Fluence Domain Research Articles

Potential of pulsed light treatment to pasteurize pomegranate juice: Microbial safety, enzyme inactivation, and phytochemical retention

The study explores the pasteurization condition of pomegranate juice using pulsed light (PL) treatment within a fluence domain of 312–2988 J cm−2. A 5-log reduction (microbial safety) in Escherichia coli ATCC 43888, aerobic mesophiles, yeasts & molds count in the juice was obtained at 761.4 J cm−2 (2.7 kV for 90 s). The thermal treatment attaining the equivalent lethality was 95 °C for 2 min. A complete inactivation in enzyme activity (polyphenol oxidase and peroxidase) along with microbial safety was attained for the treatments at 2988 J cm−2 (PL) and 95 °C/3 min (thermal treatment). The thermally pasteurized sample (95 °C/3 min) showed 30 and 37% depletion in phenolic compounds and antioxidant capacity, respectively, with only 34% vitamin C in the juice. The equivalent PL pasteurized (2988 J cm−2) juice retained 97%, 94%, and 83% phenolics, antioxidants, and ascorbic acid, respectively. The PL-pasteurized sample's quality attributes and sensory profile were on par with high-pressure and pulsed electric field pasteurized juices from the literature. In turn, PL treatment of the pomegranate juice at 2988 J cm−2 satisfies the criteria for all the stakeholders such as microbial safety (manufacturers demand), enzymatic stability (retailer's demand), and phytochemical retention (consumers demand).

Processing of optical glasses by single, 34\xa0fs pulses in the strong field ionization domain: ablation characteristics and crater morphology

The material response of Borofloat, BK7, and B270 glass targets to 34 fs pulses of 800 nm central wavelength is analyzed in the 1–30 J/cm2 fluence domain. The contours of the craters change with the fluence very much the same for all three glasses up to approximately 20 J/cm2, above which the Borofloat and BK7 continue behaving similarly, while bump formation sets on for the B270 glass. Analyzing the contours single-shot ablation thresholds are determined by applying both the conventional diameter regression technique and a multiphoton absorption-based fit to depth data. The ablation threshold values are equal within the 6.1 ± 0.55 J/cm2 domain for the three glasses as well as the three-photon absorption coefficients, which lie in the same magnitude (10–25 cm3/W2). Above the ablation threshold, the diameter values follow logarithmic dependence in the fluence range investigated, reaching similar values around 45 µm at 30 J/cm2 with 51 ± 1 µm 1/e2 beam diameter on the target surface as derived from the diameter regression technique. The onset of plasma formation derived from the changes in the energy reflected from the processed surface is also found to be similar for the three glasses (9.5, 10, and 8.0 J/cm2) in good correlation with the ablation threshold values.

Defining regimes and analytical expressions for fluence curves in pulsed laser heating of aerosolized nanoparticles.

Fluence curves are a powerful tool for understanding the mechanisms underlying nanosecond pulse laser heating of aerosolized nanoparticles, which is relevant to laser-induced incandescence (LII). This paper presents analytical expressions encompassing the entirety of the fluence domain considered in LII and uses them to formally define fluence regimes. The derived expressions and non-dimensional parameters facilitate one of the first comparisons of published experimental fluence curves. This procedure provides physical insight into the laser-nanoparticle interaction and highlights inconsistencies in the application of LII models to analyze the data.

Correlation between irradiation conditions and nanoparticles obtained in case of laser ablation of aluminum targets in liquids

The process of nanoparticles production by nanosecond pulsed laser ablation of aluminum targets situated in deionized water was studied from the point of view of laser–target interaction and incident laser fluence domain selection as a preliminary stage in the process of nanoparticles production. We have analyzed the irradiated surface morphology and crater profiles as a function of irradiation conditions (incident fluence and irradiation pulses number) by optical microscopy and white light interferometry in order to determine the most efficient coupling between the irradiation conditions and the irradiated surface immersed in liquid. The obtained nanoparticles were studied “in situ”, as obtained in suspension in water and “ex situ”, using TEM. TEM analyses have demonstrated that we have obtained nanoparticles with the lowest dimensions of 3–5 nm organized in clouds with dimensions between 40 and 80 nm. Typically the obtained nanoparticles presented two clear distributions, one corresponding to low diameters in the 6–10 or 20–40 nm regions, and another with a distribution around a maximum situated at hundreds of nanometers (250–290 nm). The obtained nanoparticles distribution was correlated with the irradiation conditions.

