Photothermal Model Research Articles

Plant responses to elevated temperatures: a field study on phenological sensitivity and fitness responses to simulated climate warming

Significant changes in plant phenology have been observed in response to increases in mean global temperatures. There are concerns that accelerated phenologies can negatively impact plant populations. However, the fitness consequence of changes in phenology in response to elevated temperature is not well understood, particularly under field conditions. We address this issue by exposing a set of recombinant inbred lines of Arabidopsis thaliana to a simulated global warming treatment in the field. We find that plants exposed to elevated temperatures flower earlier, as predicted by photothermal models. However, contrary to life-history trade-off expectations, they also flower at a larger vegetative size, suggesting that warming probably causes acceleration in vegetative development. Although warming increases mean fitness (fruit production) by ca. 25%, there is a significant genotype-by-environment interaction. Changes in fitness rank indicate that imminent climate change can cause populations to be maladapted in their new environment, if adaptive evolution is limited. Thus, changes in the genetic composition of populations are likely, depending on the species’ generation time and the speed of temperature change. Interestingly, genotypes that show stronger phenological responses have higher fitness under elevated temperatures, suggesting that phenological sensitivity might be a good indicator of success under elevated temperature at the genotypic level as well as at the species level.

Strongly tunable circular dichroism in gammadion chiral phase-change metamaterials

A metal/phase-change material/metal tri-layer planar chiral metamaterial in the shape of a gammadion is numerically modelled. The chiral metamaterial is integrated with Ge2Sb2Te5 phase-change material (PCM) to accomplish a wide tuning range of the circular dichroism (CD) in the mid-infrared wavelength regime. A photothermal model is used to study the temporal variation of the temperature of the Ge2Sb2Te5 layer and to show the potential for fast switching the phase of Ge2Sb2Te5 under a low incident light intensity of 0.016mW/μm2.

Non-radiative recombination process in BGaAs/GaAs alloys: Two layer photothermal deflection model

Photo-thermal deflection technique PTD is used to study the nonradiative recombination process in BGaAs/GaAs alloy with boron composition of 3% and 8% grown by metal organic chemical vapor deposition (MOCVD). A two layer theoretical model has been developed taking into account both thermal and electronic contribution in the photothermal signal allowing to extract the electronic parameters namely electronic diffusivity, surface and interface recombination. It is found that the increase of boron composition alters the BGaAs epilayers transport properties.

Rapid phase transition of a phase-change metamaterial perfect absorber

Phase-change materials (PCMs) have great potential in applications for data storage, optical switching and tunable photonic devices. However, heating the whole of the phase change material at a high speed presents a key challenge. Here, for the first time, we model the incorporation of the phase-change material (Ge2Sb2Te5) within a metamaterial perfect absorber (MMPA) and show that the temperature of amorphous Ge2Sb2Te5 can be raised from room temperature to > 900K (melting point of Ge2Sb2Te5) in just a few nanoseconds with a low light intensity of 150 W/m2, owing to the enhanced light absorption through strong plasmonic resonances in the absorber. Our structure is composed of an array of thin gold (Au) squares separated from a continuous Au film by a Ge2Sb2Te5 layer. A Finite Element Method photothermal model is used to study the temporal variation of temperature in the Ge2Sb2Te5 layer. It is also shown that an absorber with a widely tunable spectrum can be obtained by switching between the amorphous and crystalline states of Ge2Sb2Te5. The study lowers the power requirements for photonic devices based on a thermal phase change and paves the way for the realization of ultrafast photothermally tunable photonic devices.

