Generation and Evaluation of an Efficient Femtosecond Green Laser.

We demonstrate femtosecond ultra-stable green laser generation by an ytterbium-doped polarization-maintaining fiber laser with a 2.4 mm long lithium triborate (LBO) crystal. We generated 5.6 W of femtosecond green light at 520 nm for a fundamental power of 12 W, which corresponds to a conversion efficiency of 46.7%. The fiber chirped-pulse amplifier, which has an environmentally immune front end, delivered 170 fs pulses at a 75 MHz repetition rate centered at 1040 nm. According to the dispersion of the optical material in a double-frequency setup, the introduced dispersion had a negligible effect for the green laser, and the pulse duration of the generated green laser was calculated to be 171 fs, resulting in an excellent power stability, with fluctuation as low as 0.16% of the generated green light. This system could be of great interest in ultrafast optical and photobiology research.

Influence mechanism of the temporal duration of laser irradiation on photoacoustic technique: a review.

Significance: In the photoacoustic (PA) technique, the laser irradiation in the time domain (i.e., laser pulse duration) governs the characteristics of PA imaging-it plays a crucial role in the optical-acoustic interaction, the generation of PA signals, and the PA imaging performance. Aim: We aim to provide a comprehensive analysis of the impact of laser pulse duration on various aspects of PA imaging, encompassing the signal-to-noise ratio, the spatial resolution of PA imaging, the acoustic frequency spectrum of the acoustic wave, the initiation of specific physical phenomena, and the photothermal-PA (PT-PA) interaction/conversion. Approach: By surveying and reviewing the state-of-the-art investigations, we discuss the effects of laser pulse duration on the generation of PA signals in the context of biomedical PA imaging with respect to the aforementioned aspects. Results: First, we discuss the impact of laser pulse duration on the PA signal amplitude and its correlation with the lateral resolution of PA imaging. Subsequently, the relationship between the axial resolution of PA imaging and the laser pulse duration is analyzed with consideration of the acoustic frequency spectrum. Furthermore, we examine the manipulation of the pulse duration to trigger physical phenomena and its relevant applications. In addition, we elaborate on the tuning of the pulse duration to manipulate the conversion process and ratio from the PT to PA effect. Conclusions: We contribute to the understanding of the physical mechanisms governing pulse-width-dependent PA techniques. By gaining insight into the mechanism behind the influence of the laser pulse, we can trigger the pulse-with-dependent physical phenomena for specific PA applications, enhance PA imaging performance in biomedical imaging scenarios, and modulate PT-PA conversion by tuning the pulse duration precisely.

Sound processing in the cricket brain: evidence for a pulse duration filter.

The auditory system of female crickets allows them to specifically recognize and approach the species-specific male calling song, defined by sound pulses and silent intervals. Auditory brain neurons form a delay-line and coincidence detector network tuned to the pulse period of the male song. We analyzed the impact of changes in pulse duration on the behavior and the responses of the auditory neurons and the network. We confirm that the ascending neuron AN1 and the local neuron LN2 copy the temporal structure of the song. During ongoing long sound pulses, the delay-line neuron LN5 shows additional rebound responses and the coincidence detector neuron LN3 can generate additional bursts of activity, indicating that these may be driven by intrinsic oscillations of the network. Moreover, the response of the feature detector neuron LN4 is shaped by a combination of inhibitory and excitatory synaptic inputs, and LN4 responds even to long sound pulses with a short depolarization and burst of spikes, like to a sound pulse of natural duration. This response property of LN4 indicates a selective auditory pulse duration filter mechanism of the pattern recognition network, which is tuned to the duration of natural pulses. Comparing the tuning of the phonotactic behavior with the tuning of the local auditory brain neurons to the same test patterns, we find no evidence that a modulation of the phonotactic behavior is reflected at the level of the feature detector neurons. This rather suggests that steering to nonattractive pulse patterns is organized at the thoracic level.NEW & NOTEWORTHY Pulse period selectivity has been reported for the cricket delay-line and coincidence detector network, whereas pulse duration selectivity is evident from behavioral tests. Pulses of increasing duration elicit responses in the pattern recognition neurons, which do not parallel the behavioral responses and indicate additional processing mechanisms. Long sound pulses elicit rhythmic rebound activity and additional bursts, whereas the feature detector neuron reveals a pulse duration filter, expanding our understanding of the pattern recognition process.

