Coherent Random Lasing Research Articles

Sub-kHz-linewidth broadband-swept fiber laser based on Rayleigh scattering-enabled Brillouin random lasing oscillation with dynamic tunning Brillouin gain spectrum.

A sub-kHz-linewidth broadband-swept fiber laser using Rayleigh scattering-based Brillouin random lasing oscillation is proposed and experimentally demonstrated. Benefiting from Brillouin-involved acoustic damping and arbitrary-wavelength distributed Rayleigh feedback, leveraging instantaneously tuning Brillouin gain spectrum induced by a frequency-sweeping pump, a highly coherent random lasing emission with cavity mode elimination as well as frequency noise suppression is achieved in a sweeping manner. Results show that the proposed sweeping Stokes laser with a two-order-magnitude compressed linewidth of 840 Hz and 20 dB frequency noise suppression can unprecedentedly operate over the maximum wavelength range of 16 nm. Dynamic characteristics of the sweeping laser frequency are experimentally investigated, indicating a minimum residual nonlinearity of 0.0001 within the frequency-sweeping range of 126.63 GHz. It is believed that the proposed swept fiber laser may have attractive potential in diverse applications, including sensing and imaging.

Broad-band-enhanced plasmonic random laser in silver nanostar arrays

As a novel optical device, the plasmonic random laser has unique working principle and emission characteristics. However, the simultaneous enhancement of absorption and emission by plasmons is still a problem. In this paper, we propose a broad-band-enhanced plasmonic random laser. Two-dimensional silver (Ag) nanostar arrays were prepared using a bottom-up method with the assistance of self-assembled nanosphere templates. The plasmon resonance of Ag nanostars contributes to the pump light absorption and photoluminescence (PL) of RhB. Coherent random lasing was achieved in RhB@PVA film based on localized surface plasmon resonance (SPR) dual enhancement and scattering feedback of Ag nanostars. Ag nanostars prepared with different nanosphere diameters affect the laser emission wavelength. In addition, the random laser device achieves wavelength tunability on a flexible substrate under mechanical external force.

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.

Fabrication of a random laser gain medium using Rhodamine 101 dye doped with SiO2 nanoparticles by Sol-Gel technique

Random laser gain media are demonstrated by different concentrations of Rhodamine 101 dye solution mixed with SiO2 nanoparticles. For this purpose, these mediums are fabricated using the sol–gel technique and supplied with a pulsed blue laser to produce random lasing, while the light that reflects is collected using a spectrometer. Fluorescence and lasing activity were amplified as a consequence of nanoparticle scattering due to this optical pumping process. The results demonstrate coherent random lasing at 532–536 nm with the best FWHM equal to 2.1 nm at the optimal concentration (1 × 10−4 M).

Tunable random lasers via phase transition for information encryption

Introducing phase transition materials to random systems provides a promising route to create new optoelectronic functionalities of random lasers. Here, a phase transition random laser with switchable lasing modes is reported, which is designed with a thermoresponsive hydrogel as scattering medium. By manipulating the phase transition in hydrogel, random lasing modes can be switched reversibility between incoherent and coherent random lasing. The phenomenon derives from the changing of light scattering properties in different phase states, thus affecting the optical feedback path of random lasing. Besides, based on its controllable and easily detectable time-domain characteristics, the phase transition random laser is applied in information encoding and transmission. It is the first time that the transition from coherent to incoherent random lasing is observed by varying the sample phase states. This work will inspire the design and application of novel random lasers in photoelectric device.