EFFECTS OF TEMPERATURE AND PHOTOPERIOD ON GROWTH OF TWO LEUCOSPERMUM HYBRIDS

The aim of this study was to assess the growth of Leucospermum ‘Succession II’ (L. cordifolium × L. lineare) and L. ‘Tango’ (L. lineare × L. glabrum) cultivated in La Palma Island (Canary Islands). During the 2008 growing season, stem length measurements were weekly recorded in eight farms, in a range of altitudes from 600 to 867 m, located in most of the production areas of the island. These data were related with environmental conditions to assess if thermal (the growing degree days, the single triangle and the single sine) and photo-thermal models could be used to predict the end of the vegetative growth period of these cultivars. Base temperatures, photo-thermal and thermal units were calculated for both proteas. The model best adapted to ‘Succession II’ was the photothermal one as it showed the lowest coefficient of variation (7.42%), while for ‘Tango’ the lowest coefficient of variation (7.83%) was obtained using the growing degree days model. However, all models gave a good fit to the observed stem length data of both cultivars, although the coefficients of determination of the photo-thermal model were slightly higher than those of the thermal one. In conclusion, both models can be used to predict the date of the end of the vegetative growth of both Proteaceae.

Publisher’s Note: “Two-layer photo-thermal deflection model to study the non-radiative recombination process: Application to Ga0.7In0.3As0.23Sb0.77/GaSb and Al0.3Ga0.7As0.08Sb0.92/GaSb laser structures” [J. Appl. Phys. 113, 183705 (2013)

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Fabrication of periodic surface topographies via sequential photothermal laser microsintering of silicon nanoparticle films

Photothermal laser microprocessing is exploited in order to induce sintering and compaction of thin silicon nanoparticle (Si NP) films. Ethanolic dispersions of Si NPs with an average diameter of 45nm are spin-coated on silicon substrates yielding films with a thickness of about 400–500nm. Scanning electron and atomic force microscopy are used for characterization of the resulting surface morphologies. Sequential processing of the coated layer with a microfocused cw-laser beam at a wavelength of 532nm generates periodic surface structures. The periodicity of these structures is determined by the distance between adjacent laser-written lines. Despite a 1/e laser spot size of 1.4μm, fabrication of topographic surface structures with submicrometer periodicities is feasible. In particular, surface topographies with periodicities of 600nm and a topographic amplitude of 80nm are fabricated. These results point to a high nonlinearity, which is attributed to the strongly activated, temperature-dependent laser sintering process. These experimental observations are reproduced qualitatively considering a simple photothermal model and an activated sintering process. Prospects of photothermal laser microsintering of nanoparticle films to fabricate biomimetic surface structures are discussed.

Photothermal model fitting in the complex plane for thermal properties determination in solids

Thermal properties of solids are obtained by fitting the exact complex photothermal model to the normalized photoacoustic (PA) signal in the front configuration. Simple closed-form expressions for the amplitude and phase are presented in all frequency ranges. In photoacoustic it has been common practice to assume that all the absorptions of radiation take place in the sample. However, in order to obtain the accurate thermal properties it is necessary to consider the PA signal contributions produced at the cell walls. Such contributions were considered in our study. To demonstrate the usefulness of the proposed methodology, commercial stainless steel layers AISI 302 were analyzed. It is shown that using our approach the obtained thermal diffusivity and effusivity were in good agreement with those reported in the literature. Also, a detailed procedure for the calculation of the standard error in the thermal properties is discussed.

Ultraviolet laser deposition of graphene thin films without catalytic layers

In this letter, the formation of nanostructured graphene by ultraviolet laser ablation of a highly ordered pyrolytic graphite target under optimized conditions is demonstrated, without a catalytic layer, and a model for the growth process is proposed. Previously, graphene film deposition by low-energy laser (2.3 eV) was explained by photo-thermal models, which implied that graphene films cannot be deposited by laser energies higher than the C-C bond energy in highly ordered pyrolytic graphite (3.7 eV). Here, we show that nanostructured graphene films can in fact be deposited using ultraviolet laser (5 eV) directly over different substrates, without a catalytic layer. The formation of graphene is explained by bond-breaking assisted by photoelectronic excitation leading to formation of carbon clusters at the target and annealing out of defects at the substrate.

