Ms Pulse Duration Research Articles

Improved healing response in delayed unions of the tibia with low-intensity pulsed ultrasound: results of a randomized sham-controlled trial

BackgroundWe compared the healing response of tibial delayed unions between subjects treated with low-intensity pulsed ultrasound (LIPUS) (n = 51) and subjects treated with a sham device (n = 50). Fracture age was ≥ 4 months in all cases. Study personnel and participants were blinded to random treatment assignment throughout the study.MethodsThis multi-center randomized sham-controlled trial was undertaken at six hospitals in Germany. Adult patients who had sustained a tibial shaft fracture that subsequently showed inadequate progress toward healing (i.e., delayed union) were enrolled and randomized to receive either LIPUS (Exogen 2000/2000+, Smith & Nephew GmbH, Schenefeld, Germany) or an identical nonoperative sham device. The daily treatment duration was 20 minutes, for a period of 16 weeks. Subjects randomly assigned to active treatment had the ultrasound pressure wave signal set at the following parameters: 1.5 MHz frequency, 1 kHz repetition rate, 200 μs pulse duration, 30 mW/cm2 spatial intensity. Progress toward healing was estimated from changes in bone mineral density (BMD) and gap area as determined from computed tomography scans. Intention-to-treat analysis was conducted using a multiple imputation methodology.ResultsBased on log-transformed data, mean improvement in BMD was 1.34 (90% confidence interval (CI) 1.14 to 1.57) times greater for LIPUS-treated subjects compared to sham (p = 0.002). A mean reduction in bone gap area also favored LIPUS treatment (p = 0.014).ConclusionsThese findings demonstrate significantly greater progress toward bone healing after LIPUS treatment compared to no LIPUS treatment in subjects with established delayed unions of the tibia.

Endocardial vagal atrioventricular node stimulation in humans: reproducibility on 18-month follow-up

Control of atrioventricular (AV) node conduction by means of high-frequency stimulation (HFS) of efferent AV node vagal stimulation (AVNS) fibres enables the ventricular rate (VR) to be modulated during atrial fibrillation (AF). The aims of this study were to verify, on 18-month follow-up, the reproducibility of the dromotropic effect obtained on implantation and the long-term reliability of the system in patients who received an implantable cardioverter-defibrillator (ICD) with a standard atrial lead positioned at a location suitable for AVNS. We enrolled 12 patients with paroxysmal or persistent AF who were candidates for ICD. The right atrium was mapped to locate the pacing site, and a transvenous screw-in lead was implanted in that region. The voltages required for VR modulation (25% VR reduction) and complete AV block at different pulse durations (from 0.1 to 0.5 ms) were recorded. Eleven out of 12 patients underwent 18-month follow-up examination. Atrial pacing parameters were adequate and did not differ from the baseline values (all P > 0.05): pacing threshold 0.9 ± 0.5 V (0.5 ms pulse duration) and impedance 556 ± 121 Ω, with P-wave amplitude of 1.6 ± 0.7 mV. High-frequency stimulation induced VR modulation in nine patients and complete AV block in eight patients at pulse durations ≥0.3 ms. No differences were observed in the voltages for VR modulation and complete AV block between implantation and 18-month examination (all P > 0.100). Ventricular rate control during AF was obtained under HFS 18 months after implantation in patients with the atrial lead positioned at a location suitable for AVNS. The pacing outputs needed to achieve the dromotropic effect were comparable to those measured on implantation.

