Radio frequency excited gas laser

Abstract

Radio frequency excited carbon dioxide (CO2) or carbon monoxide (CO) gas lasers include two electrodes with passivated surfaces within a sealed enclosure. A feature in a ceramic plate or ceramic cylinder located between the electrodes defines the gain volume. The surface of the ceramic plate or ceramic cylinder is separated from the passivated surfaces of the electrodes by a small gap to prevent wear. Reducing the compressive forces that secure these components within the enclosure further reduces wear, thereby extending the useful life of the gas laser.

Description

[0001] priority

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 62 / 970475, filed February 5, 2020, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention generally relates to carbon dioxide (CO2) and carbon monoxide (CO) gas lasers. More particularly, this invention relates to radio frequency (RF) excited CO2 and CO gas lasers having a ceramic assembly that confines the RF excitation gas. Background Technology

[0004] CO2 lasers have been used in industrial processes for decades, where their infrared (IR) wavelength and relatively high power are advantageous. The laser medium is a gas discharge in a CO2 gas mixture. This gas mixture typically comprises 10% to 20% CO2 and is maintained at a pressure below one atmosphere. A gas discharge is generated by energizing the gas mixture by applying a current or radio frequency field between two electrodes. CO2 lasers can provide output laser radiation at infrared wavelengths ranging from approximately 9 micrometers (μm) to approximately 11 μm. Recently, CO lasers have been commercialized, providing output laser radiation at shorter infrared wavelengths in the range of approximately 5.2 μm to approximately 6.0 μm.

[0005] Gas lasers can be configured as waveguide lasers or plate lasers. In a waveguide gas laser, a gas discharge is established within a long and relatively narrow waveguide. A laser resonator is formed around the energized gas mixture via resonator mirrors located at both ends of the waveguide, which guide the laser radiation longitudinally. The narrow waveguide confines one or more laser radiation modes in two mutually orthogonal transverse directions. Stimulated emission amplifies the laser radiation during multiple passes through the gas discharge. CO2 and CO waveguide lasers are capable of providing inherently high-quality output beams with good power and wavelength stability, but with relatively low average power. Typically, the average power is less than about 150 watts (W). Such waveguide CO2 lasers are described in U.S. Patents 6,192,061 and 6,788,722, each of which is the property of the assignee of this invention, and the full disclosure of each patent is incorporated herein by reference.

[0006] In a plate gas laser, a gas discharge is established within a volume between the planar waveguide surfaces of two closely spaced electrodes. A laser resonant cavity is formed around the energized gas mixture by two resonant mirrors. In one transverse direction, a small gap between the two electrodes (“discharge gap”) defines a waveguide that confines the laser radiation mode. In the orthogonal transverse direction, the resonant mirrors typically define an unstable laser resonant cavity. Laser radiation exits the unstable laser resonator as an approximately collimated beam, passing through a hole in one of the resonator mirrors or through the outer edge of one of the resonator mirrors. Such plate CO2 lasers are described in U.S. Patents 6,256,332 and 7,263,116, each of which is the property of the assignee of this invention, and the full disclosure of each patent is incorporated herein by reference.

[0007] Plate CO2 and CO lasers are capable of outputting beams with average power up to approximately 8 kilowatts (kW). However, the output beam inherently has an elongated cross-section. Additional beam-tuning optics are required to convert the output beam into a more usable cross-sectional shape, such as a circular shape. Plate CO2 lasers typically operate in pulsed mode, providing laser radiation pulses with high peak power. High-power waveguide or plate gas lasers require water cooling or forced air cooling to remove waste heat.

