JP4146207B2 - Nonlinear wavelength conversion laser device - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a solid-state laser device, and more particularly to a wavelength-converted solid-state laser oscillator for stably generating a higher-order harmonic laser by nonlinear wavelength conversion.
[0002]
[Prior art]
In a solid-state laser device, a laser medium is arranged inside a pair of opposing mirrors, and this is excited optically by, for example, irradiation of excitation light by a krypton arc lamp for excitation, thereby emitting light having a wavelength unique to the laser medium. This is repeatedly reflected back and forth by a pair of reflecting mirrors, thereby generating a stimulated emission phenomenon inside the laser medium and forming an optical resonator that amplifies the phenomenon.
[0003]
Normally, one of the reflecting mirrors constituting the above-described optical resonator is a complete reflecting mirror having a reflectance of 100% with respect to light having an oscillation wavelength unique to the laser medium, and the other has a reflectance of, for example, about 90% A partially reflecting mirror coated with a dielectric multilayer film, and a part of the optical standing wave generated inside the optical resonator is output as a laser beam to the outside of the optical resonator through the partially reflecting mirror. Yes.
[0004]
In addition to this, in the case of a wavelength conversion laser, another wavelength conversion medium is inserted into the optical path of the optical standing wave generated inside the optical resonator or the laser beam output wave output outside the optical resonator. A high-order harmonic component is generated by causing the laser beam of the fundamental wavelength directly generated by the resonator and the wavelength conversion medium to interfere with each other in terms of physical properties.
[0005]
A laser that converts light of a fundamental wavelength into a higher-order harmonic using a wavelength conversion medium is called a wavelength conversion laser, and in particular, beta barium borate (β-BaB ₂ O ₄ = BBO) or lithium triborate (LiB). A laser device using a crystal having a nonlinear optical effect such as ₃ O ₅ = LBO) as a wavelength conversion medium is referred to as a nonlinear wavelength conversion laser.
[0006]
In a nonlinear wavelength conversion laser, for example, a basic laser beam with a wavelength of 1064 nm is oscillated by a YAG laser using neodymium, yttrium, aluminum, garnet (Y ₃ Al ₅ O ₁₂ = YAG) as a laser optical medium, and emitted from an output mirror The above-mentioned laser beam is irradiated on the BBO crystal or the like to generate a second harmonic wave having a wavelength of 532 nm due to the nonlinear optical effect.
[0007]
In this case, 10% of the 1064 nm light oscillating in the optical resonator is extracted outside the optical resonator and used for wavelength conversion, and the wavelength conversion efficiency cannot be increased so much.
[0008]
On the other hand, one of the two reflecting mirrors forming the optical resonator of the YAG laser is completely reflected with respect to 1064 nm light, and the other (output side) mirror completely reflects 1064 nm light and 532 nm. There is also a method of inserting a wavelength conversion medium such as a BBO crystal directly into the optical path of the fundamental standing wave inside the optical resonator while completely transmitting light.
[0009]
In this case, since the fundamental laser beam of 1064 nm is completely confined in the optical resonator, the electromagnetic field potential of the fundamental standing wave in the optical resonator is larger than the former, and is due to the nonlinear optical effect of the BBO crystal. Since the efficiency of wavelength conversion is drastically improved, it is possible to extract high-output second-order harmonics through an output mirror that completely transmits the 532 nm light.
[0010]
As a known example, in Japanese Patent Laid-Open No. 05-95144, neodymium yttrium orthovanadate (Nd-YVO ₄ = YVO4) having the same wavelength output as YAG is used as a wavelength conversion medium for generating second harmonics. A configuration is described in which a second-harmonic laser with a wavelength of 532 nm is generated by using potassium titanyl postate (KTiOPO = KTP) and inserting KTP inside the optical resonator.
[0011]
In addition, there is also an ultraviolet laser device that generates a fourth harmonic having a wavelength of 266 nm by combining the above two methods.
