.
If the upper and lower rod-shaped spring holding pieces 29 for fixing the same are used, only the center of the LD heat conduction plate 30 is pressed, and thus the LD heat conduction plate 30 is securely adhered to the heat dissipation surface of the Peltier cooler 25. Can be made. Moreover, the work is completed by simply fitting the rod-shaped spring holding piece 29 into a predetermined portion of the ceramic sub-base 23, so that the work efficiency is improved. Further, when disassembling is required, the LD-shaped heat conduction plate 3 can be easily formed simply by removing the rod-shaped spring holding piece 29.
0 and the Peltier cooler 25 can be separated.

In this embodiment, FIG. 2, FIG. 10, and FIG.
As shown in FIG. 3, the LD 20, the beam splitter 24, the photodetector 22, the Peltier cooler 25, and the LD cooling plate 26 are integrally provided inside the excitation unit 11, and constitute one unit. Therefore, finally in FIG.
Before assembling the laser device 10 as described above, it is possible to operate only the pumping section 11 to confirm the operation and check the characteristics. The defect rates of the LD 20, the laser crystal 43 and the harmonic generating element 44 in the resonator 12 are
There is no big difference. For this reason, if final assembly is performed without checking in advance and then a defect is discovered, it is difficult to specify the location of the abnormality. However, if the operation check of the optical system and the heat dissipation system is performed only by the excitation unit 11 before the final assembly, even if a problem occurs later,
It becomes easy to identify the location.

As for the photo detector 22,
It is necessary to calibrate each product, but after completely assembled, the laser light emitted from the LD 20 cannot be correctly measured by a photometer for calibration or the like, so the characteristics of only the photodetector 22 are independently investigated. It's difficult. However, as in this embodiment,
If an independent unit is configured with only the excitation unit 11, the characteristic data of the photodetector 22 can be easily obtained in advance.

Next, the laser crystal 43 in the cavity 12
The temperature control of the harmonic generating element 44 will be described.
FIG. 12 is a schematic vertical cross-sectional view showing the laser crystal 43 shown in FIG. 1, the harmonic generating element 44, and the peripheral portion thereof in an enlarged manner. The harmonic generation element 44 is fixed at a predetermined position in the crystal holder 77 made of metal. Further, the laser crystal 43 is closely fixed to the rear end of the crystal holder 77. Regarding the fixing method of this laser crystal 43,
It will be described later.

An objective lens preload spring 75 is provided around the cylindrical portion (left side portion in FIG. 12) of the crystal holder 77. The objective lens preload spring 75 includes a substantially cylindrical cap 76, copper crystal heat conduction plates 100a and 100b,
The crystal holder 77 is biased toward the tip direction (rightward in FIG. 12) via the metal ring-shaped member 101 and the ring-shaped Peltier cooler 102 for crystals. This allows
The disk portion (right side portion in FIG. 12) of the crystal holder 77 is pressed against the rear end 52b of the bent portion of the ceramic base 52 and comes into close contact therewith. Therefore, the distance from the laser crystal 43 to the rear end 52b of the bent portion of the ceramic base 52 is accurately defined by the crystal holder 77.

Since the laser crystal 43 is directly irradiated with the laser light from the LD 20 via the objective lens 40,
If it is left as it is, the temperature will become extremely high, and laser oscillation may be stopped or the laser crystal may be broken. Further, since the harmonic generating element 44 also slightly absorbs the laser light, the temperature changes during the operation of the laser. The harmonic generation element 44 also has an optimum temperature range, and when the temperature fluctuates, the effective optical path length with respect to the wavelength of the excitation light changes, and the conversion efficiency of harmonics decreases. Therefore, it is necessary to cool the laser crystal 43 and the harmonic generating element 44 sufficiently to suppress the temperature fluctuation within a narrow range.

The Peltier cooler 102 is arranged such that its cooling surface is in contact with the rear end of the disk-shaped member of the crystal holder 77 and its heat dissipation surface is in contact with the ring-shaped member 101, and heat is forced from the member with which the cooling surface is in contact. It absorbs and radiates heat to a member in contact with the heat dissipation surface. The ring-shaped member 101 is screwed to the upper and lower crystal heat conduction plates 100a and 100b close to the optical axis, and the tip portions of the crystal heat conduction plates 100a and 100b are connected to the heat dissipation shell 31. ing. Therefore, the heat generated in the laser crystal 43 and the harmonic generating element 44 is cooled on the cooling surface of the Peltier cooler 102 via the crystal holder 77. Then, the heat of the radiating surface of the Peltier cooler 102 is transmitted to the radiating shell 31 via the ring-shaped member 101 and the crystal heat conduction plates 100a and 100b, and is cooled by the outside air.