[0008] Figure 1A The waveguide gas laser shown is an early configuration that confines the gas discharge within a glass or ceramic tube sandwiched between two shaped electrodes. Another common waveguide structure, such as... Figure 1B As shown, the gas discharge is confined within a channel fabricated as a rectangular ceramic plate sandwiched between two planar electrodes. In both configurations, mirrored folding of the waveguide can be used to increase the gas discharge volume without significantly increasing the overall size of the laser. A similar configuration for a plate gas laser is shown below. Figure 1C As shown, a thin ceramic plate provides diffusion cooling for the gas and enables the average power of the flat-plate gas laser to reach kilowatts. U.S. Patent Application 2019 / 0280448, owned by the assignee of this invention (the entire disclosure of which is incorporated herein by reference), describes several arrangements of high peak power plate CO2 lasers cooled by conduction cooling through the outer surface of the laser housing.

[0009] Laser efficiency and response to changes in radio frequency power depend on the precise concentration of components in the gas mixture. In many modern industrial lasers, the laser housing is "sealed," meaning there is no circulating gas to continuously replenish the gas discharge. Such sealed lasers are smaller, simpler, and require less maintenance. These lasers use passivated metals within the housing; for example, electrodes made of passivated aluminum. A stable passivation layer on the metal surface prevents the depletion of atomic and molecular oxygen generated by the dissociation of excited CO2 or CO molecules. Otherwise, this oxygen would form metal oxides on the exposed surface, thereby reducing the CO2 or CO concentration in the gas mixture.

[0010] One drawback of the aforementioned configuration, in which a ceramic tube or plate is sandwiched between metal electrodes, is that friction between them can remove the passivation layer from the electrodes. This friction is caused by the difference in thermal expansion and contraction in response to changes in the applied radio frequency power. In CO2 lasers, the consumption rates of oxygen and CO2 are slow enough that the degraded laser performance can be considered a nuisance, which can be partially overcome by increasing the radio frequency power. However, even a tiny change of about 0.1% in the CO concentration in the CO gas mixture can cause the CO laser to fail.

[0011] There is a need for a hermetically sealed gas laser architecture with a longer operating life, without compromising the advantages of the aforementioned metal and ceramic configurations. Preferably, this architecture will add minimal cost and complexity. Invention Overview

[0013] In one aspect, a radio frequency excited gas laser according to the invention comprises: a housing containing the gas; a first electrode extending along a longitudinal axis; and a second electrode extending along the longitudinal axis and parallel to the first electrode. The first and second electrodes are located within the housing and spaced apart from each other by a distance D. A dielectric plate is located between the first and second electrodes, defining a gain volume when the gas is excited by a radio frequency field. The dielectric plate has opposing first and second surfaces parallel to the first and second electrodes. The first surface of the dielectric plate is substantially separated from the first electrode by a first gap, and the second surface of the dielectric plate is substantially separated from the second electrode by a second gap.

[0014] In another aspect, the radio frequency excited gas laser according to the invention includes: a housing containing the gas. A hollow dielectric cylinder is located within the housing and oriented along a longitudinal axis. When the gas is excited by a radio frequency field, the dielectric cylinder defines a gain volume. The gain volume is the hollow interior of the dielectric cylinder. A first electrode has a first surface concentric with the outer surface of the dielectric cylinder. A second electrode has a second surface concentric with the outer surface of the dielectric cylinder. The first and second electrodes are located on opposite sides of the dielectric cylinder. The first surface is separated from the outer surface by a first gap, and the second surface is separated from the outer surface by a second gap. Brief description of the attached diagram

[0016] The accompanying drawings, which are incorporated in and constitute a part of this specification, schematically illustrate preferred embodiments of the invention and, together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

[0017] Figure 1A and 1B It is a cross-sectional view, schematically illustrating a common waveguide configuration for gas lasers.

[0018] Figure 1C It is a cross-sectional view, schematically illustrating a common plate configuration for gas lasers.

[0019] Figure 2 is a perspective view that schematically illustrates the basic features and functions of existing CO2 or CO plate lasers.

[0020] Figure 3 is a partially cut-off perspective view, schematically illustrating a prior art CO2 or CO slab laser, including a ceramic plate (shaded) defining a rectangular gain volume.

