JPS5856488A - Specifying method for resonance mode of gas laser tube - Google Patents

Abstract

PURPOSE:To enable to simply specify the resonance mode by inserting a metal cylinder into a capillary tube and disposing a diaphragm having a diameter multiplied by 1.5-2 times of the diameter of a beam determined by a light resonator. CONSTITUTION:A cut split 12 is formed on the side surface of an elastic metal cylinder 11, and is inserted and fixed to a capillary tube 3 by utilizing the elasticity. When an adhesive is used, the split and the elastic metal are not necessary. In this case, the diameter for specifying the mode can be determined by the thickness 13 of the cylinder 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regulating resonance modes of a gas laser tube. A gas laser device is a device that extracts gas atoms forming a population inversion state through bombing and phase-aligned light in the form of an optical resonator through a reflector with a constant transmittance as a continuous output. be.

FIG. 1 shows a configuration of a He*N e laser with a cylindrical end. An anode 2 is embedded in one end of an envelope 1 made of glass, and a capillary tube 3 in which laser emission occurs is fixed and connected.

A cylindrical cathode 5 is provided across a partition wall 4 that isolates the cathode chamber, and is connected to a cylindrical cathode 6 at the end.

Here, the end cylindrical cathode 6 is fused to the envelope 1 to form a part of the core.

Next, the inside of the envelope 1 is sufficiently evacuated, and then HemNe gas is sealed in a reduced pressure state.

In a laser tube having such a configuration, an anode ai2 and a cathode 5
When a voltage is applied between them to cause a discharge, glow radiation is produced in a path from the anode L through the capillary tube 3 to the cathode 5.
The excited N atoms cause light emission, which is amplified by an optical resonator made of a reflecting mirror, causing oscillation and creating a standing wave between the optical resonators, a part of which has a certain transmittance. The light is extracted as a laser beam from the reflecting mirror 7.

Here, the optical resonator formed by the total reflection mirror 8 and the reflection mirror 7 is designed so that more light beams are concentrated in the center of the cross section of the capillary tube 3 than in the periphery. There is a distribution called a resonance mode.

Where - Resonant modes can be roughly divided into transverse modes and longitudinal modes, but in the case of a structure like the one shown in Figure 1, where the size of the reflecting mirror is much larger than the original wavelength and there is little diffraction loss. The electromagnetic field component in the axial direction of the capillary is negligible compared to the transverse component, and therefore, if only the transverse mode is considered, the beam in the optical resonator can be considered to consist only of TEM waves (transverse waves). I can do it.

In this case, the resonant mode is designated by T EMm n, m,
n is an integer that specifies the transverse mode and is called the transverse mode number, and the larger the numbers m and H, the more the beam spreads.
Moreover, there is a relationship in which the diffraction loss increases.

Here, in TEM mode, the intensity is maximum at the center of the beam, the lowest-order transverse mode vibrates in which the entire wavefront vibrates in the same phase, and the other modes vibrate when the beam cross section is divided into several parts. It consists of modes.

Therefore, when a reflecting mirror with a large diameter is used as shown in FIG. 1, oscillation is performed in multiple modes in which many transverse modes overlap. However, in actual laser devices, a method is used in which a mode regulation window is provided to exclude higher-order transverse modes from the output.

Here, the lowest-order TEMc and c modes have the smallest spread angle of the laser beam and can be focused on the smallest droplet, so they have high practical value.

That is, the beam spread angle θ (radians) is given by the following equation.

2λ θ=□−−・・・・・・・・・・(1)l Here, J...Wavelength a...Radius of the beam, the intensity at that point is the center intensity sand, where the TEMcc mode Regarding the intensity distribution of the beam cross section, the total power is 86.8mm within the beam diameter 2a.
4a includes 989 tatami and 4a includes 9997 tatami, so the laser beam spread angle is the smallest.

Therefore, the method to obtain TEMcc mode oscillation is to place an aperture in the optical resonator with a diameter 1.5 to 2 times the beam diameter determined by the optical resonator, or to select the inner diameter of the capillary to this value. It is being said.

However, the latter method has problems such as difficulty in ensuring a straight angle inside the capillary tube and difficulty in adjusting the optical axis.

The present invention relates to the former method, and an object of the present invention is to regulate resonance modes with a relatively simple configuration.

FIGS. 2 and 3 show conventional resonance mode regulation methods. In other words, in FIG. 2, the capillary tube 3 is thermally processed to form an inner diameter portion 9.
However, it has drawbacks such as poor workability and difficulty in ensuring the straightness of the capillary tube 3. FIG. 3 shows a method in which a mode regulating window 10 made of a metal cap is fixed to the end face of the capillary tube 3, and then a reflecting mirror is glued to this. In this case, in order to align the optical axis of the reflecting mirror, the end face of the capillary tube 3 or However, the disadvantage is that it is necessary to optically polish the end face of the regulating window 10, which requires a large amount of man-hours.

The present invention regulates the mode using a much simpler method than the conventional method, and regulates the mode by inserting an elastic metal cylinder having a cut portion or a flanged metal cylinder into a capillary tube.

FIG. 4 shows a case in which mode regulation is performed using an elastic metal cylinder. FIG.

In this structure, the elastic metal cylinder 11 has a cut section 12 on its side surface, and can be inserted and fixed into the capillary tube 3 by utilizing its elasticity. Note that when adhesive is used, there is no need to use the cut portion or elastic metal.

In the case of the structure shown in FIG. 4, the diameter for mode regulation is determined by the wall thickness 13 of the elastic metal cylinder 11.

Next, Fig. 5 shows the mode regulation by the metal cylinder 14 with 7 flange, and Fig. 5 shows the inserted state.
) is this perspective view.

In this structure, the dimensions of the mode regulation window are 1
The cylindrical portion is inserted into the capillary tube 3 according to the inner diameter of the capillary tube 3, and fixed to the capillary tube 3 by adhesive at the flange portion 15, and thereafter connected to a reflecting mirror using a conventional method.

The present invention regulates the resonance mode of a gas laser tube using a relatively simple method.The mode can be easily controlled by inserting a metal cylinder shown in FIG. 4 or 5 into a capillary tube. ing.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a He*Ne laser with a cylindrical end shape, Figures 2 and 3 are explanatory diagrams of a conventional resonance mode regulation method, and Figures 4 and 5 are resonance mode regulation methods according to the present invention. In this figure, the figure is a cross-sectional view, and the figure @ is a perspective view of the mode regulating structure. In the figure, 3 is a capillary tube, 11 is an elastic metal cylinder, 12 is a cut portion, 13 is a wall thickness, 14 is a metal cylinder, and 15 is a flange. 1st @

Claims (1)

[Claims] A discharge electrode consisting of an anode and a cathode is located at both ends of a tube filled with low-pressure gas, sandwiching a capillary tube that is located in the center of the tube and serves as the active region of the laser, and an optical resonator is provided on an extension of the capillary tube. A method for regulating a resonance mode in a gas laser tube, characterized in that a small hole for regulating the resonance mode is formed by inserting a metal cylinder having a cut p-split part or a flanged metal cylinder into a capillary tube.