RU2411619C1 - High-frequency discharge excited gas laser - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: transverse pumped gas laser has a housing, an optical resonator, an electrode connected to a resonance-tuned high-frequency power supply, a cooling heat exchanger and a centrifugal compressor. The housing is formed by an outer cylindrical metal casing and an inner cylindrical dielectric casing placed eccentrically inside the said outer casing, hermetically joined to front flanges and forming a gas-dynamic channel for circulating the active medium. The centrifugal compressor creates a stream of gaseous medium which envelopes the inner cylindrical dielectric casing. The section of the gas-dynamic channel with the narrowest cross section forms a plasma chamber and has a symmetrical or asymmetrical profile which varies on the height and has an arc-like or flat shape with angular opening in the direction of flow of the active medium along the width of the zone of the optical resonator. The electrode adjoins the outer surface of the inner cylindrical dielectric casing with its surface. The inner surface of the outer cylindrical casing on the said section of the gas-dynamic channel is insulated from the gas stream and the plasma by a dielectric layer, and the outer cylindrical metal casing is earthed.

EFFECT: high efficiency, power, compactness and light weight, mechanical stability and easy manufacturing and use.

18 cl, 6 dwg

Description

The invention relates to quantum electronics, in particular to the field of laser technology, and is intended for use in creating highly efficient and compact high-power gas lasers for industrial applications, for example, for high-precision welding and cutting of metals.

An analysis of existing designs of gas lasers with a transverse flow and excitation by a high-frequency discharge shows that they traditionally use plane-parallel channels that do not take into account the growth of boundary layers in the near-wall regions of the optical cavity zone due to the friction of the gas flow against the walls throughout the entire zone.

The boundary layers are low-speed stagnant zones with high static temperature. At a gas temperature in excess of the critical temperature (for a CO ₂ laser above 400 ° K), the aforementioned layers act as diaphragms, absorbing part of the laser beam energy inside the optical resonator. The thickness of the boundary layers and their temperature are proportional to the plasma intensity and, as a consequence, the gas temperature.

Ignoring these circumstances leads to significant losses in the output laser emission, a decrease in the efficiency of the optical resonator, and, as a result, a decrease in the total laser efficiency, estimated at least 1-2%.

In addition, structures with a transverse flow and a plane-parallel configuration of the laser cavity are subject to significant mechanical and thermal deformations created by the gradients of the pressure drop between the vacuum laser cavity and the external environment, as well as the temperature drop on the walls of the flat structure. To stabilize and compensate for mechanical fluctuations, they resort to hardening and compensate for mechanical fluctuations, they resort to hardening of the structure, which at the same time becomes more complex, bulky and heavy.

A known gas laser in which the housing is formed by an outer cylindrical shell and an inner cylindrical dielectric shell located therein, whose axis is parallel and eccentric to the axis of the outer cylindrical shell. The cylindrical shells are hermetically connected to the end flanges with the formation of a closed gas-dynamic channel between them, in the narrowest section of which there is a gas-discharge chamber with electrodes, the lower of which is mounted on the inner surface of the dielectric shell, and the other in the gap between the shells parallel to the bottom with the formation of a discharge gap. A heat exchanger-cooler and a fan are located in the gas-dynamic channel, creating a flow of active gas medium circulating in the gas-dynamic channel.

In the known laser, the gas-dynamic channel is limited by the curved surfaces of the cylindrical shells, however, the configuration of the discharge gap itself, determined by the nature of the mutual arrangement of the electrodes and the shells, has a traditional plane-parallel shape, which predetermines all of the above disadvantages that are inherent to lasers with a plane-parallel shape of the gas-dynamic channel.

The use of high-frequency pumping in a known laser with cylindrical shells does not solve all the problems, since the plasma between two bare electrodes located in the path of the gas flow remains unstable and is characterized by a low volume energy density due to the formation of gas flow turbulence and vortices on the electrode protrusions, as a result of which the laser It has low efficiency and large size.

