Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/09—Processes or apparatus for excitation, e.g. pumping
  • H01S3/097—Processes or apparatus for excitation, e.g. pumping by gas discharge of a gas laser
  • H01S3/0975—Processes or apparatus for excitation, e.g. pumping by gas discharge of a gas laser using inductive or capacitive excitation

Definitions

• the invention relates to a gas discharge arrangement, with a gas discharge path, in particular containing laser gas, in a cylindrical cavity, with a tubular housing surrounding the cylindrical cavity at a distance, and with a microwave transmitter, the microwaves of which for electrical excitation of the gas can be coupled into the housing.
• Such an arrangement in the form of a gas laser is known from DE-OS 37 43 258.
• the known gas discharge path is formed by a discharge module through which laser gas flows and which is designed in a T-shape.
• the laser gas is fed through the foot leg of the T and in the area of the branching of the laser gas flow the microwaves are fed perpendicular to it with a waveguide.
• ignition takes place by means of an ignition pin and thus the formation of a plasma which is transferred from the gas flow into the gas discharge. distance is transported.
• This absorbs microwave energy there, which leads to the formation of a homogeneous discharge across the cross-section of the gas discharge path or the laser beam, which is formed in the gas discharge path, which has resonator end mirrors at its ends.
• the known gas discharge arrangement enables the use of inexpensive microwave transmitters for the electrical excitation of the laser gas, its function requires a gas flow or a gas circulation. Controlled gas circulation pumps and pipelines are required for this gas flow or for this gas circuit, which increases the cost of the arrangement.
• the known arrangement uses a swirl flow to achieve the desired homogeneous discharge. This influences the quality of the laser radiation.
• the invention is based on the object of improving a gas discharge arrangement with the features mentioned at the outset in such a way that homogeneous plasma formation also takes place when a gas flow is not given or is only laminar.
• This object is achieved in that between the inner wall of the housing and the cavity forming the gas discharge path there is a distance which stabilizes the gas discharge and which is larger in air in the direction of the strongest field components of the microwaves than the largest free diameter of the the cavity penetrated by the microwaves.
• the plasma formation or gas discharge is sufficiently stabilized. This is due to the distance between the inner wall of the housing and the gas discharge line. This distance can be made sufficiently large to achieve the desired stabilization of the gas discharge. Stabilization usually occurs when the aforementioned distance is greater than the largest free diameter of the cavity.
• the gas Discharge arrangement formed in cross section so that the cavity forming the gas discharge path is arranged in the immediate vicinity of another wall section of the inner wall of the housing or to a field-forming housing installation part while maintaining the distance to the housing inner wall.
• the immediate vicinity of the cavity to the housing or a field-forming housing installation part has the effect that the cavity is arranged in an area in which the field lines run perpendicular to the metal housing or to the metal housing installation part.
• a correspondingly uniform field structure results within the cavity.
• the tubular housing can be dimensioned differently for this aforementioned uniform field structure, in particular with regard to diameter and length.
• the housing is a microwave waveguide or, if its length is suitably designed, a microwave resonator.
• the microwaves are coupled in by means of a capacitive or inductive antenna, or by means of a waveguide coupling, the configuration of which is likewise carried out with regard to the desired field formation described above.
• the plasma of the gas discharge arrangement can be used to generate light, for example in argon lamps.
• gas discharge arrangement When using laser gas, it is possible to use the gas discharge arrangement to generate laser light in a laser resonator, for example as a pump light source for solid-state lasers, or to amplify laser light.
• the gas discharges generated with the gas discharge arrangement according to the invention are preferably used to excite gas lasers.
• a metal tube coaxial therewith is advantageously arranged in the metallic tubular housing.
• This is a field-forming housing component.
• This metallic inner conductor, together with the tubular metallic housing, forms a coaxial waveguide, in which the electric field is formed in a particularly uniform manner in the radial direction.
• the metal tube can advantageously also be used for mechanical support in the gas discharge arrangement.
• the metal pipe is easy to manufacture and encloses a field-free space that is used for water cooling can be, that is, for the dissipation of the process heat of the gas discharge line.
• the cylindrical cavity forming the gas discharge path is circular or annular.
• the circular cylindrical cavity offers the optimal cross-sectional design for a correspondingly circular laser beam.
• a plurality of laser beams or beam paths can be arranged in an annular cylindrical cavity, which are grouped around a core, for example around a coaxial metal tube.
• the arrangement is advantageously designed such that the circular and the annular cylindrical cavity are delimited on the outside by a dielectric gas tube and the annular cylindrical cavity is delimited on the inside by the coaxial metal tube.
