共查询到20条相似文献,搜索用时 15 毫秒
1.
Laser action in active random media in the weak scattering regime far from Anderson localization is investigated by coupling Maxwell's equations with the rate equations of a four-level atomic system. We report systematic lasing action with resonant feedback and show that the lasing modes mostly consist of traveling waves spatially extended over the whole system. Next we address the question of the origin of the feedback mechanism in such a system where no disorder-induced long-lived resonances are available, and present strong evidence that they correspond to the quasimodes of the passive system. This in turn provides an original way to access the spatial distribution of the quasimodes of a non-Hermitian system. 相似文献
2.
The modal characteristics of localized electromagnetic waves inside random nanostructures are theoretically presented. It is crucial to know the tuneabilities of the localized modes systematically for demonstrating a specific random lasing application. By use of FDTD (Finite-Difference Time-Domain) method, we investigated the impulse response of two-dimensional random nanostructures consisting of closely packed cylindrical dielectric columns, and precisely analyzed the localized modes. We revealed the tuneability of the frequency of the localized modes by controlling the medium configurations: diameter, spatial density, and refractive index of the cylinders. Furthermore, it is found to be able to tune the Q (quality) factors of the localized modes dramatically by controlling simply the system size of the entire medium. The observed Q factors of approximately 1.6×104 were exhibited in our random disordered structures. 相似文献
3.
We present a numerical study of lasing modes in diffusive random media with local pumping. The reabsorption of emitted light suppresses the feedback from the unpumped part of the sample and effectively reduces the system size. The lasing modes are dramatically different from the quasi modes of the passive system (without gain or absorption). Even if all the quasi modes of a passive diffusive system are extended across the entire sample, the lasing modes are still confined in the pumped volume with an exponential tail outside it. The reduction of effective system volume by absorption broadens the distribution of decay rates of quasi modes and facilitates the occurrence of discrete lasing peaks. 相似文献
4.
Jiantao Lü 《中国光学快报(英文版)》2006,4(4)
The pumping rate dependence of the peak intensity of the individual lasing mode in two-dimensional (2D) active random media is investigated. The results show that these modes have a typical threshold gain behavior and different threshold pumping rates. There exists a certain correspondence between the mode's threshold pumping rate and its lifetime, and the longer the lifetime is, the lower the threshold is. 相似文献
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D. A. Anchikov A. A. Krents N. E. Molevich A. V. Pakhomov 《Bulletin of the Lebedev Physics Institute》2014,41(8):226-229
The processes of the formation of optical field structures in the transverse profile of wide-aperture laser radiation are studied within the model described by the system of Maxwell-Bloch equations. The main types of instabilities appearing above the second lasing threshold and corresponding mechanisms controlling the laser dynamics at negative frequency detuning are considered. The characteristic lasing modes and conditions of the spontaneous formation of transverse optical structures are determined. 相似文献
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当酒精的弱增益拉曼模式处于罗丹明640染料分子的激光增益范围时,在由悬垂液滴构成的圆形谐振腔中,观察到乙醇分子C—H伸缩系列模中多个弱增益拉曼模式的受激拉曼散射(SRS)光谱.随着抽运光的增强,迅速增长的强增益拉曼模式的受激辐射抑制了其他弱增益模式的SRS,并导致染料激光的完全淬灭.通过分析圆形腔腔模的光子速率方程和激光染料分子的三能级粒子数速率方程,解释了观察到的实验现象.
关键词:
受激拉曼散射
悬垂液滴
弱拉曼增益模式
激光增益 相似文献
9.
We report on random lasing from a dye-scatterer system directly excited by evanescent modes formed over a dielectric-dielectric interface. The system is quasi-two-dimensional because of the subwavelength exponential decay of the excitation energy. Spectral narrowing by a factor of approximately 13 was obtained under diffusive scattering conditions. The peak intensity exhibited a unique dual-saturation behavior due to the localized nature of the excitation. We observed a reduction of threshold for samples with a higher dye concentration because of a larger excitation-state occupation number within the same interaction volume. 相似文献
10.
Bliokh KY Bliokh YP Freilikher V Genack AZ Hu B Sebbah P 《Physical review letters》2006,97(24):243904
We consider, both theoretically and experimentally, the excitation and detection of the localized quasimodes (resonances) in an open dissipative 1D random system. We show that, even though the amplitude of transmission drops dramatically so that it cannot be observed in the presence of small losses, resonances are still clearly exhibited in reflection. Surprisingly, small losses essentially improve conditions for the detection of resonances in reflection as compared with the lossless case. An algorithm is proposed and tested to retrieve sample parameters and resonance characteristics inside the random system exclusively from reflection measurements. 相似文献
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Angular-modulated spatial distribution of ultrahigh-order modes assisted by random scattering 下载免费PDF全文
In designing an optical waveguide with metallic films on a nanometer scale, the random scattering by the natural roughness of the thin film is always ignored. In this paper, we demonstrate that for the ultrahigh-order modes (UOMs) in the symmetric metal cladding waveguide, such a scattering leads to drastic variations in their spatial distribution at different incident angles. Owing to the high mode density of the UOMs, the random scattering induced coupling can be easily related to different modes with different propagation directions or wavenumbers. At small incident angles, the intra-mode coupling dominates, which results in a spatial distribution in the form of concentric rings. At large incident angles, the inter-mode coupling plays the most important role and leads to an array-like pattern. Experimental evidence via optically trapped nanoparticles support the theoretical hypothesis. 相似文献
13.
