Soliton-assisted Random Lasing in Nematic Liquid Crystals

Random lasers are resonator-less light sources where the optical feedback for lasing arises from recurrent multiple scattering events in a disordered gain medium. During the past 20 years, random lasers have been the subject of intense theoretical and experimental investigations due to their novelty, simplicity and ruggedness as well as their great potential for applications ranging from imaging to biomedical diagnostics. Common random lasers, however, tend to emit light in a wide range of directions with poor beam quality. The lack of pre-determined directionality and its control along with poor spatial characteristics hinder the applications of random lasers in many fields.It has been shown that dye-doped nematic liquid crystals can random lase when optically pumped within the absorption region of the dye molecules. Moreover, through molecular reorientation they support the propagation of self-guided optical beams, known as nematicons, which act as real-time graded-index optical waveguides.In order to address the problems of conventional random lasers, this Thesis focuses on the demonstration of a configuration were an efficient random laser with directional output is realized in dye-doped nematic liquid crystals by combing optical gain, random scattering, and nematicons. A planar cell filled with a mixture of commercial E7 nematic liquid crystals (host) and PM 597 (guest) is used as the material. A near infrared continuous-wave beam is used to launch a nematicon, while a 6 ns pulsed beam at 532 nm is used to optically pump the material. The synergy of random lasing and nematicons in this geometry provides several breakthrough results.By adopting a pumping geometry collinear with the nematicon, we demonstrate random laser emission from the initial region of the nematicon. The nematicon waveguide provides transverse confinement to the emitted photons, resulting in directionality, high photon collection, and high slope efficiency. The nematicon also modulates the emission, allowing the realization of a random transistor laser, where a low-power continuous-wave input is able to lower the threshold for lasing.By taking advantage of the response of nematicons to external stimuli, we also demonstrate a random laser emitting in a voltage-controlled direction. Finally, we demonstrate in-plane random laser steering by external magnetic field. The latter approach allows us to steer the random laser beam over 14°

Leadership Strategies to Influence Employee Engagement in Health Care

Hospitals are in a precarious financial position with declining reimbursement, eroding profit margins, and low patient satisfaction. The Patient Protection and Affordable Care Act of 2010 reform may decrease hospital reimbursement by $500 billion from 2010 to 2020, while low patient satisfaction may decrease profitability for hospitals by 27%. Employee disengagement may decrease patient satisfaction and consumer loyalty. The purpose of this phenomenological study was to explore the lived experiences of health care leaders as they worked to engage employees and provide better patient care. Improving patient care provides opportunities to capture new market shares, which increases sustainability of health care organizations. Expectancy theory shaped the conceptual framework of this study. Inquiry consisted of personal interviews with 23 mid-level hospital managers. Data analysis occurred with a modified Van Kamm data analysis process, which entailed descriptive coding and sequential review of the interview transcripts. Member checks and data saturation ensured trustworthiness of the findings. The findings from these personal interviews led to discovery of 4 themes of leader-employee engagement to include psychological commitment, expectation realization, trust actualization, and reduction in the leadership power distance. By applying employee engagement strategies aligned with these themes, leaders may influence patient care. This study contributes to social change by increasing health care quality for patients leading to a positive influence on medical care and societal health

Soliton-assisted random lasing in optically-pumped liquid crystals

We demonstrate a guided-wave 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.See also erratum at:Appl. Phys. Lett. 110, 019902 (2017); https://doi.org/10.1063/1.4973864<br/

Enhanced Ultrafast Nonlinear Optical Response in Ferrite Core/Shell Nanostructures with Excellent Optical Limiting Performance

