`
`(12) United States Patent
`Smith
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 9,048,000 B2
`*Jun. 2, 2015
`
`(54) HIGH BRIGHTNESS LASER-DRIVEN LIGHT
`SOURCE
`_
`(71) Apphcantt Energetlq Technology: Inc» Woburns
`MA (US)
`_
`1I1VeI11OI'I Donald K.
`BOSTOII, MA
`(73) Assignee: Energetiq Technology, Inc., Woburn,
`MA
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U'S'C' 1540’) by 0 days‘
`This patent is subject to a terminal dis-
`claimer.
`
`(21) Appl. No.: 13/964,938
`
`(22)
`
`Filed:
`
`Aug. 12, 2013
`
`(65)
`
`Prior Publication Data
`US 2014/0117258 A1
`‘May 1, 2014
`Related U.S. Application Data
`(63) Continuation of application No. 13/024,027, filed on
`Feb. 9, 2011, now Pat. No. 8,525,133, which is a
`continuation-in-part of application No. 12/ 166,918,
`filed on Jul. 2, 2008, now Pat. No. 7,989,786, which is
`
`(60)
`
`(51)
`
`a continuation-in-part of application No. 11/695,348,
`filed onApr. 2, 2007, now Pat. No. 7,786,455, which is
`a continuation-in-part of application No. 11/395,523,
`filed on Mar. 31, 2006, now Pat. No. 7,435,982.
`19’ro2\(/)i1s(i)onal application No. 61/302,797, filed on Feb.
`
`Int. Cl.
`G01] 1/00
`G21K 5/04
`B82Y10/00
`G03F 7/20
`
`(2006.01)
`(2006.01)
`(201 1.01)
`(2006.01)
`.
`(Continued)
`
`(52) U.S. Cl.
`CPC ........... .. G21K 5/04 (2013.01); YIOTZ9/49002
`(2015.01); B82Y10/00 (2013.01); G03F
`
`7/70033 (2013.01); H01J 61/16 (2013.01);
`H01J 65/04 (2013.01); H05B 41/382
`(2013.01); H05G 2/001 (2013.01); H05G 2/003
`(2013.01); H05G 2/008 (2013.01); YOZB
`
`(58)
`
`(56)
`
`250/504 R
`gigédcof Classification Search
`. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
`See application file for complete search history.
`
`_
`Referenees Clted
`U s PATENT DOCUMENTS
`
`3325995 A *
`4,088,966 A
`
`7/1974 -13eg1e e131 ~~~~~~~~~~~~~~~~~~~~ ~~ 372/5
`5/1978 Samis
`
`(Continued)
`
`FOREIGN PATENT DOCUMENTS
`
`A1
`(Continued)
`OTHER PUBLICATIONS
`
`Beck, “Simple Pulse Generator for Pulsing Xenon Arcs with High
`RePe11110I1 R316,” Rev 5013 Irlslfumq V01. 45, N0. 2, Feb. 1974, PP~
`318-319.
`
`(Continued)
`
`1.
`I
`1
`N.
`.
`E
`P .
`k
`A”’f"”y flf““’””7” ” J‘°° eN1I°PE 11°
`C ormac
`sszslanl xammer — ason
`(74) Attorney] Agent] or Firm i Proskauer Rose LLP
`57
`ABSTRACT
`.
`.
`.
`)
`(
`Anapparatus for producing light includes a chamber and an
`ignition source that ionizes a gas within the chamber. The
`apparatus also includes at least one laser that provides energy
`to.the ionized gas within the chamber to produce a high
`brightness light. The laser can provide a substantially con-
`.
`.
`.
`tinuous amount of energy to the ionized gas to generate a
`substantially continuous high brightness light.
`
`26 Claims, 39 Drawing Sheets
`
`
`
`ASML 1201
`ASML 1201
`
`
`
`US 9,048,000 B2
`Page 2
`
`(51)
`
`Int. Cl.