Impact of pulse duration alterable laser ureterorenoscopic lithotripsy for upper urinary tract calculi.

To assess the effectiveness of a pulse duration alterable Holmium-YAG (Ho:YAG) laser on the stone-free rate (SFR) compared to a conventional pulse duration fixed laser after ureterorenoscopic lithotripsy (URSL). The medical records from patients with upper urinary tract calculi of ≥ 9 mm and < 30 mm were retrospectively investigated. URSL using a conventional Ho:YAG Laser (group C) or a pulse duration alterable Ho:YAG system (group A) was included. In total, 228 and 188 patients were enrolled in groups C and A, respectively. A 272 µm optical core bare-ended, reusable laser fiber was used, and the laser system was set to a standard 0.8 J and 10 Hz (8 W of average power) in both groups. URSL adopts active fragmentation using an extraction approach. SF was defined as the complete absence of stone fragments on computed tomography (CT) 1-2 months after URSL. Sex, BMI, stone length, stone volume, stone density, and the number of patients with positive preoperative urine cultures were not significantly different between the groups. However, age, rate of preoperative febrile urinary tract infection (fUTI), and pre-stenting were significantly higher in group A, and the operative times and incidence of postoperative fUTI were comparable. The SFRs were 71.5% and 80.3% in groups C and A, respectively (P = 0.035). Multivariate logistic regression revealed that the use of conventional laser was associated with non-SF (odds ratio [OR] 1.090, 95% confidence interval [CI] 1.01-1.18, P = 0.040). The present study revealed the superior performance of a pulse duration alterable Ho:YAG laser on the SFR after URSL compared to a conventional pulse duration fixed laser delivery system.

Surface Modification of Brass via Ultrashort Pulsed Direct Laser Interference Patterning and Its Effect on Bacteria-Substrate Interaction.

In recent decades, antibiotic resistance has become a crucial challenge for human health. One potential solution to this problem is the use of antibacterial surfaces, i.e., copper and copper alloys. This study investigates the antibacterial properties of brass that underwent topographic surface functionalization via ultrashort pulsed direct laser interference patterning. Periodic line-like patterns in the scale range of single bacterial cells were created on brass with a 37% zinc content to enhance the contact area for rod-shaped Escherichia coli (E. coli). Although the topography facilitates attachment of bacteria to the surface, reduced killing rates for E. coli are observed. In parallel, a high-resolution methodical approach was employed to explore the impact of laser-induced topographical and chemical modifications on the antibacterial properties. The findings reveal the underlying role of the chemical modification concerning the antimicrobial efficiency of the Cu-based alloy within the superficial layers of a few hundred nanometers. Overall, this study provides valuable insight into the effect of alloy composition on targeted laser processing for antimicrobial Cu-surfaces, which facilitates the thorough development and optimization of the process concerning antimicrobial applications.

Immunogenic Cell Death in Electroporation-Based Therapies Depends on Pulse Waveform Characteristics.

Traditionally, electroporation-based therapies such as electrochemotherapy (ECT), gene electrotransfer (GET) and irreversible electroporation (IRE) are performed with different but typical pulse durations-100 microseconds and 1-50 milliseconds. However, recent in vitro studies have shown that ECT, GET and IRE can be achieved with virtually any pulse duration (millisecond, microsecond, nanosecond) and pulse type (monopolar, bipolar-HFIRE), although with different efficiency. In electroporation-based therapies, immune response activation can affect treatment outcome, and the possibility of controlling and predicting immune response could improve the treatment. In this study, we investigated if different pulse durations and pulse types cause different or similar activations of the immune system by assessing DAMP release (ATP, HMGB1, calreticulin). Results show that DAMP release can be different when different pulse durations and pulse types are used. Nanosecond pulses seems to be the most immunogenic, as they can induce the release of all three main DAMP molecules-ATP, HMGB1 and calreticulin. The least immunogenic seem to be millisecond pulses, as only ATP release was detected and even that assumingly occurs due to increased permeability of the cell membrane. Overall, it seems that DAMP release and immune response in electroporation-based therapies can be controlled though pulse duration.

