JPH02150085A - Resonator for carbon dioxide gas laser and carbon dioxide gas laser using the same - Google Patents

Abstract

PURPOSE:To enhance light resistance intensity in case of enhancing an output and to improve reliability by composing an output mirror of GaAs having 50% or less of reflectivity. CONSTITUTION:Laser gas is circulated in a discharge tube 1 made of quartz, etc. The gas is excited by a high frequency voltage from a high frequency power source, a laser light 13 is reciprocated between an output mirror 2 and a totally reflecting mirror 3 to be amplified, and a laser output light 14 is externally output. The beam 14 is used to cut metal. The mirror 2 is composed of gallium arsenide (GaAs) in which its reflectivity is set to 50% or less. The surface of the gallium arsenide (GaAs) at the laser medium side is so PR-coated with a dielectric multilayer film 2a as to become 50% or less of reflectivity. Part of the light 13 is reflected on the mirror 2, and the remainder is output as the laser output beam 14. Thus, the reflectivity of the output mirror for a carbon dioxide gas laser resonator is reduced to suppress the light intensity in the resonator to a low value.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a carbon dioxide laser resonator and a carbon dioxide laser device using the same, and in particular to a high-power carbon dioxide laser resonator and a carbon dioxide laser device for processing metal materials. This invention relates to a carbon dioxide laser device using the same.

[Conventional technology]

The main field of application of carbon dioxide laser processing equipment is cutting and welding of metal materials (SPCC), etc.

In recent years, a carbon dioxide gas laser processing apparatus capable of cutting thick metal materials has become highly desirable. Furthermore, when welding metals is also considered, it is essential to increase the output of carbon dioxide laser processing equipment.

Conventionally, the output mirror of a resonator for a carbon dioxide laser of IKW class or below has a PR of 50% or more.
(Partial Reflection) The zinc selenium (ZnSe) coated film is coated with A on the surface of the total reflection mirror so that the reflectance is 99% or more.
Germanium (Ge) coated with a u-coating film or a dielectric coating film has been mainly used.

[Problem to be solved by the invention]

High-output carbon dioxide lasers, whether coaxial or triaxial orthogonal, mainly use roots blowers to circulate gas inside the laser resonator at high speed. For this reason, to some extent, oil and dust generated inside the resonator adhere to the optical components (the surfaces of the output mirror and total reflection mirror) inside the resonator. Then, the laser beam irradiation causes burn-in in that part. Since the burn-in that occurs in this way absorbs the laser light, the temperature of that area locally increases.

On the other hand, when the output of the Rade device increases and becomes a relatively single-mode laser beam, the density of light intensity inside the resonator becomes extremely large. That is, the laser output IKW
In laser devices below the class, the reflectance of the output mirror is usually set to 50% or more due to the relationship with laser gain. Since the light intensity inside the resonator is the value obtained by dividing the laser output by the transmittance of the output mirror, for example, the laser output is divided by 2.
Assuming 5KW and output mirror reflectance of 50% and 65%,
The light intensity inside each cavity is 5KW and 7,IK
W, which is a very large value compared to the laser output.

Therefore, even if the absorption rate of the laser beam on the surfaces of the output mirror and the total reflection mirror that constitute the resonator is on the order of a few tenths of a percent, the temperature rise in the laser beam irradiated portion becomes extremely large.

The degree of temperature rise in this case is determined by the intensity of the irradiated laser beam, the size (area) of the irradiated portion, and the light absorption rate and thermal conductivity of the output mirror and the total reflection mirror.

Generally, the absorption coefficient of an output mirror and a total reflection mirror has temperature dependence, and increases rapidly after a certain temperature.

Therefore, if the temperature exceeds this temperature by -degrees, a positive temperature feedback will occur and the material will melt. Therefore, −
If it melts, the absorption in that part will become very large, which will instantly lead to the fatal result of destruction of the output mirror and total reflection mirror by melting.