FIG. 13 shows the heat conducting plates for crystals 100a and 1a.
FIG. 10 is a schematic exploded perspective view showing the relationship between 00b and the ceramic base 52 in an easy-to-understand manner. The ceramic base 52 is provided with two notches 110a and 110b at the top and bottom as shown in FIG. The crystal heat conduction plates 100a and 100b are inserted from the two notches 110a and 110b, respectively, and screwed to the ring-shaped member 101 inside the ceramic base 52. In this way, the crystal heat conduction plates 100a and 10 having a relatively large area.
By providing 0b symmetrically in the vertical direction, heat conduction from the Peltier cooler 102 to the radiating shell 31 can be made uniform and an asymmetric temperature distribution can be prevented.

A thermistor 112 for detecting the temperature of the crystal holder 77 is embedded in the crystal holder 77. The output signal from the thermistor 112 is shown in FIG.
As shown in FIG. 2, the temperature is supplied to the temperature control unit 114 via the gain adjustment unit 113. The temperature control unit 114 performs feedback control of the current supplied to the Peltier cooler 102 based on the output signal of the thermistor 112. By this, the laser crystal 4 attached to the crystal holder 77
3 and the temperature of the harmonic generating element 44 can be maintained substantially constant.

Next, a method of fixing the laser crystal 43 to the crystal holder 77 will be described. One of the conventionally used methods is to bond the laser crystal 43 to the end face of the crystal holder 77 via the adhesive 130, as shown in FIG. In this case, a commercially available silver paste or the like having a certain degree of thermal conductivity is used as the adhesive. The silver paste is dissolved in a solvent before being applied, and when applied, the solvent volatilizes and the surface is dried to bond the adherends.

However, when the laser crystal 43 is directly adhered with an adhesive, there are the following problems. First, although the silver paste has some high thermal conductivity, it is not as high as metal. Further, when the silver paste is directly applied to the laser crystal 43, it is necessary to apply it evenly around the laser crystal by hand so that the silver paste does not block the light path. Therefore, work efficiency is reduced. Further, since the solvent of the silver paste easily flows out, the solvent may flow out to the central portion of the laser crystal during the drying process and may contaminate the laser crystal.

Therefore, in this embodiment, as shown in FIG. 15, a copper cap 131 is used instead of directly bonding the laser crystal 43 to the crystal holder 77. That is, the cap 131 is covered on the left cylindrical portion of the crystal holder 77, the laser crystal 43 is sandwiched between them, and the end portion of the cap 131 is adhered to the periphery of the cylindrical portion of the crystal holder 77 with silver paste 130 or the like. In this case, the cap 131 and the crystal holder 77 need not be attached to each other carefully, so that the work is easy and there is no concern that the solvent will flow out to the laser crystal 43. Further, since the cap 131 is made of metal, it has a high thermal conductivity, and the heat of the laser crystal 43, which has become high temperature, can be easily transferred to the crystal holder 77. As a result, there is an advantage that the life of the laser crystal 43 is extended. Aluminum or the like may be used as the material of the cap 131.

Next, the material of the ceramic base 52 will be described. In order for the harmonics to continue to properly resonate in the resonator 12, the distance from the laser crystal 43 to the output mirror 45 must be kept constant without changing. As can be seen from FIG. 12, it is mainly the crystal holder 77 and the ceramic base 52 that define the distance from the laser crystal 43 to the output mirror 45. Of these, the crystal holder 77 that internally contains a heat generating element is forcibly cooled as described above, so that it is always kept at a constant temperature, and it is not necessary to consider the variation in the length in the optical axis direction due to temperature change. . On the other hand, with respect to the ceramic base 52, no cooling means is provided in particular in this embodiment because it does not come into direct contact with a heat-generating object, the structure is complicated, and the size is hindered.

