JP2001021931A - Laser device for processing using nonlinear crystal of type 1 - Google Patents

Abstract

PROBLEM TO BE SOLVED: To diminish fluctuations of the output power of a laser beam with a laser device for processing which emits laser beam subjected to wavelength conversion by using nonlinear optical crystals. SOLUTION: Fundamental waves emitted from a basic wave laser beam source 11 is made incident on the first nonlinear optical crystal 13 for double wave generation. The nonlinear optical crystal 13 generates the double wave and the basic wave. The basic wave and double wave emitted from the nonlinear optical crystal 13 are made incident on a wavelength plate 20. The wavelength plate 20 rotates the polarization directions of the basic wave in the direction parallel with the polarization direction of the basic wave and double wave. The double wave and basic wave of the parallel polarization directions emitted from the wavelength plate 20 are made incident on the second nonlinear optical crystal 13' of TYPE1, where the double wave and the basic wave are subjected to wavelength conversion and a triple wave and the fundamental wave are emitted. Since the crystal of the TYPE1 is larger in temperature permissible range width than that of a crystal of TYPE 2, the fluctuations in the output powder of the laser beam can be diminished even if a minor temperature change occurs in the crystals by using only the crystal of TYPE1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a processing laser device for performing wavelength conversion using a wavelength conversion element, and irradiating a workpiece such as a multilayer printed board with wavelength converted light for processing.

[0002]

2. Description of the Related Art Lasers are used for forming via holes in printed circuit boards, cutting films and metals, and the like. In recent years, a laser used for processing has been shortened in wavelength due to a demand for fine processing. For generation of a short-wavelength laser, it is effective to use a wavelength conversion method using a nonlinear optical crystal. FIG. 8 shows a schematic configuration of a processing laser device 10 that generates a third harmonic (3ω) of a fundamental wave (1ω) by wavelength conversion using a nonlinear optical crystal. In the figure, reference numeral 11 denotes a fundamental laser light source 11 for generating a fundamental wave (1ω).
As the fundamental wave laser light source 11, a Nd: YAG laser device that oscillates a laser beam having a wavelength of 1064 nm, a wavelength 10
N that oscillates laser light of 53 nm or 1047 nm
d: A YLF laser device or the like can be used.

The fundamental laser light emitted from the fundamental laser light source 11 is condensed by the condenser lens 12 and
Incident on the nonlinear optical crystal 13. A part of the fundamental laser light that has entered the first nonlinear optical crystal 13 is wavelength-converted to a second harmonic (2ω) of the fundamental laser light and exits from the nonlinear optical crystal 13. The fundamental laser light emitted from the first nonlinear optical crystal 13 and its second harmonic are further incident on the second nonlinear optical crystal 13 ′, which is wavelength-converted into the third harmonic (3ω). The light emitted from the second nonlinear optical crystal 13 ′ is condensed by the condensing lens 14 and is irradiated on the workpiece 15. The first and second nonlinear optical crystals 13 and 13 'described above.
Is the temperature and phase matching angle (the angle at which the laser beam enters the crystal)
It is known that when the power changes, the output laser power changes. Therefore, the nonlinear optical crystal 13, 1
3 'is controlled so that its temperature becomes constant.

The temperature of the nonlinear optical crystals 13 and 13 ′ is controlled by bringing a temperature measuring element such as a thermocouple 16 into contact with the surfaces of the nonlinear optical crystals 13 and 13 ′ and heating the entire nonlinear optical crystal by a heating means such as a heater 18. Alternatively, it is covered with a cooling means such as a Peltier element. Then, the output of the thermocouple 16 is input to a temperature controller 17 (hereinafter, referred to as a temperature controller 17). Temperature controller 17
Feeds back the measured temperature of the nonlinear optical crystal so as to reach a preset temperature, controls the input of the heating means or the cooling means, and
Adjust the temperature of 3,13 '. FIG. 8 illustrates a case where the nonlinear optical crystal 13 is heated using the heater 18. Hereinafter, a case where the nonlinear optical crystal is heated will be described as an example.

The output from the processing laser device 10 shown in FIG. 8 is adjusted as follows. The nonlinear optical crystals 13 and 13 'are heated to a set predetermined temperature and controlled so as to be constant. In this state, the laser light from the fundamental laser light source 11 is incident on the nonlinear optical crystal 13, and the wavelength-converted and output laser light is received by a power monitor (not shown). While watching the display on the power monitor, the phase matching angles of the nonlinear optical crystals 13 and 13 'are adjusted so that the value becomes maximum, and the angle at which the nonlinear optical crystals 13 and 13' are arranged is determined.

