Coherent Random Lasers Research Articles

True random number generation based on temporal fluctuations of abalone shell coherent random lasers.

The output modes of random lasers exhibit randomness, making them a potential high-quality physical entropy source for generating random numbers. In this paper, we controlled a low-cost and easily fabricated abalone shell random laser, generating forward and backward coherent random lasers simultaneously in a single channel, resulting in highly diverse mode variations. After post-processing steps such as third-order difference calculations and exclusive-or (XOR) logic operations, we generated a random number sequence for the first time, to the best of our knowledge, based on the temporal fluctuations of biomimetic random laser coherent modes. The instantaneous generation rate reached a preliminary 40 Gbps. Moreover, the random bits satisfy requirements such as random distribution, independence, and absence of bias, successfully passing the NIST SP800-22 standard test, confirming the high quality of the random number sequence.

Random lasers with controlled emission modes by colloidal semiconductor quantum dots coupled to plasmonic nanorod arrays

Random lasers based on scattering for light amplification have gained extensive attention due to their simple structures. Colloidal semiconductor quantum dots (CSQDs) are excellent candidates as active media for random lasing. However, achieving CSQDs-based random lasers is challenging because the non-radiative Auger recombination produces a remarkable carrier loss. Here, we report random lasers with low thresholds based on the CSQDs coupled to the plasmonic nanorod arrays. The random lasers result from the enhancing excitation and emission rates of the CSQDs through plasmon resonance energy transfer induced by the spectral overlap between the resonant cavity modes of the plasmonic nanorod arrays and the excitons of the CSQDs, which reduces the carrier loss and establishes the optical gain in the CSQDs. Moreover, the incoherent and coherent emission modes can be controlled by varying the filling configurations (i.e., full-filling and partial-filling) of the plasmonic nanorods embedded in anodic aluminum oxide templates. Consequently, the incoherent random laser with a threshold of 19.3 μJ/mm2 and coherent random lasers with a threshold of 13.5 μJ/mm2 are performed, respectively. The proposed system provides a feasible method for low-threshold CSQDs-based random lasers with controlled emission modes, showing a promising avenue for potential applications.

A micro random laser of dye solution-filled tube system based on electrospun fibers

Random lasers (RLs) have good application prospects in speckle-free imaging, micro sensing and micro-nano photonic devices due to their properties such as cavityless, miniaturization and low-spatial coherence. The minimization, emission mechanism and lasing property control of RLs still need to be explored. In this paper, we present a novel micro RL system in a dye solution-filled tube, where the coherent random lasing action is facilitated by the integration of electrospun fibers and gold nanoparticles (Au NPs). The electrospun fibers serve as the scattering medium, while the Au NPs produce the local plasmon resonance effect. The interaction effect improves the photon scattering rate, makes the photons form a ring resonator in the system, and realizes the coherent RL in the tube system. The microtube RL has a very small size, a convenient preparation method and stable emission properties. It can withstand more than 2000 times pumping while maintaining a stable emission intensity. The electrospun fibers are stable and uniform in morphology, which makes it easy to achieve mass production of microtube RL. The speckle-free imaging experiment shows the RL has low spatial coherence, which indicates that it’s a good choice for micro speckle-free imaging. This work provides a convenient way to realize micro coherent RLs by electrospun fibers and could pave a way for applications in photonic devices.

Dual-band random laser based on positive replica of abalone shell

Random lasing from a polydimethylsiloxane substrate prepared from abalone shell by soft lithography was investigated. The substrate has better scattering efficiency than abalone shell and its groove structure can support both incoherent and coherent random lasing when covered with a layer of dye solution. When employing rhodamine 640 dye as gain medium, a dual-band random laser signal based on the mechanism of optical feedback intensity and mode competition can be observed, where the signals of the two bands are shown as incoherent and coherent random lasing regimes respectively. Speckle-free imaging is achieved by using incoherent and coherent random lasers as illumination sources and imaging effects are compared. This research shall promote the development of random lasers in the fields of illumination and imaging.