Highly selective CD44-specific gold nanorods for photothermal ablation of tumorigenic subpopulations generated in MCF7 mammospheres

Heterogeneous stem-like populations within tumor tissues are the primary suspects in causing cancer recurrence and malignancy. It is essential to selectively kill these tumorigenic populations. We created a novel system for photothermally ablating specific cells from three-dimensional mammospheres. A CD44-positive subpopulation, with tumorigenic and self-renewal potential, spontaneously arises in MCF7 breast cancer cell-engineered mammospheres. Using anti-CD44 antibody-linked gold nanorods, which strongly absorb near infrared light and increase local temperature, we effectively targeted and photo-ablated atypical cells. This biomarker-specific photothermal ablation model, using a smart nanoplatform, is a promising new strategy for selectively killing cancer cells, while sparing normal tissues.

Investigation of “Thermal Touch” Response of Coated Steel Plates Employing Square-Wave-Excited Photothermal Infrared Radiometry

When a person is touching an object, which is at a different temperature than the person’s body, heat starts to flow from the body to the object (or in the other direction), and as a result, the temperature of the skin starts to decrease (increase), leading to a cold (warm) perception of the object’s temperature. It is well accepted that the degree of thermal impact of touching the free surface of a bulk material is determined by the thermal effusivity of that material. In this study, the more complicated situation of touching a coating covering a substrate with different thermal properties is studied. Insight in the involved heat transport effects and their effect on the thermal touch is gained by a photothermal model experiment in which the effect of touching on the measured surface temperature, and from there, the calculated heat flux is mimicked by the effect of illumination by laser light.

A modelling approach for evaluating phenology and adaptation of two congeneric weeds (Bidens frondosa and Bidens tripartita)

The exotic species Bidens frondosa is rapidly spreading in northern Italian arable fields, while Bidens tripartita, a native congeneric, shows less invasive capacity. To characterise and model the phenology of the two species, a two-year study was conducted involving sowings at 15-day intervals between March and August. The length of the sowing-emergence phase was well described by a simple thermal model, with a base temperature of 4.5°C, for both species. A multiplicative photothermal model was found to be the best for the emergence-flowering phase. B. frondosa resulted as being less macrothermal and more sensitive to photoperiod. The flowering-maturity phase lasted for 30–32 days, on average, and was well described by a model based on soil water availability: this phase shortens when there is a lack of water, particularly in B. tripartita. The more relevant differences between the two species seem to be related to the vegetative phase length, which varied from 150 to 46 days and from 123 to 42 days in B. frondosa and B. tripartita, respectively. Thanks to the high elasticity of its vegetative phase, B. frondosa can grow taller than B. tripartita and acquire higher competitivity and seed production potential, both relevant factors in determining the success of a species.

Improving the optomechanical entanglement and cooling by photothermal force

Cooling and Entanglement in optomechanical systems coupled through radiation pressure and photothermal force is studied. To develop the photothermal model, we derive an expression for deformation constant of the force. Exploiting linearized quantum Langevin equations we investigate dynamics of such systems. According to our analysis, in addition to separate action of radiation pressure and photothermal force, their cross correlation effect plays an important role in dynamics of the system. We also achieve an exact relation for the phonon number of the mechanical resonator in such systems, and then we derive an analytical expression for it at weak coupling limit. At strong coupling regime, we show that utilizing the photothermal pressure makes the ground state cooling more approachable. The effect of photothermal force on the optomechanical entanglement is investigated in detail. According to our exact numerical and approximate analytical studies, even though the photothermal force is naturally a dissipative force, it can improve the optomechanical entanglement both quantitatively and qualitatively.

Temperature- and Radiation-Based Models for Predicting Spatial Growth of Purple Nutsedge (Cyperus rotundus)

Purple nutsedge is a troublesome C4weed, characterized by high photosynthetic efficiency, compared to C3weeds. As its dispersal is based on vegetative growth, accurate prediction of its growth could help in arriving at favorable management decisions. This article details the development and validation of predictive models of purple nutsedge spatial growth, based on temperature (thermal model), and temperature and radiation (photothermal model) measurements. Plants were grown in six experiments in the summers of 2008, 2009, and 2010, under different temperature and radiation conditions. Results indicate that under optimal temperatures, radiation becomes the main growth-limiting factor, and is highly related to the final leaf-cover area (R2= 0.89). Comparison of the thermal and photothermal models showed that under all conditions, including varied temperature and radiation, the photothermal model performs significantly better, with differences in root-mean-square error values reaching up to 0.073, compared to 0.195 with the thermal model. Validation experiments confirmed the ability of the photothermal model to predict purple nutsedge spatial growth accurately.

