2001/05/18 by R. C. Polson, M. E. Raikh, M. É. Raǐkh +5
Physics and Astronomy · #Disordered Systems and Neural Networks (cond-mat.dis-nn) #FOS: Physical sciences #Mesoscale and Nanoscale Physics (cond-mat.mes-hall) #Optical and Acousto-Optic Technologies #Quantum optics and atomic interactions #Random lasers and scattering media #cond-mat.dis-nn #cond-mat.mes-hall
paper · pdf · doi:10.48550/arxiv.cond-mat/0105360
LaTeX, 9 two-column pages, 6 EPS figures included
arxiv created 2001/05/18 · openalex publication_date 2001/05/18 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
When films of Pi-conjugated polymers are optically excited above a certain threshold intensity, then the emission spectrum acquires a multimode finely structured shape, which depends on the position of the excitation spot. We demonstrate that the power Fourier transform (PFT) of the emission spectrum exhibits a certain peak-like structure, which also depends on the excitation spot. Our intriguing observation is that averaging the individual PFTs does not lead to a structureless curve, but rather yields a series of distinct transform peaks. This suggests universality, namely that the underlying random resonators that are responsible for the laser emission from the pi-conjugated polymer film are almost identical. We argue that the reason for such an universality is the large size of a typical resonator, which we determined from the PFT, as compared to the emission wavelength, lambda. This fact is, in turn, a consequence of the large light mean free path, l* approximately 10 lambda in the polymer film. This contrasts previous observations of random lasing in powders, where l* approx. lambda. We develop a simple theory that explains the presence of peaks in the average PFT and predicts their shape. The results of the theory agree quantitatively with the data.