Cylindrical Laser With High Frequency Discharge Excitation
Alexander V. Krasnov
Cross-Reference to Related Application
 This international patent application claims priority to and benefit from Russian Patent Application RU2009138084, filed on 15 October 2009.
 The present invention relates to subsonic transfer flow gas laser utilizing a cylindrical configuration. The laser uses high frequency discharge excitation to generate the lasing plasma. The laser consists of metal external and a dielectric internal co-axial cylinders or vessels and an electrode-less plasma cavity which uses a single metal electrode placed on the outside surface of the dielectric cylinder. A high frequency power supply is electrically connected to the single electrode and an optical resonator is located within, partially downstream or downstream of the plasma excitation region. A heat exchanger is located downstream of the optical resonator and an external turbo blower is utilized for gas flow within the cylindrical laser body.
 Known transfer gas flow lasers with cylindrical configurations use AC or DC electrical discharges between exposed electrodes positioned opposite of each other within the gas flow region. Such gas flow lasers use relatively very slow gas flow speeds through the laser cavity which is generated by longitudinal blowers located inside of the laser body and gas flow cavity. These types of gas flow lasers utilize large volume plasma cavities due to the limitation on the plasma density in the lower gas flow. Such reduced gas flows, typically less than about 5 W/cm and the associated blowers result in a very low pressure ratio thereby resulting in a slow gas flow through the laser. Known high power gas lasers having a cylindrical configuration utilize extremely large dimensions and weight in order to achieve appropriate flow rates and stable plasma volumes. Other known low and high speed gas lasers with a planar excitation configuration (i.e. non-arc shaped) utilizing DC, AC or RF excitations mechanisms have other associated problems typically related to the mechanical instability of the laser cavity which is very sensitive to thermal and mechanical deformations caused by the pressure differential between the vacuum cavity and the atmosphere pressure.
 In order to compensate for these known problems, such low and high speed gas flow lasers use significantly more technically complicated designs which have heavier laser bodies and increased complexity of designs, all of which increase dimensions, weight and are significantly more costly to build.
 Other gas flow lasers may use parallel channels along the gas flow direction within the plasma or the optical resonator cavities. However, these designs do not compensate for non-laminar gas flow boundary layers in the laser cavity caused by friction between the gas flow and the laser cavity surfaces. Such non-laminar layers within the laser cavity reduces the available plasma for excitation of the laser thereby reducing the laser efficiency and power. Such reduction in laser efficiency can be directly tied to lack of utilization of the entire amplification volume within the laser cavity, directly reducing the laser output power and efficiency as noted.
 Further, known gas flow lasers may also utilize electrodes placed within the plasma chamber or cavity thereby resulting in turbulence and plasma instability. Plasma instability and non-laminar flow reduces the optical output quality of the resultant laser.
 Thus, there is a need in the art to provide a cylindrical configuration high frequency discharge excitation gas laser which utilizes a simple, compact, easy to
manufacture and configure laser body which maximizes the utilization of the amplification of the laser in the laser cavity.
 The present disclosure is directed to inventive methods and apparatus for a subsonic transfer gas flow laser having high frequency discharge excitation, the plasma excitation occurring within a plasma chamber positioned in a narrower or narrowest section of the gas flow channel, the laser cavity formed in an expanding channel area, both of such areas and the gas flow channel itself being formed between two parallel and non-concentric coaxial cylinders. For example, in some methods in order to increase the efficiency of the laser and complete or fully utilize the excitation area of the optical resonator.
 Generally, in one aspect, the laser of the present invention may have an external cylindrical metal vessel combined coaxially with an internal dielectric vessel which is placed eccentrically inside of the external vessel or cylinder. Both the external and internal vessels
may be hermetically sealed by two flat flanges in order to create a gas flow channel or path. The path may include an electrode-less plasma cavity formed between the two vessels or cylinders forming the gas dynamic channel, the plasma cavity positioned within the narrow gap-transition of the gas dynamic channel.
