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
  • H01S3/02—Constructional details
  • H01S3/03—Constructional details of gas laser discharge tubes
  • H01S3/038—Electrodes, e.g. special shape, configuration or composition
  • H01S3/0385—Shape
• • 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
  • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
  • H01S3/08—Construction or shape of optical resonators or components thereof
  • H01S3/08059—Constructional details of the reflector, e.g. shape
• • 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
  • H01S3/02—Constructional details
• • 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
  • H01S3/02—Constructional details
  • H01S3/04—Arrangements for thermal management
  • H01S3/041—Arrangements for thermal management for gas lasers
• • 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
  • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
  • H01S3/08—Construction or shape of optical resonators or components thereof
  • H01S3/08018—Mode suppression
  • H01S3/0804—Transverse or lateral modes
  • H01S3/0805—Transverse or lateral modes by apertures, e.g. pin-holes or knife-edges
• • 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
  • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
  • H01S3/08—Construction or shape of optical resonators or components thereof
  • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
  • H01S3/0813—Configuration of resonator
  • H01S3/0815—Configuration of resonator having 3 reflectors, e.g. V-shaped resonators
• • 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
  • H01S3/0971—Processes or apparatus for excitation, e.g. pumping by gas discharge of a gas laser transversely excited

Definitions

• the present invention relates to lasers generally and more particularly to gas lasers.
• RF excited diffusion cooled gas lasers having extended area thin gap electrodes are commercially available in both slab and annular configurations. Both the slab and the annular configurations require high frequency RF excitation in the typical range of 60 - 150 MHz in order to achieve uniform arc-free discharge.
• power scales to electrode area and not to electrode length thus enabling relatively compact lasers to be constructed.
• RF excited diffusion cooled gas lasers of both of the above configurations display undesirable voltage variation along the electrodes due to transmission line plasma phenomena. This voltage variation leads to unequal values of the E/N parameter along the length of the electrode and thus to reduced efficiency of the resonator. In slab electrodes, this difficulty is at least partially overcome by placing a plurality of inductors along the slab, thus reducing the voltage variations to a few percent.
• a general problem encountered in RF excited diffusion cooled gas lasers is alignment of optics with respect to each other and with respect to the thin gap electrodes.
• a general problem in RF excited diffusion cooled gas lasers having an annular configuration is undesirable creation of higher order modes in the lasing process which are difficult to filter out and which significantly degrade the quality of the output beam.
• U.S. Patents are believed to represent the state of the art: U.S. Patent 4,847,852 which describes an RF excited diffusion cooled gas laser of the annular configuration; U.S. Patent 5,123,028 which describes an RF excited diffusion cooled gas laser of the slab configuration; and U.S. Patent 5,099,492 which describes a RF excited gas laser of the annular configuration.
• the present invention seeks to provide an improved gas laser which overcomes limitations of the prior art.
• a gas laser including: an annular optical cavity defined by a pair of coaxial spaced electrodes which produces an annular coherent beam of a first diameter and a first thickness; a mirror structure located at one end of the annular optical cavity and including: a first mirror surface which is operative to decrease the diameter of the annular coherent beam from the first diameter and to expand the thickness of the annular coherent beam from the first thickness; a second mirror surface which is operative to focus a beam reflected by the first mirror surface to a location located interiorly of the pair of coaxial spaced electrodes; a third mirror surface located at an opposite end of the annular optical cavity; and an output coupler operative to receive, reflect and transmit a beam reflected by the second mirror surface.
• a gas laser including: an annular optical cavity defined by inner and outer coaxial spaced electrodes which produces an annular coherent beam; and an RF power supply coupled to the outer electrode at at least one location symmetrical with respect to the length thereof.
• a gas laser including an enclosure, an annular optical cavity defined by inner and outer coaxial spaced electrodes disposed within the enclosure and which produces an annular coherent beam and a plurality of RF power supplies mounted onto the enclosure and coupled to the outer electrode at multiple locations thereon distributed along the length and circumference thereof, thereby to provide generally homogeneous power and voltage distribution throughout the cavity.
