WO2003021729A1 - Laser a ecoulement de gaz auto-circulatoire - Google Patents

Laser a ecoulement de gaz auto-circulatoire Download PDF

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Publication number
WO2003021729A1
WO2003021729A1 PCT/GB2002/003773 GB0203773W WO03021729A1 WO 2003021729 A1 WO2003021729 A1 WO 2003021729A1 GB 0203773 W GB0203773 W GB 0203773W WO 03021729 A1 WO03021729 A1 WO 03021729A1
Authority
WO
WIPO (PCT)
Prior art keywords
gas
active region
laser apparatus
flow
barrier member
Prior art date
Application number
PCT/GB2002/003773
Other languages
English (en)
Inventor
David V. Willetts
Original Assignee
Qinetiq Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Qinetiq Limited filed Critical Qinetiq Limited
Publication of WO2003021729A1 publication Critical patent/WO2003021729A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/03—Constructional details of gas laser discharge tubes
    • H01S3/036—Means for obtaining or maintaining the desired gas pressure within the tube, e.g. by gettering, replenishing; Means for circulating the gas, e.g. for equalising the pressure within the tube
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/04—Arrangements for thermal management
    • H01S3/041—Arrangements for thermal management for gas lasers

Definitions

  • the invention relates to a laser apparatus comprising a laser cavity filled with a gaseous lasing medium and, in particular, of the type intended for pulsed laser operation in which a pulsed electrical discharge is supplied to an active region of the medium to induce lasing.
  • Gas lasers for example CO2, nitrogen or excimer lasers, include a gaseous active medium which is optically, electrically or laser pumped to induce a lasing action.
  • a pair of electrodes is arranged to pass a current, either pulsed or continuous wave (cw), through the active medium.
  • the current may be passed along the axis of the lasing medium (longitudinal excitation) or transversely to it (transverse excitation). It is a requirement of both transverse and longitudinal excitation pulsed gas laser operation to remove waste heat generated in the active gas medium by means of a heat exchanger. For this purpose, it is necessary to ensure gas within the active region is circulated during pumping. It is also important to circulate gas within the active region to remove residual ionisation and to maintain a substantially constant plasma electron temperature.
  • US 4541097 also describes a gas laser apparatus of the type in which a blower is provided to direct a gas flow through a discharge tube.
  • the gas laser is provided with an improved electrode construction which avoids local increases in glow current density and, thus, maintains a stable and uniform glow current density within the discharge tube.
  • US 4654855 describes a pulsed electrical discharge gas laser having acoustic diodes to cause the gas to circulate between the active region of the laser and a gas heat exchanger.
  • the diodes take the form of asymmetrical obstacles which are placed within the gas flow, and which exhibit asymmetrical resistance to the passage of compression waves in the gas that are generated by the electrical discharge.
  • gas is caused to circulate through the active region of the laser, and through the gas heat exchanger.
  • the laser is of complex construction and relatively expensive, however, as it requires a plurality of acoustic diode elements to be arranged within the circulation path.
  • a laser apparatus comprises a gaseous lasing medium having an active region within which lasing occurs, the active region defining, in part, a flow path for gas, excitation means including an electrode arrangement for supplying energy to the active region, and a barrier member arranged adjacent to the active region, such that net momentum is imparted to gas in the active region upon an electrical discharge being supplied to the active region of gas, thereby to generate a substantially unidirectional, circulatory gas flow within the flow path to aid heat removal from the gas, wherein the barrier member defines a plurality of flow passages for gas flow, each of which presents substantially the same impedance to gas flow in opposing flow directions.
  • the lasing medium is a gas comprising, for example, CO2 laser gas mixture or nitrogen.
  • the lasing medium may be an excimer gas mixture or a mixture appropriate to any other pulsed gas laser.
  • the electrical excitation means preferably include a pulsed electrical power supply coupled to the electrode arrangement.
  • the electrode arrangement is arranged for transverse excitation of the active region.
  • the transmission of the barrier member is between 25 % and 75%.
  • Pulsed electrical excitation of the laser is achieved by passing a pulsed current through the active region of the gas medium.
  • the rapid deposition of pulsed electrical energy in the active region results in a relatively fast, irreversible adiabatic expansion of the gas.
  • the provision of the barrier member adjacent to the active region breaks the discharge symmetry as the barrier selectively impedes gas flow on one side of the discharge. As a result, net bulk motion is imparted to the gas causing gas to be circulated within the flow path.
  • the provision of the flow passages within the barrier member ensures gas circulation is maintained when the pulsed electrical discharge ceases.
  • the present invention therefore enables a self-circulating gas flow to be achieved, removing the need for an additional fan or turbine system.
  • the laser apparatus therefore has reduced power requirements and is of reduced weight. Additionally, as the provision of the barrier member to one side of the active region imparts net bulk motion to the gas, there is no need to provide asymmetric flow devices, such as acoustic diodes, minimising the cost and complexity of the apparatus.
  • the apparatus includes an optical cavity having first and second opposing end mirrors and an optical axis which passes through the active region, the barrier member being arranged such that the flow passages extend along an axis substantially perpendicular to the optical axis.
  • the barrier member is a plate provided with a plurality of apertures extending along a first axis, each of said apertures defining a respective one of the flow passages and having a substantially uniform cross section along its axial length.
  • the flow passages enable gas circulation to continue after the pulsed electrical discharge has ceased.
  • the apertures may be shaped to define flow passages of substantially circular cross section.
  • the diameter of the apertures is between 2mm and
  • the barrier member may be formed from a stack of elongate slats, bars or rods, wherein neighbouring ones of the slats, bars or rods define therebetween the gas flow passages.
  • the barrier member may be provided with a plurality of cooling flow passages arranged to receive a flow of cooling fluid, in use.
  • This embodiment of the invention is advantageous as the barrier member causes both the generation of a self-circulating gas flow, and also acts as a heat exchange mechanism for cooling the gas.
  • the cooling flow passages are defined within the barrier member, and preferably extend along an axis substantially perpendicular to the axis of the gas flow passages.
  • cooling flow passages are mounted upon the barrier member.
  • Figure 1 is a schematic, end view of a laser apparatus in accordance with an embodiment of the present invention
  • Figure 2 is an isometric view of a plate forming part of the laser apparatus in Figure 1
  • excitation energy 480 J/l.atm, prf 20Hz
  • Figure 4 is a graph to illustrate the mean gas flow velocity as a function of electrical pulse repetition frequency over a range of excitation energies for the laser apparatus in Figure 1 ,
  • Figure 5 is a graph to illustrate the effect on gas flow circulation of varying plate aperture size and energy loading in the laser apparatus in Figure 1 .
  • Figure 6 is a graph to illustrate the effect on gas flow circulation of varying the distance of the apertured plate from the electrical discharge centreline for the gas laser apparatus in Figure 1 ,
  • Figure 7 is a schematic end view, similar to that shown in Figure 1 , of an alternative embodiment of the invention.
  • Figure 8 shows (a) a perspective view and (b) a top view of an alternative configuration for the plate in Figure 2, and
  • Figure 9 shows an alternative form of barrier member to that shown in Figure 2.
  • a gas laser apparatus includes an optical cavity 10, having an optical axis, which is filled with a gaseous medium having an active region 12 (shown generally by dashed lines), defined between opposing first and second electrodes 14, 16 forming part of an electrode arrangement, within which laser radiation is generated.
  • the laser radiation axis extends transversely to the plane of the page, along the optical axis of the cavity 10.
  • the first and second electrodes 14, 16 are arranged within an outer chamber 24, the outer walls 24a, 24b, 24c, 24d of which define, in part, a duct or flow path 11 through which a substantially unidirectional gas flow circulates, in use, as described in further detail below.
  • the outer chamber 24 is substantially sealed to prevent gas leaking out of the chamber 24 and air leaking in.
  • the flow path 11 passes through the active region 12 of the gas, the flow of gas following the direction of arrows 13 through the flow path 11.
  • an electric field is applied across the first and second electrodes 14, 16 through connecting wires 26, 28 arranged within the duct 11 and in connection with a pulsed DC power supply circuit, referred to generally as 20.
  • the supply circuit 20 is arranged to supply a pulsed DC voltage across the electrodes 14, 16, thereby causing an electrical discharge to be passed through the active region 12 of the gas.
  • An arc array 25 is provided, capacitively coupled to the first and second electrodes 14, 16, so as to enable preionisation of the gas in a manner which would be familiar to a person skilled in the art.
  • the electrical discharge passing through the active region 12 of the gas causes electrons in the electrical discharge to transfer energy to the gas molecules.
  • the upper energy levels of the laser transition become populated and, hence, lasing is induced within the active region 12 of gas.
  • One end of the optical cavity is conveniently provided with a first mirror (not shown) and the other end with a second, partially reflecting mirror through which laser radiation, generated within the active region 12, is partially transmitted.
  • the electrode arrangement 14, 16 in Figure 1 is arranged for transverse excitation of the gas, whereby the electrical discharge is passed through the gas in a direction transverse to the laser radiation axis.
  • Appropriate insulating regions 17 are provided in a conventional manner.
  • the DC power supply circuit 20 is arranged for pulsed operation and includes a high voltage source 30 (typically between 10 - 50 kV) which is arranged to charge a capacitor 32 through a charging resistor 36.
  • a high voltage source 30 typically between 10 - 50 kV
  • the capacitor 32 is charged to a high voltage by means of the high voltage source 30 and, under the control of the thyratron trigger 34, is discharged to the first and second electrodes 14, 16.
  • the thyratron 34 When the thyratron 34 is triggered, the capacitor 32 discharges to the electrodes to create a pulsed electrical discharge in the active region 12 of the gas.
  • the charging/discharging process is repeated to create a pulsed discharge having a frequency referred to as the 'pulse repetition frequency' (prf).
  • a barrier member in the form of a plate 38 is located adjacent to the active region 12 of the gas between the first and second electrodes 14, 16.
  • the plate 38 has a front face 41a and a rear face 41b and is provided with a plurality of apertures or drillings 38a, which extend through the plate 38, from the front face 41a to the rear face 41b, to define a plurality of axially aligned flow passages 39.
  • Each of the flow passages 39 extends along an axis substantially perpendicular to the optical axis.
  • the flow passages 39 are of uniform cross sectional area along their axial length, and present substantially the same impedance to flow through the plate 38 in both directions (i.e. front face to rear face, and rear face to front face). The symmetry of the flow impedance is ensured as the apertures 38a are drilled through the parallel sided plate, and the remaining lands are not profiled in any way.
  • the plate 38 extends along the entire length of the active region 12.
  • any gas flow through the passages 39 will experience the same flow impedance in opposing directions. Due to the net bulk motion imparted to the gas, a substantially unidirectional flow will eventually be caused to circulate through the flow path 11 and through the flow passages 39 to provide a 'self circulating' gas flow through the laser cavity 10 and the remainder of the flow path 11 in the direction of arrows 13.
  • the benefit of achieving a self-circulatory gas flow within the active region 12 is that the need for an additional fan or turbine system to assist removal of waste heat through heat exchangers is removed.
  • the location and size of the plate 38 is chosen to ensure a sufficient pressure differential can be developed within the active region 12, even for relatively modest discharge energy loadings.
  • the pressure differential created by the presence of the plate 38 is preferably sufficient to ensure the volume of gas within the active region 12 is displaced several times between successive pulses.
  • the plate 38 may have a transmission of anywhere between approximately 25 % and 75%, and preferably around 50%.
  • the diameter of the apertures 38a is between 2 and 4 mm. It will be appreciated, however, that the apertures need not be of circular form and may be of an alternative shape, the number and size of the apertures being selected to provide the required transmission.