Nonlinear optical nanostructured materials are gaining increased interest as optical limiters for various applications, although many of them suffer from reduced efficiencies at high-light fluences due to photoinduced deterioration. The nonlinear optical properties of ferrite core/shell nanoparticles showing their robustness for ultrafast optical limiting applications are reported. At 100 fs ultrashort laser pulses the effective two-photon absorption (2PA) coefficient shows a nonmonotonic dependence on the shell thickness, with a maximum value obtained for thin shells. In view of the local electric field confinement, this indicates that core/shell is an advantageous morphology to improve the nonlinear optical parameters, exhibiting excellent optical limiting performance with effective 2PA coefficients in the range of 10 cm W (100 fs excitation), and optical limiting threshold fluences in the range of 1.7 J cm. These values are comparable to or better than most of the recently reported optical limiting materials. The quality of the open aperture Z-scan data recorded from repeat measurements at intensities as high as 35 TW cm, indicates their considerably high optical damage thresholds in a toluene dispersion, ensuring their robustness in practical applications. Thus, the high photostability combined with the remarkable nonlinear optical properties makes these nanoparticles excellent candidates for ultrafast optical limiting applications

Soliton-assisted Random Lasing in Nematic Liquid Crystals

Random lasers are resonator-less light sources where the optical feedback for lasing arises from recurrent multiple scattering events in a disordered gain medium. During the past 20 years, random lasers have been the subject of intense theoretical and experimental investigations due to their novelty, simplicity and ruggedness as well as their great potential for applications ranging from imaging to biomedical diagnostics. Common random lasers, however, tend to emit light in a wide range of directions with poor beam quality. The lack of pre-determined directionality and its control along with poor spatial characteristics hinder the applications of random lasers in many fields.It has been shown that dye-doped nematic liquid crystals can random lase when optically pumped within the absorption region of the dye molecules. Moreover, through molecular reorientation they support the propagation of self-guided optical beams, known as nematicons, which act as real-time graded-index optical waveguides.In order to address the problems of conventional random lasers, this Thesis focuses on the demonstration of a configuration were an efficient random laser with directional output is realized in dye-doped nematic liquid crystals by combing optical gain, random scattering, and nematicons. A planar cell filled with a mixture of commercial E7 nematic liquid crystals (host) and PM 597 (guest) is used as the material. A near infrared continuous-wave beam is used to launch a nematicon, while a 6 ns pulsed beam at 532 nm is used to optically pump the material. The synergy of random lasing and nematicons in this geometry provides several breakthrough results.By adopting a pumping geometry collinear with the nematicon, we demonstrate random laser emission from the initial region of the nematicon. The nematicon waveguide provides transverse confinement to the emitted photons, resulting in directionality, high photon collection, and high slope efficiency. The nematicon also modulates the emission, allowing the realization of a random transistor laser, where a low-power continuous-wave input is able to lower the threshold for lasing.By taking advantage of the response of nematicons to external stimuli, we also demonstrate a random laser emitting in a voltage-controlled direction. Finally, we demonstrate in-plane random laser steering by external magnetic field. The latter approach allows us to steer the random laser beam over 14°

All-optical guided-wave random laser in nematic liquid crystals

Spatial solitons can affect and enhance random lasing in optically-pumped dyedoped nematic liquid crystals. Upon launching two collinear beams in the sample, the first to pump the fluorescent guest molecules and the second to induce a reorientational soliton, strikingly the second beam not only guides the emitted photons in the soliton waveguide, but also enhances the lasing efficiency and modulates its spectral width. By altering the scattering paths of the emitted photons, the soliton also contributes to the selection of the lasing modes, as further confirmed by the observed kinks in the input/output characteristics. These experimental results demonstrate that random lasing can be efficiently controlled by a light beam which does not interact with the gain molecules, opening a route towards light-controlled random lasers

Spatial solitons to mold random lasers in nematic liquid crystals [Invited]

Dye-doped nematic liquid crystals support random lasing under optical pumping, as well as reorientational optical spatial solitons acting as all-optical waveguides. By synergistically combining these two responses in a collinear pump-soliton geometry, the resulting soliton-enhanced random laser exhibits higher conversion efficiency and better directional properties. After a short account on random lasers and solitons in nematic liquid crystals–nematicons–we describe our experimental results on nematicon-molded random lasers