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`
`US007786455B2
`
`(12) Ulllted States Patent
`Smith
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,786,455 B2
`Aug. 31, 2010
`
`(54) LASER—DRIVEN LIGHT SOURCE
`
`(75)
`
`Inventor: Donald K-Smith,Be1m0nt.MA(US)
`’
`(73) Assigneez Energctiq Technology, Inc., Woburn,
`MA (US)
`.
`.
`.
`.
`.
`Subject to any disclaimer, the term 01 this
`patent is extended or adjusted under 35
`U_S_C' 15403) by 820 days.
`
`.
`.
`( " ) Notice:
`
`21
`
`PP
`A l.N0.Z 11/695,348
`
`(22)
`
`Filed:
`
`Apr. 2, 2007
`
`6,288,780 B1
`6,417,625 B1*
`6,788,404 B2
`6,956,329 132*
`7‘652,430 B11.
`2002/0021508 A1
`2003/0168982 A1
`2003/0231496 A1
`k
`2004/0264512 A1 ‘
`2005/0167618 A1*
`
`356/237.1
`9/2001 Fairley etal.
`........ .. 315/111.31
`7/2002 Brooksctal.
`9/2004 Lange ................... .. 356/2372
`10/2005 Brooksetal.
`315/111,31
`
`“2010 Delgado
`313/633
`2/2002 Ishihara .................... .. 359/853
`9/2003 K"
`......................... .. 313/634
`12/2003 SSH et al
`362/268
`' """"""""" "
`’/
`0
`’
`12/2004 Hzutlove et al.
`.............. .. 372/5
`8/2005 Hoshino etal.
`....... .. 250/504R
`
`2007/0285921 A1* 12/2007 Zulim eta].
`
`.............. .. 362/240
`
`(65)
`
`Prior Publication Data
`US 2007/0228300 Al
`Oct. 4, 2007
`
`(cominued)
`FOREIGN pA'l'EN'1‘ DOCUNIENTS
`
`Related U.S. Application Data
`
`JP
`
`51.193353
`
`3/1985
`
`(63) Continuation-in—part of application No. 11/395,523,
`filed on Mar. 31, 2006, now Pat. No. 7,435,982.
`
`Int_ CL
`(2006.()1)
`[I053 31/26
`(200601)
`G01‘, 3/10
`(2006-01)
`G210 4/00
`(2006.01)
`HOIJ 61/28
`(52) U.S.Cl.
`............................. .. 250/493.1; 250/504 R;
`315/111.21; 315/111.71; 315/111.91; 313/231.31;
`313/23141-’ 313/231'71
`(58) Field of Classification Search ........... .. 250/423 R,
`250/423 P_, 424, 426, 494.1, 493.1, 504 R,
`250/504 H; 315/111.21, 111.71, 111.91;
`313/231.31, 231.41, 231.61, 231.71, 631,
`313/632,633 A,
`
`(57)
`
`ABSTRACT
`
`,.
`
`»1‘
`
`d.
`
`,1-.1d...h.
`
`b
`
`.d.
`
`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 21
`substantially continuous high brightness light.
`
`43 Claims, 8 Drawing Sheets
`
`(55)
`
`References Cited
`
`U-S~ PATENT DOCUMENTS
`4’088’966 A *
`5/1978 Samis
`................ N 3131,3151
`4,498,029 A ,,
`2/1985 Yoshizawa et a1‘
`____ H 315/39
`4,646,215 A
`2/1987 Levin et al.
`.... ..
`. 362/296
`RE32,626 E *
`3/1988 Yoshizawa el al.
`.......... .. 315/39
`
`
`
`228
`
`ASML 1 120
`
`(51)
`
`OTHER PUBLICATIONS
`..
`ty of a High~Pressure Cascade
`‘
`“The VUV Emissivi
`,
`.
`Wilbers et al
`Argon Arc from 125 to 200 nm,”./. Qmznt. Spectrosc. Radiat. ]7'(ms—
`fer, vol. 46, 1991, pp. 299-308.
`
`(Continued)
`Primar ) Fm}m.ne,_#Bema]_d F eouw
`(74) .4tt}or7zev, Agent, or Firm—;1;roskauer Rose LLP
`"
`'
`
`

`
`US 7,786,455 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`2009/0032740 Al*
`
`2/2009 Smith etal.