• a gas laser including: an annular optical cavity defined by inner and outer coaxial spaced electrodes which produces an annular coherent beam; a grounded structure surrounding the annular optical cavity and including first and second portions having precisely formed first and second mating surfaces, the first portion having machined thereon a first mirror structure located at one end of the annular optical cavity; and the second portion having machined thereon a second mirror structure located at one end of the annular optical cavity.
• the first mirror surface is an off-axis parabolic rotation- ally symmetric surface.
• the second mirror surface is an off-axis ellipsoidal rota- tionally symmetric surface.
• the annular optical cavity is defined by inner and outer coaxial spaced electrodes which produces an annular coherent beam and the gas laser also includes an RF power supply coupled to the outer electrode at at least one location symmetrical with respect to the length thereof.
• the inner electrode is grounded and there is provided a grounded structure surrounding the annular optical cavity.
• first and second ends of the outer electrode are coupled to the grounded structure via a plurality of induction coils.
• the at least one location is a location centered with respect to the length of the outer electrode.
• the mirror structure is grounded.
• a grounded structure surrounding the annular optical cavity and including first and second portions having precisely formed first and second mating surfaces, the first portion having machined thereon a first mirror structure located at one end of the annular optical cavity; and the second portion having machined thereon a second mirror structure located at one end of the annular optical cavity.
• the first mating surface and the first mirror structure are machined together so as to ensure desired alignment therebetween.
• the second mating surface and the second mirror structure are machined together so as to ensure desired alignment therebetween.
• the first mirror structure includes: a first mirror surface which is operative to decrease the diameter of the annular coherent beam from the first diameter and to expand the thickness of the annular coherent beam from the first thickness; a second mirror surface which is operative to focus an annular beam reflected by the first mirror surface to a location located interior of the pair of coaxial spaced electrodes; and a spatial filter disposed at the location located interior of the pair of coaxial spaced electrodes.
• the second mirror structure includes a third mirror surface located at an opposite end of the annular optical cavity.
• the gas laser also includes an output coupler. BRIEF DESCRIPTION OF THE DRAWINGS
• Fig. 1 is a simplified sectional illustration of an RF excited diffusion cooled gas laser of an annular configuration constructed and operative in accordance with a preferred embodiment of the present invention
• Fig. 2 is a simplified sectional illustration showing the optical structure of the RF excited diffusion cooled gas laser of Fig. 1;
• Fig. 3A is a sectional illustration taken along lines A
• Fig. 3B is a sectional illustration taken along lines B
• Fig. 3C is a sectional illustration taken along lines C
• Fig. 3D is a sectional illustration taken along lines D
• Fig. 3E is a sectional illustration taken along lines E
• Fig. 3F is a sectional illustration taken along lines F
• Fig. 3G is a sectional illustration taken along lines G
• Fig. 3H is a sectional illustration taken along lines H
• Fig. 31 is a sectional illustration taken along lines I
• Fig. 3J is a sectional illustration taken along lines J
• Fig. 3K is a sectional illustration taken along lines K
• Fig. 4 is a simplified sectional illustration showing the aspherical surfaces of the optical structure of the laser of Figs. 1 and 2;
• Fig. 5 is a simplified illustration of the RF electrical structure of the laser of Fig. l;
• Fig. 6 is a simplified illustration of the optomechanical structure of the laser of Fig. 1;
• Fig. 7 is a simplified illustration of the RF electrical structure of an alternative embodiment of the laser of Fig. 1.
• Fig. l is a simplified sectional illustration of an RF excited diffusion cooled gas laser 100 of an annular configuration constructed and operative in accordance with a preferred embodiment of the present invention.
• the laser of Fig. 1 comprises first and second enclosure elements 102 and 104, typically formed of aluminum, and an output coupler assembly 106.
• Output coupler assembly 106 is mounted over an aperture 108 formed in an end of enclosure element 104.
• the output coupler assembly 106 preferably comprises an annular spacer element 110 and an mirror housing element 112 which secures an output coupler mirror 114 against spacer element 110.
• Output coupler mirror 114 may be any suitable output coupler mirror.
