`
`US007786455B2
`
`(12) United States Patent
`Smith
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`‘US 7,786,455 B2
`Aug. 31, 2010
`
`.......... .. 356./237.1
`9/2001 Faii-ley ctzil.
`6,288,780 B1
`..
`. 315./lll.3l
`7/2002 Brooks et nl.
`6,417,625 Bl *
`9/2004 Lnnge ......... ..
`356/237.2
`6,788,404 B2
`6,956,329 B2"" 10/2005 Brooksetzil.
`31-5/111.31
`7,652,430 131*
`1/2010 Delgado
`313/633
`2002/0021508 Al
`2/2002.
`Ishilizira ..
`359/853
`2003/0168982 Al
`9/2003 K"
`......................... .. 3l3‘6“4
`2003/0231496 M 12/7003 Sin t 1]
`362//228
`' """"""""" "
`7
`_
`’
`if
`T‘;
`‘“_’ 6 ‘
`'
`I,
`2004. 0.64312 Al
`1-/2004 Haillove et al.
`.............. .. 3726
`2005./0l676l8 Al "‘
`8/2005 lloshino ei zil.
`250/504 R
`
`
`
`2007/0285921 Al
`
`l2/2007' Zuliin el al.
`
`362/240
`
`(21) Appl. No.: 11/695,348
`
`(22)
`
`Filed:
`
`Apr. 2, 2007
`
`(65)
`
`Prior Publication Data
`
`(comjnued)
`
`Related U.S. Application Data
`
`JP
`
`51-193353
`
`3/1935
`
`(63) Coiitiii1iation—in-part of application No. 11/395,523,
`filed on Mar. 31, 2006‘, now Pat No. 7,435,982.
`
`(51)
`
`A
`Int CL
`(200601)
`17058 31/26
`(200601)
`G01‘, 3/10
`(2005-01)
`G21G 4/00
`(2006.01)
`I-I01] 61/28
`(52) U.S. Cl.
`............................. .. 250/493.1; 250/504 R;
`315/111.21;315/ll1.7l;315/]1l.9l;3l3/231.31;
`313/23141; 313/231271
`(58) Field of Classification Search. ........... .. 250/423 R,
`250/423 P, 424, 426, 494.1, 493.1, 504 R,
`250/504H; 315/111.21,111.7l,lll,9l;
`313/231.31, 231.41, 231.61, 231.71, 631,
`.
`.
`,
`3.13/632’ 633
`See apphcamm file for Complete 3earchh1StOry'
`References Cited
`l W
`_
`H V‘
`Y
`_
`V
`‘
`U-5 PA! EN1 D0(’UN“3N15
`4q088,966 A .;(
`5/1978 samis _______________ H 313/231.51
`4,498’029 A ,,
`Z/1985 Yoshizawact 31.
`315/39
`4,646,215 A
`2/1987 Levin etal.
`...........
`362/296
`RF/32,626 E ”‘
`3/1988 Yoshizawa el al.
`315/39
`
`(56)
`
`OTHER PUBLlCA"l‘lONS
`Wilbeis et al., “The VUV Emissivity of a High-Pressure Cascade
`Argon An: from 125 to 200 nm,”J. Quaul, Sper.-trosc. Radial. Tram"-
`fer, vol. 46, 1991, pp. 299-303.
`“
`
`(Continued)
`.
`.
`.,
`4.
`,
`Prmmry lL.x'anzmer—Bernard l1 fiouw
`(74) «lttornev A rent or Firm~——~Proskauer Rose LLP
`‘
`" 5
`'
`‘
`‘,u3STRACv]~
`2
`
`(57)
`
`2
`
`An apparatus for producing light includes a ehaniber and ‘am
`ignition source that ioiiizes a gas within the chamber. The
`apparatus zilso 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 '21I11OUl1l of eiiengy. to the i0iii'/.ed‘gas to geiierale a
`substantially continuous high brightness light.