Coherent Random Lasing Realized in Polymer Vesicles

We have demonstrated the realization of a coherent vesicle random lasing (VRL) from the dye doped azobenzene polymer vesicles self-assembled in the tetrahydrofuran-water system, which contains a double-walled structure: a hydrophilic and hydrophobic part. The effect of the dye and azobenzene polymer concentration on the threshold of random laser has been researched. The threshold of random laser decreases with an increase in the concentration of the pyrromethene 597 (PM597) laser and azobenzene polymer. Moreover, the scattering of small size group vesicles is attributed to providing a loop to boost the coherent random laser through the Fourier transform analysis. Due to the vesicles having the similar structure with the cell, the generation of coherent random lasers from vesicles expand random lasers to the biomedicine filed.

Recyclable coherent random lasers assisted by plasmonic nanoparticles in DCM-PVA thin films

Recyclable coherent random lasers assisted by plasmonic nanoparticles in DCM-PVA thin films are studied. Four DCM-PVA films with different nanoparticles are made, and the radiation characteristics of these random lasers are studied. The results show that the emission spectrum of the DCM-PVA film with Au nanoparticle of 50 nm in diameter is optimal, and its threshold is about 6.53 µJ/pulse. Underlying mechanisms are discussed in detail. Then the DCM-PVA film with Au nanoparticles of 50 nm in diameter is detached from a glass substrate and adhered to different substrates. Coherent random lasers also occur when the sample is based on different substrates. Finally, a method of making samples recyclable is proposed, and the emission spectrum of samples as a function of cycle index is studied. The results show that recyclable coherent random lasers can be realized with this method. This study provides a new way, to the best of our knowledge, to realize recyclable coherent random lasers with low-threshold.

Polymer-fiber random lasers based on pumping radiation effect

In this study, we coated laser dye-doped polymethyl methacrylate on the surface of a bare polymer optical fiber (POF) to fabricate new POFs. Coherent random lasers are obtained for the gain POFs under the pump of a 532 nm laser. The mechanism for the random lasers is based on the refractive index heterogeneity scattering of the coating gain polymer. The variations of random lasers with different coating thicknesses and POF lengths under radiation pumping mode have been investigated. One important finding from our experiment is that dye-doped POF exhibits good photostability and self-healing properties. In addition, polymer-fiber random lasers as a sensor are researched in different concentrations of solutions. The intensity of the random lasers increases with the increase of the content of the surrounding ethanol solution due to swollen effect of the POF with a large gain length.

Coherent random lasing controlled by Brownian motion of the active scatterer

The stability of the scattering loop is fundamental for coherent random lasing in a dynamic scattering system. In this work, fluorescence of DPP (N, N-di [3-(isobutyl polyhedral oligomeric silsesquioxanes) propyl] perylene diimide) is scattered to produce RL and we realize the transition from incoherent RL to coherent RL by controlling the Brownian motion of the scatterers (dimer aggregates of DPP) and the stability of scattering loop. To produce coherent random lasers, the loop needs to maintain a stable state within the loop-stable time, which can be determined through controlled Brownian motion of scatterers in the scattering system. The result shows that the loop-stable time is within 5.83 × 10−5 s to 1.61 × 10−4 s based on the transition from coherent to incoherent random lasing. The time range could be tuned by finely controlling the viscosity of the solution. This work not only develops a method to predict the loop-stable time, but also develops the study between Brownian motion and random lasers, which opens the road to a variety of novel interdisciplinary investigations involving modern statistical mechanics and disordered photonics.

