JPS6265488A - Waveguide type laser device - Google Patents

Abstract

PURPOSE:To reduce a waveguide loss and facilitate high efficiency oscillation even if the space between facing waveguide walls is narrow by a method wherein, in a hollow waveguide defined by metal electrodes and dielectrics, metal thin film layers and dielectric thin film layers with small absorption are successively laminated on the sides of the hollow region of the facing dielectrics. CONSTITUTION:Material such as Cu which has sufficiently large complex refractive index or complex refractive index whose imaginary part is larger than the real part and high thermal conductivity is employed as the material for metal thin film layer 4 like the material for a metal electrode 1. As material for a thin film 5 with small absorption which is laminated on the metal thin film 4, for instance chemically stable ZnSe or the like is selected and the film 4 is formed by sputtering or vacuum evaporation. A hollow waveguide 3 as a laser discharge passage has a square cross section and dimensions of about 2X2X200mm and facilitate single-mode oscillation and, as its output intensity distribution is close to a circular distribution, the waveguide 3 can be coupled easily with an external waveguide. He, CO2, N2 or mixed gas of He, CO2, N2 and Xe is enclosed in the hollow waveguide 3. A flat total reflective mirror and a partial transmitting mirror are provided at both ends of the hollow waveguide 3 and the laser beam is outputted through the partial transmitting mirror.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is useful in the field of laser processing for welding, cutting, etc., coherent light application systems, detection of atmospheric pollutants, and inter-satellite optical communication. The present invention relates to a laser light source, particularly a small and highly efficient waveguide type gas laser device.

[Prior Art] A kW-class high-output gas laser device, which is mainly intended for laser processing such as welding and cutting, has been developed, and attempts have been made to utilize laser light as thermal energy for production.

On the other hand, apart from these high-output gas laser devices, small and highly efficient waveguide laser devices are being widely considered not only for use in the field of laser processing but also as light sources for coherent optical communications and the like.

In general, waveguide type gas laser devices have the following features compared to conventional laser devices in which the resonance mode is determined by a resonance reflector.

■ Small size and high output because the laser tube diameter can be made thinner.

■ The oscillation wavelength tuning range is widened because the filled gas pressure is high.

■ Air-cooled operation is possible because the entire laser tube can be constructed from a material with high thermal conductivity.

■ Easy to maintain and low cost.

FIG. 2 shows a waveguide laser device using a lateral RF discharge method that has been previously reported (Appl.

Ph VS, Let t -43<8) P726
(1983)).

In FIG. 2, 11 is a metal electrode, 12 is a dielectric made of Al2O3, etc., 13 is a hollow waveguide, 14 is a matching coil, 15 is a matching capacitor, and 16 is an RF power source.

Waveguide-type laser snow deposition using such a lateral RF discharge method can obtain uniform and stable discharge at low voltage, and is also advantageous in terms of cooling effect because the metal that serves as the electrode forms part of the waveguide. It is.

[Problems to be Solved by the Invention] Generally, metal parallel plate type hollow waveguides have low loss in the TE mode where the electric field is parallel to the metal plate, but the loss is low in the TM mode where the magnetic field is parallel to the metal plate. This results in extremely high losses.

Therefore, in the structure shown in FIG. 2, the direction of the electric field in the excavation mode is necessarily parallel to the metal electrode. The transmission loss of a mode having such an electric field direction is mainly determined by the transmission loss of the TM mode of the dielectric parallel plate waveguide.

Table 1 shows the TEo mode (Figure 3) and TMo mode (Figure 4) when the metal electrode 17 forming the parallel plate waveguide shown in Figures 3 and 4 is made of various materials. This shows the transmission loss at

Table 1 (Units are dB/m) By configuring a flat waveguide with a distance between opposing electrodes, the metal electrodes do not contribute to waveguide loss, and the TE with lower loss than the dielectric wall Attempts have been made to oscillate in modes, but this is disadvantageous in terms of low-voltage stable power supply, and there are also problems in that multiple modes are excavated in the long side direction and the emitted beam becomes elliptical.

The present invention was devised to solve the problems of the prior art described above, and its purpose is to provide a highly efficient waveguide laser device.

[Means for Solving the Problems] In the present invention, in a hollow waveguide surrounded by a metal electrode and a dielectric, a metal thin film layer and a dielectric thin film layer with low absorption are provided on the hollow region side of the opposing dielectric. By stacking them one after another, even if the distance between opposing waveguide walls is narrow, waveguide loss can be minimized and highly efficient oscillation can be achieved.

The material forming the metal thin film layer is a material with a sufficiently large absolute value of the complex refractive index, or a material in which the imaginary part of the complex refractive index is larger than the real part, such as Cu, AQ, Au, AI, etc.
etc. The complex refractive index of each of these materials at a wavelength of 10.6 μm is Cu: 14.1-j
64.5, AQ; 13.5-j75.2, Au: 17.2-j56
．． O, At: 20.5-j58.6.

On the other hand, the dielectric thin film formed on the surface of the metal thin film layer is made of a material whose imaginary part of the complex refractive index can be ignored compared to the real part in the used wavelength band.
．． KCI at 6 μm.

NaCl, KR3-5, CdTe, 3i, Ge, Z
Examples include n5e, zns, PbFz, and chalcogenide glass.

The thickness d of this thin film is d4 under the so-called quarter wavelength condition.
It is necessary to set it so that qλ/4(a2-1)1/2...(1) is satisfied. Here, Q-1, 3, 5, ・
..., λ is the wavelength used, and a is the refractive index of the thin film formed on the metal surface.

