A temperature-tunable random laser

Wiersma, Diederik S.; Cavalieri, Stefano

doi:10.1038/414708a

Cited by 334 publications

(190 citation statements)

References 12 publications

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“…In recent years they have attracted a great deal of attention, mainly due to the versatility stemming from cavity-less geometries and the ease of realization [1][2][3][4][5][6][7][8][9]. In liquid crystals, suitable dopants can provide the gain action through optical pumping, while optical birefringence in conjunction with intense fluctuations of the dielectric tensor yield the required recurrent multiple scattering for random resonances to occur [10][11][12][13][14][15][16][17].…”

mentioning

confidence: 99%

Soliton-assisted random lasing in optically-pumped liquid crystals

Perumbilavil

Piccardi

Buchnev

et al. 2016

Applied Physics Letters

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We demonstrate a novel random laser configuration by exploiting the coexistence of optical gain and light self-localization in a reorientational nonlinear medium. A spatial soliton launched by a near-infrared beam in dye-doped nematic liquid crystals enhances and confines stimulated emission of visible light in the optically-pumped gain-medium, yielding random lasing with enhanced features.In random lasers, a disordered distribution of scattering centers provides the required feedback for oscillations in optically amplifying media. In recent years they have attracted a great deal of attention, mainly due to the versatility stemming from cavity-less geometries and the ease of realization [1][2][3][4][5][6][7][8][9]. In liquid crystals, suitable dopants can provide the gain action through optical pumping, while optical birefringence in conjunction with intense fluctuations of the dielectric tensor yield the required recurrent multiple scattering for random resonances to occur [10][11][12][13][14][15][16][17]. In the nematic phase, moreover, liquid crystals are positive uniaxial materials subject to optic axis reorientation under the action of electric fields, either at low or optical frequencies [18]. The latter response provides a low-power mechanism for nonlinear optics [19] and light localization into self-confined lightbeams, the so-called "nematicons" [20]. Nematicons are bright spatial solitons (solitary waves) which are stable in two transverse dimensions due to the nonlocal response associated with the elastic intermolecular links in the liquid state [21,22]; they support graded-index waveguides able to confine additional (incoherent) signals/beams of different wavelengths as well as powers and profiles [23][24][25][26][27][28][29][30], are robust against refractive index perturbations [31-35] and collisional interactions [36][37][38]. Aided by nematicons, reorientational and electronic nonlinear responses, characterized by distinct time-and power-scales, can synergystically be combined [39,40]. Owing to their large numerical aperture [41], nematicon waveguides solitons have also been employed in experiments involving incoherent light generation by fluorescence [42] or amplified spontaneous emission [43], offering a means to better collect and couple the emitted light into optical fibers.In this Letter we demonstrate a novel example of synergy between diverse nonlinear responses: the combination of spatial solitons and random lasing into a "nematicon random laser", whereby a low-power self-confined beam provides a guided-wave landscape for the stimu- * assanto@uniroma3.it lated emission induced by collinear optical pumping of dye-doped nematic liquid crystals (NLC).Several benefits can be expected from adopting such light-induced guided-wave configuration for random lasing. At variance with standard thin film geometries, the thick NLC cell provides an extended volume where optical pumping can produce fluorescence and, in turn, stimulated emission and lasing action via random scattering and feedback. The la...

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confidence: 99%

Soliton-assisted random lasing in optically-pumped liquid crystals

Perumbilavil

Piccardi

Buchnev

et al. 2016

Applied Physics Letters

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“…Prospective of random lasing is however strongly hindered by the absence of emission control: random lasers are highly multimode with unpredictable lasing frequencies and polydirectional output. Manipulation of the underlying random structure [14][15][16][17][18][19][20][21][22][23] and recent work constraining the range of lasing frequencies [24,25] have resulted in significant progress toward possible control. However, the ability to choose a specific frequency in generic random lasing systems has not yet been achieved.…”

