Optical and structural requirements for x-ray distributed feedback lasing across a resonant thin film

The requirements for developing chip-scale distributed-feedback x-ray lasers were investigated to address the critical challenge of miniaturizing coherent short-wavelength laser sources. A central concept introduced in this work is the use of “Röntgen materials” that can simultaneously serve as a gain medium and support the optical feedback structure required for lasing. As a model system, La0.5Sr0.5CoO3 (LSCO) was selected due to its high atomic number constituents, tunable stoichiometry, and favorable optical properties. High-quality LSCO thin films were synthesized using pulsed laser deposition to ensure epitaxial growth and precise compositional control. Structural and compositional integrity was confirmed via x-ray diffraction, reciprocal space mapping, and Rutherford backscattering spectrometry. The gain performance was evaluated based on fluorescence efficiency, crystal orientation, and lattice plane alignment. A key finding was that high-Z materials with optimal refractive index contrast and reduced non-radiative Auger losses support conditions for coherent x-ray amplification. By leveraging higher-order diffraction planes and targeted gain optimization strategies, this work advances the feasibility of compact x-ray laser systems with potential applications in biomedical imaging, materials analysis, and high-resolution spectroscopy.