`
`............ .. 250/503.1
`
`OTHER PUBLICATIONS
`
`Wilbers et al., “The Continuum Emission of an Arc Plasma,” J.
`Quam‘. Spectrosc. Radial. Transfer, vol. 45, No. 1, 1991, pp. 1-10.
`Beck, "Simple Pulse Generator for Pulsing Xenon Arcs with High
`Repetition Rate,” Rev. Sci. 1nsIrzzm., vol. 45, No. 2, Feb. 1974, pp.
`318-319.
`Raizer, “Optical Discharges,”S0v. Phys. Usp. 23(l1), Nov. 1980, pp.
`789-806.
`Fiedorowicz et 211., “X—Ray Emission form Laser-Irradiated Gas Puff
`Targets,” Appl. Phys. Len. 62 (22), May 31, 1993, pp. 2778-2780.
`Keefer et 2.1., “Experimental Study of a Stationary Laser-Sustained
`Air Plasma,” Journal 0fApplied Physics, vol. 46, No. 3, Mar. 1975,
`pp. 1080-1083.
`Jeng ct al., “Theoretical Investigation ofLaser-Sustained Argon Plas-
`mas,”J. Appl. Phys. 60 (7), Oct. l, 1986, pp. 2272-2279.
`Franzen, “CW Gas Breakdown in Argon Using 10.6-pm Laser Radia-
`tion,”/t_1Jpl. Phys. LetI., vol. 21, No. 2, Jul. 15, 1972, pp. 62-64.
`Moody, “Maintenance ofa Gas Breakdown in Argon Using 10.6-ucw
`Radiation,” Journal 0fApp1ied Physics, vol. 46, No. 6, Jun. 1975, pp.
`2475-2482.
`
`Generalov et a1., “Experimental Investigation of a Continuous Opti-
`cal Discharge,” Soviet Plrysics Jl:"[l’, vol. 34, No. 4. Apr. 1972. pp.
`763 -769.
`
`Generalov et al., “Continuous Optical Discharge,” ZIIETF Pis. Red.
`11, No. 9, May 5, 1970. pp. 302-304.
`Kozlov et al., “Radiative Losses by Argon Plasma and the Emissive
`Model ofa Continuous Optical Discharge,” Sav. Phys. JETP, vol. 39,
`No. 3, sep. 1974, pp. 463-468.
`Carlhoff et al., “Continuous Optical Discharges at Very High Pres-
`sure,” Plzysicrz 103C, I981, pp. 439-447.
`Cremers et a1., “Evaluation ofthe Continuous Optical Discharge for
`Spectrochemical Analysis,” Spectroc/zimica Acta, vol. 4013, .\lo. 4,
`1985, pp. 665-679.
`Kozlov et al., “Sustained Optical Discharges in Molecular Gases,”
`Sov. Phys. Tec/1. Phys. 49(ll), Nov. 1979, pp. 1283-1287.
`Keefer, “Laser-Sustainecl Plasmas,” Laser—Induced Plasmas and
`Applications, published by Marcel Dekker, edited by Radziemski et
`31., 1989, pp. 169-206.
`Hamamatsu Product Information, “Super-Quiet Xenon Lamp Super-
`Quiet Mercury-Xenon Lamp,” Nov. 2005.
`
`’*‘ cited by examiner
`
`

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`U.S. Patent
`
`Aug. 31, 2010
`
`Sheet 1 of8
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`US 7,786,455 B2
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`Aug. 31, 2010
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`US 7,786,455 B2
`
`1
`LASER-DRIVEN LIGHT SOURCE
`
`RELATED APPLICATIONS
`
`This application is a continuation—in—part of U.S. Ser. No.
`ll/395,523. filed on Mar. 31, 2006, now U.S. Pat. No. 7,435,
`982, the entire disclosure of which is incorporated by refer-
`ence 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 lights
`sources can, alternatively, be used as a source ofillumination
`in a lithography system used in the fabrication of wafers, a
`microscopy systems, 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 are 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 are lamps do not provide sufiicient bright-
`ness for some applications, especially in the ultraviolet spec-
`trum. Further, the position of the are can be unstable in these
`lamps.
`Accordingly, a need therefore exists for improved high
`brightness li
`it 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.
`
`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
`
`5
`
`10
`
`20
`
`M ‘J\
`
`40
`
`50
`
`55
`
`60
`
`2
`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, O2, F2, a metal halide, a halogen, Hg, Cd, Zn, Sn,
`Ga, Fe, Li, Na, an excimer fonning 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 CO3 laser, a YAG laser, or a gas discharge laser. In
`seine 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 [lash 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 ofelectromagnetic 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).