[0021] Figure 4 is a partially cut-off perspective view, schematically illustrating a prior art CO2 or CO waveguide laser, including a ceramic plate (shaded) with a channel that defines the gain volume.

[0022] Figure 5 is a cross-sectional view, typically seen in direction 5-5 of Figure 4, further illustrating prior art CO2 or CO waveguide lasers.

[0023] Figure 6 This is a cross-sectional view, schematically illustrating a preferred embodiment of a radio frequency excited CO2 or CO slab laser according to the present invention, including a grounded first electrode as the inner surface of the housing, a live second electrode, a dielectric plate located therebetween and separated by first and second gaps respectively, and a positioning pin for maintaining alignment of the dielectric plate.

[0024] Figure 7 Is with Figure 6An enlarged view of the same cross-section schematically shows the precision ball used to create the first and second gaps, the registration block used to fix the dielectric plate, the locating pin used to fix the insulating rod, and the spring used to provide controlled force and electrical connection.

[0025] Figure 8A and 8B Is with Figure 6 and 7 Enlarged views of different cross-sections schematically illustrate examples of insulating rods used to prevent parasitic discharges and locating pins used to secure sensor assemblies.

[0026] Figure 9 yes Figure 6-8B The cross-sectional plan view of the plate laser of the present invention schematically illustrates the exemplary positions of the precision ball, the positioning block, and the positioning pin.

[0027] Figure 10 This is a cross-sectional view, schematically illustrating a preferred embodiment of a radio frequency excited CO2 or common waveguide laser according to the present invention, including first and second electrodes and a hollow dielectric cylinder located therebetween and separated by first and second gaps, respectively. Invention Details

[0029] Referring now to the accompanying drawings, where similar components are designated by similar numbers, Figure 2 is a perspective view schematically illustrating the basic features and functions of a prior art flat-panel CO2 or CO laser 10. The configuration of the flat-panel laser 10 is as follows: Figure 1C As shown, it includes parallel upper and lower electrodes 12 and 14, which are rectangular in shape. Electrodes 12 and 14 are separated by a ceramic plate 16, thereby defining a discharge gap between them. The ceramic plate 16 is highlighted by diagonal shading.

[0030] The discharge gap is located in an unstable resonator formed by two concave resonator mirrors 18 and 20. The RF power supply 22 is electrically connected to the upper electrode 12. The lower electrode 14 is grounded. Typically, the electrodes are located within a hermetically sealed enclosure (not shown) containing a gas mixture. Gas mixtures of CO2 and CO lasers are well known in the art. The composition of the gas and the pressure may vary according to the manufacturer's preferences and are typically proprietary.

[0031] When RF power is applied to the upper electrode 12 to energize the gas mixture, a gas discharge is generated in the discharge gap, thereby providing optical gain in the resonator. The excitation gas is confined within a hollow ceramic plate 16, thus defining the gain volume. As shown by dashed lines, laser radiation 24 circulates within the resonator and is gradually amplified by the optical gain. The amplified laser radiation illuminates resonator mirrors 18 and 20. A portion of it overflows the resonator, passes through resonator mirror 18, and becomes output laser radiation 26. Output laser radiation 26 forms an extended beam with a rectangular cross-section. Optional beam-adjusting optics 28 can convert the beam into a more useful form, such as a collimated beam 30 with a circular cross-section. The beam-adjusting optics are typically located outside the hermetically sealed housing.

[0032] Figure 3 is a partially cut-off perspective view, schematically illustrating an example of a plate laser 10. The hermetic housing comprises a hollow metal extrusion 40, partially cut off to show the internal components and their arrangement within the laser. The extrusion 40 is electrically grounded. End plates (not depicted) at both ends of the extrusion seal the laser housing. Each end plate contains a resonator mirror.

[0033] The inner surface 42 of the extrusion 40 provides a ground electrode for the plate laser 10. Another charged electrode 44, having a lower surface 46, is located within the extrusion 40. The ground surface 42 and the charged surface 46 extend along the length of the extrusion. The charged surface 46 is separated from the ground surface 42 by a ceramic plate 16. A hollow space in the ceramic plate defines the width and height of the gain volume.

