JPH07106668A - Small-sized and sturdy gas laser device - Google Patents

Abstract

PURPOSE: To make it possible to resist the acceleration generated by movement while the output, mode quality and efficiency, etc., of a resonator are being maintained by providing a resonator which becomes the only internal radiation distribution wherein the turnaround track containing a specific number of processes. CONSTITUTION: This gas laser device contains a thin film and geometrically shaped excitation gain region 9 formed between two cooling electrodes 6 and 7, and high output is generated from this device of very small type. Accordingly, Gaussian rays, which are symmetrically focused, are radiated taking full advantage of the gain region 9 having a wide stopline excitation structure. The gas laser device is composed of a focusing mirror and the second reflection surface having the region of different reflection factors, and a resonator, which becomes the only internal radiation distribution wherein a turnaround track, containing six or more processes, are maintained in a laser cavity, is provided. Accordingly, the reflection factor of coating in an output coupling region is increased, and the loss of coupling can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightweight and rugged gas laser device having a stripline excitation structure which can physically replace a spindle unit or a machining / cutting / piercing machine in a computer controlled positioning device.

[0002]

BACKGROUND OF THE INVENTION Conventional low power (less than 100 W) laser engravers, cutters, and perforators are a series of lasers that transmit a beam of light from an opening in a laser device to a desired variable position on an object. A stationary laser with a light transmission system (flying optical system) consisting of a mirror, a lens, and an optical fiber is adopted. These systems are very complex, often require recalibration and adjustment, and generally require a significant amount of initial investment and maintenance costs, increasing the area required to install the system ( Alternatively, another option is to move the entire laser-treated object, but the disadvantage is often even greater).

The reason for placing the laser stationary in conventional systems is the large size and weight of the gas laser and its relatively fragile structure. Small, rugged lasers, on the other hand, tend to emit rays that are too low in power for the material being lasered or have such poor properties that they cannot be focused to the point where maximum power flux density is obtained (near Infrared or visible solid-state lasers can overcome these drawbacks, but are currently very expensive).

Microminiature, conductively cooled gas lasers have been designed with a stripline structure in which the pump gain region is located within the geometry of the thin envelope (FIG. 3). It is enclosed between two cooling electrodes. In such a construction, the output power per unit length is proportional to the lateral width of the sheet and also of the gain area (as is the case in a cylindrically cooled gain area around the perimeter). Depends on cross-sectional area. Therefore, it is possible to obtain a high output from a very small device as an output per unit length.

Using the case I optical resonator with one focusing total reflector and one planar output coupler, the stripline laser structure has a gain region cross-sectional shape, ie, a thin stretched strip shape. Emit the rays that have. Such ray patterns are not desirable when considering the application. This is because the ray bundle limited by the diffraction at the focal plane in the focusing system will have an asymmetrical shape, and the depth of focus will be small.
One way to extract a narrow beam from a gain region with a slab geometry is to use an unstable waveguide hybrid resonator. That is, the optical resonator (optical cavity) has a stable waveguide structure in the lateral dimension (crossing the gap) and has an unstable resonator in the lateral (length) dimension. Composed. Both positive and negative branch (FIG. 6) unstable resonators have been previously reported (US Pat. No. 4,719,639 describes a positive branch as US Pat. No. 5,048). No. 048 describes a negative branch type).

In low power, small lasers, unstable resonators have two drawbacks. One is that the rays emitted from this type of resonator have an axial mode spacing in the frequency space of c / 2L (where c is the speed of light and L is the resonator's velocity). Indicates the length.). For very short laser devices, this spacing is large, and
It is often difficult to match the axial mode peaks to the gain curve peaks.

Furthermore, in order for particularly short lasers to achieve round-trip gains greater than unity, the overall losses, including coupling losses, must be kept to a minimum. In order to reduce the coupling loss of the unstable resonator, the beam exit aperture must be small. This results in poor output beam quality due to diffraction.

An alternative method for extracting the focused light beam from the stripline structure was developed by Synrad Inc. and described in "Series 22" Poly-Lase "Micro miniature.
CO ₂ laser arrays models D22-1 and M22-1 ”. These lasers are very compact, have a relatively high power output and consist of a stripline structure with strips longitudinally divided into three regions by ceramic spacers. The outgoing radiation takes the form of three separate rays, which are not focused. Focusing of such systems is complicated and it is not possible to obtain maximum flux density with large depth of focus. Thinrad discloses the use of its laser device in applications where "the ultimate performance of the M ² factor (modal nature or pore size) is not required".

