摘要:

We successfully developed the ultra‐light single shell paraboloidal concentrators made of a sheet of aluminized or silvered polymer membrane, formed via plastic deformation due to stress relaxation under high temperature condition by means of Straight Formation Method. Furthermore, we improved the precision of the concentrators by taking the elastic deformation of residual stress into consideration, and obtained the best concentration performance equivalent to a highly precise paraboloidal glass mirror. In solar concentration, the diameter of solar focal image via the single shell polymer concentrator is almost equal to that via the glass mirror and they are twice as large as that of the theoretical. The ultra‐light single shell polymer concentrators are very useful for the concentrator in solar thermal propulsion system and solar power station in particular, and also promising item for beamed energy propulsion. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1721011

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A method of generating an unique light beam, long range nondiffracting beam (LRNB) has been studied. The LRNB propagates over a long range keeping its narrow beam width as if it does not diffract, while general light beams spread by the diffraction effect. The new beam can be generated by a technique of wave front control. We will introduce some results of experiments and theoretical analyses of the LRNB generation using an optical system with a telescope and a laser. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1721012

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The purposes of this paper are to improve the control performance of the developed laser tracking system and to develop an integrated laser propulsion/tracking system for realizing a continuous flight and control of the micro‐airplane. The laser propulsion is significantly effective to achieve the miniaturization and lightening of the micro‐airplane. The laser‐driven micro‐airplane has been studied with a paper‐craft airplane and YAG laser, resulting in a successful glide of the airplane. In the next stage of the laser‐driven micro‐airplane development, the laser tracking is expected as key technologies to achieve continuous propulsion. Furthermore, the laser propulsion system should be combined with the laser tracking system to supply continuous propulsion. Experiments are carried out to evaluate the performance of the developed laser tracking system and integrated laser propulsion/tracking system. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1721013

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A technique for obtaining a pulse‐periodic operating mode of high‐power wide‐aperture lasers was put forward and experimentally realised. In this mode, the laser radiation is a sequence of pulses with a duration of 0.1–1 &mgr;s and a pulse repetition rate of several tens of kilohertz. The main relationships of the pulsed mode were theoretically analysed and the proposed technique was subjected to a comprehensive testing employing a test‐bench gas‐dynamic laser, which confirmed the conclusions of the theoretical analysis. The possibility of realising a pulse‐periodic mode in high‐power wide‐aperture lasers without a sacrifice in average output power was experimentally demonstrated. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1721014

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The new class of diode pumped alkali vapor lasers (DPALs) offers high efficiency cw laser beams at wavelengths which efficiently couple to photovoltaic (PV) cells: silicon cells at 895 nm (cesium), and GaAs cells at 795 nm (rubidium) and at 770 nm (potassium). DPAL electrical efficiencies of 25–30&percent; are projected, enabling PV cell efficiencies ∼40&percent; (Si) and ∼60&percent; (GaAs). Near‐diffraction‐limited DPAL device power scaling into the multi‐kilowatt regime from a single aperture is projected. The potential application to power beaming propulsion to raise satellites from LEO to Geo is discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1721015

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A study to maximize the total conversion efficiency and reduce the payload for Nd/Cr doped fiber laser had been performed. Laser oscillation has been observed in a multimode Nd‐doped fiber laser with “D‐shaped” clad under quasi‐solar pumping simulated by an intense metal‐halide arc lamp of which color temperature was 5600 kelvin. The fiber is 78‐m long. The Nd doping rate was 3000 ppm in silica core‐glass. The output power obtained was 300 mW when the injected power of lamplight was1.1 W at the entrance of the fiber and the optical‐optical conversion efficiency was over 25&percent;. The threshold of the input power for laser oscillation is 24 times of the solar constant in space. This value is one order lower than the case of crystal lasers which had been reported under solar‐pumping. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1721016

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Methods for producing and focusing of energetic X‐ray beams are described. From point view of high power operation, lasing conditions and scalability of capillary discharge laser are discussed. Focusing of lasers from pulse power driven plasma is demonstrated using a Wolter mirror. A new scheme for making an intense point‐like radiation source is proposed for X‐ray manipulation experiments. Based on recent experimental results, prospects and future research plans for intense radiation sources and focusing schemes are presented. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1721017

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Experiments on a pulsed microwave‐beaming thruster were conducted using a millimeter‐wave, high‐power gyrotrons developed by the Japan Atomic Energy Research Institute. Plasma inside of 2‐dimensional and axsymmetric parabola reflectors were observed using a high‐speed camera. Propagation velocity of the discharge front was well agreed with theoretical prediction assuming nonequilibrium photo ionization. Plasma was found to develop in three directions in a reflector absorbing direct or reflected microwaves. Shock wave propagation velocity varied depending on the distance from focal point and on angle from optical axis. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1721018

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Beamed‐energy launch concepts employing a microwave thermal thruster are feasible in principle, and microwave sources of sufficient power to launch tons into LEO already exist. Microwave thermal thrusters operate on an analogous principle to nuclear thermal thrusters, which have experimentally demonstrated specific impulses exceeding 850 seconds. Assuming such performance, simple application of the rocket equation suggests that payload fractions of 10&percent; are possible for a single stage to orbit (SSTO) microwave thermal rocket. We present an SSTO concept employing a scaled X‐33 aeroshell. The flat aeroshell underside is covered by a thin‐layer microwave absorbent heat‐exchanger that forms part of the thruster. During ascent, the heat‐exchanger faces the microwave beam. A simple ascent trajectory analysis incorporating X‐33 aerodynamic data predicts a 10&percent; payload fraction for a 1 ton craft of this type. In contrast, the Saturn V had 3 non‐reusable stages and achieved a payload fraction of 4&percent;. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1721019

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The microwave thermal thruster heats propellant via a heat‐exchanger then expands it through a rocket nozzle to produce thrust. The heat‐exchanger is simply a microwave‐absorbent structure through which propellant flows in small channels. Nuclear thermal thrusters are based on an analogous principle, using neutrons rather than microwaves, and have experimentally demonstrated specific impulses exceeding 850 seconds. A microwave equivalent will likely have a similar specific impulse, since both nuclear and microwave thermal thrusters are ultimately constrained by material thermal limits, rather than the energy‐density limits of chemical propellants. We present the microwave thermal thruster concept by characterizing a novel variation for beamed‐energy launch. In reducing the thruster concept to practice, the enabling physical process is microwave absorption by refractory materials, and we examine semiconductor and susceptor‐based approaches to achieving this absorption within the heat‐exchanger structure. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1721020

出版商:AIP    

年代:1904

数据来源: AIP