Vasil P. Yashchuk O. Prygodiuk V. Koreniuk E. Tikhonov V. Bezrodny 《Applied physics. B, Lasers and optics》2008,92(4):593-597
The spectrum behavior evolution and the threshold of random lasing depending on the way of photon walk randomization in an
active random medium were investigated. The following three ways of photon walk randomization were implemented: multiple light
scattering by corundum and silica particles embedded into a solid polymer solution of dye (astrafloxin), multiple light reflection
at sub-millimeter extensive air pores (mean diameter 200 μm) produced in the medium, and the combined action of both these
effects. The most effective lasing is observed in the case of an active medium with air pores and scattering particles in
the interpore space. Such a combined porous scattering medium acts as a network of dielectric waveguides transmitting effectively
the random light. This spatial structure of the random active medium significantly increases the photon path in the medium,
thereby promoting photon multiplication due to stimulated emission. In this combined medium the random lasing reveals the
narrowest spectrum, the lowest threshold, and the highest density of spectral energy in the spectrum maximum. 相似文献
14.
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. 相似文献
15.
G. B. Malykin 《Radiophysics and Quantum Electronics》1994,37(2):159-161
Three methods for measurement of the h parameter in single-mode fiber lightguides (SFG) with different degrees of anisotropy are compared experimentally. It is shown that all three methods provide a practically identical result for an SFG with strong anisotropy, while only the method based on excitation of the SFG input by nonmonochromatic radiation of a single polarization mode has an adequate result, provided that the spectral width of the radiation source is comparable with its wavelength.Institute of Applied Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 2, pp. 265–269, February, 1994. 相似文献
16.
Using a scattering matrix formalism, we derive the general scattering properties of optical structures that are symmetric under a combination of parity and time reversal (PT). We demonstrate the existence of a transition between PT-symmetric scattering eigenstates, which are norm preserving, and symmetry-broken pairs of eigenstates exhibiting net amplification and loss. The system proposed by Longhi [Phys. Rev. A 82, 031801 (2010).], which can act simultaneously as a laser and coherent perfect absorber, occurs at discrete points in the broken-symmetry phase, when a pole and zero of the S matrix coincide. 相似文献
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Brett H. Hokr Joel N. Bixler Vladislav V. Yakovlev 《Applied Physics A: Materials Science & Processing》2014,117(2):681-685
Random Raman lasers offer a unique opportunity to study many exciting dynamics of light propagation in turbid media. One of the most notable features observed to exist in the recently discovered random Raman laser is the presence of higher order stimulated Raman scattering processes. The higher order Stokes generation likely comes from photons that have the longest pathlengths, thus have the most gain. This makes these photons particularly likely to offer interesting insight into wave propagation effects such as coherent backscattering and optical Anderson localization. In this work, we use Monte Carlo simulations to investigate how these higher order processes occur and what properties they are expected to exhibit when considering only transport equation dynamics. This knowledge will allow us to look for deviations from this theory in future experiments to determine whether wavelike properties play an active role in random Raman lasing. 相似文献
19.
Fritz Haake Felix Izrailev Nils Lehmann Dirk Saher Hans-Jürgen Sommers 《Zeitschrift für Physik B Condensed Matter》1992,88(3):359-370
We present analytical and numerical results for the level density of a certain class of random non-Hermitian matrices =H+i. The conservative partH belongs to the Gaussian orthogonal ensemble while the damping piece is quadratic in Gaussian random numbers and may describe the decay of resonances through various channels. In the limit of a large matrix dimension the level density assumes a surprisingly simple dependence on the relative strength of the damping and the number of channels. Moreover, we identify situations with cubic repulsion between the complex eigenvalues of , to within a logarithmic correction. 相似文献
20.
The transition from a photonic band-edge laser to a random laser in two-dimensional active photonic crystals is described. The lasing modes in the active photonic crystals shift from the edge of the photonic bandgap to the bulk of the gap when a certain amount of position and size disorder is introduced. The shift of lasing modes is determined with various gain profiles. The results show that the modulation of lasing modes is significant when the lasing transition wavelength overlaps the photonic bandgap. 相似文献