JP2001102665A - Method and device for adjusting solid-state laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust the position of laser parts, so that the horizontal mode in a solid-state laser is prevented from being highly ordered due to external disturbance, such as changes in environmental temperature and so on or change in position with aging changes. SOLUTION: At least one part (for example, resonator mirror) 15 constituting a solid-state laser is moved in the direction crossing the light axis of a resonator by using an x-y inching stage 40, and while it is moved, the transverse mode of a solid-state laser beam (second higher harmonic) 21 is detected by a CCD camera 42, so that a range where the horizontal mode becomes a 0-th order mode within the direction during movement is obtained, and then the part 15 is adjusted in position and fixed at around the center of the obtained range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for adjusting the oscillation state of a solid-state laser and an apparatus for implementing the method.

[0002]

2. Description of the Related Art As disclosed in, for example, JP-A-7-302946, a solid-state laser in which a solid-state laser medium to which a rare earth element such as neodymium is added is excited by a semiconductor laser (laser diode) is known. In this type of laser, Japanese Unexamined Patent Application Publication No.
As shown in No. 6, in order to obtain a laser beam having a shorter wavelength, a nonlinear optical crystal is arranged in the resonator to convert the wavelength of the solid-state laser beam into a second harmonic, a sum frequency, and the like. It is also widely practiced.

In this solid-state laser, it is necessary to adjust an optical system so as to obtain a predetermined oscillation state. Conventionally, this oscillation adjustment involves detecting all or a part of the output of the solid-state laser beam or the wavelength-converted wave when converting the wavelength, and adjusting the position of the output mirror of the resonator so that the detected output becomes maximum. I was

[0004]

However, in the conventional adjusting method as described above, dust and dirt are located at the center of the 0th-order transverse mode range on the light passing surface of the optical component disposed in the resonator. When a coat defect or the like exists, the output mirror or the like may be adjusted and fixed at a position just before the change from the 0th-order transverse mode to the higher-order mode. In such a case, the transverse mode may easily become higher-order due to disturbance such as a change in the environmental temperature or a temporal change in the fixed position.

The present invention has been made in view of the above circumstances, and has as its object to provide a method of adjusting a solid-state laser capable of preventing the transverse mode from becoming higher-order due to disturbance such as a change in environmental temperature or a temporal change in a fixed position. .

Another object of the present invention is to provide an apparatus for adjusting a solid-state laser which can easily carry out the above method.

[0007]

According to the first method for adjusting a solid-state laser according to the present invention, as described above, the oscillation state of a solid-state laser having at least a solid-state laser crystal, an excitation source for exciting the same, and a resonator is adjusted. Moving at least one component constituting the solid-state laser in a direction intersecting the optical axis of the resonator, detecting a transverse mode of the solid-state laser beam when the movement is being performed, and A range in which the lateral mode takes the zero-order mode is obtained, and the position of the component is adjusted and fixed near the center of the range in which the zero-order mode takes.

In the present invention, the solid-state laser beam for detecting the transverse mode includes not only the oscillation light itself of the solid-state laser but also light obtained by wavelength-converting the oscillation light.

A second method for adjusting a solid-state laser according to the present invention is a method for adjusting the oscillation state of a solid-state laser having at least a solid-state laser crystal, an excitation source for exciting the same, and a resonator. Is moved in a direction that intersects the optical axis of the resonator, and the transverse mode of the solid-state laser beam when the movement is performed is detected. Is determined, and the position of the component is adjusted and fixed within a region of 20% of the range centered on the center of the range in which the zero-order mode is taken.

Further, a third method for adjusting a solid-state laser according to the present invention is a method for adjusting the oscillation state of a solid-state laser having at least a solid-state laser crystal, an excitation source for exciting the crystal, and a resonator. Is moved in a direction that intersects the optical axis of the resonator, and the transverse mode of the solid-state laser beam when the movement is performed is detected. Is determined, and the position of the component is adjusted and fixed within a 50% area around the center of the range in which the zero-order mode is taken.

