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    "title": "Narrow-mode random lasing in disordered semiconductor films and powders",
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      "statement": "# Narrow-mode random lasing in disordered semiconductor films and powders\n\nCao and colleagues reported narrow spectral peaks emerging above a pump threshold in disordered zinc-oxide polycrystalline films and, in a related report, strongly scattering zinc-oxide powder films. Peak frequencies varied with position and observation angle, and the number of peaks changed with excitation area. The film study included above-threshold spatial emission images; similar behavior was reported for gallium-nitride powder. The authors interpreted the results as laser modes with coherent feedback from recurrent scattering.\n\n## Scientific scope\n\nThe separate 1998 film and 1999 powder reports have overlapping but different bylines. The scattering mean free path in the powder at a nearby probe wavelength was estimated from coherent backscattering; the authors note that direct determination at the emission wavelength requires an absorption-inclusive numerical comparison. Above-threshold spatial emission images are measured, whereas the closed-loop light paths and their interpretation as cavities are inferred rather than individually tracked photon trajectories. One reported powder critical excitation volume was 4.6 times the simplified theoretical estimate. These observations do not alone establish Anderson localization or prove a universal feedback mechanism for every random laser; earlier dye and powder-lasing results retain separate credit.\n\n## Reading status\n\nThis is a source-linked WRS catalogue note. A full explanatory guide and independent scientific reconstruction have not been completed for this entry. Read the identified original work for its complete narrative and arguments.\n\n## People and systems\n\nH. Cao; Y. G. Zhao; S. T. Ho; E. W. Seelig; Q. H. Wang; R. P. H. Chang; H. C. Ong; J. Y. Dai; J. Y. Wu\n\nThese are the listed authors of the cited contribution sources. Paper authorship does not quantify individual effort. An incomplete list is explicitly marked; same names are not automatically merged.\n\n\n\n## Original sources\n\n- [Random Laser Action in Semiconductor Powder](https://www.eng.yale.edu/caolab/papers/005.pdf)\n- [Ultraviolet lasing in resonators formed by scattering in semiconductor polycrystalline films](https://www.eng.yale.edu/caolab/papers/003.pdf)\n",
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    "what_changed": "Cao and colleagues reported narrow spectral peaks emerging above a pump threshold in disordered zinc-oxide polycrystalline films and, in a related report, strongly scattering zinc-oxide powder films. Peak frequencies varied with position and observation angle, and the number of peaks changed with excitation area. The film study included above-threshold spatial emission images; similar behavior was reported for gallium-nitride powder. The authors interpreted the results as laser modes with coherent feedback from recurrent scattering.",
    "scope": "Cao and colleagues reported narrow spectral peaks emerging above a pump threshold in disordered zinc-oxide polycrystalline films and, in a related report, strongly scattering zinc-oxide powder films. Peak frequencies varied with position and observation angle, and the number of peaks changed with excitation area. The film study included above-threshold spatial emission images; similar behavior was reported for gallium-nitride powder. The authors interpreted the results as laser modes with coherent feedback from recurrent scattering. The separate 1998 film and 1999 powder reports have overlapping but different bylines. The scattering mean free path in the powder at a nearby probe wavelength was estimated from coherent backscattering; the authors note that direct determination at the emission wavelength requires an absorption-inclusive numerical comparison. Above-threshold spatial emission images are measured, whereas the closed-loop light paths and their interpretation as cavities are inferred rather than individually tracked photon trajectories. One reported powder critical excitation volume was 4.6 times the simplified theoretical estimate. These observations do not alone establish Anderson localization or prove a universal feedback mechanism for every random laser; earlier dye and powder-lasing results retain separate credit.",
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