JPS61274377A - Waveguide type laser device - Google Patents

Abstract

PURPOSE:To reduce a waveguide loss even if a space between facing electrodes is narrow and facilitate an oscillation of high efficiency by forming thin film layers which show little absorption near an operating wavelength on the surfaces of the facing metal electrodes. CONSTITUTION:Al2O3, which is not toxic and whose thermal conductivity is not so low, is employed as a material for dielectrics 1 and Cu, whose heterorefractive index is not so large, is employed as a material for metal electrodes 2. Thin films 4 are composed of ZnSe and formed by a method such as sputtering, vacuum evaporation or CVD. A waveguide passage 3, which is a passage for a laser discharge, is surrounded by the dielectrics 1 and the metal electrodes 2 coated with the thin films 4 and has a square shape and its dimensions are about 2X2X200mm. The waveguide passage 3 can generate a single-mode oscillation and, as an output intensity distribution is close to a theta circular distribution, can be connected to an external waveguide passage easily. A mixture gas of He, CO2 and N2 or He, CO2, N2 and Xe is enclosed in the waveguide passage 3 with a gas pressure of about 100tor.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention is useful in fields such as laser processing for welding and cutting, coherent light application systems, detection of atmospheric pollutants, and inter-satellite optical communications. 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 has been developed mainly for laser processing such as welding and cutting, and attempts have been put into practical use to utilize laser light as thermal energy for production.

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

Generally, in a gas laser, when the laser tube diameter is made smaller, the laser profit 1q increases. Therefore, waveguide lasers have the following features compared to conventional lasers in which the resonance mode is determined by a resonance reflector.

(1) The diameter of the laser tube can be made thinner, resulting in small size and high output.

(2) Since the pressure of the filled gas is high, the oscillation wavelength tuning range becomes wide.

(3) Since the entire laser tube can be made of a material with high thermal conductivity, air cooling operation is possible.

(4) Easy maintenance and low cost.

Figure 3 shows an example of a COz waveguide laser device that has been studied so far (IEICE Technical Report OQ E 77-12
(1977)).

31 is a dielectric, 32 is a total reflection mirror, 33 is a partial transmission mirror, 3
4 is an anode, 35 is a cathode, and 36 is a waveguide.

An Af'zCh plate with relatively low loss and high thermal conductivity is used as the dielectric 31, and a rectangular waveguide 36 is constructed by combining four sheets. In this vertical DC discharge excitation method, the waveguide can be easily constructed entirely of low-loss materials, so
Although the waveguide loss is relatively small, it requires a high discharge voltage.

Therefore, apart from the vertical DC discharge excitation method, a horizontal RF discharge method is also being studied.

Lateral R [Discharge excitation type waveguide lasers are: (1) uniform glow discharge can be obtained at low voltage, (2) positive resistance discharge eliminates the need for a stabilizing resistor, and high efficiency operation can be expected. , (3) It has many features such as relatively easy discharge under high pressure.

As mentioned in IEICE Technical Report OQ E 83-52 (19B3>), the waveguide is entirely composed of a dielectric material with relatively low loss and high thermal conductivity, such as AfflzCh, and the electrodes and discharge active gas are Although RF discharge is possible even without contact,
In order to perform stable discharge at lower voltage, 81) t)
l, PhVS, 1. e! tt, 43(8)P7
2B (1983), it is preferable for the electrodes as shown in FIG. 2 to form part of the waveguide wall.

In FIG. 2, 21 is a dielectric material such as AJlz03, 22 is a metal electrode, 23 is a waveguide, 24 is an RF power source,
25 is a matching inductance, and 26 is a matching capacitor.

ΔJlzO3 is a dielectric material with relatively good thermal conductivity, but
Metals such as AJl and CLJ have extremely high thermal conductivity,
The method in which the metal serving as the electrode constitutes part of the waveguide is advantageous not only in terms of low-voltage stable discharge but also in terms of cooling effect.