Determination of irradiation parameters for laser-induced periodic surface structures

The spatial emergence of laser-induced periodic surface structures (LIPSS) on single-crystalline silicon, upon irradiation with linearly polarized picosecond laser pulses (wavelength λ=1030nm, pulse duration τ=6.7ps, pulse repetition frequency fp=1kHz) was studied theoretically and experimentally, under lateral displacement conditions. An experimental approach is presented for the determination of irradiation parameters of extended surface areas homogenously covered with LIPSS. The approach is based on accumulated fluence and consists of two steps, first the empirical determination of accumulated fluence domain boundaries and second the approximation of irradiation parameters. Such an approach is required for the application of LIPSS in the field of surface functionalization. The approach was successfully applied for structuring extended surface areas, which were homogenously covered with LIPSS. The areas, obtained by different irradiation parameter combinations, satisfying accumulated fluence boundary conditions, show the same type of LIPSS. This observation provides evidence, that the accumulated fluence has a decisive role in the spatial emergence of LIPSS. In the future, further experiments are required to verify the validity and boundaries of the approximations applied.

Characterization of statistical prior image constrained compressed sensing. I. Applications to time‐resolved contrast‐enhanced CT

Prior image constrained compressed sensing (PICCS) is an image reconstruction framework that takes advantage of a prior image to improve the image quality of CT reconstructions. An interesting question that remains to be investigated is whether or not the introduction of a statistical model of the photon detection in the PICCS reconstruction framework can improve the performance of the algorithm when dealing with high noise projection datasets. The goal of the research presented in this paper is to characterize the noise properties of images reconstructed using PICCS with and without statistical modeling. This paper investigates these properties in the clinical context of time-resolved contrast-enhanced CT. Both numerical phantom studies and an Institutional Review Board approved human subject study were used in this research. The conventional filtered backprojection (FBP), and PICCS with and without the statistical model were applied to each dataset. The prior image used in PICCS was generated by averaging over FBP reconstructions from different time frames of the time-resolved CT exam, thus reducing the noise level. Numerical studies were used to evaluate if the noise characteristics are altered for varying levels of noise, as well as for different object shapes. The dataset acquired in vivo was used to verify that the conclusions reached from numerical studies translate adequately to a clinical case. The results were analyzed using a variety of qualitative and quantitative metrics such as the universal image quality index, spatial maps of the noise standard deviations, the noise uniformity, the noise power spectrum, and the model-observer detectability. The noise characteristics of PICCS were shown to depend on the noise level contained in the data, the level of eccentricity of the object, and whether or not the statistical model was applied. Most differences in the characteristics were observed in the regime of low incident x-ray fluence. No substantial difference was observed between PICCS with and without statistics in the high fluence domain. Objects with a semi-major axis ratio below 0.85 were more accurately reconstructed with lower noise using the statistical implementation. Above that range, for mostly circular objects, the PICCS implementation without the statistical model yielded more accurate images and a lower noise level. At all levels of eccentricity, the noise spatial distribution was more uniform and the model-observer detectability was greater for PICCS with the statistical model. The human subject study was consistent with the results obtained using numerical simulations. For mildly eccentric objects in the low noise regime, PICCS without the noise model yielded equal or better noise level and image quality than the statistical formulation. However, in a vast majority of cases, images reconstructed using statistical PICCS have a noise power spectrum that facilitated the detection of model lesions. The inclusion of a statistical model in the PICCS framework does not always result in improved noise characteristics.

