Random Lasing Spectrum Research Articles

Exploring statistical complexity and enabling speckle-free imaging with Dye-Kaolinite colloidal random lasers

This article extends our previous investigation into random lasers (RLs), focusing on the incorporation of Rhodamine 6G (R6G) dye in methanol with Kaolinite nanoclay scatterers as a disordered active medium for colloidal RLs. Building upon the prior exploration, which specifically focused on understanding the performance dependence related to the concentration of gain medium and scatterers, this report takes a closer look. It conducts a thorough statistical analysis of the incoherent dye-Kaolinite random lasing spectra, particularly in the context of replica symmetry breaking (RSB) and Lévy statistics. This study highlights that RSB is observed around the threshold energy and can serve as an indicator of the threshold. Gaussian distribution prevailed below, near, and far above the lasing threshold estimated from the levy (α) exponent, suggesting the absence of Lévy flight behavior. Additionally, Pearson correlation coefficients (PCC) were used to quantify the correlation between intensity fluctuations at different wavelengths, with the results visually represented by heatmaps. Furthermore, the random lasing output is utilized to achieve speckle-free imaging.

Analysis of Random Lasing in Human Blood.

Random lasing (RL) is an optical phenomenon that arises from the combination of light amplification with optical feedback through multiple scattering events. In this paper, we present our investigations of RL generation from human blood samples. We tested mixtures of rhodamine B dye solutions with different blood components, including platelets, lymphocytes, erythrocytes, and whole blood. Intense coherent RL was obtained in all cases at relatively low pump thresholds, except for erythrocytes. We also studied the potential of RL signal analysis for biosensing applications using blood samples from healthy individuals and patients suffering from Chronic Lymphocytic Leukemia (CLL). CLL is a blood disease characterized by a high count of lymphocytes with significant morphological changes. A statistical analysis of the RL spectra based on principal component and linear discriminant analyses was conducted for classification purposes. RL-based sample discrimination was conducted for whole blood, platelet, and lymphocyte samples, being especially successful (86.7%) for the latter. Our results highlight the potential of RL analysis as a sensing tool in blood.

Photonic replica symmetry breaking glassy transition and Lévy flight statistics of emission intensity in dye-doped colloidal potassium sodium niobate random laser

This article explores the statistics of spectral features, particularly shot-to-shot intensity fluctuations, in a potassium sodium niobate-dye colloidal system used as a random lasing platform. Correlations between spectral intensity fluctuations were analyzed in the random laser medium, where scatterer displacement considerably varies between consecutive shots. The report investigates the underlying physical process like replica symmetry breaking by studying the spectral intensity fluctuations in the emission intensity. Pearson correlation coefficients were calculated to better understand these correlations, and correlation plots (heatmaps) were generated. A single parameter (α) derived from an α-stable Lévy fit characterized the intensity distributions in all regimes. The spectral position and spacing of the spikes were examined to gain better insights into the random lasing spectra. Additionally, the Parisi overlap parameter and the α exponent are calculated, establishing the two parameters as an indicator of threshold energy. Finally, the paper explored photonic phases and fluctuation regimes, highlighting their importance in the broad range of applications for random lasers.

Random Lasing from Label-Free Living Cells for Rapid Cytometry of Apoptosis.

A random laser carrying the scattering information on a biological host is a promising tool for the characterization of biophysical properties. In this work, random lasing from label-free living cells is proposed to achieve rapid cytometry of apoptosis. Random lasing is achieved by adding biocompatible gain medium to a confocal dish containing cells under optically pumped conditions. The random lasing characteristics are distinct at different stages of cell apoptosis after drug treatment. By analyzing the power Fourier transform results of the random lasing spectra, the percentage of apoptotic cells could be distinguished within two seconds, which is more than an order of magnitude faster than traditional flow cytometry. These results provide a label-free approach for rapid cytometry of apoptosis, which is advantageous for further research of random lasers in the biological field.

Analyzing random lasing spectra of the zinc oxide bulk and the multiple quantum wells by empirical mode decomposition and fast Fourier transform

Empirical mode decomposition (EMD) was used to efficiently distinguish weak random-cavity emission from large broad spontaneous emission of the ZnO bulk and the multiple quantum wells (MQWs) structures. By fast Fourier transforming (FFT) the EMD results, we obtained the optical cavity lengths of random lasing and their corresponding emission intensity. With increasing pumping power, the EMD-FFT method confirms that the nonlinear trend of the random lasing emission in ZnO bulk and the change in optical cavity length is a result of change in refractive index dispersion due to the bandgap renormalization with high excited carrier density in nonpolar a-plane ZnO MQWs.

Statistical properties of Er/Yb co-doped random Rayleigh feedback fiber laser

In this Letter, we experimentally investigate fast temporal intensity dynamics and statistical properties of the cladding-pumped Er/Yb co-doped random Rayleigh feedback fiber laser (EYRFL) for the first time, to the best of our knowledge. By using the optical spectral filtering method, strong and fast intensity fluctuations with the generation of extreme events are revealed at the output of EYRFL. The statistics of the intensity fluctuations strongly depends on the wavelength of the filtered radiation, and the intensity probability density function (PDF) with a heavy tail is observed in the far wings of the spectrum. We also find that the PDF of the intensity in the central part of the spectrum deviates from the exponential distribution and has the dependence on the laser operating regimes, which indicates some correlations among different frequency components exist in the EYRFL radiation and may play an important role in the random lasing spectrum stabilization process.