  • the flow resistance through the plate 38 has directional symmetry, and this may be achieved by ensuring the profile of the flow passages 39 in cross section is substantially symmetric about the mid-plane of the plate 38.
  • the most convenient way to achieve this is to drill the apertures 38a to have a uniform cross section along their entire axial length, from the front surface 41a of the plate 38 to the rear, but alternatively the apertures may have a tapered or stepped cross section, providing the shaping is substantially symmetric about the mid-plane of the plate 38.
  • Figures 3 to 6 have been obtained for a CO2 pulsed laser.
  • the measurements were made using a bistatic coherent Doppler Lidar technique, with gas flow velocities measured at measurement point X, as shown in Figure 1.
  • Figure 3 shows the velocity of gas flow through the active region 12 as a function of time for a pulse discharge of 480 J/l.atm at a prf of approximately 20 Hz.
  • the results were obtained for a laser apparatus having a plate 38 provided with apertures 38a of 2 mm diameter and having a transmission of approximately 50%.
  • Figure 4 shows the gas flow velocity as a function of pulse repetition frequency (prf) for a range of energy loadings between 160 J/l.atm and 480 J/l.atm. It can be seen that higher pulse repetition frequencies give rise to increased gas flow velocities within the active region 12.
  • Figure 5 shows the effect on gas flow velocity of varying the diameter of the apertures 38a provided in the plate 38.
  • the transmission of the plate 38 is 50% for both the plate with 2mm diameter apertures, and the plate with 3.6 mm diameter apertures. It can be seen that the diameter of the apertures 38a has little effect on the gas flow velocities generated.
  • Figure 6 illustrates the effect of varying the distance of the plate 38 from the discharge centre line (dashed line 40 in Figure 1). The measurements were carried out for two energy loadings, 330 J/l.atm and 480 J/l.atm.
  • Figure 7 shows an alternative embodiment of the invention to that shown in Figure 1 in which like reference numerals are used to denote similar parts. In Figure 7, the upper region of the chamber 22 is removed and the DC power supply circuit 20 is connected directly to the first electrode 14, thereby removing the need for the connecting wire 26.
  • Figure 8 shows an alternative configuration for the plate 38, in which it is combined with a heat exchange mechanism.
  • the plate 38 is also provided with a set second of drillings or apertures 38b extending along a second axis 44, perpendicular to the first, and interspersed between neighbouring columns of the first apertures 38a.
  • the second apertures 38b define a plurality of cooling flow passages 46 through which a cooling fluid is passed, in use, so as to cool the gas flow through the gas flow passages 39. It will be appreciated that the further apertures 38b need not be provided between every column of apertures 38a if a sufficient cooling effect can be achieved with fewer.
  • Figure 9 shows a further alternative configuration for the barrier member, in the form of a stack of slats or bars 48.
  • the flow passages 39 are defined by facing surfaces of neighbouring ones of the bars 48.
  • one or more of the bars 48 may be provided with a drilling extending therethrough to define a cooling flow passage for cooling fluid, as described previously with reference to Figure 8.
  • a support structure may be provided at either end of the bars 48 to hold the bars in place, although this is not shown for clarity.
  • the present invention may take the form of a gas laser other than that comprising a CO2 gas medium.
  • the laser may be an excimer or nitrogen gas laser.
  • the electrode arrangement for supplying an electrical discharge to the active region of the gas need not be arranged for transverse excitation, but may be a longitudinal electrode arrangement arranged to pass currents through the active region of the gas along the laser axis direction.
  • the laser apparatus may be operated over a range of pulse repetition frequencies, for example between 30 and 40 Hz. However, particularly for excimer lasers, the pulse repetition frequency may be higher (of the order of kHz).
  • the laser apparatus of the present invention need not necessarily include the particular electrode configuration shown in the accompanying drawings to achieve the advantageous benefits of a self- circulating gas flow.
  • the plate 38 may be replaced by an alternative member sufficient to impart net momentum to gas within the active region 12 following deposition of energy, and defining flow passages to ensure the gas flow is sustained after the discharge has ceased.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Lasers (AREA)