 The optical resonator included herein is or may be located, in one aspect of the laser, within, downstream or partially downstream from the plasma cavity. The electrode may be electrically connected to a resonance matched high frequency power supply and the gas dynamic channel may also include a heat exchanger and an external turbo blower which circulates the flow of active gas medium within the formed channel between two cylinders.
 In another aspect of the invention, the gas dynamic channel may include a uniform gas metal mesh screen located up stream of the plasma cavity for flow of the active gas medium into plasma chamber.
 In some embodiments the laser cavity may be defined within the gas dynamic channel within a narrow gap-transition area and may have a symmetrical or asymmetrical profile with round, arc-shaped, ovalized, ellipsoidal or flat shape and may include some opening angle along the gas flow path within the width of the optical resonator.
 In some embodiments the laser may have a metal electrode located on the external surface of internal dielectric vessel, the internal surface of external cylindrical vessel, within the narrow transition area, being insulated by a dielectric skin from the gas flow and the plasma. Alternatively, in some embodiments, may be insulated by an insert vessel segment with a zero tolerance gap as related to the external metal vessel. In some embodiments, the external metal vessel may be electrically grounded. Usage of an electrode-less plasma chamber in the cylindrical laser using a smooth interior gas flow channel creates a laminar gas flow along the boundary areas of the channel. This results in an increase in the optical quality of the laser output and laser power.
 In some embodiments the electrode may be powered by the high frequency power supply with the frequencies ranging from about 10 kHz to about 1.5MHz, which is positioned within a high frequency AC range, or alternatively by an RF range of from about 1.5MHz to about 27MHz.
 In some embodiments the laser gas active medium may include either of the following gas combinations: (1) a mixture of gases: C02 : N2 : He, or (2) a mixture of gases: CO: He. Other combinations may be utilized to achieve effective excitation levels within the plasma chamber.
 The various embodiments, the laser may utilize external and the internal cylindrical vessels to create the gas dynamic channel, each having a round, cylindrical or oval shape. In other embodiments, the external and internal cylindrical vessels may have different shapes: one of them may be round while the other can be oval.
 The some aspects and embodiments, the laser may have an external cylindrical body or vessel which can be comprised of an aluminum alloy or any other metal which also may be combined with air or water cooling.
 Other embodiments and aspects of the laser set forth may include an internal cylindrical dielectric vessel or cylindrical body which can be made of a ceramic alumina oxide [A12 03] with a thickness of between about 3 to about 13mm.
 Other embodiments and aspects may utilize an external cylindrical vessel made by an extrusion profile method.
 Generally , the laser may have a dielectric insulation layer or insert screen (i.e. fragmented section of the dielectric vessel) on an internal surface of the external cylindrical vessel which may be comprised of the quartz with a thickness between about 0.5 mm and about 6 mm. Also, the electrode may be made of various known metals and may be water cooled. A heat exchanger may be utilized in various embodiments and structures and be located downstream of the optical resonator and the gas dynamic channel may include an external turbo blower which may be in gas communication with the laser body and gas dynamic channel.
 In various embodiments, the laser may have a gas flow channel which may include an angle of opening along the flow direction and within the width of the optical resonator and which can be from about 0 to about 10 degrees.
 Various aspects may include and define a cylindrical vessel which can include a cylinder, the gas flow channel including also flattened or quasi-flattened areas as well as arc shaped or curved areas. As well, use of a gas dynamic shape for such area may include an
asymmetrical shaped channel having round or partial flat/linear flow are of the vessel and/or gas dynamic channel.