In other words, this was not a particular problem in the case of a low-power laser device with a laser output of IKW or less, but when the laser output was increased to 2KW, 3KW, or higher, the light intensity inside the resonator became extremely high. As a result, as mentioned above, the surface temperature of the inner surfaces of the output mirror and total reflection mirror increases, and the surface eventually melts (thermal runaway), contaminating the inside of the resonator. There is.

An object of the present invention is to provide a carbon dioxide laser resonator with excellent light resistance and a carbon dioxide laser device using the same when increasing the output of a carbon dioxide laser device.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a carbon dioxide laser resonator consisting of an output mirror and a total reflection mirror, in which the output mirror is made of gallium arsenide (GaAs) with a reflectance set to 50% or less. A resonator for a carbon dioxide laser is provided.

Furthermore, in order to solve the above problems, the present invention provides a carbon dioxide laser resonator comprising an output mirror and a total reflection mirror, in which the output mirror is made of zinc selenium (ZnSe) without a PR coating film. A resonator for a carbon dioxide laser is provided.

Furthermore, in order to solve the above problems, the present invention provides a carbon dioxide laser resonator comprising an output mirror and a total reflection mirror, wherein the total reflection mirror is made of gallium arsenide (GaAs). A resonator is provided.

In order to solve the above-mentioned problems, the present invention provides a carbon dioxide laser device configured with any of the above-mentioned carbon dioxide laser resonators.

(Function) When estimating the temperature rise of the contaminated part on the surface of the optical components (output mirror, total reflection mirror) inside the resonator, approximately solve the following heat conduction equation that can be applied to a thin film. Bye.

(1/r) (δT/δr)+(δ2T/δt r )−
(1/γ) (δT/δt) k ” (T −To)
= 0・−−1−−−−−・−・・(1) In the following formula, each character is: K: Thermal conductivity (TI(ERMAL C0NDUCTIV)
ITY) H: Heat transfer coefficient (CONVHCTION C0E
FFTCIENT) ρ: Density (DHNSITY) C: Specific volume specific heat (SPECIFICHEAT) D: Thickness of material (TIIICKNESS OF MATERIAL
) γ= to ρ*c) k”=2H/(KD).

The above equation (1) is solved assuming that the incident beam has a Gaussian distribution with spot radius a.

T To=f (a”rl (t tI) /(K
D(a”+8 rt+))*exp(-7k”tI
r”2 / (a2+ 8 r tI))) dt+(
0≦dt+ ≦t)−・−・・−・−・−−−−・(
2) Here, I(t-tI)a'' represents the energy absorbed by the film, but in this case, it is constant regardless of time, and if the laser power inside the resonator is Pt1n, then I(t-
t, )a”-βa! However, I = Ioexp(-2(r/a)), ■o:
Power density β at the center: Absorption rate of the membrane.

Pt1n = πa"Io /2-+Ioa" = 2Pt
in /π...-(3) holds true.

Furthermore, we define a dimensionless number as follows.

τ=8γtI/a” e=k”a” /8=a”H/ (D in 4)ζ−r/
a Ultimately, the temperature rise on the sample surface can be found from the following equations (4) and (5).

T = To + βPtinGtemp / (2πKD)
Here, G temp is temp=S<τ+1)-1 *exp(-a r-2ζ"(1+r)-')dτ(
0≦dτ≦τ)−・−1−−−・・−・−(5).

Now, assuming that the laser output is pt, the beam mode is a Gaussian distribution with spot radius (e-"PO[NT) a, and the reflectance of the resonator is R, the laser beam intensity Pt1n inside the resonator is calculated by the following formula: It is expressed as (6).

Pt1n=Pt/ (1-R) --------
---(, 6) Furthermore, when considering the case where dust adheres, it is assumed that the laser power density does not change and only the laser power changes. That is, it is assumed that a laser power Pcon of a Gaussian distribution expressed by the following equation is incident, where WO is the diameter of the attached dust and WO is the spot diameter.

