GB2252665A - Chemical laser apparatus - Google Patents

Abstract

The laser has a vessel (20) disposed at the outlet (18) for exhaust gases leaving the laser enclosure (1). The vessel contains porous members (32 to 35) containing a mixture of calcium and glass fibers to absorbing the exhaust gases. An oxygen tank (26) is connectable to the vessel via a valve (27), and a threshold manometer (30) measures the oxygen pressure in the tank (27). Before firing the laser, oxygen is admitted into the vessel (20) to heat the calcium to enable it to absorb the exhaust gases. The manometer threshold is set to trigger the supply of reactive gases to the laser via valves (11 to 14) once the pressure has dropped to a level indicating that enough oxygen has been admitted to the vessel for the calcium to have risen to a suitable temperature for absorbing the exhaust gases. Such a laser may be used to decoy or to "blind" missiles. <IMAGE>

Description

"CHEMICAL LASER APPARATUS" The present invention relates to chemical laser apparatus.

Hydracid chemical lasers are fuelled by a combustible fluid such as deuterium or hydrogen and a halogen oxidizing fluid such as fluorine, bromine, iodine or compounds thereof. The reactive fluids are generally diluted in an inert gas such as nitrogen, and they are burned in a combustion chamber to release free halogen atoms which are admitted into the optical cavity of the laser. Hydrogen or deuterium is then injected into the cavity to combine with the free halogen atoms to form halide molecules in an excited state. By dropping to a lower state of excitation, the excited molecules generate a laser beam. Such lasers generally operate at low pressure, e.g. below 50 torrs; it is therefore necessary to pump out exhaust gases leaving the cavity.

A known way of performing this pumping, especially in equipment for military aircraft, uses gas-absorbing materials in order to avoid heavy and bulky electromechanical pumps.

Thus, a hydracid chemical laser apparatus described in French patent number 2 298 205, published August 13th, 1976, includes a gas-tight metal vessel disposed at the outlet from the laser cavity and n contains metallic calcium in a vacuum. The apparatus further includes means for preheating the calcium to 0 about 400 C in order to render it capable of absorbing the exhaust gases; such preheating can be achieved by admitting a small quantity of oxygen into the vessel.

Once the calcium is heated the laser exhaust gases are admitted into the vessel by breaking a frangible disk blocking the outlet from the cavity.

The known chemical laser described above suffers from drawbacks.

Firstlyr the calcium in the vessel absorbs the exhaust gases with relatively low efficiency. It is thus necessary to provide a large amount of calcium in the vessel, thereby increasing its weight and bulk.

Secondly, the preheating time is too long for some military applications.

Preferred embodiments of the present invention mitigate these drawbacks.

The present invention provides chemical laser apparatus comprising: a laser enclosure comprising a combustion chamber and a laser cavity in communication with each other; controllable means for injecting reactive fluids into the enclosure via inlet valves, the cavity having an exhaust gas outlet passage; a vessel connected to the outlet passage and containing at least one exhaust gas absorption member including calcium; and means for injecting oxygen into the vessel; the improvements wherein: with the laser chamber evacuated and the inlet valves closed; the exhaust gas absorption member comprises porous material made up of a homogeneous mixture of calcium and glass fibers disposed between two metal meshes; the means for injecting oxygen comprise a tank connected to the vessel by a closed connection valve; and the apparatus further includes: control means for causing the connection valve to open; a threshold manometer disposed to measure the oxygen pressure in the tank and capable of delivering a signal when said pressure is below a predetermined threshold; and a control circuit connected to the inlet valves and to the manometer and capable of causing the inlet valves to open on receiving said signal.

An embodiment of the invention is described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view, partially in longitudinal section, of an embodiment of a chemical laser apparatus in accordance with the invention; and Figure 2 is a perspective view of an absorbent disk which constitutes a component of the Figure 1 apparatus.

The apparatus shown in Figure 1 comprises a laser enclosure 1 including a combustion chamber 2 and a laser cavity 3 disposed between facing mirrors 4 and 5, with the mirror 5 being partially transparent. The chamber 2 and cavity 3 are put into communication with each other by nozzles 6.