[0012]
In this case, BBO for second harmonic generation is inserted into the resonator, a laser beam of 532 nm is emitted from the output mirror, and this is finally irradiated to the BBO for fourth harmonic generation provided separately. An ultraviolet laser beam of 266 nm is generated.
[0013]
[Problems to be solved by the invention]
Usually for the purpose of arranging optical elements such as reflection mirrors, optical crystals as wavelength conversion media, lenses and pinholes for shaping the fundamental wave and higher-order harmonic beams. It is common to use a positioning stage or mirror holder with a position and orientation adjustment function.
[0014]
For example, it is necessary to adjust the angles of the two reflecting mirrors constituting the optical resonator strictly so that the optical resonator continues to oscillate the fundamental standing wave most efficiently and stably.
[0015]
In addition, BBO crystals and LBO crystals, which are often used as wavelength conversion media, have angle dependence, and it is necessary to strictly adjust the angle of the crystal with respect to the laser beam to be irradiated in order to optimize wavelength conversion efficiency. There is.
[0016]
In an actual nonlinear wavelength conversion laser, each optical element that needs to be adjusted is held by a positioning stage or mirror holder so that the above adjustment can be performed optimally, and an output beam obtained by oscillating the laser Optimization adjustment is performed using the shape and output of the image as an index.
[0017]
In the above method, the optimal adjustment of one optical element sometimes contradicts the optimal position of another optical element. In such a case, the adjustment operation using the output beam as an index adjusts the entire system to the optimal optical arrangement. It is extremely difficult to do so, and it is often the case that adjustment work for a long time is performed while repeating trial and error.
[0018]
The most difficult case will be described below.
[0019]
The center of the laser beam is called the optical axis, and the path through which the optical axis passes is called the optical path. However, if the fundamental oscillation is optimized by adjusting the reflecting mirror, the optical resonator is adjusted according to the change in the tilt of the reflecting mirror. The optical axis angle of the standing wave and the optical axis angle of the output beam change.
[0020]
On the other hand, the nonlinear optical crystal as the wavelength conversion medium is positioned and arranged so as to coincide with the optical path of the fundamental wave beam, and is strictly adjusted in angle with respect to the optical axis of the fundamental wave beam.
[0021]
If the angle of the reflection mirror of the optical resonator is adjusted during the optimization adjustment of the fundamental wave beam, the angle of the optical axis changes, so that wavelength conversion cannot be performed. As a result, the second harmonic laser that is an adjustment index Since the output decreases, the adjustment work itself cannot be performed.
[0022]
Since it is impossible to determine whether the output of the second harmonic laser used as an indicator is due to a deviation from the optimum point of the fundamental oscillation or due to a change in the optical axis of the fundamental beam. As described above, it is extremely difficult to optimize and adjust the entire optical system including the optical resonator and the wavelength conversion medium, and it has been necessary to repeat trial and error depending on chance.
[0023]
Therefore, true optimization adjustment is practically impossible, and the laser output becomes unstable due to slight temperature changes and state changes after adjustment, or the shape of the beam deteriorates for a long time. There was also a problem with stable operation.
[0024]
The present invention has been made to solve the above-mentioned problems of the prior art, and is a non-linear type that allows easy optical adjustment and easy optimization of optical elements, resulting in long-term stable operation. A wavelength conversion laser device is provided.
[0025]
[Means for Solving the Problems]
A nonlinear wavelength conversion laser device according to the present invention obtains excitation light having a specific wavelength of a laser optical medium by exciting a laser optical medium, and an optical unit for emitting the excitation light and an optical unit sandwiching the optical unit. An optical resonator having a first reflecting mirror and a second reflecting mirror disposed opposite to each other on the base, and at least one optical unit that performs nonlinear wavelength conversion on the fundamental laser beam obtained from the optical resonator A non-linear wavelength conversion laser device including an element, provided on a base is a positioning stage capable of adjusting movement in the y direction and x direction and inclination in the θx direction, θy direction, and θz direction. A first reflecting mirror and at least one optical element are arranged, and a second reflecting mirror and an optical unit are arranged on a base where no positioning stage is present, A second reflecting mirror and an optical unit are disposed on the substrate, and the first reflecting mirror and at least one of the optical elements are disposed on a base on which no positioning stage exists. To do.