Pcon= x (Wo/2)"Io/2=W
o” Pt1n/ (4a ”) --------
−−−−−−(7) Putting the above in order, the laser output is pt
, when the laser beam mode is Gaussian mode with spot radius a and the reflectance of the output mirror is R, the surface temperature distribution T (?, t) inside the output mirror is (a), the absorption rate α on the sample surface is If T(r
, t) =To+cx (pt/ (1-R))G
temp/ (2πKD)−・−・−・−・(8) (b) When dust adheres to the sample surface (the diameter of the dust is taken as the diameter and β is the absorption rate) T (r, t) = To + β (Pt/(1-R))(Wo/(2a))”
Gtemp/(2πKD)・−・・−・・−・−(9”
) However, temp = S (τ+1) publication*exp(-a τ-2ζ”(1+r)-')dr
It can be obtained as (0≦dτ≦τ).

The above results will be explained based on the drawings.

Figure 2 shows the materials used for the output mirror or total reflection mirror when a Gaussian mode carbon dioxide laser beam with a laser output of 2.5 KW and a spot diameter of 10 mm is emitted using an output mirror with a reflectance of 50%. , commonly used Zn
5e shows how the maximum temperature of the surface exposed to the laser medium changes depending on the absorption rate of the surface when GaAs and Ge are used.

The temperature at which thermal runaway (melting) occurs is 250°C for Zn5e.
Since the temperature is 300"C for 5GaAs and 70"C or less for Ge, the allowable surface absorption rate is about 0.3% or less for Zn5e, about 0.9% or less for GaAs, and about 0.2% or less for Ge. I understand that there is something.

Normally, the absorption rate in the case of PR coating film and total reflection coating film is about 0.05 to 0.1%, so if the absorption on the surface increases only slightly, Zn5e and G
In case e, there is a high risk of thermal runaway occurring. In this respect, in the case of GaAs, there is a considerable margin, and its usefulness can be seen.

Figure 3 shows a spot diameter of 10n with a laser output of 2.5KW.
Maximum temperature reached on the surface of the output mirror on the side exposed to the laser medium when Zn5e is used as the output mirror and the reflectance R of the output mirror is changed when a cmφ Gaussian mode carbon dioxide laser beam is emitted. The surface absorption rate dependence of

From this, the allowable surface absorption is that the reflectance R is 65%.
, 50%, and 17% (reflectance of Zn5e itself without PR coating), respectively, about 0
．． It can be seen that they are 2%, 0.3%, and 0.5%. Considering that the surface absorption rate of the base material is usually 0.05% or less when no coating film is applied, the advantage of using an output mirror without a PR coating film becomes even clearer.

However, since the reflectance is significantly reduced, one must be prepared for a slight decrease in laser efficiency.

Figure 4 shows the maximum temperature reached on the sample surface and the diameter of the attached dust when dust adheres to the sample surface under the same operating conditions as in Figure 1 and the absorption rate in that area is assumed to be 100%. The relationships between the two are shown for the cases where the materials are Zn5e, GaAs, and Ge, respectively.

From this, the allowable size of dust is approximately 40 for Zn5e.
0 um, GaAs about 700μm, Ge about 300μm
m. Even in this case, the superiority of GaAs over Zn5e is clear. It can be seen that Ge is rather inferior to Zn5e.

Therefore, when increasing the output of a carbon dioxide laser device, it is desirable to keep the light intensity inside the resonator as low as possible and to increase the transmittance (reflectance) of the output mirror as much as possible.

Furthermore, for the same light intensity, by selecting the material of the output mirror or the total reflection mirror, it is possible to suppress the temperature rise of the surface exposed to the laser medium as low as possible.

In order to cope with the increase in the absorption rate of the mirror surface due to contamination such as dust inside the resonator, the base material of both the output mirror and the total reflection mirror is Ga.
It can be said that it is most desirable to use As.