`
`H01] 65/04
`H053 41/38
`H05G 2/00
`G21K 5/00
`
`<2006~m>
`(200601)
`(200601)
`(2006.01)
`(2006.01)
`
`(56)
`
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`JP
`JP
`JP
`JP
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`1-296560
`04-144053
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`
`
`U.S. Patent
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`Jun. 2, 2015
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`U.S. Patent
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`Jun. 2, 2015
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`Sheet 23 of 39
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`US 9,048,000 B2
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`Spectral Radiance vs NA
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`U.S. Patent
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`Jun. 2, 2015
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`Sheet 24 of 39
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`US 9,048,000 B2
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`U.S. Patent
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`Jun. 2, 2015
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`Sheet 25 of 39
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`US 9,048,000 B2
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`FIG. 24
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`Jun. 2, 2015
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`Sheet 26 of 39
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`US 9,048,000 B2
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`2500
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`Sheet 27 of 39
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`US 9,048,000 B2
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`an error signal
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`FIG. 26
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`Jun. 2, 2015
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`Sheet 28 of 39
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`U.S. Patent
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`Jun. 2, 2015
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`Sheet 29 of 39
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`US 9,048,000 B2
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`U.S. Patent
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`Jun. 2, 2015
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`Sheet 30 of 39
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`US 9,048,000 B2
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`2900
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`U.S. Patent
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`Jun. 2, 2015
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`Sheet 31 of 39
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`Jun. 2, 2015
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`Sheet 32 of 39
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`Sheet 33 of 39
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`Jun. 2, 2015
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`FIG. 33
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`Jun. 2, 2015
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`FIG. 34
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`3500
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`Jun. 2, 2015
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`US 9,048,000 B2
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`US 9,048,000 B2
`
`1
`HIGH BRIGHTNESS LASER-DRIVEN LIGHT
`SOURCE
`
`RELATED APPLICATIONS
`
`This application is a continuation of U.S. Ser. No. 13/024,
`027, filed on Feb. 9, 2011, which is a continuation-in-part of
`U.S. Ser. No. 12/166,918, filed on Jul. 2, 2008, now U.S. Pat.
`No. 7,989,786, which is a continuation-in-part of U.S. Ser.
`No. 11/695,348, filed on Apr. 2, 2007, now U.S. Pat. No.
`7,786,455, which is a continuation-in-part of U.S. Ser. No.
`11/395,523, filed on Mar. 31, 2006, now U.S. Pat. No. 7,435,
`982, the entire disclosures each of which are hereby incorpo-
`rated by reference herein. This application claims the benefit
`of, and priority to U.S. Provisional Patent Application No.
`61/302,797, filed on Feb. 9, 2010, the entire disclosure of
`which is incorporated by reference herein.
`
`FIELD OF THE INVENTION
`
`The invention relates to methods and apparatus for provid-
`ing a laser-driven light source.
`
`BACKGROUND OF THE INVENTION
`
`High brightness light sources can be used in a variety of
`applications. For example, a high brightness light source can
`be used for inspection, testing or measuring properties asso-
`ciated with semiconductor wafers or materials used in the
`
`fabrication of wafers (e.g., reticles and photomasks). The
`electromagnetic energy produced by high brightness light
`sources can, alternatively, be used as a source of illumination
`in a lithography system used in the fabrication of wafers, a
`microscopy system, or a photoresist curing system. The
`parameters (e.g., wavelength, power level and brightness) of
`the light vary depending upon the application.
`The state of the art in, for example, wafer inspection sys-
`tems involves the use of xenon or mercury arc lamps to
`produce light. The arc lamps include an anode and cathode
`that are used to excite xenon or mercury gas located in a
`chamber of the lamp. An electrical discharge is generated
`between the anode and cathode to provide power to the
`excited (e.g., ionized) gas to sustain the light emitted by the
`ionized gas during operation of the light source. During
`operation, the anode and cathode become very hot due to
`electrical discharge delivered to the ionized gas located
`between the anode and cathode. As a result, the anode and/or
`cathode are prone to wear and may emit particles that can
`contaminate the light source or result in failure of the light
`source. Also, these arc lamps do not provide sufiicient bright-
`ness for some applications, especially in the ultraviolet spec-
`trum. Further, the position of the arc can be unstable in these
`lamps.
`Accordingly, a need therefore exists for improved high
`brightness light sources. A need also exists for improved high
`brightness light sources that do not rely on an electrical dis-
`charge to maintain a plasma that generates a high brightness
`light.
`The properties of light produced by many light sources
`(e.g., arc lamps, microwave lamps) are affected when the light
`passes through a wall of, for example, a chamber that includes
`the location from which the light is emitted.
`Accordingly, a need therefore exists for an improved light
`source whose emitted light is not significantly affected when
`the light passes through a wall of a chamber that includes the
`location from which the light is emitted.
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`2
`SUMMARY OF THE INVENTION
`
`The present invention features a light source for generating
`a high brightness light.
`The invention, in one aspect, features a light source having
`a chamber. The light source also includes an ignition source
`for ionizing a gas within the chamber. The light source also
`includes at least one laser for providing energy to the ionized
`gas within the chamber to produce a high brightness light.