FIG. 9 is a view showing the type of phase matching of a nonlinear optical crystal used in the processing laser device shown in FIG. 8 and the polarization direction. In the figure, a fundamental wave of 1ω oscillated from a fundamental wave laser oscillator 11 enters a nonlinear optical crystal 13 (SHG) for generating a second harmonic, and is wavelength-converted.
A harmonic (2ω) and a fundamental wave (1ω) are emitted. here,
Arrows and circles (with black circles) in the figure indicate the polarization directions, respectively, and the arrows and the circles indicate that the polarization directions are orthogonal to each other. Nonlinear optical crystal for generating second harmonic 1
Since the polarization directions of 1ω incident on 3 are parallel to each other,
As the non-linear optical crystal 13 for generating the second harmonic, a TYPE for performing wavelength conversion by inputting lights whose polarization directions are parallel to each other is used.
One crystal is used. Non-linear optical crystals that can be used include LBO, CLBO, BBO, and the like.

The second harmonic (2ω) and the fundamental wave (1ω) emitted from the second harmonic generation nonlinear optical crystal 13 enter the third harmonic generation nonlinear optical crystal 13 ′ (THG). ,
The wavelength is converted, and a third harmonic (3ω), a second harmonic (2ω), and a fundamental wave (1ω) are emitted. The nonlinear optical crystal 13 for generating the second harmonic is TYPE 1 as described above, and the polarization direction of the wavelength-converted second harmonic (2ω) emitted from the TYPE 1 crystal is the same as the polarization direction of the fundamental wave (1ω). At right angles to it. Therefore, the nonlinear optical crystal 13 ′ for generating the third harmonic wave
Is a TYPE2 crystal that converts wavelengths by entering light whose polarization directions are perpendicular to each other. Types of nonlinear optical crystals used include LBO and CLBO.

When a via hole is formed in a multilayer printed board by the above-described processing laser device, the laser light is turned on / off by a shutter or a Q-SW, and the pulsed laser light is intermittently processed. Irradiate the object. FIG.
0 shows the state of via hole processing by laser light. As shown in FIG. 1A, usually, a plurality of irradiation areas A1, A2,... Are formed on a single substrate, and each irradiation area A1, A2,. Is provided. Then, the laser beam emitted from the processing laser device is scanned by a control means such as a galvanometer and positioned at each hole-forming position of the multilayer printed board, and each hole-forming position is irradiated with pulsed laser light a plurality of times. To perform via hole processing.

That is, as shown in FIG. 1D, the full width at half maximum (pulse width at half the peak value) is several tens ns.
To several hundred ns, and the repetition frequency is several kHz to several tens.
A laser pulse of kHz is applied a plurality of times to each of the drilled locations in the area A1 as shown in FIG. 3 (c) to perform drilling processing. The laser light is moved, and the operation of making a hole is repeated in the same manner. Then, when all the holes in the area A1 are completed, the laser light is turned off, the laser light is moved to the next area A2, and similar drilling is performed, as shown in FIG. Hereinafter, similarly, each area A1, A of the multilayer printed board
The drilling process of 2,... Is sequentially performed, and when the drilling of one multilayer printed board is completed, the multilayer printed board is replaced and the next printed board is processed. Here, the number of laser shots is 1 to 30 shots for processing one hole. In FIG. 10C, immediately after the start of laser beam emission,
The size of the laser light gradually increases, but this is output fluctuation due to an increase in the internal temperature of the nonlinear optical crystal, as described later.

As described above, when a processing laser device is used for processing a via hole or the like of a multilayer printed board, a processed work (multilayer printed board) is replaced with an unprocessed work, or a single multilayer printed board is processed. Therefore, an operation such as moving an area to be irradiated with a laser beam is required (this operation is called “setup change”). The setup change time usually takes several seconds to several tens of seconds (sometimes several minutes). When the setup change is performed, the laser light is not emitted from the laser light source as described with reference to FIG.
The processing laser device does not output a laser. After the completion of the setup change, the laser light is emitted from the laser light source, and the work is irradiated with the wavelength-converted laser light.