In the present invention, the positions of the above-mentioned parts do not have to be defined by absolute positions.
Anyway, a range in which the transverse mode takes the 0th-order mode when the component is moved is obtained, and the component may be arranged and fixed in the vicinity of the center based on the range or in the region as described above. is there. In other words, it may be completely unknown what position the fixed position of the component is, for example, with respect to the optical axis of the resonator. Therefore,
The “range” does not need to be defined based on the absolute position of the component, but may be defined by a movement scale of the component moving means.

In each of the above-described adjustment methods, it is desirable that the movement of the component and the position adjustment and fixing of the component based on the movement are performed in a plurality of different directions, particularly preferably in two directions substantially orthogonal to each other.

The component to be moved as described above is preferably a component constituting a resonator, particularly preferably an output mirror of the resonator. Further, the component to be moved may be a component of the excitation unit including the excitation source.

On the other hand, a solid-state laser adjusting apparatus according to the present invention is for carrying out each of the above-described methods, and moves at least one component constituting the solid-state laser in a direction intersecting the resonator optical axis. Means, a transverse mode of the solid-state laser beam, that is, a transverse mode detecting means for detecting a beam shape or a beam diameter, and, based on an output of the transverse mode detecting means, the moving so as to arrange the component at a predetermined adjustment position. Control means for controlling the driving of the means.

[0015]

According to the first method for adjusting a solid-state laser according to the present invention, the components of the solid-state laser are moved in a direction intersecting the optical axis of the resonator, and the transverse mode of the solid-state laser beam when the movement is performed. Is detected, and the position of the component is adjusted and fixed at the center of the range in which the transverse mode takes the zero-order mode, so that dust, coat defects, etc. may be present on the light passing surface of the optical component disposed in the resonator. Even if the lateral mode exists and is affected by the transverse mode, the component is always adjusted and fixed at the center of the actual zero-order mode range. Therefore, in the solid-state laser adjusted by this method, when a disturbance such as an environmental temperature change or a change with time in the fixed position occurs, it is difficult for the transverse mode to have a higher order.

It is most preferable to position and fix the component at the center of the range where the transverse mode takes the zero-order mode, as described above. However, as in the second method or the third method of the present invention, In addition, even if the position of a component is fixed within a region of 20% or 50% of the range where the lateral mode takes the 0th-order mode as the center, the mode changes from the 0th-order transverse mode to the higher-order transverse mode. Compared to the case where the component is adjusted and fixed at the last position, when a disturbance such as an environmental temperature change or a temporal change in the fixed position occurs, it is less likely that the transverse mode will be higher.

On the other hand, the solid-state laser adjusting apparatus according to the present invention comprises a moving means for moving the solid-state laser component, a transverse mode detecting means for detecting a transverse mode of the solid-state laser beam, and an output from the means as described above. Control means for controlling the driving of the moving means so as to dispose the component at a predetermined adjustment position. Therefore, if this device is used, the above-described method for adjusting a solid-state laser according to the present invention can be simplified. It can be implemented.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an apparatus for adjusting a solid-state laser by the method according to the first embodiment of the present invention, and a profile of a semiconductor laser-excited solid-state laser to be adjusted by the apparatus.

First, the semiconductor laser pumped solid-state laser will be described. The following description is made on the assumption that the laser has been adjusted. This solid-state laser excited by a semiconductor laser includes a semiconductor laser 11 that emits a laser beam 10 as excitation light, a condensing lens 13 formed of, for example, a gradient index lens for condensing the laser beam 10 that is divergent light, and a neodymium ( Nd) is a YVO ₄ crystal (hereinafter referred to as N
d: YVO ₄ crystal) 14 and this Nd: YVO ₄
A front resonator mirror 15 disposed (the right side in the drawing) of the crystal 14, Nd: YVO ₄ optical wavelength conversion device 16 disposed between the crystal 14 and the resonator mirror 15, Brewster plate 17 and etalon 18.

The elements 14 to 18 described above are adhesively fixed to a common holder 30 made of, for example, copper, and the holder 30 is fixed on a Peltier element 31 constituting a temperature control means via a base plate 32. I have. The semiconductor laser 11 and the condenser lens 13 are also mounted on a holder 33 made of copper or the like, and this holder 33 is also fixed on the Peltier element 31 via a base plate 32.