[0026]
[Action]
The operation of the present invention will be described below.
[0027]
In the optical resonator of the laser oscillator, a fundamental standing wave oscillating with a pair of opposing reflecting mirrors oscillates, and its optical axis is always perpendicular to the reflecting surfaces of the reflecting mirrors at both ends.
[0028]
Even if one reflection mirror is used as a partial reflection mirror and part of the fundamental standing wave is taken out of the optical resonator, it is normally output as a laser beam with an optical axis that matches the optical axis of the fundamental standing wave in the optical resonator. Will be.
[0029]
As described above, the direction of the optical axis of the laser beam of the fundamental wavelength, which is the basis for wavelength conversion, is determined by the reflection mirror of the optical resonator, so when adjusting the optical resonator and optimizing the oscillation of the basic laser beam As the angle of the reflecting mirror is adjusted, the optical axis always changes in a direction perpendicular to the reflecting mirror.
[0030]
On the other hand, the nonlinear optical crystal, which is positioned on the optical axis of the fundamental laser beam and converts the wavelength of the fundamental laser beam to generate higher-order harmonics, is precisely adjusted in angle with the optical axis of the fundamental laser beam and held as it is. Therefore, it is fixed to a positioning holder or the like having a position and orientation adjustment function.
[0031]
If the reflecting mirror and the positioning holder for the non-linear optical crystal are combined here, the orientation of the positioning holder will change in the same way as the reflecting mirror is adjusted, and eventually the relative angle between the reflecting mirror and the positioning holder Can always keep the same.
[0032]
That is, the nonlinear optical crystal held by the positioning holder can always be held at a constant angle with the optical axis of the fundamental laser beam regardless of the adjustment of the optical resonator.
[0033]
After adjusting the optical resonator so that the fundamental laser beam is optimized in this way, the angle of the nonlinear optical crystal can be adjusted to the optimum with respect to the optical axis of the fundamental laser beam by the positioning holder. Both the fundamental laser beam and the nonlinear optical crystal can be easily optimized.
[0034]
Once the angle of the nonlinear optical crystal is optimized by the positioning holder, even if the optical resonator needs to be readjusted for some reason after that, the fundamental laser beam and the nonlinear optics will be adjusted according to the adjustment of the reflecting mirror. The relative angle with the crystal does not change, and the output change of the wavelength-converted second harmonic laser beam simply depends on the state of the optical resonator, that is, the change of the fundamental laser beam.
[0035]
Therefore, the fundamental laser beam can be adjusted using the output of the second harmonic laser beam as an index.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to FIG.
FIG. 1 is an overall configuration diagram of an embodiment of the present invention.
[0037]
A laser optical medium such as YAG and a krypton arc lamp for electro-optically exciting the laser optical medium are built in, and the laser optical medium is electrically excited to emit excitation light having a wavelength specific to the laser optical medium from the exit. The optical unit 2 configured as described above, and the first reflection mirror 4 and the second reflection mirror 5 disposed on the optical base 1 so as to sandwich the optical unit 2 constitute an optical resonator.
[0038]
The first reflecting mirror 4 is optically coated so as to completely reflect light having a fundamental oscillation wavelength of 1064 nm of YAG and completely transmit light having a wavelength of 532 nm, which is the second harmonic, and the second reflecting mirror 5 has a wavelength of 1064 nm. It is optically coated so as to completely reflect the light.
[0039]
In addition, the fundamental wave label is rapidly generated in the optical resonator with a pinhole 6 for the purpose of removing the optical noise component by limiting the beam diameter of the YAG basic laser beam having a wavelength of 1064 nm excited and oscillated by the optical resonator. An acousto-optic device 10 for interrupting and releasing the oscillation and generating a laser beam on a pulse is provided in the optical resonator.