Coherent Random Lasing in Subwavelength Quasi‐2D Perovskites

AbstractQuasi‐2D lead halide perovskites have garnered increasing interest as lasing gain media. Relatively simple fabrication, high refractive index, and unique quantum well structure encourage their use in traditional cavity lasers and cavity‐free systems called random lasers (RLs). Despite tremendous advances reported thus far, coherent random lasing in quasi‐2D perovskite subwavelength films has not been reported. Consequently, coherent optical feedback mechanisms in quasi‐2D perovskite systems are still unexplored. Here, this work reports the observation of coherent random lasing in subwavelength quasi‐2D perovskite films. Statistical analysis of spectral measurements reveals Lévy‐like intensity fluctuations, replica symmetry breaking confirms random lasing, and the coherent modes are studied with spectral and spatial correlation techniques. The observed coherent lasing modes are found to be extended states that arise from the random crystal grain structure during fabrication and span the entire pump volume. These modes out‐compete diffusive lasing due to their coherence.

Random laser on the surface of polymer optical fibre- A comparison of the effect of dielectric and plasmonic nanostructures

Here we demonstrate the effect of dielectric and plasmonic nanoparticles on the random lasing behaviour of a polymer optical fibre coated with an organic dye, Rh-640- perchlorate. Coherent random lasing was observed both in the presence of ZnO nanorods and Au nanourchins upon transverse optical pumping using a Q-switched Nd: YAG laser. With the same particle density, a significant reduction in the lasing threshold was observed in the case of the plasmonic random laser. The polymer optical fibre was fabricated using a custom-made fibre drawing tower, and the random lasing media was coated on its surface by the dip-coating method. The present analysis demonstrates that the combined effect of scattering by the nanoparticles and the cylindrical fibre geometry is responsible for the low threshold coherent random laser.

The differentiation procedure between amplified spontaneous emission and lasing phenomena

The lasing process emerges from an amplified spontaneous emission (ASE) when an optical resonator is present. The ASE is often observed during the laser emission, especially in random lasing studies. The differentiation between ASE and random lasing is difficult, particularly considering coherent and incoherent random lasing from polymeric dye-doped systems. In this article, we present the straightforward procedure of differentiation of both processes, in order to simultaneously designate the ASE and lasing emission properties and performance.

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.

Replica symmetry breaking in coherent and incoherent random lasing modes.

We investigate intensity fluctuations of a weakly scattering optofluidic random laser having coherent and incoherent emission fractions. The coherent part comprises random spikes, whereas the incoherent part forms a broad pedestal in the emission spectra. Evaluating the fractional ratio of the coherent and incoherent parts of the emission, a replica symmetry breaking phase transition is observed independently in both coherent and incoherent parts of the intensity. Also, the incoherent component has higher non-zero correlation values compared to those of the coherent part, implying a larger contribution to mode coupling. Moreover, survival function analysis reveals a significant contribution of the incoherent part on determining the decay profile of lasing intensity.

Random lasing from hybrid optical fiber composed of polymer cladding and glass core

In this study, a hybrid optical fiber was designed and fabricated, which composed of glass core and polymer cladding. The coherent random lasing are obtained from the hybrid fiber under the pump of a 532 nm laser. The random lasing comes from the scattering from the refractive index heterogeneity and the fluorescence from the PM597 in the polymer coating. The hybrid optical fiber proposed for the directionality of the random lasing is easily fabricated and connected with commercial optical fiber.

Large-Area Biocompatible Random Laser for Wearable Applications.

Recently, wearable sensor technology has drawn attention to many health-related appliances due to its varied existing optical, electrical, and mechanical applications. Similarly, we have designed a simple and cheap lift-off fabrication technique for the realization of large-area biocompatible random lasers to customize wearable sensors. A large-area random microcavity comprises a matrix element polymethyl methacrylate (PMMA) in which rhodamine B (RhB, which acts as a gain medium) and gold nanorods (Au NRs, which offer plasmonic feedback) are incorporated via a spin-coating technique. In regards to the respective random lasing device residing on a heterogenous film (area > 100 cm2), upon optical excitation, coherent random lasing with a narrow linewidth (~0.4 nm) at a low threshold (~23 μJ/cm2 per pulse) was successfully attained. Here, we maneuvered the mechanical flexibility of the device to modify the spacing between the feedback agents (Au NRs), which tuned the average wavelength from 612.6 to 624 nm under bending while being a recoverable process. Moreover, the flexible film can potentially be used on human skin such as the finger to serve as a motion and relative-humidity sensor. This work demonstrates a designable and simple method to fabricate a large-area biocompatible random laser for wearable sensing.