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confidence: 99%

Taming Random Lasers through Active Spatial Control of the Pump

et al. 2012

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Active control of the pump spatial profile is proposed to exercise control over random laser emission. We demonstrate numerically the selection of any desired lasing mode from the emission spectrum. An iterative optimization method is employed, first in the regime of strong scattering where modes are spatially localized and can be easily selected using local pumping. Remarkably, this method works efficiently even in the weakly scattering regime, where strong spatial overlap of the modes precludes spatial selectivity. A complex optimized pump profile is found, which selects the desired lasing mode at the expense of others, thus demonstrating the potential of pump shaping for robust and controllable singlemode operation of a random laser.PACS numbers: 42.55. Zz,42.25.Dd Multiple scattering of light in random media can be actively manipulated through spatial shaping of the incident wavefront [1]. This technique has allowed advances in focusing [2][3][4], and imaging [5,6], paving the road to actual control of light transport in strongly scattering media [7][8][9]. Introducing gain in disordered media allows amplification of multiply scattered light, leading to the observation of random lasing [10]. The broad range of systems where it has been studied [11] and the fundamental questions it has raised [12,13] has captivated the community for this last decade. Prospective of random lasing is however strongly hindered by the absence of emission control: random lasers are highly multimode with unpredictable lasing frequencies and polydirectional output. Manipulation of the underlying random structure [14][15][16][17][18][19][20][21][22][23] and recent work constraining the range of lasing frequencies [24,25] have resulted in significant progress toward possible control. However, the ability to choose a specific frequency in generic random lasing systems has not yet been achieved. The spatial profile of the pump is an interesting degree of freedom readily available in random laser (e.g., [26,27]). In a regime of very strong scattering where the modes of the random system are spatially localized [28], local pumping allows selection of spatially non-overlapping modes [29,30]. In weaker scattering media however (e.g., [31][32][33]), several hurdles appear toward achieving fine control. Selecting modes is complicated by a narrow distribution of lasing thresholds [34,35] and spatial mode overlap. Increased pumping required in these lossy systems begins to alter the random laser itself. Moreover, modifying the shape of the pump introduces changes to both the spatial and spectral properties of lasing modes [33,[36][37][38]. Such difficulties are typically absent in more conventional lasers, which have employed pump shaping, both electrically [39][40][41][42] and optically [43], to select favorable lasing modes. The question is, can shaping of the incident pump field achieve taming of random lasers?In this letter, we exercise control over the distribution of lasing thresholds via the pump geometry to choose the random laser em...

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“…7 The most extensively studied LC phase for random lasers, however, is the nematic phase. [8][9][10][11][12][13] In random lasers, an important parameter is the transport mean free path l, which is defined as the distance a photon travels before its direction is randomized, because it influences the excitation threshold for laser emission. This property, which is also inversely proportional to the scattering cross-section, is sensitive to external fields in nematic LCs.…”

Section: Introductionmentioning

confidence: 99%

“…This property, which is also inversely proportional to the scattering cross-section, is sensitive to external fields in nematic LCs. Consequently, reports have typically focused on thermally, [8][9][10] optically, 12 and electrically 13 driven changes in the scattering properties and the subsequent effect they have on the laser characteristics. There have also been studies carried out on the statistical properties of the emission from dye-doped nematic random lasers.…”

Section: Introductionmentioning

confidence: 99%

Lowering the excitation threshold of a random laser using the dynamic scattering states of an organosiloxane smectic A liquid crystal

Morris

Gardiner

Qasim

et al. 2012

Journal of Applied Physics

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Smectic A liquid crystals, based upon molecular structures that consist of combined siloxane and mesogenic moieties, exhibit strong multiple scattering of light with and without the presence of an electric field. This paper demonstrates that when one adds a laser dye to these compounds it is possible to observe random laser emission under optical excitation, and that the output can be varied depending upon the scattering state that is induced by the electric field. Results are presented to show that the excitation threshold of a dynamic scattering state, consisting of chaotic motion due to electro-hydrodynamic instabilities, exhibits lower lasing excitation thresholds than the scattering states that exist in the absence of an applied electric field. However, the lowest threshold is observed for a dynamic scattering state that does not have the largest scattering strength but which occurs when there is optimization of the combined light absorption and scattering properties.

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A temperature-tunable random laser

Cited by 334 publications

References 12 publications

Soliton-assisted random lasing in optically-pumped liquid crystals

Soliton-assisted random lasing in optically-pumped liquid crystals

Taming Random Lasers through Active Spatial Control of the Pump

Lowering the excitation threshold of a random laser using the dynamic scattering states of an organosiloxane smectic A liquid crystal

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