Wavelength-modulated differential photothermal radiometry: Theory and experimental applications to glucose detection in water

A differential photothermal radiometry method, wavelength-modulated differential photothermal radiometry (WM-DPTR), has been developed theoretically and experimentally for noninvasive, noncontact biological analyte detection, such as blood glucose monitoring. WM-DPTR features analyte specificity and sensitivity by combining laser excitation by two out-of-phase modulated beams at wavelengths near the peak and the base line of a prominent and isolated mid-IR analyte absorption band (here the carbon-oxygen-carbon bond in the pyran ring of the glucose molecule). A theoretical photothermal model of WM-DPTR signal generation and detection has been developed. Simulation results on water-glucose phantoms with the human blood range (0-300 mg/dl) glucose concentration demonstrated high sensitivity and resolution to meet wide clinical detection requirements. The model has also been validated by experimental data of the glucose-water system obtained using WM-DPTR.

A photothermal model of selective photothermolysis with dynamically changing vaporization temperature

The theory of selective photothermolysis (SP) is used in many fields of laser surgery and medicine. As several parameters and a number of complicated photothermal interactions are involved in SP, numerical simulations have been providing an important and effective way in SP studies. However, with different photothermal models of SP, simulated results differ considerably. In addition, insufficient attention has been paid to tissue pressure variation during SP in these models, so that vessel rupture and other clinical phenomena cannot be explained. A novel photothermal model of SP was proposed using a Monte Carlo method to simulate the laser transport in the tissue, a heat transfer equation with dynamically changing vaporization temperature to calculate the temperature distribution, and the Arrhenius equation to predict the thermal damage. A factor of trapped vaporized tissue water k was introduced to describe the effects on tissue pressure, temperature, and other related parameters. It was shown that the simulation results are affected significantly by k. Temperature and thermal damage volume are almost identical, respectively, to those obtained with models with vaporization at 100°C and models without vaporization when k = 0 and 1, while thermal damage volume is close to that obtained with models of vaporization at 110°C and 130°C, respectively, when k = 0.022 and k = 0.18. To some extent, the current models without vaporization and models with vaporization at constant temperature can be regarded as special cases at specific situations of this new photothermal model of SP. In addition, more descriptive simulation results, such as temperature, thermal damage, and pressure, are accessible with this model, although the accuracy depends on the value of k, the estimation of which is planned as future work.

Temperature and Photoperiod Effects on Vicia faba Phenology Simulated by CROPGRO‐Fababean

Models may be useful tools to design efficient crop management practices provided they are able to accurately simulate the effect of weather variables on crop performance. The objective of this work was to accurately simulate the effects of temperature and day length on the rate of vegetative node expression, time to flowering, time to first pod, and time to physiological maturity of faba bean (Vicia faba L.) using the CROPGRO‐Fababean model. Field experiments with multiple sowing dates were conducted in northwest Spain during 3 yr (17 sowing dates: 12 used for calibration and five for validation). Observed daily minimum and maximum air temperatures were within the range of –9.0 and 39.2°C and observed photoperiods within 10.1 to 16.6 h. Optimization of thermal models to predict leaf appearance raised the base temperature (Tb) from the commonly used value of 0.0 to 3.9°C. In addition, photothermal models detected a small accelerating effect of day length on the rate of leaf appearance. Accurate prediction of the flowering date required incorporating day length, but the solved Tb approached negative values, close to –4°C. All the reproductive phases after flowering were affected only by temperature, but postanthesis Tb was also >0°C and approached values close to 8°C for time to first pod set and 5.5°C for time from first pod to physiological maturity. Our data indicated that cardinal base temperatures are not the same across all phenological phases.