• the output coupler mirror 114 is preferably a ZnSe mirror .
• First and second enclosure elements 102 and 104 are joined together as shown in Fig. 1 to define an enclosure 116 in which are mounted respective coaxial inner and outer generally circular cylindrical electrodes 120 and 122, which are centered about a longitudinal axis 123.
• Inner electrode 120 is typically formed of aluminum and has a circular cylindrical configuration. It is mounted within enclosure 116 at one end by means of a cylindrical mounting element 124 which is fixed to an interior cylindrical surface 126 of electrode 120 and is tightly secured against corresponding interior surfaces 128 and 130 of enclosure element 104.
• an annular RF contact spring 134 is interposed between an end surface 136 of mounting element 124 and a corresponding interior surface 138 of enclosure element 104.
• Inner electrode 120 is preferably mounted at its opposite end to the interior of enclosure element 102 by means of a plurality of spider struts 140, typically three in number.
• Each spider strut 140 includes a first end 142 fixed to an end surface 144 of electrode 120, a central knife-like portion 146 and a second end 148 which is tightly seated in a cylindrical recess 150 formed in an interior surface of enclosure element 102.
• an annular RF contact spring 154 is interposed between an end surface 156 of the second end 148 of each spider strut and a corresponding interior facing surface 158 of recess 150.
• Outer electrode 122 preferably comprises an integrally formed generally circular cylinder including a generally cylindrical inner recess 170 bounded by cylinder ends 172 and 174 having respective outwardly facing surfaces 176 and 178. Outer electrode 122 is preferably fixedly mounted onto respective interior surfaces 180 and 182 of enclosure elements 102 and 104 respectively by means of respective ceramic annuli 184 and 186 respectively. A generally cylindrical, electrically insulative, cover element 190 surrounds outer electrode 122.
• Recess 170 defines a coolant circulation chamber, which preferably communicates with a coolant fluid supply (not shown) and a coolant fluid drain (not shown) via fluid communication conduits 194 and 195.
• the inner electrode 120 is also cooled preferably by cooling fluid passing through a channel 196 extending therethough via conduits 197 and 198.
• a plurality of induction termination coils 199 are formed in bores 200 located at locations distributed about the circumference of ceramic annuli 184 and 186.
• An RF input connection 202 is provided at the center of the outer electrode 122 and comprises a metal rod 204 preferably surrounded by an insulator 206.
• a cylindrical discharge gap 210 is defined between the inner and outer electrodes 120 and 122 in the region between ceramic annuli 184 and 186.
• An inner facing surface of enclosure element 102 is preferably configured to define a first mirror surface 220, which is operative to decrease the diameter of an annular coherent beam formed in the discharge gap 210 from a first diameter and to expand the thickness of the annular coherent beam from a first thickness corresponding to the thickness of the discharge gap 210.
• the inner facing surface of enclosure element 102 is also preferably configured to define a second mirror surface 222 which is centered about longitudinal axis 123.
• Second mirror surface 222 is operative to focus an annular beam reflected by the first mirror surface 220 to a location 224 located interior of the pair of coaxial spaced electrodes 120 and 122 and along longitudinal axis 123.
• An inner facing surface of enclosure element 104 is preferably configured to define a third mirror surface 230, which, together with the first and second mirror surfaces 220 and 222 and the output coupler mirror 114 defines a laser resonator.
• a spatial filter 240 is preferably located within inner electrode 120 at location 224.
• Fig. 2 is a simplified sectional illustration showing the optical structure of the RF excited diffusion cooled gas laser of Fig. 1. It is seen that first mirror surface 220, which is preferably an off-axis parabo- loidal rotationally symmetric surface, is operative to decrease the diameter of an annular coherent beam 250 from a first diameter corresponding to the diameter of discharge gap 210 (Fig. 1) and to expand the thickness of the annular coherent beam 220 from a first thickness T corresponding to the thickness of discharge gap 210 (Fig. 1). Thickness T is illustrated in Fig. 3A.
• First mirror surface 220 is thus operative to provide a beam 252, a sectional illustration of which appears in Fig. 3B, which passes through a ring focus at a location 254.