[0011]

In a processing laser apparatus for generating a third harmonic of a fundamental wave by wavelength conversion and performing processing, as described above, a nonlinear optical crystal 1 for generating a third harmonic is used.
As 3 ′, an LBO crystal or a CLBO crystal of TYPE 2 was used. The nonlinear optical crystal is controlled by the temperature controller to have a constant temperature as described with reference to FIG. 8. However, in order to make the fluctuation of the output power of the laser beam 10% or less, the temperature of the crystal must be controlled. At present, it is necessary to control the temperature to about 0.5 ° C., and it is currently difficult to control the temperature as described above.

In particular, when the laser apparatus using the TYPE 2 nonlinear optical crystal shown in FIG. 9 is applied to a processing laser apparatus for processing a multilayer printed board or the like by intermittently irradiating a laser beam, the temperature control is performed. It is difficult to reduce the fluctuation of the output power of the laser light even if the surface temperature of the non-linear optical crystal is controlled to be constant by the device. That is, immediately after the start of laser light emission, the nonlinear optical crystal absorbs the wavelength-converted light, and the temperature inside the crystal through which the laser passes increases.
Further, when the emission of the laser beam stops and a predetermined time elapses, the temperature inside the crystal decreases. Such a temperature change inside the crystal is repeated every time the laser light is turned on / off, and accordingly, the wavelength conversion efficiency of the crystal fluctuates, and the output power of the laser fluctuates.

In particular, in the processing of a multilayer printed board as described with reference to FIG. 10, since the internal temperature of the nonlinear optical crystal decreases during the setup change, when the laser light is emitted after the setup change, the nonlinear optical crystal is cut. The internal temperature rises,
The output power fluctuates greatly as shown in FIG. In the processing of a via hole or the like, if the output power of the laser beam fluctuates, a problem occurs in the depth of the hole or the processing shape, which causes a practical problem.

FIG. 11 and FIG. 12 show changes in laser power of the LBO crystal of TYPE 2 immediately after the start of laser beam emission, where the output power of the laser is 3 W, and the horizontal axis represents time. (Sec), the vertical axis is the output power (W). Here, FIG. 11 shows a change when the surface temperature of the crystal is controlled to, for example, 55.1 ° C., and FIG. 12 shows a change when the surface temperature of the crystal is controlled to, for example, 55.4 ° C. As is clear from FIGS. 11 and 12, the laser power changes immediately after the start of laser beam emission in each case. That is, in FIG. 11, the output power continues to increase immediately after the start of laser light emission, and in FIG. 12, the output power temporarily increases immediately after the start of laser light emission,
Thereafter, the output power has decreased. As described above, in the conventional processing laser device using the TYPE 2 nonlinear optical crystal, the output power of the laser light fluctuates, causing a problem in processing.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a processing laser device that emits laser light whose wavelength has been converted using a nonlinear optical crystal. An object of the present invention is to provide a processing laser device capable of reducing fluctuations in output power of laser light even when a temperature change occurs.

[0016]

In order to solve the above-mentioned problems, the present invention relates to a laser device that performs wavelength conversion by using a nonlinear optical crystal and generates an ultraviolet laser beam. Use only It has been found that the TYPE 1 crystal has a larger allowable temperature range than the TYPE 2 crystal, and that the output power does not fluctuate much with a change in temperature. Therefore, TYP
By using only the crystal of E1, fluctuation of the output power of the laser beam can be suppressed even if the temperature of the crystal fluctuates somewhat. Here, in order to perform wavelength conversion using a TYPE 1 crystal, the polarization directions of the wavelength-converted lights must be parallel to each other. Therefore, using a wave plate,
Fundamental wave, second harmonic wave or 3 incident on TYPE 1 crystal
One of the harmonics is rotated by 90 °.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the relationship between the crystal temperature and the wavelength conversion efficiency will be described. In general, the wavelength conversion efficiency η (eta) of a nonlinear crystal can be expressed by the following equation (1). η∝ ｛sin ² (ΔkL / 2)｝ / (ΔkL / 2) ² (1) where L is the optical distance of the nonlinear crystal, and Δk is the wave number of the laser beam incident on the nonlinear crystal and the laser beam emitted therefrom. The difference is expressed by the following equation (2).

