Thermal Nonlinearity Research Articles

Solitons in liquid crystals with competing nonlinearities

We employ a model which is proposed by P. S. Jung et al. [see P. S. Jung et al. Opt. Express 25 (2017) 23893–23897] to analytically demonstrate properties of individual bright solitons in liquid crystals with competing nonlinearities. These results are confirmed by the numerical simulations. In addition, we numerically find that the competition between thermal and reorientational nonlinearities can lead to the formation of bright or dark-like solitons whose formation depends on the intensity profiles of the input beams. We show that the competing nonlinearities drastically affect the interaction of out-of-phase bright solitons, such as the change of attraction of out-of-phase bright solitons into repulsion force at certain initial separations of the input solitons.

Soliton bursts and deterministic dissipative Kerr soliton generation in auxiliary-assisted microcavities

Dissipative Kerr solitons in resonant frequency combs offer a promising route for ultrafast mode-locking, precision spectroscopy and time-frequency standards. The dynamics for the dissipative soliton generation, however, are intrinsically intertwined with thermal nonlinearities, limiting the soliton generation parameter map and statistical success probabilities of the solitary state. Here, via use of an auxiliary laser heating approach to suppress thermal dragging dynamics in dissipative soliton comb formation, we demonstrate stable Kerr soliton singlet formation and soliton bursts. First, we access a new soliton existence range with an inverse-sloped Kerr soliton evolution—diminishing soliton energy with increasing pump detuning. Second, we achieve deterministic transitions from Turing-like comb patterns directly into the dissipative Kerr soliton singlet pulse bypassing the chaotic states. This is achieved by avoiding subcomb overlaps at lower pump power, with near-identical singlet soliton comb generation over twenty instances. Third, with the red-detuned pump entrance route enabled, we uncover unique spontaneous soliton bursts in the direct formation of low-noise optical frequency combs from continuum background noise. The burst dynamics are due to the rapid entry and mutual attraction of the pump laser into the cavity mode, aided by the auxiliary laser and matching well with our numerical simulations. Enabled by the auxiliary-assisted frequency comb dynamics, we demonstrate an application of automatic soliton comb recovery and long-term stabilization against strong external perturbations. Our findings hold potential to expand the parameter space for ultrafast nonlinear dynamics and precision optical frequency comb stabilization.

Preparation and optoelectronic studies of the organic compound [2-(2,3-dimethyl phenylamino)-N-Phenyl benzamide doped(PMMA)

The optical characteristics of organic compound, 2- (2,3-dimethyl phenylamino)-N-Phenyl benzamide, for two configurations, compound solution and compound doped PMMA as a film have been investigated. The compound was characterized by elemental analysis, FTIR, 1HMR, 13CNMR and theoretical study by using AM1-semi-empirical method. The optical properties were studied by using microscopic image surface, Fourier Transform Infrared (FT-IR), Atomic Force Microscopy images and an Ultraviolet–visible spectrometer. The thermal optical nonlinearity of organic compound has been studied by using Diode laser with the wavelength 473 nm. The samples were prepared by the microwave irradiation under solvent free condition within short time and appreciable yields. The Morphological structure dependence of the optoelectronic properties was also studied. The values of optical energy gaps to the direct ( $$E_{g}^{d}$$ ) and indirect ( $$E_{g}^{in}$$ ) for the compound doped film estimated to be 2.99 eV, 2.75 eV respectively. Optically smooth and homogeneous 2-(2,3-dimethyl phenylamino)-N-Phenyl benzamide doped Poly methyl methacrylate (PMMA) film was experimentally investigated for the surface distribution by scan with 2θ. Also, the spatial self-phase modulation (SSPM) is characterized. The observed induced patterns have been simulated numerically by using Fresnel-Kirchhoff’s theory. The value of nonlinear refractive index n2 in the case of compound solution is confirmed to have less value than in a compound doped film.