Randomized, Placebo Controlled Study of Electrical Stimulation With Pelvic Floor Muscle Training for Severe Urinary Incontinence After Radical Prostatectomy

We evaluated electrical stimulation combined with pelvic floor muscle training for urinary incontinence after radical prostatectomy in a randomized controlled study. A total of 56 men with severe urinary incontinence (more than 200 gm daily), mean ± SD age 66.6 ± 6.2 years, were randomized to an active treatment group (26) or a sham group (30). All patients performed pelvic floor muscle training preoperatively and continued throughout the study. For active stimulation 50 Hz square waves of 300 μs pulse duration and a 5 seconds on, 5 seconds off duty cycle were applied for 15 minutes twice daily with an anal electrode. Sham stimulation was limited to 3 mA with a 2 seconds on, 13 seconds off duty cycle. In the active group 8 (36%), 14 (63%), 18 (81%) and 19 (86%) patients were continent (22) vs 1 (4%), 4 (16%), 11 (44%) and 17 (86%) in the sham group (25) (leakage less than 8 gm daily) after 1, 3, 6 and 12 months, respectively. There was a significant difference in the number of continent patients between the groups at 1, 3 and 6 months (p = 0.0161, p = 0.0021 and p = 0.0156, respectively). The time to achieve continence was significantly shorter in the active group (2.71 ± 2.6 months) than in the sham group (6.82 ± 3.9 months, p = 0.0006). Changes in the amount of leakage, the International Consultation on Incontinence Questionnaire-Short Form score and the King's Health Questionnaire score were significantly larger in the active group at 1 month but there was no difference at 12 months. Electrical stimulation resulted in earlier recovery of continence in patients with urinary incontinence after radical prostatectomy.

Dipolar cortico-muscular electrical stimulation: a novel method that enhances motor function in both - normal and spinal cord injured mice

BackgroundElectrical stimulation of the central and peripheral nervous systems is a common tool that is used to improve functional recovery after neuronal injury.MethodsHere we described a new configuration of electrical stimulation as it was tested in anesthetized control and spinal cord injury (SCI) mice. Constant voltage output was delivered through two electrodes. While the negative voltage output (ranging from -1.8 to -2.6 V) was delivered to the muscle via transverse wire electrodes (diameter, 500 μm) located at opposite ends of the muscle, the positive output (ranging from + 2.4 to +3.2 V) was delivered to the primary motor cortex (M1) (electrode tip, 100 μm). The configuration was named dipolar cortico-muscular stimulation (dCMS) and consisted of 100 pulses (1 ms pulse duration, 1 Hz frequency).ResultsIn SCI animals, after dCMS, cortically-elicited muscle contraction improved markedly at the contralateral (456%) and ipsilateral (457%) gastrocnemius muscles. The improvement persisted for the duration of the experiment (60 min). The enhancement of cortically-elicited muscle contraction was accompanied by the reduction of M1 maximal threshold and the potentiation of spinal motoneuronal evoked responses at the contralateral (313%) and ipsilateral (292%) sides of the spinal cord. Moreover, spontaneous activity recorded from single spinal motoneurons was substantially increased contralaterally (121%) and ipsilaterally (54%). Interestingly, spinal motoneuronal responses and muscle twitches evoked by the test stimulation of non-treated M1 (received no dCMS) were significantly enhanced as well. Similar results obtained from normal animals albeit the changes were relatively smaller.ConclusionThese findings demonstrated that dCMS could improve functionality of corticomotoneuronal pathway and thus it may have therapeutic potential.

Considerations for pacing of thecricoarytenoid dorsalismuscle by neuroprosthesis in horses