The thermal conductivity of AJl203, Af', and Cu is 0, respectively.
, 06 cal/cIItsec℃, 0.487 Cal/
cm sec'c, 0,923 Cal/n sec'c
It is. BeO has a thermal conductivity of 0.5 Cal/cm se
It has a high c'C and is the best dielectric material to construct a waveguide instead of Af7zO3, but it is a toxic substance and poses a problem in laser production, so it is avoided as a material for waveguide-type laser devices. ing.

[Problems to be Solved by the Invention] By the way, when a metal electrode forms part of a waveguide, waveguide loss due to the metal cannot be ignored. Therefore, the waveguide type laser device having the conventionally reported structure as shown in FIG. 2 cannot realize highly efficient laser oscillation as expected.

In order to reduce the waveguide loss due to metal, attempts have been made to construct a flat waveguide by widening the distance between opposing electrodes, and to create a structure in which the electrodes do not contribute to the waveguide characteristics, but in terms of low voltage stable discharge, This is disadvantageous, and also causes problems such as multimode oscillation in the long side direction and an elliptical output beam.

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, a film layer with low absorption in the used wavelength band is formed on the surface of the opposing metal electrodes, so that even if the spacing between the opposing electrodes is narrow, the waveguide loss can be reduced. This enabled high-efficiency oscillation to be achieved.

The thin film formed on the surface of the metal electrode is a material in which the imaginary part of the complex dielectric constant can be ignored compared to the real part in the wavelength band used. For example, at a wavelength of 10.6μ7H, KCJl, Na(J?, KR3) -5, CdTe, 3i
, (3e, Zn5e, Zns, PbFz, etc.), chalcogenide glass, etc. Among these materials, the material whose refractive index is close to FΣ has a remarkable effect.

In the light wave band, substances such as scales act as important transmission media for electromagnetic waves and all behave as dielectric materials, but even if they are formed on a metal surface, a stable discharge is generated due to RF discharge excitation.

On the other hand, the material used for the metal electrode is a material with a large complex refractive index or a material in which the imaginary part of the complex refractive index is sufficiently larger than the real part, such as Cu, ACJ, Au, and A.
F etc. are failed.

The complex refractive index of each of these materials at a wavelength of 10.6 μm is Cu: 14.1-j64.5, Aq: 13.5-j
75.2, Au:17.2-j 56. O, Af:
20.5-j 58.6.

These materials also have high thermal conductivity and can provide a large cooling effect.

In this way, by coating the metal electrode with a thin film with low absorption, it functions not only as an electrode, but also as a waveguide wall with low loss, making it easy to provide a higher cooling effect, and making it more compact. It enables high efficiency and low voltage stable discharge.

[Function] Generally, in a metal parallel plate type hollow waveguide, the loss is low in the TE mode where the electric field is parallel to the metal plate, but the loss is extremely high in the TE mode where the magnetic field is parallel to the metal plate. Therefore, in the structure shown in FIG. 2, the direction of the electric field in the oscillation mode is necessarily parallel to the metal electrode. Therefore, the transmission loss of a mode having such an electric field direction is mainly evaluated by the transmission loss of the TM mode of the dielectric parallel plate waveguide.

However, in a metal parallel plate waveguide in which a thin film with a suitable thickness and low absorption is formed on the metal surface, the transmission loss of the TE mode and TM mode may be reversed, or both may be caused by dielectric parallel plate waveguides. It is shown that the loss of the wavepath is lower than that of T[, TM mode.

In the waveguide laser device of the present invention having a metal electrode formed with a thin film with low absorption, it is possible to oscillate the laser so that the electric field in the oscillation mode is parallel to the dielectric plate.

Therefore, the waveguide loss of the waveguide laser in the present invention is evaluated by the transmission loss of the TE mode of the dielectric parallel plate waveguide. Highly efficient oscillation is possible compared to waveguide lasers.