`In some embodiments, the at least one laser is a plurality of
`lasers directed at a region from which the high brightness
`light originates. In some embodiments, the light source also
`includes at least one optical element for modifying a property
`of the laser energy provided to the ionized gas. The optical
`element can be, for example, a lens (e.g., an aplanatic lens, an
`achromatic lens, a single element lens, and a fresnel lens) or
`mirror (e.g., a coated mirror, a dielectric coated mirror, a
`narrow band mirror, and an ultraviolet transparent infrared
`reflecting mirror). In some embodiments, the optical element
`is one or more fiber optic elements for directing the laser
`energy to the gas.
`The chamber can include an ultraviolet transparent region.
`The chamber or a window in the chamber can include a
`
`material selected from the group consisting of quartz, Supra-
`sil® quartz (Heraeus Quartz America, LLC, Buford, Ga.),
`sapphire, MgF2, diamond, and CaF2. In some embodiments,
`the chamber is a sealed chamber. In some embodiments, the
`chamber is capable of being actively pumped. In some
`embodiments, the chamber includes a dielectric material
`(e.g., quartz). The chamber can be, for example, a glass bulb.
`In some embodiments, the chamber is an ultraviolet transpar-
`ent dielectric chamber.
`
`The gas can be one or more of a noble gas, Xe, Ar, Ne, Kr,
`He, D2, H2, 02, F2, a metal halide, a halogen, Hg, Cd, Zn, Sn,
`Ga, Fe, Li, Na, an excimer forming gas, air, a vapor, a metal
`oxide, an aerosol, a flowing media, or a recycled media. The
`gas can be produced by a pulsed laser beam that impacts a
`target (e.g., a solid or liquid) in the chamber. The target can be
`a pool or film of metal. In some embodiments, the target is
`capable of moving. For example, the target may be a liquid
`that is directed to a region from which the high brightness
`light originates.
`In some embodiments, the at least one laser is multiple
`diode lasers coupled into a fiber optic element. In some
`embodiments, the at least one laser includes a pulse or con-
`tinuous wave laser. In some embodiments, the at least one
`laser is an IR laser, a diode laser, a fiber laser, an ytterbium
`laser, a C02 laser, a YAG laser, or a gas discharge laser. In
`some embodiments, the at least one laser emits at least one
`wavelength of electromagnetic energy that
`is
`strongly
`absorbed by the ionized medium.
`The ignition source can be or can include electrodes, an
`ultraviolet ignition source, a capacitive ignition source, an
`inductive ignition source, an RF ignition source, a microwave
`ignition source, a flash lamp, a pulsed laser, or a pulsed lamp.
`The ignition source can be a continuous wave (CW) or pulsed
`laser impinging on a solid or liquid target in the chamber. The
`ignition source can be external or internal to the chamber.
`The light source can include at least one optical element for
`modifying a property of electromagnetic radiation emitted by
`the ionized gas. The optical element can be, for example, one
`or more mirrors or lenses. In some embodiments, the optical
`element is configured to deliver the electromagnetic radiation
`emitted by the ionized gas to a tool (e.g., a wafer inspection
`tool, a microscope, a metrology tool, a lithography tool, or an
`endoscopic tool).
`
`
`
`US 9,048,000 B2
`
`3
`The invention, in another aspect, relates to a method for
`producing light. The method involves ionizing with an igni-
`tion source a gas within a chamber. The method also involves
`providing laser energy to the ionized gas in the chamber to
`produce a high brightness light.
`In some embodiments, the method also involves directing
`the laser energy through at least one optical element for
`modifying a property of the laser energy provided to the
`ionized gas. In some embodiments, the method also involves
`actively pumping the chamber. The ionizable medium can be
`a moving target. In some embodiments, the method also
`involves directing the high brightness light through at least
`one optical element to modify a property ofthe light. In some
`embodiments, the method also involves delivering the high
`brightness light emitted by the ionized medium to a tool (e.g.,
`a wafer inspection tool, a microscope, a metrology tool, a
`lithography tool, or an endoscopic tool).
`In another aspect, the invention features a light source. The
`lights source includes a chamber and an ignition source for
`ionizing an ionizable medium within the chamber. The light
`source also includes at least one laser for providing substan-
`tially continuous energy to the ionized medium within the
`chamber to produce a high brightness light.