Holmium: Yttrium-aluminum-garnet laser lithotripsy: Is there a difference in ablation rates between short and long pulse duration?

Introduction: The high-power holmium: yttrium-aluminum-garnet lasers provide a wide variety of settings for stone disintegration. The aim of this in vitro study is to evaluate the effect of short and long pulse duration on ablation rates on urinary stones. Materials and Methods: Two types of artificial stones were created by BegoStone™ with different compositions (15:3 and 15:6, stone/water ratio). Stones with a 15:3 and 15:6 powder-to-water ratio were defined as hard and soft stones, respectively. Lithotripsy was performed with different laser settings using a custom-made in vitro model consisting of a 60 cm long and 19 mm diameter tube. The ablation rate is defined as the final total mass subtracted from the initial total mass and divided to the time of treatment. Stone ablation rates were measured according to different laser settings with total power of 10W (0,5J-20 Hz, 1J-10 Hz, 2J-5 Hz) and 60W (1J-60 Hz, 1,5J-40 Hz, 2J-30 Hz). Results: Higher pulse rates and higher total power settings were related to higher ablation rates. Short pulse duration was more effective on soft stones, whereas long pulse duration was more effective on hard stones. For the same power settings, the highest energy-lowest frequency combination resulted in higher ablation rate in comparison to the lowest energy-higher frequency combination. Finally, short and long pulse average ablation rates do not differ so much. Conclusion: Regardless of the stone type and pulse duration, utilization of higher power settings with higher energies increased the ablation rates. Higher ablation rates were demonstrated for hard stones using long pulse duration, and for soft stones with short pulse duration.

Intense Pulsed Light Thermal Treatment of Pb(Zr,Ti)O3 /Metglas Heterostructured Films Resulting in Extreme Magnetoelectric Coupling of over 20 V cm-1 Oe-1.

Magnetoelectric (ME) film composites consisting of piezoelectric and magnetostrictive materials are promising candidates for application in magnetic field sensors, energy harvesters, and ME antennas. Conventionally, high-temperature annealing is required to crystallize piezoelectric films, restricting the use of heat-sensitive magnetostrictive substrates that enhance ME coupling. Herein, a synergetic approach is demonstrated for fabricating ME film composites that combines aerosol deposition and instantaneous thermal treatment based on intense pulsed light (IPL) radiation to form piezoelectric Pb(Zr,Ti)O3 (PZT) thick films on an amorphous Metglas substrate. IPL rapidly anneals PZT films within a few milliseconds without damaging the underlying Metglas. To optimize the IPL irradiation conditions, the temperature distribution inside the PZT/Metglas film is determined using transient photothermal computational simulation. The PZT/Metglas films are annealed using different IPL pulse durations to determine the structure-property relationship. IPL treatment results in an enhanced crystallinity of the PZT, thus improving the dielectric, piezoelectric, and ME properties of the composite films. An ultrahigh off-resonance ME coupling (≈20 V cm-1  Oe-1 ) is obtained for the PZT/Metglas film that is IPL annealed at a pulse width of 0.75 ms (an order of magnitude higher than that reported for other ME films), confirming the potential for next-generation, miniaturized, and high-performance ME devices.

Pulse Duration Effects on Solution-Phase Protein Desorption in Laser Electrospray Mass Spectrometry.

