EP0490933A1 - A laser - Google Patents
A laserInfo
- Publication number
- EP0490933A1 EP0490933A1 EP90913120A EP90913120A EP0490933A1 EP 0490933 A1 EP0490933 A1 EP 0490933A1 EP 90913120 A EP90913120 A EP 90913120A EP 90913120 A EP90913120 A EP 90913120A EP 0490933 A1 EP0490933 A1 EP 0490933A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- laser
- gain medium
- state
- energy
- noble gas
- Prior art date
- Legal status (The legal status 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 status listed.)
- Withdrawn
Links
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
- H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
- H01S3/22—Gases
- H01S3/223—Gases the active gas being polyatomic, i.e. containing two or more atoms
- H01S3/225—Gases the active gas being polyatomic, i.e. containing two or more atoms comprising an excimer or exciplex
Definitions
- This invention relates to a laser. It relates particularly to a laser in which the gain medium consists principally of a noble gas.
- a laser comprises a means for the controlled excitation and de-excitation of particles in a gain medium in such a way that the de-excitation is accompanied by the emission of highly coherent electro-magnetic radiation (light).
- the operation of a laser generally depends upon the ability of the individual particles of the gain medium to adopt at least three separate energy states.
- the first energy state is an excited state which is sufficiently stable to allow a substantial number of particles to achieve that energy level simultaneously.
- the second energy state is a lower energy state than the first and is generally unstable to enable a low concentration of that species.
- photons of an energy equal to the energy difference between the first and second energy level can induce a transition from the first state to the second state that produces a second photon of identical wavelength.
- the medium amplifies the light. The rate of stimulated emission is therefore dependent on the amount of particles in the first energy level and the number of photons of the appropriate energy into the medium.
- the photons are capable of being absorbed by particles in the second energy state, reinstating the particles to the first energy state and deminishing and preventing amplification of the light, it is desirable that the second energy state be unstable so that the particles quickly decay to a third energy state which is transparent to the photons.
- the elements may be planar and parallel, they may be confocal and spherical, or they may be any other suitable configuration.
- the elements are generally constructed or coated to be selectively reflective of photons of the relevant wavelength. This permits the elements to confine radiation of the appropriate wavelength while allowing transmission of radiation of other wavelengths.
- Transmission of laser radiation from such a system is usually effected either by allowing transmission of about 2% of radiation of the relevant wavelength through one of the reflective elements or by inserting a beam-splitting element between the two existing elements to split out approximately 2% of the radiation.
- the energy level transitions which are useful particularly for gaseous atomic lasers in producing laser radiation usually result in the production of photons having a wavelength range of a few angstroms. It is possible to tune the wavelength of the standing wave within this wavelength range to ensure that the laser radiation produced has a specific wavelength. Numerous different techniques are available for tuning of the wavelength. These include the use of prisms such as those described in Australian patent 284799, or the use of filters and diffraction gratings, such as lithrow mount diffraction gratings. Another suitable means for tuning comprises the use of another laser, which is already providing laser radiation of the desired wavelength, as incident radiation. Providing that the incident radiation is within the available wavelength range, the standing wave will then tend to adopt an identical wavelength.
- the ability to tune a laser is limited by the range of wavelengths which the relevant energy level transition is capable of producing, and this range is generally very small, particularly those involving atomic energy levels.
- Lasers whose gain medium is a combination of gases have been known for some time.
- Australian patent number 254702 describes in some detail examples of such lasers, including in particular lasers the gain medium of which is a combination of helium and neon.
- the helium-neon laser takes advantage of the fact that helium has a metastable excited energy level
- Neon also has a lower energy level (2 ⁇ g ), and the transition between the two energy levels of neon is the relevant one for the purposes of lasing.
- the helium-neon lasing process is inefficient for a number of reasons.
- the major inefficiencies are attributable to the energetic electrons created by the ionisation of helium, inhibiting the efficient formation of the desired population inversion by promoting reactions which increase the number of neon atoms at levels other than the 2S t - state or by accelerating reactions which tend to restore the system to equilibrium.
- Australian patent number 254702 sought to overcome these inefficiencies by pulsing the radiation used to cause the ionisation of helium so that the creation of high energy free electrons is periodic and the lifetime of 3 helium atoms in the 2 S. level is longer than the lifetime of the free electrons.
- pulsing parameters it is possible to induce stimulated emission which approximates continuous lasing, but true continuous lasing is never achieved and the helium-neon laser remains inefficient.
- excimer laser Another type of commonly used gas laser is the excimer laser.
- This type of laser uses as its gain medium a noble gas in conjunction with a halide gas, and produces photons which are in the ultraviolet range.
- Examples of excimer lasers are lasers which comprise neon and chlorine or xenon and fluorine. Such lasers produce only a narrow range of wavelengths, typically having a range of about l ⁇ .
