Laser Triggering Research Articles

Externally Triggered Glass Transition Switch for Localized On‐Demand Drug Delivery

I want a new drug dose: External on-demand laser triggering is used in a drug-delivery concept, with on/off ratios in excess of 1000/1. The switching mechanism involves the glass transition of hydrophobic polymers with a large change in diffusivity. Formation of a glassy surface layer of the implant in the off state plays a key role, resulting in negligible off-release. (Picture: data points indicate ibuprofen concentration).

Effects of Laser Triggering Parameters on Runtime and Jitter of a Gas Switch

Parameters affecting the runtime and jitter of a laser triggered gas switch have been studied. Experiments tested a variety of switch parameters including percentage of selfbreak and switch pressure. The effects of laser beam parameters were also considered, including focal length, laser energy, laser spark length, and laser wavelength. Experiments were performed on the Tiger pulsed power machine. Measurements were taken on a spark gap switch built from the trigger section of a Rimfire switch. A Marx bank consisting of 32, 3.1 uF, capacitors that fed into a 7 nF intermediate storage capacitor was used to drive the switch into a 4 ? resistive load. The test switch was pressurized to 306 kPa (30 psig) with SF6 and operated near 1 MV. A New Wave Tempest Nd:YAG laser was used to trigger breakdown of the switch. The laser was focused at the mid-gap between the switch electrodes using lenses with focal lengths between 30 cm and 100 cm. Focused laser energy in the switch ranged from <5 mJ to 80 mJ. The effects of switch and laser beam parameters on the runtime and jitter of a laser triggered gas switch are presented. The end goal of the research is to determine optimal conditions for improved switch performance.

Achieving Size Independent Hit-Rate in Single Particle Mass Spectrometry

Recent improvements in single particle mass spectrometers make it possible to optically detect, size, and characterize the compositions of individual particles with diameters larger than a micron and smaller than 100 nm. In these instruments, two stages of optical detection are used to generate a precisely timed trigger pulse that is used to fire the ion generation laser or lasers. However, experience shows that the wide particle size range results in significant differences in laser trigger timing between small and large particles. If not treated these differences produce an instrument with size dependent hit-rate. In this case the operator is forced to optimize the instrument for the desired size range, while contending with a significantly lower hit-rate for other particle sizes. This article presents an analysis of the phenomenon and demonstrates that the dependence of laser trigger timing on particle size stems from the differences in the particle position within the detection laser beam at the insta...

Development of a hard nano-structured multi-component ceramic coating by laser cladding

The present paper reports laser-assisted synthesis of a multi-component ceramic composite coating consisting of aluminum oxide, titanium di-boride and titanium carbide (Al 2O 3–TiB 2–TiC). A pre-placed powder mixture of aluminum (Al), titanium oxide (TiO 2) and boron carbide (B 4C) was made to undergo self-propagating high-temperature synthesis (SHS) by laser triggering. Laser subsequently effected cladding of the products of SHS on the substrate. The effect of laser scanning speed on the hardness, microstructure and phase composition of the composite coating was investigated. The coating exhibited an increase in hardness and a decrease in grain size with increase in laser scanning speed. A maximum micro-hardness of 2500 HV 0.025 was obtained. X-ray diffraction (XRD) of the top surface of the coating revealed the presence of aluminum oxide (Al 2O 3), titanium di-boride (TiB 2) and titanium carbide (TiC) along with some non-stoichiometric products of the Ti–Al–B–C–O system. Field emission gun scanning electron microscopy (FESEM) and high-resolution transmission electron microscopic (HRTEM) analysis revealed some nano-structured TiB 2 and Al 2O 3, which are discussed in detail.