`
`43 Claims, 8 Drawing Sheets
`
`
`
`ASML 1301
`
`(54) LASER~DRIVEN LIGHT SOURCE
`
`(75)
`
`Inventor: Donald K-Smith,,Be1I11011LMA (US)
`_
`W
`_
`‘
`,
`(73) Asslgneei
`]‘~“"8e‘“l 1°°h“°l°83’» 111°-= Wobumz
`MA‘ (US)
`.
`.
`.
`.
`,
`.
`of this
`b11b_]63CI to any dlSCl€l1l11€l‘_,tl1Cfel’1I1
`patent is extended or adjusted under 35
`U_S’C_v 154(1)) by 320 dayS_
`V
`
`..,.
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`.
`) Notice:
`
`(
`
`
`
`US 7,786,455 B2
`Page 2
`
`Us. IA'I‘EN'[‘ DOCUMENTS
`
`2009‘/0032740 Al"‘
`
`2/2009 Smith et 21].
`
`............ .. 250/503.1
`
`OTHER"PUBLICATIONS
`
`7'
`
`Wilbers et 211., “The Continuum Emission of an Arc Plasma,” J.
`Quant. S]](’('/I'()S(‘. Radial. Transfer, vol. 4S,No. I, I991, pp. l-IO.
`Beck, “Simple Pulse Generator for Pulsing Xenon Arcs with High
`Repetition Rate,” Rev. Sci. Inrrrm'n., vol. -45, No. 2, Feb. 1974, pp.
`318-319.
`Rat/,er, “Optical Discharges,” Sov. P/zys. Usp. 23(l 1). Nov. 1980, pp.
`789-805.
`Fiedorowicz et 21]., ‘‘X—Ray Emission form Laser-Irradiated Gas Puff
`Targets,” Appl. Phys. Letr. 62 (22), May 31, 1993, pp.i277S-2780.
`Keefer et 11],, “Experimental Study of :1 Stationary Laser-Sustained
`Air Plasma,” Journal q/"AppIiea' PI)y.s'ib.v, vol. 46, No. 3', Mar. 1975,
`pp. lO80-1083.
`Jeng et al., “Theoretical Investi gal ion ofI;,:1ser—S11stained Argon Plas-
`mas,”.I. Appl. Phys. 60 (7), Oct. 1, 1986, pp. 2272-2279.
`Franzen, “CW Gas Breakdown in Argon Using t0.6~1un Laser Radia-
`tion,”/lppl. Phys. I.ct(., vol. 21, No. 2, Jul. 15, 1972, pp. 62-64.
`Moody, “Maintenance oFa Gas Breakdown in Argon Using 10.6-pew
`Radiation,” Journal Q/'A,r)plied Physics, vol. 46, 1\'o. 6, Jun. 1975, pp.
`2475-2432.
`
`Generalov et al., “Eixperimental Investigation of :1 Continuous Opti-
`cal Discharge,” S0vie!Pl1ys1'c'S JETP. Vol. 34, No. 4, Apr. 1972, pp.»
`763-769.
`V
`Generalov et al., “Continuous Optical Discharge,” Z}1ETFPix. Red.
`11, No. 9, May 5, 1970, pp. 302-304.
`_
`Kozlov et 21]., “Radiative Losses by Argon Plasma and the Emissive
`Model ofa Continuous Optical Discharge.” Sou Plzys.
`TP, vol. 39.
`No. 3, Sep. 1974, pp. 463-468.
`Carlhoffet al., “Continuous Optical Discharges at Very High Pres-
`sure,” 1’/zysica 103C, 1981, pp. 439-447.
`Cremers ct .11., “Evaluation of the Continuous Optical Discharge for
`Spectrocheniical Analysis,” Spec'II'ocIn'/nica Acta, Vol. 40B, No. 4,
`1985, pp. 665-679.
`Kozlov et al., “Sustained Optical Discharges in Molecular Gases,”
`Sov. Phys. Teclz. Phys. 49(.l1), Nov. l979,pp. l2S3-128.7.
`Keefer, “l..ase1'-Sustained Plasmas,” Laser—1/rduced Plasmas and
`.4pplim!i0n.v, published by Marcel Dekker, edited by Radziemski et
`211., 1989, pp. 169-206.