`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 seine embodiments, the method also involves
`actively pumping the chamber. The ionizablc 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 of the 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).
`
`

`
`US 7,786,455 B2
`
`3
`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 ofenergy 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 CaI72 material. In some embodiments, the cham-
`ber is a sealed chamber. The chamber can be capable ofbeing
`actively ptunped.
`In some embodiments,
`the chamber
`includes a dielectric material (eg, 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, 21 metal halide, a halogen, Hg,
`Cd, Zn, Sn, Ga, Fe. Li, Na, an exeimer 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 seine 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.
`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 seine 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
`
`4
`
`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 refiector
`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 (eg, 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) of the cham-
`ber and the reflective surface directs at least a portion of the
`first set ofwavelengths 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 refiector refiects at least a
`portion of the first wavelengths of electromagnetic energy
`towards the reflective surface of the chamber, and the refiec—
`tive surface directs a portion of the first set of wavelengths of
`electromagnetic energy toward the plasma.
`In some embodiments, at least a portion of the 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
`refiected toward the refiector, and electromagnetic energy
`comprising the second set of predefined wavelengths of elec-
`tromagnetie energy passes through the reflector.
`The chamber of the light source can include a window. In
`seine embodiments, the chamber is a sealed chamber. In some
`embodiments, the reflective surface of the chamber com-
`
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`6
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`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 refiective 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, refiector 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-
`lot‘.
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`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 lascr 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 V
`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
`method involves directing at least a portion ofthe high bright-
`ness light toward the reflective surface of the chamber which V
`is reflected toward the reflector and is reflected by the reflec-
`tor toward a tool.
`
`In some embodiments, the method involves directing the
`laser energy comprising a first set of wavelengths of electro-
`magnetic energy toward the reflector, the reflector reflects at
`least a portion of the first wavelengths of electromagnetic
`energy toward the reflective surface of the chamber,
`the
`reflective surface directs a portion of the first set of wave-
`lengths ofelectromagnetic energy toward the plasma. In some
`embodiments, the method involves directing a portion of the
`high brightness light toward the reflective surface of the
`chamber which is refiected toward the reflector and, electro-
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`magnetic energy comprising the second set of predefined
`wavelengths of electromagnetic energy passes through the
`reflector.
`The method can involve directing the laser energy through
`an optical element that modifies a property ofthe laser energy
`to direct the laser energy toward the plasma over a large solid
`angle. In some embodiments, the method involves directing
`the laser energy through an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`the plasma over a solid angle of approximately 0.012 stera-
`dians. In some embodiments, the method involves directing
`the laser energy through an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`the plasma over a solid angle of approximately 0.048 stera—
`dians. In some embodiments, the method involves directing
`the laser energy through an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`the plasma over a solid angle of greater than about 2:: (about
`6.28) steradians. In some embodiments, the reflective surface
`of the chamber is adapted to provide the laser energy 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.
`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 refiective sur-
`face. The method also involves directing electromagnetic
`energy from a laser toward a reflector that at least substan-
`tially reflects a first set of wavelengths of electromagnetic
`energy toward the ionized gas in the chamber to produce a
`plasma that generates a high brightness light.
`In some embodiments, the electromagnetic energy from
`the laser first is reflected by the reflector toward the refiective
`surface of the chamber. In some embodiments, the electro-
`magnetic energy directed toward the refiective surface of the
`chamber is reflected toward the plasma. In some embodi-
`ments, a portion of the high brightness light is directed toward
`the refiective surface of the chamber, reflected toward the
`reflector and passes through the reflector.
`In some embodiments, the electromagnetic energy from
`the laser first passes through the reflector and travels toward
`the reflective surface of the chamber. In some embodiments,
`the electromagnetic energy directed toward the reflective sur-
`face of the chamber is reflected toward the plasma. In some
`embodiments, a portion ofthe high brightness light is directed
`toward the reflective surface ofthe chamber, reflected toward
`the reflector and reflected by the reflector.
`The invention. in another aspect, features a light source that
`includes a chamber having a reflective surface. The light
`source also includes a means for ionizing a gas within the
`chamber. The light source also includes a means for at least
`substantially reflecting a first set ofpredefined wavelengths of
`electromagnetic energy directed toward the reflector and at
`least substantially allowing a second set ofpredefined wave-
`lengths of electromagnetic energy to pass through the reflec-
`tor. The light source also includes a means for providing
`electromagnetic energy to the ionized gas within the chamber
`to produce a plasma that generates a high brightness light.
