(12) United States Patent
`Kane et al.
`
`(10) Patent N0.:
`
`(45) Date of Patent:
`
`US 6,541,924 B1
`Apr. 1, 2003
`
`US006541924B1
`
`(54) METHODS AND SYSTEMS FOR PROVIDING
`EMISSION OF INCOHERENT RADIATION
`AND USES THEREFOR
`
`Kogelschatz, U. et al. “Dielectric-Barrier Discharges. Prin-
`ciple and Applications” J. Phys. IVFrance vol. 7 (1997) pp
`47-66.
`
`(75)
`
`Inventors: Deborah Maree Kane, North Epping
`(AU); Richard Paul Mildren, Mosman
`(AU); Robert John Carman, North
`Epping (AU)
`
`(73) Assignee: Macquarie Research Ltd., New South
`Wales (AU)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 165 days.
`
`(21)
`
`(22)
`
`(30)
`
`Appl. No.: 09/660,021
`
`Filed:
`
`Sep. 12, 2000
`
`Foreign Application Priority Data
`
`Massines, F. et al. “Experimental and Theoretical Study of
`a Glow Discharge at Atmospheric Pressure Controlled by
`Dielectric Barrier” J. Applied Physics vol. 83 (1998) pp
`2950-2957.
`
`Pashaie, R. et al. “Experimental Investigation of Microdis-
`charges in a Dielectric-Barrier Discharge” IEEE Transac-
`tions of Plasma Science vol. 27, No. 1 (1999) pp 22-23.
`Mildren, R.P. et al. “Enhanced Efficiency from a Xe Excimer
`Barrier Discharge Lamp .
`.
`. Excitation” Proceedings on
`SPIE vol. 4071 (2000) pp 283-290 Eds. Tarasenko, V.F. et
`al.
`
`Vollkommer, F. et al. “Dielectric Barrier Discharge” Proc.
`8'” Int. Symp. On Sci. and Tech. 0fLight Sources (1998) pp
`51-60.
`
`Primary Examiner—Don Wong
`Assistant Examiner—Ephrem Alemu
`(74) Attorney, Agent, or Firm—Ladas & Parry
`
`Apr. 14, 2000
`Jun. 15, 2000
`
`(AU) ............................................ .. PQ6907
`(AU) ............................................ .. PQ8176
`
`(57)
`
`ABSTRACT
`
`(51)
`
`Int. Cl.7 .............................................. .. H05B 41/00
`
`(52) U.s. Cl.
`
`.................. .. 315/246; 315/268; 315/169.3;
`313/607
`
`(58) Field of Search ............................ .. 315/169.3, 246,
`315/268, 224, DIG. 5, 313/607
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,099,557 A
`5,364,645 A
`5,455,074 A
`5,604,410 A
`
`3/1992 Engelsberg .............. .. 29/25.01
`11/1994 Lagunas—Solar et al.
`426/248
`10/1995 Nohr et al.
`............... .. 427/386
`2/1997 Vollkommer et al.
`..... .. 315/246
`
`(List continued on next page.)
`OTHER PUBLICATIONS
`
`Eliasson, B. et al.“UV Excimer Radiation from Dielec-
`tric-Barrier Discharges” Applied Physics B vol. 46 (1988)
`pp 299-303.
`
`Methods and systems for providing emission of incoherent
`radiation and uses therefor are disclosed. A system for
`providing emission of high peak power (in watts) incoherent
`radiation, comprises an electrically impeded discharge lamp
`linked to an electrical energy supply. The lamp comprises a
`discharge chamber which is at least partially transparent to
`the incoherent radiation, a discharge gas in the chamber, two
`electrodes disposed with respect to the chamber for dis-
`charging electrical energy therebetween, at least one dielec-
`tric barrier disposed between the two electrodes to electri-
`cally impede electrical energy passing between the two
`electrodes, an electrical energy supply capable of providing
`fast risetime, high peak power unipolar linking the elec-
`trodes with the supply, the energy supply being capable of
`providing a sequence of high peak power unipolar voltage
`pulses from the energy supply to the electrodes and means
`to control
`(i
`interpulse period, and (ii) pulse risetime,
`whereby,
`in use, a substantially homogeneous discharge
`occurs between the two electrodes which causes emission of
`incoherent radiation pulses of high peak power from the
`lamp.
`
`14 Claims, 7 Drawing Sheets
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`405
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`

`
`US 6,541,924 B1
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`6,084,360 A *
`
`7/2000 Yokokawa et al.
`
`....... .. 313/607
`
`nge s erg ............... ..
`,
`,
`lb
`10/1998 E
`5821 175 A
`438/795
`5,831,394 A * 11/1998 Huber et al.
`.............. .. 315/219
`5,965,988 A * 10/1999 Vollkommer et al.
`..... .. 315/246
`5,994,849 A * 11/1999 Vollkommer et al.
`..... .. 313/607
`
`6,310,442 B1 * 10/2001 Vollkommer et al.
`6376989 B1 *
`4/2002 V°“k°mm°r°t al‘
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`..... .. 315/246
`315/209 R
`
`* cited by examiner
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`U.S. Patent
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`Apr. 1, 2003
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`US 6,541,924 B1
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`US 6,541,924 B1
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`U.S. Patent
`
`Apr. 1, 2003
`
`Sheet 7 of 7
`
`US 6,541,924 B1
`
`
`
`UV/l/UV LAMP
`
`{
`REFLECTOR
`
`5,4/V/,C>1_,/_:
`(7764/V61/4 new
`
`FIG. /2
`
`

`
`US 6,541,924 B1
`
`1
`METHODS AND SYSTEMS FOR PROVIDING
`EMISSION OF INCOHERENT RADIATION
`AND USES THEREFOR
`
`TECHNICAL FIELD
`
`This invention relates to methods and systems for pro-
`viding emission of incoherent radiation and uses for there-
`for.
`
`BACKGROUND ART
`
`Currently, commercial dielectric barrier discharge (DBD)
`lamp sources of incoherent ultraviolet (UV) are inherently
`low-peak power and are poorly suited to many practical
`applications Alternative sources of high-peak power UV
`radiation (laser-based) are comparatively high-cost and not
`cost-effective for many desired industrial processes. Dielec-
`tric barrier discharge lamps used to generate ultraviolet
`output generally employ electrical excitation schemes based
`on an AC voltage waveform (50 Hz—200 kHz). Although the
`UV emitted by the plasma can be generated with high
`efficiency (~10—20%) and with high average power,
`the
`present
`inventors have realised that
`the UV output has
`inherently low-peak power due to the dynamics of the
`plasma excitation when using AC excitation.
`OBJECTS OF THE INVENTION
`
`10
`
`15
`
`20
`
`25
`
`It is an object of this invention to provide methods and
`systems for providing emission of incoherent radiation and
`uses therefor.
`
`30
`
`DISCLOSURE OF INVENTION
`
`According to a first embodiment of this invention there is
`provided a method of operating a system for providing
`emission of incoherent radiation, said system comprising an
`electrically impeded discharge lamp linked to an electrical
`energy supply, said lamp comprising:
`(a) a discharge chamber which is at least partially trans-
`parent to said incoherent radiation;
`(b) a discharge gas in said chamber;
`(c) two electrodes disposed with respect to said chamber
`for discharging electrical energy there between;
`(d) at least one dielectric barrier disposed between said
`two electrodes to electrically impede electrical energy
`passing between said two electrodes;
`(e) an electrical energy supply capable of providing fast
`risetime unipolar voltage pulses;
`(f) means of electrically linking said electrodes with said
`supply; said method comprising:
`providing a sequence of unipolar voltage pulses from
`said energy supply to said electrodes and controlling
`(i) interpulse period, an (ii) pulse risetime, whereby
`a substantially homogeneous discharge occurs
`between said two electrodes which causes emission
`
`of pulses of incoherent radiation from said lamp.
`According to a second embodiment of this invention there
`is provided a method of operating a system for providing
`emission of high peak power incoherent radiation, said
`system comprising an electrically impeded discharge lamp
`linked to an electrical energy supply, said lamp comprising:
`(a) a discharge chamber which is at least partially trans-
`parent to said incoherent radiation;
`(b) a discharge gas in said chamber;
`(c) two electrodes disposed with respect to said chamber
`for discharging electrical energy there between;
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`
`(d) at least one dielectric barrier disposed between said
`two electrodes to electrically impede electrical energy
`passing between said two electrodes;
`(e) an electrical energy supply capable of providing fast
`risetime, high peak unipolar voltage pulses;
`(f) means of electrically linking said electrodes with said
`energy supply; said method comprising;
`providing a sequence of high peak power unipolar
`voltage pulses from said energy supply to said elec-
`trodes and controlling
`interpulse period, and (ii)
`pulse risetime, whereby a substantially homoge-
`neous discharge occurs between said two electrodes
`which causes emission of incoherent radiation pulses
`of high peak power from said lamp.
`According to a third embodiment of this invention there
`is provided a system for providing emission of incoherent
`radiation, said system comprising an electrically impeded
`discharge lamp linked to an electrical energy supply, said
`lamp comprising:
`(a) a discharge chamber which is at least partially trans-
`parent to said incoherent radiation;
`(b) a discharge gas in said chamber;
`(c) two electrodes disposed with respect to said chamber
`for discharging electrical energy there between;
`(d) at least one dielectric barrier disposed between said
`two electrodes to electrically impede electrical energy
`passing between said two electrodes;
`(e) an electrical energy supply capable of providing fast
`risetime unipolar voltage pulses;
`(f) means of electrically linking said electrodes with said
`energy supply;
`said energy power supply being capable of providing a
`sequence of unipolar voltage pulses from said energy
`supply to said electrodes; and
`means to control
`interpulse period, and (ii) pulse
`risetime, whereby, in use, a substantially homoge-
`neous discharge occurs between said two electrodes
`which causes emission of pulses of incoherent radia-
`tion from said lamp.
`According to a fourth embodiment of this invention there
`is provided a system for providing emission of high peak
`power (in watts) incoherent radiation, said system compris-
`ing an electrically impeded discharge lamp linked to an
`electrical energy supply, said lamp comprising:
`(a) a discharge chamber which is at least partially trans-
`parent to said incoherent radiation;
`(b) a discharge gas in said chamber;
`(c) two electrodes disposed with respect to said chamber
`for discharging electrical energy there between;
`(d) at least one dielectric barrier disposed between said
`two electrodes to electrically impede electrical energy
`passing between said two electrodes;
`(e) an electrical energy supply capable of providing fast
`risetime, high peak unipolar voltage pulses;
`(f) means of electrically linking said electrodes with said
`supply;
`said energy supply being capable of providing a
`sequence of high peak unipolar voltage pulses from
`said energy supply to said electrodes; and
`means to control
`interpulse period, and (ii) pulse
`risetime, whereby, in use, a substantially homoge-
`neous discharge occurs between said two electrodes
`which causes emission of incoherent radiation pulses
`of high peak power from said lamp.
`
`

`
`US 6,541,924 B1
`
`3
`Other embodiments of the invention include:
`
`(1) a method of releasing contaminants from a surface by
`irradiating the surface with incoherent radiation pulses
`generated by a method of the invention, said pulses
`being of sufficient intensity (W/cm2) to release said
`contaminants from said surface;
`(2) a method of modifying a surface by irradiating the
`surface with incoherent radiation pulses generated by a
`method of the invention, said pulses being of sufficient
`intensity to modify said surface;
`(3) a method of ablating/etching a material by irradiating
`the material with incoherent radiation pulses generated
`by a method of the invention, said pulses being of
`sufficient intensity to ablate/etch said surface;
`(4) a method of pumping a laser active medium by
`irradiating the active medium with incoherent radiation
`pulses generated by a method of the invention, said
`pulses being of sufficient intensity to pump said active
`medium;
`(5) a method of killing micro-organisms and/or bacteria
`by irradiating the bacteria with incoherent radiation
`pulses generated by a method of the invention, said
`pulses being of sufficient intensity to kill said micro-
`organisms and/or bacteria;
`(6) a method of irradiating an object with incoherent
`radiation pulses generated by a method of the
`invention, comprising irradiating said object with said
`pulses;
`(7) a method of removing surface contaminants by irra-
`diating the surface with incoherent radiation pulses
`generated by a method of the invention, comprising
`irradiating said surface with said pulses using various
`methods to achieve inert gas flow over the irradiated
`surface, said pulses being of sufficient
`intensity to
`remove said surface contaminants (see U.S. Pat. No.
`5,821,175 for methods to achieve inert gas flow over
`the irradiated surface);
`(8) a method of controlling insects and/or mites by
`irradiating the insects and/or mites with incoherent
`radiation pulses generated by a method of the
`invention, said pulses being of sufficient intensity to kill
`said insects and/or mites;
`(9) a system for releasing contaminants from a surface
`said system being capable of irradiating the surface
`with incoherent radiation pulses, said pulses being of
`sufficient intensity to release said contaminants from
`said surface;
`(10) a system for modifying a surface said system being
`capable of irradiating the surface with incoherent radia-
`tion pulses, said pulses being of sufficient intensity to
`modify said surface;
`(11) a system for ablating/etching a material said system
`being capable of irradiating the material with incoher-
`ent radiation pulses, said pulses being of sufficient
`intensity to ablate/etch said surface;
`(12) a system for pumping a laser active medium said
`system being capable of irradiating the medium with
`incoherent radiation pulses, said pulses being of suffi-
`cient intensity to pump said active medium;
`(13) a system for killing micro-organisms and/or bacteria
`said system being capable of irradiating the bacteria
`with incoherent radiation pulses, said pulses being of
`sufficient intensity to kill said micro-organisms and/or
`bacteria;
`(14) a system of removing surface contaminants said
`system being capable of irradiating the surface with
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`incoherent radiation pulses, said pulses being of suffi-
`cient intensity to remove said surface contaminants;
`(15) a system of controlling or killing insects and/or mites
`said system being capable of irradiating the insects
`and/or mites with incoherent radiation pulses, said
`pulses being of sufficient intensity to control or kill said
`insects and/or mites;
`Typically the two electrodes are disposed in the chamber.
`The methods of the invention usually comprise:
`providing a sequence of unipolar voltage pulses from said
`energy supply to said electrodes, and controlling
`interpulse period, (ii) pulse risetime, and (iii) pulse
`width, whereby a substantially homogeneous discharge
`occurs between said two electrodes which causes emis-
`sion of pulses of incoherent radiation from said lamp.
`The methods of the invention may comprise:
`providing a sequence of unipolar voltage pulses from said
`energy supply to said electrodes and controlling
`interpulse period, (ii) pulse risetime, (iii) pulse width,
`(iv) interpulse voltage level, and (v) unipolar pulse
`voltage level; whereby a substantially homogeneous
`discharge occurs between said two electrodes which
`causes emission of pulses of incoherent radiation from
`said lamp.
`The systems of the invention usually comprise:
`means to control
`interpulse period, (ii) pulse risetime,
`and (iii) pulse width, whereby, in use, a substantially
`homogeneous discharge occurs between said two elec-
`trodes which causes emission of pulses of incoherent
`radiation from said lamp.
`The systems of the invention may comprise:
`means to control
`interpulse period, (ii) pulse risetime,
`(iii) pulse width, (iv) interpulse voltage level, and (v)
`unipolar pulse voltage level; whereby, in use, a sub-
`stantially homogeneous discharge occurs between said
`two electrodes which causes emission of pulses of
`incoherent radiation from said lamp.
`More typically the high peak power methods of the
`invention comprise:
`providing a sequence of unipolar voltage pulses from said
`energy supply to said electrodes and controlling
`interpulse period, (ii) pulse risetime, and (iii) pulse
`width, whereby a substantially homogeneous discharge
`occurs between said two electrodes which causes emis-
`
`sion of pulses of incoherent radiation of high peak
`power from said lamp.
`The high peak power methods of the invention may
`comprise:
`providing a sequence of unipolar voltage pulses from said
`energy supply to said electrodes and controlling
`interpulse period, (ii) pulse risetime, (iii) pulse width,
`(iv) interpulse voltage level, and (v) unipolar pulse
`voltage level; whereby a substantially homogeneous
`discharge occurs between said two electrodes which
`causes emission of pulses of incoherent radiation of
`high peak power from said lamp.
`More typically the high peak power systems of the
`invention comprise:
`interpulse period, (ii) pulse risetime,
`means to control
`and (iii) pulse width, whereby, in use, a substantially
`homogeneous discharge occurs between said two elec-
`trodes which causes emission of pulses of incoherent
`radiation of high peak power from said lamp.
`The high peak power systems of the invention may
`comprise:
`interpulse period, (ii) pulse risetime,
`means to control
`(iii) pulse width, (iv) interpulse voltage level, and (v)
`
`

`
`US 6,541,924 B1
`
`5
`unipolar pulse voltage level; whereby, in use, a sub-
`stantially homogeneous discharge occurs between said
`two electrodes which causes emission of pulses of
`incoherent radiation of high peak power from said
`lamp.
`The chamber may have a discharge gas inlet and a
`discharge gas outlet. The discharge gas pump may be linked
`to the chamber to either increase or reduce and/or provide
`discharge gas to the chamber. A supply of discharge gas may
`be linked to the chamber.
`
`At high peak power, one pulse of UV/VUV emission is
`observed following the application of each unipolar voltage
`pulse and passage of the associated discharge current pulse.
`At high peak power the output of the discharge chamber
`comprises high output pulse energy (in joules) (within
`-20%, more usually within -10% of the maximum output
`pulse energy) and small output pulse width (in nanoseconds)
`(within -20%, more usually within -10% of minimum
`output pulse width). Usually to generate UV/VUV output
`with high peak power characteristics, the specific operating
`conditions of the discharge chamber or lamp should be
`selected so as to substantially maximise the output pulse
`energy (in joules) and substantially minimise the output
`pulse width (in nanoseconds). By monitoring a typical
`UV/VUV pulse emitted by the lamp of known (fixed)
`surface area, high peak power operation can be characterised
`by measuring the instantaneous peak output power (in watts)
`which should be substantially maximised in amplitude.
`The systems and/or methods of the invention may include
`means to control
`the amplitude of the unipolar voltage
`pulses, means to control pressure and/or temperature of said
`discharge gas, and means to control pulse width.
`The systems and/or methods of the invention may include
`means to adjust the amplitude of the unipolar voltage pulses
`(e.g. an adjustable power supply), means to adjustably
`control gas pressure in the discharge chamber (e.g. via an
`adjustable gas pressure supply to the discharge chamber)
`and/or temperature of said discharge gas (e.g. via an adjust-
`able temperature controller to a heat element coupled or
`operably associated with the discharge chamber), means to
`adjustably control pulse interpulse period (e.g. an adjustable
`power supply), means to adjustably control pulse width (e.g.
`via an adjustable power supply), means to adjustably control
`interpulse voltage level (e.g. via an adjustable power
`supply), and/or means to adjustably control pulse risetime
`(e.g. via an adjustable power supply).
`The systems and/or methods of the invention may include
`means to detect the amplitude of the unipolar voltage pulses
`(e.g. an oscilloscope or voltmeter), means to detect pressure
`(e.g. a pressure gauge) and/or temperature (e.g. a thermo-
`couple linked to appropriate electronics) of said discharge
`gas, means to detect interpulse period (e.g. an oscilloscope
`or voltmeter), means to detect pulse width, amplitude and/or
`means to detect pulse risetime (e. g. an oscilloscope means to
`detect
`interpulse voltage level (e.g. an oscilloscope or
`voltmeter), and/or means to detect discharge current (e.g. an
`oscilloscope or ammeter).
`The systems and/or methods of the invention may include
`means to trigger the energy pulse.
`The systems and/or methods of the invention may include
`means to monitor the amplitude of the unipolar voltage
`pulses pulses (e.g. an oscilloscope or voltmeter), means to
`monitor pressure (e.g. a pressure gauge or a pressure detec-
`tor linked to appropriate electronics) and/or temperature
`(e.g. a thermocouple linked to appropriate electronics) of
`said discharge gas, means to monitor pulse idle time pulses
`(e.g. an oscilloscope or voltmeter), means to monitor pulse
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`width pulses (e.g. an oscilloscope), and/or means to monitor
`pulse risetime (e.g. an oscilloscope), and/or means to moni-
`tor discharge current (e.g. an ammeter).
`The systems and the methods of the invention may
`include means to adjust the composition of the discharge
`gas.
`The systems,and methods of the invention may include
`means to detect the emission of incoherent radiation pulses.
`The systems and methods of the invention may include
`means to detect the emission of incoherent radiation pulses
`and to measure the intensity of the pulses.
`The systems and methods of the invention may include
`means to focus the emitted incoherent light.
`The embodiments of the invention provide methods of
`and systems for generating light usually ultraviolet light or
`vacuum ultraviolet light from dielectric barrier discharges
`(DBD). The methods generate and the systems are capable
`of generating UV or VUV pulses of short duration (100—500
`ns) and, where required, high-peak power UV or VUV
`pulses. This has been made possible through the use of
`electrical circuits, which supply single-pulse voltage wave-
`forms of short duration (typically up to 5 ys, more typically
`tip to 1 ys) and operating procedures to “synchronise”
`excitation of the plasma throughout the volume of the lamp
`resulting in a homogeneous discharge. The excitation pulses
`from the circuit are separated by relatively long “idle” or
`“off” periods,
`typically in the range 5-2000 ys (or 500
`Hz-200 kHz), 5-1000 ys, 5-1500 ys, 5-750 ys, 5-500 ys,
`5-250 s, 5-100ys, 250-800 ys, 275-800 ys. 275-700 ys,
`275-600 ys. 275-500 ys, 275-400 ys, 275-350 ys, 275-325
`ys, where the applied voltage is set to zero and where no
`plasma excitation occurs in the discharge chamber or a value
`other than 0 volts and where no plasma excitation occurs
`discharge chamber. Typically, excitation pulses from the
`circuit are separated by relatively long “idle” or “off”
`periods, of 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110,
`120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230,
`240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350,
`360, 370, 380, 390, 400, 425, 450, 475, 500, 550, 600, 650,
`700, 750, 800, 1000, 1250, 1500, 1750 or 2000 microsec-
`onds.
`
`The amplitude of the unipolar voltage pulses is dependent
`on lamp geometry and required output but
`is usually
`between 0.5 kV-70 kV, 3 kV-50 kV, or 5 kV-30 kV, 5
`kV-25 kV, more usually between 5 kV-20 kV, 5 kV-17 kV,
`5 kV-16 kV, 5 kV-15 kV, 6 kV-15 kV, 6 kV-14 kV and
`even more typically between 6 kV-13 kV. The amplitude of
`the unipolar voltage pulses may be, for example, 1 kV, 2 kV,
`3kV,4kV,5kV,6kV,7kV,8kv,9kV, 10kV, 11kV, 12
`kV, 13 kV, 14 kV, 15 kV, 16 kV, 17 kV, 18 kV, 19 kV, 20 kV,
`25 kV, 30 kV, 35 kV, 40 kV, 45 kV, 50 kV, 55 kV, 60 kV, 65
`kV or 70 kV. Usually the amplitudes of the unipolar voltage
`pulses are less than about 16 kV. The amplitude of each of
`the unipolar voltage pulses may be the same or different.
`The voltage waveform pulse duration is typically in the
`range 0.05 to 5, 0.1 to 4, 0.1 to 3, 0.1 to 2.5, 0.1 to 2, 0.1 to
`1.75, 0.1 to 1.5, 0.1 to 1.25, 0.1 to 1, 0.1 to 0.75, 0.1 to 0.5,
`0.5 to 1.5, 0.5 to 1.25, 0.5 to 1, 0.5 to 0.75, 0.75 to 1.5, 0.75
`to 1.25, 0.75 to 1, 1 to 1.5, 1 to 2, or 0.9 to 1.1 microseconds.
`The pulse duration is typically 0.05, 0.1, 0.2, 0.3, 0.4, 0.5,
`0.6, 0.7, 0.8, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.4,
`1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.5, 3, 3.5, 4.0, 4.5 or 5.0
`microseconds.
`
`Usually the interpulse voltage level is 0 volts or at a
`voltage level whereby no discharge occurs between the two
`electrodes in the system. More usually the interpulse voltage
`level is 0 volts or at a voltage level which is substantially
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`below the voltage level whereby a discharge occurs between
`the two electrodes in the system (typically in the range
`between 0 volts up to 75%, 0 volts up to 50%, 0 volts up to
`25%, 0 volts up to 10% or 0 volts up to 5% of the voltage
`level whereby a discharge occurs between the two electrodes
`in the system).
`As well as optimising the excitation circuitry for high
`peak power operation it has been found that higher gas
`pressures are needed for this new type of operation than are
`typical for standard DBD lamps. Typically, for high peak
`power operation (and for other operations, if required) the
`gas pressure in the discharge chamber is greater than 1
`atmosphere pressure. Typically the gas pressure in the
`discharge chamber is in the range of from about 1.001
`atmospheres-3 atmospheres, 1-5 atms, 1-3 atms, 1-2 atms.
`1.001-2.5 atms, 1.001-2 atms, 1.001-1.75 atms, 1.001-1.5
`atms or 1.001-1.3 atms especially for high peak power
`operation. The gas pressure may be below atmospheric for
`certain uses (for example, high efficiency operation and in
`some instances high peak power operation). Where the gas
`pressure is below or at atmospheric pressure it is typically in
`the range of 180 to 760 torr, more typically to 250 to 760,
`more typically 350 to 760, and even more typically 400 to
`760 and yet even more typically 500 to 760 or 600 to 760
`torr. Usually, the gas pressure in the discharge chamber for
`high peak power operation is 761, 762, 763, 764, 765, 766,
`767, 768, 769, 770, 775, 780, 785, 790, 795, 800, 810, 820,
`830, 840, 850, 875, 900, 925, 950, 975, 1000, 1050, 1100,
`1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550,
`1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, 2000,
`2050, 2100, 2200, 2300, 2400 or 2500 torr.
`The risetime of the voltage pulse is typically in the range
`of5 to 1300, 10 to 1250, 15 to 1150, 20 to 1100, 25 to 1050,
`30 to 1000, 35 to 950, 50 to 900, 75 to 850, 100 to 800, 100
`to 750, 100 to 720, 100 to 700, 100 to 675, 100 to 650, 100
`to 625, 100 to 600, 100 to 575, 100 to 550, 100 to 525, 100
`to 500, 100 to 475, 100 to 450, 100 to 425, 100 to 400, 100
`to 375, 100 to 350, 100 to 325, 100 to 300, 100 to 275, 100
`to 250, 100 to 225, 100 to 200, 100 to 175, 100 to 150, 100
`to 125, 125 to 350, 125 to 300, 125 to 250, 125 to 225, 125
`to 200, 125 to 175, 125 to 150, 150 to 325, 1,50 to 300, 150
`to 275, 150 to 250, 150 to 225, 150 to 200, 150 to 175, 175
`to 325, 175 to 300, 175 to 275, 175 to 250, 175 to 225, 175
`to 200, 200 to 350, 200 to 325, 200 to 300, 200 to 275, 200
`to 250, 200 to 230, 200 to 225, 200 to 220, 200 to 210, 200
`to 400, 200 to 350, 200 to 500, 200 to 450, 200 to 425, 210
`to 400, or 220 to 250 nanoseconds. The risetime of the
`voltage pulse is typically 50, 60, 70, 80, 90, 100, 110, 120,
`130, 140, 150, 160, 170, 180, 190, 200, 205, 210, 220, 230,
`240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350,
`360, 370, 380, 390, 400, 450, 500, 550, 600, 700, 800, 900,
`1000, 1100, 1200, or 1300 nanoseconds.
`The methods and systems of the invention are capable of
`providing a source of high-peak-power incoherent ultravio-
`let (UV) light (80-350 nm, more typically 11-320 nm). The
`high-peak-power mode of operation is made possible by the
`method of the invention using a short-pulse excitation
`scheme of a plasma lamp of the dielectric barrier discharge
`(DBD) type. Although there has been considerable effort
`worldwide in developing DBD lamp technology as efficient
`sources of high-average power UV over the past ten years,
`no attention has been directed towards operating these lamps
`to generate short-pulse, high-peak-power UV output. Such a
`source of high-peak-power UV radiation may be used for a
`variety of industrial applications relating to surface modifi-
`cation (ablation and chemical reactions) and materials pro-
`cessing for which processing rates are strongly dependent on
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`the rate of UV energy density deposition and which may be
`characterised by a threshold fluence. This category of mate-
`rials processing cannot be easily undertaken with commer-
`cial DBD lamps currently available as these operate with
`high-average power, but low-peak-power UV output and
`hence yield poor performance such as low etch rates. More
`commonly,
`laser-based sources of high-peak power UV
`radiation are used for such applications. Several different
`output wavelengths are possible from DBD lamps depend-
`ing on the gas mixture used in the discharge namely, XeCl
`(308 nm), KrF (248 nm), KrCl (222 nm), ArCl (175 nm),
`XeF (354 nm), Xel (253 nm), XeBr (283 nm), Krl+ (190 nm)
`KrBr (207 nm), ArBr (1.65 nm), Xe; (172 nm), Kr; (146
`nm) and Ar; (126 nm) and Ne; (88 nm), and He2+. The
`methods of the invention may be applied to provide short
`pulsed, high peak power output is applicable to DBD lamps
`based on all these gas mixtures.
`The discharge gap is in the range in which a substantially
`homogeneous discharge can take place and be stably sus-
`tained. Usually the discharge gap is less than or equal to
`about 10 mm. Typically the discharge gap is in the range 0.5
`to 10 mm, more typically 1.0 to 7 mm, more typically 1.5 to
`5 mm, and more typically 2 to 3 mm.
`To operate a dielectric barrier discharge (DBD) lamp,
`being a source of incoherent ultraviolet (UV) radiation, in a
`manner whereby the UV generated by the DBD appears in
`the form of single (and intense) pulses of short duration (e.g.
`50-500 ns) during each cycle of the lamp excitation, these
`pulses constituting high peak-power UV output. The lamp
`geometry, operating conditions and procedures are opti-
`mised so as to maximise the peak power of the individual
`UV output pulses.
`This mode of operation is achieved through the use of
`pulsed electrical excitation (in particular using voltage
`pulses with rapid rise times) and by optimising the lamp
`operating parameters so as to increase the production rate
`(and shorten the formation time) of the dimer molecules
`from which the UV radiation is derived. An important
`characteristic of the high-peak power operation is that the
`UV radiation is often generated (but not necessarily) from a
`spatially uniform or homogeneous discharge plasma, rather
`than a filamentary type (streamer) plasma more commonly
`associated with conventional AC excited DBD lamps. The
`cause of the homogeneous discharge is thought to be caused
`by the rapid rate at which the applied E-field reaches the
`necessary condition for homogeneous discharge to occur at
`a faster rate than the formation of filaments. It i