Inverse planning for IMRT with nonuniform beam profiles using total‐variation regularization (TVR)

Radiation therapy with high dose rate and flattening filter-free (FFF) beams has the potential advantage of greatly reduced treatment time and out-of-field dose. Current inverse planning algorithms are, however, not customized for beams with nonuniform incident profiles and the resultant IMRT plans are often inefficient in delivery. The authors propose a total-variation regularization (TVR)-based formalism by taking the inherent shapes of incident beam profiles into account. A novel TVR-based inverse planning formalism is established for IMRT with nonuniform beam profiles. The authors introduce a TVR term into the objective function, which encourages piecewise constant fluence in the nonuniform FFF fluence domain. The proposed algorithm is applied to lung and prostate and head and neck cases and its performance is evaluated by comparing the resulting plans to those obtained using a conventional beamlet-based optimization (BBO). For the prostate case, the authors' algorithm produces acceptable dose distributions with only 21 segments, while the conventional BBO requires 114 segments. For the lung case and the head and neck case, the proposed method generates similar coverage of target volume and sparing of the organs-at-risk as compared to BBO, but with a markedly reduced segment number. TVR-based optimization in nonflat beam domain provides an effective way to maximally leverage the technical capacity of radiation therapy with FFF fields. The technique can generate effective IMRT plans with improved dose delivery efficiency without significant deterioration of the dose distribution.

Plan Optimization for IMRT with Flattening-filter-free (FFF) Beams by using Compressed Sensing Technique

High dose rate photon beam with flattening-filter-free (FFF) has recently become available in Varian Trilogy MX LINAC for clinical use. The purpose of this work is to develop a novel inverse planning with consideration of the cone-shaped beam fluence for IMRT with FFF beams so that the number of segments and MUs are minimized. FFF beam data measured from a Varian Trilogy MX unit was utilized for dose calculation and optimization. An incident beam was divided into a collection of 0.5x0.5cm beamlets. To accommodate the inherent non-flatness of FFF fluence, a total-variation regularization (TVR) was introduced in the objective function to encourage piecewise constant fluence in the FFF fluence domain, which was mathematically equivalent to working in the conventional flat fluence domain when the beamlet intensities were normalized according to the measured FFF fluence profile. The system was optimized by using MOSEK software package in Matlab. The performance of the proposed method was evaluated by comparing with IMRT plans obtained using conventional beamlet and direct-aperture optimization strategies for two head and neck patients and a prostate patent. Dose volume histograms (DVH), dose distributions number of segments and MUs of each field are compared for the cases. TVR-based inverse planning utilizes the known cone-shaped profiles of the incident beams and provides clinically sensible IMRT solutions with much reduced number of segments and MUs as compared to conventional approaches. Because the TVR CS technique encourages the piecewise constant condition in FFF fluence domain, the fluence map complexity is markedly simplified in the FFF domain. For instance, an inverted cone-shaped isodose distribution can be obtained with only one segment when TVR is used. In this situation, a large number of segments and much higher MUs would be necessary when conventional beamlet-based or direct aperture optimization is employed. For the head and neck cases, the proposed method slightly improves the target dose uniformity and organs-at-risk sparing, but the numbers of segments and MUs are reduced considerably as compared to the beamlet-based optimization without regularization. The level of improvement in the prostate case is found to be modest, primarily due to the fact that the beam is relatively flat for a small target. The final dose distributions are found to be more conformal than that obtained using DAO using 6 segments for each field. This study presents a TVR-based IMRT inverse planning with explicit inclusion of FFF beam profiles. The proposed method provides a clinically acceptable IMRT plans with minimized number of segments or MUs and may find natural application in IMRT with FFF beams.