Regularities of stimulated Raman scattering of dyes in a multiple scattering media

ABSTRACTThe main regularities influencing stimulated Raman scattering (SRS) occurrence of laser dyes in effective multiple scattering media (vesicular polymeric films) were studied on rhodamine series (R6G, R575, RB and R110) and summarized. It is shown that SRS interact closely with random lasing (RL) of dye what determines its behavior and causes appearance of all Stokes lines within RL spectrum. These effects forms coupled SRS-RL phenomenon. For its occurrence two resonances must be provided: pumping and RL radiation (as two component pump) with dye molecule vibration and pumping radiation with the electronic transition of dye molecule. Both resonances are realized if RL spectrum matches with spectral range of Stokes lines.This matching may be control with “pseudo-Stokes” spectrum constructed with vibration frequencies revealing in IR absorption spectrum of dye. The matching may be achieved by change of dye concentration and frequency of pumping radiation. The best SRS-RL occurrence realizes when the optimal matching achieves at highest dye concentration.The obtained data may by useful for development of Raman spectroscopy for laser dyes.

Emission regimes of random lasers with spatially localized feedback.

We report the experimental results obtained with a novel architecture for random lasing, in which the active material, free of scatterers, is placed between two large scattering regions. Lasing emission is investigated as a function of the illuminated area of the scattering regions, obtaining typical "resonant" and "non-resonant" random lasing spectra, depending on the device geometry. We propose a theoretical approach for the understanding of the observed phenomena, modelling the scattering elements with arbitrary spectral profiles in amplitude and phase and considering strong coupling between lasing modes. Good agreement between experiments and simulation results is obtained.

Random lasing based on rough dye-doped polymer thin film

In this work, a random laser action from rough dye film processed by surface rubbing with flannelette is reported. For the dye-doped polymer films with high surface roughness by surface rubbing, laser mode is stable, and threshold energy is found to be very low that is 333 μJ/cm2. By analyzing the random lasing spectrum using power Fourier transforms, an average resonator length was estimated as about 18.99 μm, which is 6.4 times larger than the film thickness. Furthermore, the influence of the concentration of Pyrromethene 597 (PM597) on the random laser was studied, and the results indicate that there is an optimum concentration for achieving the lowest threshold. Compared with glass groove structure with the dye doped film, the random laser based on the rough structure has reasonable time stability. This microstructure type random laser reported in this work is in low cost and easy to make compared with other laser structures of this category.

Coupled effect of stimulated Raman scattering and random lasing of dyes in multiple scattering medium

Random lasing (RL) and stimulated Raman scattering (SRS) of dye in multiple scattering media (MSM) appears simultaneously and each couple with other. This coupling has considerable influence on the SRS regularities of dye in MSM. The main feature of this impact is that RL radiation promotes the Raman lines revealing in the RL spectrum range as part of total radiation. SRS initiation occurs owing to the CARS-like mechanism provided by the two component pump: incident monochromatic radiation (laser pump) and RL radiation arising inside the MSM. It leads to important consequences: the RL spectrum must overlap with the spectral region of the possible Stokes lines of the dye; only those Stokes lines appear which are in a range of the RL spectrum; all conditions which promote RL assist SRS also. It is shown MSM promotes the best conditions for SRS and RL coupling due to optimal matching of RL localization regions and pump radiation.

Stimulated Raman scattering of laser dye mixtures dissolved in multiple scattering media

Stimulated Raman scattering (SRS) of a mixture of rhodamine 6G and pyrromethene 605 laser dyes in vesicular films is studied. It is shown that a peculiar interaction of dyes occurs under conditions of multiple scattering of light from vesicles. This interaction manifests itself as SRS excitation of one of the dyes by random lasing of the other dye, provided that the random lasing spectrum overlaps the Stokes lines of the first dye. In addition, there is energy transfer between molecules of these dyes if their luminescence and absorption spectra overlap. The results obtained confirm that the mechanism of SRS from laser dyes in multiple scattering media is similar to that in coherent-active Raman spectroscopy. These results extend the possibility of determining the vibrational spectrum of dye molecules from their secondary radiation in these media.

Surface roughness induced random lasing in bio-polymeric dye doped film

Here we report on the surface roughness induced random lasing phenomenon observed in thin film of biophotonic matrix – an modified deoxyribonucleic acid with cationic surfactant cetyltrimethylammonium chloride, doped with Rhodamine 6G laser dye. The random lasing was achieved using doubled in frequency Nd:YAG nanosecond pulse laser as a source of excitation. The experiments were carried out for different lengths of excitation areas resulting in lasing fluence threshold reduction from 16.6mJ/cm2 down to 33μJ/cm2. Using Fast Fourier Transformation analysis of random lasing spectra an average resonator length was estimated to amount 37μm.