Tail-free self-accelerating solitons and vortices

Self-accelerating waves in conservative systems, which usually feature slowly decaying tails, such as Airy waves, have drawn great interest in studies of quantum and classical wave dynamics. They typically appear in linear media, while nonlinearities tend to deform and eventually destroy them. We demonstrate, by means of analytical and numerical methods, the existence of robust one- and two-dimensional (1D and 2D) self-accelerating tailless solitons and solitary vortices in a model of two-component Bose-Einstein condensates, dressed by a microwave (MW) field, whose magnetic component mediates long-range interaction between the matter-wave constituents, with the feedback of the matter waves on the MW field taken into account. In particular, self-accelerating 2D solitons may move along a curved trajectory in the coordinate plane. The system may also include the spin-orbit coupling between the components, leading to similar results for the self-acceleration. The effect persists if the contact cubic nonlinearity is included. A similar mechanism may generate 1D and 2D self-accelerating solitons in optical media with thermal nonlinearity.

Impact of thinning the GaN buffer and interface layer on thermal and electrical performance in GaN-on-diamond electronic devices

We demonstrate that GaN-on-diamond technology with an ultra-thin GaN buffer and interface layer offers excellent thermal resistance alongside good electrical performance. Two device sets were investigated, one with 354 nm thick GaN buffer and 17 nm thick interface layers, the other with 700 nm thick GaN buffer and 36 nm thick interface layers. The samples demonstrate excellent thermal resistances of 9 ± 1 K/(W/mm) and 10.0 ± 0.5 K/(W/mm), respectively. Trade-offs between GaN buffer thickness and effective thermal boundary resistance are discussed demonstrating pathways for the advancement of GaN-on-diamond technology. IV measurements show low trapping and reduced thermal non-linearity in devices with ultra-thin GaN layers.

A Resistorless High-Precision Compensated CMOS Bandgap Voltage Reference

A resistorless high-precision compensated CMOS bandgap voltage reference (BGR), which is compatible with a standard CMOS process, is presented in this paper. A higher-order curvature correction method called base-emitter voltage linearization is adapted to directly compensate the thermal nonlinearity of base–emitter voltage. With proper mathematical operations of high-order temperature currents, most of the nonlinear temperature terms in $V_{\mathrm {BE}}$ can be greatly eliminated. The proposed BGR, which is implemented in 0.35- $\mu \text{m}$ CMOS technology, is capable of working down to 2 V supply voltages with 1.14055 V mean output voltage. A minimum temperature coefficient of 1.01 ppm/°C with a temperature range from −40 °C to 125 °C is realized, and a power-supply noise attenuation of 61 dB is achieved without any filter capacitors. The line regulation is better than 2 mV/V from 2 V to 5 V supply voltage while dissipating a maximum supply current of $33~\mu \text{A}$ . The active area of the presented BGR is 180 $\mu \text {m}\times 220\,\,\mu \text{m}$ .

Nonlinear electrochemical and electrokinetic effects in 3omega hot wire measurements of thermophysical properties of nanofluids

This work focuses on the nonlinear electrochemical (EC) activity of fluids and its impact on the accuracy of their thermophysical property measurements using the transient or periodically modulated hot wire method (THW or 3ωHW). This underestimated source of errors becomes crucial for nanofluids, where the thermal conductivity enhancement coefficient (k/k0 − 1) is small, requiring high-resolution measurements (below 1%). Theoretical predictions combining thermal and EC nonlinearities are confronted to experimental results obtained with two variants of 3ω cells. Water-based nanofluids (TiO2 and Al2O3) and water solutions of acetic acid, sodium hydroxide and sodium chloride were tested. The two classes of samples show different 3ω amplitude and phase behaviors, which is attributed to additional electrokinetic effects in nanofluids. For all studied samples an anti-correlation between the magnitude of the harmonics and the dc electrical resistivity of the samples was observed. A simple estimation method of 3ωHW errors is proposed consisting in measuring the 2nd harmonic in addition to the 3rd one. The combination of 2nd and 3rd harmonics allowed determining the nonlinearity coefficient which quantitatively characterizes the EC activity of samples. Eventually, the radical solution to avoid the discussed sources of errors is to use an electrically insulated hot wire sensor.

Interplay of Thermo-Optic and Reorientational Responses in Nematicon Generation.

Employing several nematic liquid crystal mixtures, we investigate how the thermo-optic response of nonlinear birefringent soft-matter affects the propagation of light beams and the features of self-induced waveguides. We address the formation of optical spatial solitons and the control of their trajectories versus temperature, comparing the measurements with the expectations based on a simplified model, showing an excellent agreement. Moreover, in a guest–host mixture with an absorbing dye dopant, we study the competition between reorientational and thermal nonlinearities, demonstrating that the two processes can be adjusted independently in order to tune the soliton properties, i.e., trajectory and confinement strength. Our results are an important contribution to better comprehend the role played by material properties on linear and nonlinear beam propagation, as well as their exploitation for signal processing and addressing.