Fuel gas tanks 7, 8, 9 and 10 have respective electrically controlled valves 11, 12, 13 and 14 controlling their outlets which are disposed at the inlet to the laser enclosure 1. The wall of the enclosure also includes an orifice 15 connected to a valve 16.

The laser cavity 3 includes a gas outlet passage 18 which, via a valve 19, puts the inside volume of the cavity 3 in communication with the inside volume of a cylindrical metal vessel 20. The orifice 15 may be situated, for example, in the wall of the passage 18.

The wall of the vessel 20 includes an orifice 25 connected to an oxygen tank 26 via an electrically controlled valve 27 which is powered by an electrical power supply 28. The tank 26 is fitted with a pressure gauge 29 connected to the input of a threshold manometer 30 whose output is connected to the valves 11 to 14 via a relay control circuit 31.

Gas absorption members 32 to 35 are disposed inside the vessel 20. Each of these members is in the shape of a disk with a central opening. The disks are fixed to the inside walls of the vessel in such a manner that the axis 36 along which the exhaust gases are injected into .the vessel 20 from the valve 19 passes perpendicularly through the centers of the disk openings.

Furthermore, as can be seen in the figure, the further the disk is located from the valve 19 controlling the passage 18, the smaller the opening the disk.

Figure 2 is a perspective view of the gas absorption member 34 shown partially in section. This disk-shaped member 34 has an outer frame or rim 37 and an inner frame or hub 38. Two annular metal meshes 39 and 40 are welded to the frames 37 and 38 to lie in parallel planes. The meshes and the frames may be made of stainless steel.

Porous material 41 made of a homogeneous mixture of calcium and glass fibers is disposed between the meshes 39 and 40.

This material is made from calcium powder, itself obtained by the known process of dissolving calcium in anhydrous liquid ammonia and then evaporating in a vacuum. The resulting powder is mixed with glass fibers and compressed between the metal meshes. Absorption members obtained in this way are very porous and have good mechanical properties.

The gas absorption members are assembled in the vessel 20 under an argon atmosphere using a glove box.

The vessel is then fixed to the output from the laser cavity with the valve 19 closed.

The enclosure 1 is then evacuated by pumping through the orifice 15 and the open valve 16 using an auxiliary pump. Finally the valve 16 is closed and the valve 19'is opened to evacuate the vessel 20. The laser apparatus is then ready to operate and is installed, e.g.

on board an aircraft.

A laser fire command is transmitted to the power supply circuit 28 in order to immediately open the valve 27. The oxygen contained in the tank 26 expands inside the vessel 20 and reacts vigorously with the calcium in the absorption members 32 to 35. This reaction evolves heat which quickly raises the temperature of the absorption members to 3000c to 4000C to enable them to absorb the laser exhaust gases. As soon as the valve 27 is opened, the oxygen pressure in the tank 26 begins to drop. The threshold manometer 30 delivers a signal when the oxygen pressure measured by the gauge 29 drops below a predetermined threshold. The threshold is determined in such a manner that it is reached when the temperature of the absorption members has reached 3000C to 4000C.

The signal is received by the relay circuit 31 which then opens the valves 11 to 14, thereby feeding the reaction gases to the laser and thus causing it to operate.

The laser may be a deuterium fluoride (DF) acid laser. In which case the tanks 7, 8, and 9 contain hydrogen, fluorine and an inert gas such as nitrogen respectively. The mixture of these gases is injected into the combustion chamber 2 to produce free atoms of fluorine which enter the laser cavity 3.

The tank 10 contains deuterium which is injected directly into the cavity 3 via the nozzles 6 by opening the valve 14. The free atoms of fluorine combine with the molecules of deuterium injected into the cavity to form excited DF molecules which cause a laser beam to leave the cavity via the mirror 5. The exhaust gases from the laser include nitrogen, deuterium, hydrofluoric acid and deuterium fluoride acid and they pass through the open valve 19 to be absorbed by the absorption members 32 to 35 which have been raised to their absorption temperature as explained above.

The quantity of oxygen stored in the tank 26 is determined so as to heat the absorption disks only superficially, and laser operation is triggered automatically once the surface of the disks reaches the exhaust gas absorption temperature.

