Abstract:
The invention herein is directed to a dual-chamber combustion laser assembly having lighter weight (per unit flow area), a more compact, flexible configuration for packaging in spacecraft, aircraft, or ground mobile vehicles, higher mass efficiency from lower heat loss and proven power extraction efficiency of linear lasers, superior output beam quality by incremental compensation of gain medium optical path disturbances and by reduction in time-dependent variations in structural and gain medium characteristics, lower cost and shorter fabrication time for modular dual flow laser and linear optics, more efficient pressure recovery with side-wall isolation nozzles and compact diffuser configurations, and increased small signal gains for more efficient extraction of overtone power.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 10/933,344, filed Sep. 3, 2004, now U.S. Pat. No. 6,973,114, which is hereby incorporated by reference in its entirety, which is a continuation of U.S. patent application Ser. No. 09/963,486, now U.S. Pat. No. 6,847,674, filed Sep. 27, 2001, which is hereby incorporated by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally involves chemical lasers. More particularly, the present invention involves an improved chemical laser configuration for space and ground applications. 
   2. Description of the Related Art 
   Conventional linear lasers provide a single chemical laser gain region from a combustion chamber as shown in  FIG. 1 . With this configuration, mass efficiency is limited by heat loss to the large surface area i.e., three sides of the combustion chamber. The high weight of the conventional laser is driven by the structural requirement to contain combustion gases at high pressure and high temperature. Finally, the medium quality of the conventional laser is degraded with increasing device length and power due to systematic optical path disturbances in gain medium that cannot be compensated. 
   The use of a chemical reaction to produce a continuous wave chemically pumped lasing action is well known. The basic concept of such a chemical laser is described, for example, in U.S. Pat. No. 3,688,215, the subject matter of which is incorporated herein by reference. As therein described, the continuous wave chemical laser includes a plenum in which gases are heated by combustion or other means to produce a primary reactant gas containing dissociated atoms of a reactant element such as fluorine mixed with diluting gases, such as helium or nitrogen. The resulting reaction between the hydrogen (or deuterium) and fluorine produces vibrationally excited HF or DF molecules. These molecules are unstable at the low temperature and pressure condition in the cavity and return to a lower vibrational state by releasing photons. Mirrors spaced in the cavity along an axis transverse to the flow field amplify the lasing action from the released photons within the optical cavity formed by the mirrors. The lasing action is of the continuous wave type, which is pumped by the high-energy vibrationally excited molecules formed in the optical cavity. The lasing action depends on producing vibrationally excited states in the HF or DF molecules. This in turn requires that the molecules be formed under conditions of low temperature and pressure. As the pressure and temperature increase, the number of vibrationally excited molecules decreases and more energy goes into translational movement of the molecules, defeating the lasing action. 
   Cylindrical lasers as illustrated in  FIG. 2  provide compact packaging of the gain generator, but require large volumes for handling the radial outflow of laser exhaust gas. End domes are required to contain the combustion products with atomic fluorine in the chamber. The domes are large surface area, heavy structural members that reduce mass efficiency from heat loss effects. Gain medium optical path disturbances increase with cylinder length and cannot be compensated, thereby limiting length and power scaling. Cylindrical combustion devices and optics for power extraction require stringent tolerances during fabrication and alignment, resulting in very high costs for a fragile beam generator. Conventional linear and cylindrical lasers experience large temperature gradients in the structure resulting in time-varying medium quality and laser performance. The radial flow of laser gas lowers the mass flux at the entrance to the diffuser, resulting in lower pressure recovery than linear flow devices. 
   A low-pressure hydrogen fluoride (HF) laser is a chemical laser, which combines heated atomic fluorine (produced in a combustion chamber similar to the one in a rocket engine) with hydrogen gas to produce excited hydrogen fluoride molecules. The light beam that results radiates on multiple lines between 2.7 μm and 2.9 μm. These wavelengths transmit poorly through the atmosphere. Conventional HF lasers utilize primary nozzles, referred to as hypersonic low temperature or HYLTE nozzles, the surfaces of which are smooth, curved planes that result in nearly parallel flow of gases at the exit of the nozzle. Helium and hydrogen cavity fuel are injected at oblique angles from the nozzle sidewalls. Mixing, reaction and laser gain are produced internal to the primary nozzles and in the downstream optical cavity region. A large base region is formed between adjacent primary nozzles. In a process referred to as helium base purge, helium or other gas must be introduced into these base regions to prevent recirculation of laser gas with ground-state HF that would reduce laser gain and mass efficiency. Conventional HYLTE nozzle configurations wherein hydrogen is injected with wall-jets produces gain internal to the primary nozzle and the large base region between the adjacent primary nozzles is subsonic helium flow that produces no gain. Further, there are flow regions at the laser cavity exit with unmixed atomic fluorine, hydrogen rich regions, and a large subsonic base flow region. These attributes of the conventional HYLTE nozzle result in inefficiencies within the HF laser and a significant loss of power. 