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

1 is a dielectric, 2 is a metal electrode, 3 is a waveguide, 4 is a thin film coated on the wall of the waveguide 3 of the metal electrode 2, 5 is a water cooling cavity, 6 is an R power source, 7 is a matching inductance, 8 is covered by a matching capacitor.

As the material for the dielectric 1, HA1203, which is not toxic and whose thermal conductivity is not so low, is used, and as the material for the metal electrode 2, Cu, which has a large complex refractive index, is used.

For example, Zn5e is used for 1ffliI4, and it can be easily formed by sputtering or vacuum deposition, or by CV
It can also be formed by the D method. In addition, Si and Ge
When using , it can also be easily formed by plating.

A waveguide 3 as a laser discharge path is surrounded by a dielectric 1 and a metal electrode 2 coated with a thin film 4.

The cross section is square, the dimensions (width Become.

Inside the waveguide 3, there are He, CO2, and gases with a gas pressure of about 100 torr.
A mixed gas of Nz, lle, CO2, Nz, and Xe is sealed.

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

The cooling effect is enhanced by providing a water cooling cavity 5 within the metal electrode.

The metal electrode 2 is connected to a power source 6 via a matching circuit consisting of a matching inductance 7 and a matching capacitor 8.

The effects of the present invention are more pronounced as the metal constituting the metal electrode 2 has a larger complex refractive index or the imaginary part of the complex refractive index is larger than the real part. In that sense, C
It is more advantageous to use Aq than U. However, it is not economical to construct the entire electrode using AQ. Therefore, when using Act, it is economical to interpose an Act thin film (about 1 μm thick) between the Cu electrode 2 and the thin film 4.

Furthermore, the closer the refractive index of the material for forming the thin film 4 is to FΣ, the greater the effect. In that sense (Zn5 than 3e
KCf is more suitable than Zn5e and Zn5e.

However, KCffl has deliquescent properties, so it is not preferable to expose it to an external atmosphere. Therefore, a thin film that is strong against the external atmosphere and has low absorption may be laminated on the K(4> thin film).

Furthermore, the effects of the present invention can be further enhanced by alternately laminating two or more types of thin films having different refractive indexes.

In the embodiment shown in Figure 1, the electrode surfaces that form the waveguide wall are of a parallel plate type, but if the electrode surfaces are made concave, the beam focusing ability can be improved and the output intensity distribution can be made closer to a circular shape. becomes.

[Effects of the Invention] According to the present invention described above, the following remarkable effects are exhibited.

(1) Even if the spacing between metal electrodes is small, waveguide loss can be reduced and highly efficient oscillation is possible.

(2) Since the spacing between the metal electrodes can be reduced, a small size and stable low voltage RF discharge are possible.

(3) Since the waveguide wall is made of metal with high thermal conductivity,
The cooling effect can be increased.

(4) Since the spacing between the metal electrodes and the spacing between the opposing dielectrics can be made to be approximately the same, 1q of single mode linearly polarized waves with a nearly circular intensity distribution can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional explanatory diagram of an embodiment of the present invention, FIG. 2 is a cross-sectional explanatory diagram of a waveguide-type COz laser device using a conventional horizontal RF discharge excitation method, and FIG. 3 is a conventional vertical DC FIG. 2 is an explanatory longitudinal cross-sectional view of a discharge excitation type waveguide type CO2 laser device. 1: dielectric, 2: metal electrode, 3: waveguide, 4: thin film.

Claims (1)

[Claims] (1) In a waveguide gas laser that has a hollow waveguide surrounded by electrodes for laterally exciting high-frequency discharge and a dielectric material with relatively high thermal conductivity, the electrode material has a A metal with a sufficiently large complex refractive index or an imaginary part of the complex refractive index larger than the real part is used, and a thin film with small absorption loss is provided on the surface of the metal electrode constituting the hollow waveguide wall. A waveguide type laser device characterized by: