GB2107109A

GB2107109A - Catalyzed CO2 laser

Info

Publication number: GB2107109A
Application number: GB08226041A
Authority: GB
Inventors: Stanley John Scalise; Walter Reginald Kaminski
Original assignee: United Technologies Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1981-09-25
Filing date: 1982-09-13
Publication date: 1983-04-20
Also published as: CH659154A5; GB2107109B; DE3234384A1; FR2513824B1; FR2513824A1; DE3234384C2

Abstract

A CO2 laser, especially a sealed laser, employs a catalyst to promote the recombination of CO and oxygen. The catalyst is contained within a porous electrode forming one of the laser discharge electrodes and is brought into contact with the gas by means of the pressure pulse caused by the electric discharge, by diffusion or by circulating the gas. A preferred structure comprises catalyst pellets contained within a wire mesh electrode.

Description

SPECIFICATION Catalyzed sealed-off CO2 laser Technical field The technical field of the invention is that of a sealed-off CO2 laser.

Background art It has long been known in the CO2 laser art that an electrically excited CO2 gain medium will partially decompose into CO and oxygen, and that products of this decontamination tend to suppress lasing action. Oxygen in quantities as small as 1% leads to arcing between the laser electrodes and subsequent loss in optical power.

One prior art approach to this problem has been to use a heated platinum wire to encourage the re-combination of CO and oxygen to form CO2.

This method has the obvious drawbacks of requiring an additional power supply to heat the platinum wire and also of increasing the heat within the laser-discharge volume.

Several experiments have been made to test the.use of an ambient temperature catalyst, the materials including-activated copper, activated platinum and hopcalite, a commercial mixture of magnesium oxide, copper oxide and trace quantities of other oxides. This material is available commercially from the Mine Safety Appliances Company. An article by C. Willis and J.

G. Purdon in the Journal of Applied Physics, Vol.

50, No.-4 in April 1979 discloses the use of hopcalite in an external gas loop joined to the active laser volume, but in which the catalyst is not present within the laser volume. An article by R. I. Rudko and J. W. Barnie in the Proceedings of the SPIE, Vol. 227, entitled CO2 Laser Devices and Applications, published in 1980, reports the successful application of a solid ambient temperature catalyst within a laser cavity, but does not give any detail as to the type of catalyst and arrangement of the catalyst in the cavity.

Such details were said in that article to be proprietary.

Disclosure of invention The invention relates to a sealed-off CO2 laser, in which the CO2 gas is maintained in purity by a solid, ambient temperature catalyst contained within a porous electrode.

Brief description of drawings Figure 1 shows an embodiment of the invention employing catalyst in the form of solid pellets; and Figure 2 shows a cross-section of an electrode in Figure 1.

Best mode for carrying out the invention Figure 1 illustrates schematically a sealed-off laser constructed according to the invention.

Cover plates 102 and 104 form two sides of the laser cavity. Electrodes 106 and 108 are shaped according to conventional means to form electrodes for passage of an electric discharge through CO2 gas. The electrodes are formed according to a known configuration, illustrated in copending application Serial No. GB 8209617 incorporated herein by reference, which discloses a sealed-off CO2 laser without a catalyst.

In operation, a pulsed electric discharge is generated between electrodes 106 and 108 thereby exciting the CO2 gain medium and initiating laser action. The electrical discharge heats up the CO2 gas within a confined spaced and thus increases the pressure. A pressure pulse forms within the central discharge region and spreads rapidly outwards to equalize the pressure within the confined volume. This pressure pulse passes through the porous electrodes 106 and 108 forcing a portion of the CO2 gain medium through holes in the electrodes and from the laser cavity region into the interior of electrodes. This gas motion serves to circulate the gas thus bringing dissociated CO2, i.e. CO and 0, into the interior of the electrodes.In the electrode interior, the gas comes in contact with a catalyst which is illustrated as being in the form of solid pellets, 120, although a catalyst may also be coated on a substrate if that is found to be convenient.

A second mechanism of bringing dissociated gas into contact with the catalyst is diffusion, which will take place even when the laser is not in pperation. Because the dissociation products of O2 and CO will initially be concentrated between the electrodes, they will tend to diffuse outward from their original location, i.e. will diffuse into the interior of electrodes 106 and 108, thus coming into contact with the catalyst.

The catalyst may ne any well known catalyst, such as platinum, activated copper or hopcalite, which tends to promote the recombination of CO and 0 into CO2.

In the illustration, the sidewalls, mirrors, electrical discharge connections and other components of the laser have been omitted for the sake of simplicity and clarity in presentation.

The electrodes illustrated in the drawing are formed from wire mesh having openings in the form of rectangular holes, but the size and shape of the openings are not critical to the invention.

Any convenient form of aperture, such as circular holes, hexagons or rectangular holes may be used. The holes need not be distributed uniformly over the electrode surface and may be formed by any convenient means, mechanical or chemical.

The size of the holes will be related to the size of the catalyst pellets, of course, since it is desirable to keep catalyst particles out of the laser discharge region. The exact hole and catalyst size will depend on the particular application used, and particularly upon the amount of energy in the laser discharge and thus the amount of pressure pulse generated. If the catalyst particles are light enough so that they are set in motion during the pressure pulse, an advantageous further benefit of the invention is that the catalyst surface will be constantly turned over, thus exposing the catalyst surface evenly.

Although the invention was made in connection with a sealed-off laser, it may also be used in connection with a recirculating gas laser.

For example, a fan could be used to circulate gas through electrode 106, around an external loop and back through electrode 108, thus exposing the gas efficiently to the catalyst and retaining one of the chief advantages of the invention, namely the compact active volume of the laser that is made possible by use of the catalystcontaining electrodes.

The practicality of mesh electrodes (without catalyst) has previously been demonstrated in a report by L. J. Denes entitled "Ultraviolet Initiated CO2 Laser Research, Phase II", Report No. AFWL TR-76-136,Jaji. 1977.

This embodiment employs a TEA laser, as described in copending application Serial No. GB 82 09617 but the type of excitation, type of ionization and pressure of the laser are not relevant to this invention, which relates to the use of ambient temperature catalysts within a porous electrode.

Claims

1. A CO2 laser comprising: first and second electrodes disposed in a discharge region containing a gain medium; means for exciting said gain medium with an electric discharge: and; means for resonating laser radiation in said discharge region, characterized in that: at least one of said first and second electrodes includes an interior portion containing a catalytic material, said interior portion being in communication with said discharge region by means of a plurality of apertures passing between said interior portion and said discharge region.

2. A laser according to claim 1 , in which said catalytic material is in the form of solid granular particles disposed loosely within said interior portion.

3. A laser according to claim 1, in which said catalytic material is disposed along a plurality of substrates positioned within said interior portion.

4. A laser according to any of claims 1,2 or 3, in which said apertures are formed by the interstices of a wire mesh forming a portion of said at least one electrode.

5. A laser according to any of claims 1, 2 or 3, in which said apertures are mechanically formed openings in a predetermined portion of said at least one electrode.