SU-GG-T-145: Inverse Planning for IMRT with Flattening Filter Free (FFF) Beams

Purpose: High dose rate photon beam with FFF has recently become available for clinical use. For IMRT with FFF beams, the strategy of inverse planning should be modified to minimize the segments and MUs by accommodating the cone‐shaped beam fluence. Method and Materials: FFF beam data measured from a Varian Trilogy MX unit was employed for dose calculation and optimization. An incident beam is divided into a collection of 0.5×0.5cm beamlets. To accommodate the inherent non‐flatness of FFF fluence, a total‐variation regularization (TVR) is introduced in the objective function to encourage piece‐wise constant fluence in the FFF fluence domain, which is mathematically equivalent to working in the conventional flat fluence domain when the beamlet intensities are normalized according to the measured FFF fluence profile. The system was optimized by using MOSEK software package. The performance of the method is evaluated by using phantom and clinical cases. Results: TVR‐based inverse planning utilizes the known profiles of the incident beams and provides clinically sensible IMRTsolutions with much reduced number of segments as compared to conventional approaches. To obtain an inverted cone‐shaped isodose distribution (phantom case), the solution requires only one segment when TVR is used. Multiple segments and much higher MUs would be required when conventional beamlet‐based or direct aperture optimization is used. For clinical cases, the total numbers of segments are reduced significantly as compared to the beamlet‐based optimization without regularization. The final dose distributions are found to be more conformai than that obtained of DAO using 6 segments for each field. Conclusion: A TVR‐based inverse planning with explicit inclusion of FFF profiles provides an effective way to find IMRT plans with minimized number of segments or MUs and may find natural application in IMRT with FFF beams.

Positive and negative nanohole-fabrication on glass surface by femtosecond laser with template of polystyrene particle array

We demonstrate a new nano-processing technique using the near- electromagnetic field around a small transparent particle irradiated by an 820 nm femtosecond laser pulse. We fabricate a 2D nanohole array with negative and positive patterns on a soda lime glass surface by irradiating a monolayer of 790 nm diameter polystyrene (PS) particles, arranged in a close-packed hexagonal lattice, with a femtosecond laser pulse. At the lower laser fluence domain, PS particles act as focusing lenses and/or near-field enhancers due to Mie scattering; it enables nanohole processing just under the particle (positive patterning). Nanoholes with diameters ranging from 84 to 170 nm are fabricated in this regime. At the higher fluence domain, the PS particle acts as a mask; while the positive nanohole formation disappears, then it enables nano-patterning of the surface in gap areas corresponding to the region between particles (negative patterning). Nanoholes with diameters ranging from 65 to 110 nm are fabricated in this case. The switching of negative and positive nano-patterning by simply controlling the incident laser fluence is experimentally demonstrated for the first time to our knowledge. A simple theoretical explanation for the switching of the positive and negative patterning is presented by FDTD simulation of the near-field distribution.

Deep drilling on a silicon plate with a femtosecond laser: experiment and model analysis

The ablation rate when drilling fine holes having large aspect ratios in silicon substrates with femtosecond laser pulses was estimated from mechanically ground cross sections of the ablated holes. The ablation rate shows a dramatic change at the depth at which the laser pulse reaches a certain fluence, which is nearly constant when the initial laser fluence was varied from 14.5 to 59.4 J/cm2. The ablation rate, threshold fluence, in three fluence domains, and the transition fluences at which the ablation rate shows a dramatic change, were derived. However, when a pulse energy of 200 μJ was used a much greater ablation rate was obtained, suggesting that another fluence domain for larger ablation rates exists. The experimentally obtained hole depths as a function of shot numbers were reproduced by a theoretical model, which incorporates laser pulse attenuation in the holes that is the same as that in waveguides for some attenuation coefficient and ablation rates for three fluence domains.