• the cross section of beam 252 at location 254 is illustrated in Fig. 3C. Downstream of location 254, beam 252 expands sequentially as shown in the sectional illustrations of Figs. 3D and 3E.
• Second mirror surface 222 is typically an off-axis, ellipsoidal rotationally symmetric surface and is operative to focus beam 252 reflected by first mirror surface 220 to location 224 located interiorly of coaxial spaced electrodes 120 and 122.
• Fig. 3F shows the beam as it is impinges on second mirror surface 222.
• the beam reflected by second mirror surface 222, designated by reference numeral 260 is a generally solid beam which is sequentially focussed, as illustrated in the sectional illustrations of Figs. 3G, 3H and 31.
• Fig. 31 shows beam 260 at location 224.
• beam 260 Downstream of location 224, beam 260 sequentially expands as illustrated in the sectional illustrations of Figs. 3J and 3K until it impinges on surface 270 of output coupler 114.
• Third mirror surface 230 located at an opposite end of the annular optical cavity defined by discharge gap 210 is a flat mirror which reflects beam 250 back into discharge gap 210.
• Output coupler 114 is operative to receive, reflect and transmit a beam 260 reflected by the second mirror surface 222.
• Output coupler 114 defines a first partially reflective surface 270 which is spherical and has a radius of curvature equal to the distance between the surface 270 and location 224 and is thus operative to reflect part of the beam 260 back to location 224.
• the remainder of beam 260, which is not reflected by surface 270 is collimated by a second surface 272 of output coupler 114 and exits as useful laser power.
• Spatial filter 240 located at location 224 is operative to substantially prevent occurrence of high order modes, thus enabling the laser to operate in the lowest order mode.
• mirror surfaces 220 and 222 are constructed such that location 254 lies at the common focus of both mirror surfaces 220 and 222.
• mirror surface 220 is based on an off-axis section of a parabola 280. This off-axis section is rotated about axis 123 to define the annular mirror surface 220.
• mirror surface 222 is based on an off-axis section of an ellipse 282. This off-axis section is rotated about axis 123 to define the mirror surface 222.
• location 254 is located both at the focus of the parabola 280 and at one of the foci of the ellipse 282.
• Location 224 is located at the second focus of ellipse 282.
• This structure ensures that substantially each light ray passing through location 254 arrives at location 224. In this way, an annular beam is effective transformed to a solid conical beam.
• Mirrors 220 and 222 serve three important functions: They transform an annular beam into a solid beam of round cross section; they serve as intracavity expansion optics and they couple rear mirror 230 and output coupler 114.
• FIG. 5 is a simplified illustration of the RF electrical structure of the laser of Fig. 1.
• an annular optical cavity is defined by discharge gap 210 between by inner and outer coaxial spaced electrodes 120 and 122.
• An RF power supply 300 is coupled to the outer electrode 122 at at least one location 302 symmetrical with respect to the length of outer electrode 122.
• the RF power supply 300 is typically coupled to outer electrode 122 at location 302 via a conventional RF matching unit 304 and via RF input connection 202 (Fig. 1).
• the inner electrode 120 is grounded, preferably via enclosure elements 102 and 104.
• RF power supply 300 is grounded and provides grounding of enclosure elements 102 and 104 via RF matching unit 304 .
• first and second ends 310 and 320 of the outer electrode 122 are coupled to respective grounded enclosure elements 102 and 104 via a plurality of induction coils 199.
• induction coils 199 is operative to reduce undesirable voltage variation along the electrodes due to transmission line plasma phenomena.
• the outer electrode 122 is insulated from ground by ceramic annuli 184 and 186 and by cover element 190, which is an insulator preferably formed of a polymer.
• This structure effective restricts discharge to the region bounded by ceramic annuli 184 and 186. Beyond this region, the thin gap cavity 210 extends, typically 15 - 25 mm, and thus the hot excited gas reaching the extension of cavity 210 is effectively cooled and quenched by diffusion to the walls of cavity 210.
• cover element 190 is an insulator preferably formed of a polymer.
