Random Laser Emission Research Articles

Creating directional random lasers using cracked light-emitting material

Researchers gather spatially localized feedback (SLF) via self-assembled crack sidewalls made of biomaterials and generate directional random laser emissions due to the diffuse reflection by these sidewalls.

High-Q, directional and self-assembled random laser emission using spatially localized feedback via cracks

Lasers based on Fabry–Pérot or whispering gallery resonators generally require complex fabrication stages and sensitive alignment of cavity configurations. The structural defects on reflective surfaces result in scattering and induce optical losses that can be detrimental to laser performance. On the other hand, random lasers can be simply obtained by forming disordered gain media and scatterers, but they generally show omnidirectional emission with a low Q-factor. Here, we demonstrate directional random lasers with a high Q-factor emission (∼1.5 × 104) via self-assembled microstructural cracks that are spontaneously formed upon radial strain-release of colloidal nanoparticles from the wet to dry phase. The rough sidewalls of cracks facilitate light oscillation via diffuse reflection that forms a spatially localized feedback, and they also serve as the laser out-coupler. These self-assembled cracks exhibit random lasing at optical pump powers as low as tens of μJ/mm2. We demonstrate a wide variety of random lasers from nano- and biomaterials including silica nanoparticles, fluorescent proteins, and biopolymers. These findings pave the way toward self-assembled, configurable, and scalable random lasers for sensing, displays, and communication applications.

Random laser action under picosecond laser pumping

This study was aimed to investigate the effect of scattering mean free path of different concentrations of silver nanoparticles in Rhodamine B (RhB) solution. To get the random lasing, the samples were exposed to Picosecond laser. Our results show a gradual increase in the random lasing emission by increase in the concentrations and thus scattering mean free path until the threshold amount. The emission intensity was enhanced by enhancing the laser power due to an increase in scattering, which cannot make a close loop path in the gain medium to reach the coherence random lasing. Our results showed efficient emission intensity due to the absorption of Rhodamine B with Ag NPs in the pumping wavelength where it has been observed that the lasing threshold is reduced from 0.628 A (without scatterer) to 0.62 A at $$9.2*10^{17}\, \hbox{cm}^{ - 3}$$ Likewise, the lowest FWHM (full width at half maximum) for this concentration was 34 nm, while without concentration it was 37 nm, but the clear and important difference is that the first occurred at 72 A, while the second state at 80 A.

Titanium nitride random lasing induced by the plasmon resonance effect

Titanium nitride (TiN) is a promising plasmonic material with hard and abrasion-resistant specialities. In this study, a gain regime, namely, plasmon-enhanced random laser emission, is demonstrated in the Pyrromethene-597 (PM597) assisted by titanium nitride (TiN) film. For this, photoluminescence and random lasing are measured at different pumping energies from PM597/Silicon and PM597/TiN/Silicon samples. Enhanced lasing efficiency is observed in the PM597/TiN/silicon sample where a plasmon resonance is formed, which increases the energy transfer between TiN and PM597. Furthermore, the multiple scattering mediated by the TiN film also plays an important role for the lasing efficiency. It is worth mentioning that the random laser emission has a strong dependence on pump position. The study of the random laser from PM597/TiN/Silicon sample with film structure is aimed to obtain a good alternative (TiN) to replace noble metals at a lowest cost.

Random laser spectroscopy and replica symmetry breaking phase transitions in a solvent-rich polymer thin film waveguide

We present the statistical analysis of random lasing intensity fluctuations in a 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminos-styryl)-4H-pyran (DCM) doped polyvinyl alcohol (PVA) thin film waveguide subjected to a constant heat treatment. The microscopic changes occurring in the density of the polymer thin film during the various stages of solvent evaporation are probed using the changes in the statistics of random laser (RL) emission intensities. In the solvent rich wet film, stronger RL emission intensity fluctuations are observed compared to the dried film, leading to a relatively slower decay of the survival function distribution of the emission intensities for a mode at the gain maxima of the averaged spectrum. The mode interactions in the wet and dried films, studied using covariance between lasing mode intensities, are found to be different. Further, replica symmetry breaking studies indicate the changes in the mode interactions with the microscopic modifications in the system during solvent evaporation at a constant pump energy above the lasing threshold. The statistical analyses of the RL emission intensity fluctuations are proposed as a spectroscopic tool to probe material properties.

Hybrid electronically addressable random fiber laser.

