Showing papers on "Pulse duration published in 2007"
TL;DR: In this paper, the performance of a free-electron laser operating at a wavelength of 13.7 nm where unprecedented peak and average powers for a coherent extreme-ultraviolet radiation source have been measured.
Abstract: We report results on the performance of a free-electron laser operating at a wavelength of 13.7 nm where unprecedented peak and average powers for a coherent extreme-ultraviolet radiation source have been measured. In the saturation regime, the peak energy approached 170 J for individual pulses, and the average energy per pulse reached 70 J. The pulse duration was in the region of 10 fs, and peak powers of 10 GW were achieved. At a pulse repetition frequency of 700 pulses per second, the average extreme-ultraviolet power reached 20 mW. The output beam also contained a significant contribution from odd harmonics of approximately 0.6% and 0.03% for the 3rd (4.6 nm) and the 5th (2.75 nm) harmonics, respectively. At 2.75 nm the 5th harmonic of the radiation reaches deep into the water window, a wavelength range that is crucially important for the investigation of biological samples.
1,390 citations
Patent•
Rohm1
TL;DR: In this article, an H-bridge circuit is connected to a coil of a vibration motor that is to be driven, and a comparator receives Hall signals indicating position information of a rotor of the vibration motor, and converts to an FG signal.
Abstract: An H-bridge circuit is connected to a coil of the vibration motor that is to be driven. A comparator receives Hall signals indicating position information of a rotor of the vibration motor, and converts to an FG signal. A pulse width modulator generates a pulse-modulated pulse signal specifying energization time of the coil of the vibration motor. The pulse width modulator, in a first mode, after commencing start-up of the vibration motor, sets a duty ratio of the pulse signal to 100%, and after that, switches the duty ratio to a predetermined value in accordance with rotational frequency of the motor. In a second mode, the duty ratio of the pulse signal continues to be set to 100%. In a third mode, frequency and the duty ratio of the pulse signal are set based on a control signal of a pulse form inputted from outside. The control signal is used also in switching mode.
339 citations
TL;DR: Experimental studies have confirmed the hypothesis that the application of nanosecond pulses induces a type of programmed cell death, apoptosis, in biological cells, and shown that the similarity law allows one not only to predict cell viability based on pulse parameters, but has also been shown to be applicable for inducing platelet aggregation.
Abstract: Electrical models for biological cells predict that reducing the duration of applied electrical pulses to values below the charging time of the outer cell membrane (which is on the order of 100 ns for mammalian cells) causes a strong increase in the probability of electric field interactions with intracellular structures due to displacement currents. For electric field amplitudes exceeding MV/m, such pulses are also expected to allow access to the cell interior through conduction currents flowing through the permeabilized plasma membrane. In both cases, limiting the duration of the electrical pulses to nanoseconds ensures only nonthermal interactions of the electric field with subcellular structures. This intracellular access allows the manipulation of cell functions. Experimental studies, in which human cells were exposed to pulsed electric fields of up to 300 kV/cm amplitude with durations as short as 3 ns, have confirmed this hypothesis and have shown that it is possible to selectively alter the behavior and/or survival of cells. Observed nanosecond pulsed effects at moderate electric fields include intracellular release of calcium and enhanced gene expression, which could have long term implications on cell behavior and function. At increased electric fields, the application of nanosecond pulses induces a type of programmed cell death, apoptosis, in biological cells. Cell survival studies with 10 ns pulses have shown that the viability of the cells scales inversely with the electrical energy density, which is similar to the "dose" effect caused by ionizing radiation. On the other hand, there is experimental evidence that, for pulses of varying durations, the onset of a range of observed biological effects is determined by the electrical charge that is transferred to the cell membrane during pulsing. This leads to an empirical similarity law for nanosecond pulse effects, with the product of electric field intensity, pulse duration, and the square root of the number of pulses as the similarity parameter. The similarity law allows one not only to predict cell viability based on pulse parameters, but has also been shown to be applicable for inducing platelet aggregation, an effect which is triggered by internal calcium release. Applications for nanosecond pulse effects cover a wide range: from a rather simple use as preventing biofouling in cooling water systems, to advanced medical applications, such as gene therapy and tumor treatment. Results of this continuing research are leading to the development of wound healing and skin cancer treatments, which are discussed in some detail.
326 citations
TL;DR: To the knowledge, this work presents the highest pulse energy ever extracted from fiber based femtosecond laser systems, and a nearly 2 orders of magnitude higher repetition rate than in previously published millijoule-level fiber CPA systems.
Abstract: We report on an ytterbium-doped fiber chirped-pulse amplification (CPA) system delivering millijoule level pulse energy at repetition rates above 100 kHz corresponding to an average power of more than 100 W. The compressed pulses are as short as 800 fs. As the main amplifier, an 80 μm core diameter short length photonic crystal fiber is employed, which allows the generation of pulse energies up to 1.45 mJ with a B-integral as low as 7 at a stretched pulse duration of 2 ns. A stretcher-compressor unit consisting of dielectric diffraction gratings is capable of handling the average power without beam and pulse quality distortions. To our knowledge, we present the highest pulse energy ever extracted from fiber based femtosecond laser systems, and a nearly 2 orders of magnitude higher repetition rate than in previously published millijoule-level fiber CPA systems.
291 citations
TL;DR: In this article, a Cr:forsterite master oscillator at 1250 nm, a stretcher, three optical parametrical amplifiers based on KD*P crystals providing 38 J energy in the chirped pulse at 910 nm central wavelength, and a vacuum compressor providing 43 fs pulse duration.
Abstract: 560 TW peak power has been achieved experimentally using a Cr:forsterite master oscillator at 1250 nm, a stretcher, three optical parametrical amplifiers based on KD*P crystals providing 38 J energy in the chirped pulse at 910 nm central wavelength, and a vacuum compressor providing 43 fs pulse duration. To our knowledge, it is a world-record OPCPA system and one of the five most powerful laser systems currently available.
215 citations
Patent•
12 Oct 2007TL;DR: In this article, a user configurable variable mode pulse indicator provides a user the ability to influence outputs indicative of a pulse occurrence at least during distortion, or high-noise events.
Abstract: A user configurable variable mode pulse indicator provides a user the ability to influence outputs indicative of a pulse occurrence at least during distortion, or high-noise events. For example, when configured to provide or trigger pulse indication outputs, a pulse indicator designates the occurrence of each pulse in a pulse oximeter-derived photo-plethysmograph waveform, through waveform analysis or some statistical measure of the pulse rate, such as an averaged pulse rate. When the configured to block outputs or not trigger pulse indication outputs, a pulse indicator disables the output for one or more of an audio or visual pulse occurrence indication. The outputs can be used to initiate an audible tone “beep” or a visual pulse indication on a display, such as a vertical spike on a horizontal trace or a corresponding indication on a bar display. The amplitude output is used to indicate data integrity and corresponding confidence in the computed values of saturation and pulse rate. The amplitude output can vary a characteristic of the pulse indicator, such as beep volume or frequency or the height of the visual display spike.
182 citations
01 Jan 2007
TL;DR: In this article, the authors present results of plasma assisted combustion experiments in premixed hydrocarbon-air flows excited by a low-temperature transverse repetitively pulsed discharge plasma.
Abstract: The paper presents results of plasma assisted combustion experiments in premixed hydrocarbon–air flows excited by a low-temperature transverse repetitively pulsed discharge plasma. The experiments have been conducted in methane–air and ethylene–air flows in a wide range of equivalence ratios, flow velocities, and pressures. The plasma was generated by a sequence of high-voltage (∼10 kV), short pulse duration (∼50 ns), high repetition rate (up to 50 kHz) pulses. The high reduced electric field during the pulse allows efficient electronic excitation and molecular dissociation. On the other hand, the extremely low duty cycle of the repetitively pulsed discharge, ∼1/500, greatly improves the discharge stability and helps sustaining diffuse and uniform nonequilibrium plasma. Generating this repetitively pulsed plasma in premixed hydrocarbon–air flows results in ignition and flameholding, occurring at low plasma temperatures, 140–300 °C, inferred from the nitrogen second positive band system spectra. At these conditions, the reacted fuel fraction, measured by the FTIR absorption spectroscopy, is up to 80%. The experiments demonstrate significant methane and ethylene conversion into CO, CO2, and H2O even at the conditions when there is no flame detected in the test section. At these conditions, fuel oxidation occurs due to plasma chemical reactions, without ignition. This provides additional evidence for the nonthermal fuel oxidation triggered by plasma-generated radicals.
178 citations
TL;DR: The temporal and spatial stability of the first tunable femtosecond undulator hard-x-ray source for ultrafast diffraction and absorption experiments is reported and optical control of coherent lattice motion is demonstrated.
Abstract: We report on the temporal and spatial stability of the first tunable femtosecond undulator hard-x-ray source for ultrafast diffraction and absorption experiments. The 2.5-1 Angstrom output radiation is driven by an initial 50 fs laser pulse employing the laser-electron slicing technique. By using x-ray diffraction to probe laser-induced coherent optical phonons in bulk bismuth, we estimate an x-ray pulse duration of 140+/-30 fs FWHM with timing drifts below 30 fs rms measured over 5 days. Optical control of coherent lattice motion is demonstrated.
174 citations
TL;DR: Using a simple model, it is demonstrated that two- and three-photon absorption strongly limit the THz generation efficiency at high pump fluences in ZnTe and GaP.
Abstract: We demonstrate efficient generation of THz pulses by optical rectification of 1.03 um wavelength laser pulses in LiNbO3 using tilted pulse front excitation for velocity matching between the optical and THz fields. Pulse energies of 100 nJ with a spectral bandwidth of up to 2.5 THz were obtained at a pump energy of 400 uJ and 300 fs pulse duration. This conversion efficiency of 2.5×10-4 was an order of magnitude higher than that obtained with collinear optical recitification in GaP, and far higher still than that measured using ZnTe in an optimized geometry. Using a simple model we demonstrate that two- and three-photon absorption strongly limit the THz generation efficiency at high pump fluences in ZnTe and GaP respectively.
173 citations
Journal Article•
TL;DR: In this article, the divergence of the electrons accelerated into the target was determined from spatially resolved measurements of x-ray Kemission and from transverse probing of the plasma formed on the back of the foils.
Abstract: required for fast ignition inertial fusion. The divergence of the electrons accelerated into the target was determined from spatially resolved measurements of x-ray Kemission and from transverse probing of the plasma formed on the back of the foils. Comparison of the divergence with other published data shows that it increases with I� 2 and is independent of pulse duration. Two-dimensional particle-in-cell simulations reproduce these results, indicating that it is a fundamental property of the laser-plasma interaction.
167 citations
TL;DR: It is concluded that control of ionization processes with tailored femtosecond pulses is suitable for robust manipulation of breakdown and thus control of the initial steps of laser processing of high band gap materials.
Abstract: Control of two basic ionization processes in dielectrics i.e. photo ionization and electron–electron impact ionization on intrinsic time and intensity scales is investigated experimentally and theoretically. Temporally asymmetric femtosecond pulses of identical fluence, spectrum and pulse duration result in different final free electron densities. We found that an asymmetric pulse and its time reversed counterpart address two ionization processes in a different fashion. This results in the observation of different thresholds for surface material modification in sapphire and fused silica. We conclude that control of ionization processes with tailored femtosecond pulses is suitable for robust manipulation of breakdown and thus control of the initial steps of laser processing of high band gap materials.
TL;DR: This Letter presents a consistent quantum and relativistic model of short-pulse Child-Langmuir (CL) law, of which the pulse length tau is less than the electron transit time in a gap of spacing D and voltage V.
Abstract: This Letter presents a consistent quantum and relativistic model of short-pulse Child-Langmuir (CL) law, of which the pulse length $\ensuremath{\tau}$ is less than the electron transit time in a gap of spacing $D$ and voltage $V$. The classical value of the short-pulse CL law is enhanced by a large factor due to quantum effects when the pulse length and the size of the beam are, respectively, in femtosecond duration and nanometer scale. At high voltage larger than the electron rest mass, relativistic effects will suppress the enhancement of short-pulse CL law, which is confirmed by particle-in-cell simulation. When the pulse length is much shorter than the gap transit time, the current density is proportional to $V$, and to the inverse power of $D$ and $\ensuremath{\tau}$.
TL;DR: In this article, finite element techniques have been applied to predict the residual stress fields induced in two different stainless steels, combining shock wave hydrodynamics and strain rate dependent mechanical behaviour.
Abstract: Laser shock processing, also known as laser shock peening, generates through a laser-induced plasma, plastic deformation and compressive residual stresses in materials for improved fatigue or stress corrosion cracking resistances. The calculation of mechanical effects is rather complex, due to the severity of the pressure loading imparted in a very short time period (in the ns regime). This produces very high strain rates (106 s−1), which necessitate a precise determination of dynamic properties.Finite element techniques have been applied to predict the residual stress fields induced in two different stainless steels, combining shock wave hydrodynamics and strain rate dependent mechanical behaviour. The predicted residual stress fields for single or multiple laser processes were correlated with those from experimental data, with a specific focus on the influence of process parameters such as pressure pulse amplitude and duration, laser spot size or sacrificial overlay.Among other results, simulations confirmed that the affected depths increased with pulse duration, peak pressure and cyclic deformations, thus reaching much deeper layers (> 0.5 mm) than with any other conventional surface processing. To improve simulations, the use of experimental VISAR determinations to determine pressure loadings and elastic limits under shock conditions (revealing different strain-rate dependences for the two stainless steels considered) was shown to be a key point.Finally, the influence of protective coatings and, more precisely, the simulation of a thermo-mechanical uncoated laser shock processing were addressed and successfully compared with experiments, exhibiting a large tensile surface stress peak affecting a few tenths of micrometres and a compressive sub-surface stress field.
TL;DR: Repeated pulsed electrical stimulation is used in a multitude of neural interfaces; damage resulting from such stimulation was studied as a function of pulse duration, electrode size, and number of pulses using a fluorescent assay on chick chorioallontoic membrane in vivo and chick retina in vitro.
Abstract: Repeated pulsed electrical stimulation is used in a multitude of neural interfaces; damage resulting from such stimulation was studied as a function of pulse duration, electrode size, and number of pulses using a fluorescent assay on chick chorioallontoic membrane (CAM) in vivo and chick retina in vitro. Data from the chick model were verified by repeating some measurements on porcine retina in-vitro. The electrode size varied from 100 mum to 1 mm, pulse duration from 6 mus to 6 ms, and the number of pulses from 1 to 7500. The threshold current density for damage was independent of electrode size for diameters greater than 300 mum, and scaled as 1/r2 for electrodes smaller than 200 mum. Damage threshold decreased with the number of pulses, dropping by a factor of 14 on the CAM and 7 on the retina as the number of pulses increased from 1 to 50, and remained constant for a higher numbers of pulses. The damage threshold current density on large electrodes scaled with pulse duration as approximately 1/t0.5, characteristic of electroporation. The threshold current density for repeated exposure on the retina varied between 0.061 A/cm2 at 6 ms to 1.3 A/cm2 at 6 mus. The highest ratio of the damage threshold to the stimulation threshold in retinal ganglion cells occurred at pulse durations near chronaxie - around 1.3 ms.
TL;DR: The ability to predictably control torque output by simultaneously controlling pulse frequency and duration is demonstrated and the need to minimize stimulation frequency to control fatigue is suggested.
Abstract: Neuromuscular electrical stimulation (NMES) involves the use of electrical current to facilitate contraction of skeletal muscle. However, little is known concerning the effects of varying stimulation parameters on muscle function in humans. The purpose of this study was to determine the extent to which varying pulse duration and frequency altered torque produc- tion and fatigability of human skeletal muscle in vivo. Ten subjects under- went NMES-elicited contractions of varying pulse frequencies and durations as well as fatigue tests using stimulation trains of equal total charge, yet differing parametric settings at a constant voltage. Total charge was a strong predictor of torque production, and pulse trains with equal total charge elicited identical torque output. Despite similar torque output, higher- frequency trains caused greater fatigue. These data demonstrate the ability to predictably control torque output by simultaneously controlling pulse frequency and duration and suggest the need to minimize stimulation frequency to control fatigue. Muscle Nerve 35: 504 -509, 2007
TL;DR: In adult neurosurgical patients with a normal motor status under total intravenous anesthesia, an individual pulse duration of 0.5 ms and an ISI of 4 ms provide the lowest motor thresholds, which confirm not only studies for D wave recovery but also provide optimal stimulation parameters for intraoperative near threshold stimulation.
TL;DR: Intense sub-5-fs pulses were generated by filamentation in a noble gas and subsequent chirped-mirror pulse compression and the transversal spatial dependence of the temporal pulse profile was investigated by spatial selection of parts of the output beam.
Abstract: Intense sub-5-fs pulses were generated by filamentation in a noble gas and subsequent chirped-mirror pulse compression. The transversal spatial dependence of the temporal pulse profile was investigated by spatial selection of parts of the output beam. Selecting the central core of the beam is required for obtaining the shortest possible pulses. Higher energy efficiency is only obtained at the expense of pulse contrast since towards the outer parts of the beam the energy is spread into satellite structures leading to a double-pulse profile on the very off-axis part of the beam. Depending on the requirements for a particular application, a trade-off between the pulse duration and the pulse energy has to be done. The energy of the sub-5-fs pulses produced was sufficient for the generation of high order harmonics in Argon. In addition, full simulation is performed in space and time on pulse propagation through filamentation that explains the double-pulse structure observed as part of a conical emission enhanced by the plasma defocusing.
TL;DR: The authors generated 1 mW of average output power at 2.8 THz in a diffraction-limited beam by placing a 6-mm-long quasi-phase-matched GaAs crystal inside the cavity of a synchronously pumped optical parametric oscillator (OPO).
Abstract: We generated 1 mW of average output power at 2.8 THz (bandwidth of ∼300 GHz) in a diffraction-limited beam by placing a 6-mm-long quasi-phase-matched GaAs crystal inside the cavity of a synchronously pumped optical parametric oscillator (OPO). The OPO used type-II-phase-matched periodically poled lithium niobate as a gain medium and was pumped by a mode-locked laser at 1064 nm, with a 7 ps pulse duration, 50 MHz repetition rate, and 10 W average output power. The terahertz radiation was generated by difference frequency mixing between the signal and idler waves of the near-degenerate doubly resonant OPO.
TL;DR: In this paper, the influence of the machining parameters (including pulse duration, discharge current, sustained pulse time, pulse interval time, polarity effect, material and dielectric) on surface roughness in the finish cut of wire electrical discharge machining (WEDM) was investigated.