However, the ceramic base 52 also
Since a part of the resonator constitutes a resonator, it is desirable to use a material having a small coefficient of thermal expansion to suppress dimensional fluctuation due to temperature changes. On the other hand, the ceramic base 52 needs to be subjected to various mechanical processes, as can be seen from FIG. Therefore, the present inventor examined various materials on condition that the coefficient of thermal expansion is small, easy to process, excellent in heat insulating property, and low in cost, and the above conditions are satisfied. I found some matching materials.

That is, 46% Al ₂ O ₃ and 45%
Ceramic containing the TiO _2, 65% of the SiO ₂ 25% CaO and ceramic consisting of 10% Al ₂ O _3, 49% of SiO _2, 43% of the Al ₂ O _3, 6% of M
These are ceramics containing gO, ceramics composed of a composite of AlN and BN, and ceramics composed of 96% BN. The coefficient of thermal expansion of these ceramics is generally about one-half to one-third that of metals, and the dimensional elongation when temperature rises is very small. Therefore, by forming the ceramic base 52 using these, the oscillation wavelength is less likely to change due to mode hopping, and the output mode is stabilized.

As shown in FIG. 12, a lid member 66 made of SUS material is fixed to the tip of the ceramic base 52 with screws, and mirror yawing made of SUS material is also in contact with the lid member 66. An adjustment cam 50 is provided. The mirror yawing adjustment cam follower 48 provided on the output mirror holder 46 is pressed against the cam surface 50a of the mirror yawing adjustment cam 50 by the output mirror preload spring 65 as described above. Therefore, although the temperature rises and the dimension of the mirror yawing adjustment cam 50 in the optical axis direction expands to some extent, the mirror yawing adjustment cam 50 extends in a direction opposite to the extending direction of the ceramic base with the tip of the ceramic base 52 as a reference. . Therefore, even if the temperature rises and the dimension of the ceramic base 52 expands to some extent, the expansion of the mirror yawing adjustment cam 50 acts to cancel it. If the temperature decreases and the dimensions of each member shrink,
Similarly, it acts to counteract dimensional variations.

Although the coefficient of thermal expansion of ceramics is small, it is not completely zero. Therefore, it is difficult to completely suppress the dimensional fluctuation of the ceramic base 52 when the temperature fluctuates. Therefore, as shown in FIG. 16, instead of the ceramic base 52, a base member 120 integrated with the crystal holder 77 may be provided and formed of a metal such as copper having a high thermal conductivity. In that case, a heat insulating material 121 is provided around the base member 120 to block heat from entering and exiting from the outside. In this way, the crystal holder 77
The temperature of the base member 120 is controlled by the thermistor 112 and the Peltier cooler 102, so that the temperature variation of the distance between the laser crystal 43 and the output mirror 45 is prevented and kept constant.

The present invention is not limited to the above embodiment, but various modifications can be made within the scope of the gist thereof.

[0063]

As described above, according to the first aspect of the present invention, the laser light emitted from the laser diode is guided to the light detecting means by the optical means, and the output thereof is used to supply the current to the laser diode. Control
The output of the laser light emitted from the laser diode is kept substantially constant, so that the laser crystal excited by receiving the laser light stably emits the laser light.

According to the second aspect of the present invention, by using the half mirror as the optical means or as a part of the optical means, the reflected light of the light which has passed through the half mirror and reaches the front side is the light detecting means. Since it does not reach, the accuracy of controlling the supply current to the laser diode is improved,
Therefore, the laser crystal excited in response to this is
It emits laser light more stably.

According to the third aspect of the invention, since the laser diode cools the cooling means that generates heat in the operating state to prevent the temperature from becoming high, it is possible to suppress fluctuations in the laser light output and wavelength. Moreover, since the current supplied to the cooling means is also controlled, the temperature can be kept constant with higher accuracy.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an overall configuration of a laser device according to the present invention.

FIG. 2 is a partially cutaway perspective view showing the excitation part of FIG. 1 in an enlarged manner.

FIG. 3 is a partially cutaway perspective view showing an enlarged resonance portion of FIG.

4 is a perspective view showing an output mirror holder of FIG. 1 and a mirror pitching adjustment cam follower and a mirror yawing adjustment cam follower provided in the holder, and an optical axis defined corresponding to the output mirror holder of FIG. It is a figure which shows the relationship of two axes perpendicular | vertical to this.