Previous papers (Optics Letters Vol. 14, N
o. 23, (1989), pp. 1309-1311, and SPIE Vol. 12
76, CO ₂ Lasers and Applications II (1990), pp. 98-
In 105), the inventor of the above patent describes a tentative solution to the problem of extracting Gaussian rays from a wide gain region of a stripline structure. The M-mode folding trajectory is obtained by placing a stop in the semi-confocal resonator next to the total internal reflection mirror to suppress the formation of alternative modes. The M-mode optical resonator design has the following three drawbacks.

1. There are only four strokes in the trajectory,
Therefore, it is not suitable for a large laterally extended excitation region. This is because the excitation region is not used efficiently. Therefore, the M model cannot be used so that the output per unit length becomes very high.

2. The insertion of a stop between the electrode and the total internal reflection mirror (thus widening the distance between the electrode and the total internal reflection mirror) results in a significant increase in power and efficiency due to the substantial diffraction loss at the end of the electrode. Cause a reduction. This effect is more likely to occur when the distance between the electrodes is small (as required for high power).

3. The stop area is placed on a total internal reflection spherical mirror. Therefore, both the plane mirror and the spherical mirror are required to be made-to-order optical components. This adds to the cost of the resonator components.

[0013]

SUMMARY OF THE INVENTION The present invention is a gas laser device that includes a thin film geometrically shaped pump gain region between two cooling electrodes to produce high power from a very small device. And efficiently utilize the wide gain region of the stripline pumping structure to emit a symmetrically focused Gaussian-like light beam, and is composed of one focusing mirror and a second reflecting surface composed of regions having different reflectances. Characterized by a cavity with a folded trajectory comprising more than 6 strokes, which is the only internal radiation distribution maintained in the laser cavity,
The present invention relates to a small and sturdy gas laser device.

The above laser device can be incorporated into a computer-controlled positioning device to be used as a spindle unit or an engraving / cutting / drilling machine.

The present invention also relates to a resonator of a gas laser device. This resonator is composed of one focusing mirror and a second reflecting surface composed of regions having different reflectivities, and a folding locus having a stroke of 6 or more is provided with a single internal radiation distribution maintained inside the laser cavity. It is supposed to be.

Furthermore, the present invention relates to a beam emitted from a resonator parallel to its optical axis, which beam has an optical axis mode spacing of a beam emitted from a resonator having a length of 6 times or more. Have.

It is an object of the present invention to provide a robust gas laser capable of withstanding the acceleration caused by movement while maintaining its operation (ie power, mode quality, efficiency, etc.).

Further, the above-mentioned laser is compact and lightweight, and can be easily moved by a positioning device (that is, robot arm, pantograph, etc.) controlled by a small computer.

The laser is also compatible in shape and size with existing computer controlled cutting, drilling or cutting machines, allowing it to physically replace existing machinery or spindle assemblies. it can. In this way, the existing mechanical work capacity can be enhanced by the work capacity of the laser and the spot size area of the workpiece through the Z axis of the positioning device can be dynamically controlled.

A further object of the invention is to provide a laser with excellent beam characteristics (ie symmetry, Gaussian distribution, small loss), such laser having a wide gain region of the pumped medium. It is expected to provide maximum flux density and M ² factor while sampling efficiently.

Furthermore, the coupling loss of the optical resonator in the present invention can be made considerably small without impairing the quality of the generated beam. In addition, the configuration of the optical resonator of this laser is excellent in that its length is short, and has an optical axis mode spacing value corresponding to a laser cavity that is 6 times or more the actual length. This makes it possible to obtain a larger density of optical axis modes within a given frequency range, and facilitates matching the optical axis mode peak to the maximum value of the gain curve of the excited medium.

Furthermore, the device according to the invention is compact and robust, coupled with a relatively high power (per unit length) and symmetrically focused beam,
It can be directly integrated into existing positioners instead of machining, drilling, cutting or cutting instruments, or spindle assemblies.

[0023]

1 is a sectional view of a laser head according to the present invention. Two parallel electrodes (6, 7) are held by ceramic spacers (2, 3, 4) and fixing screws (5). One electrode (6) is electrically insulated from the other electrode (7) and the surrounding metal sheath (1). An RF voltage is applied between these two electrodes, and the region (9) between them forms the gas exhaust path. A through hole (8) is provided in each of these electrodes and is cooled by flowing water there. The metal sheath (1) constitutes a wall surface, seals gas in the laser, and functions as a Faraday cage to shield RF electromagnetic radiation and suppress leakage of RF noise. Figure 2
Shows the electrodes and spacers except for the surrounding metal sheath (1).

