Bichromatic Emission Research Articles

Time sequence variation of incoherent and coherent random laser based on positive replica of abalone shell

Besides the scattering structures, the energy transfer (ET) process in the gain medium plays a significant role in the competition between coherent (comprising strongly coherent components) and incoherent (consisting of weakly coherent or “hidden” coherent components) modes of random lasers. In this study, bichromatic emission random lasers were successfully created using polydimethylsiloxane (PDMS) replicas with grooved structures that imitate the inner surface of abalone shells as scattering substrates. The influence mechanism of the ET process from the monomer to dimer in the Rhodamine 640 dye on the competition of random laser modes was thoroughly investigated from both spectral and temporal dimensions. It was confirmed that the ET process can reduce the gain of monomers while amplifying the gain of dimers. By considering the dominant high-efficiency ET processes, an energy transfer factor associated with the pump energy density was determined. Notably, for the first time, it was validated that the statistical distribution characteristics of the time sequence variations in the coherent random laser generated by dimers closely resemble a normal distribution. This finding demonstrates the feasibility of producing high-quality random number sequences.

Bi-chromaticity and tunability of random lasing in mesoporous silica SBA16 doped with rhodamine B

The random laser emission from ordered mesoporous silica SBA16 doped with rhodamine B (RB) organic dye was investigated. Powdered SBA16 with 16 nm average pore diameter have been synthesized and doped with five different concentrations of the organic dye. Typical incoherent feedback random laser behavior was observed. The bi-chromatic emission was characterized for the sample with the highest dye concentration. Tunable random laser emissions from 578 to 618 nm were obtained depending on the excitation laser spot diameter and the rhodamine-B load. The results indicate that mesoporous RB-doped SBA16 is a promising material for the development of solid-state random lasers.

Bichromatic Laser Dye As a Photonic Random Number Generator

This Article describes the effect of the excitation wavelength on the spectra of random laser emission obtained in a dye-doped polymeric system, composed of a PMMA layer and a laser dye exhibiting a bichromatic gain profile, the 3-(2,2-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP). We are showing that the change of pumping wavelength can be used to switch the laser emission between particular lasing bands and control the relative intensity between them if the bichromatic light amplification is achieved. We present that the random lasing phenomenon can strongly influence the resulting bichromatic emission, randomly selecting the dominating lasing band. Mentioned random band switching behavior was investigated using a statistical approach, indicating that the obtained distribution is dependent on the excitation wavelength. This feature can be used to design new types of laser-based optical random number generators that can find applications in integrated optical logic devices. To the best of the authors’ knowledge, this is the first demonstration of an optical random number generator based on the bichromatic laser dye described in the literature.

Mode competition of bichromatic laser emission in two-dimensional strong scattering random medium

The mode competition of the bichromatic laser emission in two-dimensional (2D) random medium was studied. Based on the time-dependent theory, a model for dual-wavelength random laser was established. The Maxwell equations and rate equations were combined and solved by using the finite different time domain (FDTD) method. Results show that the emission intensity of both wavelength ranges increases simultaneously with the increasing of the surface-filling fraction. The mode dominance of the bichromatic emission can be switched by changing the scatterer radius. The emission intensity of the longer wavelength increases when enlarging the excitation area. The controllability of these lasing modes may provide a potential application of optical switches.

Bichromatic random laser from a powder of rhodamine-doped sub-micrometer silica particles

We studied the random laser (RL) bichromatic emission (BCE) from a powder consisting of silica particles infiltrated with Rhodamine 640 (Rh640) molecules. The BCE is attributed to Rh640 monomers and dimers. Because of the efficient monomer-dimer energy transfer, we observed RL wavelength switching from ≈ 620 nm to ≈650 nm and the control of the emitted wavelength was made by changing only the excitation laser intensity. None of external parameters such as excitation laser spot size or radiation detector position was changed as in previous experiments. Two laser thresholds associated either to monomers or dimers were clearly observed. Moreover, an effect analog to frequency-pulling among two coupled oscillators was identified measuring the RL spectra as a function of the excitation laser intensity. A wavelength shift, Δλ, was measured between the monomer and dimer resonance wavelengths, changing only the excitation laser intensity. The maximum value of Δλ ≈ 16 cm−1 was obtained for laser pulses of 7 ns with 30 μJ.

