GB2171244A - Hydrochloric acid chemical laser - Google Patents

Abstract

Molecular chlorine from a tank (1) is dissociated by an electrical discharge along a dissociation chamber (3,4,5) to provide atomic chlorine at the inlet to a nozzle (7). Hydriodic acid is injected via openings (13) into the nozzle and reacts with the atomic chlorine to produce excited hydrochloric acid which passes transversally through a laser chamber (19). The exhaust gases are received in an exhaust chamber (23) which includes zeolite to absorb the exhaust gases and to maintain suction for the required period of laser operation. Unlike similar systems using calcium to absorb the exhaust gases, zeolite does not need preheating. Such lasers may be used on board aircraft, for example. <IMAGE>

Description

SPECIFICATION Hydrochloric acid chemical laser The present invention relates to a hydrochloric acid chemical laser.

A known laser of this type comprises a dissociation chamber into which a mixture of helium and molecular chlorine is injected and in which an electrical discharge is established to obtain atoms of chlorine in the mixture. The mixture containing chlorine atoms is passed through a nozzle which has hydriodic acid injected into its exit to react with the chlorine atoms to form excited hydrochloric acid.

The excited gas is passed through a resonant optical cavity to generate a laser beam. Gas flow from the dissociation chamber inlet to the laser outlet is provided by a pumping system downstream from the laser cavity outlet.

The laser has the disadvantage of not being useable in some applications, e.g. on board aircraft, since the laser exhaust gases cannot be dumped in the atmosphere because of their high degree of toxicity.

In other known chemical lasers, the exhaust gases are absorbed by calcium. However, the calcium must be heated to about 400"C in order to have the required absorption properties, which is a considerable drawback.

The present invention seeks to mitigate these drawbacks and to provide a hydrochloric acid chemical laser in which the exhaust gases are absorbed in a material which does not require pre-heating.

The present invention provides a hydrochloric acid chemical laser, including: a gas dissociation chamber having two electrodes; means for injecting pure molecular chlorine into the dissociation chamber; means for applying a potential across the two electrodes; a convergent divergent nozzle the inlet of which communicates with the dissociation chamber; means for injecting hydriodic acid into the outlet of the nozzle; a laser chamber with which the outlet from the nozzle communicates and incorporating a resonant optical cavity; a triggering system for simultaneously operating said chlorine injection means, said potential application means and said hydriodic acid injection means; a gas evacuation system in communication with the laser chamber and constituted by an exhaust chamber containing zeolite; and means for initially evacuating the dissociation laser and exhaust chambers prior to operation of the triggering system.

An embodiment of the invention is described by way of example with reference to the accompanying drawing, in which: Figure 1 is a schematic view of a laser in accordance with the invention; and Figure 2 is a section on a plane ll-ll in Figure 1.

Figure 1 shows three insulating tubes 3, 4, 5, which may be made of glass, for example. One end of each tube is connected to the outlet from a tank of molecular chlorine 1 via pipes and an electrically controlled valve 2. The axes of the tubes are parallel to one another and lie in the same plane as the plane of the figure. A metal electrode such as an anode 6 is placed inside each tube at the end connected to the tank 1. The electrodes are conical in shape and have respective fine calibrated axial orifices to inject chlorine into the tube at sonic speeds. The other ends of the tubes feed a nozzle 7 and are equipped with electrodes of opposite polarity, such as a cathode 8. The anodes are connected to the positive pole of a switchable source of electricity 9 and the cathodes are connected to its negative terminal.

As can be seen in Figure 2, the nozzle 7 comprises, when going from its inlet to its outlet, a converging portion 10, a throat 11 and a diverging portion 12. In an advantageous embodiment, the electrodes 8 are fixed to the converging portion. The throat is of elongated rectangular cross section with its long sides extending parallel to the plane of Figure ion either side thereof, and at right angles to the axes of the tubes. There are openings 13 in the diverging portion 12 of the nozzle.The openings 13 preferably comprise two portions: a cylindrical outer portion 14 having an axis perpendicular to the plane of symmetry 15 of the nozzle; and a cylindrical inner portion 16 of smaller diameter than the outer portion 14 and at a small angle of about 10" thereto, pointing slightly in the direction of flow through the nozzle as shown in Figure 2. The openings 13 are arranged in two straight lines running parallel to the large dimension of the throat and one on each side thereof.

The openings 13 are connected via pipes to a controllable outlet form a tank of hydriodic acid 24.

The valve 2, the source of electricity 9, and the outlet from the tank 24 are all under electrical control from a triggering circuit 25.

A laser chamber 19 is disposed in communication with the outlet from the nozzle 7. Two facing mirrors 20 and 21 are mounted in the chamber 19 to constitute a resonant optical cavity having an axis 22 situated in the same plane as the axes of the tubes 3, 4 and 5, and extending perpendicularly to said tube axes. The mirror 21 is partially transparent. An exhaust chamber 23 containing industrial zeolite is disposed in communication with the outlet from the laser chamber 19. By way of example, the zeolite may be type 200 H as sold by the company NORTON under the trade mark ZEOLON.

The laser described above operates as follows.

Initially, the exhaust chamber 23, the laser chamber 19, the nozzle 7 and the tubes 3,4, and 5 are evacuated.

