Theoretical Framework for a Directed-Energy Atmospheric Thruster Utilising Pulsed Isochoric Heating and Evanescent Wave Extraction

This paper presents the complete mathematical framework for a novel atmospheric jet propulsion system that replaces hydrocarbon combustion with pulsed electromagnetic energy deposition. The architecture employs a spheroidal photonic crystal cavity for electromagnetic energy buffering via total internal reflection and slow-light enhancement. Energy is extracted through evanescent wave coupling at surface grooves, buffered in dielectric pulse-compression elements, and injected into ram-compressed atmospheric air at rates up to 22,400 Hz. The energy absorption mechanism is multi-photon ionisation of molecular nitrogen, creating a transient plasma whose expansion follows the cylindrical Sedov–Taylor blast wave solution. The resulting high-enthalpy gas is expanded through a convergent-divergent De Laval nozzle to produce supersonic exhaust. The thermodynamic cycle is identified as a Humphrey (isochoric heating) cycle, which is shown analytically to provide a 20.8 percentage-point thermal efficiency advantage over the conventional Brayton cycle at identical heat input. End-to-end thrust verification at Mach 2 cruise (10 km altitude) yields 96 kN at full power and 107 kN with magnetohydrodynamic boost, with a sea-level takeoff thrust of 125 kN. The engine core contains zero moving parts. The paper includes a comprehensive literature review covering laser propulsion, pulsed detonation engines, MHD-augmented propulsion, photonic energy storage, and laser-plasma interactions. Parametric sensitivity analysis demonstrates graceful performance scaling across slow-light factors from S = 100 (experimentally demonstrated) to S = 10,000 (design target). A continuous-feed architecture is proposed for near-term implementation. Thermal analysis confirms that the moderate operating temperature (T₃ = 826 K) allows standard aerospace alloys without thermal barrier coatings. Limitations and future work directions are explicitly discussed. This is a purely theoretical framework — no experimental data are presented. All equations are derived from first principles. 31 references. 9 figures including system schematic and parametric analysis.