(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2001/0035720 A1
`Guthrie et al.
`(43) Pub. Date:
`NOV. 1, 2001
`
`US 20010035720A1
`
`(54) HIGH INTENSITY LIGHT SOURCE
`
`(76)
`
`Inventors: Charles Guthrie, San Jose, CA (US);
`Edmund Sandberg, Monte Sereno, CA
`(US); Donald Wilson, San Jose, CA
`(US); Gregory Prior, San Jose, CA
`(US)
`
`Correspondence Address:
`GARY CARY WARE & FREIDENRICH LLP
`1755 EMBARCADERO RD
`PALO ALTO, CA 94303-3340 (US)
`
`(21) Appl. No.:
`
`09/818,092
`
`(22)
`
`Filed:
`
`Mar. 26, 2001
`
`Related U.S. Application Data
`
`application No.
`(63) Non-provisional of provisional
`60/192,731, filed on Mar. 27, 2000. Non-provisional
`of provisional application No. 60/224,059, filed on
`Aug. 9, 2000. Non-provisional of provisional appli-
`cation No. 60/224,298, filed on Aug. 10, 2000. Non-
`provisional of provisional application No. 60/224,
`290,
`filed on Aug. 10, 2000. Non-provisional of
`provisional application No. 60/224,291, filed on Aug.
`10, 2000. Non-provisional of provisional application
`No. 60/224,257, filed on Aug. 10, 2000. Non-provi-
`
`sional of provisional application No. 60/224,289,
`filed on Aug. 10, 2000. Non-provisional of provi-
`sional application No. 60/224,866, filed on Aug. 11,
`2000. Non-provisional of provisional application No.
`60/234,415, filed on Sep. 21, 2000.
`
`Publication Classification
`
`Int. Cl.7 .................................................... ..H01J 65/04
`(51)
`(52) U.S.Cl.
`............................................ .. 315/39; 315/248
`
`(57)
`
`ABSTRACT
`
`In one aspect the plasma lamp according to the present
`invention comprises a gas envelope that is constructed from
`ceramic material and a sapphire Window rather than quartz.
`According to another aspect of the present
`invention, a
`plasma lamp comprises an RF structure for the radio Wave
`radiation and an envelope for housing the excitation gas that
`are formed so as to constitute a single, integrated ceramic
`structure. According to yet another aspect of the present
`invention, the plasma lamp comprises a Waveguide structure
`having solid material such as ceramic rather than air for the
`dielectric and a gas housing made of a combination of solid
`ceramic and a sapphire Window. In this Way, the separate
`quartz gas envelope and air-filled Waveguide structure
`employed in the prior art are replaced by a single, integrated
`structure.
`
`ASML 1115
`
`ASML1115
`
`

`
`Patent Application Publication
`
`Nov. 1, 2001 Sheet 1 of 4
`
`US 2001/0035720 A1
`
`

`
`Patent Application Publication
`
`Nov. 1, 2001 Sheet 2 of 4
`
`US 2001/0035720 A1
`
`52
`
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`
`72
`
`70
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`

`
`52
`
`as
`
`FIG. 4A
`
`FIG. 4B
`
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`M
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`

`
`‘cation Publication
`
`Nov. 1, 2001 Sheet 4 of 4
`
`US 2001/0035720 A1
`
`84
`
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`
`

`
`US 2001/0035720 A1
`
`Nov. 1, 2001
`
`HIGH INTENSITY LIGHT SOURCE
`
`[0001] This application claims the benefit of the following
`U.S. Provisional Applications: U.S. Provisional Application
`Nos. 60/192,731 filed Mar. 27, 2000; 60/224,059 filed Aug.
`9, 2000; 60/224,298 filed Aug. 10, 2000; 60/224,290 filed
`Aug. 10, 2000; 60/224,291 filed Aug. 10, 2000; 60/224,257
`filed Aug. 10, 2000; 60/224,289 filed Aug. 10, 2000; 60/224,
`866 filed Aug. 11, 2000; and 60/234,415 filed Sep. 21, 2000.
`All of these provisional applications are hereby incorporated
`by reference in their entireties.
`
`FIELD OF THE INVENTION
`
`[0002] The present invention is directed generally to high
`intensity light sources and more particularly to plasma light
`sources for use in applications such as projection systems
`based on reflective microdisplays.
`
`BACKGROUND OF THE INVENTION
`
`[0003] There is a continuing need for long-lived, efficient,
`compact, and high intensity white light sources for applica-
`tions such as projection-based televisions and computer
`monitors as well as movie screen projectors. The various
`kinds of light sources which have been used previously
`include arc lamps and plasma lamps. Although an arc lamp
`produces an intense light by maintaining an electric arc
`between two electrodes, arc lamps have not tended to be
`long-lived for at
`least two reasons. First,
`the electrodes
`between which the arc is formed inevitably deteriorate and
`erode during the operation of the arc lamp, and ultimately
`this erosion leads to lamp failure. Second, arc lamps con-
`ventionally employ an envelope or bulb made from a
`transparent material in order to contain the gas fill of the
`lamp. Quartz has conventionally been used for such bulbs or
`gas envelopes.
`
`[0004] Quartz bulbs, however, have several disadvan-
`tages. Because quartz devitrifies or recrystalizes at elevated
`temperatures, quartz bulbs do not endure well
`the high
`temperatures and repeated heatings inherent in lamp opera-
`tion, and they tend to eventually discolor or crack causing
`lamp failure and limiting the useful life span of the lamp. In
`addition, because quartz has a low thermal conductivity, the
`use of the quartz bulb limits the maximum operating tem-
`perature of the lamp, and, therefore, the maximum obtain-
`able brightness. Furthermore, quartz is partially permeable
`so that gas tends to slowly diffuse out of the bulb envelope.
`Ultimately, this diffusion causes the lamp to fail.
`
`[0005] Unlike arc lamps, plasma lamps do not rely on
`electrodes, but rather produce light by creating a plasma
`discharge in a gas contained in a bulb by exposing the lamp
`gas to intense radio wave or radio frequency radiation. (As
`used herein, the phrase “radio wave radiation”, as well as the
`acronym “RF”, is intended to encompass electromagnetic
`radiation frequencies in either the conventional radio fre-
`quency range or in the conventional microwave frequency
`range.) Although there are no electrodes to fail in the case of
`a plasma lamp, the transparent bulb that is conventionally
`used to contain the gas is also typically made of quartz and
`has the same disadvantages discussed above in connection
`with the arc lamp because of the high operating temperatures
`involved.
`
`In order to mitigate the bulb failure problem,
`[0006]
`various mechanical cooling arrangements have been devel-
`
`oped to rotate the bulb and to propel cooling air onto its outer
`surface during lamp operation. However, such mechanical
`arrangements are complex, expensive, and occupy space
`which is often a scarce resource in the intended application
`for the lamp. In addition, the presence of these mechanical
`arrangements compromises the ability to collect the light
`generated by the lamp, thereby reducing efficiency.
`
`[0007] Plasma lamps also conventionally require a sepa-
`rate mechanism to couple the radio wave radiation generated
`by the radiation source to the bulb filled with the plasma
`discharge-forming medium. The need for such a separate
`coupling mechanism is another problem with the plasma
`lamp because inefficiency of the coupling correspondingly
`constrains the overall efficiency of the plasma lamp. One
`conventional approach to such coupling is to mount the bulb
`near a separate air-filled RF structure, such as a waveguide,
`that receives the radio wave radiation from the radiation
`
`source and transmits the radiation to the bulb. In practice this
`approach may lead to a power loss as high as 60% because
`of coupling inefficiencies. In addition, the resulting structure
`is not physically compact because the RF structure is
`separate from the bulb.
`
`[0008] Alternatively, it is known to mount the quartz bulb
`inside a separate structure and to place coils near to the bulb
`in order to inductively transfer radio wave radiation energy
`to the gas in the bulb. Again, however, the resulting structure
`lacks integration and compactness because the RF structure
`is separate from the bulb.
`
`It is desirable to provide improved light sources
`[0009]
`that avoid these and other problems with known light
`sources, and it is to these ends that the present invention is
`directed.
`
`SUMMARY OF THE INVENTION
`
`[0010] According to one aspect of the invention, a plasma
`lamp is provided that comprises a gas housing containing a
`plasma discharge forming medium, and a source of radio
`frequency energy coupled to the plasma discharge medium.
`The gas housing is constructed from ceramic material and
`has a window transparent to visible light.
`
`the window may be a
`In more specific aspects,
`[0011]
`sapphire window. The invention greatly extends the operat-
`ing life expectancy of the plasma lamp as compared with the
`prior art lamps which use quartz because the problems of
`quartz devitrification at high temperature and quartz gas
`permeability are eliminated.
`
`[0012] According to another aspect of the present inven-
`tion, the RF structure used for the radio wave radiation and
`the envelope used to house the gas fill are formed so as to
`constitute a single, integrated ceramic structure.
`
`[0013] According to another aspect of the present inven-
`tion, solid material such as ceramic rather than air is used for
`the dielectric and the gas fill is contained by a combination
`of solid ceramic and a sapphire window. In this way the
`separate gas envelope and air-filled waveguide structure
`employed in the prior art are replaced by a single, integrated
`structure.
`
`[0014] Because the integration of the RF structure and the
`gas envelope permits the quartz bulb to be done away with
`entirely, plasma lamps according to the present invention
`
`

`
`US 2001/0035720 A1
`
`Nov. 1, 2001
`
`enjoy an unprecedented operating life expectancy as com-
`pared with the prior art. This is so in part because the
`problems associated with the inability of the quartz bulb to
`withstand heatings are eliminated.
`
`the integrated design of the present
`In addition,
`[0015]
`invention enables a much higher proportion of the radio
`wave radiation energy to be focused onto the gas fill. As a
`result, the plasma lamp according to the present invention is
`made much more efficient.
`
`invention enables these and many
`[0016] The present
`other benefits to be obtained.
`
`BRIEF DESCRIPTION OF THE FIGURES
`
`[0017] FIG. 1 is a side cross-sectional view of a gas
`housing for a plasma lamp according to a first embodiment
`of the invention.
`
`[0018] FIG. 2 is a side cross-sectional view of a plasma
`lamp according to a second embodiment of the invention.
`
`[0019] FIG. 3 is a side cross-sectional view of a plasma
`lamp according to a third embodiment of the invention in
`which the gas housing is integral with a waveguide com-
`prising a solid dielectric material.
`
`[0020] FIG. 4A is an end view of a plasma lamp according
`to a fourth embodiment of the invention in which the gas
`housing is integral with a waveguide comprising a solid
`dielectric material while FIG. 4B is a side cross-sectional
`
`view of the same plasma lamp.
`
`[0021] FIG. 5 is a side cross-sectional view of a plasma
`lamp according to a fifth embodiment of the invention in
`which the gas housing is also integral with a waveguide
`comprising a solid dielectric material.
`
`[0022] FIG. 6 shows a process suitable for sealing a gas
`housing according to the present invention.
`
`[0023] FIG. 7 is a side cross-sectional view of an alter-
`native embodiment of the plasma lamp of FIG. 2.
`
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`[0024] FIG. 1 shows a first embodiment of an improved
`light source in accordance with the invention. The light
`source may be a plasma lamp comprising a gas housing 20
`preferably formed from a ceramic material 22, as will be
`described below, with an interior cavity or chamber 24 for
`containing gas. The housing may generally be rectilinear or
`cubic, and the chamber may be spherical. Achannel 30 may
`connect the chamber to an exterior surface 32 of the housing.
`The channel 30 may be made of light transmissive material,
`preferably of sapphire in order to form a window 34 for
`emitting visible light from the chamber. The window pref-
`erably has a generally tapered, conical shape; i.e., a frusto-
`conical shape. The sapphire window seals the chamber to
`contain the gas, while affording an exit for the light pro-
`duced by the plasma discharge.
`
`[0025] Sapphire is preferred for the window since it is less
`gas permeable than quartz, for example, and better with-
`stands the heat cyclings and high temperatures associated
`with lamp operation. Furthermore, the gas housing 20 is
`preferably made from a ceramic material, as described
`below, since ceramics are much more durable under heating
`
`than other materials such as quartz. As a result, the ceramic
`housing affords a much longer life expectancy for the plasma
`lamp than the conventional quartz bulb of the prior art. In
`addition, the ceramic housing advantageously enables the
`plasma lamp to be operated at a much higher maximum
`temperature than the quartz bulb, because it avoids the lower
`softening temperature point and low thermal conductivity
`limitations of quartz.
`[0026] The sapphire window 34 may function as a “light
`integrator” for transmitting the light of the plasma lamp
`from the chamber,
`for example,
`to application-specific
`optics. The tapered, conical sapphire window 34 may be
`sealed against the surrounding ceramic material forming the
`channel 30 by coating the outside edges of the sapphire
`window with a material such as a glass containing MgO, or,
`alternatively, with SiO3 or SiO2. Next the mating surfaces of
`both the window and the ceramic channel may each be
`coated with a thin layer of metallic material, such as copper,
`a copper alloy, or platinum. Then a piece of preferably pure
`platinum wire may be placed between the two thin film
`layers. Finally, a laser is used to heat the wire, and thereby
`melt the metallic material and bond the layers together.
`[0027] Alternatively, the coated sapphire window 34 may
`be sealed to the ceramic housing by heating a glass frit. In
`yet another alternative, the ceramic housing may be “shrunk
`down” onto the sapphire window during high temperature
`firing.
`[0028] The gas fill in the plasma lamp according to the first
`embodiment of the invention can be coupled to a source of
`electromagnetic energy, such as radio wave radiation in any
`of a variety of ways in order to create a plasma discharge
`within chamber 24. Preferably this should be done so that
`the RF structure that is active with the radio wave radiation
`
`energy is integrated with the gas housing 20, as will be
`described.
`
`[0029] The gas fill may appropriately be a combination of
`a metal compound and a carrier gas. The metal compound
`may preferably be a metal halide such as indium bromide.
`Other examples of suitable metal compounds are praseody-
`mium and mercury. Preferred gases for the carrier gas are
`xenon, neon, argon, or krypton.
`[0030] FIG. 2 shows a second embodiment of a lamp in
`accordance with the invention which is somewhat similar to
`
`FIG. 1 except that the gas housing has an integrated RF
`energy structure. In FIG. 2, the elements are designated
`similarly to FIG. 1, using like reference numerals for like
`elements. The gas fill chamber 24 may be housed in a gas
`housing 20 preferably comprising a ceramic material 22 and
`provided with a light transmissive window 34, preferably of
`a tapered rod of sapphire and a fill plug 38 as previously
`described. In this embodiment, an RF energy structure such
`as one or more coils 36 may be formed within the ceramic
`housing. The coils 36 function to inductively couple radio
`wave radiation energy to the gas fill in chamber 24 in order
`to create the plasma discharge. In this way, the RF structure
`of the plasma lamp that is active with radio wave energy is
`integral with the ceramic housing 20 that contains the
`plasma gas fill. This integration of the RF structure of the
`plasma lamp and the gas housing into a single structure, as
`shown, improves the coupling of RF energy to the gas, and
`allows significant gains in lamp efficiency and compactness.
`[0031] The second embodiment may also comprise seg-
`ments of ferrite material 41 placed adjacent the coils 36 in
`
`

`
`US 2001/0035720 A1
`
`Nov. 1, 2001
`
`order to help concentrate the magnetic field associated with
`the coils 36 on the gas fill. An illustration of this embodiment
`is shown in FIG. 7.
`
`[0032] FIG. 3 shows a third embodiment of a lamp in
`accordance with the invention which integrates both the gas
`housing and an RF energy source within the same structure.
`A gas housing 50 for the gas fill may be formed so as to be
`integral with a waveguide 52 which preferably comprises a
`ceramic structure having a substantially rectangular cross-
`section. Because no separate bulb is used, the housing 50
`and waveguide 52 comprise a single, integrated structure. A
`source of radio wave radiation 54 may be disposed within
`the ceramic structure, for example, near one end of the
`waveguide. The RF source 54 may be an RF antenna, a
`probe, or
`the like for
`introducing RF energy into the
`waveguide. The gas housing 50 may be located near the
`other end of the waveguide, for example. As shown, the gas
`housing may further include a light transmissive window 56
`connected to the end wall of the housing. The window is
`preferably made from sapphire.