〔Example〕 Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 5 shows the overall configuration of a carbon dioxide laser device according to the present invention. In the figure, a carbon dioxide laser resonator consisting of an output mirror 2 and a total reflection mirror 3 is arranged at both ends of a discharge tube 1. Two metal electrodes 4 and 5 are attached to the outer circumference of the discharge tube 1. A high-frequency voltage is applied between the picture electrodes 4 and 5 by a high-frequency power source 6, and a high-frequency glow discharge is generated within the discharge tube 1 to perform laser excitation. The laser beam optical axis within the discharge tube 1 is indicated by 13, and the laser beam output optical axis taken out from the output coupling mirror 2 is indicated by 14.

When the laser oscillation device is started, the entire interior of the device is first evacuated by the vacuum pump 12. Then, the valve 11 is opened and a predetermined flow rate of laser gas is introduced from the gas cylinder 10, and the gas pressure inside the device reaches the specified value.After that, the vacuum pump 12 is evacuated and the supplementary gas is introduced, and the gas pressure is maintained at the specified value. However, part of the laser gas is continuously replaced with fresh gas, thereby preventing gas contamination.

Further, in FIG. 5, a roots blower 9 circulates the laser gas within the apparatus. Its purpose is to cool the laser gas. In a carbon dioxide (CO□) gas laser, about 20% of the injected electrical energy is converted into laser light, and the rest is consumed for gas heating. According to theory, the laser oscillation gain depends on the absolute temperature T.
Since it is proportional to the -(3/2) power of , forced cooling of the laser gas is necessary to increase the oscillation efficiency. The laser gas passes through the discharge tube 1 at a flow rate of about 100 m/sec, flows in the direction shown by the arrow, and is guided to the cooler 8.

Here, heating energy mainly due to discharge is removed. Since compression heat is generated in the Roots blower 9, the gas passes through the cooler 7 before being led back to the discharge tube l. Since these coolers 7 and 8 are well known, detailed explanation will be omitted.

FIG. 1 shows a sectional view of the vicinity of the output mirror and total reflection mirror of the carbon dioxide laser device of the present invention.

In the figure, 1 is a discharge tube made of quartz or the like. Laser gas circulates inside the discharge tube 1. The laser gas is excited by the high frequency voltage from the high frequency power supply 6 shown in FIG. 5, the laser light 13 is amplified by going back and forth between the output mirror 2 and the total reflection mirror 3, and the laser output light 14 is outputted to the outside. This laser output light 14 is used for cutting metal, etc.

The output v12 is made of gallium arsenide (GaAs) whose reflectance is set to 50% or less. This gallium arsenide (G
A dielectric multilayer film 2a is PR-coated on the laser medium side surface of aA s so that the reflectance is 50% or less. A portion of the laser beam 13 is reflected by the output mirror 2, and the remainder is output as a laser output beam 14.

Note that the reflectance of gallium arsenide (GaAs) itself without the PR coating film is about 28%, and even if this is used as the output mirror 2 as it is, the effects of the present invention can be sufficiently achieved.

The total reflection mirror 3 is made of gallium arsenide (GaAs), which is the same as the output mirror 2.
Consists of. An Au coating film 3b is applied to the surface of this gallium arsenide (GaAs) on the laser medium side, and its reflectance is set to 99% or more.

Although not shown, an anti-reflection film (AR film) is applied to each of the output mirror 2 and the total reflection mirror 3 on the surface side opposite to the laser medium (the side in contact with the outside air).

Reference numeral 16a denotes an output mirror holder. Reference numeral 16b denotes a total reflection mirror holder, which is attached to the discharge tube 1 and holds the output mirror 2 and the total reflection mirror 3, respectively. 17a and 17b are O-rings, which are used to shield the inside and outside of the discharge tube 1. Fixed flanges 15a and 15b hold the output mirror 2 and the total reflection mirror 3 against the output mirror holder 16a and the total reflection mirror holder 16b.