X radiation from a laser-triggered spark gap

Laser triggering of spark gaps is now widely used for low-jitter firing of one or several spark gaps [1–5]. The most important advantage of laser-triggered high-voltage spark gaps is no galvanic coupling between the gap electrodes and the laser. This allows low-jitter firing of one or several spark gaps to which electrodes a dc or a pulsed voltage is applied. Conduction between the spark gap electrodes is initiated by the plasma produced at one of the electrodes or in the gas-filled gap. For a laser-triggered spark gap, the trigger delay and jitter depend on the gas mixture composition and pressure, laser beam focusing site, electric field strength, laser wavelength, radiation power density and pulse duration, and laser beam divergence. For low radiation pulse energies, the shortest trigger delays are achieved for systems with uv lasers, though in some cases, pulsed lasers operating in other spectral ranges are used. Elegas (SF6) or its mixtures with nitrogen are generally used for the working gas in high-voltage spark gaps. SF6 is electronegative gas possessing high electric strength. In optimum conditions (high electric fields, optical breakdown of the gas in a gap at the cathode) the delay time of the spark gap triggering after application of a laser pulse is a few nanoseconds, and the jitter is no more than 1 ns even for a rather short length of the laser spark (about ten gap spacings). Recently it has been shown [6] that the spark preionization systems that are widely used to initiate a volumetric discharge in pulsed lasers generate not only uv and vuv radiation, but also x rays. This makes preionization more uniform and improves the lasing performance for some lasers. There are many reports on x radiation and runaway electron beams in nanosecond discharges initiated in a nonuniform electric field (see, e.g., [7, 8–14]). Supershort avalanche electron beams (SAEBs) where produced in gas diodes at a pressure of 12 atm for helium, 4 atm for nitrogen, and 2 atm for xenon and elegas [8, 10, 14]. It was natural to suggest that runaway electrons and x radiation are generated in a laser-triggered discharge gap as well, and it is just the runaway electrons and x radiation that provide low-jitter laser triggering. However, we have found no information on this subject in the available literature. Note that in conditions of laser triggering, the threshold of optical breakdown for gases used in spark gaps is in the range 5⋅10– 5⋅10 W/cm [1, 15], which is several orders of magnitude lower than the threshold for the appearance of runaway electrons and x radiation in a laser plasma [16]. The goal of the work under discussion was to detect x radiation from a laser-triggered spark gap and to demonstrate that the generation of x radiation in the gap is due to the electric field enhancement by the laser-produced plasma.

Study of novel plasma devices generated by high power lasers coupled with a micro-pulse power technology

The authors have proposed introducing a micro pulse power technology in high power laser plasma experiments to boost up the return current, resulting in efficiently guiding of energetic electrons. High current pulse power generators with a pulse laser trigger system generate high-density plasma that is well conductor. To efficiently guiding by using a micro pulse power, we estimated parameter of a micro pulse power system that is voltage of rise time, current, charging voltage and capacitance.

The Progress of the Front-end Source of the SG-II High Power Laser System

This article describes the front-end system for the SG-II high power laser facility. The front-end of SG-II is based on amplitude waveguide modulator pulse shaping technology and short pulse laser trigger synchronization technology. A phase modulator is used to broaden the frequency spectrum to suppress SBS effect. And a wide spectrum Nd:glass regenerative amplifier pumped by LD is developed. In order to improve the fill factor of the output laser beam to acquire maximum energy of SG-II, the spatial shaping system is developed to control the intensity distribution.

Architecture of petawatt-classz-pinch accelerators

We have developed an accelerator architecture that can serve as the basis of the design of petawatt-class $z$-pinch drivers. The architecture has been applied to the design of two $z$-pinch accelerators, each of which can be contained within a 104-m-diameter cylindrical tank. One accelerator is driven by slow ($\ensuremath{\sim}1\text{ }\ensuremath{\mu}\mathrm{s}$) Marx generators, which are a mature technology but which necessitate significant pulse compression to achieve the short pulses ($\ensuremath{\ll}1\text{ }\ensuremath{\mu}\mathrm{s}$) required to drive $z$ pinches. The other is powered by linear transformer drivers (LTDs), which are less mature but produce much shorter pulses than conventional Marxes. Consequently, an LTD-driven accelerator promises to be (at a given pinch current and implosion time) more efficient and reliable. The Marx-driven accelerator produces a peak electrical power of 500 TW and includes the following components: (i) 300 Marx generators that comprise a total of $1.8\ifmmode\times\else\texttimes\fi{}{10}^{4}$ capacitors, store 98 MJ, and erect to 5 MV; (ii) 600 water-dielectric triplate intermediate-store transmission lines, which also serve as pulse-forming lines; (iii) 600 5-MV laser-triggered gas switches; (iv) three monolithic radial-transmission-line impedance transformers, with triplate geometries and exponential impedance profiles; (v) a 6-level 5.5-m-diameter 15-MV vacuum insulator stack; (vi) six magnetically insulated vacuum transmission lines (MITLs); and (vii) a triple-post-hole vacuum convolute that adds the output currents of the six MITLs, and delivers the combined current to a $z$-pinch load. The accelerator delivers an effective peak current of 52 MA to a 10-mm-length $z$ pinch that implodes in 95 ns, and 57 MA to a pinch that implodes in 120 ns. The LTD-driven accelerator includes monolithic radial transformers and a MITL system similar to those described above, but does not include intermediate-store transmission lines, multimegavolt gas switches, or a laser trigger system. Instead, this accelerator is driven by 210 LTD modules that include a total of $1\ifmmode\times\else\texttimes\fi{}{10}^{6}$ capacitors and $5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ 200-kV electrically triggered gas switches. The LTD accelerator stores 182 MJ and produces a peak electrical power of 1000 TW. The accelerator delivers an effective peak current of 68 MA to a pinch that implodes in 95 ns, and 75 MA to a pinch that implodes in 120 ns. Conceptually straightforward upgrades to these designs would deliver even higher pinch currents and faster implosions.

Examining the Influence of Changing Laser Pulse Repetition Frequencies on Conifer Forest Canopy Returns

The distribution of laser pulses within conifer forest trees and canopies are examined by varying the rate of laser pulse emission and the inherent laser pulse properties (laser pulse energy, pulse width, pulse length, and roll-over or trigger time). In this study, an Optech, Inc. ALTM 3100 airborne lidar is used, emitting pulses at 50 kHz and 100 kHz, allowing for changes in laser pulse characteristics while also keeping all other survey parameters equal. We found that: 1. Pulses and associated characteristics emitted at 50 kHz penetrated further into the canopy than 100 kHz for a significant number of individual trees. 2. At tall tree plots with no understory, pulses emitted at 50 kHz penetrated further into the canopy than 100 kHz for a significant number of plots. 3. For plots with significant understory and shorter trees, pulses emitted at 100 kHz penetrated further into the canopy than 50 kHz. We suspect that this may be due, in part, to canopy openness. Laser pulse energy and character differences associated with different laser pulse emission frequencies are likely a contributing factor in laser pulse penetration through the canopy to the ground surface. Efforts to understand laser pulse character influences on canopy returns are important as biomass and vegetation structure models derived from lidar are increasingly adopted.

Particle-in-Cell Model of a Laser-Triggered Spark Gap

A particle-in-cell simulation of the streamer formation process in a laser-triggered spark gap has been developed to estimate streamer radius and conductivity under a variety of conditions. The motivation for developing the model was to understand the initial conditions of the switching arc in a laser-triggered spark gap, with the goal of accelerating the resistive decay of the arc. In a parallel plate switch configuration with dimensions of 0.6 mm times 0.3 mm, the electric field was varied from 2 to 5 MV/m, the gas pressure was varied from 1 to 1.5 atm, and the gas type was varied between Ar and Ne. The laser triggering parameters, including the laser ionization rate (from 5 to 20middot10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ), laser spot area (from 1200 to 4800 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), and laser spot orientation relative to the electric field, were also varied. The electric field had a large influence on radius, increasing it by 19% with increasing field, and on conductivity, resulting in a 285% increase with increasing field. Among the laser triggering parameters, a linear focal spot-oriented transverse relative to the electric field direction was observed to produce a very large increase in streamer radius

Multichannel and Impedance Analysis of the Laser-Triggered Rimfire Gas Switch

Many pulsed power applications require multichannel switching because of stringent low erosion and low impedance requirements. Rimfire, which is a multigap multichanneling switch, has been implemented extensively for this purpose at Sandia National Laboratories for several decades, but with incomplete understanding. This paper presents a thorough experimental analysis of impedance and multichanneling characteristics for a multigap switch under the influence of a laser trigger and in an SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> environment. The implications of these results on the future design of multichanneling multigap gas switches are also presented

Four-channel laser-triggered spark gap

Results on the simultaneous discharge initiations in a modified geometry of four-channel gas-filled spark gap with 45° angle of laser beam incidence on the electrode surface are presented. Laser triggering of the spark gap in our capillary-discharge driver CAPEX-U by a single laser system has been realised. A Q-switched YAG laser (λ = 1 064 nm) irradiated each of four spark gap channels with 200 mJ energy in a 6-ns pulse by use of a beam-splitting technique.

Primary Investigation into the Laser Triggering Multi-Gap Multi-Channel Gas Switch in a Single Test Module Facility

A high precision laser trigger system is built up in the single test module of Primary Test Stand (PTS) facility. A fourth harmonic, with a wavelength λ of 266 nm, Q-switched Nd:YAG laser was used to trigger the 5 MV multi-gap multi-channel gas switch which was filled with high pressure SF6-N2 mixture gas. The maximum deviation and the standard deviation in the jitter time of the trigger system is ± 0.7 ns and 0.3 ns respectively. The maximum deviation and the standard deviation in the jitter time for the multi-gap multi-channel laser triggering switch is ± 2.4 ns and 1.5 ns respectively. The curve of switch delay-time versus laser energy is obtained, which is helpful for the choice of fitting laser energy. The successful test with two lasers indicated that the design of using twenty-four lasers to trigger twenty-four switches respectively is feasible in ``PTS''.

Improved laser triggering and guiding of meqavolt discharges with dual fs-ns pulses

We demonstrate that the capacity of ultrashort high-power laser pulses to trigger and guide high-voltage discharges can be significantly enhanced by a subsequent visible nanosecond laser pulse. The femtosecond pulse induces a bundle of filaments, which creates a conducting channel of low density and cold plasma connecting the electrodes. The subsequent laser pulse photodetaches electrons from O2− ions in the electrode leader. The resulting electrons allow efficient heating by Joule effect in a retroaction loop, resulting in a 5% reduction of the breakdown voltage.

Comparison of low intensity laser therapy and trigger point injection in the management of myofascial pain syndrome

AbstractMyofascial Pain Syndrome (MPS) is quite a common clinical manifestation characterised by the presence of trigger points (TrP), muscle spasm, tenderness, motion restriction, weakness and autonomic dysfunction. The ideal therapy should be fast, cheap and long-term effective. Local anesthetic injection and low-intensity laser therapy are two types of such treatments. Aim: The main purpose of this study was to compare the effectiveness of TrP injection and low intensity laser therapy in patients with MPS. Method: 43 patients (14 men, 29 women) diagnosed as MPS were included in this study. In the first group (23 cases), laser therapy was applied for 3 min to each TrP within 12 sessions. In the second group (20 cases), 1 ml prilocaine 2% was injected to the TrP once a week for four consecutive weeks. The evaluation was made before the treatment (BT), after the treatment (AT) and sixth months after the treatment (SMT). Effectiveness of treatment was evaluated by a visual analog scale (VAS), a pressure al...

Design of a timing circuit for random laser triggering on aerosol particles

A versatile timing device has been developed that permits a variety of lasers, including Nd:YAG (yttrium aluminum garnet), excimer, and CO2 lasers, to be triggered at random times. The present application is to single-particle mass spectrometry, where the corresponding arrival times are random and signaled by a laser light-scattering apparatus. The timing circuit triggers the Nd:YAG laser flashlamps approximately 200μs prior to the desired laser output pulse, followed by the Q-switch triggering pulses, which can also be used to control other lasers and/or the ion extraction optics. The flashlamps are discharged ten times per second to maintain the proper heat load on the Nd:YAG laser flashlamps. If fewer than 10particles∕s are detected by light-scattering apparatus, the unit sends substitute pulses to maintain the average of 10discharges∕s. When the particle flux is higher than ten per second, the circuit is designed to ignore the extra particle events. A simpler version of the circuit is also described, ...

