AWhat 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.
Scientific 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.
Evidence
The linked original works support the scoped statement and contribution attribution. WRS has not independently replayed experiments or reconstructed a full mathematical proof. 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.
Contributors
- The named authors in the research record · SCIENCE: These 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.
- Random Laser Action in Semiconductor Powder
- Ultraviolet lasing in resonators formed by scattering in semiconductor polycrystalline films
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