Bichromatic emission in one-dimensional active random media

The relationship between spatial localization and bichromatic emission phenomena in one-dimensional (1D) active random media with gain is investigated by simultaneously solving Maxwell's equations and rate equations of electronic population. Results indicated that the increase of the concentration of the dye increases the spectral intensity of the dimer and the increase of the pump energy produces major radiative and nonradiative energy transfers from monomers to dimers. The increase of the ratio of the concentration of monomer to that of dimer would reduce the intensity of localization and increase the threshold of lasing mode. The competition between two lasing modes in 1D active random media can be controlled by local pumping. The results agree very well with the experimental data and offer a useful method for mode-selection.

Erratum: Bichromatic emission and multimode dynamics in bidirectional ring lasers [Phys. Rev. A81, 043817 (2010)

Erratum: Bichromatic emission and multimode dynamics in bidirectional ring lasers [Phys. Rev. A<b>81</b>, 043817 (2010)

Bichromatic emission and multimode dynamics in bidirectional ring lasers

The multimode dynamics of a two-level ring laser is explored numerically using a bidirectional traveling wave model retaining the spatial effects due to the presence of counter-propagating electric fields in the population inversion. Dynamical regimes where the emission in each direction occurs at different wavelengths are studied. Mode-locked unidirectional emission for large gain bandwidth and relatively small detuning is reported.

Synchronously pumped femtosecond optical parametric oscillator at 1053 nm

A femtosecond optical parametric oscillator synchronously pumped by a Ti:Sapphire oscillator is reported. By the cavity length tuning, the signal wavelength is continuously tuned from 1000 to 1200 nm. The average output power of 32 mW is obtained at 1053 nm. The pulse width is measured to be 342 fs by intensity autocorrelation method. In addition, we observed bichromatic emission during the cavity length tuning process.

On the origin of bichromatic laser emission in Nd^3+-doped fluoride glasses

In this work we present a detailed study about the influence of the host matrix in the spectroscopic and laser properties of Nd3+ in three different fluoride glasses. Site-selective time-resolved techniques have been used to investigate the crystal field changes felt by the Nd3+ ion as a consequence of glass inhomogeneity. Stimulated emission experiments performed under selective wavelength laser pumping show the existence of bichromatic emission from two distinguishable site distributions for Nd3+ in fluoride glasses. This result can be explained by the moderate inter-site energy transfer among Nd3+ ions found in these systems.

Bichromatic laser emission from dipyrromethene dyes incorporated into solid polymeric media

Bichromatic laser emission from dipyrromethene-based solid-state dye lasers is reported. The dependence of this dual emission on different factors and its origin and causes are discussed in the light of different models proposed in the literature. Our experimental results indicate that the long-wavelength emission can be explained in terms of reabsorption/reemission effects and inhomogeneous broadening of the S0-S1 transition. The short-wavelength emission corresponds to the usual S0-S1 transition and dominates at low dye concentration.

Controlling bichromatic emission in scattering gain media

It is experimentally shown that the competition between the two lasing modes of bichromatic emission in a dye solution with nanoparticle scatterers within the diffuse regime can be externally controlled by varying only the excitation beam diameter and the radiation detector position. It is established that this feature is a consequence of the changes in the reabsorption process strengths between monomer and dimer dye aggregates. The controllable switching of these lasing modes could open the real possibility of implementing previously suggested applications for this effect as optical switches.