- Excimer lasers suffer the disadvantage that the halide gases have a corrosive effect on the vessel in which they are contained, so that frequent restoration or replacement of the vessel is necessitated. In practice, this occurs after about ten days of continuous operation. The gases are also dangerous, requiring special ventilation for the apparatus.
- the operative particles creating the laser effect in excimer lasers are short-lived molecules comprising a combination of noble gas atoms and halide gas atoms. These molecules are formed in the afterglow of an electrical discharge or other suitable means of excitation, so that the laser operates as a series of pulses, each pulse comprising electrical discharge followed by a formation of molecules, followed by de-excitation and emission of laser radiation. These molecules have an unbound lower state which quickly decays, enabling population inversion.
- Neutral dimer lasers involve the combination of a noble gas atom in the ground state and a further atom of the same noble gas in an excited state to form a molecule.
- a further object is to provide a laser which is capable of continuous operation.
- a further object is to provide a laser which is powerful and efficient.
- a laser which uses dimer ions of a noble gas as its gain medium.
- the preferred laser excitation means is an electrical discharge, and indeed any suitable means of excitation including microwave radiation and particle beam excitation may be used.
- the noble gas used in the present invention may be any noble gas including helium, argon, xenon or krypton.
- the laser of the present invention be capable of operation at high temperatures, because it has been found that noble gas dimer ions form more readily at high temperatures (activation energy ⁇ 1 eV) which allow for a high degree of efficiency.
- the active medium be contained within a ceramic, graphite or other refractory material vessel which is capable of withstanding high temperatures, rather than a conventional water-cooled glass vessel.
- Figure 1 of the drawings is an energy level diagram showing a plot of energy against inter-nuclear separation for a helium atom and a He ion.
- FIG. 2 is a schematic representation of laser apparatus embodying the present invention.
- dimer lasers have not yet been commonly used because of practical difficulties such as providing a sufficient population of the dimer in the afterglow of the electrical discharge, requiring the use of expensive and exotic relativistic electron accelerators (Wrobel, Appl Phys. Let. Vol. 136, page 113, 1980).
- the present invention results from the discovery of a new energy state in a noble gas dimer ion which is actually formed during the electric discharge, rather than in the afterglow.
- the presence of this new energy state was determined by the present inventor's analysis of experimental results, such as those given in "New Vacuum - Ultraviolet Emission Continua of Helium produced in High-Pressure Discharges", by R E Huffman, Y Tanaka and J C Larrabee, published in the Journal of the Optical Society of America, Volume 52 No. 8 (March 1962) (high energy pulse form); D Simon and K Rodgers, J. Appl. Phys. 37,2225 (1966) (continuous operation); and Y Tanaka, A Jursa and F LeBlanc, J. Opt. Soc. Am. 8,304 (1958) (low energy continuous operations) .
- the lower energy state is labelled A ⁇ + .
- the C ⁇ state represents the interaction of an He + ion with a helium atom excited to the 2 P level.
- the dimer ion Upon absorbing a photon with wavelength between 2500 and 10000 X, the dimer ion decays to the A 2 ⁇ + state, emitting 2 photons y having wavelengths identical to that of the incident photon.
- the A ⁇ * state is an unbound state.
- the He + molecule rapidly decays into individual He + and He atoms, thus becoming transparent to the photons.
- the symbolic representation of the process is as follows:
- the formation of the excited dimer ion occurs in the presence of another helium atom (any ion, electron or neutral or multiple particle which can remove momentum) which absorbs momentum, allowing the dimer ion to settle in the bound state.
- another helium atom any ion, electron or neutral or multiple particle which can remove momentum
- Equation 2 shows the stimulated emission of the excited helium dimer ion from the C 2 ⁇ state to the
- Equation 3 shows the rapid decay of the A 2 ⁇ + state into He + and He atoms.
- the Helium ions in the high temperature conditions of an arc act as a catalyst to liberate the energy trapped in the excited states of Helium. This process is highly efficient and operates at high power densities.
- the laser of the present invention is capable of converting very large quantities of energy into laser radiation.
- Excimers on the other hand, deteriorate very quickly when the energy input is increased significantly.
- the pressure of the noble gas which forms the gain medium for the laser be approximately 2 atmosphere.
- the pressure may be any other suitable amount, but should in any event be greater than 200 Torr in order for the invention to work in an appropriate manner. It is further preferred that there be provided appropriate valves gauges and vacuum pump to ensure the desired pressure and purity of noble gas.
- the preferred means for exciting the gain medium comprises a cathode and an anode one of which is connected to a capacitor which sends an electrical discharge through the active medium once the capacitor has reached the breakdown voltage of the active medium.
