JPS6342428B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a carbon dioxide laser device, and particularly to a carbon dioxide laser device.
This relates to a carbon dioxide laser device having a structure obtained by selecting the TEM ₀₁ * mode of laser light.

[Technical background of the invention and its problems]

An example of a gas laser device will be described with reference to FIG. 1. For example, a total reflection mirror 2 and a half reflection mirror 3 are provided facing each other with a laser medium 1 containing carbon dioxide gas in between. Laser medium 1
A diaphragm plate 4 with an aperture ₄₁ is disposed on the side.

In such a gas laser device, when the laser medium 1 is excited by glow discharge and the optical energy resulting from the excitation is pumped between the total reflection mirror 2 and the half-reflection mirror 3 to cause resonance, the laser beam 5 is emitted from the half-reflection mirror 3. It is starting to be ejected.

In such a gas laser device, the oscillation transverse mode of the laser beam is determined by the excited state of the laser medium 1 due to glow discharge, the resonator configuration determined by the radius of curvature and spacing of the total reflection mirror 2 and the half reflection mirror 3, and the aperture 4 of the aperture plate 4. Determined by the shape and size of ₁ . The oscillation transverse mode of this laser is Transverse
It is expressed as TEMmn (where m and n are the orders of the modes) using the abbreviation for electromagnetic waves, and each mode corresponds to a unique electric field intensity distribution.

This TEMmn mode has TEM ₀₀ as shown in Figure 2.
Mode 7 TEM ₀₁ shown in Figure 3 *Mode 8, 4th
There are TEM ₁₀ mode 9 shown in the figure, TEM ₁₁ mode 10 shown in FIG. 5, TEM ₀₂ mode 11 shown in FIG. 6, and multimode 12 shown in FIG. 7.

It can be seen from these curves that the lower the mode order, the smaller the beam diameter of the laser light, and the higher the mode order, the larger the beam diameter of the laser light.

When processing a workpiece by concentrating laser light in each of these modes through an optical system such as a lens, due to the characteristics of the laser light, the spot diameter of the lower mode is smaller and the higher the The larger the spot diameter, the larger the spot diameter, and in the case of multi-mode 12, the wavefront is uneven, which further deteriorates the light focusing ability.

However, when a glow discharge is generated in a laser medium and a resonant path is formed in a uniform discharge-excited region, the output of the laser device is clearly proportional to the volume of the laser medium included in the resonant path. . Therefore, in a laser device that generates uniform discharge excitation, the lower the oscillation mode and the smaller the beam diameter, the lower the laser output, and the higher the laser output in higher-order modes. In reality, the laser output is small in single mode (equivalent to TEM ₀₀ mode), and large in multimode (higher-order mode mixture).

However, conventionally, this oscillation mode is achieved by using a diaphragm plate 4 with an aperture ₄₁ formed on the side of the laser medium 1 of the total reflection mirror 2 and the half reflection mirror 3, which are provided with the laser medium 1 in between, as explained in FIG. This aperture ₄₁ is used to select the beam outer diameter of the oscillation transverse mode by limiting it within the resonator, but in this case, although the TEM ₀₀ mode with a small outer diameter can be selected, the larger diameter Since the beam diameter of the mode is larger than that of the TEM ₀₀ mode, the diameter of the aperture ₄₁ must be made larger, and as a result, the TEM ₀₀ mode occurs simultaneously, resulting in the problem that a single mode cannot be selected.

[Purpose of the invention]

The present invention was made in view of the above-mentioned conventional problems, and is a TEM ₀₁ which is between single mode and multimode and has the advantages of both.
*The purpose is to provide a carbon dioxide laser device that allows mode selection.

[Summary of the invention]

That is, the present invention arranges at least two reflecting mirrors facing each other, circulates a laser medium containing carbon dioxide gas between the reflecting mirrors, and generates a glow discharge in the laser medium to generate laser light. The carbon dioxide laser device is characterized in that a diaphragm plate with an aperture of a predetermined diameter is disposed on the laser medium side of at least one of the reflecting mirrors, and at least one of the reflecting mirrors is formed into an annular shape. Further, the aperture has a size that suppresses the gain of oscillation in TEM ₁₀ mode or higher, and the annular center has a size that suppresses the gain of TEM ₀₀ mode oscillation.

[Embodiments of the invention]

According to experiments, the light focusing ability of TEM ₀₁ *mode is
It is almost the same as the TEM ₀₀ mode, and the beam diameter is 1.5 times that of the TEM ₀₀ mode, so when a resonant path is incorporated in a uniform discharge excitation region,
More than twice the laser output as in TEM ₀₀ mode can be obtained. Furthermore, as can be seen from Figure 3, the energy distribution of the TEM ₀₁ * mode is donut-shaped, so when considering the total output, the energy density per unit area is clearly low. Also, the total output proportional to area can be lower than in TEM ₀₀ mode. This makes it possible to greatly reduce the thermal load due to energy loss on the reflecting mirror, especially the semi-reflecting mirror on the output side. Furthermore, for the semi-reflector on the output side, which has a structure in which only peripheral cooling is possible in order to allow the laser beam to pass through, the cooling effect can be maximized by placing the heat source generated by the absorption of the laser beam as close to the peripheral area as possible. Can be done. On the other hand, in the TEM ₀₀ mode, as can be seen from Figure 2, the energy distribution is extremely high in the center, so the heat load due to energy loss to the output side semi-reflector is high, and In a semi-reflecting mirror that can only be cooled, the heat source generated by absorption of laser light is located in the center, so increasing the output increases the risk of deteriorating or destroying the semi-reflecting mirror.