Nanoparticle mediated microcavity random laser

This paper reports a coherent random microcavity laser that consists of a disordered cladding (scattering) layer and a light-amplification core filled with dye solution. Cold cavity analysis indicates that the random resonance modes supported by the proposed cavity can be effectively excited. With introducing the gain material, random lasing by specific modes is observed to show typical features of coherent random lasers, such as spatially incoherent emission of random modes. By inserting a metal nanoparticle into the gain region, emission wavelength/intensity of the random lasers can be considerably tuned by changing the position of the inserted nanoparticle, opening up new avenues for controlling output of random lasers and sensing applications (e.g., small particle identification, location, etc.).

Broadband plasmonic silver nanoflowers for high-performance random lasing covering visible region

Abstract Multicolor random lasing has broad potential applications in the fields of imaging, sensing, and optoelectronics. Here, silver nanoflowers (Ag NF) with abundant nanogaps are fabricated by a rapid one-step solution-phase synthesis method and are first proposed as effective broadband plasmonic scatterers to achieve different color random lasing. With abundant nanogaps and spiky tips near the surface and the interparticle coupling effect, Ag NFs greatly enhance the local electromagnetic field and induce broadband plasmonic scattering spectra over the whole visible range. The extremely low working threshold and the high-quality factor for Ag NF-based random lasers are thus demonstrated as 0.24 MW cm−2 and 11,851, respectively. Further, coherent colorful random lasing covering the visible range is realized using the dye molecules oxazine (red), Coumarin 440 (blue), and Coumarin 153 (green), showing high-quality factor of more than 10,000. All these features show that Ag NF are highly efficient scatterers for high-performance coherent random lasing and colorful random lasers.

Resonance energy transfer process in nanogap-based dual-color random lasing

The resonance energy transfer (RET) process between Rhodamine 6G and oxazine in the nanogap-based random systems is systematically studied by revealing the variations and fluctuations of RET coefficients with pump power density. Three working regions stable fluorescence, dynamic laser, and stable laser are thus demonstrated in the dual-color random systems. The stable RET coefficients in fluorescence and lasing regions are generally different and greatly dependent on the donor concentration and the donor-acceptor ratio. These results may provide a way to reveal the energy distribution regulars in the random system and to design the tunable multi-color coherent random lasers for colorful imaging.

Decoupling gain and feedback in coherent random lasers: experiments and simulations.

We propose and demonstrate a coherent random laser in which the randomly distributed scattering centres are placed outside the active region. This architecture is implemented by enclosing a dye solution between two agglomerations of randomly positioned titanium dioxide nanoparticles. The same spectral signature, consisting of sharp spikes with random spectral positions, is detected emerging from both ensembles of titanium dioxide nanoparticles. We interpret this newly observed behaviour as due to the optical feedback given by back-scattered light from the scattering agglomerations, which also act as output couplers. A simple model is presented to simulate the observed behaviour, considering the amplitude and phase round trip conditions that must be satisfied to sustain lasing action. Numerical simulations reproduce the experimental reports, validating our simple model. The presented results suggest a new theoretical and experimental approach for studying the complex behavior of coherent random lasers and stimulate the realization of new devices based on the proposed architecture, with different active and scattering materials.

Physical manifestation of extreme events in random lasers.

We report our studies on exponentially-tempered Lévy sums that explain coherent random lasers based on nonresonant feedback. We investigate the hierarchy in the sums and identify the contribution of the extremes over a wide range of excitation energies and disorder strengths. Subsequently, we carry out experiments in which the physical manifestation of these extremes is revealed. At the appropriate gain and disorder, the extremes manifest as the sharp ultranarrow modes in the spectrum. At stronger excitation and disorder, the peaks disappear due to the reduced rarity of the extremes, compounded by the decreased magnitude effected by the tempering.

Exponentially tempered Lévy sums in random lasers.

