Disordered Gain Medium Research Articles

Tunable replica symmetry breaking in random laser

Abstract Replica symmetry breaking (RSB) has been widely recognized as a statistical analysis approach to understand the disorder and nonlinear interactions in complex systems ranging from atoms to the cosmic scale. However, it is challenging to analyze the nonlinear optical characteristics of random laser (RL) in disordered gain medium via RSB due to the lack of a general RSB-based statistical analysis framework. In this work, we report the tunable RSB in polymer fiber RL, where the effects of temperature and different structures on RSB are investigated experimentally and theoretically. It experimentally proves that RSB in RL is not robust, and disorder and temperature are responsible for tunable RSB in RL, which contributes to the improvement of the statistical analysis framework for investigating the optical principles of RL using RSB. And the finding of the tunable RSB allows to investigate the dynamical differences for various RL systems, which broadens the directions for the use of spin-glass theory to explore the physical mechanism of RL.

Influence of fifth-order nonlinearities on the statistical fluctuations in emission intensities in a photonic open-cavity complex system

High-order nonlinear optical effects have become an important feature of photonic systems, both ordered and disordered. In this work, a very large and robust set of experimental data obtained from the emission spectra of a trivalent neodymium ion-based random laser, whose action mechanism relies upon gain and disorder, was characterized in detail. Using an effective model, it was possible to describe how the optical nonlinearities of the disordered gain medium affect the statistical behavior of the intensity fluctuations of the random laser for excitations close to and well above the laser threshold. A theoretical framework is presented and, in particular, in the regime well above threshold a nice fit to the experimental data is obtained with a distribution that incorporates nonlinearities up to fifth order, the Izrailev distribution.

Lasing action from dye doped polymeric nanofibers: A comparison study of well aligned with randomly oriented nanofibers

Abstract Ordering properties of a scattering media plays important role in a lasing emission system. In this work, we report a comparison study of optical amplification and lasing action from well aligned and randomly oriented dye doped polymeric nanofibers. Parallel aligned and randomly oriented dye doped polymeric nanofibers were prepared by electrospinning. Different optical phenomenon has been obtained from such two type fiber systems: amplified spontaneous emission from the well aligned nanofibers, and multimode random lasing emission with many sharp peaks from the randomly oriented nanofibers. To evaluate the effect of the microcavity effect, we carry out a comparative study of the optical pumped emission, threshold, and polarization properties of the two systems. Based on the comparison results, we try to discuss the mechanism for the optical cavity formation, where packing arrangement of the fibers plays a key role in the luminescence mechanism. Our comparative study of emission properties from well aligned and randomly oriented fibers manifest that the essence of random lasing is a highly disordered gain medium.

TUNABLE ULTRA-LONG RANDOM DISTRIBUTED FEEDBACK FIBER LASER

A 72 km open-ended symmetrical tunable random distributed feedback fiber laser (RDB-FL) with different pumping schemes is presented in this study. The random distributed feedback was contributed by Rayleigh scattering in the single-mode fiber while distributed gain was provided by the effect of stimulated Raman scattering. The pumping schemes tested with the configuration was outward and inward pumping, where these would be backward and forward pumping in a non-symmetrical configuration of a fiber laser, respectively. The tuning range was also varied in conjunction with the different pumping schemes to determine the optimum performance. Random lasing in the RDB-FL was achieved by utilizing multiple scattering in the disordered gain medium to achieve resonance. With pump power limited to 1.5 W, the best threshold was measured as low as 1.4 W while the highest total output power was at 8 mW. In outward pumping configuration, the wavelengths that are within the maximum Raman gain (1555-1565 nm) show the best peak powers and total output power with a narrow linewidth, as low as 0.25 nm.

Bright emission from a random Raman laser.

Random lasers are a developing class of light sources that utilize a highly disordered gain medium as opposed to a conventional optical cavity. Although traditional random lasers often have a relatively broad emission spectrum, a random laser that utilizes vibration transitions via Raman scattering allows for an extremely narrow bandwidth, on the order of 10 cm−1. Here we demonstrate the first experimental evidence of lasing via a Raman interaction in a bulk three-dimensional random medium, with conversion efficiencies on the order of a few percent. Furthermore, Monte Carlo simulations are used to study the complex spatial and temporal dynamics of nonlinear processes in turbid media. In addition to providing a large signal, characteristic of the Raman medium, the random Raman laser offers us an entirely new tool for studying the dynamics of gain in a turbid medium.

Suppression of interactions in multimode random lasers in the Anderson localized regime

Understanding random lasing is a formidable theoretical challenge. Unlike conventional lasers, random lasers have no resonator to trap light, they are highly multimode with potentially strong modal interactions, and they are based on disordered gain media, where photons undergo random multiple scattering. Interference effects notoriously modify the propagation of waves in such random media, but their fate in the presence of nonlinearity and interactions is poorly understood. Here, we present a semiclassical theory for multimode random lasing in the strongly scattering regime. We show that Anderson localization, a wave interference effect, is not affected by the presence of nonlinearities. To the contrary, its presence suppresses interactions between simultaneously lasing modes. Consequently, each lasing mode in a strongly scattering random laser is given by a single long-lived, Anderson localized mode of the passive cavity, the frequency and wave profile of which do not vary with pumping, even in the multimode regime when modes spatially overlap. Random lasing in the presence of nonlinearities and disordered gain media is still poorly understood. Researchers now present a semiclassical theory for multimode random lasing in the strongly scattering regime. They show that Anderson localization — a wave-interference effect — is not affected by the presence of nonlinearities, but instead suppresses interactions between simultaneously lasing modes.

Random Lasers: Characteristics, Applications and Some Research Results

s: The random laser differs from other types of laser in that its cavity is formed not by mirrors but by multiple scattering in a disordered gain medium. Over the course of ten years, random lasers have been attentive by many researchers in the world because their characteristics can lead to unique applications. This report presents the mechanism of random laser operation, classification, characteristics and prediction of different applications. Some research results of authors about random laser have also been noted in report.

Dynamics of random laser and coherent backscattering of light from ZnO amplifying random medium

We investigated the dynamics of coherent backscattering cone and random laser in a disordered gain medium of ZnO powder. Theoretical fit to the coherent backscattering cone yields a transport mean free path l approximately equal to the probe wavelength λ, indicating that the scattering process is in the strong scattering regime. Supernarrow emissions from the laser are accompanied by enhancement and sharpening of the coherent backscattering cone. This enhanced and sharpened backscattering cone returns to a normal profile within 10–20ps, indicating an ultrafast gain lifetime in the medium, which is in good agreement with the time-resolved measurement of the random laser emissions.

Organic random lasers in the weak-scattering regime

We used the ensemble-averaged power Fourier transform (PFT) of random laser emission spectra over the illuminated area to study random lasers with coherent feedback in four different disordered organic gain media in the weak scattering regime, where the light mean free path, $\ensuremath{\ell}*$ is much larger than the emission wavelength. The disordered gain media include a $\ensuremath{\pi}$-conjugated polymer film, an opal photonic crystal infiltrated with a laser dye (rhodamine 6G; R6G) having optical gain in the visible spectral range, a suspension of titania balls in R6G solution, and biological tissues such as chicken breast infiltrated with R6G. We show the existence of universality among the random resonators in each gain medium that we tested, in which at the same excitation intensity a dominant random cavity is excited in different parts of the sample. We show a second universality when scaling the average PFT of the four different media by $\ensuremath{\ell}*$; we found that the dominant cavity in each disordered gain medium scales with $\ensuremath{\ell}*$. The excellent agreement obtained with computer simulations using a distribution of random microdisks, each contributing a number of longitudinal whispering gallery modes within the gain spectrum, unambiguously shows that random lasers in the weak scattering regime cannot be described by gain amplification of localized photon states.

Random Lasers: Development, Features and Applications

The random laser differs from other types of laser in that its cavity is formed not by mirrors but by multiple scattering in a disordered gain medium. The unique characteristics of the technology have encouraged scientists to explore new applications.

Random Lasing in π-Conjugated Films and Infiltrated Opals

The properties of random lasers in π-conjugated polymer films and solutions infiltrated into opal photonic crystals are reviewed. We show that random lasing is a generic phenomenon that occurs in disordered gain media at an excitation intensity regime higher than that giving rise to amplified spontaneous emission. The emission radiation is coherent as demonstrated by photon statistics methods, and its spectrum contains many laser modes from which a typical cavity length can be obtained using Fourier transform spectroscopy. Since the random cavities are independent from each other, we show that laser emission in several colors is possible when mixing different dyes in the same random cavities. In addition, it is demonstrated that random lasing is formed in many disordered media with various scattering properties ranging from a regime of light prelocalization to that of weak scattering.

Sharpening of enhanced backscattering peak in a disordered gain medium.

We study theoretically the phenomenon of enhanced backscattering (EBS) from a bulk disordered gain medium due to the presence of a dye and a pump beam. We show that the presence of the gain, in combination with the effect of saturation, can dramatically sharpen the EBS peak function. In the particular case of a point source incidence for the probe beam along with the presence of a plane-wave pump beam, the EBS approaches a \ensuremath{\delta} function in angular space.\textcopyright{} 1996 The American Physical Society.