The driving of the Peltier element 31 is controlled by a thermistor 34 attached to the holder 30 for detecting the temperature of the resonator section and a temperature control circuit (not shown), and the semiconductor laser 11 and the solid-state laser resonator (described later) are controlled. as Nd: YVO ₄ crystal 14 and elements within the configured) by the resonator mirror 15 is controlled in all common predetermined temperature.

The light wavelength conversion device 16 is a device in which a periodic domain inversion structure is provided in a MgO-doped LiNbO ₃ crystal, which is a nonlinear optical material. Brewster plate 17 acts as a polarization control element, and etalon 18
Acts as a wavelength selection element for unifying the oscillation wavelength.

The wavelength of the semiconductor laser 11 is 809 nm.
Which emits a laser beam 10 is used. N
The d: YVO ₄ crystal 14 has a wavelength of 1064 nm when neodymium ions are excited by the laser beam 10.
emits m light. Laser oscillation is caused by a resonator constituted by the rear end face 14a of the Nd: YVO ₄ crystal 14 and the mirror face 15a of the resonator mirror 15, and a wavelength of 1064
A solid state laser beam 20 of nm is obtained. This laser beam 20 enters the optical wavelength conversion element 16 and has a wavelength of １ ／.
That is, it is converted to the second harmonic 21 of 532 nm.

The resonator mirror 15 is a concave mirror having a radius of curvature of 50 mm, and its mirror surface 15a and Nd: YVO ₄ crystal are used.
The rear end face 14a is disposed so as to be separated from the rear end face 14a by about 10 mm on the optical axis. The mirror surface 15a of the resonator mirror 15 is provided with a coating that reflects the laser beam 10 and the solid-state laser beam 20 as excitation light with high reflectivity and transmits the second harmonic 21. Bowl mirror
Almost only the second harmonic 21 is emitted from 15.

Next, an apparatus for adjusting the oscillation state will be described. This adjusting device includes an xy fine movement stage 40 for moving the resonator mirror 15 in two directions orthogonal to the resonator optical axis, that is, an x direction in FIG. 1 and a y direction orthogonal thereto, and an xy fine movement stage Control means 41 for controlling the driving of 40
And a CCD camera 42 arranged at a position for receiving the second harmonic 21 output from the resonator mirror 15.

When adjusting the oscillation state, the control means 41 drives the xy fine movement stage 40 according to a predetermined program so as to first move the resonator mirror 15 in the x direction.
When the resonator mirror 15 moves as described above, the CCD camera
42 continuously detects the beam shape of the second harmonic 21, that is, the transverse mode, and inputs a video signal S indicating this to the control means 41.

When the resonator mirror 15 is moved in the x direction orthogonal to the resonator optical axis as described above, the transverse mode of the laser beam 20, that is, the second harmonic 21, changes according to the position of the movement. FIG. 2 illustrates this state. For example, as shown in the figure, when the resonator mirror 15 is sufficiently moved in the + (plus) x direction from the position on the − (minus) x side, the 0th-order transverse mode state is obtained at the x2 position. The mode is switched to the lateral mode state, and then switches from the 0th-order lateral mode state to the high-order lateral mode state at the x1 position.

Although only the x direction has been described above, the range in which the second harmonic 21 takes the zero-order transverse mode extends two-dimensionally in a plane intersecting the resonator optical axis. FIG. 3 shows this state. The large circle in FIG. 3 indicates the range in which the second harmonic 21 takes the 0th-order transverse mode, and in this example, this range is a substantially circular range having a diameter of about 100 μm.

As described above, the movement of the resonator mirror 15 is shifted from the position sufficiently on the-(minus) x side to + (plus).
Although it may be moved in the x direction, in the present embodiment, first, the resonator mirror 15 is coarsely moved and oscillated by hand, and the second harmonic 21 is visually observed. The position is initially set near the center of the 0th-order transverse mode range in the x direction, and is moved from there. A small white circle in FIG. 3A indicates the initial position of the resonator mirror 15.

As described above, the moving position of the resonator mirror 15 does not need to be defined by an absolute position. In this embodiment, this position is defined by the scale of the xy fine movement stage 40.