Spatial structure and scale feature of the atmospheric pollution source impact of city agglomeration

The spatial structure and multi-scale feature of the atmospheric pollution influence domain of Beijing and its peripheral areas (a rapidly developed city agglomeration) is dissected and analyzed in this paper on the basis of the atmospheric pollution dynamic-chemical process observation data of the urban building ensemble boundary layer of the Beijing City Air Pollution Observation Experiment (BECAPEX) in winter (February) and summer (August) 2003, and relevant meteorological elements and satellite retrieval aerosol optical depth (AOD), etc. com- prehensive data with the dynamic-statistical integrated analysis of “point-surface” spatial struc- ture. Results show that there existed significant difference in the contribution of winter/summer different pollution emission sources to the component character of atmospheric pollution, and the principal component analysis (PCA) results of statistical model also indicate that SO 2 and NO X dominated in the component structure of winter aerosol particle; instead, CO and NO X dominated in summer. Surface layer atmospheric dynamic and thermal structures and various pollutant species at the upper boundary of building ensembles at urban different observational sites of Beijing in winter and summer showed an “in-phase” variation and its spatial scale feature of “in- fluence domain”. The power spectrum analysis (PSA) shows that the period spectrum of win- ter/summer particle concentration accorded with those of atmospheric wind field: the longer pe- riod was dominative in winter, but the shorter period in summer, revealing the impact of the seasonal scale feature of winter/summer atmospheric general circulation on the period of at- mospheric pollution variations. It is found that from analyzing urban area thermal heterogeneity that the multi-scale effect of Beijing region urban heat island (UHI) was associated with the het- erogeneous expansion of tall buildings area. In urban atmospheric dynamical and thermal char- acteristic spatial structures, the turbulent scale feature of the urban boundary layer (UBL) of ar- chitectural complexes had important impact on the multi-scale feature of urban atmospheric pollution. The comprehensive analyses of the variational analysis field of Moderate Resolution Imaging Spectroradiometer (MODIS) AOD-surface PM10 under the condition of clear sky and the correlation resultant wind vector field for pollution source-tracing suggest that the emission sources for winter Beijing atmospheric pollution aerosols particle might be remotely traced to the south peripheral greater-scale spatial range of Hebei, Shandong, Tianjin, etc., and the spatial distribution of the high value area of AOD was associated with that of the high value area of resident family number (heating surface source). The backward trajectory feature of winter/ summer air particles exhibits analogous multi-scale feature, and depicts the difference in the scale feature of the pollution sources spatial distribution in different seasons. The peripheral source trajectory paths of urban atmospheric pollution (UAP) mainly come from the fixed indus- trial surface source or heating surface source in the outskirt of Beijing, and the diffusion and transport distance of peripheral sources in winter is larger than one in summer. The above con- clusions depict the multi-scale spatial influence domain and seasonal features caused by UAP source influence and atmospheric dynamical structure. The high value area of the winter Total Ozone Mapping Spectrometer (TOMS) AOD lay in the Beijing region and its south peripheral area, an S-N zonal pattern, which reflects the dynamical effect of peripheral topographic pattern on the diffusion of regional scale atmospheric pollution sources. Study suggests that the extent of winter atmospheric pollution within the “valley” megarelief in Beijing and periphery was close related with the pollution emission sources of the south peripheral area; and the significant “anti-phase” variation feature of winter AOD and sunshine duration in Beijing and its peripheral areas, and the regional scale correlation of low cloud cover, fog days, and aerosols reflects the local climatic effect of aerosol influence in this region. Besides, analysis of the impacts of at- mospheric dry/wet deposition distributions within a valley-scale on the regional water body of Miyun reservoir also reveals the possible influence of the multi-scale spatial structure of summer water, soil and atmospheric pollution sources on the water quality of Miyun reservoir.

Morphology and composition of ArF excimer laser deposited carbon nitride films as determined by analytical TEM

Carbon nitride films deposited onto room temperature silicon substrates by ArF excimer laser ablation of a graphite target in nitrogen atmosphere have been investigated after floating off in transmission electron microscope (TEM). All films fabricated in the 1–100 Pa N 2 pressure and 1–10 J cm −2 fluence domain are amorphous. It is the nitrogen pressure that governs both the composition and the morphology of the films, the effect of the laser fluence being weaker. The morphologies range from dense films grown in 1–5 Pa N 2, to structures composed of carbon nitride clusters and voids between them, obtained at and above 50 Pa N 2. Ablation with pulses of high fluence (10 J cm −2) results in more compact films. The oxygen content determined by energy dispersive X-ray spectrometry well correlates with the compactness of the films, being significantly higher in those fabricated at higher pressures and composed of clusters.