   There is a need in the art for a laser and nozzle configuration that reduces the inefficiencies currently found in the conventional configurations. 
   SUMMARY OF THE INVENTION 
   Summary of the Problem 
   Available chemical lasers, including linear and cylindrical lasers, have limited mass efficiency due to heat loss and are structurally burdensome and heavy. Power is limited due to optical path disturbances resulting from the need for longer combustion chambers. Further, conventional chemical lasers experience large temperature gradients, which result in time-varying medium quality and reduced laser performance. Finally, available nozzle configurations are in efficient due to a number of non-gain regions resulting therefrom. 
   Summary of the Solution 
   An embodiment of the present invention includes a chemical combustion laser component comprising: a first and a second gain region, a combustion region, and a first and a second nozzle blade, wherein the first and second nozzle blades separate the combustion region from the first and second gain regions. 
   In a further embodiment, each of the first and second nozzle blades is comprised of a primary structure and a secondary structure, wherein the primary structure is formed from a first material and the secondary structure is formed of a second material. 
   In a yet a further embodiment of the present invention, the second material is able to withstand higher temperatures than the first material. 
   In yet a further embodiment of the present invention, the first material is aluminum and the second material is nickel. 
   In yet a further embodiment of the present invention, the first and second nozzle blades are self-cooling. 
   In still a further embodiment of the present invention a component for a combustion laser comprises: at least one inlet manifold for receiving and distributing combustion fuel; at least one upper manifold sheet having holes therein for receiving combustion fuel from the at least one inlet manifold and further distributing the combustion fuel; at least one pair of nozzle blade structures for receiving the combustion fuel from the at least one upper manifold sheet; and at least one lower manifold sheet, wherein the at least one inlet manifold, the at least one upper manifold sheet, the at least one pair of nozzle blade structures, and the at least one manifold sheet are stacked one on the other and affixed one to the other in a stacked relationship. 
   In still a further embodiment of the present invention, each of the nozzle blade structures includes a primary nozzle having a serrated tip. 
   These embodiments result in a combustion laser having lighter weight (e.g., per unit flow area), a more compact, flexible configuration for packaging in spacecraft, aircraft, or ground mobile vehicles, higher mass efficiency from lower heat loss and proven power extraction efficiency of linear lasers, superior output beam quality by incremental compensation of gain medium optical path disturbances and by reduction in time-dependent variations in structural and gain medium characteristics, lower cost and shorter fabrication time for modular dual flow laser and linear optics, more efficient pressure recovery with side-wall isolation nozzles and compact diffuser configurations, and increased small signal gains for more efficient extraction of overtone power. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the Figures: 
       FIG. 1  depicts a conventional linear combustion laser; 
       FIG. 2  depicts a conventional cylindrical combustion laser; 
       FIG. 3  depicts a dual-chamber combustion laser component according to an embodiment of the present invention; 
       FIG. 4  depicts a dual-chamber combustion laser component according to an embodiment of the present invention; 
       FIG. 5  depicts a dual-chamber combustion laser component according to an embodiment of the present invention; 
       FIG. 6  depicts a nozzle blade structure according to an embodiment of the present invention; 
       FIGS. 7(   a ) and ( b ) depict a manifold assembly according to an embodiment of the present invention; 
       FIG. 8  depicts a nozzle blade according to an embodiment of the present invention; and 
       FIG. 9  depicts a combustion laser assembly according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   According to an embodiment of the present invention, a chemical combustion laser is provided having a modular, aluminum design that produces two linear, supersonic gain regions from a single combustion chamber as shown in  FIG. 3 . This structure results in a minimum surface area combustion chamber and a balanced thermal design. The laser module is referred to herein as a boxer laser module  1 .  FIG. 3  is an end view of the boxer laser module that includes a combustion chamber  22  and on the left and the right sides, gain regions  28 . Gain is produced in the gain regions  28  by the out-flow of combustion products such as, deuterium fluoride, nitrogen, atomic fluorine, and heated helium and by the helium and hydrogen gases injected into the cavity which produce a chemical reaction. 