[0040]
In the nonlinear wavelength conversion laser, the efficiency of wavelength conversion by the nonlinear optical crystal increases nonlinearly as the peak value of the oscillation energy of the fundamental laser beam increases. It is used to generate laser oscillation on the pulse so that the peak value of energy for each pulse is maximized.
[0041]
An optical axis 7 shown in FIG. 1 is an optical axis in an optical resonator of a YAG laser beam having a fundamental wavelength of 1064 nm that is excited and oscillated by the above method, and is constrained by the pinhole 6 and passes through the center of the pinhole 6. And excited and oscillated along only one optical path perpendicular to the first reflecting mirror 4.
[0042]
The second reflecting mirror 5 is held by a holder h1, and the tilt can be freely adjusted by adjusting a knob.
[0043]
The first reflecting mirror 4 is also fixed to the positioning stage 3 provided on the base 1 in order to adjust the tilt.
[0044]
The positioning stage 3 is capable of minute movement in the directions y and z and fine inclination adjustment in the directions of θx, θy, and θz by appropriately rotating the adjustment knobs T1, T2, T3, T4, and T5. Thus, the tilt of the first reflecting mirror 4 can be adjusted.
[0045]
The above is the configuration of the optical resonator of the fundamental wave laser. In this embodiment, the wavelength conversion is performed from the fundamental laser beam having a wavelength of 1064 nm excited and oscillated thereby to the second and fourth harmonics, and finally the wavelength is changed. In order to generate a 266 nm ultraviolet laser beam, a BBO crystal 8 for generating a second harmonic and a BBO crystal 9 for generating a fourth harmonic are held in holders h2 and h3, respectively.
[0046]
These BBO crystals are indicated by dotted lines in FIG.
[0047]
Both the holders h2 and h3 have the same mechanism as the holder h1 that holds the second reflecting mirror 5, and the inclination of the BBO crystals 8 and 9 held by the adjustment knob can be adjusted.
[0048]
The BBO crystal 8 for generating the second harmonic is arranged inside the first and second reflecting mirrors 4 and 5 constituting the optical resonator so as to convert the wavelength from the high intensity basic laser beam in the optical resonator. Then, the BB0 crystal 9 for generating the fourth harmonic irradiates the second harmonic laser beam of 532 nm generated by wavelength conversion in the optical resonator after passing through the first reflecting mirror 4 and then emitting it. And converted to the fourth harmonic.
[0049]
An optical axis 11 shown in FIG. 1 is an optical axis of an output laser beam that is finally output as a 266 nm ultraviolet laser after two wavelength conversions.
[0050]
The feature of this embodiment is that the pinhole 6, the holder h2 holding the BBO crystal 8 for generating the second harmonic on the positioning stage 3 for adjusting the tilt of the first reflecting mirror 4, and the fourth harmonic. The holder h3 holding the generating BBO crystal 9 is arranged, whereby the first adjusting mirror T1 to T5 of the positioning stage 3 is rotated in order to adjust the tilt of the first reflecting mirror 4, so that the first Since not only the reflection mirror 4 but also the pinhole 6, the holder h2, and the holder h3 are all tilted together, the BBO crystal 8 for generating the second harmonic and the BBO for generating the fourth harmonic for the first reflection mirror 4 are used. The relative angle of the crystal 9 can always be kept constant regardless of the adjustment of the reflecting mirror.
[0051]
The YAG fundamental wave laser beam in the optical resonator is excited and oscillated along a single optical path that passes through the pinhole 6 that restricts the YAG and is perpendicular to the first reflecting mirror 4. Further, the position and inclination of the optical path of the YAG fundamental wave laser beam with respect to the optical unit 2 and the second reflection mirror 5 can be changed by minutely moving or rotating the first reflection mirror 4.
[0052]
While searching for an optical path that optimizes the oscillation of the YAG fundamental laser beam in this way, adjusting the tilt of the second reflecting mirror 5 accordingly adjusts the oscillation of the YAG fundamental laser optimally. can do.