Lévy fluctuations have associated infinities due to diverging moments, a problem that is circumvented by putting restrictions on the magnitude of the fluctuations, realizing a process called the truncated Lévy flight. We show that a perfect manifestation of this exotic process occurs in coherent random lasers, and it turns out to be the single underlying explanation for the complete statistical behavior of nonresonant random lasers. A rigorous parameter estimation of the number of summand variables, the truncation parameter, and the power-law exponent is carried out over a wide range of randomness, inversion, and system size. Random laser intensity is modeled on a unique platform of exponentially tempered Lévy sums. The computed behavior exhibits an excellent agreement with the experimentally observed fluctuation behavior.

Frequency behavior of coherent random lasing in diffusive resonant media

We investigate diffusive propagation of light and consequent random lasing in an amplifying medium comprising resonant spherical scatterers. A Monte-Carlo calculation based on photon propagation via three-dimensional random walks is employed to obtain the dwell-times of light in the system. We compare the inter-scatterer and intra-scatterer dwell-times for representative resonant and non-resonant wavelengths. Our results show that more efficient random lasing, with intense coherent modes, is obtained for a system with intra-scatterer gain. This is also coupled with a larger reduction in frequency fluctuations. We find that such a system can yield almost thresholdless random lasing. Inspired by these results, we discuss a possible practical situation, based on a monodisperse aerosol, wherein frequency controlled coherent random lasing can be obtained. Since our analysis essentially investigates transport of intensity, the results are relevant to coherent random lasers under nonresonant feedback.

Persistent coherent random lasing using resonant scatterers

We study the frequency behavior of coherent random lasers consisting monodisperse scatterers with single-particle resonances. A three-dimensional photon propagation model is employed to compute the wavelength-sensitive path length distribution of fluorescence photons in this system. We observe that a persistence interval of wavelengths exists for the coherent random lasing modes, corresponding to the Mie resonances of the individual resonant scatterer. Within the interval, characteristic pulse to pulse fluctuations continue to be observed from the system. The gain competition in the random laser suppresses likely coherent modes in other regions of the emission band, thereby reducing the wavelength fluctuations in the random laser. We further illustrate the tunability of this persistence interval by varying the size parameter of the resonant scatterers.

Quantification of lineshape fluctuations in coherent random lasers

Quantification of lineshape fluctuations in coherent random lasers

Random laser spectroscopy for nanoscale perturbation sensing

We report a spectroscopic method using coherent random lasers for a simple, yet nanoscale, sensing approach. Unique spectral properties of coherent random laser emission can be detectably altered when introducing nanoscale perturbations to a simple nanocomposite film that consists of dielectric nanospheres and laser-dye-doped polymer to serve as a transducer. Random lasing action provides a means to amplify subtle perturbations to readily detectable spectral shifts in multiple discrete emission peaks. Owing to several advantages, such as large-area detection, narrow and multiple emission peaks, straightforward detection, and simple fabrication, random laser spectroscopy has the potential for ultrasensitive, yet simple, biosensors in various applications.

Coherent random lasers in weakly scattering polymer films containing silver nanoparticles

We report on the observations of coherent random lasers in weakly scattering polymer films embedded with silver nanoparticles. The dominant oscillation cavity calculated from the ensemble-averaged power Fourier transform spectrum of single-shot emission spectra is shorter by more than two orders of magnitude than the scattering mean-free path, indicating that the oscillation cavity is loosely associated with multiple scattering. We suggest that the coherent feedback arises from the cooperative effect of light scattering and field enhancement in the vicinity of silver nanoparticles.

Coherent random lasers from weakly scattering polymer films embedded with superfine silver nanoparticles

AbstractRandom lasers with coherent feedback have been obtained in highly transparent polymer films embedded with silver (Ag) nanoparticles. The hybrid materials were fabricated via in situ synthesis, through which Ag nanoparticles were precipitated by heat treatment. Sharp peaks with linewidth of ∼0.3 nm emerge on a broad emission background when the pump energy reaches a threshold. Random lasers with coherent feedback induced by Ag nanoparticles have been little reported, and hence, we believe that this work brings about an important aspect to random lasers. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)