[0034] A pair of ceramic insulating rods 48 electrically isolate the charged electrode 44 from the grounded extruder 40. The insulating rods 48 also support the inductor assembly 50, which includes multiple inductors to ensure uniform gas discharge throughout the gain volume. An electrical feedthrough 52 connects the RF power of the RF power supply to the charged electrode 44. The feedthrough 52 is electrically connected to the charged electrode 44 and electrically isolated from the grounded extruder 40. The inductor assembly 50 is electrically connected to the extruder 40 via a spring bar 54, forming a complete parallel resonant circuit. The spring bar 54 and the insulating rods 48 work together to hold the charged electrode 44, the ceramic plate 16, and the inductor assembly 50 in proper position within the extruder. Very strong spring bars are required to apply a large clamping force to secure all these components. The clamping force must be sufficient to precisely hold these components in place during the fabrication, handling, and transport of the plate laser.

[0035] Figure 4 is a partially cut-off perspective view, schematically illustrating a prior art waveguide CO2 or CO laser 60. Figure 5 is a cross-sectional end view of the waveguide laser 60, which is folded and has... Figure 1BThe configuration is shown. The waveguide laser 60 is similar to the plate laser 10, but its channels 62 are machined into the ceramic plate 64 that defines the waveguide. Here, the channels 62 have a rectangular cross-section with acute angles. These channels may also have rounded corners or a circular cross-section. Otherwise, the parts arrangement within the extrusion 40 is the same. The resonator consists of two resonator mirrors and two folded mirrors, which are incorporated into the end plate (not shown in the drawings). One resonator mirror is highly reflective at the laser radiation wavelength. The other resonator mirror partially reflects, allowing the output laser radiation to couple out of the resonator.

[0036] Figure 6 This is a schematic cross-sectional end view illustrating one embodiment of a radio frequency excited gas laser 80 according to the present invention. The gas laser 80 includes a housing 82 containing gas. Here, the housing 82 is in the form of a hollow metal extrusion. A first electrode 84, in the form of an inner surface of the housing 82, is elongated along the longitudinal axis of the gas laser (perpendicular to the plane of the drawing). A second electrode 86 extends along the longitudinal axis and is parallel to the first electrode. A dielectric plate 88 having a processed channel 90 is located between the first and second electrodes. The channel 90 extends along the entire length of the dielectric plate 88 and is arranged to form a folded waveguide. The channel 90 defines the gain volume when the gas is excited by a radio frequency field. The first electrode, the dielectric plate, and the second electrode are located within the housing and are therefore immersed in the gas.

[0037] The dielectric plate 88 has a first surface 92 parallel to the first and second electrodes and an opposing second surface 94. The first surface 92 separates from the first electrode 84 by a first gap, and the second surface 94 separates from the second electrode 86 by a second gap. The first and second gaps are created and maintained by precision balls 96 located in holes through the dielectric plate 88, the diameter of which is slightly larger than the precision balls. Each precision ball 96 contacts both electrodes, and therefore the precision balls are made of an electrically insulating material. The diameter of the precision balls 96 is chosen to achieve the desired sum of the separation distances of the first and second gaps. As shown, optional grooves can be machined into the second electrode 86 to precisely set these separations. Alternatively, grooves can be machined into the housing 82, or complementary grooves can be machined into both the second electrode and the housing. Thus, the dielectric plate 88 “floats” between the two electrodes and has no mechanical contact with them.

[0038] The effective operation of the gas laser 80 depends heavily on maintaining the precise alignment of the dielectric plate 88 relative to the resonant and folding mirrors. Lateral alignment is maintained between the dielectric plate 88 and the preloaded spring assembly 100 connected to the opposing inner surfaces of the housing 82 by compression positioning blocks 98, each positioning block 98 mating with a spring assembly 100. At least two pairs are required to secure the dielectric plate within the housing, thereby positioning it relative to the mirrors. Preferably, these pairs are located close to each end of the dielectric plate. The dielectric plate can be further secured by additional positioning blocks and / or spring assemblies located between it.