   As shown in  FIGS. 4 and 5 , each boxer laser module consists of two nozzle blade structures  10  with combustor injectors  12 , cavity injectors  14 , combustor sidewalls  16  and cavity shrouds  18  with integral cavity isolation nozzles  20 . A combustion chamber  22  is formed between two nozzle blade structures  10  connected by combustor sidewalls  16 . The nozzle blade structures  10  are self-cooled by gaseous combustor reactants such as, nitrogen trifluoride, deuterium, and helium, which are injected and burned in the combustion chamber  22  to produce, for example, atomic fluorine, deuterium fluoride, nitrogen, and heated helium and by cavity injectant gases, hydrogen and helium. Boxer laser modules  1  are placed side-by-side to increase the length of the combustion chamber  22  and to form converging-diverging primary nozzles  26  between adjacent nozzle blade structures  10 . Combustion product gases, e.g., atomic fluorine, deuterium fluoride, nitrogen and helium are expanded through these primary nozzles  26  from a high-pressure of approximately 0.5 atmospheres, a high-temperature of, e.g., approximately 1500K to 1700K condition to a low pressure of approximately 0.005 atmospheres, supersonic, e.g., Mach number of 3 to 5 condition, where cavity fuel, e.g., hydrogen and helium gas mixtures, is injected to produce laser gain. The heat is transferred to the combustor sidewalls  16  and by making the chamber length short, all of the heat that is transferred to the combustor sidewalls  16 , even in the case of a small quantity, can be conducted to the nozzle blade structures  10  and cooled. The nozzle blade structures  10 , combustor sidewalls  16 , and cavity shrouds  18  are designed to achieve dynamic and static thermal balance conditions. This thermal balance condition results in equal heating rates and nearly equal steady-state temperatures for nozzle blade structures  10 , combustor sidewalls  16 , and cavity shrouds  18 . Uniform heating and isothermal steady-state temperatures of the boxer modules  24  results in nearly time-constant combustor pressure and laser cavity flow conditions to maintain desired conditions for laser power and medium quality. According to this embodiment, all parts of the boxer laser module  1  can be heated at a nearly equal rate and operate at nearly equal steady state temperature, such that the throat gap of the primary nozzle  26  which is formed between side-by-side boxer laser modules  1  remains constant. If the throat gap remains constant, all of the properties in the laser gain region  28  remain time-independent and increase the efficiency of the gain regions  28 . This is important to efficient gain production, efficient power extraction, and the medium quality that is required for a high-power laser. 
     FIG. 5  is a side view of a boxer laser module  1 . The boxer laser module  1  incorporates isolation nozzles  20  in the cavity shrouds  18  downstream of the laser gain regions  28 . In an exemplary embodiment, helium is injected through the nozzles to energize flow along the cavity shrouds  18  to allow formation of strong shock waves just downstream of the laser gain regions  28  for efficient pressure recovery with compact diffuser configurations. Diffuser lengths can be factors of three to five times shorter than for conventional linear lasers when using the boxer laser modules  1  described above. The placement of the isolation nozzles  20 , ensures that the gain regions  28  are independent of their environment. Utilizing a boxer laser comprised of the boxer laser modules  1  having a single minimum surface area combustor region  22  which produces laser gain regions  28  described above, the structural weight to support the combustor is minimized, the heated surface area is minimized, and thereby heat loss to the combustor which drives mass efficiency is minimized. The boxer laser configuration described herein minimizes non-functional structure and facilitates incremental production of very long gain paths, such as those required for an overtone laser. 