Strong reverse saturable absorption and negative nonlinear refractive index in S and N co-doped GQDs at 532 nm CW laser

In this study, a bottom up pyrolysis approach is pursued in the preparation of sulphur: nitrogen co-doped graphene quantum dots (SN-GQDs). For the first time, 5V direct current light emitting diode (LED) is used as an excitation source and the influence of solvent’s nature such as dipole moment and polarity on fluorescence is studied. The investigated third order nonlinear optical behaviour reveals a strong reverse saturable absorption (RSA) and negative nonlinear refractive (NLR) index at 532 nm wavelength of continuous wave (CW) laser. The thermal nonlinearity in closed aperture is addressed employing thermal lens model.

Third order nonlinear optical properties of monoclinic and orthorhombic CuNb2O6 under CW laser illumination

Third-order nonlinearity of monoclinic and orthorhombic phase of CuNb2O6 is studied in low power regime of 532 nm by Z-scan technique. In open aperture, monoclinic CuNb2O6 possess stronger saturable absorption due to the distorted structure arising from unequal arrangement of copper atoms. Closed aperture exposes the self-defocusing nature and orthorhombic phase exhibits stronger nonlinear refraction. Variation in third-order NLO coefficient due to change in phase and morphology of CuNb2O6 confirms the influence of sintering temperature and time. Microrod monoclinic CuNb2O6 possess maximum nonlinear absorption coefficient (6.47 × 10−3 cm/W) and pure orthorhombic CuNb2O6 attains maximum nonlinear refractive index (5.13 × 10−8 cm2/W) along with higher third-order nonlinear optical susceptibility (1.91 × 10−6 esu). Higher thermal nonlinearity resulted in stronger optical limiting action with pure orthorhombic CuNb2O6 (5.16 mW, 1.26 mW) compared to other phases. For understanding the material suitability for laser safety device, nonlinearity and limiting action of CuNb2O6 thin films were demonstrated. Earlier formation of monoclinic phase with morphology change (700 °C) and transition of monoclinic rich mixed orthorhombic phase to pure orthorhombic phase (900 °C) with increase in sintering time (3–12 h) was confirmed by XRD, FTIR and SEM analysis. Thus orthorhombic CuNb2O6 material with stronger self-defocusing and optical limiting action makes it more preference than monoclinic CuNb2O6 for third-order NLO applications.

Solidification behavior of binary eutectic phase change material in a vertical finned thermal storage system dispersed with graphene nano-plates

Thermal energy storage systems (TES) find their extensive application in industrial and solar-powered thermal systems due to their high energy storage density and ability to deliver heat at isothermal conditions. But, the lower thermal conductivity of phase change materials (PCM) reduces the overall rate of heat transfer. In the present work, solidification behavior in a medium temperature (160–200 °C) finned TES with varying proportion of Graphene nano plates (GNP) is presented. The effect of anisotropy, aspect ratio, concentration, interfacial thermal resistance and non-linearity has been included to evaluate the overall thermal conductivity of GNP-PCM composite. The objective of the present study is to enhance the solidification process of a binary eutectic salt LiNO3-KCl in an optimized finned TES dispersed with the different volume fraction of GNP. The detailed experimentation process starts with the preparation of binary eutectic mixture, followed by dynamic Differential scanning calorimetry analyses along with rheology testing. Empirical correlations have been developed using quadratic and cubic polynomials for viscosity and specific heat respectively. Several numerical models are analyzed to study the solidification enhancement of binary eutectic PCM using the real-time plant data of a high-temperature solar absorption chiller. Effects of Stefan and Reynolds number on the thermal performance of storage system has also been studied. Reducing the Stefan number and increasing the Reynolds number of heat transfer fluid (HTF) results in enhancing the rate of solidification process. It has been observed that natural convection currents enhances the rate of solidification and causes faster solidification in the upper annulus of TES. A reduction of 49% in the solidification time has been observed with finned TES dispersed with 5% GNP as compared to pure binary eutectic PCM.