[0039] The dielectric plate 88 is maintained in longitudinal alignment by locating pins 102 located in holes passing through the dielectric plate and in corresponding blind holes in each electrode. At least one locating pin 102 is required to securely position the dielectric plate relative to the housing.

[0040] The second electrode 86 is secured to the horizontal axis (drawing) and vertical axis by locating pins 102. For ease of description, terms such as "horizontal" and "vertical" are used herein, but this does not imply a restriction on the spatial orientation of the gas laser during operation. At least two locating pins 102 are required to mechanically constrain the second electrode 86 to the dielectric plate 88 and the housing 82. Preferably, the locating pins 102 will be made of an electrically insulating material. Preferably, these locating pins are widely spaced relative to the length of the second electrode 86. The second electrode can be further secured by additional locating pins located therebetween.

[0041] The sensor assembly 104, a pair of insulating rods 106, and the second electrode 86 are fixed to the vertical horizontal axis (in the drawing) by the compressive force provided by the spring 108. The insulating rods 106 are highlighted by diagonal shading. Figure 7 This is an enlarged view; its cross-section is similar to... Figure 6 Similarly, details of these components in the gas laser 80 are illustrated. Springs 108 located on each horizontal side of the gas laser 80 push these components onto a precision ball 96. The first electrode 84 and the second electrode 86 are spaced apart by a distance D, the first surface 92 is separated from the first electrode 84 by a first gap d1, and the second surface 94 is separated from the second electrode 86 by a second gap d2.

[0042] These separations are uniform throughout the entire volume between the parallel electrodes. Preferably, the first gap is at least 0.001D (0.1% of D), and the second gap is also at least 0.001D. More preferably, the first gap is at least 0.0025D (0.25% of D), and the second gap is also at least 0.0025D. The practical upper limit for each of the first and second gaps is approximately 0.15D (15% of D). The distance D between the electrodes is typically in the range of about 2 mm to about 6 mm. Precision spheres 96 with a diameter specification tolerance of 2.5 μm or less will achieve sufficient uniformity. Precision spheres made of electrically insulating materials (such as ceramics) are commercially available, for example from CCR Products LLC in West Hartford, Connecticut.

[0043] Here, spring 108 refers to a rod spring that extends longitudinally along the length of the sensor assembly, the insulating rod, and the second electrode. This type of finger spring provides a controlled force per unit length and provides an electrical connection between the housing 82 and the sensor assembly 104. As shown, grooves of optional shapes can be machined into the sensor assembly to help secure the finger spring within it. Fingerstock springs are commercially available as catalog items and come in various cross-sectional shapes and are made of different materials.

[0044] Insulating rods 106 are secured to the horizontal and vertical axes by locating pins 110 located in holes passing through the second electrode 86 and in corresponding blind holes in each insulating rod 106. The locating pins 110 are located on the second surface 94 of the dielectric plate 88. Alternatively, the locating pins 110 may be located in the blind holes in the second electrode 86 and the insulating rods 106. At least two locating pins 110 are required to mechanically constrain each insulating rod 106 relative to the second electrode 86. These locating pins are preferably oriented towards the end of each insulating rod. The insulating rods may be further secured by additional locating pins located therebetween.

[0045] Figure 8A Is with Figure 6 and 7 Another enlarged view of the gas laser 80 with different cross-sections. The sensor assembly 104 is secured to the horizontal and vertical axes by locating pins 112 located within blind holes in the insulating rod 106 and corresponding blind holes in the sensor assembly. Preferably, the locating pins 112 face the end of each insulating rod. The sensor assembly can be further secured by additional locating pins located therebetween.