We report here a novel architecture for a random fiber laser exploiting the combination of a semiconductor optical amplifier (SOA) and an erbium doped fiber (EDF). The EDF was optically biased by a continuous wave pump laser, whereas the SOA was arranged in a fiber loop-mirror and driven by nanosecond duration current pulses. Laser pulses were obtained by synchronizing the SOA driver to the returning amplified Rayleigh back-scattered light from a selected short section of the EDF. By tuning the SOA pulse rate, random lasing was achieved by addressing selected meter-long sections of the 81-m long EDF, which was open-ended. Laser oscillation can be potentially obtained with SOA modulation frequencies from several kHz to the MHz regime. We discuss the mechanism leading to the hybrid random laser emission, connecting with phase sensitive optical time domain reflectometry and envision potential applications of this electronically addressable random laser.

High-Efficiency Random Fiber Laser Based on Strong Random Fiber Grating for MHz Ultrasonic Sensing

An Erbium-gain random fiber laser based on a strong random fiber grating (RFG) is experimentally demonstrated and applied to MHz ultrasound wave detection. The strong RFG with up to −10 dB reflectivity as well as a highly-doped Erbium doped fiber (HD-EDF) enabled a highly efficient random laser radiation with 1-kHz narrow linewidth. With the RFG as the feedback and the sensing head, both burst and continuous ultrasonic signals of up to 8 MHz can be demodulated by dynamics analysis from the random lasing emission. Results show that the detected signal-to-noise ratio (SNR) of 5.1 MHz ultrasound signal remains larger than 43 dB. The proposed random fiber laser sensor provides a broad ultrasonic bandwidth, high sensitivity, simple structure, low cost and robustness to the harsh environment, suggesting prospective applications for ultrasonic wave-associated acoustic emission (AE) detection in structure health monitoring and biomedical diagnosis.

Deep UV random lasing from NaGdF4:Yb3+,Tm3+ upconversion nanocrystals in amorphous borosilicate glass.

The realization of lanthanide-doped upconversion nanocrystals embedded in a robust and transparent solid medium is highly desired to achieve deep UV (<300nm) lasing. Here, we fabricate NaGdF4:Yb3+,Tm3+ upconversion nanocrystals inside amorphous borosilicate glass to support ∼290nm random lasing emission under 980 nm excitation. We found that with careful control of the growth process, which is the key to achieve high-crystallinity nanocrystals, the nanocrystals can suppress defect-related quenching and enhance 1I6→3H6(6IJ→8S7/2) transition of Tm3+ (Gd3+) ions under five-photon absorption excitation so that high optical gain (>45cm-1) at ∼290nm can be obtained.

Temperature dependent fluorescence properties and mid-infrared random lasing emission in Ho3+ and Tm3+ co-doped lead lanthanum zirconate titanate ceramics

In this study, obvious up-conversion emission peaks centred at 553 nm and 696 nm were investigated in transparent Ho3+ and Tm3+ co-doped lead lanthanum zirconate titanate (PLZT) ceramics. Temperature dependent visible up-conversion emission and mid-infrared photoluminescence at approximately 2.0 μm were studied, and obvious luminous color modulation from yellow-green to red was observed. Energy transfer between Ho3+ and Tm3+ ions was studied by analyzing the suppression and enhancement of the emission peaks. Moreover, random lasing emission peaks at 1.95 μm were achieved with a full width at half maximum of 5 nm, which was desirable for developing mid-infrared lasers in ceramics materials.

Random laser in dye-doped electrospun nanofibers: Study of laser mode dynamics via temporal mapping of emission spectra using Pearson's correlation

The development of optically active flexible nanostructures has been pursued in the last years owing to their potential application in photonic devices. Herein, we report a random laser architecture based on a flexible Rhodamine B-doped PMMA nanofibers produced via electrospinning technique with 1% and 5% (w/w) of dye. The lower concentrated sample provided only incoherent emission due to the low absorption mean free path. The most concentrated one provided both coherent and incoherent random laser emission depending on the position of the sample the excitation took place. Pearson's correlation coefficient maps showed a clear correspondence with the already established mode locking transition in random laser. A temporal mapping of successive emission spectra was performed, which provided qualitative information about mode competition dynamic when applied to coherent emission spectra and a highly sensitive way of tracking line widening and red/blueshift in incoherent random laser emission spectra. The developed system can be further employed to design novel miniaturized chemical and temperature 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.