 Included within the description hereof is a high frequency discharge excitation laser, comprising an external cylindrical metal electrically grounded vessel, an internal dielectric cylindrical vessel aligned eccentrically inside of said external vessel, wherein said external vessel and said internal vessel form a gas flow path and further form a narrowed gap transition area ,a plasma cavity formed between said external and said internal vessel within said gas flow path and said narrow gap transition area, an optical resonator cavity between said external vessel and said internal vessel and further having resonator mirrors, a high frequency discharge electrode positioned on an internal surface of said internal dielectric vessel and also positioned adjacent said plasma cavity, a dielectric insulating layer on an internal surface of said external vessel and adjacent with said plasma and optical resonator cavities, a high frequency discharge power supply in electrical contact with said high frequency discharge electrode, a heat exchanger downstream of said optical resonator cavity, an external turbo blower in gas flow communication with the said laser gas flow path, a uniform distributor of said gas flow upstream of said plasma cavity thereby introducing gas to said plasma cavity.
 The laser may have an internal dielectric vessel made of ceramic Alumina Oxide [Al2 03]. The high frequency discharge excitation laser further may have a dielectric insulating layer on the internal surface of the external vessel made of Quartz. The external vessel may be comprised of Aluminum or an Aluminum Alloy. The optical resonator cavity may have an angle of opening between 1 and 5 degrees. The optical resonator may further be positioned within said plasma cavity or partially downstream of said plasma cavity. The external and internal vessel may be hermetically sealed by two flat flanges. The laser may include a high frequency discharge power supply having a frequency range from about 10kHz up to about 27MHz. The gas laser medium may be [C02:N2:He] or [CO:He]. The wall thickness of the internal dielectric vessel may be between about 3 and about 13 mm. The wall thickness of the dielectric insulating layer may be between about 0.5 and about 6 mm.
 It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not
mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.
Brief Description of the Drawings
 In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.
 FIG. 1 illustrates a partial perspective sectional view of the high frequency discharge excitation laser of the present invention described herein.
 FIG. 2 illustrates a combined side and top sectional view of the laser of FIG. 1.
 FIG. 3 illustrates a side sectional view of the laser of FIG. 1.
 FIG. 4 illustrates a top plan view of one embodiment of the laser cavity for use in the laser of FIG 1.
 FIG. 5 illustrates a side view of the plasma resonator channel area with an exemplary arc shaped channel for the cylindrical laser with high frequency discharge excitation.
 When utilizing high frequency discharge excitation (HFDE) for laser activity, it is important to insure smooth laminar flow of the gas dynamic channel. Introduction of various structures within the gas flow channel can cause interruptions of the gas flow, reduction in the dynamic plasma activity within the plasma chamber and also reduce the ultimate efficiency of the laser or lasing activity. Significant structural requirements for high gas flow volumes, speed and expansive optical resonators reduces the overall desirability of the laser design, reduces efficiency and increases the cost of manufacturing of the particular laser.
 Thus, Applicant has recognized an appreciated that there is a need in the art to provide a method and apparatus for a cylindrical HFDE gas laser design which is easy to
manufacture, compact, highly efficient, economical and provides high power output for both industrial and alternative uses thereby removing the requirement of large, intrusive laser, optical and gas flow bodies and associated power supplies.
 More generally, Applicant has recognized and appreciated that it would be beneficial to provide a method and apparatus that increases the power of the laser and correspondingly reduces the overall laser body size and dimensions by designing a gas dynamic channel which maximizes the effectiveness of the plasma cavity and the associated optical resonator. Such maximization can occur by specifically designing the dynamic gas flow channel within the resonator cavity to include an opening or expanding angle which limits the effect of non-laminar gas flow along the gas flow boundary areas of the flow channels directly adjacent to the boundary layer.
 In view of the foregoing, various embodiments and implementations of the present invention are directed to a HFDE laser which utilizes an internal and external coaxial cylindrical vessel or laser body which has round or oval shapes or mixed round/ovalized shapes. The external cylinder defines the outer boundary of the dynamic gas flow channel while the internal cylinder is a dielectric cylinder placed eccentrically and coaxially within the external cylinder and retaining the high frequency discharge electrode. Thus, the electrode is maintained outside of the gas flow channel and the external cylinder is appropriate electrically grounded thereby forming a plasma chamber or cavity within the space of the dynamic gas flow channel between the internal dielectric cylinder and the external cylinder. Correspondingly within the optical resonator the separation between the internal and external cylinder or the wide of the gas flow channel is increased by a predetermined amount so that the optical resonator may fully and effectively utilize the available plasma generated from the matched HFD electrode.