Influence of reabsorption and reemission on stimulated Raman scattering of polymethine dyes in multiple scattering media

It is shown that reabsorption of the luminescence radiation in the range of its overlapping with the absorption spectrum and the following reemission to a long-wavelength range may noticeably affect the process of stimulated Raman scattering (SRS) in polymethine dyes in multiple scattering media (MSM). This is related to the fact that SRS in such media occurs jointly with the random lasing (RL), which favors SRS and makes up with it a united nonlinear process. Reemission into the long-wavelength spectrum range amplified in MSM causes the RL spectrum to shift to longer wavelengths and initiates the long-wavelength band of RL, in which a main part of the lasing energy is concentrated. This weakens or completely stops the SRS if the band is beyond the range of possible spectral localisation of Stokes lines. This process depends on the efficiency of light scattering, dye concentration, temperature and pump intensity; hence, there exist optimal values of these parameters for obtaining SRS in MSM.

Establishing the regularities and modelling the diffusion regime of random lasing in strongly scattering media

This paper describes how the experimental dependences of the energy parameters and the random lasing (RL) spectrum in the diffusion regime depend on the pump intensity, the concentration and refractive index of the scattering particles, the thickness of the sample, and the reflection at its boundaries. An algorithm is proposed for calculating these RL characteristics in the diffusion regime of light propagation by the Monte Carlo method, and calculated dependences of these RL characteristics on the parameters of the medium are obtained that agree with the experiment. It is shown that, because of reflection from the sample boundaries, there is an optimum thickness of the sample for which the RL energy is maximal, and its spectrum is narrowest. The dynamics of the number of excited dye molecules and the photons that they emit in a sample are calculated, along with the RL spectrum as a function of time. The existence of three stages in the formation of RL is established: accumulation of excited molecules, formation of multimode radiation, and relaxation with persistent lasing in high-Q modes. It is shown that the dominant role in the formation of RL radiation is played by the highest-Q modes.

Stimulated resonance Raman scattering from organic dyes in a multiple-scattering medium as a potential method for determining their vibrational spectra

A method is described for deriving Raman spectra of organic dyes from their random lasing spectra. The method was tested using Rhodamine 6G. The Raman spectrum obtained for this dye agrees well with the spectra measured by standard techniques but is more structured, which allows unresolved features to bedetected. The spectrum provides more detailed information owing to the interference between the Raman scattered light and amplified spontaneous emission of the dye molecules within a photon meanfree path. One advantage of the method is that the luminescence of the dye helps to observe Raman lines, which allows one to work in the Stokes region and facilitates the measurement procedure.

Stimulated Raman Scattering of Dyes Under Random Lasing in Polymeric Vesicular Films

The random lasing emission of dyed vesicular polymeric films under the diffusive regime of light propagation is investigated at helium temperature. It represents itself the coupling effect of the stimulated emission and the stimulated Raman scattering (SRS). Due to this effect, all the Raman lines are revealed in the random lasing spectrum. A distinguishing feature of the effect is that the stimulated emission (SE) promotes revealing the Raman lines. The intensity of Raman lines quadratically depends on the pumping intensity. Furthermore, the SRS under this condition has a more structured spectrum than the spontaneous Raman one. It makes it possible to detect even weak and closely located spectral lines.

Electrically pumped wavelength-tunable ultraviolet random lasing from Mg_xZn_1-xO films on Si

We report the electrically pumped wavelength-tunable ultraviolet random lasing from Mg(x)Zn(1-x)O films with different bandgap energies, which act as the semiconductor components in metal-insulator- semiconductor (MIS) structures fabricated on Si substrates. When the metal (Au herein) gates of the MIS structures are applied with sufficiently high positive voltages, random lasing from the Mg(x)Zn(1-x)O films occurs, featuring a series of narrow spikes in the emitted spectra. Overall, the central wavelength of the random lasing spectrum is tuned from approximately 377 to 352 nm with the increase of x value in Mg(x)Zn(1-x)O from 0 to 0.35. The mechanism for the electrically pumped random lasing has been tentatively elucidated taking into account both the multiple optical scattering and the optical gain proceeding in the Mg(x)Zn(1-x)O films.

Effect of stimulated raman scattering on the formation of the random lasing spectrum of dyes

The nature of the line structure of the random lasing spectrum of vesicular films activated by dyes (rhodamine 6G, pyrromethene 597) has been analyzed. The spectral lines appear above the random lasing threshold and are manifested only within the spectrum of the amplified spontaneous radiation of dye molecules against the continuous-pedestal background. Their intensities are proportional to the product of the intensities of the pump and continuous spectrum at the frequencies of these lines, and the frequencies are exactly reproduced from pulse to pulse. The shifts of the lines are strongly correlated with the pump frequency and the frequencies of these lines coincide with the frequencies of the Raman scattering lines of dye molecules. Using these properties, it has been shown that the observed lines are due to stimulated resonant Raman scattering by dye molecules, which occurs simultaneously with the stimulated emission of these molecules. These two processes affect each other and jointly form a united nonlinear process where all of the oscillations active in Raman scattering are manifested.