[0046] An insulating rod 106 extends along most of its length into the volume V (indicated by dashed lines) between the second electrode 86 and the housing 82. Extending the insulating rod into the volume V increases the threshold potential, potentially inducing unwanted parasitic discharges between the second electrode and the housing. In the gas laser 80, the capacitance between the first gap d1 and the second gap d2 requires higher applied RF power to trigger discharges in the gain volume and couple a given power into the gas plasma therein. Extending the insulating rod mitigates parasitic discharges that could otherwise be impacted by higher RF power.

[0047] Figure 8B This is an enlarged view of the gas laser 80, its cross-section is similar to... Figure 8A Similarly, but schematically shown is another example of an insulating rod 106, which has been found to be more effective in preventing parasitic discharges. Figure 8B The insulating rod occupies most of the volume V between the second electrode and the housing. However, the insulating rod 106 remains separate from the housing 82 and the second electrode 86. Avoiding physical contact between the insulating rod and the metal surfaces of the housing and the second electrode prevents metal surface friction, thereby preventing the depletion of oxygen in the gas mixture.

[0048] The housing 82, including the first electrode 84, and the second electrode 86 are preferably made of passivating metal. For example, they are made of self-passivating aluminum alloy or anodic aluminum alloy. The dielectric plate 88 is preferably made of a ceramic material with relatively high thermal conductivity. For example, it is made of aluminum nitride (AlN), aluminum oxide (Al2O3), or beryllium oxide (BeO). The insulating rod 106 and the locating pin 102 are also preferably made of ceramic material. In practice, the dielectric plate 88, the insulating rod 106, the precision ball 96, and the locating pin 102 can all be made of the same ceramic material, such as aluminum oxide.

[0049] Figure 9 This is a cross-sectional plan view of the gas laser 80, schematically showing the exemplary positions of the positioning block 98, spring assembly 100, precision balls 96, and positioning pins 102 relative to the dielectric plate 88. In the example shown, eight precision balls 96 are located in holes (open circles) distributed on the dielectric plate to ensure uniformity of the first gap d1 and the second gap d2. Two positioning pins 102 are located in holes (shaded circles) widely spaced along the length of the dielectric plate. Four positioning pins 110 are located on the second surface 94 of the dielectric plate 88, at exemplary positions indicated by the filled circle. Four positioning pins 112, captured within the insulating rod 106 and inductor assembly 104, are close to exemplary positions indicated by the diagonal forks.

[0050] Compared to existing gas lasers, the gas laser of this invention has a small gap between the dielectric plate and each electrode. Its advantage lies in the fact that the passivation layer cannot be scraped off the electrode surface from the dielectric plate surface. Each electrode has only one contact point with each precision ball. Because the surfaces of the dielectric plate and the electrodes move relative to each other due to differences in thermal expansion and contraction, the precision balls essentially act as bearings, rolling on the passivated surface of the electrodes, minimizing scratching.

[0051] Another advantage of the gas laser of the present invention is that the sensor assembly 104, the insulating rod 106, and the second electrode 86 are fixed to two shafts by locating pins 110 and 112. These components are fixed to another shaft by a relatively moderate compressive force provided by spring 108. Existing designs rely on static friction between contacting surfaces to fix these components, thus requiring greater compressive force. Reducing this compressive force prevents the precision ball from deforming the electrode and minimizes friction between the precision ball and the electrode.

[0052] In the gas laser of this invention, the compressive force must be sufficient to hold the components in place and prevent the dielectric plate from moving relative to the resonator mirror due to mechanical shock and vibration. For example, the compressive force measured in different arrangements of the laser of this invention is between 65 Newtons (N) and 105 Newtons. In equivalent prior art arrangements, the required compressive force measurement is between 525 N and 1050 N.