 As shown in a depicted embodiment set forth in Fig. 1, a general view of the assembled laser body is shown. A dielectric cylinder 2 is placed eccentrically and parallel inside of a metal electrically grounded external cylindrical vessel 1. A single HFD electrode 3 is placed on the internal surface of the dielectric cylinder. The gas inlet tube-distributer 4 is placed inside of the external cylindrical housing or vessel 1 upstream or before the plasma cavity 5. A uniform gas metal mesh or flow through screen 6 is placed on the outlet rectangular window of the gas inlet tube distributer 4. The plasma cavity 5 is located within
the narrow dynamic gas flow channel area between the external cylindrical vessel 1 and dielectric internal cylinder 2. A dielectric insulator 7 is placed on at least a part of the internal surface of the external cylindrical vessel 1 along and at least partially wider than the dimensions of the calculated plasma cavity 5. A heat exchanger 9 is located downstream of the optical resonator region 8 with an optical resonator's mirrors 8a, 8b positioned within the optical resonator for generation of the laser. The high frequency discharge electrode 3 is in electrical communication to a high frequency discharge power supply 10 depicted. The external turbo-blower 11 is in gas flow communication to the gas inlet distributer 4 and the laser body 1 in order to maintain proper dynamic gas pressure within the gas flow channel and the plasma cavity. Flanges 12a and 12b are utilized to hermetically seal and close off the external vessel 1. A deflector 20 which separates the outlet gas flow from the inlet flow area and allows the transition of the dynamic gas from the flow channel, plasma chamber, optical resonator and heat exchanger.
 Referring to FIG.2, in another embodiment, the cross section view of a laser using aspects of the present invention is shown. The inlet laser gas flow 13 is supplied by a turbo blower 11 through the gas inlet distribution tube 18 to the gas inlet distributer 4. Gas expands from the inlet distribution tube through the uniform metal mesh screen 6 to create a uniform gas flow 13 prior to entry into the plasma chamber. Gas flow deflectors 20 are provided to concentrate and direct the dynamic gas into the plasma cavity 5. The plasma cavity 5 is formed between the internal dielectric vessel 2 and the dielectric layer or boundary 7 which insulates the external metal vessel 1. The plasma cavity forms the area where HFD excitation takes place of the dynamic gas 13. The excited laser gas 13 flows to the optical resonator cavity 8 where the amplification of the resonance laser emission occurs between the resonator's mirrors 8a and 8b. Multiple traversals of the excited gas by the laser light may occur in order to fully utilize the generated plasma therein. The hot gas 13 is then directed towards the heat exchanger 9 for appropriate cooling from about 400K to room temperature after which the cooled gas flow 17 leaves the laser body 1 through window 15 passing through the gas return channel 16. The gas is then returned to the turbo blower 11 for recycling through the closed loop system. The external metal vessel 1 is electrically grounded by 19 and the electrode 3 is in electrical communication with a HFD power supply 10.
 In a further embodiment, aspects of the invention and various features are shown in Fig.3. A side sectional view of the described embodiment and laser is shown wherein the gas flow path for the dynamic gas is visible along with the optical resonator and plasma generation cavity. An inlet laser gas supply 13 is provided by turbo blower 11 to the laser body 1 through the inlet gas pipe 18 and further through inlet gas flow distributer 4. The dynamic gas is then passed through a uniform metal mesh screen 6 in order to form a uniform and laminar longitudinal gas flow within the length of the laser body 1 and gas channel. The dynamic gas then passes through the plasma cavity 5 which is formed between the dielectric insulator 7 and the dielectric vessel 2. The HFD power supply 10 is in electrical
communication with metal electrode 3 which is located on the internal surface of the dielectric vessel 2 within the plasma cavity 5. The output laser beam 21, before leaving the optical resonator cavity 8, exhibits amplification between-the optical resonator's mirrors 8a, 8b, located within the resonator cavity 8. Flanges 12a and 12b hermetically seal the optical resonator and laser as well as internal and external cylinders 1 and 2.