Model for bichromatic laser emission from a laser dye with nanoparticle scatterers

In this work, we present model for bichromatic laser emission from laser dye solutions containing randomly distributed scattering particles. We suggest that bichromatic emission is produced by two fluorescent aggregates: monomers and dimers. The shorter-wavelength laser peak was attributed to the monomer emission and the secondary longer-wavelength peak was attributed to the dimer emission. From neat dye solutions, using absorption and emission spectroscopies, the monomer and dimer absorption and emission cross sections were obtained. The partial overlap between the dimer absorption cross section and the monomer emission cross section indicates a unidirectional radiative and nonradiative energy transfers from excited monomers to fundamental dimers. The dynamics of the laser emission was modeled by a set of rate equations, whose solutions agree with our experimental data. It is also shown that nonradiative energy transfer plays a very important role in the dimer laser process, and helps to explain the relatively strong dimer laser peak intensities.

Spectral features in emissions from random amplifying media

We have examined the phenomena of line-narrowing and bichromatic emission in random amplifying media by means of Monte Carlo simulations. We explain the various reported experimental features through a model that includes only the stimulated emission and self-absorption of photons performing a three dimensional random walk inside the amplifying medium. We present the results for all three regimes of scattering, L<l ∗ , L∼l ∗ and L>l ∗ .

Understanding bichromatic emission from scattering gain media

Intense optical pumping of solutions of high-gain laser dyes and TiO(2) nanoscatterers in methanol is found to result in narrow-linewidth bichromatic emission. Experimental studies of the long-wavelength emission peak show that weak pumping of the scattering gain medium by the primary lasing emission results in a random system that lases at longer wavelengths. Measurements with other dyes show that the bichromatic emission effect is very general.

Ti:sapphire second-harmonic-pumped visible range femtosecond optical parametric oscillator

A β-barium borate (BBO) femtosecond optical parametric oscillator (OPO) pumped by the second-harmonic of a modelocked 82 MHz Ti:sapphire laser is described. With intracavity dispersion compensation, pulse durations down to 30 fs are obtained with a total average power up to 100 mW. The current wavelength range, with a 400 nm pump, is from 566 nm to 676 nm. Unusual tuning characteristics, including bichromatic emission, are presented in detail and explained theoretically.

Self-pulsing and bichromatic emission in homogeneously broadened bidirectional ring lasers

We study the effects of saturation-induced Bragg gratings on the mode structure and dynamics of bidirectional homogeneously broadened ring lasers. The grating is viewed as a distributed feedback medium in a ring cavity and modes appropriate to such a structure are used. A Fourier decomposed rate equation model is developed to study the behavior of these modes above threshold. The difference in the properties of these solutions from the modes of an unfilled ring cavity lead to the possibility of bichromatic emission and both regular undamped and irregular damped self-pulsing.

Bichromatic emission in a ring dye laser.

We have performed an experimental study of a high-Q Rhodamine 6G ring dye laser and have measured bichromatic emission with wavelength spacings as large as 110 A\r{} when the laser operated bidirectionally. The bichromatic emission vanished at all excitations when the laser was forced into unidirectional operation using a Faraday isolator. However, when a weak reflected beam was allowed to make a single pass in the direction opposite to that allowed by the Faraday device, bichromatic emission is recovered at the higher pump powers. The experiments show that no discontinuities occur in the intracavity power as a function of excitation and that the intracavity fields which are completely consistent with the measured thresholds are not capable of producing Rabi splittings larger than a few angstroms. In addition, we have observed no structure in the spontaneous emission spectrum of the dye when the bichromatic emission (80-A\r{} splitting) was present in the laser mode. We have been able to quantitatively fit the threshold and wavelengths of the bichromatic emission using a distributed feedback mode analysis with a cavity-mode-induced susceptibility grating.

Instabilities of a homogeneously broadened laser.

We report on instabilities of a single-mode laser operating under homogeneous broadening conditions. Bichromatic emission as recently predicted from the Lorenz model as well as the correspondingly high second thresholds are found.