When the resonator mirror 15 is moved from the initial position in the + x direction, the transverse mode of the second harmonic 21 is switched from the zero-order mode to the higher-order mode at the position x1.
The control means 41 controls the image signal S received from the CCD camera 42.
, The switching of the lateral mode is detected, and the position x1 (the x scale of the xy fine movement stage 40) at that time is detected and stored.

Thereafter, the control means 41 controls the xy fine movement stage 40.
Is driven to move the resonator mirror 15 in the −x direction. When the resonator mirror 15 moves in this way, when the position reaches x2, the transverse mode of the second harmonic 21 becomes 0.
The mode is switched from the next mode to the higher mode. The control means 41 is C
Based on the video signal S received from the CD camera 42, the switching of the horizontal mode is detected, and the position x2 at that time is detected.
Is detected and stored.

From the stored positions x2 and x1, the control means 41 calculates the center position xc of the 0th-order mode range in the x direction based on the following equation: xc = x2 + | x1-x2 | / 2.
Is calculated, and the resonator mirror 15 is moved to the center position xc (that is, the position where the x scale of the xy fine movement stage 40 becomes xc), and fixed there in the x direction. The center position xc obtained in this way is indicated by a black circle in FIG.

Next, the same operation is performed in the y direction.
Based on the following equation, yc = y2 + | y1-y2 | / 2, the center position yc of the 0th-order mode range in the y direction
Is required. Note that y1 and y2 are positions in the y direction at which the mode switches between the 0th-order mode and the higher-order mode. This center position yc is indicated by a double circle in FIG.
This center position yc is naturally on the center position xc in the x direction, and the resonator mirror 15 is finally fixed to the holder 30 at this position. The fixing of the resonator mirror 15 is performed by, for example, bonding or the like.

By the above operation, the resonator mirror 15 is
The transverse mode of the harmonic 21 is adjusted and fixed at the center position of the range in which the transverse mode is the zero-order mode, so that a stable oscillation state in the zero-order transverse mode can be obtained.

According to the present embodiment, the center of the range in which the 0th-order horizontal mode is taken is 20% vertically and horizontally, that is, 20 μm.
The resonator mirror 15 can be adjusted and fixed in the area of m. In addition, even if the resonator mirror 15 is adjusted and fixed within a range of 50% in the vertical and horizontal directions of the above range, that is, in this example, 50 μm in the vertical and horizontal directions,
A relatively stable oscillation state in the 0th-order transverse mode can be obtained. Instead of using the automatic adjustment device as described above, it is also possible to adjust the position of the laser component such as the resonator mirror 15 by manual operation by applying the method of the present invention. It is also possible to adjust the position of the laser component to a position very close to the center of the range for taking the transverse mode.

In the above embodiment, the resonator mirror 15 is adjusted in the x direction and then in the y direction. However, the order may be reversed. The moving direction of the resonator mirror 15 is such that the x direction (horizontal direction) and the y direction
The direction is not limited to the direction (vertical direction), and may be set to any direction in the xy plane. The direction of adjustment is 2
The direction may be one direction or three or more directions.

Further, the present invention is not limited to the case where the position of the resonator mirror is adjusted, but is similarly applicable to the case where the position of other laser components is adjusted. FIG. 4 shows a semiconductor laser-excited solid-state laser according to a second embodiment of the present invention, in which the excitation section is moved as a whole to adjust oscillation. In FIG. 4, elements that are the same as the elements in FIG. 1 are given the same reference numerals, and overlapping descriptions thereof will be omitted.

Here, the holder 33 holding the semiconductor laser 11 for excitation and the condenser lens 13 and the holder 30 holding all the resonator units are fixed to the unit bases 50 and 51, respectively. This constitutes a resonator unit. The unit base 50 is movable in the x-direction and the y-direction orthogonal to the resonator optical axis and orthogonal to each other. On the other hand, the unit base 51 is combined in advance with an excitation optical system for adjustment different from the above-mentioned excitation unit, and the resonator mirror 15 is adjusted and fixed by using it.

Thereafter, the excitation unit and the resonator unit are combined, and the unit table 50 is moved in the x direction and the y direction with respect to the unit table 51 as a whole, so that the oscillation is adjusted. The movement of the unit base 50 and the setting to the optimum position for this adjustment may be performed basically in the same manner as in the previous embodiment.