 Downstream of the optical resonator cavity 8 is positioned a heat exchanger 9 through which the longitudinal return gas flow 17 passes for cooling of the excited dynamic medium. Return gas flow path exits the laser cylindrical body 1 through outlet pipe 16 to the turbo blower 11 for recycling of the dynamic gas back into the system.
 In a further aspect of the various embodiments shown, depicted in Figure 4 and 5 is a section of the round laser channel within the plasma cavity 5 and the optical resonator 8 cavity. The plasma cavity 5 is located between the external metal cylinder 1 and the dielectric cylinder 2. The optical resonator cavity 8, in various embodiments, may be located partially, completely or within the plasma cavity 5. The dielectric insulator 7, as shown in the examples of the figures, may be placed on the internal surface of the external cylinder 1. An HFD electrode 3, which is in electrical communication with HFD power supply 10, is placed on the internal surface of the vessel 2within the plasma cavity 5 and opposite the dielectric insulator. As can be seen from the various diagrams and examples, the dynamic gas flow 13 passes through the laser cavity 5. The gas boundary layers 14 are forming adjacent to or near the surfaces of the gas channel between the dielectric internal cylindrical vessel 2 and the dielectric insulator 7 thereby creating non-laminar gas flow and reducing the efficiency of the lasing activity within the optical resonator 8.
 In accordance with the various embodiments of the Figures, the opening angle a of the gas dynamic channel within the width of optical resonator 8 is determined by the thickness of top and bottom boundary layers 14 and by the length of the optical resonator cavity 8 along the gas flow path and may be calculated by the formula:
 a~— , 6* 1.74 Re^2
 Re = ^
 Re - Reynolds Number;
 Lz - width of optical resonator;
 δ* - thickness of boundary layer;  ϋ- density of the gas;
 U -average velocity of the dynamic gas flow;
 μ - dynamic viscosity of gas into the layer;
 T -average temperature of the gas into the layer;
 h- middle height of the channel;
 For the typical gas data of C02 Laser with Re=3000 and h =20 mm, the angle should be around 4 degrees. This angle compensation of the channel will allow the internal resonator's laser beam avoid the dissipation resulting in the increase of efficiency of the optical resonator and overall efficiency of the laser by approximately 1-2%.
 The internal dielectric vessel 2 is utilized for a dual purpose. Firstly, it forms a portion of the gas dynamic flow path and channel while, at the same time, it acts as a dielectric insulator of the HFD electrode 3 from the gas and plasma which increases the plasma density up to 50 W/cm . At the same time, the dielectric insulator 7 prevents the external metal cylinder 1 from the generating hot spots within the plasma and gas flow. The insulator 7 in the various embodiments depicted may be of quartz or similar construction.
 In some embodiments, the laser may have an electrode-less plasma cavity wherein the plasma cavity is free from intrusion of the electrical connections, electrodes or other excitation mechanism or structure.
 In various embodiments, the metal HFD electrode 3 is placed on the internal surface of dielectric vessel 2 and is in electrical contact with HFD power supply 10 which supplies high frequency pulses to the electrode exhibiting a frequency of from 10kHz to 1.5MHz in the HFAC implementation and from about 3 up to about 27 MHz for an RF range.
 The optical resonator 8 in the various embodiments is a multi-pass type for increased laser amplification and which is placed downstream from the plasma cavity 5 in order to obtain the most efficient amplification gain. Alternatively, in other embodiments, the optical resonator 8 may be only partially downstream of the plasma cavity or integral therewith. Each variation results in dynamic modification of the lasing activity within the optical resonator and resulting laser qualities.