`In some embodiments, the at least one laser is a continuous
`wave laser or a high pulse rate laser. In some embodiments,
`the at least one laser is a high pulse rate laser that provides
`pulses of energy to the ionized medium so the high brightness
`light is substantially continuous. In some embodiments, the
`magnitude of the high brightness light does not vary by more
`than about 90% during operation. In some embodiments, the
`at least one laser provides energy substantially continuously
`to minimize cooling of the ionized medium when energy is
`not provided to the ionized medium.
`In some embodiments, the light source can include at least
`one optical element (e.g., a lens or mirror) for modifying a
`property of the laser energy provided to the ionized medium.
`The optical element can be, for example, an aplanatic lens, an
`achromatic lens, a single element lens, a fresnel lens, a coated
`mirror, a dielectric coated mirror, a narrow band mirror, or an
`ultraviolet transparent infrared reflecting mirror. In some
`embodiments, the optical element is one or more fiber optic
`elements for directing the laser energy to the ionizable
`medium.
`In some embodiments, the chamber includes an ultraviolet
`transparent region. In some embodiments, the chamber or a
`window in the chamber includes a quartz material, suprasil
`quartz material, sapphire material, MgF2 material, diamond
`material, or CaF2 material. In some embodiments, the cham-
`ber is a sealed chamber. The chamber can be capable ofbeing
`actively pumped.
`In some embodiments,
`the chamber
`includes a dielectric material (e.g., quartz). In some embodi-
`ments, the chamber is a glass bulb. In some embodiments, the
`chamber is an ultraviolet transparent dielectric chamber.
`The ionizable medium can be a solid, liquid or gas. The
`ionizable medium can include one or more of a noble gas, Xe,
`Ar, Ne, Kr, He, D2, H2, 02, F2, a metal halide, a halogen, Hg,
`Cd, Zn, Sn, Ga, Fe, Li, Na, an excimer forming gas, air, a
`vapor, a metal oxide, an aerosol, a flowing media, a recycled
`media, or an evaporating target. In some embodiments, the
`ionizable medium is a target in the chamber and the ignition
`source is a pulsed laser that provides a pulsed laser beam that
`strikes the target. The target can be a pool or film of metal. In
`some embodiments, the target is capable of moving.
`In some embodiments, the at least one laser is multiple
`diode lasers coupled into a fiber optic element. The at least
`one laser can emit at least one wavelength of electromagnetic
`energy that is strongly absorbed by the ionized medium.
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`The ignition source can be or can include electrodes, an
`ultraviolet ignition source, a capacitive ignition source, an
`inductive ignition source, an RF ignition source, a microwave
`ignition source, a flash lamp, a pulsed laser, or a pulsed lamp.
`The ignition source can be external or internal to the chamber.
`In some embodiments, the light source includes at least one
`optical element (e.g., a mirror or lens) for modifying a prop-
`erty of electromagnetic radiation emitted by the ionized
`medium. The optical element can be configured to deliver the
`electromagnetic radiation emitted by the ionized medium to a
`tool (e.g., a wafer inspection tool, a microscope, a metrology
`tool, a lithography tool, or an endoscopic tool).
`The invention, in another aspect relates to a method for
`producing light. The method involves ionizing with an igni-
`tion source an ionizable medium within a chamber. The
`
`method also involves providing substantially continuous
`laser energy to the ionized medium in the chamber to produce
`a high brightness light.
`In some embodiments, the method also involves directing
`the laser energy through at least one optical element for
`modifying a property of the laser energy provided to the
`ionizable medium. The method also can involve actively
`pumping the chamber. In some embodiments, the ionizable
`medium is a moving target. The ionizable medium can
`include a solid, liquid or gas. In some embodiments, the
`method also involves directing the high brightness light
`through at least one optical element to modify a property of
`the light. In some embodiments, the method also involves
`delivering the high brightness light emitted by the ionized
`medium to a tool.
`
`The invention, in another aspect, features a light source
`having a chamber. The light source includes a first ignition
`means for ionizing an ionizable medium within the chamber.
`The light source also includes a means for providing substan-
`tially continuous laser energy to the ionized medium within
`the chamber.
`
`The invention, in another aspect, features a light source
`having a chamber that includes a reflective surface. The light
`source also includes an ignition source for ionizing a gas
`within the chamber. The light source also includes a reflector
`that at least substantially reflects a first set of predefined
`wavelengths of electromagnetic energy directed toward the
`reflector and at least substantially allows a second set of
`predefined wavelengths of electromagnetic energy to pass
`through the reflector. The light source also includes at least
`one laser (e.g., a continuous-wave fiber laser) external to the
`chamber for providing electromagnetic energy to the ionized
`gas within the chamber to produce a plasma that generates a
`high brightness light. A continuous-wave laser emits radia-
`tion continuously or substantially continuously rather than in
`short bursts, as in a pulsed laser.