`The invention, in another aspect, features a light source that
`includes a sealed chamber. The light source also includes an
`ignition source for ioni7.ing a gas within the chamber. The
`light source also includes at least one laser external to the
`sealed 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 curved reflective surface disposed external to the
`
`

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`US 7,786,455 B2
`
`7
`sealed chamber to receive at leas a portion of the high bright-
`ness light emitted by the sealed chamber and refiect the high
`brightness light toward an output of the light source.
`In some embodiments, the light source includes an optical
`element disposed along a path the electromagnetic energy 5
`from the laser travels. In some embodiments,
`the sealed
`chamber includes a support element that locates the sealed
`chamber relative to the curved reflective surface. In some
`embodiments, the sealed chamber is a quartz bulb. In some
`embodiments, the light source includes a second curved
`reflective surface disposed internal or external to the sealed
`chamber to receive at least a portion of the laser electromag-
`netic energy and focus the electromagnetic energy on the
`plasma that generates the high brightness light.
`The invention, in another aspect, features a light source that
`includes a sealed chamber and an ignition source for ionizing
`a gas within the chamber. The light source also includes at
`least one laser external to the sealed chamber for providing
`electromagnetic energy. The light source also includes a
`curved reflective surface to receive and reflect at least a por-
`tion of the electromagnetic energy toward the ionized gas
`within the chamber to produce a plasma that generates a high
`brightness light, the curved reflective surface also receives at
`least a portion of the high brightness light emitted by the
`plasma and rellects the high brightness light toward an output
`of the light source.
`the curved refiective surface
`In some embodiments,
`focuses the electromagnetic energy on a region in the cham-
`ber where the plasma is located. In some embodiments, the
`curved reflective surface is located within the chamber. In
`some embodiments, the curved reflective surface is located
`external to the chamber. In some embodiments, the high
`brightness light is ultraviolet light, includes ultraviolet light
`or is substantially ultraviolet light.
`The foregoing and other objects, aspects, features, and
`advantages ofthe invention will become more apparent from
`the following description and from the claims.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`The foregoing and other objects, feature and advantages of
`the invention, as well as the invention itself, will be more fully
`understood from the following illustrative description, when
`read together with the accompanying drawings which are not
`necessarily to scale.
`FIG.
`1
`is a schematic block diagram of a light source,
`according to an illustrative embodiment of the invention.
`FIG. 2 is a schematic block diagram of a portion of a light
`source, according to an illustrative embodiment ofthe inven-
`tion.
`FIG. 3 is a graphical representation of UV’ brightness as a
`function ofthe laser power provided to a plasma, using a light
`source according to the invention.
`FIG. 4 is a graphical representation of the transmission of 5
`laser energy through a plasma generated from mercury, using A
`a light source according to the invention.
`FIG. 5 is a schematic block diagram of a light source,
`according to an illustrative embodiment of the invention.
`FIG. 6 is a schematic block diagram of a light source,
`according to an illustrative embodiment of the invention.
`FIG. 7 is a schematic block diagram of a light source.
`according to an illustrative embodiment of the invention.
`FIG. 8A is a schematic block diagram ofa light source in
`which electromagnetic energy from a laser is provided to a 65
`plasma over a first solid angle, according to an illustrative
`embodiment of the invention.
`
`60
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`8
`FIG. 8B is a schematic block diagram ofthe light source of
`FIG. 8A in which the electromagnetic energy from the laser is
`provided to the plasma over a larger solid angle, according to
`an illustrative embodiment of the invention.
`
`DF,TAll.F,D DESCRIPTION OF IIIUSTRATIVF.
`EMBODIMENTS
`
`FIG. 1 is a schematic block diagram of a light source 100
`for generating light, that embodies the invention. The light
`source 100 includes a chamber 128 that contains an ionizable
`medium (not shown). The light source 1 00 provides energy to
`a region 130 ofthe chamber 128 having the ionizable medium
`which creates a plasma 132. The plasma 132 generates and
`emits a high brightness light 136 that originates from the
`plasma 132. The light source 100 also includes at least one
`laser source 104 that generates a laser beam that is provided to
`the plasma 132 located in th