Generalized extreme-value distribution of maximum intensities and Lévy-like behavior in an SOA-based random feedback laser emission

We report on generalized extreme value distribution of the maximum output intensities in a random feedback laser (RFL) emission, with localized gain provided by a semiconductor optical amplifier (SOA). Feedback due to Rayleigh backscattering from a single-mode fiber sustains the laser oscillation in a half-open cavity configuration. The experimental distribution of maximum output intensities near threshold is described by Fréchet distribution, and the distribution of intensities is associated with a heavy-tail power-law distribution. Increasing the pump above the threshold, the distribution of maxima tends to a Gumbel distribution. We also present experimental evidence of Lévy-like behavior in the SOA-RFL output intensities operating near the laser threshold, which is in agreement with extreme value statistics predictions.

Perovskite random lasers on fiber facet

Abstract Hybrid lead halide perovskites have made great strides in next-generation photovoltaic and optoelectronic devices. Random lasers based on perovskite materials have been intensively investigated, but the miniaturization of perovskite random lasers has not been achieved up to now. Here, we report the fabrication of perovskite random lasers based on perovskite films deposited on the optical fiber facets using a dip-coating method. Under optical pumping conditions, random lasing was observed with minimum threshold energy of 32.3 μJ/cm2 at ~550 nm; also, the lasing threshold decreased with increasing diameter of the optical fiber. The results show that the random lasing emission originates from the scattering between the perovskite crystal grains, and the decreased threshold is attributed to the increased active area of the perovskite film. The directionality of perovskite random lasers indicates that the divergence angle of the laser beam is less than 60°. We also demonstrate that the perovskite random laser on the fiber facet can prevent speckle formation and improve image quality. These results may promote the applications of random lasers in compact sources and integrated optoelectronic devices.

An investigation into random lasing from thin film on a sandpaper substrate

The blender of active material R6G and film forming agent PDMS are spincoated onto a sandpaper substrate to fabricate the random laser of thin layer. The sandpaper provides support for the random laser and the sand particles on the sandpaper substrate provide the scattering mechanism of random lasing output. The random lasing emission centres at 560 nm, with a threshold of about 13 mJ/cm2. This design provides a new and cheap method to fabricate random lasers.

Multi-wavelength coherent random laser in bio-microfibers.

In this paper, pure silk protein was extracted from Bombyx mori silks and fabricated into a new kind of disordered bio-microfiber structure using electrospinning technology. Coherent random lasing emission with low threshold was achieved in the silk fibroin fibers. The random lasing emission wavelength can be tuned in the range of 33 nm by controlling the pump location with different scattering strengths. Therefore, the bio-microfiber random lasers can be a wide spectral light source when the system is doped with a gain or energy transfer medium with a large fluorescence emission band. Application of the random lasers of the bio-microfibers as a low-coherence light source in speckle-free imaging had also been studied.

Influence of annealing time on random lasing from ZnO nanorods

Highly stabile single mode and multi-mode random lasing emissions were observed from ZnO nanorods array prepared on glass substrates using chemical deposition technique. By varying the post-growth-annealing time, nanorod diameters between 54 and 78 nm with population densities between 75 and 95 nanorods/µm2 were obtained. Depending on the population density and diameter of the nanorods, single, double and triple random lasing emissions were observed with lowest threshold of 209 mJ/cm2. Furthermore, the lasing threshold showed an obvious dependency on the nanorods density. The lasing emission maintained its wavelength with increasing pump power, indicating high stability of the lasing mode(s).

Steric Poly(diarylfluorene‐co‐benzothiadiazole) for Efficient Amplified Spontaneous Emission and Polymer Light‐Emitting Diodes: Benefit from Preventing Interchain Aggregation and Polaron Formation