In the present invention, the laser components such as the resonator mirror and the excitation system component are moved in the direction orthogonal to the resonator optical axis as in the above-described embodiment.
The transverse mode may be changed by moving in a direction inclined with respect to the resonator optical axis. Further, a beam diameter measuring device may be used instead of the CCD camera.

[Brief description of the drawings]

FIG. 1 is a side view showing a semiconductor laser-excited solid-state laser that is adjusted according to a first embodiment of the present invention and a device that performs the adjustment.

FIG. 2 is a view for explaining switching of a transverse mode of a solid-state laser.

FIG. 3 is a diagram for explaining adjustment movement of a resonator in the apparatus of FIG. 1;

FIG. 4 is a side view showing a semiconductor laser pumped solid-state laser tuned according to a second embodiment of the present invention.

[Explanation of symbols]

10 Laser beam (excitation light) 11 Semiconductor laser 13 Condensing lens 14 Nd: YVO ₄ crystal 15 Resonator mirror 16 Optical wavelength conversion element 17 Brewster plate 18 Etalon 20 Laser beam (Solid laser beam) 21 Second harmonic 30, 33 Holder 31 Peltier element 32 Base plate 40 XY fine movement stage 41 Control means 42 CCD camera 50, 51 Unit base

Claims (9)

[Claims] 1. A method for adjusting an oscillation state of a solid-state laser having at least a solid-state laser crystal, an excitation source for exciting the crystal, and a resonator, wherein at least one component constituting the solid-state laser is provided with a resonator optical axis. Moving in the intersecting direction, detecting the transverse mode of the solid-state laser beam while the movement is being performed, obtaining a range in which the transverse mode takes the zero-order mode in the direction of the movement, and taking the zero-order mode. Adjusting the position of the component near the center of the solid-state laser. 2. A method for adjusting an oscillation state of a solid-state laser having at least a solid-state laser crystal, an excitation source for exciting the same, and a resonator, wherein at least one component constituting the solid-state laser is connected to a resonator optical axis. Moving in the intersecting direction, detecting the transverse mode of the solid-state laser beam while the movement is being performed, obtaining a range in which the transverse mode takes the zero-order mode in the direction of the movement, and taking the zero-order mode. Of the range around the center of
A method for adjusting a solid-state laser, wherein the position of the component is adjusted and fixed within a region of 20%. 3. A method for adjusting an oscillation state of a solid-state laser having at least a solid-state laser crystal, an excitation source for exciting the same, and a resonator, wherein at least one component constituting the solid-state laser is provided with a resonator optical axis. Moving in the intersecting direction, detecting the transverse mode of the solid-state laser beam while the movement is being performed, obtaining a range in which the transverse mode takes the zero-order mode in the direction of the movement, and taking the zero-order mode. Of the range around the center of
A method for adjusting a solid-state laser, wherein the position of the component is adjusted and fixed within a 50% area. 4. The solid-state laser adjustment method according to claim 1, wherein the movement of the component and the position adjustment and fixing of the component based on the movement are performed in a plurality of different directions. 5. The solid-state laser adjustment method according to claim 4, wherein the movement of the component and the position adjustment and fixing of the component based on the movement are performed in two directions substantially orthogonal to each other. 6. The device according to claim 1, wherein the moving component is a component forming a resonator.
The method for adjusting a solid-state laser according to the above item. 7. The method according to claim 6, wherein the moving component is an output mirror of a resonator. 8. The pump according to claim 1, wherein the moving component is a component of an excitation unit including the excitation source.
8. The method for adjusting a solid-state laser according to any one of items 1 to 7. 9. An apparatus for performing the method for adjusting a solid-state laser according to claim 1, wherein at least one component of the solid-state laser is moved in a direction intersecting the optical axis of the resonator. Means, a transverse mode detecting means for detecting a transverse mode of the solid-state laser beam, and control for controlling driving of the moving means so as to arrange the component at a predetermined adjustment position based on an output of the transverse mode detecting means. And a means for adjusting a solid-state laser.