Abstract: Surface roughness is significant to the finish cut of wire electrical discharge machining (WEDM). This paper describes the influence of the machining parameters (including pulse duration, discharge current, sustained pulse time, pulse interval time, polarity effect, material and dielectric) on surface roughness in the finish cut of WEDM. Experiments proved that the surface roughness can be improved by decreasing both pulse duration and discharge current. When the pulse energy per discharge is constant, short pulses and long pulses will result in the same surface roughness but dissimilar surface morphology and different material removal rates. The removal rate when a short pulse duration is used is much higher than when the pulse duration is long. Moreover, from the single discharge experiments, we found that a long pulse duration combined with a low peak value could not produce craters on the workpiece surface any more when the pulse energy was reduced to a certain value. However, the condition of short pulse duration with high peak value still could produce clear craters on the workpiece surface. This indicates that a short pulse duration combined with a high peak value can generate better surface roughness, which cannot be achieved with long pulses. In the study, it was also found that reversed polarity machining with the appropriate pulse energy can improve the machined surface roughness somewhat better compared with normal polarity in finish machining, but some copper from the wire electrode is accreted on the machined surface.
TL;DR: The physical basis of the dependence of tissue erosion on pulse parameters, an optical method was used to monitor the effects of pulse parameters on the cavitating bubble cloud generated by histotripsy pulses at a tissue-water interface, and results show the duration of growth and collapse of the bubble cloud increased with increasing pulse duration, peak rarefactional pressure, and PRF.
Abstract: High intensity pulsed ultrasound can produce significant mechanical tissue fractionation with sharp boundaries (“histotripsy”). At a tissue-fluid interface, histotripsy produces clearly demarcated tissue erosion and the erosion efficiency depends on pulse parameters. Acoustic cavitation is believed to be the primary mechanism for the histotripsy process. To investigate the physical basis of the dependence of tissue erosion on pulse parameters, an optical method was used to monitor the effects of pulse parameters on the cavitating bubble cloud generated by histotripsy pulses at a tissue-water interface. The pulse parameters studied include pulse duration, peak rarefactional pressure, and pulse repetition frequency (PRF). Results show that the duration of growth and collapse (collapse cycle) of the bubble cloud increased with increasing pulse duration, peak rarefactional pressure, and PRF when the next pulse arrived after the collapse of the previous bubble cloud. When the PRF was too high such that the next pulse arrived before the collapse of the previous bubble cloud, only a portion of histotripsy pulses could effectively create and collapse the bubble cloud. The collapse cycle of the bubble cloud also increased with increasing gas concentration. These results may explain previous in vitro results on effects of pulse parameters on tissue erosion.
TL;DR: The response of the electronic system of LiH to a few-cycle strong field is computed by a time-dependent multiconfiguration method using a large, adaptive, basis set and it is shown possible to direct the electrons to move along the Li-H bond or normal to it.
Abstract: The response of the electronic system of LiH to a few-cycle strong field is computed by a time-dependent multiconfiguration method using a large, adaptive, basis set. The intensity, pulse duration, polarization, and phase of carrier frequency can all be tuned to steer the motion of the electrons. It is shown possible to, e.g., direct the electrons to move along the Li-H bond or normal to it. By shifting the phase, the electrons can be driven toward the Li nucleus or away from it. When the pulse is polarized not along the bond the result is a rotation of the charge density.
TL;DR: A proof of the concept using transmit SENSE 3D tailored RF pulses designed for small flip angles that produced more homogeneous images than those obtained from the complex sum of images from all receivers excited with a standard RF pulse is presented.
Abstract: Parallel transmitter techniques are a promising approach for reducing transmitter B1 inhomogeneity due to the potential for adjusting the spatial excitation profile with independent RF pulses. These techniques may be further improved with transmit sensitivity encoding (SENSE) methods because the sensitivity information in pulse design provides an excitation that is inherently compensated for transmitter B1 inhomogeneity. This paper presents a proof of this concept using transmit SENSE 3D tailored RF pulses designed for small flip angles. An eight-channel receiver coil was used to mimic parallel transmission for brain imaging at 3T. The transmit SENSE pulses were based on the fast-k(z) design and produced 5-mm-thick slices at a flip angle of 30 degrees with only a 4.3-ms pulse length. It was found that the transmit SENSE pulses produced more homogeneous images than those obtained from the complex sum of images from all receivers excited with a standard RF pulse.
TL;DR: In this paper, the authors developed a RF driven negative ion source for the ITER neutral beam injection system, which is now an interesting alternative to the reference design with filamented sources due to its in principle maintenance-free operation.
Abstract: IPP Garching has successfully developed a RF driven negative ion source for the ITER neutral beam injection system. The RF source is now an interesting alternative to the reference design with filamented sources due to its in principle maintenance-free operation. Current densities of 330 A/m 2 and 230 A/m 2 have been achieved for hydrogen and deuterium, respectively, at a pressure of 0.3 Pa and an electron/ion ratio of 1 for a small extraction area (7.0x10 -3 m 2 ) and short pulses (< 4 s). Reliable deuterium operation with more than 150 pulses in the required parameter range was obtained by an improved cesium operation utilizing a control of all source temperatures (grid as well as source body) and monitoring the amount of cesium in the source. The de- velopment concentrates now on extending the pulse length to up to 1 hour and extending the size of the source. The long pulse test bed went into operation last year; pulses of up to some 100 seconds with more or less stable conditions in terms of extracted currents and Cs dynamics have been achieved with current densities in the range of 150 - 200 A/m 2 in hydrogen operation. The pulse length, however, is still limited by non-sufficient cooling of some parts of the source and the RF circuit. The commissioning of the so-called "half-size" source test facility started recently with the first plasma pulses; this large RF source with the width and half the height of the ITER NNBI source is dedicated to the demonstration of the homogeneity of a large RF plasma — extraction is fore- seen in a latter phase — and the tests of an ITER-relevant RF circuit.
TL;DR: In this paper, the authors apply ultra-short pulse laser ablation to create local contact openings in thermally grown passivating SiO2 layers, which can be used for locally contacting oxide passivated Si solar cells.
Abstract: We apply ultra-short pulse laser ablation to create local contact openings in thermally grown passivating SiO2 layers. This technique can be used for locally contacting oxide passivated Si solar cells. We use an industrially feasible laser with a pulse duration of τpulse ∼ 10 ps. The specific contact resistance that we reach with evaporated aluminium on a 100 Ω/sq and P-diffused emitter is in the range of 0·3–1 mΩ cm2. Ultra-short pulse laser ablation is sufficiently damage free to abandon wet chemical etching after ablation. We measure an emitter saturation current density of J0e = (6·2 ± 1·6) × 10−13 A/cm2 on the laser-treated areas after a selective emitter diffusion with Rsheet ∼ 20 Ω/sq into the ablated area; a value that is as low as that of reference samples that have the SiO2 layer removed by HF-etching. Thus, laser ablation of dielectrics with pulse durations of about 10 ps is well suited to fabricate high-efficiency Si solar cells. Copyright © 2007 John Wiley & Sons, Ltd.
TL;DR: A rod-type ytterbium-doped photonic crystal fiber with a 70 microm core as gain medium is employed, allowing for very short pulse durations, high energy storage, and emission of a single-transverse-mode beam.
Abstract: We report on a Q-switched short-length fiber laser producing 100 W of average output power at 100 kHz repetition rate and pulse durations as short as 17 ns. Up to 2 mJ of energy and sub-10-ns pulse duration are extracted at lower repetition rates. This performance is obtained by employing a rod-type ytterbium-doped photonic crystal fiber with a 70 microm core as gain medium, allowing for very short pulse durations, high energy storage, and emission of a single-transverse-mode beam.
TL;DR: In this paper, the influences of EDM pulse condition on the micro-EDM properties were investigated and the experimental results showed that the voltage and current of the pulse exert strongly to the machining properties and the shorter EDM pulses are more efficient to make a precision part with a higher material removal rate.
TL;DR: A new, high-frequency, time-resolved scanning acoustic microscope developed for studying dynamical processes in biological cells and able to measure acoustical properties of a single HeLa cell in vivo and to derive elastic parameters of subcellular structures is described.
Abstract: In this paper, we describe a new, high-frequency, time-resolved scanning acoustic microscope developed for studying dynamical processes in biological cells. The new acoustic microscope operates in a time-resolved mode. The center frequency is 0.86 GHz, and the pulse duration is 5 ns. With such a short pulse, layers thicker than 3 mum can be resolved. For a cell thicker than 3 mum, the front echo and the echo from the substrate can be distinguished in the signal. Positions of the first and second pulses are used to determine the local impedance of the cell modeled as a thin liquid layer that has spatial variations in its elastic properties. The low signal-to-noise ratio in the acoustical images is increased for image generation by averaging the detected radio frequency signal over 10 measurements at each scanning point. In conducting quantitative measurements of the acoustic parameters of cells, the signal can be averaged over 2000 measurements. This approach enables us to measure acoustical properties of a single HeLa cell in vivo and to derive elastic parameters of subcellular structures. The value of the sound velocity inside the cell (1534.5 plusmn 33.6 m/s) appears to be only slightly higher than that of the cell medium (1501 m/s).
TL;DR: In this paper, a fine-finish power supply for wire-EDM was developed and applied in eliminating titanium's bluing and rusting effect and reducing micro-cracking in tungsten carbide caused by electrolysis and oxidation, which can achieve a fine surface finish as low as 0.22μm R a.
Abstract: This paper presents the development and application of a new fine-finish power supply in wire-EDM. The transistor-controlled power supply composed of a full-bridge circuit, two snubber circuits and a pulse control circuit was designed to provide the functions of anti-electrolysis, high frequency and very-low-energy pulse control. Test results indicated that the pulse duration of discharge current can be shortened through the adjustment of capacitance in parallel with the sparking gap. High value of capacitance contributes to longer discharge duration. A high current-limiting resistance results in the decrease of discharge current. Peak current increases with the increase of pulse on-time and thus contributes to an increase in thickness of recast layer. Experimental results not only verify the usefulness of the developed fine-finish power supply in eliminating titanium's bluing and rusting effect and reducing micro-cracking in tungsten carbide caused by electrolysis and oxidation, but also demonstrate that the developed system can achieve a fine surface finish as low as 0.22 μm R a .
TL;DR: The plateaulike region observed between 100 fs and 1 ps for the corneal layers indicates that for use in laser surgery, laser pulse durations chosen within this range should be practically equivalent.
Abstract: The surface ablation threshold fluence of fused silica and two porcine cornea layers, the epithelium and the stroma, is characterized as a function of the laser pulse duration in the range of 100 fs-5 ps for a wavelength of 800 nm (Ti:sapphire laser system). The plateaulike region observed between 100 fs and 1 ps for the corneal layers indicates that for use in laser surgery, laser pulse durations chosen within this range should be practically equivalent. Our model predicts that the ablation threshold will decrease rapidly for pulse durations in the low end of the femtosecond regime.
TL;DR: The results show that a soliton pulse can be generated during the two-photon resonant propagation of few-cycle pulse in the polar molecule medium and depend crucially on the carrier-envelope phase of the incident pulse.
Abstract: We theoretically investigate carrier-envelope phase dependence of few-cycle ultrashort laser pulse propagation in a polar molecule medium. Our results show that a soliton pulse can be generated during the two-photon resonant propagation of few-cycle pulse in the polar molecule medium. Moreover, the main features of the soliton pulse, such as pulse duration and intensity, depend crucially on the carrier-envelope phase of the incident pulse, which could be utilized to determine the carrier-envelope phase of a few-cycle ultrashort laser pulse from a mode-locked oscillator.