   According to an embodiment of the present invention,  FIG. 6  illustrates a nozzle blade structure  10  configuration for reducing heat loss. Combustor injector triplets  32  are incorporated into secondary structure  30  made of high temperature fluorine-compatible material such as nickel, stainless steel, or ceramics like lanthanum hexaboride or alumina. Referring to  FIG. 6 , the secondary structure  30  fits into the primary structure  34  which is formed of a lightweight material such as aluminum. By making the secondary structure  30  out of high temperature fluorine-compatible material as opposed to aluminum, the secondary structure  30  can operate at significantly higher temperatures of e.g., 900K to 1300K, as compared to the safe operating temperature of 600K for aluminum. The secondary structure  30  is inserted into the primary structure  34  of the nozzle blade structure  10  in order to reduce heat transfer that would otherwise occur when operating with wall temperatures higher than allowed for an all aluminum nozzle blade structure. The secondary structure  30  is cooled by injected combustor reactants such as, nitrogen trifluoride, deuterium and helium and by conduction to the primary structure  34  that is cooled by the cavity injected hydrogen and helium. In a further embodiment of the present invention, the above-identified combustor reactants as well as cavity injectants hydrogen and helium are transferred from at least one boxer laser module  1  to at least one adjacent boxer laser module  1  for cooling and for injection into the combustor  22  and cavity flow. 
   In an embodiment of the present invention, the nozzle blade structures  10  and consequently, the boxer laser modules  1 , are connected by a thin, laminated manifold assembly  60  as shown in  FIGS. 7(   a ) and  7 ( b ). The thin manifold sheets  62  have flow channels  64  machined into their surfaces to provide gas flow passages from oxidizer inlet manifolds  66  to coolant and distribution passes (not shown) internal to the nozzle blade structures  10 . The manifold sheets  62  also contain and connect combustor fuel inlet manifolds  67  for facilitating the efficient conduction of fuel to the nozzle blade structures  10 . The manifold sheets  62  are joined together by brazing, diffusion bonding, or the like in order to form upper and lower manifold assemblies  60  and  68  on the top and bottom surfaces of the nozzle blades  10 . This configuration places parent material, e.g., aluminum, with no bond joints, between the oxidizer and the combustion fuels to eliminate the possibility of interpropellant leakage that could cause failure. This configuration also reduces the number of external connections that have to be made to the hardware. 
   In a further embodiment of the present invention, nozzle blade structures  10  as described in relation to  FIG. 6 , increase laser chemical efficiency when used in, for example, HE (Helium Fluoride), HF-overtone, DF (Deuterium Fluoride), and gaseous iodine combustion driven lasers and increase the small signal gain for more efficient extraction of power. Referring to  FIG. 8 , a nozzle blade  70  according to an embodiment of the present invention has serrated primary nozzle surfaces  72  to direct primary nozzle flow into the region  74  between primary nozzles. Cavity fuel, e.g., helium gas  76  and hydrogen gas  78 , is injected from the base region through pairs of nozzles that enhance molecular mixing and prevent recirculation of laser gas. Further, a secondary flow of atomic fluorine, is injected into the laser cavity between adjacent pairs of nozzles by means of the serrated primary nozzle surfaces in order to control the flow trajectory of the cavity fuel. This nozzle configuration eliminates the gas flow normally required for base purge, simplifies the design and fabrication of the nozzles, and increases overall mass efficiency of the laser by utilizing all of the cavity area  28  to produce gain. In this embodiment of the present invention, the placement of nozzle blades at the base, allows the laser to fully utilize a conventionally inactive zone that occupies approximately 40 percent of the length of gain region. By injecting the fuel internal to the nozzle, the expansion that the fuel will undergo in the cavity is limited. Referring to helium and hydrogen flow jet patterns  76  and  78 , respectively, complete use of the laser gain region  28  is illustrated. 
   In a further embodiment of the present invention, the components described above are assembled into a boxer laser  100  as shown in  FIG. 9 . At least one boxer laser module is contained in a housing comprised of upper and lower manifold assemblies  160  and  168  surrounded by enclosed gain regions  128 . The at least one boxer laser module comprises the boxer laser  100  along with a surrounding optical train comprised of various optical elements (e.g., mirrors, reflectors, beamsplitters, lenses, switches, and the like)  180 . One skilled in the recognizes the necessity for optical elements and the many configurations of optical elements available for use within a combustion laser. 
   The embodiments described herein are intended to be exemplary, and while including and describing the best mode of practicing, are not intended to limit the invention. Those skilled in the art appreciate the multiple variations to the embodiments described herein, which fall within the scope of the invention.