Dependence of nitrogen content and deposition rate on nitrogen pressure and laser parameters in ArF excimer laser deposition of carbon nitride films

The effect of N2 pressure and laser fluence on the chemical composition and growth rate of CNx (0.07<x<0.45) films deposited by ArF excimer laser ablation of a graphite target in nitrogen environment is reported. Between 1 and 50Pa the nitrogen content of the films monotonously increases with increasing pressure. Films deposited at various N2 pressures differ not only in their (average) nitrogen but also in their oxygen content. The chemical composition of the films deposited using pulses of fluences between 0.7 and 2Jcm−2 remains the same within experimental error, while in the 2–10Jcm−2 domain the nitrogen incorporation steeply increases. The growth rates vary from 0.003 to 0.56Å/pulse, increasing linearly with fluence and decreasing with increasing pressure in the 0.7−2Jcm−2 fluence domain, while followed by a supralinear dependence on fluence and less sensitivity to N2 pressure at higher fluences. Changes in film porosity account for the striking features reported.

Laser ablation acoustical monitoring

Short pulses laser generated shock waves in air during the ablation of ceramics have been monitored with acoustical techniques. We have found that on a given laser fluence domain the ablation rate can be related to the shock wave energy. This shock wave energy is measured both with the laser beam deflection technique and a microphone. We demonstrate that it is possible, after a calibration procedure, to simply use a microphone for a real time control of the ablation process.

Low-fluence excimer laser irradiation-induced defect formation in indium-tin oxide films

DC sputtered indium-tin oxide (ITO) films of 500 nm thickness are irradiated with single pulses of fluences between 190 and 510 mJ/cm2 from a KrF excimer laser. The irradiation induced changes in optical spectra are consistently described through the behaviour of four (Gaussian-like) absorption bands at 0.7, 1.0, 1.6 and 2.6 eV. Being absent in the original films and emerging at fluences exceeding 300 mJ/cm2, the 2.6 eV contribution is most characteristic to excimer laser processing. X-ray photoelectron spectroscopic analysis suggests that the irradiation-induced changes should be associated with oxygen displacement within the atomic network rather than surface reduction via oxygen removal. Thermal model calculations reveal that the principal effect of single pulse processing in this fluence domain is deep melting of the films. Defects created during molten phase resolidification are assumed to be responsible for the irradiation-induced changes in the short range chemical structure of the films.

The fluence spectrum allowing the formation of a connected buried layer in silicon by oxygen implantation

The synthesis of a connected buried oxide (BOX) via oxygen implantation into silicon followed by high-temperature annealing is discussed. A theoretical scheme able to predict the fluence domain which allows the formation of a connected BOX is proposed. This scheme is validated in a few cases by studying the evolution with fluence of the buried interfaces. The BOX insulating quality is discussed in relation to fundamental factors as well as to technological constraints.

Silicon on thin insulator: prediction of the oxygen fluence required for the formation of a continuous buried oxide

Abstract A scheme is proposed to explain the fluence domain in which a continuous buried SiO 2 layer is formed to oxygen implantation and subsequent high temperature annealing. This scheme correctly describes the minimum fluence observed in single step implantation experiments and its temperatures and energy dependence; moreover, it also explains the seemingly extravagant structure of this fluence domain (showing a narrow window of allowed values at relatively low fluence) recently reported by Nakashima and Izumi ( Electron Lett., 26 (1990) 1647, J. Mater. Res., 8 (1993) 523) and the reasons making it possible the low fluence process reported by Meda et al. ( Nucl. Instrum. Methods B, 80/81 (1993) 813.