FIG. 5 is a schematic horizontal sectional view of a resonance part.

FIG. 6 is a schematic view of a portion of an output mirror holder as seen from the front of the optical axis.

FIG. 7 is a diagram of a part of an objective lens and an objective lens holder as viewed from the front in the optical axis direction.

FIG. 8 is a side view of a cylindrical objective lens adjustment cam provided around the ceramic base, and a development view showing a state in which the objective lens adjustment cam is rotated.

FIG. 9 is an exploded view showing a method of mounting an activated carbon filter.

FIG. 10 is a schematic vertical cross-sectional view in which the configuration of the excitation unit shown in FIGS. 1 and 2 is partially omitted.

FIG. 11 is a schematic vertical cross-sectional view of an excitation unit showing an embodiment in which a photodetector is provided in an arrangement different from that in FIG.

FIG. 12 is a schematic vertical cross-sectional view showing the configuration of a resonator of a laser device.

FIG. 13 is a schematic perspective view showing a positional relationship between a ceramic base and a heat conduction plate inserted in the cutout portion.

FIG. 14 is a schematic vertical sectional view showing a method of directly bonding a laser crystal to a crystal holder.

FIG. 15 is a schematic vertical sectional view showing a method of mounting a laser crystal on a crystal holder by using a special cap.

FIG. 16 is a schematic vertical sectional view of an example in which a booth member is thermally integrated with a crystal holder and a heat insulating member is covered around the booth member.

FIG. 17 is a principle diagram of a general laser device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Laser device 11 Excitation part 12 Resonance part 20 Laser diode (LD) 21 LD holder 22 Photodetector 23 Collimating lens 24 Beam splitter 25 LD Peltier cooler 26 LD cooling plate 27 Ceramic sub-base 28 Rod spring 29 Rod-shaped spring holding piece 30 Heat conduction plate for LD 31 Heat dissipation shell 40 Objective lens 41 Objective lens holder 42 Objective lens adjustment cam 43 Laser crystal 44 Harmonic generator 45 Output mirror 46 Output mirror holder 47 Mirror pitching adjustment cam follower 48 Mirror yawing adjustment cam follower 49 Mirror pitching adjustment cam 50 Mirror yawing adjustment cam 51 Infrared filter 52 Ceramic base 61 to 64 Cam follower guide groove 65 Output preload spring 66 Lid member 7 a-70c Cut 71a-70c Cantilever spring 72a-72c Convex part 73a-73c Objective lens adjustment cam follower 74a-74c Cam follower guide groove 75 Objective lens preload spring 76, 78 Cap 77 Crystal holder 80, 83, 113 Gain adjusting part 81 Power Control unit 82, 112 Thermistor 84, 114 Temperature control unit 85 Total reflection mirror 90 Reference shell pressing spring 91 Spring pressing screw 100a, 100b Crystal heat conduction plate 101 Heat conduction plate 102 Crystal Peltier cooler 110a, 110b Notch 120 Metal base Member 121 Heat insulating material 130 Silver paste 131 Metal cap 140 Activated carbon filter 141 Holder 142 Lid member

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01S 3/094 3/109 (72) Inventor Ryuji Fukuyama 2-6-3 Otemachi, Chiyoda-ku, Tokyo No. Nippon Steel Corporation (72) Inventor Yoshimasa Saito 2-3-6 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Steel Corporation

Claims (3)

[Claims] 1. A laser device for irradiating a laser medium to a laser medium from a laser diode which emits a laser beam for excitation, and resonating the laser beam emitted by the excited laser medium or a harmonic thereof to the outside, Light detection means for detecting the output of the laser light emitted by the laser diode, optical means for guiding a part of the laser light emitted by the laser diode to the light detection means, and the laser based on the detection signal from the light detection means A laser device comprising: a laser diode control means for controlling a current supplied to the diode. 2. The laser device according to claim 1, wherein the optical means includes a half mirror that reflects a part of the laser light at a substantially right angle. 3. A holding means for holding the laser diode and the light detecting means so as to be thermally integrated with each other, and a cooling for absorbing heat from the holding means by supplying an electric current and radiating the heat to the outside. Means, temperature detecting means for detecting the temperature of the holding means, and cooling control means for controlling a current supplied to the cooling means based on a detection signal from the temperature detecting means. The laser device according to claim 1 or 2.