The gain region of this laser is a thin film region (FIG. 3) enclosed by the two electrodes. This stripline cavity is thin and long, and the Maxwell equation for the radiation distribution in this cavity can be assumed separately in the direction parallel to (y) and the direction parallel to (x). , This cavity can be treated substantially two-dimensionally in considering the radiation distribution in the y-direction (the actual two-dimensional distribution is the waveguide mode in the x-direction and the mode in the y-direction in the present invention). Described as a free-space mode and mixed-component cloth). The optical resonator of Case I (mirror having a single reflection characteristic across the height a of the gain region) has a Fresnel number (N = a ² / λ).
L) is large, and the light emission pattern substantially has a cross-sectional shape of the gain region (rectangle of height a and width b), and includes high-dimensional Hermite-Gauss mode (HG mode). It is a superposition of many H-G modes.

The cavity length, mirror radius of curvature, and intercavity loss distribution can be set so that a particular H-G mode dominates. This is intuitively understood in light (geometric) optics considerations. FIG. 4 shows a resonator with one plane mirror (1) and one focusing mirror (2) whose focal length is twice the distance L between the mirrors. The beam originating at the point P ₁ of the plane mirror (1) and running parallel to the optical axis is reflected by the focusing mirror (2), hits the point P _{2 of the} plane mirror and then reaches the center of the spherical mirror. This continues at points P ₃ and P ₄ symmetrically about the optical axis. At point P ₄ , a similar light trace is drawn and the flow returns. This locus is closed. That is, the beam returns to a similar position and direction through a finite number of optical paths in the cavity (12 optical paths in this case).

This argument is also in agreement with the results of an ABCD ray matrix analysis for an optical cavity with one mirror spherical and the other mirror planar, which also applies to Gaussian and geometrical rays. The matrix of unit cells starting from a plane mirror is given by (Laser Electronics, JT Verdeyen, Prentice Hal
l, 1981, pp. 35-41).

[Equation 1] In the above configuration of f = 2L,

[Equation 2] In the unit cell, the position of the light ray after the s-th stroke can be expressed by the following equation.

In Equation 3] planes of _{r s = r max sin (sθ} + α) s = 0 , the beam starts running parallel to the optical axis a from the optical axis at a distance of r _max. In this case, α is immediately determined as π / 2. θ is given by the following equation.

## EQU00004 ## cos .theta. = (A + D) / 2 = 1/2

[Mathematical formula-see original document] Therefore, the position of this ray after the round trip is given by the following equation.

## EQU00006 ## r _s = r _max sin (sπ / 3 + π / 2) Obviously, as mentioned above, this function has 6 round trips or 12 rounds.
It will be repeated with a single reflection.

A stop (3) is inserted in the cavity in order to suppress any other radiation distribution or closed trajectory that can be maintained in the cavity. This radiation (electromagnetic radiation)
Since the plane mirror intersects this mirror at points P _{1 to} P ₄ which are clear, it is possible to design the plane mirror so as to totally reflect at three points P _{2 to} P ₄ and partially transmit at the point P _1. it can.

FIG. 5 shows a side view of the above optical resonator structure according to the invention. A spherical total internal reflection mirror has a focal length of 2L, where L is the distance between the mirrors. The plane mirror is aligned in a single plane with one substrate, using different coatings on the inside surface of the cavity. Areas (3) and (5) are coated for maximum reflectivity and area (2) is to be partially transmissive. The area (4) of the plane mirror is made non-reflecting and corresponds to the stop (3) in FIG.

The emitted radiation (6) has the characteristic of a Gaussian beam parallel to the optical axis. Furthermore, the same radiation (in terms of beam divergence, axial mode spacing, etc.) can be obtained as in a conventional laser device having a cavity 6 times longer (6 L) than the length of the structure of this embodiment. A lens, mounted directly on the laser device housing, focuses the beam at a particular point.

In the case of the optical resonator described in the preceding article (FIG. 6) (unstable resonator with both positive and negative branches),
In order to reduce the overall coupling loss, the aperture to reflective surface ratio (a ₁ / a ₂ ) must be reduced. For a constant lateral extent of the emission area (a),
As the aperture (a ₁ ) becomes smaller, the diffraction phenomenon further deteriorates the nature of the emitted beam.