The reaction of the oxygen with the calcium uses up a portion of the calcium. The quantity of calcium placed -inside the vessel 20 is so determined that there remains sufficient calcium after the reaction with the oxygen to absorb the exhaust gases for the entire period of laser operation.

Because of the porous structure of the calcium based material contained in the absorption members, absorption efficiency is very high, with the gases being absorbed throughout the volume of the material. The glass fibers give the material sufficient rigidity to withstand the contractions that take place during absorption and which could otherwise impose a limit on the absorption capacity of the porous members.

By way of example, a DF laser that delivers an output power of 30 to 40 watts for a period of 10 seconds, using a gas flow rate of 30 millimoles per second at a pressure of less than 5 torrs, requires absorption members containing 120 grams of calcium and 12 grams of glass fiber, with the disks being about 10 mm thick giving a total active surface area of about 1300 2 cm . The oxygen is stored in a 0.7 liter tank at a pressure of 1.1 bars. The manometer threshold is set at 2 mbars.

Under such conditions, the overall response time between the command to fire and effective laser operation is about 0.9 seconds. This response time is occupied as follows: opening time for the valve 27 0.05 s oxygen pressure drop to 2 m bars 0.4 s opening time for the valves 11 to 14 0.15 s gas arrival in laser enclosure and operation 0.3 s A chemical laser in accordance with the present invention is applicable in particular to decoying or blinding missiles.

Claims (4)

Claims:

1. Chemical laser apparatus comprising: a laser enclosure comprising a combustion chamber and a laser cavity in communication with each other; controllable means for injecting reactive fluids into the enclosure via inlet valves, the cavity having an exhaust gas outlet passage; a vessel connected to the outlet passage and containing at least one exhaust gas absorption member including calcium; and means for injecting oxygen into the vessel; the improvements wherein: with the laser chamber evacuated and the inlet valves closed; the exhaust gas absorption member comprises porous material made up of a homogeneous mixture of calcium and glass fibers disposed between two metal meshes; the means for injecting oxygen comprise a tank connected to the vessel by a closed connection valve; and the apparatus further includes: control means for causing the connection valve to open; a threshold manometer disposed to measure the oxygen pressure in the tank and capable of delivering a signal when said pressure is below a predetermined threshold; and a control circuit connected to the inlet valves and to the manometer and capable of causing the inlet valves to open on receiving said signal.

2. Apparatus according to claim 1, wherein the absorption member is in the shape of a disk having a central opening, and wherein the disk is fixed to the vessel in such a manner that the axis along which the exhaust gases are injected into the vessel passes perpendicularly through the center of the disk.

3. Apparatus according to claim 2, wherein the vessel contains a plurality of absorption members each in the shape of a disk having a central opening, and wherein the further the disk is located from said outlet passage, the smaller the size of its central opening.

4. Chemical laser apparatus substantially as hereinbefore described with reference to the accompanying drawings.

4. Chemical laser apparatus substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows

1. Chemical laser apparatus comprising: a laser enclosure comprising a combustion chamber and a laser cavity in communication with each other; controllable means for injecting reactive fluids into the enclosure via inlet valves, the cavity having an exhaust gas outlet passage; a vessel connected to the outlet passage and containing at least one exhaust gas absorption member including calcium; and means for injecting oxygen into the vessel; wherein: the exhaust gas absorption member comprises porous material made up of a homogeneous mixture of calcium and glass fibers disposed between two metal meshes; and the means for injecting oxygen comprise a tank connected to the vessel by a connection valve; and the apparatus further includes: control means for causing the connection valve to open; a threshold manometer disposed to measure tile oxygen pressure in the tank and capable of delivering a signal when said pressure is below a predetermined threshold; and a control circuit connected to the inlet valves and to the manometer and capable of causing the inlet valves to open on receiving said signal.

2. Apparatus according to claim 1, wherein the absorption member is in the shape of a disk having a central opening, and wherein the disk is fixed to the vessel in such a manner that the axis along which the exhaust gases are injected into the vessel passes perpendicularly through the center of the disk.

3. Apparatus according to claim 2, wherein the vessel contains a plurality of absorption members each in the shape of a disk having a central opening, and wherein the further the disk is located from said outlet passage, the smaller the size of its central opening.