Single‐Shot Interaction and Synchronization of Random Microcavity Lasers

AbstractControl coupling and synchronization of lasers has been a promising topic, while complex lasers in disordered system make this more challenging and interesting for their potential applications in the internet of everything. Here, a way to realize the interaction and synchronization of random microcavity lasers, is proposed. The lasers are developed based on homemade amorphous microcavities, performing as nodes that can work in a single‐shot coherent random lasing regime. The nodes connect with each other by multimode fibers with variable coupling strength, and their multiple lasing modes can be well‐synchronized pulse‐by‐pulse through injection locking. A spectral coding method is demonstrated, providing an attractive way to generate and share information between disordered nodes. The synchronization is also extended to a one‐to‐many network, laying a solid foundation for the study of photonic interconnection and networking of complex systems.

Transition from incoherent to coherent random lasing by adjusting silver nanowires

Transition from incoherent to coherent random lasing by adjusting silver nanowires

Random lasing based on abalone shell

Here we reported on a tunable and stable random laser based on the abalone shell. The groove structure on the inner surface of abalone shell can support coherent random lasing when covered with a layer of dye doped film. By changing the pump position, the emission spectrum wavelength can be tuned by 12.10 nm due to the random distribution of the groove structure on the inner surface of abalone shell. The random laser can also be tuned by 13.85 nm using different concentrations of dye solutions. Furthermore, several different kinds of dyes were used to extent the emission wavelength range of the random laser. The normalized scattering efficiency spectrum confirms the experimental results. The excellent mechanical properties of the abalone shell endow the random laser with good stability. The random laser has potential applications in speckle-free imaging and probing nanoscale structural alterations.

Whispering-Gallery-Mode for Coherent Random Lasing in a Dye-Doped Polystyrene Encapsulated Silica-Glass Capillary

Dye-doped polystyrene (DDPS) encapsulated in a silica-glass capillary with a diameter of 300 μm was fabricated through radical polymerization of styrene within the capillary. The coherent random lasing (RL) with full width at half maximum (FWHM) of 0.36 nm and a quality factor of 1608 was produced in the DDPS with the capillary when pumping at 532 nm. However, the incoherent RL with FWHM of 6.62 nm and a quality factor of 92 was produced in the DDPS without the capillary. A detailed investigation on this phenomenon by changing the diameter of the capillary and core refractive index (RI) reveals that there exists a strong whispering gallery mode (WGM) resonance in the capillary, which helps generate the coherent RL. The findings may open up a new approach for the fabrication of highly efficient photonic devices.

Plasmon-assisted random lasing from a single-mode fiber tip.

Random lasing occurs as the result of a coherent optical feedback from multiple scattering centers. Here, we demonstrate that plasmonic gold nanostars are efficient light scattering centers, exhibiting strong field enhancement at their nanotips, which assists a very narrow bandwidth and highly amplified coherent random lasing with a low lasing threshold. First, by embedding plasmonic gold nanostars in a rhodamine 6G dye gain medium, we observe a series of very narrow random lasing peaks with full-width at half-maximum ∼ 0.8 nm. In contrast, free rhodamine 6G dye molecules exhibit only a single amplified spontaneous emission peak with a broader linewidth of 6 nm. The lasing threshold for the dye with gold nanostars is two times lower than that for a free dye. Furthermore, by coating the tip of a single-mode optical fiber with gold nanostars, we demonstrate a collection of random lasing signal through the fiber that can be easily guided and analyzed. Time-resolved measurements show a significant increase in the emission rate above the lasing threshold, indicating a stimulated emission process. Our study provides a method for generating random lasing in the nanoscale with low threshold values that can be easily collected and guided, which promise a range of potential applications in remote sensing, information processing, and on-chip coherent light sources.

Chromaticity-tunable white random lasing based on a microfluidic channel.

The color and/or chromaticity controllability of random lasing is a key factor to promote practical applications of random lasers as high luminance sources for speckle-free imaging. Here, white coherent random lasing with tunable chromaticity is obtained by using broadband enhancement Au-Ag nanowires as scatterers and the resonance energy transfer process between different dyes in the capillary microfluidic channel. Red, green and blue random lasers are separately fabricated with low thresholds, benefiting from the plasmonic resonance of the nanogaps and/or nanotips with random distribution and sizes within Au-Ag nanowires and positive optical feedback provided by the capillary wall. A white random laser system is then designed through reorganizing the three random lasers. And, the chromaticity of the white random laser is flexibly tunable by adjusting pump power density. In addition, the white random laser has anisotropic spectra due to the coupling role between the lasers. This characteristic is then utilized to obtain different random lasing with different chromaticity over a broad visible range. The results may provide a basis for applying random laser in the field of high brightness illumination, biomedical imaging, and sensors.

Origin of light scattering in dye doped polymeric waveguides and the dependence of excitation geometry on coherent random lasing

We present an experimental investigation on the origin of coherent random laser (RL) emission from 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminos-tyryl)-4H-pyran (DCM) doped polyvinyl alcohol (PVA) thin film (DCM-PVA) planar waveguide using various characterization techniques. Absorption and fluorescence spectra of the DCM-PVA thin film confirm the presence of aggregates at dye concentrations greater than 0.08 wt. %. Time correlated single photon counting measurements were perfomed to confirm the presence of dye aggregates in PVA matrix. x-ray diffraction studies reveal the semi-crystalline nature of the DCM-PVA thin film. The optical gain coefficient was determined by the variable stripe length method under 532 nm pulsed laser excitation and was found to be 2.1 cm−1 using the one-dimensional amplifier model for the 0.08 wt. % thin film. The RL emission of the planar waveguide depends on the geometry of the excitation spot. The emission spectrum consists of randomly positioned narrow spectral lines under stripe excitation geometry whereas, a smooth spectrum lacking the narrow peaks is observed under circular spot excitation, both above the lasing thresholds. The origin of weak scattering in DCM-PVA waveguide is attributed to the formation of dye aggregates and inhomogeneities created by the semi-crystalline nature of the film. The RL threshold decreases with an increase of the stripe length due to weak waveguiding in the planar film under stripe excitation. The high optical gain and low lasing thresholds attainable in DCM-PVA waveguides make them a promising candidate for the fabrication of polymer waveguide based photonic devices.

Replica Symmetry Breaking in a Weakly Scattering Optofluidic Random Laser

We report the observation of replica symmetry breaking (RSB) in a weakly scattering optofluidic random laser (ORL). Coherent random lasing is indicated by the presence of narrow peaks rising out of the spectral background. This coherence helps to identify a random laser threshold, which is expected to be gradual with weak scattering. We find that lasing action initiated using optical pulsed pumping coincides with the onset of both RSB and Lévy flight statistics. However, the transition from the photonic paramagnetic to photonic glass phase is more subtle in that the Parisi overlap function broadens instead of completely changing shape. This subtlety is balanced by an accompanying result of identical experimental conditions giving rise to lasing or no lasing depending on the shot. Additional statistical calculations and investigations into the fundamental physical mechanisms present in the ORL support this conclusion. Using simple numerical models, we study the critical spectral properties required for RSB to occur, as indicated by the Parisi overlap function. The simplicity of the models helps demonstrate the sensitive nature of this tool and the necessity of additional verification of the physical mechanisms present in the experiment.