Substrate-induced Conformational Changes in the Membrane-embedded IICmtl-domain of the Mannitol Permease from Escherichia coli, EnzymeIImtl, Probed by Tryptophan Phosphorescence Spectroscopy

Membrane-bound transport proteins are expected to proceed via different conformational states during the translocation of a solute across the membrane. Tryptophan phosphorescence spectroscopy is one of the most sensitive methods used for detecting conformational changes in proteins. We employed this technique to study substrate-induced conformational changes in the mannitol permease, EnzymeII(mtl), of the phosphoenolpyruvate-dependent phosphotransferase system from Escherichia coli. Ten mutants containing a single tryptophan were engineered in the membrane-embedded IIC(mtl)-domain, harboring the mannitol translocation pathway. The mutants were characterized with respect to steady-state and time-resolved phosphorescence, yielding detailed, site-specific information of the Trp microenvironment and protein conformational homogeneity. The study revealed that the Trp environments vary from apolar, unstructured, and flexible sites to buried, highly homogeneous, rigid peptide cores. The most remarkable example of the latter was observed for position 97, because its long sub-second phosphorescence lifetime and highly structured spectra in both glassy and fluid media imply a well defined and rigid core around the probe that is typical of beta-sheet-rich structural motifs. The addition of mannitol had a large impact on most of the Trp positions studied. In the case of position 97, mannitol binding induced partial unfolding of the rigid protein core. On the contrary, for residue positions 126, 133, and 147, both steady-state and time-resolved data showed that mannitol binding induces a more ordered and homogeneous structure around these residues. The observations are discussed in context of the current mechanistic and structural model of EII(mtl).

Method for acquiring extended real-time kinetic signals in nanosecond laser flash photolysis experiments

We report a data acquisition method for detecting transient absorbance signals extended in time which require nanosecond resolution and need to span several decades in time up to the hundreds of milliseconds. A microprocessor is used to generate a sequence of up to 100, 2.120 μs wide radio frequency signals at 500 MHz which are used to trigger the analog-to-digital conversion on a digital oscilloscope, operating in the external clock mode. During these radio frequency bursts the data are sampled at a sampling rate of 500 Ms/s. The delay of each sampling burst can be set at arbitrary values with respect to the first signal, with a minimum delay of 0.96 μs for the second pulse, and 1.2 μs for all other pulses. The microprocessor provides accessory synchronization outputs for laser triggering and for shutter opening and closing. This data acquisition system allows measuring the complete time course of extended kinetics after each laser shot, thus reducing acquisition times and data size. We prove the complete equivalence of the proposed acquisition method with standard methods, where several time bases are acquired to cover the complete kinetic trace for the ligand rebinding to myoglobin after photolysis of a gel embedded myoglobin-CO complex.

Development of a video trigger for ultra high-speed video camera

An ultra high-speed video camera whose frame rate is 1 million frames/second was developed by a cooperative R and D project of Kinki University and Shimadzu Corporation in September, 2001. In this ultra high-speed video camera, the continuous overwriting system is used. Number of recorded frame is 103. In case of high-speed image capturing, a method of sending a trigger signal for stopping continuous overwriting becomes important. Currently available trigger systems are mainly a trigger by sound and a trigger by laser. In the case of image capturing of a bursting balloon, we can use the sound and/or laser trigger. However, it is difficult to capture images at an ultra-high frame rate under a microscope. A video trigger system, which can be applied to microscopic ultra high-speed image capturing, is under development. In this paper, an algorithm for detection of a sudden change of brightness in an image is presented.

Design of a laser-triggered driver for fast capillary discharge

We are developing a new upgraded capillary discharge device. The assembled set-up consists of a Marx generator, a pulse forming line, a gas-filled laser-triggered spark gap and a ceramic capillary. The special attention has been paid to the design of the spark gap. The laser triggering of this spark gap ensures a very low jitter in comparison with the present capillary discharge device CAPEX, where the main spark gap works in a self-breakdown regime. The description of the assembled apparatus, the main predicted parameters of the designed device (such as capillary current, capillary current rise-rte, and/or voltage at the end of pulse forming line) are presented.