In the above embodiment, the output mirror 2 is gallium arsenide (GaA
s), but as is clear from the data in FIG. 3, zinc selenium (ZnSe) without a PR coating film may also be used. In this case as well, it goes without saying that it is better to apply an AR film as described above.

Although it is the best mode for implementing the present invention to use gallium arsenide (GaAs) for both the output mirror 2 and the total reflection mirror 3 as in the above embodiment, the present invention is not restricted in any way. There was no problem, and only the output mirror 2 was coated with gallium arsenide (Ga
Even if gallium arsenide (G
Needless to say, aAs) may be used, and various combinations thereof are possible.

〔Effect of the invention〕

As described above, the present invention has the effect that the light intensity inside the resonator can be kept low by reducing the reflectance of the output mirror of the resonator for a carbon dioxide laser. At the same time, by appropriately selecting the material used for the output mirror or total reflection mirror (for example, using GaAs with high thermal conductivity, or without a PR film with low surface absorption), the side exposed to the laser medium can be It is now possible to suppress the maximum temperature reached on the sample surface, greatly reducing the risk of thermal runaway of optical components during laser operation, and greatly improving the reliability of carbon dioxide laser equipment at high output. It has the excellent effect of improving

[Brief explanation of the drawing]

Figure 1 is a diagram showing the cross-sectional structure near the output mirror and total reflection mirror of the resonator for a carbon dioxide laser according to the present invention, and Figure 2 is a diagram showing the surface absorptivity and surface absorption rate on the side exposed to the laser medium using the laser medium as a parameter. Figure 3 shows the relationship between the surface absorption rate on the side exposed to the laser medium and the maximum temperature reached when the material of the output mirror is Zn5e and its reflectance is used as a parameter. Figure 4 is a diagram showing the relationship between the size of dust and the maximum temperature reached on the surface when dust is attached to the surface exposed to the laser medium and the absorption rate is 100χ. 1 is a diagram showing the overall configuration of a carbon dioxide laser device that is an embodiment of the present invention. 1 ・−・・−・・−・−・Discharge tube 2 −・−・
−・・−・−Output mirror 3 −−−−−−−・−1−−−−−Total reflection mirror 5−・
・−・・−・−・−・Metal electrode・−・・−・・・・・−・High frequency power supply 8−・−・・−−1−−−Cooler−・・・〜・・・・−・・−Roots blower・・−・
・−・−・・−Gas cylinder−・−・・−・・−Valve・−・・−・・−・・−Vacuum pump−・−・−・−
Laser light -----1---... Laser output light a, 15
b-------1--Fixed flange a--
・・−・−・−Output mirror holder b−・・−・・−・−・
- Total reflection mirror holder a, 17b ---
-0-Ring Patent Applicant Fanuc Co., Ltd. Agent Patent Attorney Takeshi Hattori

Claims (7)

[Claims] (1) A resonator for a carbon dioxide laser comprising an output mirror and a total reflection mirror, wherein the output mirror is made of gallium arsenide (GaAs) with a reflectance set to 50% or less. vessel. (2) The reflectance is 50% due to the PR coating film.
% or less, the resonator for a carbon dioxide laser according to claim 1. (3) The resonator for a carbon dioxide laser according to claim 1, wherein the output mirror is made of gallium arsenide (GaAs) without a PR coating film. (4) A resonator for a carbon dioxide laser comprising an output mirror and a total reflection mirror, wherein the output mirror is made of zinc selenium (ZnSe) without a PR coating film. (5) The resonator for a carbon dioxide laser according to any one of claims 1 to 4, wherein the total reflection mirror is made of gallium arsenide (GaAs). (6) A carbon dioxide laser resonator comprising an output mirror and a total reflection mirror, wherein the total reflection mirror is made of gallium arsenide (GaAs). (7) A carbon dioxide laser device comprising the carbon dioxide laser resonator according to any one of claims 1 to 6.