Optical re-injection in cavity-enhanced absorption spectroscopy Rev. Sci. Instrum. 85, 093101 (2014); 10.1063/1.4893972 Pressure tuning of laser diodes in the near-infrared up to 1850 nm: Operational characteristics and reliability studies Rev. Sci. Instrum. 85, 063107 (2014);

We investigate the mode structure of a random laser consisting of a porous semiconductor matrix infiltrated with and surrounded by laser dye. The experimental parameters that influence the types of lasing that are observed are identified. The spatial structure of random laser modes is accessed experimentally by a spatially and spectrally selective detection scheme. We show that random laser modes are distinct from laser speckle.

We study (1 + 1)D transverse localization of electromagnetic radiation at microwave frequencies directly by two-dimensional spatial scans. Since the longitudinal direction can be mapped onto time, our experiments provide unique snapshots of the buildup of localized waves. The evolution of the wave functions is compared with semianalytical calculations. Studies beyond ensemble averages reveal counterintuitive surprises. Oscillations of the wave functions are observed in space and explained in terms of a beating between the eigenstates.

We systematically study the presence of narrow spectral features in a wide variety of random laser samples. Less gain or stronger scattering are shown to lead to a crossover from spiky to smooth spectra. A decomposition of random laser spectra into a set of Lorentzians provides unprecedented detail in the analysis of random laser spectra. We suggest an interpretation in terms of mode competition that enables an understanding of the observed experimental trends. In this interpretation, smooth random laser spectra are a consequence of competing modes for which the loss and gain are proportional. Spectral spikes are associated with modes that are uncoupled from the mode competition in the bulk of the sample.

Emission from a molecular light source depends on its optical and chemical environment. This dependence is different for various sources. We present a general classification in terms of Constant Amplitude and Constant Power Sources. Using this classification, we have described the response to both changes in the LDOS and stimulated emission. The unforeseen consequences of this classification are illustrated for photonic studies by random laser experiments and are in good agreement with our correspondingly developed theory. Our results require a revision of studies on sources in complex media. PACS numbers: 42.25.Dd, 42.55.Zz, 32.50.+d 1 arXiv:1009.2377v2 [physics.optics]