• the limitation of the cylindrical cavity or the gas discharge path by dielectric gas tubes enables a structurally free configuration of the gas discharge arrangement in the area of a coaxial hollow waveguide.
• the arrangement can also be designed in such a way that the housing has a rectangular cross section in which a cavity forming the gas discharge path is provided at a distance from at least one broad side of the housing.
• the housing is a rectangular waveguide in which hollow wave types can be formed using the microwave transmitter, the strongest electrical field components of which are arranged perpendicular to the largest cross-sectional width and thus perpendicular to the outer circumference of the cavity forming the gas discharge path and thus a precondition for a homogeneous large-volume gas discharge.
• At least one dielectric gas tube is arranged inside the rectangular metallic housing on a wall forming one of the broad sides of the housing and is thus connected in a heat-conducting manner.
• the gas pipe or several gas pipes are arranged in a region of the housing where the electric field lines of the strongest field components run perpendicular to the housing wall, correspondingly uniformly also in the gas discharge path, which is consequently excited uniformly.
• At least one dielectric gas tube is arranged on the wall forming one of the broad sides of the housing within the rectangular metallic housing and is thus connected in a heat-conducting manner.
• the arrangement can be extremely simple in that the gas pipe is simply placed on one longitudinal wall and fastened there. The immediate vicinity between the metallic housing and the gas tube ensures without further ado that the gas discharge path is penetrated by the strongest field components in the sense of a uniform electrical excitation by the microwave fields.
• All gas discharge sections are independent of one another, that is to say they can be operated with different gas pressures and also with different dimensions, for example for laser beams with different cross sections and intensities.
• the arrangement can also be designed such that a dielectric cooling tube which surrounds the dielectric gas tube at a distance is filled with a coolant which has a low absorption coefficient for the microwaves when it is arranged in the microwave field.
• the coolant allows the power loss of the gas discharge to be transported away in the form of heat without absorbing excessive portions of the energy of the microwaves and, as a result, being removed from the electrical excitation of the gas.
• silicone oil can be used as a coolant with a low absorption coefficient. Under certain circumstances, this is difficult to handle or, in particular in the case of cross sections with a small gap width, is to be pumped through the cooling system due to high adhesion to the walls with high pumping capacity.
• the arrangement is therefore designed in an embodiment of the invention so that the distance between the housing inner wall and the cavity forming the gas discharge gap is filled with a solid dielectric of high thermal conductivity. It is understood that the distance is correspondingly shorter due to the higher dielectric constant, possibly smaller than the free diameter of the cavity.
• the solid dielectric primarily serves to dissipate the heat loss from the gas discharge path. However, it can also be used to define the cavity forming the gas discharge path, so that, for example, the outer dielectric gas tube can be omitted.
• the dielectric is, for example, an aluminum oxide ceramic as used for sanitary ceramics. This solid dielectric has low material costs.
• the housing is surrounded on the outside by a cooling water jacket and / or the metal tube (16) is filled with cooling water.
• the cooling water With the cooling water, the heat loss of the gas discharge line can be dissipated with little pumping power. There is no need to take into account any absorption of microwave power, since the rooms in question are field-free.
• the rectangular housing is filled with a dielectric spacer in cross-section except for a gap forming the cavity that extends in the direction of the greatest cross-sectional width.
• the arrangement is also designed so that between the gas tube delimiting the cavity and the metallic housing there are connecting webs made of metal where the The microwave mode used has a minimal tangential electrical field strength component.
• the connecting webs process heat generated in the discharge path can be removed to the metallic housing and from there by means of cooling.
• the metallic connecting webs do not hinder the longitudinal propagation of the microwave fields in the longitudinal direction of the housing, since they are arranged in areas of minimal tangential field components.
• the connecting webs are particularly advantageous when the cut-off frequency of the housing is in the range of the excitation frequency of the microwaves because it then has a specific one. Force microwave mode.
• the above-mentioned object can also be achieved with a gas discharge arrangement, with a gas discharge path, in particular containing laser gas, in a cylindrical cavity, with a tubular housing surrounding the cylindrical cavity at a distance, and with a microwave transmitter whose microwaves in the metallic housing can be coupled in, and with a dielectric gas tube enclosing the gas discharge path, which is surrounded on the outside by a metal tube, one end of which forms an area for a high electrical field strength with an end wall of the housing.
• gas discharge in the sense of the above-mentioned task also becomes at the other end of the housing in that the metal tube forms an area for high electrical field strength at its two ends, each with an end wall of the housing.