- Other suitable means for exciting include microwave excitation means, particle beam excitation means, flashlamp excitation means, and Tesla coils.
- the laser of the present invention may be subjected to continuous excitation and may provide a continuous laser pulse, provided that a sufficiently large quantity of power is available for excitation.
- the laser of the present invention may be operated in pulses by means of a capacitor of approximately 1 microfarad, charged to approximately 30 kV, although these figures are arbitary.
- the capacitor discharges along transmission lines, designed to have no impedance mismatches, when the voltage reaches such a value that an electrical discharge occurs between anode and cathode.
- One suitable means for tuning is the use as incident radiation of a laser of a set wavelength within the noble gas dimer ion spectrum.
- the laser of the present invention will then adopt the wavelength of the input laser and amplify the incident light.
- filters and diffraction gratings such as lithrow mount diffraction gratings. These may be placed according to known techniques between a mirror and the gain medium in order to feed the desired wavelength back into the active medium, ensuring that the desired wavelength becomes the one which is amplified.
- a noble gas such as helium is contained at a pressure of approximately 2 atmosphere within refractory discharge guide c.
- Refractory discharge guide c is bounded at one end by polished aluminium block mirror a and at the other end by partially transmitting mirror e.
- cathode b Arranged at separate ends of refractory annular discharge guide c are cathode b and anode d. Anode d is electrically grounded, while cathode b is electrically connected to pulsed capacitor f. Pulsed capacitor f is in turn connected both to ground and via limiting resistor g to 30 kilovolt DC power supply h.
- the present invention provides a laser which may be tuned within a broader range of wavelengths than any previous laser. It further provides a more efficient laser and a laser capable of continuous operation.
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Optics & Photonics (AREA)
- Lasers (AREA)
Abstract
On a découvert que des ions dimères à courte durée de vie sont créés dans un gaz noble dans des conditions d'énergie élevée, par exemple pendant une décharge électrique. Ces ions dimères de gaz noble présentent des états énergétiques excités, qui les rendent appropriés pour être utilisés comme milieu de gain dans un laser. Un laser créé au moyen d'ions dimères de gaz noble comme milieu de gain se caractérise par un degré d'efficacité élevé, est syntonisable dans une large gamme de longueurs d'ondes et est capable de fonctionner en continu.It has been discovered that short-lived dimer ions are created in a noble gas under high energy conditions, for example during an electric discharge. These noble gas dimer ions have excited energetic states, which make them suitable for use as a gain medium in a laser. A laser created using noble gas dimer ions as a gain medium is characterized by a high degree of efficiency, is tunable over a wide range of wavelengths and is capable of operating continuously.
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AUPJ622289 | 1989-09-06 | ||
AU6222/89 | 1989-09-06 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0490933A1 true EP0490933A1 (en) | 1992-06-24 |
EP0490933A4 EP0490933A4 (en) | 1992-09-23 |
Family
ID=3774173
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19900913120 Withdrawn EP0490933A4 (en) | 1989-09-06 | 1990-09-06 | A laser |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0490933A4 (en) |
BR (1) | BR9007610A (en) |
CA (1) | CA2060180A1 (en) |
WO (1) | WO1991003850A1 (en) |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CA1049639A (en) * | 1976-02-11 | 1979-02-27 | Georges Fournier | Lasing device and method |
US4159453A (en) * | 1976-11-30 | 1979-06-26 | Max-Planck-Gesellschaft Zur Foerderung Der Wissenschaften E.V. | Hydrogen-gas-laser method and apparatus |
FR2608943B1 (en) * | 1986-12-24 | 1989-10-20 | Commissariat Energie Atomique | METHOD AND DEVICE FOR OBTAINING AN EXCIMER, APPLICATION TO LASER |
SU1674299A1 (en) * | 1987-01-28 | 1991-08-30 | Научно-исследовательский центр по технологическим лазерам АН СССР | Neon laser with 3p-3s junction |
-
1990
- 1990-09-06 CA CA 2060180 patent/CA2060180A1/en not_active Abandoned
- 1990-09-06 BR BR909007610A patent/BR9007610A/en not_active Application Discontinuation
- 1990-09-06 EP EP19900913120 patent/EP0490933A4/en not_active Withdrawn
- 1990-09-06 WO PCT/AU1990/000403 patent/WO1991003850A1/en not_active Application Discontinuation
Non-Patent Citations (2)
Title |
---|
No further relevant documents disclosed * |
See also references of WO9103850A1 * |
Also Published As
Publication number | Publication date |
---|---|
CA2060180A1 (en) | 1991-03-07 |
BR9007610A (en) | 1992-06-30 |
EP0490933A4 (en) | 1992-09-23 |
WO1991003850A1 (en) | 1991-03-21 |
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Legal Events
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