Thermal nonlinearities for three curcuminoids measured by diffraction ring patterns and Z-scan under visible CW laser illumination

The Gaussian visible Continuous-wave (CW) laser beam propagation in three curcuminoids compounds has led to diffraction ring patterns. These patterns believed to be originated due to self-phase modulation. The study focuses on the effect of input power on the diffraction ring patterns. As a result of increasing input power each circular ring pattern flattened in the upper part due to the convection. These results are reproduced numerically using the Fresnel-Kirchhoff integral. It appears that each ring pattern evolve with time from circular to flattened ones. The thermal nonlinear refractive indexes of the curcuminoids are calculated based on diffraction ring patterns and the Z-scan technique.

Frictional heating of the brake disc with essential nonlinearity thermal barrier coating

A mathematical model to investigate temperature field distributions in a brake disc with thermal barrier coating (TBC) was proposed. For this purpose, a one-dimensional boundary-value heat conduction problem was formulated for the coating (TBC) - substrate (disc) system. It was assumed that the materials of both the coating and the substrate are thermally sensitive and characterized by essential thermal nonlinearity. The surface of the coating was heated by a heat flux with intensity proportional to the friction power during single braking. Thermal contact between the coating and substrate is perfect. The solution to the problem was obtained by means of an integro-interpolation variant of the method of lines and the DIFSUB package for numerical solving of systems of ordinary differential equations. Quasi-static thermal stresses in the strip with taking into account change in temperature mechanical properties, were determined, too. Numerical analysis was conducted for a coating made from Yttria-Stabilized Zirconium ZrO2–3Y2O3 (YSZ) deposited on an AISI 1040 steel disc.

Four-wave mixing on thermal nonlinearity in a scheme with positive feedback

The influence of feedback for both signal and object waves on the amplitude reflection coefficient of a four-wave radiation converter on thermal nonlinearity has been considered. The dependences of the reflection coefficient of a four-wave converter on the parameters of a ring-type resonator, which provides the feedback, and the pump intensity have been obtained and analyzed. It was shown that the use of a ring-type resonator allows one to increase the reflection coefficient of a four-wave radiation converter on thermal nonlinearity by several times.

Thermal nonlinear optical response of meso-tetraphenylporphyrin under aggregation conditions versus that in the absence of aggregation

In this work, measurement of thermally induced nonlinear refractive index of meso-tetraphenylporphyrin (H2TPP) at different concentrations in 1,2-dicoloroethane using a double-grating interferometer set-up in a pump–probe configuration is reported. The formation of aggregates of H2TPP at concentrations greater than ca. 5 × 10−5 M was evident by deviation from Beer’s law. An almost focused pump beam passes through the solution. A part of the pump beam energy is absorbed by the sample and therefore a thermal lens is generated in the sample. An expanded probe beam propagates through the sample and indicates the sample refractive index changes. Just after the sample a band-pass filter cuts off the pump beam from the path but the distorted probe beam passes through a double-grating interferometer consisting of two similar diffraction gratings with a few centimetres distance. A CCD camera is installed after the interferometer in which on its sensitive area two diffraction orders of the gratings are overlying and producing interference pattern. The refractive index changes of the sample are obtained from the phase distribution of the successive interference patterns recorded at different times after turning on of the pump beam using Fourier transform method. In this study, for different concentrations of H2TPP in 1,2-dichloroethane solution the thermal nonlinear refractive index is determined. Also, we present the measurement of the temperature changes induced by the pump beam in the solution. We found that value of nonlinear refractive index increased by increasing the concentration up to a concentration of 5 × 10−4 M and then decreased at higher concentrations. In addition, we have investigated the stability of the observed thermal nonlinearity after a period of two weeks from the sample preparation.

Temporal Dynamics of Localized Exciton-Polaritons in Composite Organic-Plasmonic Metasurfaces.

We use femtosecond transient absorption spectroscopy to study the temporal dynamics of strongly coupled exciton-plasmon polaritons in metasurfaces of aluminum nanoantennas coated with J-aggregate molecules. Compared with the thermal nonlinearities of aluminum nanoantennas, the exciton-plasmon hybridization introduces strong ultrafast nonlinearities in the composite metasurfaces. Within femtoseconds after the pump excitation, the plasmonic resonance is broadened and shifted, showcasing its high sensitivity to excited-state modification of the molecular surroundings. In addition, we observe temporal oscillations due to the deep subangstrom acoustic breathing modes of the nanoantennas in both bare and hybrid metasurfaces. Finally, unlike the dynamics of hybrid states in optical microcavities, here, ground-state bleaching is observed with a significantly longer relaxation time at the upper polariton band.