`
`[0033] The dimensions of the waveguide and the locations
`of the RF source and gas housing preferably are chosen so
`that the electromagnetic field produced by the radio wave
`radiation in the waveguide exhibits a maximum in intensity
`at or near to the location of the housing in order to optimize
`the energy coupling to the gas. The waveguide may form a
`resonant structure having a resonant mode at the frequency
`of the radiation from the RF source 54. The necessary
`relationship among the waveguide dimensions, dielectric
`constant, and RF frequency can be determined in a well-
`known way using electromagnetic waveguide theory. For
`example, it is well-known that for a rectangular waveguide
`cavity containing a dielectric with permeability and permit-
`tivity constants y and E, and having length, width and depth
`dimensions a, b, and d and metal boundaries, the frequencies
`w(m,n,p) for the resonant modes are given by the following
`equation:
`
`w(m,n,p)=(,uE)’vz(m27:2/a2+n2r:2/b2+p2r:2/dz)”
`
`[0034] where m, n, and p are integers.
`
`the
`the dimensions of
`[0035] Furthermore, because
`waveguide scale with the square root of the dielectric
`constant of the dielectric, use of a solid dielectric material
`instead of an air dielectric permits a dramatic reduction in
`waveguide size, particularly if a ceramic material with an
`appropriately high dielectric constant
`is chosen. The
`waveguide is preferably made from a solid ceramic material
`with a high dielectric constant (higher than air or greater
`than 1), such as titanium dioxide (TiO2) or barium neody-
`mium titinate. In practice,
`it is found that materials that
`exhibit a suitably high dielectric constant are typically
`porous and unable to provide the required hermicity to
`contain the gas fill. Accordingly, as shown in FIG. 3, a liner
`58 of a better hermetic ceramic, such as alumina (A1203), is
`preferably deposited along the inner boundary of the
`ceramic material that forms the gas housing. This liner 58
`improves the sealing of the gas fill.
`
`[0036] FIGS. 4A and 4B show a fourth embodiment of a
`light source in accordance with the invention. A gas housing
`60 for the gas fill is formed so as to be integral with a
`cylindrical resonant waveguide structure 62 comprising
`ceramic material. Because a separate bulb is not used, the
`
`gas housing 60 and waveguide 62 comprise a single, inte-
`grated structure. A source of radio wave radiation 64 may be
`disposed near one end of the waveguide, while the gas
`housing is formed at an opposite end. The gas housing 60
`may include a window 66 preferably made from sapphire.
`
`[0037] As with the embodiment of FIG. 3, the dimensions
`of the waveguide structure, the locations of the RF source
`and gas housing, and the frequency of the radio wave
`radiation source may be chosen so as to support resonant
`modes which optimize the RF energy coupling from the RF
`source to the gas housing. The gas housing 60 may, there-
`fore, be appropriately located so that the housing receives a
`high level of radio wave radiation energy from the source 64.
`
`[0038] FIG. 5 shows a fifth embodiment of the present
`invention.
`In this case the waveguide 72 may have a
`cross-section with a varying dimension, such as a varying
`profile rather than a rectangular cross-section in order to
`improve the matching of the impedance of the waveguide to
`that of a gas housing 70 in the waveguide. In turn, this
`improved impedance matching broadens somewhat
`the
`range of frequencies over which the waveguide forms a
`resonant structure so as to efficiently deliver power to the gas
`housing. As with the first embodiment, however, a separate
`bulb is not used so that the gas housing 70, waveguide 72,
`and radio wave radiation source 74 comprise a single,
`integrated structure. The dimensions of the waveguide and
`the locations of the radio wave radiation source and housing,
`may appropriately be chosen to produce a resonant mode
`that maximizes the energy coupled from the source to the
`gas housing for the operating frequency band of the source.
`[0039]
`In other embodiments of the invention, the interior
`of the gas housing may be coated with a thin film of
`protective material such as MgO. The MgO will protect the
`inner surface of the gas housing from the spontaneous
`conversion of ceramic to elemental metal that sometimes
`
`occurs in the presence of a partial vacuum and high tem-
`perature. This effect is not desirable and may cause failure
`of the bulb. Because the film of MgO acts as a secondary
`electron emitter, the film can also add to the brightness of the
`plasma lamp.
`[0040]
`In alternative embodiments of the invention, a bulb
`made from quartz or another suitable material may be
`retained as a structure which houses the gas fill, but the
`quartz structure is sized so as to fill the interior space in the
`ceramic gas housing, which ceramic gas housing may be
`integrated into a ceramic waveguide as described above.
`This variation can be utilized in conjunction with any of the
`embodiments of the invention shown in FIGS. 1-5 by
`expanding the bulb into the interior of the ceramic gas
`housing with a heating process. One possible heating pro-
`cess is to electrically overdrive the bulb. Alternatively, the
`outer surface of the quartz bulb may be ground so as to fit
`closely into the ceramic gas housing or integrated ceramic
`gas housing and waveguide structure.
