Coherent light generators – Particular active media – Gas
Reexamination Certificate
1998-12-01
2001-01-16
Font, Frank G. (Department: 2877)
Coherent light generators
Particular active media
Gas
C372S055000, C372S056000, C372S058000, C372S060000, C372S061000
Reexamination Certificate
active
06175583
ABSTRACT:
TECHNICAL FIELD
This invention relates to metal vapour lasers and to methods for operating metal vapour lasers.
BACKGROUND ART
Pulsed metal vapour lasers are a class of cyclic pulsed laser which generate high average power at high pulse repetition rates (kilohertz to tens of kilohertz) in the visible and infrared regions of the spectrum. They have been known since 1966 and are utilised commercially in a range of applications, particularly where relatively high power devices are required. Metal vapour lasers producing greater than 120 W are currently available. Such lasers find application in fields such as medicine, forensic science, machining, as pump sources for tunable dyes, and in isotope separation, for example in uranium enrichment.
The active region of a pulsed metal vapour laser is the discharge plasma tube, which is an extended tubular zone in which the metal vapour is confined and through which a pulsed high-current electrical gas discharge passes. The discharge plasma tube is normally formed from refractory ceramic material (usually recrystallized alumina) and surrounded by high-temperature insulation. The discharge plasma tube itself must be maintained at very high temperatures (for example 1400-1700° C. for a copper vapour laser) to ensure adequate vapour pressure (by way of thermal evaporation) of the metal, which is usually distributed along the tube. A buffer gas, usually He or Ne, is invariably present at a pressure of tens or hundreds of millibar to stabilise the metal vapour discharge.
Thus, in operation, metal vapour lasers typically include small pieces of the metal distributed in the plasma discharge tube, and, with the buffer gas flowing slowly through the tube, it is heated externally and/or by the discharge to a temperature such that the vapour pressure of metal in the buffer gas is sufficient to enable lasing to take place. For example, for a copper vapour laser the copper vapour density is typically about 1-10 Pa which requires a temperature of typically 1400-1700° C.
Although previously known metal vapour lasers are typically capable of operating at relatively high efficiencies (up to about 1%) and producing relatively high power output, there is a need for an improved metal vapour laser which provides higher output power than presently known metal vapour lasers, with at least comparable efficiencies, but which is relatively simple to use and is capable of stable operation. Desirably, such an improved metal vapour laser would be capable of operating with no flowing buffer gas.
OBJECTS OF THE INVENTION
It is an object of this invention to provide an improved metal vapour laser. It is a further object of this invention to provide an improved process for operating a metal vapour laser. In particular, it is an object of the present invention to provide a process for operating a metal vapour laser, by including in the laser one or more additives, to improve the output power and output beam characteristics of the laser in comparison to known high temperature metal vapour lasers.
SUMMARY OF THE INVENTION
According to a first form of the present invention, there is provided a metal vapour laser comprising a discharge tube having a buffer gas therein and operating at high temperature, the buffer gas including a laser output power enhancing substance in an amount sufficient to substantially increase the power output of the laser.
According to a second form of the present invention, there is provided a process for operating a metal vapour laser comprising a discharge tube having a buffer gas therein and operating at high temperature, utilising a buffer gas which includes a laser output power enhancing substance in an amount sufficient to substantially increase the power output of the laser. As described below, the buffer gas may have the laser output power enhancing substance premixed therewith, or the laser output power enhancing substance may be generated in the discharge tube under the opening conditions of the laser.
Thus, the second form of the invention provides a process for operating a metal vapour laser comprising a discharge tube having a buffer gas therein and operating at high temperature, comprising premixing a laser output power enhancing substance with the buffer gas or generating a laser output power enhancing substance in the discharge tube, the laser output power enhancing substance being present in the discharge tube at an operating condition of the laser in an amount sufficient to substantially increase the power output of the laser.
It is presently theorised by the inventors that the laser output power enhancing substance acts as an electron scavenger in the active region of the laser when the laser is in operation, though the inventors do not wish to be bound by this theory.
As used herein, the expression “an amount sufficient to substantially increase the power output” in connection with a laser or the operation of a laser, means an amount which, when included in the buffer gas of the operating laser, results in a substantial increase in the power output of the laser compared to the power output of the laser when it is operated under the same conditions in the absence of the laser output power enhancing substance.
Typically the metal vapour of the metal vapour laser of the present invention is a copper vapour, gold vapour, manganese vapour, cadmium vapour, zinc vapour, mercury vapour, tin vapour, magnesium vapour, barium vapour, chromium vapour, iron vapour, cobalt vapour, nickel vapour, silver vapour, gallium vapour, indium vapour, europium vapour, thallium vapour, bismuth vapour, antimony vapour, tellurium vapour, selenium vapour, strontium vapour, calcium vapour or a lead vapour.
More typically, the metal vapour is selected from copper vapour, gold vapour, manganese vapour, europium vapour, thallium vapour, barium vapour, iron vapour, bismuth vapour, strontium vapour, calcium vapour and lead vapour. Even more typically, the metal vapour is a copper vapour.
Generally, the operating temperature of the metal vapour laser is sufficient to provide a partial pressure of metal vapour in the laser tube of from about 13 Pa to about 130 Pa. For a copper vapour laser, for example, the operating temperature is from about 1400-1700° C., usually from 1400-1600° C., while for a lead vapour laser it is from about 900-1100° C. and for a gold vapour laser it is from about 1550-1850° C. Operating temperatures for other metal vapour lasers are known to persons skilled in the relevant art.
Typically, the laser output power enhancing substance is a species comprising one or more atoms selected from oxygen, sulfur, fluorine, chlorine, bromine and iodine. For example, the laser output power enhancing substance may be fluorine; chlorine; bromine; iodine; a hydrogen halide such as HF, HCl, HBr or HI; H
2
O; H
2
S; SF
6
; BF
3
; oxygen; sulfur; a halogenated hydrocarbon such as methyl chloride, methyl bromide, dichloromethane, trichloromethane, tetrachloromethane, trichloroethane, trichloroethene, tetrachloroethane, tetrachloroethene or any of the “freons”; a mixture of two or more of the foregoing; or a species derived from any of the foregoing under the operating conditions of the laser. Typically the laser output power enhancing substance is provided in a mixture of one or more of the foregoing with hydrogen and/or an additive such as a hydrogen source, or a species derived therefrom.
The buffer gas is typically an inert gas, such as krypton, xenon, argon, helium or neon or a mixture of two or more thereof, or a mixture of an inert gas with hydrogen or deuterium. More typically, the buffer gas is selected from neon and helium.
The pressure of the buffer gas depends on which gas is selected as the inert gas. Usually, the pressure of the buffer gas in the operating laser ranges from 0.1 kPa to 20 kPa, more usually from 0.5 kPa to 15 kPa, or from 1.3 kPa to 13 kPa, or from 2 kPa to 10 kPa or from 3 kPa to 7 kPa, or from 5 kPa to 6 kPa. Even more usually the pressure of the buffer gas is about 5.2 kPa when the buffer gas is predominantly neon.
In a third form o
Brown Daniel John
Carman Robert John
Piper James Austin
Withford Michael John
Flores Ruiz Delma R.
Font Frank G.
Jones Tullar & Cooper PC
Macquarie Research LTD
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