Coherent light generators – Particular pumping means – Electrical
Patent
1980-06-20
1983-06-07
Davie, James W.
Coherent light generators
Particular pumping means
Electrical
H01S 309
Patent
active
043874630
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electrical discharge apparatus in which a glow discharge is produced within a gas between two electrodes. More particularly, but not exclusively, it relates to a gas laser in which the laser is pumped or excited by means of such a discharge.
Such apparatus may be provided with a pre-ionising system to provide a high background concentration of electrons before the main discharge is initiated. This facilitates the initiation of the main discharge and enables a larger amount of energy to be put into the discharge without production of an arc between the discharge electrodes. One pre-ionising system known in relation to gas lasers utilises a trigger wire which gives rise to pre-ionisation by electrostatic emission. In another such known system, small sparks are introduced into the volume of gas and ultra-violet radiation from these sparks gives rise to the pre-ionisation. Each of the above known systems suffers respective disadvantages which may be more or less important, dependent upon the application and it is one object of this invention to provide an alternative pre-ionising arrangement for a gas laser, which alternative may be more advantageous than the known ones for some applications. A further object is to provide a simple, rugged and low cost pre-ionising system for a gas laser or other gas discharge device to improve the efficiency of the discharge therein.
According to one aspect of the invention, there is provided electrical discharge apparatus comprising first and second electrodes for passing an electrical discharge through gas in a discharge space between the electrodes and a pre-ionising member which is made of intermediate resistivity material and which is positioned at least near said space such that the application of a discharge potential between the electrodes results in a current flow within the member and pre-ionisation of said gas.
According to a second aspect of the invention, there is provided gas laser apparatus comprising an optical cavity first and second electrodes for producing an electrical discharge through the gas in a discharge space between the electrodes to excite the laser and at least one pre-ionising member which is made of intermediate resistivity material and which is positioned at least near said space such that the application of a discharge potential between the electrodes results in a current flow within the member and pre-ionisation of said gas.
Advantageously, the apparatus includes a least one further pre-ionising member made of intermediate resistivity material, the pre-ionising members extending along respective sides of said space.
Preferably a portion of the or each pre-ionising member is at least substantially adjacent to the first electrode and the member extends alongside said space towards the second electrode. Even more preferably, respective portions of the or each pre-ionising member are at least substantially adjacent to the two electrodes or, better still, the or each pre-ionising member is in physical contact with at least one of the electrodes. Advantageously, the or each pre-ionising member extends in the direction transverse to that between the electrodes, along at least the major part of the extent, in this transverse direction, of the electrodes.
Throughout this specification, the term "intermediate resistivity material" means material which is neither a dielectric nor a good metallic conductor and includes for example, materials such as crystalline semiconductors, and carbon and carbon compositions of the kind used for making resistors. The suitability of particular materials and the usable range of resistivities can be easily determined by experimentation since, if the resistivity is too low or too high, the pre-ionising effect will become degraded or will disappear altogether. Further information concerning the choice of suitable materials is given later in this specification.
Preferably, the resistivity of the material is at least 50 ohm. cm. Further, although as stated, other materials such as carbon and carbon
REFERENCES:
patent: 4085386 (1978-04-01), Farish et al.
Burnett et al., "Simple Electrode Configuration for UV Initiated High-Power TEA Laser Discharges", J. of Appl. Phys., vol. 44, No. 8, Aug. 1973, pp. 3617-3618.
Belanger et al., "Atmospheric Pressure CO.sub.2 Pulsed Laser with Semiconducting Plastic Electrodes", Canadian Journal of Physics, vol. 50, No. 22, Nov. 15, 1972, pp. 2753-2755.
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