• a gas discharge can also be formed between the two ends of the metal tube, that is to say in a region which is discharge-free in the known arrangement.
• the total length of the gas discharge path can thereby be increased without increasing the structural outlay.
• the maximum length is limited to values in the range of a few tens of centimeters. This results from the required dimensions of the arrangement, their loss of electrical excitation energy, the required pressure in the gas discharge path and the limited transmission power of the microwave transmitter.
• the arrangement is designed such that the dielectric gas tubes and / or metal tubes and / or cooling tubes of a plurality of gas discharge arrangements are arranged one behind the other in the sense of free passage, and that a correspondingly large number of those surrounding the tube structure are formed there are tubular housings into which microwaves can be coupled.
• gas discharge paths of several gas discharge arrangements are thus connected to one another and can produce gas discharges which protrude beyond the end faces of the tubular housings and which are connected to one another or merge into one another, so that the desired greater discharge path length is achieved.
• gas discharge arrangement can be designed such that it works with several microwave transmitters, one of which have comparatively low power, but are inexpensive because of their widespread use, for example in microwave ovens.
• the metallic housing has a diameter at which its cutoff or resonance frequency lies in the range of the excitation frequency of the microwaves.
• FIG. 1 shows a longitudinal section through a first embodiment of an arrangement according to the invention with a coaxial design of a microwave structure
• FIG. 1 shows the cross section II of FIG. 1
• FIG. 1b shows a cross section similar to FIG. 2
• FIG. l similar metallic microwave structure with a plurality of gas discharge sections parallel to one another
• FIGS. 3, 3a microwave structures with rectangular cross sections FIG. 4 a further embodiment of the invention
• FIG. 5 a series connection of several gas discharge sections.
• the gas discharge arrangement shown in FIG. 1 essentially consists of a tubular housing 13 in which a metal tube 16 is arranged coaxially.
• the metal tube 16 is surrounded by a dielectric gas tube 17, so that a cylindrical cavity 11 is present between this tube 17 and the metal tube 16.
• This cavity 11 is filled with gas, for example argon, and forms the gas discharge path 10.
• the outer dielectric gas tube 17 is surrounded concentrically by a dielectric cooling tube 15 at a distance 24.
• This distance 24 is filled with a coolant 19 which has a low absorption coefficient for the microwaves.
• the metal tube 16 is also filled or cooled accordingly. Since it encloses a field-free space, water can be used for cooling.
• the arrows on the right side of the arrangement indicate that the coolant 19 and / or the gas are to be circulated.
• the circulation or pumping around of the cooling liquid 19 is necessary in order to transport away the process heat. Circulation of the laser gas is not necessary for the gas discharge to function. The desired stable, homogeneous plasma is obtained even without such a circulation.
• a distance 12 is present between the housing 13 and the cavity 11, into which the microwaves are fed by an antenna 25 of a microwave transmitter (not shown).
• a microwave transmitter for example, a 2.45 GHz magnetron is used as the microwave transmitter.
• the housing 13 forms with the metal tube 16 a coaxial metal waveguide in which the electrical microwave field with its strongest field components radially to the inner wall 14 of the housing and above all perpendicular to the outer circumference 11 'of the cavity 11 forming the gas discharge path 10 and thus ent ⁇ spreading vertically in the gas discharge path 10 itself.
• This radial spreading or radial formation of the electrical microwave field brings about a correspondingly uniform electrical excitation of the gas of the gas discharge path, combined with a discharge distribution which is homogeneous over its cross section.
• the spacing 12 between the gas discharge path 10 and the inner wall 14 of the housing 13 serves to stabilize the discharge, which has no metallic internals which hinder the propagation of the microwaves and forms a capacitive series resistor, which has a stabilizing effect on the discharge.
• the housing 13 in FIG. 1 is a coaxial microwave waveguide. Its diameter can be such that its cut-off frequency lies in the range of the excitation frequency of the microwaves.
• the length of the housing 13 is to be matched to the desired field distribution, as is the coupling of the microwaves via the antenna 25.
• a microwave resonator can also be created from the microwave waveguide of FIG. 1 by reducing the length of the housing 13. is chosen speaking.
• the housing 13 can thus be used to carry this cooling tube 15 .
• the cross-sectional dimensioning of the gas discharge path 10 of FIG. 1 and all similar configurations depends, among other things, on the gas pressure. The latter is chosen as high as possible in order to achieve the greatest possible laser power or the greatest possible amplification power.