Abstract

L'invention a trait à un appareil laser comprenant un matériau actif gazeux. Ledit appareil comporte une région active (12) dans laquelle a lieu l'action laser, la région active(12) définissant, en partie, un circuit d'écoulement pour le gaz. L'appareil comprend également des moyens d'excitation fournissant de l'énergie à la région active. Ces moyens d'excitation comprennent un agencement d'électrodes (14, 16) et un élément barrière (38 ; 48) adjacents à la région active. Une énergie cinétique nette est communiquée au gaz dans la région active (12) lorsqu'une décharge électrique est envoyée à cette région active (12) de gaz. Un écoulement de gaz circulatoire sensiblement unidirectionnel est ainsi généré à l'intérieur du circuit d'écoulement afin de contribuer à la dissipation de la chaleur du gaz. L'élément barrière (38 ; 48) définit une pluralité de passages d'écoulement (39) pour le gaz, chacun desquels présente sensiblement la même résistance à l'écoulement de gaz dans des directions d'écoulement opposées.
PCT/GB2002/003773 2001-08-29 2002-08-15 Laser a ecoulement de gaz auto-circulatoire WO2003021729A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0120845.3 2001-08-29
GB0120845A GB0120845D0 (en) 2001-08-29 2001-08-29 Laser apparatus

Publications (1)

Publication Number Publication Date
WO2003021729A1 true WO2003021729A1 (fr) 2003-03-13

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TW (1) TW569511B (fr)
WO (1) WO2003021729A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022201843A1 (fr) * 2021-03-24 2022-09-29 ギガフォトン株式会社 Dispositif de chambre, et procédé de fabrication de dispositif électronique

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115347439B (zh) * 2022-08-23 2024-08-20 西北核技术研究所 气体激光器和输出脉冲激光的方法

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4550408A (en) * 1981-02-27 1985-10-29 Heinrich Karning Method and apparatus for operating a gas laser
US4598406A (en) * 1985-01-18 1986-07-01 Texas Instruments Incorporated Pressure-wave cycled, repetitively pulsed gas laser
US4654855A (en) * 1985-04-05 1987-03-31 Northrop Corporation Pulsed gas laser using acoustic diodes for circulation of the gas
US4873695A (en) * 1987-07-27 1989-10-10 Compagnie Generale D'electricite Laser with discharge in a turbulent transverse flow
JPH01260871A (ja) * 1988-04-12 1989-10-18 Komatsu Ltd 無声放電ガスレーザ装置の誘電体電極冷却方法及びその装置

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4550408A (en) * 1981-02-27 1985-10-29 Heinrich Karning Method and apparatus for operating a gas laser
US4598406A (en) * 1985-01-18 1986-07-01 Texas Instruments Incorporated Pressure-wave cycled, repetitively pulsed gas laser
US4654855A (en) * 1985-04-05 1987-03-31 Northrop Corporation Pulsed gas laser using acoustic diodes for circulation of the gas
US4873695A (en) * 1987-07-27 1989-10-10 Compagnie Generale D'electricite Laser with discharge in a turbulent transverse flow
JPH01260871A (ja) * 1988-04-12 1989-10-18 Komatsu Ltd 無声放電ガスレーザ装置の誘電体電極冷却方法及びその装置

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 014, no. 018 (E - 873) 16 January 1990 (1990-01-16) *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022201843A1 (fr) * 2021-03-24 2022-09-29 ギガフォトン株式会社 Dispositif de chambre, et procédé de fabrication de dispositif électronique

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GB0120845D0 (en) 2001-10-17
TW569511B (en) 2004-01-01

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