`Hamamatsu Product Information, “Super-Quiet Xenon Lamp Super-
`Quiet Mercury—Xcnon Lamp,” Nov. 2005.
`
`cited by exznnirrer
`
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`US. Patent
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`Aug. 31, 2010
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`US 7,786,455 B2
`
`1
`LASER-DRIVEN LIGHT SOURCE
`
`RELATED Al’l’LlCA'l‘lONS
`
`This application 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 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 waters (e.g., reticles and photomasks). The
`electromagnetic energy produced by high brightness lights
`sources can, altematively, be used as a source of illumination
`in a lithography system used in the fabrication of waters, 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 areused 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 a_node' 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, thesearc lamps do not provide sullicient bright-
`ness for some applications, especially in the ultraviolet spec-
`trum. Furthcr, the position ofthc 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.
`
`SUMMARY OF THE INVENTION
`
`S.
`
`10
`
`15
`
`20
`
`30
`
`40
`
`45
`
`The present invention ‘l'eatures 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 fresncl lens) or
`mirror (e.g., a coated mirror. a dielectric coated mirror. a
`
`60
`
`65
`
`2
`narrow band mirror, and 2111 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.
`_
`V
`_
`,
`The chamber can include an ultraviolet transparent region.
`The chamber or a window in the chamber can include a
`material selected from the group consistingof quartz, Supra-
`sil® quartz (lleraeus 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
`(eg., 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, ()2, F2, 21 metal halide, a halogen, Hg, Cd, Zn, Sn,
`Ga, Fe, Li, Na, an excimer forming gas, air, a vapor, ametal
`oxide, an aerosol, a flowing: media, or a recycled media. The
`gas can be produced by a pulsed laser beam that impacts at
`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 regionfrorn which the.hig_h~bri_ghtness
`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-
`tinuouswave laser. In some embodiments, the at least one
`laser is an IR laser, a diode laser, a fiber laser, an ytterbium
`laser, a C03 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 acontinuous 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 mctrology tool, a lithography tool, or an
`endoscopic tool).
`I
`The invention, in another aspect, relates to a method for
`- producing light. The method involves ionizing with an igni-
`lion 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. 1 he ionizable medium can be
`a moving target. In seine embodiments, the method also
`involves directing the high brightness light through at least
`one optical element to modify a property ofthc light. In some
`embodiments, the method also involves delivering the high
`brightness light emitted by the ionized medium to a tool (eg.
`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, thejnvention featttres 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 ofthe high brightness light does not vary by more‘
`than about 90% during operation. In some einbodiinents, the
`at least one laser provides energ ' 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 (eg, a lens‘ or mirror) for modifying a
`property ofthe laser energy provided to the ionized medium.
`The optical element can be, for example, anaplanatic 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 thcichamber includes a quartz material, suprasil
`quartz material, sapphire material, Mgllz material, diamond
`material, or Caliz material. In some embodiments, the cham-
`ber is a sealed chamber. The chamber can be capable of being
`actively pumped.
`In some embodiments,
`the chamber
`includes a dielectric material (e.g., quartz). In some embodi-
`ments, the chamber is a glass bulbqln 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 ofa noble gas, Xe,
`Ar, Ne, Kr, He, D2, I-I2, O3, F2, a metal halide, a halogen, I’-lg,
`Cd, 7n, 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 ofelectromagnetic
`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 some embodiments, the light source includes at least one
`optical element (eg, 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 (c.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
`
`30
`
`40
`
`50
`
`vi U1
`
`60
`
`4
`method also involves providing substantially continuous
`laser energy to the ionized medium in the chamber to produce
`a. high brightness light.
`Insome 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 czm‘
`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 modifya. property of
`the light. In some embodiments, the method also involves
`delivering the high brightness light emitted by the ionized
`medium to a tool.
`
`10
`
`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 \vithin the chamber.
`The light source also includes a means for providing substan-
`tially continuous laser energy to the ionized medium within
`the chamber.