[Lambda] 1 and [lambda] 2 are the wavelengths of the laser beam incident on the nonlinear crystal, [lambda] 3 is the wavelength of the wavelength-converted laser beam emitted from the nonlinear crystal, and ni is the refractive index with respect to the wavelength [lambda] i. It is determined by the incident angle (θ) of light, its polarization direction (φ), and the temperature (T) of the nonlinear crystal. That is, the refractive index n can be expressed as a function of θ, φ, and T as shown in the following equation (3). n = f (θ, φ, T) (3)

Therefore, from the equations (1), (2) and (3), the wavelength conversion efficiency η can be expressed as a function of the temperature T of the nonlinear crystal. Therefore, when the wavelength conversion efficiency η is expressed with respect to the crystal temperature, it becomes as shown in FIG. Here, the temperature range allowed until the wavelength conversion efficiency is reduced by half (to 0.5) is referred to as a temperature range, and is usually defined by the entire range. As is apparent from FIG. 3, the crystal temperature T at which the conversion efficiency η of the crystal is maximized.
If o is present and the internal temperature of the nonlinear optical crystal (the temperature of the portion through which the laser beam passes) is maintained at this temperature, the wavelength conversion efficiency can be maximized. However, as described above, in the processing laser device, it is difficult to keep the internal temperature of the nonlinear optical crystal constant. For this reason, it is desirable to select a nonlinear optical crystal that has a small change in the conversion efficiency with respect to a change in the temperature of the crystal.

Therefore, the LBO of TYPE1 and TYPE2
The allowable temperature range of the crystal was examined. FIG. 4 to FIG.
It is a figure which shows the allowable temperature range of the LBO crystal of PE1 and TYPE2. FIG. 4 shows 104 emitted from the Nd: YLF laser.
7 nm laser light and its second harmonic, 523.5 nm
5 is incident on the LBO crystal to generate a third harmonic of 349 nm, FIG.
When a 64 nm laser beam and its second harmonic, 532 nm, are incident on the LBO crystal to generate a 354.7 nm third harmonic, FIG.
053 nm laser light and its second harmonic, 526.5
When the light of nm is incident on the LBO crystal to generate a third harmonic of 351 nm, the allowable temperature range of the TYPE1 and TYPE2 crystals is shown. I have.

As is clear from FIGS. 4 to 6, TYPE
The allowable temperature range of the 1 LBO crystal is at least 10 times larger than that of the TYPE 2 crystal. A large allowable temperature range means that the fluctuation of the output power with respect to a temperature change is small.
The variation of the output power with respect to the temperature change can be reduced as compared with the case where the crystal of E2 is used.

FIG. 1 is a diagram showing the configuration of a laser device according to an embodiment of the present invention using a TYPE 1 crystal as the first and second nonlinear optical crystals. Although FIG. 8 shows the type of phase matching of the nonlinear optical crystal and the polarization direction, the present invention can be applied to the processing laser device shown in FIG. 8, the same components as those shown in FIGS. 8 and 9 are denoted by the same reference numerals, and 11 is a fundamental laser light source for generating a fundamental wave (1ω). 11 is the wavelength 106 as described above.
An Nd: YAG laser device which oscillates 4 nm laser light, an Nd: YLF laser device which oscillates laser light having a wavelength of 1053 nm or 1047 nm, or the like can be used.

13 is a first nonlinear optical crystal (SHG),
13 ′ is a second nonlinear optical crystal (THG),
As the non-linear optical crystal 13 and the second non-linear optical crystal 13 ′, a TYPE 1 crystal that performs wavelength conversion by incident light having parallel polarization directions is used. The types of crystals that can be used as the first nonlinear optical crystal 13 include L
BO, CLBO, BBO and the like. The type of crystal that can be used as the second nonlinear optical crystal is LBO
There is. Reference numeral 20 denotes a wave plate that rotates the fundamental wave (1ω) emitted from the first nonlinear optical crystal 13 by 90 °.
In the present embodiment, since the TYPE 1 crystal is used for the second nonlinear optical crystal 13 ′ as described above, the wavelength between the first nonlinear optical crystal 13 and the second nonlinear optical crystal 13 ′ is set. A plate 20 is provided.

In FIG. 1, a fundamental wave (1ω) emitted from a fundamental laser light source 11 enters a first nonlinear optical crystal 13 for generating a second harmonic. First nonlinear optical crystal 1
In 3, the nonlinear optical crystal 13 converts the wavelength of the fundamental wave (1ω) to generate a second harmonic (2ω) and a fundamental wave (1ω). The nonlinear optical crystal 13 for generating the second harmonic is TYPE 1 as described above, and the polarization direction of the wavelength-converted second harmonic (2ω) emitted from the crystal of TYPE 1 is the fundamental wave (2ω) as shown in FIG. 1ω) is perpendicular to the polarization direction. The fundamental wave (1ω) and the second harmonic (2ω) emitted from the nonlinear optical crystal 13 enter the wave plate 20, and the wave plate 20 rotates the polarization direction of the fundamental wave (1ω) by 90 °. As a result, the fundamental wave (1ω) and the second harmonic (2ω) emitted from the wave plate 20 become parallel as shown in FIG.