• the power of the microwave transmitter has a further influence on the volume of the gas discharge path 10 to be excited. Since inexpensive microwave transmitters have a power of only 1 KW because of their widespread use in microwave ovens, there is a corresponding limitation in length or length when used the outer diameter of the gas discharge path 10.
• Fig. 1b relates to an embodiment similar to Fig. 1, 1a, in which, however, there are connecting webs 28 made of metal between the gas tube 17 enclosing the gas discharge path 10 and the outer metal housing 13. Copper, for example, is used as the metal, which conducts heat very well. With these webs it is possible to dissipate process heat from the gas section 10.
• the gas pipe 17 has a comparatively thick wall, in order to be able to conduct the process heat generated between two connecting webs 28 to these webs.
• a somewhat thicker gas pipe 17 also has the advantage that, as shown, the connecting webs 28 can be assembled with the gas pipe 17 in the sense of a low heat transfer resistance, e.g. by gluing. With the aid of the connecting webs 28, it is possible to omit the cooling tube 15 according to FIG. 1 and to dissipate the process heat derived into the housing 13 with a cooling water jacket 21 surrounding this housing.
• the connecting webs 28 are arranged where the mode of the microwaves used has no tangential component.
• the longitudinally arranged connecting webs 28 thus hinder the spread of the micro don't wave. They are also advantageous in the event that the limit frequency of the housing 13 is in the range of the excitation frequency of the microwaves, since they then force the desired mode or prevent the microwave field from accidentally settling in an undesired mode.
• the microwave mode is an H 2 i ⁇ mode.
• FIG. 2 shows a gas discharge arrangement only in cross section, the longitudinal extent of which may be similar to FIG.
• a metal tube 16 which can achieve the desired configuration of the electrical microwave field, namely with the strongest field components radially, in particular with respect to the metal tube 16 itself.
• gas discharge sections 10 which run parallel to one another and the metal tube 16. It would also be possible to arrange three, four or more such gas discharge sections 10.
• Each gas discharge path 10 is delimited on the outside by a dielectric gas tube 17, which in turn is surrounded by / at a distance 24 from a dielectric cooling tube 15, the space between the two tubes 15, 17 being filled by a coolant 19 which can be recirculated.
• the gas discharge paths 10 have a spacing 7 that stabilizes the gas discharge from the housing inner wall 14.
• the cross-sectional design according to FIG. 2 can also be modified according to requirements, for example a plurality of gas discharge lines 10 or their dielectric gas tubes 17 can be accommodated in a single cooling tube which surrounds all tubes 17.
• the gas discharge paths 10 could also be arranged adjacent to the inner wall of the housing 13, where, due to the radial field formation, a uniform excitation of the gas in the gas discharge path 10 is also achieved.
• the housing 13 is designed as a rectangular metallic tube, that is to say as a microwave waveguide, in which certain types of waves with their strongest field components are perpendicular to the wide housing inner walls 14, but above all perpendicular to the outer peripheral surface 11 'of the cavity 11 in the direction perpendicular to the plane of the representation.
• the cavity 11 or the gas discharge path 10 extend over the largest part of the cross-sectional width B of this rectangular cross-section of the housing 13 and is arranged in the vicinity of a broad side 13 ′′ of the housing 13.
• the distance 12 between the cavity 11 and the other inner wall of the housing is completely filled by a dielectric spacer 22, which therefore delimits the gap or the cavity 11, so that special limiting dielectric gas plates or tubes are not necessary .
• the heat dissipation from the gas discharge path 10 takes place without problems via the metallic housing 13.
• Waves of the Hio type are particularly suitable as microwaves. They result in a field strength distribution which is formed between the narrow sides 13 '' 'of the housing 13 in accordance with a circular function with a central maximum. Since the field strength is therefore zero or minimal near the narrow sides 13 '' 'of the housing, the dielectric spacer 22 can have projections or strips 22' in this region which ensure support of the U-shaped spacer 22, contact of the gas prevent the discharge gap 10 with the metal of the housing 13 except with a partial section of the one inner wall 14 and at the same time serve to dissipate heat from the gas discharge gap 10.
• the microwave energy is radiated with an antenna, not shown, which has a design adapted to the cross section of the arrangement, for example according to FIG.
• the heat lost in the gas discharge path 10 is removed by the spacer 22, which has a high thermal conductivity and is at the same time designed as a solid dielectric 20.
• a solid dielectric 20 For this purpose, an aluminum oxide ceramic is used, for example, which is commercially available.
• FIG. 3a also shows a housing 13 in the form of a rectangular metallic tube, in which the microwaves spread as described for FIG.