 The heat exchanger 9 is located downstream of the optical resonator 8 in order to effectuate cooling of the laser gas. The dynamic gas channel works in a closed circle loop for more efficient utilization of the gas and maintenance of the appropriate environmental requirements.
 The dynamic gas inlet distributer pipe 4 has a metal mesh 6 in an outflow section thereby resulting in uniform gas flow parameters along the length of the laser cavity thereby reducing turbulence prior to entry into the plasma 7 and resonator cavity 8. The turbo blower 11 is in gas flow communication with the distributer 4 and the-laser body 1 wherein the laser gas is circulated through the gas channel. The compact and efficient turbo blower creates a significant ratio of pressure (up to 1.4) for providing a high volume of the gas flow through the laser cavity which maintains a high subsonic speed of the gas within the laser cavity. Such design further maintains a high subsonic speed of the laser medium within the plasma cavity 6.
 In various embodiments, the external cylindrical vessel 1 is made of conductive material such as an aluminum alloy which is thereby employed as the main body of the laser and also acts as an electrically grounded external electrode. The internal cylindrical vessel 2 may be comprised of a dielectric material, such as, for example, ceramic alumina [Al2 03] which forms an internal boundary of the plasma cavity 6. The external 1 and internal 2
vessels may have alternative geometric profiles including round, circular, ovalized or other shapes. The various depictions of the profiles discussed herein are not to be considered as limiting as multiple combinations of geometric profiles of the vessels may be utilized to achieve the benefits noted herein.
 In some embodiments, the laser operates on the following basis:
 A turbo compressor 11 with a speed rotation of about 20,000 rpm supplies cooled laser gas flow with a pressure ratio of about 1.1 to about 1.4. The gas dynamic medium may be, for example, [C02 N2:He] or [CO:He] and is supplied to the distributer 4 and further through uniform screen 6 after which the gas flow passes through the plasma cavity 6 and on to the optical resonator 8. Within the plasma cavity 5, the gas may be excited by a high frequency field of low voltage (about 1000 V) between the electrode and the electrically grounded vessel 1. The HFD excitation of the laser gas thereby takes place resulting in excitation of the gas active medium by ionization of atoms and molecules of the laser gas through electronic oscillation in the thin layers adjacent the surface of the internal dielectric vessel 2 and the internal insulated surface of the external vessel 1. Dynamic gas flow may also pass through deflectors as needed for adjustment and narrowing of the gas into the optical resonator. Passing the excited dynamic gas into and within the optical resonator cavity 8, the laser 22 achieves amplification by passing between the resonator mirrors 8a and 8b and exiting the resonator via an output coupler positioned at mirror 8a.
 Leaving the plasma cavity 6, the hot flow of about 400K passes along the gas dynamic channel towards the heat exchanger 9 wherein the gas is cooled down to ambient temperature. The gas flow then returns to the turbo-blower 11 to form a closed-loop system.
 The laser of the present invention has several exhibited advantages such as an increase of laser output and overall efficiency. Further, the resultant laser body is compact, lightweight, mechanically stable and technologically simple to build. These laser designs are compact and result in a high efficiency gas laser which utilizes multiple laser gases such as [CON:N2:He] or [CO:He] and others.
 As an example, a laser in accordance to aspects and embodiments set for the herein was implemented using C02, resulting in the following specifications and laser output:
 Average Laser Power Output 3000 W
 Laser Efficiency 20%
 Overall Efficiency 15%
 Dimension of the Laser: 35x35x100 cm
 Weight of Laser 40 kg
 While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.
 All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.
 The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."
 The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and/or B", when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
 As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e. "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law.
 As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A
and/or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.
 It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.
 In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "composed of," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of and "consisting essentially of shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.
What is claimed is: