Vacuum Pulse Research Articles

Particle acceleration by subcycle laser pulse in vacuum

An analytical model based on the diffraction-induced transformation [A. E. Kaplan, J. Opt. Soc. Am. B 15, 951 (1998)] for an ultrashort subcycle laser pulse propagating in vacuum is considered. The pulse is initially Gaussian. To the lowest order of the diffraction angle its evolution satisfies Maxwell’s equations. The model is used to study the motion of charged particles in the pulse. It is shown that the delta-function representation is an excellent approximation of a subcycle pulse for studying charged-particle dynamics in subcycle pulse.

Study on pulsed laser ablation and deposition of ZnO thin films by L-MBE

ZnO, as a wide-band gap semiconductor, has recently become a new research focus in the field of ultraviolet optoelectronic semiconductors. Laser molecular beam epitaxy (L-MBE) is quite useful for the unit cell layer-by-layer epitaxial growth of zinc oxide thin films from the sintered ceramic target. The ZnO ceramic target with high purity was ablated by KrF laser pulses in an ultra high vacuum to deposit ZnO thin film during the process of L-MBE. It is found that the deposition rate of ZnO thin film by L-MBE is much lower than that by conventional pulsed laser deposition (PLD). Based on the experimental phenomena in the ZnO thin film growth process and the thermal-controlling mechanism of the nanosecond (ns) pulsed laser ablation of ZnO ceramic target, the suggested effective ablating time during the pulse duration can explain the very low deposition rate of the ZnO film by L-MBE. The unique dynamic mechanism for growing ZnO thin film is analyzed. Both the high energy of the deposition species and the low growth rate of the film are really beneficial for the L-MBE growth of the ZnO thin film with high crystallinity at low temperature.

Comment on “Electron acceleration by a chirped Gaussian laser pulse in vacuum” [Phys. Plasmas 13, 123108 (2006)

Sohbatzadeh et al. [Phys. Plasmas 13, 123108 (2006)] have presented a scheme of vacuum electron acceleration by using a chirped Gaussian laser pulse. They assume a linear polarization of the laser pulse in this scheme. We point out that this might be an important assumption in their work and it can seriously influence the electron energy gain during laser acceleration. In this Comment, the circular polarization of a chirped laser pulse is employed and our results show higher electron energy gains.

Response to “Comment on ‘Electron acceleration by a chirped Gaussian laser pulse in vacuum’” [Phys. Plasmas 14, 044701 (2007)

Response to “Comment on ‘Electron acceleration by a chirped Gaussian laser pulse in vacuum’” [Phys. Plasmas 14, 044701 (2007)

Application of SAFES (systematic approach to food engineering systems) methodology to apple candying

The application of a vacuum pulse for a specified time before long term osmotic dehydration has been proposed to obtain candied fruits at mild temperatures, thus maintaining the characteristic attributes of fresh fruits. Information about main changes involved in apple candying by long term pulsed vacuum osmotic dehydration is missed by applying traditional methods of modelling foods and processes. A new systematic approach to food engineering systems (SAFES) methodology has been recently developed and applied to predict quality and safety attributes from compositional and volumetric changes taking part throughout food processing. Identification and quantification of main components, phases and aggregation states at different stages of changes in which the process can be divided into would be required. Apart from experimental data and data found in references, several hypotheses related to water and soluble solids flow were also formulated for this purpose. The application of SAFES methodology to the apple candying process highlights the usefulness of this tool in making evident that different mechanisms are involved in the process in a coupled way. Indeed, not only osmotic, but also pseudo-difusional and hydrodynamic mechanisms were responsible for compositional and volumetric changes occurring during apple candying to a different extend, depending on the concrete stage of the process. As a result, it should be necessary to analyse the process in different steps in order to avoid a confused knowledge of it.

Determination of water effective diffusion coefficient of sardine sheets during vacuum pulse osmotic dehydration

The water effective diffusion coefficient of sardine sheets during vacuum pulse osmotic dehydration was determined. Sardine sheets (20.1×15.0×6.4 mm 3) were osmotic dehydrated at brine concentrations between 0.15 and 0.27 g NaCl/g, and temperatures between 32 and 38 °C. The water effective diffusion coefficient ranged approximately from 1.46×10 −10 m 2/s to 2.41×10 −10 m 2/s. In general, diffusion coefficient increased with increasing concentration and temperature. Dependence on temperature followed an Arrhenius relationship, regardless of concentration Diffusion coefficient at 0.18 g NaCl/g was found to be the most temperature sensitive ( E a=39.62 kJ/mol) while that at 0.15 g NaCl/g was the least temperature sensitive ( E a=23.67 kJ/mol). The water effective diffusion coefficient was empirically correlated with concentration and temperature of osmotic solution. A high degree of correlation was observed between predicted and experimental values of the water effective diffusion coefficient ( R 2=0.856).