AbstractThe effect of introducing side‐chain steric hindrance on the optoelectronic properties of the well‐studied green light emitting polymer (poly(9,9‐di‐n‐octylfluorene‐alt‐benzothiadiazole), F8BT) is investigated by means of replacing the 9,9‐dioctylfluorene unit by two novel steric hindrance functionalized monomers, namely, poly(9,9‐diarylfluorene‐alt‐benzothiadiazole) (FDFBT) and poly(9,9‐diarylfluorene‐4‐carbazole‐alt‐benzothiadiazole) (FCzBT). Bathochromic shifts of the optical spectra concomitant with enhanced photoluminescence quantum yields and improved film morphologies are found on the novel copolymers compared to F8BT. Femtosecond transient absorption spectroscopy demonstrates how steric hindrance effect in the novel copolymers manifests into enhanced stimulated emission and longer excited state lifetimes, associated with the suppression of polaron formation, all these being favorable features for light amplifying applications. Consequently, random lasing emission is achieved in films based on these copolymers with a threshold of three times lower than that of F8BT (22.95 µJ cm−2 for F8BT; 6.36 µJ cm−2 for FDFBT and 8.44 µJ cm−2 for FCzBT). Polymer light‐emitting diodes based on the novel copolymers exhibit performances comparable to the best reported on fluorene‐based devices. All of these results manifest the great potential of these novel copolymers for the application in the field of light‐emitting devices.

Unveiling the Effects of Interchain Hydrogen Bonds on Solution Gelation and Mechanical Properties of Diarylfluorene-Based Semiconductor Polymers.

The intrinsically rigid and limited strain of most conjugated polymers has encouraged us to optimize the extensible properties of conjugated polymers. Herein, learning from the hydrogen bonds in glucose, which were facilitated to the toughness enhancement of cellulose, we introduced interchain hydrogen bonds to polydiarylfluorene by amide-containing side chains. Through tuning the copolymerization ratio, we systematically investigated their influence on the hierarchical condensed structures, rheology behavior, tensile performances, and optoelectronic properties of conjugated polymers. Compared to the reference copolymers with a low ratio of amide units, copolymers with 30% and 40% amide units present a feature of the shear-thinning process that resembled the non-Newtonian fluid, which was enabled by the interchain dynamic hydrogen bonds. Besides, we developed a practical and universal method for measuring the intrinsic mechanical properties of conjugated polymers. We demonstrated the significant impact of hydrogen bonds in solution gelation, material crystallization, and thin film stretchability. Impressively, the breaking elongation for P4 was even up to ~30%, which confirmed the partially enhanced film ductility and toughness due to the increased amide groups. Furthermore, polymer light-emitting devices (PLEDs) based on these copolymers presented comparable performances and stable electroluminescence (EL). Thin films of these copolymers also exhibited random laser emission with the threshold as low as 0.52 μJ/cm2, suggesting the wide prospective application in the field of flexible optoelectronic devices.

Monolayer 2D ZrTe2 transition metal dichalcogenide as nanoscatter for random laser action

We demonstrate random laser emission from Rhodamine 6G with ZrTe2 transition metal dichalcogenide (TMD) as nanoscatters, both in powder and 2D nanoflakes liquid suspension. The 2D semimetal ZrTe2 was synthesized by a modified redox exfoliation method to provide single layer TMD, which was employed for the first time as the scatter medium to provide feedback in an organic gain medium random laser. In order to exploit random laser emission and its threshold value, replica symmetry breaking leading to a photonic paramagnetic to photonic spin glass transition in both 2D and 3D (powder) ZrTe2 was demonstrated. One important aspect of mixing organic dyes with ZrTe2 is that there is no chemical reaction leading to dye degradation, demonstrated by operating over more than 2 hours of pulsed (5 Hz) random laser emission.

Effect of Al concentration on optically pumped random lasing in Zn1−xAlxO (0 ≤ x ≤ 0.10) thin films fabricated via pulsed laser deposition technique

Effect of Al content on the lasing emission of pulsed laser deposited nanostructured Zn1−xAlxO (0 ≤ x ≤ 0.10) thin films is reported in the present paper. The thin films were grown onto fused silica substrate employing 2nd harmonic of a Q-switched Nd:YAG laser (532 nm, 10 ns, 10 Hz). The Random lasing emission was observed in these films by pumping with 3rd harmonic of the Q-switched Nd:YAG laser (355 nm, 10 ns, 10 Hz). The longitudinal modes of nearly equal separation of ~3 nm were observed having FWHM in the range of 0.38–0.56 nm. The optical cavity length in these was found to be in the range of 7.3–8.1 μm. The lasing mechanism in the films having spherical particulates was due to the pure Random Lasing action where as that of containing the nano rods and nano wire was due to the formation of Fabry-Perot and Whispering Gallery Mode cavity together. The quality factor was observed to be highly influenced with Al content in the films and was found to be in the range of 691–1004. The maximum quality factor of 1004 was obtained for the thin film having x = 0.05 containing nanorods. The RL threshold was estimated to be ~3.2 × 102 MW/cm2.