However, in the present invention, the coupling loss can be arbitrarily reduced by increasing the reflectance of the coating in the output coupling region ((2) in FIG. 5). Thus, for short length cavities, where the overall gain is small and therefore the coupling loss must be small to obtain a round trip gain of 1 or more, this optical resonator embodiment provides an unstable resonance. Preferred over the vessel example.

Because of these two advantages (corresponding to the long laser device characteristics and the ability to reduce coupling losses), the present invention is particularly advantageous for very short cavities.

The laser device of the present invention realizes a combination of a very compact and robust device having a high output per unit length and excellent beam characteristics. As a result, the laser can be changed to a pantograph, a CNC milling device,
It can be attached to a computer controlled positioning device such as a drilling machine, cutting device, robot arm. By designing the laser device of the present invention to have dimensions that closely resemble the machining tools and spindles currently installed in such positioning devices, such tools can be physically replaced by the laser device of the present invention. . In this way, the laser light can be used in the manufacturing process without purchasing a positioning device dedicated to the laser. This can save considerable cost and space and also reduce the time and skill for an employee to become proficient in two separate systems.

A further advantage of the present invention is that the beam spot size can be changed by changing the distance between the laser device and the workpiece. By changing the position of the laser device in the z-axis direction, the width of the engraving groove can be dynamically controlled, for example, from a minimum of 0.1 mm to 1 mm or more. Movement in the z-axis is possible with current pantographs and CNC systems, and the use of a laser device eliminates the interaction between the rotating tool and the workpiece. Since the operation of the laser system is done by the excitation circuit (power supply circuit),
The size of the focal zone can be controlled by freely moving in the z-axis direction.

One example of one particular embodiment of the invention is applied to plastic engraving. Laser engraving has several advantages over mechanical systems.・ No shavings on the work piece. • No resistance (important for work pieces that are fragile and difficult to hold). -Fine continuous resolution (up to 0.1 mm). -Dynamic control of line width is possible (by changing the distance from the work piece).

The computer controlled mechanical engraving system currently in use is the Gravograph System VX2.
(Gravograph system VX2) is available. 18 cm x size
The cutter is held by a cutter holding spindle (spindle) (part number 63435-000) having a diameter of 3.5 cm and a weight of 2 kg. The size of the laser head of the present invention can be matched to the size of the main shaft. The main spindle unit can be replaced with a laser head, and laser engraving can be performed using the existing mechanical engraving device, and the cost will be a fraction of the cost of a separate dedicated laser engraving system. .

[Brief description of drawings]

FIG. 1 is a conceptual cross-sectional view of a laser head according to a first embodiment of the present invention.

FIG. 2 is a perspective view illustrating internal structures of electrodes and spacers.

FIG. 3 is a perspective view illustrating dimensions of a gain region of a stripline laser.

FIG. 4 is a conceptual side view of an optical axis resonator according to the present invention, which optically describes the internal radiation distribution and the generated beam.

FIG. 5 is a side view illustrating an embodiment of the optical resonator according to the present invention.

FIG. 6 (a) is a positive branch type (positive bran)
ch) Side view of unstable resonator, (b) shows negative branch type (n
egative branch) It is a side view of an unstable resonator.

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Claims (5)

[Claims] 1. A gas laser device including a thin film geometrical pumping gain region between two cooling electrodes to produce high power from a very small device, having a wide stripline pumping structure. Efficient use of the gain region to emit a symmetrically focused Gaussian-like light beam, which is composed of one focusing mirror and a second reflecting surface having regions with different reflectivities, and includes a folding path including six or more strokes. A compact and rugged gas laser device with a resonator whose trajectory is the only internal radiation distribution maintained in the laser cavity. 2. The miniature laser device according to claim 1, which can be incorporated in a computer-controlled positioning device and used as a spindle unit, or as an engraving or cutting or punching machine. 3. The area of the spot on the workpiece is moved by the z-axis of the positioning device without the need to perform any manipulations on the beam for engraving, cutting, drilling, or otherwise working on the material. 3. The miniature laser device according to claim 2, which can be controlled mechanically. 4. A single internal radiation distribution in which a folding locus having one or more focusing mirrors and a second reflecting surface composed of regions having different reflectances and having a stroke of 6 or more is maintained inside the laser cavity. Become a resonator. 5. A beam emitted from a resonator parallel to the optical axis with an axial mode spacing of the beam emitted from the resonator having a length of 6 times or more.