Therefore, the present invention selectively generates only the TEM ₀₁ * mode and eliminates the TEM ₀₀ mode and the TEM ₁₀ mode or higher.

Next, the simplest first embodiment of the carbon dioxide laser device of the present invention will be described with reference to FIG.

That is, a laser medium 21 containing carbon dioxide gas is circulated by a circulation mechanism (not shown), and a concave total reflection mirror 22 and a concave semi-reflection mirror 23 are provided facing each other with the laser medium 21 in between.
Laser medium 21 of total reflection mirror 22 and half reflection mirror 23
The diaphragm plate 24 with an aperture 24 ₁ is disposed therein, which is almost the same as the conventional one, but in this embodiment, the total reflection mirror 22 is annular and the center part 22 ₁ of this annular shape is formed. This is a so-called energy loss region where energy is lost due to absorption or scattering of laser light.

With such a structure, the aperture 24 ₁ is made large enough to suppress the gain of oscillation in TEM ₁₀ mode or higher, and the aperture 24 1 is made large enough to suppress the gain of oscillation in TEM ₀₀ mode in the energy loss region of the central portion 22 ₁ , When the laser medium 21 is excited by glow discharge and the light energy resulting from this excitation is caused to resonate between the total reflection mirror 22 and the half-reflection mirror 23, only the laser beam 25 in the TEM ₀₁ * mode is selected from the half-reflection mirror 23. It will be ejected.

To explain this example in more detail, the beam diameter of the oscillation mode inside the resonator is characterized as 2ω ₀ . Here, this ω ₀ is the radius at which the energy intensity at the center becomes 1/e ² when the energy distribution of the TEM ₀₀ mode is shown.

Next, the distribution formulas are shown for TEM ₀₀ mode, TEM ₀₁ * mode, and TEM ₁₀ mode, and are also shown as curves in FIGS. 9 to 11.

First, in the case of TEM ₀₀ mode, when the intensity at the center is I ₀ , it is expressed as I=I ₀ exp (−2r ² /ω ₀ ² ), resulting in a distribution shown by curve 27 in FIG.

Next, in the case of TEM ₀₁ * mode, change the intensity at the center.
If I ₀ , then I=I ₀ (2r ² /ω ₀ ² )exp(−2r ² /ω ₀ ² ), resulting in a distribution shown by curve 28 in FIG.

In addition, in the case of TEM ₁₀ mode, the intensity at the center is I ₀
Then, I=I ₀ (1−2r ² /ω ₀ ² ) ² exp(−2r ² /ω ₀ ² ), resulting in a distribution shown by curve 29 in FIG.

Furthermore, curve group 3 in Figure 12 shows the energy loss due to the aperture 24 ₁ using these.
0, 31, 32, curve 30 is TEM ₀₀ mode, curve 31 is TEM ₀₁ * mode, curve 32 is
The TEM ₁₀ mode is shown, and the loss of the TEM ₀₁ * mode and the loss of the TEM ₁₀ mode can be appropriately selected according to this figure 12, but from the experimental results, the radius of the aperture 24 ₁ is 1.69ω ₀ ~ 1.95 It is best to set it in the range of ω ₀ .

Furthermore, curve groups 33, 34, and 35 in FIG. 13 show the energy loss due to the loss region of the central portion 22 ₁ of the total reflection mirror 22, and the curve 33 is TEM ₀₀
Mode, curve 34 is TEM ₀₁ *Mode, curve 35
shows the TEM ₁₀ mode, and the loss of the TEM ₀₀ mode and the loss of the TEM ₀₁ * mode can be appropriately selected according to Fig. 13, but from the experimental results, the radius of the center 22 ₁ is 0.01ω. It is best to set it to ₀ to 0.30ω ₀ .

Applying these values to Fig. 8, we find that the diaphragm plate 24 is black alumite treated, the diameter of the aperture ₂₄₁ is 21 mm, the outer diameter of the total reflection mirror 22 is 50 mm,
The center part ₂₂₁ has a concave mirror with an inner diameter of 2 mm and a radius of curvature of 20 m, and the semi-reflecting mirror 23 is a concave mirror with a curvature of 20 m.The interval between the total reflecting mirror 22 and the semi-reflecting mirror 23 is 7.5 m. Depending on the configuration, a TEM ₀₁ * mode laser beam with a laser energy of 2.5KW was obtained.