`[0041] An example of a waveguide structure according to
`these alternative embodiments is a rectangular waveguide
`structure having dimensions of 34.72 mm by 38.84 mm by
`17.37 mm and composed of alumina (A1203) ceramic. For
`such a waveguide,
`the RF structure, e.g., antenna, may
`appropriately be driven at a frequency of 2.4 gigahertz
`(GHz) in order to efficiently couple radio wave radiation of
`that frequency to the gas fill in the quartz bulb within the
`waveguide.
`
`

`
`US 2001/0035720 A1
`
`Nov. 1, 2001
`
`[0042] When the plasma lamp is constructed in such a
`way, the heat produced by the bulb operated in the normal
`drive mode will be dissipated more uniformly and rapidly
`than in the prior art because of the tight fit between the
`quartz bulb and the surrounding ceramic. In this way the
`ceramic encasing the quartz bulb acts as a heat sink and
`ameliorates the problems associated with the heating of a
`quartz material.
`
`[0043] These alternative embodiments having a quartz
`bulb can be improved by depositing a thin, non-conductive
`reflective coating on either the inside or outside walls of the
`quartz bulb. The reflective coating can be deposited by
`evaporation, spraying, painting or other method and should
`cover the bulb apart from an “exit” window for the light. The
`material used may be liquid bright platinum or a similar
`reflective material. The function of the coating is to improve
`upon the reflectance of the ceramic and thereby increase the
`brightness yielded by the lamp.
`
`In other embodiments of the invention, the bulb for
`[0044]
`containing the gas fill may be made entirely from sapphire
`rather than quartz. Sapphire is transparent to visible light and
`can better withstand high temperatures than quartz. Sapphire
`is also less permeable than quartz. Accordingly, the use of
`sapphire for the bulb can significantly improve the perfor-
`mance of the plasma lamp as compared with the prior art
`quartz bulb lamp.
`
`representative
`constructing a
`[0045] A method for
`embodiment of the ceramic gas housing for the fill gas of the
`plasma lamp will now be described with reference to FIG.
`6. The first step in this method is to fabricate the housing 80
`as by pressing ceramic into a mold. A small fill hole 40 may
`be left in one end of the housing. A sapphire window 84 is
`then sealed to the other end of the housing. The ceramic
`housing may then be placed in a vacuum chamber. An
`appropriate metal halide material may then be put into the
`enclosure through the fill hole 40. Next, the vacuum cham-
`ber can be pumped down. After the proper subatmospheric
`pressure is reached, the chamber can then be backfilled with
`an excitation gas.
`
`[0046] The excitation gas is allowed to backfill until the
`chamber and, hence, the ceramic housing reaches the desired
`pressure. A ceramic plug 85 may then be used to seal the fill
`hole in a manner discussed more fully below in connection
`with FIG. 6. After the fill hole is sealed in such a manner,
`the lamp is then removed from the vacuum system and
`tested.
`
`[0047] FIG. 6 illustrates an improved sealing procedure
`that is useful for making plasma lamp gas housings accord-
`ing to the present invention. In particular, it has been found
`that a tapered fill hole 40 and a matchingly tapered plug 85
`provide a stronger seal than a straight-edged fill hole and
`matching plug. The actual seal between the hole and the plug
`is made with a glass frit or a ceramic material 82. The seal
`is formed by suitably heating the fill hole region such as by
`using laser light 86. The use of laser light is advantageous
`because it allows the sealing process to be conveniently
`accomplished while the plasma gas housing is still in the
`vacuum chamber immediately after the fill material has been
`added. Furthermore, lasers are especially well suited for this
`application which requires the quick heating of a small
`region to a high temperature.
`
`[0048] The scope of the present invention is meant to be
`that set forth in the claims that follow and equivalents
`thereof, and is not limited to any of the specific embodi-
`ments described above.
`
`What is claimed is:
`
`1. A plasma lamp comprising:
`
`a source of radio wave radiation;
`
`a waveguide structure for coupling said radio wave radia-
`tion to a plasma discharge-forming medium so as to
`excite a plasma discharge, said waveguide structure
`being at
`least
`largely composed of solid dielectric
`material; and
`
`a housing for said plasma discharge-forming medium.