Further, among the above-mentioned materials, the effect of the present invention is remarkable in materials whose refractive index is close to f2.

Table 2 shows the metal electrode 1 as shown in FIGS. 5 and 6.
In a parallel plate waveguide in which the surface of the metal electrode 17 and the dielectric thin film 18 are coated with a thin dielectric film 18 having a small absorption loss at a thickness that satisfies equation (1), when the metal electrode 17 and the dielectric thin film 18 are made of various materials, TEo mode (Figure 5), T
It shows the transmission loss in Mo mode (Fig. 6).

Table 2 (Units are dB/m) As can be seen from Tables 1 and 2, in the waveguide laser of the present invention, the TE mode is used for the waveguide wall made of only metal, and the TE mode is used for the waveguide wall made of only metal. 7M for coated waveguides
The oscillation mode is determined so that the oscillation mode is the same as that of the dielectric parallel plate, and higher efficiency oscillation is possible than in conventional waveguide lasers in which the electric field in the propagation mode has a large component perpendicular to the dielectric parallel plate.

[Embodiment] FIG. 1 is an explanatory diagram of an embodiment of the present invention, showing a cross section of a discharge path of a waveguide laser device and an outline of an excitation circuit.

1 is a metal electrode, which also constitutes a waveguide wall.

2 is a dielectric material for insulating between the electrodes, and for example, Al2O3 having a relatively high thermal conductivity or quartz glass which easily provides a smooth surface is used. 3 is a hollow waveguide.

The dielectric 2 is coated with a metal thin film layer 4 and a thin film 5 made of a dielectric with low absorption.

The thickness of the metal thin film layer 4 only needs to be sufficiently thicker than the skin depth, and precise thickness control is not required.

The light is confined in the area surrounded by the metal wall and the insulator 2
is no longer directly involved in the waveguide characteristics. The material for the metal thin film layer 4 is Cu, which has a sufficiently large complex refractive index like the metal electrode 1, or whose imaginary part of the complex refractive index is larger than the real part and has high thermal conductivity.

On the other hand, the material of the thin film 5 with low absorption, which is roughly laminated on the gold RA thin film layer 4, is selected from, for example, chemically stable Zn5e, and the film thickness is set such that the formula (1) is satisfied. It can be easily formed by sputtering or vacuum deposition.

The hollow waveguide 3 as a laser discharge path has a square cross section surrounded by a metal thin film layer 4 coated with a metal electrode 1 and a thin film 5, and has dimensions (width x length x length) of approximately 2 x 2 x 200 mm. It is possible to detect a single mode, and the output intensity distribution is close to a circular distribution, making it easy to couple with an external waveguide. Inside the hollow waveguide 3, He, Cog
, Nz or a mixed gas of 1-1e, COz, Nz, and Xe is sealed.

A flat totally reflecting mirror and a partially transmitting mirror are attached to both ends of the hollow waveguide 3, and the laser beam is outputted through the partially transmitting mirror.

The metal electrode 1 is connected to a matching coil 6 and a matching capacitor 7.
The RF power source 8 is connected to the RF power source 8 through a matching circuit consisting of the following.

In the present invention, as the material constituting the metal electrode 1, CLJ is generally used in consideration of thermal conductivity and economic efficiency, but Ag thin film with a larger absolute value of complex refractive index, or Au which is stable in the external environment is used. A thin film may be coated onto the Cu.

Further, the thin film 5 laminated on the metal thin film layer 4 is not limited to a single layer as in the case of FIG. 1, but two or more types of thin films having different refractive indexes such as Qe and Zn5e are alternately laminated. The effects of the present invention can also be further enhanced by this.

In the embodiment shown in Fig. 1, the waveguide walls constituting the hollow waveguide are flat plates, but if the waveguide walls are made concave, the beam focusing ability will be improved and the output intensity distribution will be closer to a circular shape. Can be done.

[Effects of the Invention] As explained above, according to the present invention, the following remarkable effects are exhibited.

(1) Waveguide loss can be reduced even if the waveguide spacing is small,
Highly efficient oscillation becomes possible.

(2) Since the spacing between the metal electrodes can be reduced, small-sized and low-voltage RFtli electricity is possible.

(3) Since the cross section of the waveguide can be made substantially square, a single mode linearly polarized wave with a substantially circular intensity distribution can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of a conventional example, and FIGS. 3 to 6 are explanatory diagrams of configuration examples of a parallel plate waveguide. 1: metal electrode, 2: dielectric, 3: hollow waveguide, 4: metal thin film layer, 5: dielectric thin film. Agent Patent Attorney Sato Fujio Sai 3 Mouthwitness 1η TEo Te, -do T'+l ■ Sai 6 ■ TM, MoF°゛

Claims (1)

[Claims] (1) In a waveguide type gas laser device having a hollow waveguide surrounded by a metal electrode and a dielectric material for exciting high-frequency discharge in the lateral direction, almost the entire surface of the hollow region of the dielectric material is covered with the wavelength used. A thin film layer made of a metal whose absolute value of the complex refractive index is sufficiently large or whose imaginary part of the complex refractive index is larger than the real part is provided, and the entire surface of the metal thin film layer is made of a dielectric material with low absorption at the oscillation wavelength. A waveguide type laser device characterized by being constructed by coating with a thin film.