Abstract
Stochastic noise is incorporated in the numerical simulation of weakly scattering random lasers, which qualitatively captures lasing phenomena that have been observed experimentally. We examine the behavior of the emission spectrum while pumping only part of the entire one-dimensional random system. A decrease in the density of lasing states is the dominant mechanism for observing discrete lasing peaks when absorption exists in the unpumped region. Without such absorption, the density of lasing states does not reduce as dramatically but the statistical distribution of (linear) lasing thresholds is broadened. This may facilitate incremental observation of lasing in smaller-threshold modes in the emission spectrum with fine adjustments of the pumping rate.
Highlights
After early research on light diffusion with gain [1] the first experiments [2,3,4,5,6] on “random lasers” [7] exhibited strong amplification around the center frequency of the gain spectrum
In subsequent experiments on strongly scattering semiconductor powders and polycrystalline films with gain, emission spectra showed multiple narrow peaks occurring at frequencies other than the gain center frequency [8, 9]
Two types of situations occur when partial pumping is employed: (i) significant absorption exists in the unpumped region, (ii) little or no absorption exists in the unpumped region
Summary
After early research on light diffusion with gain [1] the first experiments [2,3,4,5,6] on “random lasers” [7] exhibited strong amplification around the center frequency of the gain spectrum. Similar narrow peaks, appearing on top of a broad and featureless spectrum, were observed in weakly scattering random systems [10,11,12] In these cases, only part of the entire spatial region of the random structures was pumped. This paper intends to address the question: how can discrete lasing peaks be observed in weakly scattering random lasers for both partial pumping situations (i and ii)? It becomes more clear that for both partial pumping situations, the DLS decreases and facilitates the observation of discrete lasing peaks This is because the number of small-threshold lasing modes decreases and their frequency spacing increases.
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