`
`20
`
`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 (c.g._. inner surface) of the chan1—
`ber and the reflective surface directs at least a portion of the
`first set ofwavelengths of electromagnetic energy toward the
`plasma. In some einbodiinents, 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 refiector, the reflector reflects at least a
`portion of the first wavelengths of electromagnetic energy
`towards the reflective surface ofthe chamber, and the reflec-
`tive surface directs a portion ofthe first set o‘f’wavelcngths of
`electromagnetic energy toward the plasma.
`In some embodiments, at lea st 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 ofpredefined 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-
`
`
`
`5
`
`US 7,786,455 B2
`
`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 enibodi-
`nients, a coating or flhn 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 plasmaover
`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.0., are coated or include) amaterial to filter pre-
`defined wavelengths (c.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 ion_izing 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 ofwavelengths of electro-
`magnetic energy through a reflector toward the reflective
`surface of the cliamber, the reflective surface reflecting at
`least a portion of the first set of wavelengths of electromag-
`netic energy toward the plasma. In some cnibodinients, the
`method involves directing at least a portion of the high bright-
`ness light toward the reflective surface of the chamber which
`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 ofelcctromagnctic energy toward the plasma. In some
`enibodinients. the method involves directing a portion of the
`high brightness light toward the reflective surface of the
`chamber which is reflected toward the reflector and, electro-
`
`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 theplasnia 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. ln 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 solidangle of greater than about 2:: (about
`6.28) steradians. In sonieembodiments, 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 ofthe 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 niethocl 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 directing electromagnetic
`energy from a laser toward a reflector that at least substan-
`tially rcflects a first set of wavelengths of clectroniagnetic
`energy toward the ionized gas in ‘the chamber to produce a
`plasma that generates a high briglitness light.
`In some embodiments, the electromagnetic energy from
`the laser first is reflected by the reflector toward the reflective
`surface of the chamber. In some embodiments, the electro-
`magnetic energy directed toward the reflective surface of the
`chamber is reflected toward the plasma. In some embodi-
`ments, a portion ofthe high brightness light is directed toward
`the reflective surface of the chamber, reflected toward the
`reflector and passes through the reflector.
`In some cmbodiiiiciits, 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. ln some
`embodiments, a portion ofthe liighbrightness light is directed
`toward the reflective surface of the 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 ofpredcfined wavelcngtlis of
`electromagnetic energy directed toward the reflector and at
`least substantially allowing a second set of predefined wave-
`lengths ofelectromagnctic 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 limit.
`The invention, in another aspect, features alight source that
`includes a sealed chamber. Tlic light source also includes an
`ignition source for ioni'/.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 briglitncss light. The light source also
`includes a curved reflective surface disposed external to the
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`sealed chamber to receive at leas a portion ofthe high bright-
`ness light emitted by the sealed chamber _and reflect thehigh
`brightness light toward an output of the lightsource.
`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 retlective surface. In sortie
`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 cnerg ' 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 includesat
`least one laser external to the sealed chamber for providing
`electromagnetic energy. The light source also includes a
`curved rellective surface to receive and rellect 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 retlcctive surface also receives at
`least a portion of the high brightness light emitted by the
`plasma and reflects the high brightness light toward an output
`of the light source.
`the curved reflective surface
`In some embodiments,
`focuses the electromagnetic energy on a region in the cham-
`her where the plasma is located. In some embod_iments,‘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 of the invention will become more apparent from
`the following description and from the claims.
`
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`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 diagam ofa portion of a light
`source, according to an illustrative embodiment of the 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
`laser energy through a plasma generated from mercury. using
`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.
`l’lG. SA is a schematic block diagram ofa light source in
`which electromagnetic energy from a laser is provided to a
`plasma over a first solid angle. according to an illustrative
`embodiment of the invention.
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`US 7,786,455 B2
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`8
`FIG. 8B is a schematic block diagram of the 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. g
`
`DETAILED DESCRIPTION OF ILLlISTRA'I‘lVI‘;‘
`A 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 "100 provides energy to
`a region 130 ofthe chamber 128 having the ionizable medium
`which creates a plasma 132.