When the laser is to be operated, the triggering circuit 25 is activated to simultaneously open the valve 2, apply voltage from the source of electricity 9 to the electrodes in the tubes 3 to 5 and to inject hydriodic acid through the openings 13. The tank 1 contains pure molecular chlorine which moves at the speed of sound in the direction of arrow 26 into the tubes 3 to 5 via the fine axial openings through the electrodes 6. The voltage applied across the electrodes 6 and 8 gives rise to a longitudinal electrical discharge through the gas, partially dissociating the molecular chlorine. The resulting mixture of atomic chlorine gas and molecular chlorine gas is sucked into the laser chamber 19 via the throat 11 of the nozzle 7 in the direction of arrow 27.

Hydriodic acid is injected into the nozzle via the openings 13 at the outlet from the throat. The angle 28 at which the internal portions 16 of the openings 13 are inclined promotes mixing with the mixture of gases containing atomic chorine and flowing along arrow 27. The atomic chlorine reacts with the hydriodic acid as follows: Cl + HlHCl + I The excited hydrochloric acid passes through the resonant optical cavity and causes a laser beam 29 to be generated leaving via the mirror 21, said beam having a wavelength of about 3.8 microns.

The exhaust gases from the laser comprising atomic and molecular chlorine, hydrochloric acid, hydriodic acid and iodine are absorbed by the zeolite. A sufficient quantity of zeolite is housed in the exhaust chamber 23 to absorb all the gas during the entire period of operation expected of the laser.

It should be observed that zeolite absorbs such gases rapidly at ambient temperature (20 C), and that its absorption capacity increases as its temperature drops below200C. The use of this material thus provides an important advantage over prior devices using calcium as the absorbing material, since calcium needs to be heated to 400"C in order to obtain pumping that is fast enough. Saturated zeolite can be regenerated by heating to 250"C under a vacuum.

In order for zeolite to absorb the laser exhaust gases, it is important for the reactive gases, and in particular the chlorine, to be pure gases. In particu lay, the chlorine cannot be diluted in helium as is conventional.

To obtain a homogenous discharge in pure chlorine, it is necessary to select suitable dimensions for the tube 3 to 5. Thus, for an electrical discharge potential of 3500 to 4000 volts, the inside diameter of the tubes should be in the range 2 to 5 centimeters (cm), and the distance between the electrodes along the tubes should be in the range 10 to 15 cm.

By way of example, supposing the tubes are 3 cm in diameter, the electrodes are 10 cm apart, and the discharge potential is 3500 volts, then using a chlorine flow of 12 millimoles per second along the tubes, the pressure in the tubes lies in the range 10 to 15 torrs, the discharge current through all three tubes is 200 to 250 miliiamps, the hydriodic acid is injected at 1.5 to 3 millimoles per second, giving a delivered laser power of 10 watts and an electrical efficiency of 1%. Further, 4 kilograms of ZEOLON contained in a 5 litre exhaust chamber is sufficient to absorb the laser exhaust gases for an operating period of 20 seconds, provided the reactive gases are 99.5% pure.

A chemical laser in accordance with the invention can be used to equip aircraft.

Claims (6)

1. Ahydrochloricacid laser including: a gas dissociation chamber having two electrodes; means for injecting pure molecular chlorine into the dissociation chamber; means for applying a potential across the two electrodes; a convergent divergent nozzle the inlet of which communicates with the dissociation chamber; means for injecting hydriodic acid into the outlet of the nozzle; a laser chamber with which the outlet from the nozzle communicates and incorporating a resonant optical cavity; a triggering system for simultaneously operating said chlorine injection means, said potential application means and said hydriodic acid injection means;; a gas evacuation system in communication with the laser chamber and constituted by an exhaust chamber containing zeolite, and means for initially evacuating the dissociation laser and exhaust chambers prior to operation of the triggering system.

2. A chemical laser according to claim 1, wherein the dissociation chamber comprises a plurality of cylindrical insulating tubes having axes lying in a plane which also includes the axis of the resonant optical cavity, each tube including two electrodes, one at each end, with the electrode at the upstream end having a conical passage therethrough to enable the molecular chlorine to be injected into each tube travelling at sonic speed towards the downstream end of the tube, the downstream end of each tube terminating at the inlet to the nozzle, and wherein the throat of the nozzle is elongate, having its major dimension in the same plane as the axes of the tubes and of the optical cavity, and extending parallel to the axis of the optical cavity.

3. A chemical laser according to claim 2, wherein the tubes have an inside diameter in the range 2 to 5 centimeters, and wherein the distance between the electrodes in each tube is in the range 10 to 15 centimeters for a discharge potential of 3500 to 4000 volts.

4. A chemical laser according to claim 2, wherein the electrodes at the downstream ends of the tubes are fixed to the converging portion of the nozzle.

5. A chemical laser according to claim 2, wherein the diverging portion ofthe nozzle includes openings through which in operation the hydriodic acid is injected, said openings being arranged along two straight lines extending along either side of the throat and running parallel to the axis thereof.

6. A hydrochloric chemical laser substantially as hereinbefore described with reference to the accompanying drawing.