Practical quantum key distribution over 60 hours at an optical fiber distance of 20km using weak and vacuum decoy pulses for enhanced security

Experimental one-way decoy pulse quantum key distribution running continuously for 60 hours is demonstrated over a fiber distance of 20km. We employ a decoy protocol which involves one weak decoy pulse and a vacuum pulse. The obtained secret key rate is on average over 10kbps. This is the highest rate reported using this decoy protocol over this fiber distance and duration.

Principal Component Analysis of Results Obtained from Finite-Difference Time-Domain Algorithms

Finite-Differences Time-Domain (FDTD) algorithms are well established tools of computational electromagnetism. Because of their practical implementation as computer codes, they are affected by many numerical artefact and noise. In order to obtain better results we propose using Principal Component Analysis (PCA) based on multivariate statistical techniques. The PCA has been successfully used for the analysis of noise and spatial temporal structure in a sequence of images. It allows a straightforward discrimination between the numerical noise and the actual electromagnetic variables, and the quantitative estimation of their respective contributions. Besides, The GDTD results can be filtered to clean the effect of the noise. In this contribution we will show how the method can be applied to several FDTD simulations: the propagation of a pulse in vacuum, the analysis of two-dimensional photonic crystals. In this last case, PCA has revealed hidden electromagnetic structures related to actual modes of the photonic crystal.

Electron acceleration by a chirped Gaussian laser pulse in vacuum

Electron acceleration by a chirped Gaussian laser pulse is investigated numerically. A linear and negative chirp is employed in this study. At first, a simple analytical description for the chirp effect on the electron acceleration in vacuum is provided in one-dimensional model. The chirp mechanism is then extended to the interaction of a femtosecond laser pulse and electron. The electron final energy is obtained as a function of laser beam waist, laser intensity, chirp parameter, and initial phase of the laser pulse. It is shown that the electron final energy depends strongly on the chirp parameter and the initial phase of the laser pulse. There is an optimal value for the chirp parameter in which the electron acceleration takes place effectively. The energy gain increases with laser beam waist and intensity. It is also shown that the electron is accelerated within a few degrees to the axial direction. Emphasis is on the important aspect of the chirp effect on the energy gained by an electron from the electromagnetic wave.

Predicting the moisture and salt contents of sardine sheets during vacuum pulse osmotic dehydration

Application of the Peleg model was investigated for predicting the moisture and salt contents of sardine sheets during vacuum pulse osmotic dehydration using brine at different concentrations (0.15–0.27 g NaCl/g), temperatures (30–38 °C), and applying a vacuum pulse at 11.0 kPa for 10 min. The high regression coefficients ( R 2 > 0.97) and low mean relative error (<10%) indicated the acceptability of Peleg model for predicting both moisture and salt contents. The effects of temperature on rate and capacity constants of Peleg model for moisture and salt contents depend of the value of concentration of brine. The equilibrium moisture and salt contents were estimated using Peleg capacity constant. Models for equilibrium moisture and salt contents as a function of brine concentration and temperature were found.

Obtaining fruit segments from a traditional orange variety (Citrus sinensis (L.) Osbeck cv. Sangrina) by enzymatic peeling

A process for obtaining fruit segments from a traditional orange of Sangrina variety by enzymatic peeling was optimized. Enzymatic peeling was carried out by fruit infusion under vacuum conditions in a commercial preparation of pectinases and cellulases (Peelzym II). For the optimization of vacuum conditions, the potential enzymatic saturation of albedo was determined. To obtain a final product with good quality, it was necessary to prove the effectiveness of different concentration of Peelzym II for the degradation of the fruit albedo and also the incubation time of the fruits with the enzymatic solution. The best condition to obtain Sangrina segments by enzymatic peeling was 1 ml L−1 of Peelzym II applied at 67 kPa with two vacuum pulses of 2 min and a subsequent period of 40 min in the enzymatic solution at atmospheric pressure. The reuse of the enzyme preparation in an industrial peeling process was also studied. Results show that it is possible to reuse the enzymatic preparation in an industrial peeling process, although a 30% decrease in the pectinase activity occurred after four peeling cycles.

Impregnation and Infiltration Kinetics of Isotonic Solution in Whole Jalapeño Pepper Using a Vacuum Pulse

ABSTRACT: The kinetics incorporation of an isotonic solution (IS) into the whole jalapeño pepper, as a function of the vacuum pressure (p1, vacuum application time (t1), and relaxation time (t2), is necessary to determining the conditions leading to the highest incorporation of IS. This study was aimed at determining the operation conditions to achieve maximum impregnation (Min) of whole jalapeño pepper tissue, and a complete infiltration (Min) of its inner void with an IS, using a vacuum pulse. Impregnation of whole jalapeño peppers was conducted using an IS (aw= 0.993 ± 0.001), a vacuum pulse, and 5 levels for each process variable (t1, t2, p1), according to a central composite design. The amounts of impregnated and infiltrated IS were measured by following changes in pepper weight. The p1, t2 had a significant effect (P < 0.01) on the rate of Mim and Min (g IS/g pepper). It was found that the structure of whole jalapeño plays an important role in the deformation-relaxation process, which also affects the impregnation and infiltration kinetics. A high level of p1 (666 mbar) and t2 (840 min) allowed to achieve the maximum values of Mim and Min (0.07 and 0.29 g IS/g pepper, respectively). These results suggest that different driving force acts in promoting the Mim and Min, during the t1 and t2. This information will be of great value in the analysis of the pickling process of whole jalapeño pepper with a hypertonic solution and a vacuum pulse.

Hetero-epitaxial ZnO 버퍼층이 As-doped ZnO 박막의 증착조건에 미치는 영향

ZnO thin films prepared by PLD method exhibit an excellent optical property, but may have some problems such as incomplete surface roughness and crystallinity. In this study, undoped ZnO buffer layers were deposited on (0001) sapphire substrates by ultra high vacuum pulse laser deposition (UHV-PLD) and molecular beam epitaxy (MBE) methods, respectively. After post annealing of ZnO buffer layer, undoped ZnO thin films were deposited under different oxygen pressure (<TEX>$35{\sim}350$</TEX> mtorr) conditions. The Arsenic-doped (1, 3 wt%) ZnO thin layers were deposited on the buffer layer of undoped ZnO by UHV-PLD method. The optical property of the ZnO thin films was analyzed by photoluminescence (PL) measurement. The <TEX>${\theta}-2{\theta}$</TEX> XRD analysis exhibited a strong (002)-peak, which indicates c-axis preferred orientation. Field emission-scanning electron microscope (FE-SEM) revealed that microstructures of the ZnO thin films were varied by oxygen partial pressure, Arsenic doping concentration, and deposition method of the undoped ZnO buffer layer. The denser and smoother films were obtained when employing MBE-buffer layer under lower oxygen partial pressure. It was also found that higher Arsenic concentration gave the enhanced growing of columnar structure of the ZnO thin films.

Real-time active control of RFX-mod plasma equilibrium

The design and implementation of a real-time control system of the plasma equilibrium was required in RFX-mod, the load assembly of the machine being characterized by a thin copper shell to prevent the growth of MHD resistive wall modes with a time constant much shorter than the typical pulse length. The control system design was carried out on a linearized model of the plasma response. Detailed schemes were developed to use a tool for automatic code generation to implement the regulators. Dedicated vacuum and plasma pulses were executed for system commissioning and characterization. The first results showed the system satisfactory accuracy in tracking the plasma position reference and its contribution to extend the pulse length. A modified version of the control system aimed at keeping the shell surface as a flux surface throughout the pulse was also successfully tested.

Vacuum pulse-assisted pickling whole jalapeño pepper optimization

Response surface methodology (RSM) was used for the optimization of the pickling process of whole jalapeño pepper, using a vacuum pulse. The pickling variables were the brine to pepper mass ratio ( R = 1–10, w/w), sodium chloride concentration in the pickling brine ([NaCl] brine = 10–15%), and processing time ( t 2 = 10–30 d). The main response variables were solutes gain to water loss ratio (SG/WL), weight reduction (WR), concentration of sodium chloride ([NaCl] pepper), acetic acid ([CH 3COOH] pepper) in the pepper tissue, and water activity of treated pepper and pickling solution. The polynomial models developed by RSM were highly significant to describe the relationships between the studied factors and the responses ( p < 0.0001). Analytical optimization gave water activity values near equilibrium, the highest SG/WL ratio (2.1), and up to 6% of [NaCl] pepper and 2% of [CH 3COOH] pepper, when using a [NaCl] brine = 12%, R = 4.6 and t 2 = 22 d.

Volatile profile of mango ( Mangifera indica L.), as affected by osmotic dehydration

The effect of osmotic dehydration on the volatile fraction of mango fruit was studied. Osmotic treatments were carried out at atmospheric pressure (OD) and by applying a vacuum pulse (PVOD). Sucrose at 35, 45, 55 and 65 °Brix was used as osmotic solution until reaching 20 or 30 °Brix in the liquid phase of dehydrated mango. Volatile compounds of fresh and dehydrated samples were obtained by simultaneous distillation–extraction, and analyzed by GC–MS. In general, osmotic dehydration provoked changes in the concentration of analyzed compounds to different extents, depending on process conditions. The use of highly concentrated osmotic solutions, and the high level of sample osmodehydration, induced losses of volatiles with respect to the fresh samples. On the other hand, more heavily diluted solutions and shorter treatment times (lower osmodehydration level) could give rise to the enhancement of volatile production. In these cases, sample mass loss was reduced during treatment since sugar gain was promoted against water loss.

Vacuum pulse and brine composition effect on pickling kinetics of whole jalapeño pepper

The combined effect of pickling time and pickling solutes concentration was studied on pickling whole jalapeño pepper by applying a vacuum pulse (VP) of 666 mbar for 5 min. Sodium chloride and acetic acid concentrations ranged from 10–15.1% to 2.3–3.2% (w/w), respectively, and the pickling or processing time varied from 0.3 to 30 days. The response surface methodology was used to evaluate the influence of the process variables on water loss (WL), solutes gain (SG) and weight reduction (WR) of jalapeño pepper. Processing time showed a linear effect on most of the pickling rate parameters ( p < 0.01). Sodium chloride concentration affected WL, SG and WR of pepper pickled with VP, but the interaction between acetic acid and processing time affected WL ( p < 0.10) and WR ( p < 0.05). In general, the use of VP enhanced solutes and weight gain and it also reduced pickling time by around 50%, in comparison to pickling conducted without VP. Industrial relevance Vacuum pulse application in conjunction with increasing pickling solutes concentration resulted in a significant reduction of pickling time of whole jalapeño pepper, compared to industrial pickling. Thus, mass transfer rates of cold packing can be accelerated by vacuum pulse without heat treatment application, which can lead to significant time and energy savings in the pickling industry.

Development and multiplexed control of latching pneumatic valves using microfluidic logical structures

Novel latching microfluidic valve structures are developed, characterized, and controlled independently using an on-chip pneumatic demultiplexer. These structures are based on pneumatic monolithic membrane valves and depend upon their normally-closed nature. Latching valves consisting of both three- and four-valve circuits are demonstrated. Vacuum or pressure pulses as short as 120 ms are adequate to hold these latching valves open or closed for several minutes. In addition, an on-chip demultiplexer is demonstrated that requires only n pneumatic inputs to control 2(n-1) independent latching valves. These structures can reduce the size, power consumption, and cost of microfluidic analysis devices by decreasing the number of off-chip controllers. Since these valve assemblies can form the standard logic gates familiar in electronic circuit design, they should be useful in developing complex pneumatic circuits.

Electron acceleration by a chirped short intense laser pulse in vacuum

Electron acceleration by a chirped short intense laser pulse has been studied in a vacuum. A linear frequency chirp ω(t)=ω0(1−αt) has been considered, where ω0 is the laser frequency at z=0 and α is frequency chirp parameter. Transverse electron momentum increases due to frequency chirp and the electron escapes from the laser pulse near the pulse peak. Longitudinal momentum also increases due to increase in longitudinal force. Retained electron energy is much higher with frequency chirp than that without frequency chirp. Retained energy peaks for a suitable value of α; the value of which decreases with laser intensity and initial electron energy.

Calculation of electromagnetic field components for a fundamental Gaussian beam

Using a perturbative method, we carefully calculate seventh- and ninth-order expressions for electromagnetic field components for a fundamental Gaussian beam (i.e., a focused TEM00 mode laser beam) propagating in the medium analogous to vacuum. The interaction of a single electron and a focused laser pulse in vacuum has a promising application in the design of a powerful electron accelerator which could compete with the traditional ones. For this, ninth-order accuracy in the expansion describing the focused laser beam is required. When the vector potential corresponds to polarization along the direction of propagation, the number of electromagnetic field components can be reduced from 5 or 6 to 3. Furthermore, we find two rules obeyed by all orders of the vector potential, which greatly simplify the calculation procedure of the vector potential order by order, and make it possible to investigate the behavior of high orders.