`In some embodiments, at least one laser directs a first set of
`wavelengths of electromagnetic energy through the reflector
`toward the reflective surface (e.g., inner surface) ofthe cham-
`ber and the reflective surface directs at least a portion of the
`first set of wavelengths of electromagnetic energy toward the
`plasma. In some embodiments, at least a portion of the high
`brightness light is directed toward the reflective surface of the
`chamber, is reflected toward the reflector, and is reflected by
`the reflector toward a tool. In some embodiments, at least one
`laser directs a first set of wavelengths of electromagnetic
`energy toward the reflector, the reflector reflects at least a
`portion of the first wavelengths of electromagnetic energy
`towards the reflective surface of the chamber, and the reflec-
`tive surface directs a portion of the first set of wavelengths of
`electromagnetic energy toward the plasma.
`
`
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`US 9,048,000 B2
`
`5
`In some embodiments, at least a portion ofthe high bright-
`ness light is directed toward the reflective surface of the
`chamber, is reflected toward the reflector, and passes through
`the reflector toward an output of the light source. In some
`embodiments, the light source comprises a microscope, ultra-
`violet microscope, wafer inspection system, reticle inspec-
`tion system or lithography system spaced relative to the out-
`put of the light source to receive the high brightness light. In
`some embodiments, a portion of the high brightness light is
`directed toward the reflective surface of the chamber,
`is
`reflected toward the reflector, and electromagnetic energy
`comprising the second set of predefined wavelengths of elec-
`tromagnetic energy passes through the reflector.
`The chamber of the light source can include a window. In
`some embodiments, the chamber is a sealed chamber. In some
`embodiments, the reflective surface of the chamber com-
`prises a curved shape, parabolic shape, elliptical shape,
`spherical shape or aspherical shape. In some embodiments,
`the chamber has a reflective inner surface. In some embodi-
`
`ments, a coating or film is located on the outside of the
`chamber to produce the reflective surface. In some embodi-
`ments, a coating or film is located on the inside ofthe chamber
`to produce the reflective surface. In some embodiments, the
`reflective surface is a structure or optical element that is
`distinct from the inner surface of the chamber.
`
`The light source can include an optical element disposed
`along a path the electromagnetic energy from the laser travels.
`In some embodiments, the optical element is adapted to pro-
`vide electromagnetic energy from the laser to the plasma over
`a large solid angle. In some embodiments, the reflective sur-
`face of the chamber is adapted to provide electromagnetic
`energy from the laser to the plasma over a large solid angle. In
`some embodiments, the reflective surface of the chamber is
`adapted to collect the high brightness light generated by the
`plasma over a large solid angle. In some embodiments, one or
`more of the reflective surface, reflector and the window
`include (e.g., are coated or include) a material to filter pre-
`defined wavelengths (e.g., infrared wavelengths of electro-
`magnetic energy) of electromagnetic energy.
`The invention, in another aspect, features a light source that
`includes a chamber that has a reflective surface. The light
`source also includes an ignition source for ionizing a gas
`within the chamber. The light source also includes at least one
`laser external to the chamber for providing electromagnetic
`energy to the ionized gas within the chamber to produce a
`plasma that generates a high brightness light. The light source
`also includes a reflector positioned along a path that the
`electromagnetic energy travels from the at least one laser to
`the reflective surface of the chamber.
`
`In some embodiments, the reflector is adapted to at least
`substantially reflect a first set of predefined wavelengths of
`electromagnetic energy directed toward the reflector and at
`least substantially allow a second set of predefined wave-
`lengths of electromagnetic energy to pass through the reflec-
`tor.
`
`The invention, in another aspect, relates to a method for
`producing light. The method involves ionizing with an igni-
`tion source a gas within a chamber that has a reflective sur-
`face. The method also involves providing laser energy to the
`ionized gas in the chamber to produce a plasma that generates
`a high brightness light.
`In some embodiments, the method involves directing the
`laser energy comprising a first set of wavelengths of electro-
`magnetic energy through a reflector toward the reflective
`surface of the chamber, the reflective surface reflecting at
`least a portion of the first set of wavelengths of electromag-
`netic energy toward the plasma. In some embodiments, the
`
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`method involves directing at least a portion ofthe high bright-
`ness light toward the reflective surface of the chamber which
`is reflected toward the reflector and is reflected by th