• the special feature is that a plurality of dielectric gas pipes 17 are arranged in the housing 13 near an inner wall 14 of a broad side 13 ′′ of the housing 13, namely at a distance from the narrow sides 13 ′′ ′′ of this housing 13, that is to say in the region the maximum of the field strength with field lines arranged perpendicular to the broad side 13 ′′.
• Each gas tube 17 encloses a circular cavity 11, which forms the gas discharge path 10.
• Each gas tube 11 is connected to the inner wall 14 in a heat-conducting manner, namely, for example, by means of an adhesive 28, so that the process heat of the gas discharge path 10 resulting from the gas discharge easily contacts the metallic one via the comparatively good heat-conducting gas tube 17 and the likewise good heat-conducting adhesive 28 Housing 13 for further heat dissipation in the cooling water jacket 21 can be derived.
• FIG. 3a a field line of the strongest field components of the microwaves is shown in dashed lines at 29. It is clearly evident that the field line 29 within the distance 12 of the cavity 11 of the upper inner wall 14 is significantly longer than within the cavity 11. Accordingly, the distance 12 in the direction of the strongest field component is also greater than the largest free diameter D of the cavity 11. ' This also applies in principle to all other embodiments, cf.zBFig.la.
• FIG. 4 shows a gas discharge arrangement, which likewise works with a tubular metallic housing 13 and a metal tube 16 arranged coaxially therein.
• metal tube 16 is arranged outside of the cavity 11 and on both sides at a distance 26 from the end walls 13 'of the housing 13. As a result, it cannot serve to enclose the gas of the gas discharge path 10. Rather, this is provided by a dielectric gas tube 17 that extends over the entire required length of the gas discharge arrangement and beyond.
• the gas tube 17 In the interior of the gas tube 17 there is a gas tube 18 which is internally delimited by the gas discharge path 10 and which, on the other hand, is filled with cooling liquid 19.
• the distance 12 between the inner wall 14 of the housing and the cavity 11 or the metal tube 16 or the gas tube 17 could be filled with a solid dielectric.
• the distance 26 between the two ends 16 of the metal tube 16 from the end walls 13 ' is designed such that a region 23 for high electrical field strength results in the gas tube 17, in which a plasma discharge ignites when microwave energy is fed in through the antenna 25.
• outward surface waves are formed on the inner wall of the dielectric gas tube 17 and are stabilized by the wall contact.
• the creation of an annular cylindrical cavity 11 within the metal tube 16 has the effect that not only on the inner wall of the gas tube 17, but also on the outer wall of the gas tube 18 near the areas 23, a surface wave develops which is directed out of the housing 13 .
• the gas discharge formed by the surface wave is not concentrated on the near wall areas of the tubes 17, 18, but rather there is a homogeneous discharge over the entire cross section of the cavity 11.
• such an arrangement with two areas 23 has the effect that the homogeneous gas discharge also extends in the cavity 11 between the areas 23.
• the maximum length of the gas discharge arrangements is limited to a few ten centimeters due to the various parameters. borders. However, it is desirable to stimulate plasmas of greater length. This is achieved by an arrangement according to FIG. 5.
• Several gas discharge arrangements are arranged one behind the other in terms of flow, in that the dielectric gas tubes 17 and the metal tubes 16 are connected together or in one piece. 5 shows a single continuous metal tube 16, through which a coolant 19 flows and on the outside is surrounded by a dielectric gas tube 17, which forms the gas discharge path 10 with the metal tube 16.
• housings 13 which have the required radial distance 12 from the gas discharge path 10 and which each receive microwave energy radiated via an antenna 25.
• the microwaves are fed in a metallic waveguide 27 in the direction of the arrow, microwave power being taken from the waveguide 25 by the antennas and fed into the housing 13.
• the configuration of the gas discharge arrangement according to FIG. 5 is only an example. All of the design options given for the above-described arrangements are also possible in the case of cascading in accordance with FIG. 5. They are particularly advantageous in the case of arrangements according to FIG. 4, because there the gas discharge extends particularly far in both directions over the end walls 13 'of the housing 13.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Optics & Photonics (AREA)
• Lasers (AREA)

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• 1989
  • 1989-07-14 DE DE19893923277 patent/DE3923277A1/de active Granted
• 1990
  • 1990-07-12 WO PCT/DE1990/000526 patent/WO1991001580A1/de unknown
  • 1990-07-12 AU AU59412/90A patent/AU5941290A/en not_active Abandoned

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