[0053] Because of the reduced friction between the dielectric plate surface and the electrodes, the relatively moderate compressive force required to secure the laser assembly of the present invention allows for some contact between the dielectric plate surface and the electrodes in the embodiments. The gas laser 80 described above lacks this contact, essentially eliminating scratching of the passivation layer on the electrode surfaces. However, in the embodiments, the dielectric plate is substantially separated from each electrode by gaps, which sufficiently reduces the consumption rate of components in the gas mixture to achieve the desired operating life. Here, "substantially separated" means that at least 75% of the mutually facing surfaces of the dielectric plate and the electrodes are not in contact; a higher fraction will further reduce the loss rate. At least 85% is more preferred, and at least 95% is even more preferred.

[0054] The inventor manufactured and tested a device with Figure 6 The invention's gas laser features a folded waveguide structure as shown in Figure -8. The gap distances d1 and d2 are approximately 50 μm. The housing is sealed and contains a CO gas mixture. The power of the test laser of this invention is periodically turned on and off over an extended period simulating typical industrial use conditions for such lasers. The test laser of this invention maintains an average power above a target minimum without any gas replacement. Another test laser with an equivalent prior art arrangement requires refilling the gas twice under the same time and conditions to maintain the same target average power.

[0055] As described above, the gas laser of the present invention has Figure 1B The waveguide structure of the present invention. The gas laser of the present invention can also have... Figure 1C The plate-like structure. The channel 90 in the dielectric plate 88 fabricated into the gas laser 80 will be replaced by a laterally extending hollow that defines the gain volume when the gas is excited by a radio frequency field. A precision ball 96 and a positioning pin 102 will be located inside the dielectric plate 88, but outside the hollow, so as not to interrupt the laser radiation circulating through the gain volume therein.

[0056] The gas laser of the present invention may also have Figure 1A The waveguide structure. Figure 10 This is a schematic cross-sectional end view illustrating another embodiment of the radio frequency excited gas laser 120 according to the present invention. A hollow dielectric cylinder 122 is oriented along the longitudinal axis of the gas laser 120 and defines a gain volume when the gas is excited by an RF field. The gain volume is the hollow interior of the dielectric cylinder 122.

[0057] The outer surface of the dielectric cylinder 122 is concentric with the first surface 134 of the first electrode 124 and the second surface 136 of the second electrode 126. The first and second electrodes are located on opposite sides of the dielectric cylinder. The first surface 134 and the second surface 136 are separated by a diameter D. The first surface is separated from the outer surface of the dielectric cylinder 122 by a first gap d3. The second surface is separated from the outer surface of the dielectric cylinder 122 by a second gap d4. These small gaps are formed by a precision rod 128, which is located in a longitudinal groove machined into the dielectric cylinder and the electrode. The diameter of the precision rod 128 is selected to achieve the desired gaps d3 and d4. Preferably, the gaps d3 and d4 are at least 0.001D. More preferably, the gaps d3 and d4 are at least 0.0025D. The rod is made of a dielectric material, preferably a ceramic material.

[0058] Although the embodiments presented herein are within a resonator arrangement, including a resonator mirror for progressively amplifying laser radiation through multiple passes through a gain volume, the principles of the invention can also be applied to amplifier arrangements. In a master oscillator power amplifier (MOPA) arrangement, the master oscillator is a laser resonator that supplies laser radiation to the power amplifier for further amplification. The power amplifier may include a gain volume containing a radio frequency excited CO2 or CO gas mixture for scaling the pulse energy and average power of the laser radiation directed through it.

[0059] The invention has been described above with reference to preferred embodiments and other embodiments. However, the invention is not limited to the embodiments described and depicted herein. Rather, the invention is limited only by the appended claims.

Claims

1. A radio frequency excited gas laser comprising: a housing containing said gas; a first electrode elongated along a longitudinal axis; a second electrode elongated along said longitudinal axis and parallel to said first electrode, said first and second electrodes being located in said housing and spaced apart from each other by a distance D; and a dielectric plate located between said first and second electrodes, said dielectric plate defining a gain volume when said gas is excited by a radio frequency field, said dielectric plate having opposing first and second surfaces parallel to said first and second electrodes; wherein said first surface of said dielectric plate is substantially separated from said first electrode by a first gap and said second surface of said dielectric plate is substantially separated from said second electrode by a second gap.