In the embodiment described above, the diaphragm plate 24 was provided on both the total reflection mirror 22 side and the half reflection mirror 23 side.
The same effect can be obtained even if it is not provided on the third side.

Next, a second embodiment of the present invention will be described with reference to FIG. In the drawings, the same reference numerals as in the first embodiment indicate the same parts and will not be particularly described.

That is, this embodiment has a folded resonator structure, and is characterized by providing a pair of flat total reflection mirrors 26 in addition to the first embodiment. Therefore, it is possible to downsize the carbon dioxide laser device.

Next, an application example of the present invention is shown in FIG. In the figure, the same reference numerals as those in the first embodiment indicate the same parts, and no particular explanation will be given.

That is, in this application example, the annular total reflection mirror 22
For example, a laser beam 43 ₁ from a He-Ne laser device 41 is reflected by a pair of reflecting mirrors 42 and reflected laser beam 43 ₂ is emitted from the outside using the central portion 22 ₁ of the carbon dioxide laser device. It is used to align the resonator reflecting mirrors 22 and 23 and also to guide the laser output beam.

〔Effect of the invention〕

As mentioned above, according to the carbon dioxide laser device of the present invention, between single mode and multimode,
It is possible to take out the advantages of both by selecting TEM ₀₁ * mode, and a high-energy laser beam can be obtained. Also, in this TEM ₀₁ * mode, the energy distribution is donut-shaped, and only peripheral cooling is possible. Deterioration of the output side semi-reflector,
It is a good device with very little risk of destruction, and its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional laser device, and FIGS. 2 to 7 are diagrams showing waveforms of each mode.
The figure is a graph showing the waveform of TEM ₀₀ mode, Fig. 3 is a graph showing the waveform of TEM ₀₁ * mode, Fig. 4 is a graph showing the waveform of TEM _{10 mode, and Fig. 5 is a graph showing the waveform of TEM 10} mode.
The graph showing the waveform of TEM ₁₁ mode, Figure 6 is
Graph showing the waveform of TEM ₀₂ mode, FIG. 7 is a graph showing the mixed waveform of higher order mode, FIG. 8 is an explanatory diagram showing one embodiment of the carbon dioxide laser device of the present invention, and FIGS. 9 to 11 are FIG. 9 is a diagram showing the relationship between the beam radius and power density of each mode.
The graph showing the waveform of TEM ₀₀ mode, Figure 10 is
Graph showing the waveform of TEM ₀₁ * mode, Figure 11 is a graph showing the waveform of TEM ₁₀ mode, Figure 12 is the relationship between output loss due to aperture and aperture radius for TEM ₀₀ , TEM ₀₁ *, and TEM ₁₀ modes. 13 is a graph showing the relationship between the TEM ₀₀ , TEM ₀₁ *, and TEM ₁₀ modes in the relationship between the output loss due to the loss region in the center and the radius of the loss region. FIG. 15 is an explanatory diagram showing the second embodiment, and FIG. 15 is an explanatory diagram showing an application example of the present invention. 1, 21... Laser medium, 2, 22... Total reflection mirror,
3, 23... Semi-reflector, 4, 24... Diaphragm plate, 4 ₁ ,
24 ₁ ...Aperture, 5, 25...Laser light, 22 ₁
...Central part, 41...He-Ne laser device.

Claims (1)

[Claims] 1. At least two reflecting mirrors are arranged facing each other,
In the carbon dioxide laser device configured to circulate a laser medium containing carbon dioxide gas between the reflecting mirrors and generate a glow discharge in the laser medium to generate laser light, at least one of the reflecting mirrors A carbon dioxide laser device characterized in that a diaphragm plate having an aperture of a predetermined diameter is disposed on the laser medium side, and at least one of the reflecting mirrors is annular. 2 The reflecting mirrors arranged facing each other are composed of a total reflecting mirror and a semi-reflecting mirror, and an aperture is formed on the laser medium side between the total reflecting mirror and the semi-reflecting mirror, or only on the total reflecting mirror side. 2. The carbon dioxide laser device according to claim 1, wherein the total reflection mirror has an annular shape having an energy loss region in the center thereof. 3 The reflecting mirrors arranged opposite to each other are composed of a first total reflecting mirror, a second total reflecting mirror, and a half reflecting mirror in the order of the optical path of the laser beam, and the laser beam between the totally reflecting mirror and the half reflecting mirror is The carbon dioxide laser device according to claim 1, characterized in that a diaphragm plate with an aperture is provided on each of the medium side or only on the total reflection mirror side, and the total reflection mirror is formed into an annular shape. . 4. Claims 1 to 4, characterized in that the visible laser light from another laser device passes through the center of the annular total reflection mirror and then becomes guided light via the semi-reflection mirror. The carbon dioxide laser device according to any one of Item 3. 5 The aperture is large enough to suppress the gain of oscillations in TEM ₁₀ mode and above, and the annular center is
The carbon dioxide laser device according to any one of claims 1 to 4, characterized in that the size is such that the gain of TEM ₀₀ mode oscillation is suppressed.