• the mirror surfaces 220 and 230 may be placed at a relatively short distance from the respective ends of cavity 210, typically less than 10 mm. This relatively short distance enables the wavefront exiting the cavity 210 to be maintained generally planar, providing optimal performance of the focusing optics 220, 222 and 270 and minimizing energy losses due to beam divergence.
• Fig. 6 is a simplified illustration of the opto-mechanical structure of the laser of Fig. 1. It is seen that mirror surfaces 220 and 222 are preferably integrally formed with enclosure element 102, as by diamond turning. Similarly mirror surface 230 is preferably integrally formed with enclosure element 104, as by diamond turning.
• respective mating surfaces 350 and 352 of enclosure elements 102 and 104 at their junction are flat diamond turned surfaces.
• enclosure elements 102 and 104 are clamped together.
• joined enclosure elements define an integral mechanical, optical and electrical structure for the laser.
• surfaces 350, 220 and 222 may all be machined in a single operation, and similarly surfaces 352 and 230 may be machined in a separate single operation, mutual alignment of surfaces 220, 222 and 230 may be realized by mutual attachment of mating surfaces 350 and 352 at junction 354. This greatly simplifies the structure and assembly of the laser and significantly lowers its cost.
• the laser may be formed with multiple mating surfaces .
• the laser with the exception of the output coupler, is formed entirely of aluminum. This enables thermal effects to be readily minimized.
• FIG. 7 is a simplified illustration of the RF electrical structure of an alternative embodiment of the laser of Fig. 1. As seen in Fig. 7, similarly to the embodiment of Figs, l - 6, an annular optical cavity is defined by discharge gap 210 between by inner and outer coaxial spaced electrodes 120 and 122.
• an RF is coupled to the outer electrode 122 via multiple discrete solid state RF power supply units 402.
• Suitable solid state RF power supply units are commercially available from various suppliers including, for example, Delta Sigma Inc. of Riverside, California, U.S.A..
• Solid state RF power supply units 402 are preferably mounted exteriorly of first and second enclosure elements 102 and 104 (Figs. 1 & 5) and provide power outputs at multiple locations at the outer electrode 122 (Figs. 1 & 5) as shown in Fig. 7, thereby to provide a generally homogeneous distribution of power and voltage along the length and circumference of the laser cavity.
• a DC power supply 404 preferably supplies electrical power to the RF power supply units 402.
• each RF power supply unit 402 is provided with a conventional RF matching unit 406 which outputs via an RF input connection 408.
• the inner electrode 120 is grounded, preferably via enclosure elements 102 and 104.
• DC power supply 404 is grounded and provides grounding of enclosure elements 102 and 104 via RF power supply units 402.
• the provision of a plurality of induction coils 199 is optional.
• the outer electrode 122 is insulated from ground by ceramic annuli 184 and 186 and by cover element 190, which is an insulator preferably formed of a polymer.
• This structure effective restricts discharge to the region bounded by ceramic annuli 184 and 186. Beyond this region, the thin gap cavity 210 extends, typically 15 - 25 mm, and thus the hot excited gas reaching the extension of cavity 210 is effectively cooled and quenched by diffusion to the walls of cavity 210.
• cover element 190 is an insulator preferably formed of a polymer.
• Figs. 1 - 6 and of Fig. 7 provide alternative solutions to the problem of voltage variations leading to unequal values of the E/N parameter along the length of the electrode and thus to reduced efficiency of the resonator.
• the solution of Fig. 7 is applicable to slab lasers as well as to co-axial lasers.

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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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• 1998
  • 1998-10-26 IL IL12676598A patent/IL126765A0/xx unknown
• 1999
  • 1999-10-26 WO PCT/IL1999/000566 patent/WO2000025393A2/en not_active Application Discontinuation
  • 1999-10-26 EP EP99952771A patent/EP1147580A4/de not_active Withdrawn
  • 1999-10-26 AU AU64855/99A patent/AU6485599A/en not_active Abandoned
  • 1999-10-26 JP JP2000578879A patent/JP2002528918A/ja active Pending

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