A known gas laser in which the active medium is pumped by a current of a high voltage pulse discharge generated in the interelectrode gap of the laser [2]. However, gas heating and plasma-chemical processes that occur in a gas mixture as a result of the passage of a pulsed current lead to a change in the properties of the gas mixture in the discharge gap and, as a result, limit the repetition rate of periodic laser pulses [3]. In this case, the operation of a laser with a high pulse repetition rate can be realized using a special means of pumping gas, which allows timely replacement of the exhaust gas in the interelectrode gap.

A known gas laser with a transverse gas flow through a discharge, the emitter of which has a closed gas-dynamic circuit, including a gas discharge chamber, in which electrodes, a heat exchanger, a pumping device and transition sections connecting the above elements are mounted. The gas-dynamic circuit has the widest cross section at the heat exchanger location section, and the gas-discharge chamber section from the front of the electrodes to its trailing edge is made in the form of a flat diffuser, while the length of this section is about (8-9) the transverse dimensions of the channel at the front in front of the electrodes [4 ].

A disadvantage of the known laser is the power limitation (or low specific energy characteristics), which is associated primarily with the relatively large interelectrode gap and the presence of long transition sections, in particular a diffuser of the laser discharge chamber. The dimensions of the emitter in such a laser are, as a rule, about 3 m ³ per 1 kW of lasing power. By reducing the length of the transition sections, the dimensions of the emitter can be reduced to 1-1.5 m ³ / kW, however, this increases the cost of power for pumping up to 2.5-3.5 kW of radiated power.

In addition, the use of bare electrodes located inside the flow channel and directly washed by the gas stream creates a number of fundamental problems, such as large discharge volumes with a low bulk energy density, chemical cartamation (decomposition) of the laser gas itself, dangerous high voltage, etc.

The objective of the present invention is to develop a gas laser with a cross flow and excitation by a high-frequency discharge, the design of which provides an increase in power and specific energy characteristics, increased efficiency, ultimate compactness and lightness, mechanical stability and technological simplicity in manufacturing and operation.

The solution to this problem is achieved by the fact that a gas laser with transverse pumping and excitation by a high-frequency discharge contains a housing formed by an external cylindrical metal shell and an internal cylindrical dielectric shell eccentrically mounted in it, hermetically connected to the end flanges and forming a gas-dynamic channel for circulating the active medium, a section with the narrowest cross section of which forms a plasma chamber, an optical resonator, an electrode connected to a high-frequency power supply unit, a cooling heat exchanger and a centrifugal-type turbocharger that generates a flow of active gas medium, envelopes the inner cylindrical dielectric shell, while the gas-dynamic channel in the section with the narrowest section has a symmetric or asymmetric profile of an arcuate or flat shape with an angular opening of variable height the direction of the flow of the active medium along the width of the zone of the optical resonator, the electrode is closely adjacent to its surface directly continuously to the outer surface of the inner dielectric cylindrical shell, the inner surface of the outer cylindrical shell in said portion of gas-dynamic channel is isolated from the gas flow and the plasma by a dielectric layer, and an outer cylindrical metal shell grounded.

In addition, the high-frequency power supply can be configured to supply electrical pulses with frequencies from 10 kHz to 1.5 MHz at alternating current and from 1.5 MHz to 27 MHz in the radio frequency range.

As an active gas medium, a mixture of CO ₂ : N ₂ : He gases can be used, or a CO: He gas mixture.

The outer and inner cylindrical shells can be made with round or oval profiles.

The outer and inner cylindrical shells can be made with different profiles: one with a round and the other with an oval profile.

The outer cylindrical shell may be made of aluminum alloy or other metal.

The outer cylindrical shell can be made with air or water cooling.

The inner cylindrical dielectric sheath can be made with a wall thickness of 5 to 13 mm.

The inner cylindrical dielectric sheath can be made of ceramic based on aluminum oxide or composite material.

The outer cylindrical shell can be made by profile extrusion.

The dielectric coating on the inner surface of the outer cylindrical shell in the region of the discharge cavity can be made with a thickness of 0.1 to 5 mm.

The dielectric coating on the inner surface of the outer cylindrical shell in the region of the discharge cavity and the inner cylindrical dielectric shell can be made by plasma spraying and has a multilayer structure formed of particles from 45 to 15 microns in size.

The electrode may be made of metal and water-cooled.

In addition, a cylindrical gas laser can be equipped with two deflectors located at the entrance to the optical cavity and two deflectors located at the exit of the optical cavity.

Also, a radiator-heat exchanger with a turbocompressor can be located in a remote channel connected to the gas-dynamic channel by transition elements.

In addition, the range of angles of opening of the gas-dynamic channel in the area with the narrowest cross section in the direction of flow of the active medium along the width of the zone of the optical resonator can be 1-10 °.

The term "cylindrical shell" in this application is understood to mean a shell having a cylindrical surface, i.e. surface formed by a straight line (generatrix) moving parallel to a given direction along a certain curve (guide) - IN Bronshtein and K. A. Semendyaev "Handbook of mathematics", M., Nauka, 1965, p. 174, 232, 233, according to which, depending on the type of guide, this surface can have flat or quasi-flat sections (see Fig. 118), which allows the possibility of a gas-dynamic circuit in the form of an asymmetric, variable-height channel arcuate or partially flat shape.

When using a shell, the radius of which significantly exceeds the width of the optical resonator, the arcuate fragment of the shell becomes almost flat or quasi-flat. In addition, a groove may be formed on the surface of the cylindrical shell to form a flat portion of the shell.

The invention is illustrated by drawings, in which: figure 1 shows a General view of the laser; on figa - the optimal channel with a partially flat configuration (shape) of the plasma cavity (chamber) and its angular opening; on figb - the optimal channel with an arched configuration (shape) of the plasma cavity (chamber) and its angular opening; figure 3 is a top view of the plasma cavity; figure 4 - profile of the dielectric layer on the inner surface of the outer cylinder; figure 5 - laser in section, passing through the axis of the optical resonator.

The described gas laser (Fig. 1) comprises a housing 1 formed by an external cylindrical metal sheath 2 and an internal cylindrical dielectric sheath 3 mounted eccentrically to it. The laser body is sealed at its ends by flanges 4 and 5 (Fig. 3).

The gap between the shells 2 and 3 forms a gas-dynamic channel 6 for circulation of the active medium.

In the narrowest section of the gas-dynamic channel 6, a passage plasma chamber 7 is formed, which is a section of the channel with a symmetric or asymmetric profile of an arcuate or flat shape with a variable height and with an angular opening (Fig. 2a and 2b) in the direction of flow of the active medium. An optical resonator is also located there (FIG. 5).

The value of the angular opening of the channel is determined by the double thickness of the extruded laminar boundary layers (indicated by 22 in Fig. 2a and 2b) on the upper and lower walls of the plasma chamber 7 (i.e., on the walls of the cylindrical shells 2 and 3), as well as the length (width) of the optical cavity along the flow of the active medium and can be calculated in accordance with the relation

α ~ 2δ * / Lr,

Where

Re is the number of Reynolds, defined as ρuh / µ, and µ ~ T ^0.75

Lr is the width of the optical resonator,

δ * - layer thickness equal to 1.74 × Re ^1/2 ,

ρ is the gas density,

u is the average flow rate,

µ is the dynamic viscosity of the gas in the layer,

T is the average temperature of the gas in the layer,

h is the average height of the channel.

At the values of the indicated parameters for typical operating conditions of a CO ₂ laser equal to: Re ~ 3000; δ * ≅1.5 mm; h = 20 mm, the opening angle is 4 °, which will save the intracavity laser beam from losses on the dissipative layers and can increase the efficiency of the optical resonator and, accordingly, the total laser efficiency by 1-2%.

The electrode 8 is made tightly adjacent its surface directly to the outer surface of the inner cylindrical dielectric sheath 3 and is connected to a resonantly tuned high-frequency power supply 9.

The inner surface of the outer cylindrical shell 2 in the zone of formation of the plasma chamber 7 is isolated from the gas stream and plasma by the dielectric layer 10, and the outer cylindrical metal shell 2 is grounded.

Thus, the electrode 8 is moved outside the chamber 7, and therefore, the chamber 7 is “electrodeless”, which determines the specifics of the RF pumping in the described invention.

The gas-dynamic channel 6 is divided by a partition 11 into a section 12 for supplying a cooled active medium and a section 13 for removing the gas stream after pumping and is connected to a bypass channel 14, in which there is a cooling radiator-heat exchanger 15 using water cooling, as well as a centrifugal type turbocharger 16, which ensures speed gas flow of the order of 20,000 rpm and capable of creating a pressure drop from 1.1 to 1.4.

The functions of these elements are ordinary and come down to driving the laser gas through the plasma cavity in a sufficiently necessary volume and cooling the gas after the plasma action, however, due to their technical characteristics, the laser is compact and economical.

In the gasdynamic channel 6, at the section 12 for supplying the cooled active medium to the plasma chamber 7, a leveling screen 17 is installed in the form of a fine mesh or perforated screen with small holes with a diameter of 0.1 mm and a 50% transmittance, which ensure equalization of the gas flow velocity over the cross section of the gasdynamic channel 6 .

The outer cylindrical shell 2 is made of aluminum alloy or of another electrically conductive material and simultaneously plays the role of a laser housing and the role of an external electrode in electrical contact with a high-resistance load due to its grounding.

The inner shell 3 is made of a dielectric material (for example, ceramic based on aluminum oxide, composite material or polymer) and forms a plasma chamber 7 from the inside.

Outer 2 and inner shell 3 are made with round profiles in cross sections.

In the plasma chamber 7, a dielectric coating 10 is deposited on the inner surface of the outer shell 2, made in the form of a dielectric layer with a profile tightly adjacent to the inner surface of the outer shell 2. The coating 10 is used as a neutral material to increase the plasma capacity potential, and also as a deflector that protects the metal surface of the outer cylindrical shell 2 from the action of plasma, and the inner dielectric shell 3 contribute to the stabilization of the plasma.

Deflectors 18 are installed at the entrance to the gasdynamic channel 6, and deflectors 19 are installed at the exit, allowing the volume of the gas stream to be used more economically by passing it directly through the plasma region in the chamber 7. In addition, the presence of deflectors 18 and 19 allows the optical mirrors 20a and 20b to be protected resonator from possible microdamage caused by plasma exposure and bombardment of possible microparticles in the gas stream.

The work of the invention is as follows.

Using a turbocompressor 16, a cold stream A of laser gas, consisting of a mixture of gases [CO ₂ : N ₂ : He] (in the case of a CO ₂ laser), with a static pressure of 50 to 100 Torr, is fed through a leveling screen 17 in the form of a fine mesh gas-dynamic channel 6, where an active gas medium flow is created, enveloping the inner cylindrical dielectric shell 3.

The laser gas stream A, passing between the inlet deflectors 18a and 186, falls into the narrowest region of the gas-dynamic channel 6 (into the resonance region), where it is excited by a high-frequency low-voltage discharge (of the order of 1000 volts) between the electrode 8 and the grounded outer metal shell 2.

In this case, the ionization of gas molecules and atoms occurs through electronic oscillation in thin layers adjacent to the outer surface of the inner dielectric shell 3 and the inner surface of the dielectric layer of the outer shell 2, energy is transferred to the vibrational degrees of freedom of the gas molecules, amplification and generation of resonant radiation between the mirrors 20a and 20b optical system with the subsequent exit of the laser beam 21 from the optical cavity through a partially transmitting mirror 20b.

A hot gas stream B with a temperature of the order of 400 ° K after leaving the plasma chamber 7 follows along channel 6 and enters a cooling radiator - heat exchanger 15. The gas cooled to room temperature is pumped by a turbocharger 16 and then is sent as a stream A for a repeated cycle.

The described laser has an increased efficiency, is extremely compact and lightweight, mechanically stable and technologically simple to manufacture and operate. The invention opens up the real possibility of creating compact and highly efficient lasers using such gas media as a mixture of CO ₂ : N ₂ : He or a mixture of CO: He, as well as other active laser media.

In particular, a CO ₂ laser based on the present invention has the following data:

 Continuous Power Output: 3 kW  Electro-optical laser efficiency: twenty%  Total laser efficiency: fifteen%  Laser Size: 35 × 40 × 100 cm  Laser Weight: 40 kg

Information sources

1. US 4,611,327 A, cl. H01S 3/097, 1986;

2. US 4,817,107 A, Cl. H01S 3/03, 03/28/1989;

3. "Quantum Electronics", t.4, No. 9, 1977, p. 1861;

4. US 4,114,114 A, cl. H01S 3/097, 09/12/1978.

Claims (18)

1. A gas laser with transverse pumping and excitation with a high-frequency discharge, comprising a housing formed by an external cylindrical metal shell and an eccentrically mounted internal cylindrical dielectric shell hermetically connected to the end flanges and forming a gas-dynamic channel for circulating the active medium, a section with the narrowest section which forms a plasma chamber, an optical resonator, an electrode connected to a resonantly tuned high-frequency power supply , a cooling heat exchanger and a centrifugal type turbocharger, creating a flow of active gas medium, enveloping the inner cylindrical dielectric shell, while the gas-dynamic channel in the section with the narrowest section has a symmetric or asymmetric profile of an arcuate or flat shape, variable in height, with an angular opening in the direction of flow of the active medium along the width of the zone of the optical cavity, the electrode tightly adjoins with its surface directly to the outer surface of the inner cylinder of the dielectric shell, the inner surface of the outer cylindrical shell in the said section of the gas-dynamic channel is isolated from the gas flow and plasma by the dielectric layer, and the outer cylindrical metal shell is grounded. 2. The laser according to claim 1, in which the high-frequency power supply unit is configured to supply electrical pulses with frequencies from 10 kHz to 1.5 MHz at alternating current and from 1.5 to 27 MHz in the radio frequency range. 3. The laser according to claim 1, in which the mixture of gases CO ₂ : N ₂ : He is used as the active gas medium. 4. The laser according to claim 1, in which a mixture of CO: He gases is used as the active gas medium. 5. The laser according to claim 1, in which the outer and inner cylindrical shells are made with round profiles. 6. The laser according to claim 1, in which the outer and inner cylindrical shells are made with oval profiles. 7. The laser according to claim 1, in which the outer and inner cylindrical shells are made with different profiles: one with a round and the other with an oval profile. 8. The laser according to claim 1, in which the outer cylindrical shell is made of aluminum alloy or another metal. 9. The laser according to claim 1, in which the outer cylindrical shell is made with air or water cooling. 10. The laser according to claim 1, in which the inner cylindrical shell is made of dielectric material with a wall thickness of 5 to 13 mm 11. The laser of claim 10, in which the inner cylindrical shell is made of ceramic based on aluminum oxide or composite material. 12. The laser according to claim 1, in which the outer cylindrical shell is made by profile extrusion. 13. The laser according to claim 1, in which the thickness of the dielectric coating on the inner surface of the outer cylindrical shell in the plasma cavity is from 0.1 to 5 mm 14. The laser according to item 13, in which the dielectric coating on the inner surface of the outer cylindrical shell and the inner cylindrical dielectric shell is made by plasma spraying and have a multilayer structure formed of particles ranging in size from 45 to 15 microns. 15. The laser according to claim 1, in which the electrode is made of metal and water-cooled. 16. The laser according to claim 1, which is equipped with two deflectors located at the entrance to the optical cavity, and two deflectors located at the exit of the optical cavity. 17. The laser according to claim 1, in which the radiator-heat exchanger and turbocharger are located in a remote channel connected to the gas-dynamic channel by transition elements. 18. The laser according to claim 1, in which the range of angles of opening of the gas-dynamic channel in the area with the narrowest section in the direction of flow of the active medium along the width of the zone of the optical resonator is 1-10 °.

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