Coherent light generators – Particular pumping means – Electrical
Patent
1987-10-19
1990-07-31
Sikes, William L.
Coherent light generators
Particular pumping means
Electrical
372 56, 372 61, 372 62, 372 85, 372 88, H01S 3097, H01S 322
Patent
active
049455451
DESCRIPTION:
BRIEF SUMMARY
This invention relates to lasers and has particular application to lasers of a type wherein a metal vapour is excited by an electrical discharge pulsed through a metal vapour.
Pulsed metal vapour lasers are potentially very efficient generators of ultra violet, visible and infrared radiation. This radiation has applications in areas as diverse as laser isotope separation, with copper as the lasant, communications, with manganese as the lasant, treatment of cancer by photochemotherapy, with gold as the lasant and photochemical research, with strontiums as the lasant.
Pulsed metal vapour lasers generally comprise two electrodes between which there is a column of gas known as the discharge volume The electrodes are attached to terminating flanges that provide gas containment at either end of the volume Initially, the discharge volume contains a buffer gas and beads of a metal. The application of a fast high voltage pulse to the discharge volume produces a high current (hundreds of thousands of amperes) discharge pulse which heats the gas and the electrodes and thereby transfer heat to the inner walls of the chamber which substantially confine the active volume The walls of the chamber, the electrodes and the metal therein are heated and with repeated discharges, and with appropriate insulation, the temperature may rise sufficiently to melt and vapourise the metal. The resultant metal vapour may be excited by collisions with the stream of electrons and other discharge constituents and, under certain circumstances, laser action may occur This class of laser is well known in the art.
Hitherto, the technique generally employed for the transfer of electrical energy to the discharge volume has been to use tubular, co-axial electrodes located at, or adjacent to, the ends of the walls of the chamber. The electrodes operate at high temperatures and thermionic emission of electrons sustains the discharge for the duration of the current pulse. Since the electrodes are required to operate at temperatures of up to 2000 degrees centigrade, they are generally constructed from a refractory metallic material, such as tantalum, molybdeneum or tungsten. The electrodes are attached to the terminating flanges of the laser by a variety of mechanical techniques and electrical energy is transferred to the electrodes through the terminating flanges.
This technique of electrode construction has several disadvantages. The major disadvantage is that suitable materials are rare and consequently expensive whilst the refractory properties which make the materials suitable for use at elevated temperatures also make the materials brittle and difficult to fabricate into the desired shape.
Another disadvantage resulting from the elevated operating temperature is the removal of material from the electrode surface and subsequent redeposition on the walls of the vessel. This transfer of material to the walls is caused by both thermal evaporation and sputtering that is enhanced by the reduced resistance of the material to discharge induced erosion at high temperatures. Such material removal gradually destroys the function of the electrode, captures gas from the discharge volume and deposits metal on the walls of the vessel in positions that may be deleterious to the voltage holdoff requirement of the laser. This, and the embrittlement that accompanies high temperature operation, necessitates the periodic replacement of the electrodes, resulting in the need for a demountable structure. Such a structure necessarily includes a junction that exhibits less than desirable thermal and electrical energy transfer characteristics and is sensitive to degradation of these transfer characteristics by the differential expansion and contraction which accompanies the thermal cycling.
Another disadvantage is that energy is isotropically radiated away from the surface of the electrode. This requires thermally sensitive components, located in close proximity to the terminating flange, to be shielded from the deleterious effects of the radiation.
The present inventio
REFERENCES:
patent: 3548335 (1970-12-01), Willett
patent: 3868593 (1975-02-01), Fukuda et al.
patent: 4257014 (1981-03-01), Hattori et al.
patent: 4696011 (1987-09-01), Kearsley
patent: 4771435 (1987-09-01), Tobin et al.
Epps Georgia Y.
Metalaser PTY
Sikes William L.
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