[0053]
Next, with respect to the optical axis 7 of the YAG fundamental wave laser beam thus determined, the tilt is adjusted by the knob of the holder h2 so that the angle of the BBO crystal 8 for generating the second harmonic is optimum for wavelength conversion. In this case, the wavelength is converted by the BBO crystal 8 as a result of adjustment, and this is in a good state while observing the output and shape of the second harmonic wave having a wavelength of 532 nm that is transmitted through the first reflecting mirror 4 and output. Like that.
[0054]
Next, the BBO crystal 9 for generating the fourth harmonic performs tilt adjustment with respect to the optical axis of the second harmonic of 532 nm irradiated to the fourth harmonic, but this time the wavelength is 266 nm which is emitted after being converted by the BBO crystal 9. The output and shape of the ultraviolet laser beam 11 may be used as an index and optimized.
[0055]
Once the inclination of the BBO crystals 8 and 9 with respect to the first reflecting mirror 4, that is, the optical axis 7, is determined by the above procedure, the optical resonator needs to be readjusted for some reason and positioned. Even if the read mirror is readjusted by the stage 3, the relative inclination of the BBO crystals 8 and 9 with respect to the optical axis 7 does not change, and the output and shape of the 266 nm fourth harmonic laser beam that is finally output. Is simply determined only by the state of YAG fundamental wave laser oscillation by adjusting the optical resonator.
[0056]
For this reason, adjustment work can be easily performed while observing the final output beam, and as a result, the arrangement of the entire laser oscillator including the angle between the optical resonator and the BBO crystal can be easily optimized.
[0057]
FIG. 2 shows another embodiment of the present invention, which basically has the same configuration as that of FIG.
[0058]
1 is different from FIG. 1 in that optical elements such as the optical unit 2, the second reflecting mirror 5, and the acousto-optic element 10 which are installed on the optical base 1 in FIG. One reflecting mirror 4, pinhole 6, and BBO crystals 8 and 9 are installed on the optical base 1, and the relative relationship between them is the same.
[0059]
According to this embodiment, it is possible to easily optimize and adjust the ultraviolet laser oscillator using the nonlinear wavelength conversion crystal in a short time.
[0060]
【The invention's effect】
According to the present invention, optimization adjustment of a nonlinear wavelength conversion laser device can be facilitated, and as a result, it is possible to provide a nonlinear wavelength conversion laser device that is stable and reliable for a long period of time and is easy to maintain such as readjustment. .
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a nonlinear wavelength conversion laser oscillator according to an embodiment of the present invention.
FIG. 2 shows another embodiment of the present invention, similar to FIG.
[Explanation of symbols]
1: Optical base 2: Optical unit 3: Positioning stage 4: First reflecting mirror 5: Second reflecting mirror 6: Pinhole 7: Optical axis 8 of YAG fundamental wave laser beam: BBO for generating second harmonic Crystal 9: BBO for fourth harmonic generation 10: Acoustooptic element 11: Optical axes T1 to T5 of fourth harmonic: Positioning stage adjustment knobs x, y, z: Positioning stage moving directions θx, θy, θz: tilt adjustment direction of positioning stage h1, h2, h3: holder

Claims (1)

  A laser optical medium is excited to obtain excitation light having a specific wavelength of the laser optical medium, an optical unit that emits the excitation light, and a first that is disposed on the optical base so as to sandwich the optical unit. An optical resonator having a reflecting mirror and a second reflecting mirror, and at least one optical element disposed in the optical resonator and performing nonlinear wavelength conversion on a fundamental laser beam obtained from the optical resonator In the nonlinear wavelength conversion laser apparatus, a positioning stage capable of adjusting movement in the y direction and x direction and inclination in the θx direction, θy direction, and θz direction is provided on the base, and the first stage is provided on the positioning stage. Disposing a reflection mirror and at least one optical element, and disposing the second reflection mirror and the optical unit on the base without the positioning stage; or The second reflecting mirror and the optical unit are arranged on the positioning stage, and the first reflecting mirror and at least one optical element are arranged on the base where the positioning stage does not exist. A non-linear wavelength conversion laser device characterized by comprising:

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