Predicting Flowering Dates in Wheat with a New Statistical Phenology Model

Wheat growers in Western Australia (WA) value flowering date predictions for risk aversion from frost and terminal stresses. Currently used statistical models such as the “flowering calculator” (referred to as photothermal model as programmed by Tennant and Tennant [2000] [TT]) are less robust in colder regions and/or higher latitudes of WA. We developed a new statistical model (named DM) that includes a vernalization component in addition to photoperiod and temperature components, the three biological drivers of reproductive growth and development in wheat (Triticum spp.). The model assumes that heatsums required for flowering comprise a variety specific minimum, plus some more that are linearly contingent on sowing day, daylength, and the statistical summaries of daily temperature profiles. The vernalization opportunity was quantified using a term named “coldsum” calculated as equal to the sum of daily periods under 5°C in hourly temperature profile, while “heatsum” referred to the periods above 0°C. Environments were characterized using a log‐log transformation on heatsums and a segmented‐lines approach on coldsums. The model coefficients were estimated using data from four sowing dates spanning prevalent sowing times in WA over 4 yr at three diverse locations. The DM predictions were statistically far superior to TT (F probability < 0.001; RMSD 6.1 and 17.4, respectively) in all respect of location, season, sowing date, and cultivar factors when compared in independent datasets from six cultivar × sowing date trials across WA wheatbelt. Since DM relies on a structured application of seasonal profiles, it should be applicable to other geographic areas, cultivars, and crops.

Simulation and modeling of laser-tissue interactions based on a liposome-dye system.

This work presents an overview of the use of liposomes for targeted delivery of photosensitizers to tumors for Photodynamic Therapy (PDT). It assesses the results of a quantitative model to explain the interaction of short-pulsed lasers (in the nanosecond and picosecond domains) with a liposome-dye complex in terms of a localized photo-induced thermal mechanism. Incorporation of an organic dye (sulforhodamine) within lipid vesicles has been investigated in conjunction with the effect of laser irradiation on the integrity of the liposome-dye complex. The variation of the absorption coefficient as a function of wavelength for dye-encapsulated liposomes before and after laser-induced release of dye was studied and modeled. The commercial software Mathematica was used to develop a Gaussian model for the energy absorption by the liposome-dye complex. Dye release from 3 microm - liposome encapsulating 25 mM aqueous solution of sulforhodamine dye was studied using 8 ns laser pulses at the second harmonic of the Nd:YAG laser (at 532 nm) and compared with dye release employing 25 ps - laser pulses. In addition, the temperature-dependence of the dye release has been included in the photo-thermal model.

Excimer laser ablation of single crystal 4H-SiC and 6H-SiC wafers

A 248 nm, 23 ns pulsed excimer laser was used to compare the ablation characteristics of single crystal wafers of the polytypes 4H-SiC and 6H-SiC over a wide range of energy fluence (0.8–25 J cm−2). Photothermal models based on Beer–Lambert equation using thermal diffusivity and absorption coefficient, energy balance, and heat transfer were presented to predict the ablation mechanisms. Micromachining of trenches was demonstrated at 7 J cm−2 to demonstrate the potential of UV laser ablation. Results indicate that the ablation process is characterized by two well-defined threshold fluences: (a) decomposition threshold ~1 J cm−2 and (b) melting threshold ~1.5 J cm−2 for both polytypes. Contrary to the modeling expectations, the ablation rates were lower and did not increase rapidly with energy fluence. Four types of ablation mechanisms—chemical decomposition, vaporization, explosive boiling, and plasma shielding—either singly or in combination occur as a function of energy fluence. The predictions of photothermal models were not in good agreement with the experimental data implying that a complex interplay among various physical phenomena occurs during ablation. Micromachined trench exhibited ripple patterns, microcracks and recast layers, most of which could be eliminated by a subsequent chemical cleaning process. It is concluded that excimer laser ablation is an effective but slow material removal process for SiC wafers compared to other lasers such as 1064 nm Nd:YAG.