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Study On The Cylindrical Continuous Wave HF Chemical High Energy Lasers

Posted on:2005-02-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:W G LiuFull Text:PDF
GTID:1118360155972193Subject:Optical Engineering
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Cylindrical lasers are proposed as a smart choice for compact high-energy lasers. A CW HF chemical cylindrical laser, which composed of annular Gain Generator Assembly and annular Optical Resonator Assembly, is designed and analyzed in this paper. The cylindrical laser designed in this paper possesses many attractive qualities such as highly stable structure, small volume, near-diffractive-limited beam quality, uniform heat load on the cavity mirrors and axis-symmetric ejected flow which is specially suitable for space application.Cylindrical lasers have been applied to TEA CO2 lasers, high-energy chemical lasers and Lamp-pumped solid-state lasers. Many design concepts of annular resonator and supersonic nozzles are proposed in the developments of chemical cylindrical lasers. These concepts are analyzed and compared in this paper. Hyper-sonic Low Temperature nozzle (HYLTE) has outstanding features such as fast mixing rate, fast flow velocity, low temperature in the laser cavity, and Beam-Converting Annular Resonator (BCAR) possesses outstanding features such as high extraction efficiency, insensitive to misalignments, high compensation to un-uniform gain medium, and good beam quality .So HYLTE and BCAR are chosen in this paper as GGA and ORA.The structure of BCAR is composed of many aspherical conic mirrors. An Equal OPL method is applied to design these complex mirrors, and this method is much easy and clever, which avoids the heavy iteration methods used in conventional aspherical mirror design. Based on the Kirchhoff-Fresnel diffraction integral equation, a fast computation method with FFT and FHT in the compact leg propagation is introduced. Based on the partial differential wave equation, a fast computation method with coordinates transform in the annular leg is introduced. Also the polarization mixing effects in the Waxicon and Rearcone are concluded in this paper, and the simplified calculation method of optical field propagating between complex surfaces such as Waxicon Inner cone and Waxicon Outer cone is provided in this paper. A Simi vector field eigenvalue equation of BCAR modes is built at last.Based on the above-mentioned eigenvalue equation, the modes of BCAR under different gain medium are calculated, and it shows that BCAR has highly azimuzal mode discrimination ability, and all the resonator modes are zero level azimuzal modes. The output optical field phase distribution is quite uniform, which insures good propagation ability, and the heat load on cavity mirror is quite uniform, which largely reduce the danger of mirror damage usually occurs in HEL utility. Also, the modes of BCAR under different misalignments are calculated. The numerical result shows that the output power is insensitive to rearcone decentration and compact leg tilt, which means the extraction efficiency is insensitive to misalignment. Beam quality is very sensitive to the decentration and tilt. The rearcone decentration and compact tilt will result in aphase shear on the output plane and phase tilt along the misalignments direction. Among these misalignments the decentration has more sever effects on the resonator output.Two methods are presented to form annular nozzle array. One is arranging linear nozzle blades along a circle, the other is pile up annular nozzle blade. The former method is much simple, but gain medium is un-uniform along azimuzal direction, this will has passive effect on beam quality. The later method is complex, but gain medium is uniform along azimuzal direction. The design methods of annular HYLTE nozzle are presented in this paper. Also a self-cooled annular HYLTE nozzle blade is designed in this paper.Based on 3D Navier-Stokes equations and Realizable k-e model, multi-species reacting flow field of the annular HYLTE nozzle designed by this paper is calculated .The numerical simulation results shows that eddies along flow and highly twisted contact surface between fuel and oxidizer are two important factors that ensure rapid mixing rate and reaction rate of HYLTE. Mass concentration of HF molecule on high vibration level is reduced along flow direction, and that on lower level is increased by collision deactivating effect between different species. The peak and grade of small signal gain (SSG) is reduced when rotation level increase, and the change of refractive index is less than 1/10 wavelength per meter. Multi spectra outputs are calculated at different spectra SSG, and all the output field still maintain the outstanding features such as high extraction efficiency, high beam quality, and uniform heat load on cavity mirrors.
Keywords/Search Tags:laser technique, high energy lasers (HEL), chemical lasers, cylindrical laser, gain generator assembly, annular gain medium, annular HYLTE nozzle, annular resonator, beam-converting annular resonator, multi species reacting flow
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