The second harmonic wave (2ω) and the fundamental wave (1ω) whose polarization directions emitted from the wave plate 20 are parallel to each other are
Incident on the non-linear optical crystal 13 ′ and wavelength-converted,
A third harmonic (3ω) and a fundamental wave (1ω) are emitted from the nonlinear optical crystal 13 ′. As described above, in the present embodiment, since the wave plate 20 is provided between the first nonlinear optical crystal 13 and the second nonlinear optical crystal 13 ′, the nonlinear optical crystal of TYPE 1 is used as the second nonlinear optical crystal. A crystal can be used, and a change in wavelength conversion efficiency with a change in temperature can be reduced.

FIG. 2 is a view showing a modification of the above embodiment. In FIG. 2, a fundamental wave (1ω) and a second harmonic (2ω) emitted from the first nonlinear optical crystal 13 are used as a wave plate 20 ′. ) Uses a wave plate that rotates the polarization direction of the second harmonic wave by 90 °. Also in FIG.
Since the polarization direction of the light incident on the second nonlinear optical crystal 13 'is made parallel by 0', a TYPE 1 crystal can be used as the second nonlinear optical crystal. , The change in the wavelength conversion efficiency can be reduced. FIG. 7 is a diagram showing a change in laser power immediately after the start of laser beam emission in the laser device of the present embodiment. The figure shows that the temperature is 5 as the second nonlinear optical crystal.
This shows a case where an LBO crystal of TYPE 1 maintained at 0 to 51 ° C. is used, and the output power is 3 W as in FIGS. 11 and 12. As is clear from FIG.
In the laser apparatus of this embodiment using the crystal of No. 1,
There is almost no change in the laser power immediately after the start of laser light emission. For this reason, even when it is applied to the processing of a multilayer printed board as described above, no problem occurs in the processing.

[0027]

As described above, the following effects can be obtained in the present invention. (1) A non-linear crystal for wavelength conversion has a wide temperature tolerance T
Since only YPE1 is used, even if a slight temperature change occurs in the crystal, it is possible to suppress the fluctuation of the output power of the wavelength-converted laser light. (2) Particularly, even if the internal temperature of the crystal slightly changes immediately after the start of laser light emission, the output power hardly fluctuates, so that it is used as a processing laser device for intermittently applying pulsed laser light. In this case, it is possible to prevent the occurrence of defects in the depth of the hole and the processed shape.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a laser device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a modification of the embodiment of FIG. 1;

FIG. 3 is a diagram showing wavelength conversion efficiency η with respect to crystal temperature.

FIG. 4 is a diagram (1) showing an allowable temperature range of LBO crystals of TYPE1 and TYPE2.

FIG. 5 is a diagram (2) illustrating an allowable temperature range of LBO crystals of TYPE1 and TYPE2.

FIG. 6 is a diagram (3) showing an allowable temperature range of LBO crystals of TYPE1 and TYPE2.

FIG. 7 is a diagram illustrating a change in laser power immediately after the start of laser beam emission in the laser device according to the embodiment of the present invention.

FIG. 8 is a diagram showing a schematic configuration of a processing laser device that generates a third harmonic by wavelength conversion using a nonlinear optical crystal.

9 is a diagram showing a type of phase matching and a polarization direction of a nonlinear optical crystal used in the processing laser device shown in FIG.

FIG. 10 is a diagram showing a state of via hole processing by laser light.

FIG. 11 is a diagram (1) illustrating a change in laser power emitted from the LBO crystal of TYPE2.

FIG. 12 is a diagram (2) illustrating a change in laser power emitted from the LBO crystal of TYPE2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Fundamental-wave laser light source 13 1st nonlinear optical crystal 13 '2nd nonlinear optical crystal 20 Wave plate

Claims (1)

[Claims] 1. A laser device that performs wavelength conversion by a nonlinear optical crystal and generates an ultraviolet laser beam, comprising: a laser oscillator that oscillates a fundamental laser beam; A nonlinear optical crystal of the first type 1 that emits a second harmonic thereof, a wave plate that makes the polarization directions of the fundamental wave laser light and the second harmonic wave parallel to each other, and the fundamental wave that passes through the wave plate. A laser device for processing, comprising: a second type 1 LBO crystal that receives a laser beam and the second harmonic and emits a third harmonic of a fundamental laser beam.