2. The radio frequency excited gas laser of claim 1, wherein said first and second gaps are created by precision balls, each precision ball being in contact with said first electrode and said second electrode.

3. The radio frequency excited gas laser of claim 2, wherein said precision balls are made of a ceramic material.

4. The radio frequency excited gas laser of claim 1, wherein distance D is between 2 millimeters and 6 millimeters.

5. The radio frequency excited gas laser of claim 1, wherein the first gap is at least 0.001 D and the second gap is at least 0.001 D.

6. The radio frequency excited gas laser of claim 5, wherein the first gap is at least 0.0025 D and the second gap is at least 0.0025 D.

7. The radio frequency excited gas laser of claim 1, wherein the lateral alignment of said dielectric plate is maintained by compressing said dielectric plate between at least two positioning blocks and at least two pre-loaded spring assemblies, said positioning blocks and said pre-loaded spring assemblies being attached to opposing interior surfaces of said housing.

8. The radio frequency excited gas laser of claim 1, wherein the longitudinal alignment of said dielectric plate is maintained by at least one positioning pin located in a hole through said dielectric plate and a corresponding blind hole in each electrode.

9. The radio frequency excited gas laser of claim 1, wherein said second electrode is laterally and longitudinally fixed by at least two positioning pins located in a hole through said dielectric plate and a corresponding blind hole in each electrode.

10. The radio frequency excited gas laser of claim 1, wherein an inductor assembly, a pair of insulating rods and a second electrode are laterally fixed by springs located on both sides of said gas laser.

11. The radio frequency excited gas laser of claim 10, wherein said springs extend longitudinally along said inductor assembly, said insulating rods and said second electrode.

12. The radio frequency excited gas laser of claim 10, wherein each spring provides a compression force between 65 and 105 Newtons.

13. The radio frequency excited gas laser of claim 10, wherein said springs are finger springs. ​ 14. The radio frequency excited gas laser of claim 10, wherein the first and second gaps are created by precision balls, each precision ball in contact with the first electrode and the second electrode, each spring pushing the inductor assembly, the insulator rod, and the second electrode towards the precision balls.

15. The radio frequency excited gas laser of claim 10, wherein each insulator rod is laterally fixed by at least two locating pins in a hole in the second electrode and a corresponding hole in the insulator rod.

16. The radio frequency excited gas laser of claim 10, wherein the inductor assembly is laterally and longitudinally fixed by locating pins in a hole in the insulator rod and a corresponding hole in the inductor assembly.

17. The radio frequency excited gas laser of claim 10, wherein each insulator rod extends into a volume between the second electrode and the housing, thereby increasing the potential required for a discharge therebetween.

18. The radio frequency excited gas laser of claim 17, wherein the insulator rod occupies a substantial portion of the volume between the second electrode and the housing while being separated from the second electrode and the housing.

19. The radio frequency excited gas laser of claim 1, wherein the housing contains a carbon dioxide or carbon monoxide gas mixture.

20. The radio frequency excited gas laser of claim 1, wherein a hollow in the dielectric slab defines a gain volume of a slab laser.

21. The radio frequency excited gas laser of claim 1, wherein a channel in the dielectric slab defines a gain volume of a waveguide laser.

22. A radio frequency excited gas laser, comprising: a housing containing the gas; a hollow dielectric cylinder oriented along a longitudinal axis in the housing, the dielectric cylinder defining a gain volume when the gas is excited by a radio frequency field, the gain volume being a hollow interior of the dielectric cylinder; a first electrode having a first surface concentric with an outer surface of the dielectric cylinder; and a second electrode having a second surface concentric with the outer surface of the dielectric cylinder, the first and second electrodes being on opposite sides of the dielectric cylinder; wherein the first surface is separated from the outer surface by a first gap and the second surface is separated from the outer surface by a second gap. ​

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