The success rate of prosthetic laryngoplasty is limited and may be associated with significant sequelae. Nerve muscle pedicle transplantation has been attempted but requires a year before function is restored. To determine the optimal parameters for functional electrical stimulation of the recurrent laryngeal nerve in horses. An experimental in vivo study was performed on 7 mature horses (2-21 years). A nerve cuff was placed on the distal end of the common trunk of the recurrent laryngeal nerve (RLN). In 6 horses the ipsilateral adductor branch of RLN was also transected. The electrodes were connected to programmable internal stimulator. Stimulation was performed using cathodic phase and then biphasic pulses at 24 Hz with a 0.427 ms pulse duration. Stimulation-response experiments were performed at monthly intervals, from one week following implantation. The study continued until unit failure or the end of project (12 months). Two of the horses were stimulated continuously for 60 min to assess onset of fatigue. Excellent arytenoid cartilage abduction (mean arytenoid angle of 52.7 degrees, range 48.5-56.2 degrees) was obtained in 6 horses (laryngeal grades I or II (n = 3) and III (n = 2). Poor abduction was obtained in grade IV horses (n = 2). Arytenoid abduction was maintained for up to a year in one horse. Technical implant failure resulted in loss of abduction in 6 horses at one week to 11 months post operatively. Mean tissue impedance was 1.06 kOhm (range 0.64-1.67 kOhm) at one week, twice this value at 2 months (mean 2.32, range 1.11-3.75 kOhm) and was stable thereafter. Maximal abduction was achieved at a stimulation range of 0.65-7.2 mA. No electrical leakage was observed. Constant stimulation of the recurrent laryngeal nerve for 60 min led to full abduction without evidence of muscle fatigue. Functional electrical stimulation of the recurrent laryngeal nerve leading to full arytenoid abduction can be achieved. The minimal stimulation amplitude for maximal abduction angle is slightly higher than those for man and dogs. This treatment modality could eventually be applicable to horses with recurrent laryngeal neuropathy.

Right ventricular stimulation threshold at ICD implant predicts device therapy in primary prevention patients with ischaemic heart disease

Myocardial excitability is known (amongst other reasons) to be related to the degree of ischaemia, contractile dysfunction and heart failure. It was hypothesized that the right ventricular (RV) stimulation threshold has prognostic value with respect to the occurrence of ventricular arrhythmias (VAs) and patient survival in recipients of an implantable cardioverter defibrillator (ICD). Ischaemic heart disease patients receiving an ICD at Leiden University Medical Center as primary prevention for sudden cardiac death were included in this study. Right ventricular thresholds were determined at ICD implant. Data were collected on VAs triggering ICD therapy and on all-cause mortality. A total of 689 consecutive patients were included (87% male, age 63 ± 11 years, left ventricular ejection fraction (LVEF) 29 ± 11%) and followed for a median of 28 months. Post-implant RV-threshold was 0.7 ± 0.5 volt (V) at 0.5 ms pulse duration. Best dichotomous separation was reached at a cut-off of 1 V. During follow-up, 167 (24%) patients received appropriate ICD therapy, 88 (13%) had appropriate shocks and 134 (19%) died. Cumulative appropriate shock incidence for patients with RV threshold ≥ 1 V (n = 166) was 16% at 1 year, 24% at 3 years and 34% at 5 years compared with 4, 11 and 17% for patients with an RV-threshold < 1 V (n = 523). Adjusted hazard ratio of RV threshold ≥ 1 V was 2.0 (95% CI: 1.4-2.9) for appropriate therapy, 3.3 (95% CI: 2.0-5.4) for appropriate shocks and 1.6 (95% CI: 1.1-2.5) for mortality. The RV stimulation threshold at ICD implant has a strong independent prognostic value for the occurrence of VAs triggering appropriate ICD therapy, appropriate shocks and mortality.

Optical cochlear implants: Evaluation of surgical approach and laser parameters in cats

Previous research has shown that neural stimulation with infrared radiation (IR) is spatially selective and illustrated the potential of IR in stimulating auditory neurons. The present work demonstrates the application of a miniaturized pulsed IR stimulator for chronic implantation in cats, quantifies its efficacy, and short-term safety in stimulating auditory neurons. IR stimulation of the neurons was achieved using an optical fiber inserted through a cochleostomy drilled in the basal turn of the cat cochlea and was characterized by measuring compound action potentials (CAPs). Neurons were stimulated with IR at various pulse durations, radiant exposures, and pulse repetition rates. Pulse durations as short as 50 μs were successful in evoking CAPs in normal as well as deafened cochleae. Continual stimulation was provided at 200 pulses per second, at 200 mW per pulse, and 100 μs pulse duration. Stable CAP amplitudes were observed for up to 10 h of continual IR stimulation. Combined with histological data, the results suggest that pulsed IR stimulation does not lead to detectable acute tissue damage and validate the stimulation parameters that can be used in future chronic implants based on pulsed IR.

Pulsed Nd:YAG laser seam welding of AISI 316L stainless steel thin foils

Experimental investigations were carried out using a pulsed neodymium:yttrium aluminum garnet laser weld to examine the influence of the pulse energy in the characteristics of the weld fillet. The pulse energy was varied from 1.0 to 2.25 J at increments of 0.25 J with a 4 ms pulse duration. The base material used for this study was AISI 316L stainless steel foil with 100 μm thickness. The welds were analyzed by optical microscopy, tensile shear tests and microhardness. The results indicate that pulse energy control is of considerable importance to thin foil weld quality because it can generate good mechanical properties and reduce discontinuities in weld joints. The ultimate tensile strength of the welded joints increased at first and then decreased as the pulse energy increased. The process appeared to be very sensitive to the gap between couples.

Pattern scan laser photocoagulation: safety and complications, experience after 1301 consecutive cases

Background/aimsThe pattern scan laser photocoagulator (PASCAL) is a novel laser device that uses 10–30 ms pulse duration for retina photocoagulation. The aim of this study was to analyse the safety...

Finite element thermal study of the Linac4 plasma generator

The temperature distribution and heat flow at equilibrium of the plasma generator of the rf-powered noncesiated Linac4 H(-) ion source have been studied with a finite element model. It is shown that the equilibrium temperatures obtained in the Linac4 nominal operation mode (100 kW rf power, 2 Hz repetition rate, and 0.4 ms pulse duration) are within material specifications except for the magnet cage, where a redesign may be necessary. To assess the upgrade of the Linac4 source for operation in the high-power operation mode of the Superconducting Proton Linac (SPL), an extrapolation of the heat load toward 100 kW rf power, 50 Hz repetition rate, and 0.4 ms pulse duration has been performed. The results indicate that a significant improvement of the source cooling is required to allow for operation in the high-power mode of SPL.

Microbubble mediated sonoporation of cells in suspension: Clonogenic viability and influence of molecular size on uptake

This work investigates whether the application of sonoporation is limited by the size of a macromolecule being delivered and by the ability of cells to proliferate following uptake. KHT-C cells in suspension were exposed to variations in ultrasound pressure (0–570 kPa) and microbubble shell-type (lipid and protein) at fixed settings of 500 kHz centre frequency, 32 μs pulse duration, 3 kHz pulse repetition frequency and 2 min insonation. Reversible permeability ( P R), defined as the number of cells stained with FITC-dextran and unstained with propidium iodide (i.e., PI-viable), was measured with flow cytometry for marker molecules ranging from 10 kDa to 2 MDa in size. Viable permeability ( P V) defined as the number of permeabilised cells that maintained their ability to proliferate, was measured by clonogenic assay. Comparable intracellular delivery of all sizes of molecules was achieved, indicating that intracellular delivery of common therapeutic drugs may not be limited by molecular size. Maximum P R’s of 80% (at 10 kDa) and 55% (at 10 kDa) were achieved with lipid coated bubbles at 3.3% v/v and protein coated bubbles at 6.7% v/v concentrations. The PI-viability was approximately 80% at 570 kPa in both cases. The maximum P V achieved with both agents was 22%, while inducing a lower overall clonogenic viability with the lipid (39%) compared to the protein (56%) shelled bubbles. This study demonstrates that large macromolecules, up to 2 MDa in size, can be delivered with high efficiency to cells which undergo reversible permeabilisation, maintaining long-term viability in approximately half of the cells.

Treatment of resistant port wine stains (PWS) with pulsed dye laser and non-contact vacuum: a pilot study

The blanching of resistant port wine stains (PWS) with a pulsed dye laser (PDL) requires a large number of treatments, resulting in substantial discomfort to patients, many of them children. Pneumatic skin flattening (PSF - Serenity Pro) is a new technology that generates a vacuum over the skin and reduces pain in laser-based treatments of the skin, while creating contact between the skin and an upper window. The same technology can be utilized to increase skin blood fraction while operated in a non-contact mode. The objective of this study was to test the enhancement in the efficacy of PWS treatment with PDL and Serenity Pro while vacuum is being utilized in the non-contact, blood-enrichment mode. Fifteen patients with resistant PWS underwent 1-4 treatments (interval of 5-20 weeks) under general anesthesia with a 595-nm PDL at 10-14 J/cm(2), 1.5-3 ms pulse duration, and 7-mm spot size. Lesion blanching with DCD chilling and with vacuum were photographed and compared. Better blanching of various degrees was observed on resistant PWS with the blood-enrichment technique in seven out of 11 patients who returned for follow-up. There were no cases of decrease in efficacy. Blood enrichment with the Serenity Pro non-contact vacuum technology has the potential of enhancing the capability of treating resistant port wine stains in over 50% of cases. Further studies will better quantify the number of treatments necessary for better lesion clearance. The vacuum-assisted technique may be of particular importance in view of the fact that achieving complete lesion clearance remains a challenge in PWS treatments.

Genotoxic effects of 1064-nm Nd:YAG and 532-nm KTP lasers on fibroblast cell cultures

Several different laser types are used in cutaneous surgery. The neodymium:yttrium-aluminium-garnet (Nd:YAG) and frequency-doubled Nd:YAG (KTP, potassium titanyl phosphate) lasers are widely used in dermatology. To investigate the possible genotoxic effects on fibroblasts of irradiation with a 1064-nm Nd:YAG laser and a 532-nm KTP laser. Fibroblast cell cultures were exposed to each of the lasers, using 10-mm spot size at 60 ms pulse duration with 10, 20, 40 J/cm(2) and 3, 6, 12 J/cm(2) fluences, respectively. Fibroblasts in passages 1-6 were used. During laser irradiation, 96-well microplate cultures were kept on a cooling block and transported on ice and in the dark, and processed immediately for single-cell gel electrophoresis (SCGE) assay (also known as a comet assay). DNA damage was determined by computerized assessment of comet assay. There was increasing damage with increasing numbers of passages. For the Nd:YAG laser, the greatest damage occurred on passages 5 and 6, whereas the greatest damage appeared at passages 3 and 4 for KTP and returned to baseline at passages 5 and 6. Damage also increased with each dose increment for both wavelengths. At the highest dose for both wavelengths (Nd:YAG 40 J/cm(2) and KTP 12 J/cm(2)), damage was higher with the Nd:YAG laser. Different patterns of cellular damage were seen for different cell-culture passages, treatment doses, and laser wavelengths. These dose ranges are generally used for the treatment of vascular and pigmented lesions and for rejuvenation purposes. As replicative ageing or cell senescence is one of the critical factors determining the extent of cell damage induced by laser therapy, these results may have important implications for clinical practice.

Comparison of two dye lasers in the treatment of port-wine stains

Port-wine stains (PWS) are congenital capillary malformations that persist throughout life. Laser therapy is a common treatment for PWS, and pulsed-dye laser is the current treatment of choice. To compare the clinical results on untreated PWS of two dye lasers with different wavelengths and pulse duration: a flashlamp-pumped dye laser (FPDL) and a long-pulse-duration dye laser (LPDL). In total, 24 patients were treated on 4-6 test areas with both laser types using high-energy and low-energy fluences. An FPDL with 0.45 ms pulse duration tuned to 585 nm was compared with an LPDL with 1.5 or 3.0 ms pulse duration tuned to 595 nm. Twelve weeks later the degree of lightening was evaluated by a blinded assessor. Pain was assessed directly after treatment with both lasers, using a visual analogue scale. There was no significant difference overall between the two systems in lightening of the lesion or in patient-reported pain. Both laser systems are equivalent in terms of efficacy and pain.