`2. A plasma lamp as recited in claim 1, wherein said
`waveguide structure is a resonant structure which supports at
`least one resonant mode of said radio wave radiation.
`
`3. A plasma lamp as recited in claim 1, wherein said
`housing and said waveguide structure form a single, inte-
`grated structure.
`4. A plasma lamp as recited in claim 3, wherein said
`housing is formed from ceramic material.
`5. A plasma lamp as recited in claim 4, wherein said
`ceramic material includes alumina.
`
`6. A plasma lamp comprising:
`
`a source of radio wave radiation;
`
`a waveguide structure for coupling said radio wave radia-
`tion to a plasma discharge-forming medium so as to
`excite a plasma discharge said waveguide structure
`being at least largely composed of a ceramic material;
`and
`
`a housing for said plasma discharge-forming medium.
`7. A plasma lamp as recited in claim 6, wherein said
`waveguide structure is a resonant structure which supports at
`least one resonant mode of said radio wave radiation.
`
`8. A plasma lamp as recited in claim 6, wherein said
`housing and said waveguide structure are integrated into a
`single structure.
`9. A plasma lamp as recited in claim 8, wherein said
`housing is formed from another ceramic material.
`10. A plasma lamp as recited in claim 9, wherein said
`other ceramic material includes alumina.
`
`11. A plasma lamp as recited in claim 6, wherein said
`first-mentioned ceramic material includes alumina.
`
`12. A plasma lamp as recited in claim 6, wherein said
`first-mentioned ceramic material includes titanium dioxide.
`
`13. A plasma lamp as recited in claim 6, wherein said
`first-mentioned ceramic material includes barium neody-
`mium titinate.
`
`14. A plasma lamp as recited in claim 9, wherein said
`other ceramic material is the same material as said first-
`mentioned ceramic material.
`
`15. A plasma lamp comprising:
`
`a source of radio wave radiation;
`
`a waveguide structure for coupling said radio wave radia-
`tion to a plasma discharge-forming medium so as to
`excite a plasma discharge;
`
`a housing for said plasma discharge-forming medium, and
`
`wherein said waveguide structure is at least largely com-
`posed of a first ceramic material and said housing is
`
`

`
`US 2001/0035720 A1
`
`Nov. 1, 2001
`
`formed from a second ceramic material and includes a
`
`window that is transparent to Visible light.
`16. A plasma lamp as recited in claim 15, wherein said
`window is formed from sapphire.
`17. A plasma lamp as recited in claim 15, wherein said
`waveguide structure is a resonant structure which supports at
`least one resonant mode of said radio wave radiation.
`
`18. A plasma lamp as recited in claim 15, where said
`housing and said waveguide structure are integrated into a
`single structure.
`19. A plasma lamp as recited in claim 15, wherein said
`second ceramic material includes alumina.
`
`20. A plasma lamp as recited in claim 15, wherein said
`first ceramic material includes alumina.
`
`21. A plasma lamp as recited in claim 15, wherein said
`first ceramic material includes titanium dioxide.
`
`22. A plasma lamp as recited in claim 15, wherein said
`first ceramic material includes barium neodymium titinate.
`23. A plasma lamp as recited in claim 15, wherein said
`second ceramic material is the same as said first ceramic
`material.
`
`24. A plasma lamp comprising:
`a housing containing
`a plasma discharge-forming
`medium, said housing being formed of ceramic mate-
`rial and including a window that
`is transparent
`to
`Visible light produced by said plasma discharge.
`a source of electromagnetic energy; and
`means for coupling said electromagnetic energy to the
`plasma discharge-forming medium so as to excite a
`plasma discharge.
`25. A plasma lamp as recited in claim 24, wherein said
`window comprises sapphire.
`26. A plasma lamp as recited in claim 24, wherein said
`ceramic material comprises alumina.
`27. A plasma lamp as recited in claim 24, wherein the
`source of electromagnetic energy and the housing are
`formed within the ceramic material as an integrated struc-
`ture.
`
`28. A plasma lamp as recited in claim 27, wherein said
`source of electromagnetic energy comprises electrical coils.
`29. A plasma lamp as recited in claim 27, wherein said
`source of electromagnetic energy comprises an antenna.
`*
`*
`*
`*
`*