Role of the sample thickness on the performance of cholesteric liquid crystal lasers: Experimental, numerical, and analytical results

Sanz-Enguita, Gerardo; Ortega, J.; Folcia, C. L.; Aramburu, I.; Etxebarría, J.

doi:10.1063/1.4942010

Cited by 17 publications

(8 citation statements)

References 26 publications

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“…We finish this section by giving a link between

and the threshold energy per pulse E th in order to compare the previous theoretical analysis with experimentally measurable quantities. In the case of nanosecond or picosecond pump pulses, an approximate analytical expression for E th was obtained by Sanz-Enguita et al [ 10 ]

where h is Planck’s constant. This equation was deduced from the kinetic equations of the excited state populations of dyes and emitted light developed by Shtykov and Palto [ 40 ].…”

Section: Theoretical Analysis Of Different Cell Architecturesmentioning

confidence: 99%

“…In fact, when CLCs are doped with fluorescent dyes, mirrorless laser generation can be obtained at the edges of the PBG. Since the discovery of laser emission in CLCs by Kopp et al in 1998 [ 1 ], many efforts have been made to build up CLC lasers with increasing performance and durability [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ].…”

Section: Introductionmentioning

confidence: 99%

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Upgrading the Performance of Cholesteric Liquid Crystal Lasers: Improvement Margins and Limitations

2017

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The topic of cholesteric-liquid-crystal lasers is a rapidly expanding research area in the field of soft-matter photonics. The increasing interest in this field is due to the high versatility that these lasers may possibly present and the prospects of giving rise to new miniaturized devices. However, further improvements in their operation capabilities are still required for potential applications. In this paper, we critically analyze the main strategies proposed up to now to optimize their performance. We show theoretically and experimentally that possible innovations in the device structure cannot produce lasers with threshold energies below a certain limit. This limit is determined by the light scattering and absorption losses inside the liquid crystal. Even assuming the case of samples free of defects and perfectly non-absorbing, an intrinsic light scattering, typical of mesogens, still remains. Numerical estimates of the thresholds indicate that these lasers could hardly be driven by compact light sources such as current electroluminescent or light-emitting diodes. Since the improvement possibilities regarding cell architecture seem to be exhausted, the advance must come from the use of new dye molecules. These molecules should show enhanced emission cross-sections and be efficiently integrable within the mesogenic solvent. In addition, the fluorescent systems must present very small quantum yields to triplet states if continuous-wave lasing is sought. In this respect, quantum dots are an alternative to explore for further investigations.

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“…We finish this section by giving a link between

where h is Planck’s constant. This equation was deduced from the kinetic equations of the excited state populations of dyes and emitted light developed by Shtykov and Palto [ 40 ].…”

Section: Theoretical Analysis Of Different Cell Architecturesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Upgrading the Performance of Cholesteric Liquid Crystal Lasers: Improvement Margins and Limitations

2017

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Section: Resultsmentioning

confidence: 99%

“…The dependence of lasing threshold on particle size can be attributed to changes in the resonant strength of the CLC cavity and the amount of nonquenched dye available for stimulated emission. , Analytical forms for lasing threshold originate from the laser rate equations and/or density of state considerations, but result in the following dependence on particle diameter: E th = Ad + B / d 2 , where E th is lasing threshold, d is particle diameter, and A and B are constants. Increasing the particle size increases the number of periods of the molecular helix within the droplet, thereby enhancing coherent scattering and increasing both the amplitude of the Bragg reflectance and the efficiency of the resonant cavity, Q .…”

Section: Resultsmentioning

confidence: 99%

Bioresorbable Microdroplet Lasers as Injectable Systems for Transient Thermal Sensing and Modulation

et al. 2021

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Minimally invasive methods for temperature sensing and thermal modulation in living tissues have extensive applications in biological research and clinical care. As alternatives to bioelectronic devices for this purpose, functional nanomaterials that self-assemble into optically active microstructures offer important features in remote sensing, injectability, and compact size. This paper introduces a transient, or bioresorbable, system based on injectable slurries of well-defined microparticles that serve as photopumped lasers with temperature-sensitive emission wavelengths (>4−300 nm °C−1 ). The resulting platforms can act as tissue-embedded thermal sensors and, simultaneously, as distributed vehicles for thermal modulation. Each particle consists of a spherical resonator formed by self-organized cholesteric liquid crystal molecules doped with fluorophores as gain media, encapsulated in thin shells of soft hydrogels that offer adjustable rates of bioresorption through chemical modification. Detailed studies highlight fundamental aspects of these systems including particle sensitivity, lasing threshold, and size. Additional experiments explore functionality as photothermal agents with active temperature feedback (ΔT = 1 °C) and potential routes in remote evaluation of thermal transport properties. Cytotoxicity evaluations support their biocompatibility, and ex vivo demonstrations in Casper fish illustrate their ability to measure temperature within biological tissues with resolution of 0.01 °C. This collective set of results demonstrates a range of multifunctional capabilities in thermal sensing and modulation.

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“…The gap region is located between pn e and pn o , where p is the pitch and n e and n o the extraordinary and ordinary refractive indices, respectively. The photonic character of CLCs is the basis for their application to build distributed feedback (DFB) lasers. − These lasers are made of CLC materials doped with fluorescent dyes whose emission spectra are significantly altered by the photonic structure. , …”

mentioning

confidence: 99%

Cone-Shaped Emissions in Cholesteric Liquid Crystal Lasers: The Role of Anomalous Scattering in Photonic Structures

2018

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The out-of-normal emission in cholesteric liquid-crystal lasers is studied experimental and theoretically. Apart from the well-known dominant laser in the direction of the helix axis, three other types of radiation, with cone-shaped spatial patterns, are identified and characterized. The physical mechanisms responsible for the different emissions are clarified. One of the radiations is a weak colorful lasing emission whose wavelength changes continuously depending on the propagation direction. The wavelengths of the other two radiations take place at the longwavelength and short-wavelength edges of the photonic bandgap. These emissions are attributed to an anomalous scattering phenomenon that gives rise to energy transfer from the main laser beam to some specific directions where the amount of final photonic states is high. An expression for the scattering cross section, reminiscent of Fermi's golden rule for spontaneous emission in photonic structures, is proposed. Some other phenomena independent of the lasing occurrence but driven by the anomalous scattering are briefly presented.

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Role of the sample thickness on the performance of cholesteric liquid crystal lasers: Experimental, numerical, and analytical results

Cited by 17 publications

References 26 publications

Upgrading the Performance of Cholesteric Liquid Crystal Lasers: Improvement Margins and Limitations

Upgrading the Performance of Cholesteric Liquid Crystal Lasers: Improvement Margins and Limitations

Bioresorbable Microdroplet Lasers as Injectable Systems for Transient Thermal Sensing and Modulation

Cone-Shaped Emissions in Cholesteric Liquid Crystal Lasers: The Role of Anomalous Scattering in Photonic Structures

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