Human Model Simulating Right Ventricular Outflow Tract Tachycardia by High‐Frequency Stimulation in the Left Pulmonary Artery: Autonomics and Idiopathic Ventricular Arrhythmias

Frequent monomorphic premature ventricular contractions (PVC) and/or ventricular tachycardia (VT) in patients with structurally normal heart usually arise from the right ventricular outflow tract (RVOT). An animal model simulating RVOT tachycardia by high-frequency stimulation (HFS) of the sympathetic input to the proximal pulmonary artery (PA) has been previously described. The aim of this study was to similarly induce RVOT tachycardia in humans. In 9 patients with no history of ventricular arrhythmias, a circumferential catheter was placed in the left, main, and proximal PA to contact the endovascular circumference of the PA. A 50-ms train of HFS (200 Hz/0.3 ms pulse duration), coupled to atrial pacing, was applied at each bipolar pair of the circumferential catheter. The coupling interval was adjusted so that the 50-ms train occurred during the ventricular refractory period. In 6 out of 9 patients, HFS in the left PA during dobutamine infusion induced monomorphic PVCs and/or VT with left bundle branch block (LBBB) morphology and inferior axis at an average stimulation level of 12.5 +/- 2.7 V. HFS in the main PA and in the proximal PA did not induce any ventricular arrhythmias with the highest energy of 15 V in baseline state and during dobutamine infusion. HFS in the left PA was associated with hiccough in all patients. Stimulation of the sympathetic input to the left PA during dobutamine infusion induces PVCs and/or VT exhibiting LBBB-morphology and inferior axis, closely simulating clinical RVOT tachycardia in humans.

Skin fluorescence controlled photodynamic photorejuvenation (wrinkle reduction)

Identical skin fluorescence can be obtained after one hour spraying with 0.5% liposome-encapsulated 5-ALA and after 0.5 hour application of 20% 5-ALA in a cream base. In this study the clinical outcome and side effects using the 0.5% 5-ALA in Caucasian skin are investigated and compared to earlier reported non-ablative treatments for wrinkles and improvements of skin texture using 20% ALA photodynamic photorejuvenation. 37 healthy Caucasian female patients participated in a randomized, prospective split face study. Two different intense pulsed light (IPL) treatment modalities were investigated; both employed a pre-treatment of approximately one hour of spraying with 0.5% liposome encapsulated 5-ALA. One modality combined type I photorejuvenation with wrinkle reduction (C-PDT) using a waveband from 530 to 750 nm and short pulse durations (7 J/cm(2), 2 x 2.5 ms, delay 10 ms). The other modality (PDT alone) emitted a band of wavelengths from 400 to 720 nm, three passes were performed (3.5 J/cm(2), 30 ms pulse duration). After a series of three C-PDT or PDT-alone treatments, the patients obtained statistically significant (P< 5 x 10-5) reductions in periorbital and perioral wrinkles. Using the Fitzpatrick wrinkle scale, periorbital wrinkles were reduced by 1.2 grades (SD: 1.1) and 1.1 (SD: 1.1), respectively and perioral wrinkles were reduced by 0.8 grades (SD: 1.0) and 0.7 (SD: 0.9) respectively. The difference in treatment efficacy between. C-PDT and PDT alone treated sides was not statistically significant (P = 0.224). The present study shows that statistically significant improvements in wrinkle reduction and skin texture, equivalent to previously reported results obtained with 20% ALA, can be obtained with 0.5% liposome encapsulated 5-ALA. Only minor and infrequent side effects were registered at the 0.5% 5-ALA treated areas. Skin fluorescence monitoring during pre-treatrnent with 5-ALA may improve clinical efficacy, reduce time consumption and increase safety of the treatment.

Dynistor Switches for Micro- and Nanosecond Power Pulse Generators

Gigawatt power switches for microsecond range applications based on an assembly of Reverse Switch-on Dynistors (RSD) and fast compact generators for nanosecond range applications based on new semiconductor devices Deep Level Dynistors (DLD) are discussed. As an example design and operation principles of 25 kV, 300 kA, 600 μs pulse duration power switch based on 76 mm diameter RSDs and 25 kV, 10 kA switch based on 16 mm diameter DLDs are described. It is possible to increase the pulse power by increasing both diameter of dynistor structure and number of devices connected in series or in parallel.

CO2 Laser (10.6 μm) Parameters for Caries Prevention in Dental Enamel

Although CO₂ laser irradiation can decrease enamel demineralisation, it has still not been clarified which laser wavelength and which irradiation conditions represent the optimum parameters for application as preventive treatment. The aim of the present explorative study was to find low-fluence CO₂ laser (λ = 10.6 μm) parameters resulting in a maximum caries-preventive effect with the least thermal damage. Different laser parameters were systematically evaluated in 3 steps. In the first experiment, 5 fluences of 0.1, 0.3, 0.4, 0.5 and 0.6 J/cm², combined with high repetition rates and 10 μs pulse duration, were chosen for the experiments. In a second experiment, the influence of different pulse durations (5, 10, 20, 30 and 50 μs) on the demineralisation of dental enamel was assessed. Finally, 3 different irradiation times (2, 5 and 9 s) were tested in a third experiment. In total, 276 bovine enamel blocks were used for the experiments. An 8-day pH-cycling regime was performed after the laser treatment. Demineralisation was assessed by lesion depth measurements with a polarised light microscope, and morphological changes were assessed with a scanning electron microscope. Irradiation with 0.3 J/cm², 5 μs, 226 Hz for 9 s (2,036 overlapping pulses) increased caries resistance by up to 81% compared to the control and was even significantly better than fluoride application (25%, p < 0.0001). Scanning electron microscopy examination did not reveal any obvious damage caused by the laser irradiation.

Synchronization and Coherent Combining of Two Pulsed Fiber Ring Lasers Based on Direct Phase Modulation

We demonstrate a scalable architecture for coherent combining of pulsed fiber ring lasers based on mutual injection and direct phase modulation. By direct phase modulation in the common arm of two ring lasers, synchronous pulsed lasers can be generated and coherent combining of the two synchronous lasers is obtained. Two pulsed fiber ring lasers are coherently combined with 0.55 μJ pulse energy and 10 μs pulse duration at a repetition rate of 27.5 kHz. Experimental results show that the two fiber ring lasers are phase locked with an invariable phase difference of π and have good temporal synchronization and spatial coherence. The combining efficiency of the two pulsed fiber laser reaches 90% and the fringe contrast is larger than 40%. Neither active phase control nor polarization control is used in our experiment and this method can be extended to combine more beams and higher repetition rate scaling up to higher power.

Failure modes of vacuum plasma spray tungsten coating created on carbon fibre composites under thermal loads

Vacuum plasma spray tungsten (VPS-W) coating created on a carbon fibre reinforced composite (CFC) was tested under two thermal load schemes in the electron beam facility to examine the operation limits and failure modes. In cyclic ELM-like short transient thermal loads, the VPS-W coating was destroyed sub-layer by sub-layer at 0.33 GW/m 2 for 1 ms pulse duration. At longer single pulses, simulating steady-state thermal loads, the coating was destroyed at surface temperatures above 2700 °C by melting of the rhenium containing multilayer at the interface between VPS-W and CFC. The operation limits and failure modes of the VPS-W coating in the thermal load schemes are discussed in detail.