Thermal Nonlinearity of Functionalized Graphene Enhanced by Gold Nanorods

Thermal Nonlinearity of Functionalized Graphene Enhanced by Gold Nanorods

Metal nanospheres under intense continuous-wave illumination: A unique case of nonperturbative nonlinear nanophotonics.

We show that the standard perturbative (i.e., cubic) description of the thermal nonlinear response of a single metal nanosphere to intense continuous-wave (CW) illumination is sufficient only for a temperature rise of up to 100 degrees above room temperature. Beyond this regime, the slowing down of the temperature rise requires a nonperturbative description of the nonlinear response, even though the permittivity is linearly dependent on the temperature and despite the deep subwavelength effective propagation distances involved. Using experimental data, we show that, generically, the increase of the imaginary part of the metal permittivity dominates the increase of the host permittivity as well as the resonance shift due to the joint changes to the real parts of the metal and host. Thus, the main nonlinear effect is a decrease of the quality factor of the resonance. We further analyze the relative importance of the various contributions to the temperature rise and thermal nonlinearity, compare the nonlinearity of Au and Ag, demonstrate the potential effect of the nanoparticle morphology, and show that although the thermo-optical nonlinearity of the host typically plays a minor role, its thermal conductivity and its temperature dependence is important. Finally, we discuss the differences between CW and ultrafast thermal nonlinearities.

Nonlinear continuous-wave optical propagation in nematic liquid crystals: Interplay between reorientational and thermal effects.

We investigate nonlinear optical propagation of continuous-wave (CW) beams in bulk nematic liquid crystals. We thoroughly analyze the competing roles of reorientational and thermal nonlinearity with reference to self-focusing/defocusing and, eventually, the formation of nonlinear diffraction-free wavepackets, the so-called spatial optical solitons. To this extent we refer to dye-doped nematic liquid crystals in planar cells excited by a single CW beam in the highly nonlocal limit. To adjust the relative weight between the two nonlinear responses, we employ two distinct wavelengths, inside and outside the absorption band of the dye, respectively. Different concentrations of the dye are considered in order to enhance the thermal effect. The theoretical analysis is complemented by numerical simulations in the highly nonlocal approximation based on a semi-analytic approach. Theoretical results are finally compared to experimental results in the Nematic Liquid Crystals (NLC) 4-trans-4'-n-hexylcyclohexylisothiocyanatobenzene (6CHBT) doped with Sudan Blue dye.

Study of Nonlinear Optical Properties of Disperse Yellow – 7 Dye-doped Polymer Films using CW Laser

The materials with an ability of self-focusing/defocusing through their light intensitydependent refractive index and phase shift properties are potential candidates for all-optical photonic devices. Several organic materials including dye-doped polymer films are attracting many researchers due to their advantages in terms of enhanced efficiency, and acceptable mechanical properties to fabricate useful devices. In this paper, we have reported the nonlinear optical properties like nonlinear absorption and nonlinear refraction of an organic dye Disperse Yellow - 7 (DY-7) doped in Polymethyl methacrylate-methacrylic acid (PMMA-MA) polymer matrix using open aperture and closed aperture Z-scan experimental methods by means of low power continuous wave (CW) laser beam. The optical limiting properties of these films are also studied using Type 1 and Type 2 configurations at different input powers using continuous wave (CW) laser beams of 532 nm wavelength. The nonlinear refractive index n2, nonlinear absorption coefficient β, changes in refractive index with input intensity, and the magnitude of third-order optical nonlinearity of the dye-doped film are experimentally determined. The sample is tested for optical power limiting in which the input limiting threshold and saturated output power level for both type 1 and type 2 optical limiting configurations are recorded. DY-7 dye-doped in PMMA-MA polymer film has shown saturation absorption at lower input irradiance and reverse saturation absorption at higher input irradiance along with thermal nonlinearity and hence found to be a potential candidate for the third harmonic property based photonic devices.