The effect of laser pulse duration on the ablation of aqueous myoglobin is investigated using laser electrospray mass spectrometry (LEMS). Pulse durations of 55 femtoseconds (fs), 56 piscoseconds (ps), and 10 nanoseconds (ns) were used to ablate aqueous myoglobin from stainless-steel and quartz substrates. The integrated signal intensity of myoglobin increases with decreasing pulse duration for both substrates. Laser-induced thermal effects are assessed by the relative amount of solvent adduction and number of phosphate moieties adducted to myoglobin by each laser pulse duration. The mass spectra for 55 fs vaporization shows myoglobin with appreciable solvent and phosphate adduction and baseline elevation. The mass spectra for 10 ns ablation have minimal adduction and limited baseline elevation. Heat-induced conformation changes in myoglobin were used to measure the amount of thermal energy deposited by each laser pulse duration. Ablation using the 55 fs pulse revealed the highest ratio of unfolded to folded myoglobin in comparison to the 56 ps and 10 ns measurements due to increased droplet lifetime and consequent interaction with the acid in the electrospray solvent. Collisional activation and heated capillary temperature were employed to reduce the droplet lifetime and demonstrate that fs ablation preserves approximately 2 times more myoglobin folded conformation in comparison to ps and ns pulses.

Wide-pulse electrical stimulation of the quadriceps allows greater maximal evocable torque than conventional stimulation.

PURPOSE: The effectiveness of a neuromuscular electrical stimulation (NMES) program has been shown to be proportional to the maximal evocable torque (MET), which is potentially influenced by pulse characteristics such as duration and frequency. The aim of this study was to compare MET between conventional and wide-pulse NMES at two different frequencies. METHODS: MET-expressed as a percentage of maximal voluntary contraction (MVC) torque-and maximal tolerable current intensity were quantified on 71 healthy subjects. The right quadriceps was stimulated with three NMES protocols using different pulse duration/frequency combinations: conventional NMES (0.2 ms/50 Hz; CONV), wide-pulse NMES at 50 Hz (1 ms/50 Hz; WP50) and wide-pulse NMES at 100 Hz (1 ms/100 Hz; WP100). The proportion of subjects reaching the maximal stimulator output (100 mA) before attaining maximal tolerable current intensity was also quantified. RESULTS: The proportion of subjects attaining maximal stimulator output was higher for CONV than WP50 and WP100 (p < 0.001). In subjects who did not attain maximal stimulator output in any protocol, MET was higher for both WP50 and WP100 than for CONV (p < 0.001). Maximal tolerable current intensity was lower for both WP50 and WP100 than for CONV and was also lower for WP100 than for WP50 (p < 0.001). CONCLUSION: When compared to conventional NMES, wide-pulse protocols resulted in greater MET and lower maximal tolerable current intensity. Overall, this may lead to better NMES training/rehabilitation effectiveness and less practical issues associated with maximal stimulator output limitations.

Feasibility and optimal choice of stimulation parameters for supramaximal stimulation of motor evoked potentials.

PURPOSE: The aim was to investigate the feasibility and optimal stimulation parameters for supramaximal stimulation of muscle recorded transcranial electrical stimulation motor evoked potentials (mTc-MEP). METHODS: Forty-seven consecutive patients that underwent scoliosis surgery were included. First, the feasibility of supramaximal stimulation was assessed for two settings (setting 1: pulse duration 0.075ms, interstimulus interval (ISI) 1.5ms; setting 2: pulse duration 0.300ms, ISI 3ms). Thereafter, three mTc-MEP parameters were considered for both settings; (1) elicitability, (2) amplitude, and (3) if supramaximal stimulation was achieved with ≥ 20 V below maximum output. Finally, ISIs (1ms-4ms) were optimized for setting 1. RESULTS: Nine patients (19.15%) were excluded. Of the remaining patients, supramaximal stimulation was achieved in all patients for setting 1, and in 26 (68.42%) for setting 2. In one patient, mTc-MEPs were elicitable in more muscles for setting (1) Amplitudes were not significantly different. Stimulation voltage could be increased ≥ 20 V in all 38 patients for setting 1 and in 10 (38.46%) for setting (2) Optimal ISI's differed widely. CONCLUSION: We recommend using setting 1 when monitoring mTc-MEPs with supramaximal stimulation, after which an individualized ISI optimization can be performed. Moreover, when using supramaximal stimulation, short ISI's (i.e. 1ms or 1.5ms) can be the optimal ISI for obtaining the highest mTc-MEP amplitude.

Influence of pulse duration and water/air cooling ratio on the efficiency of Er:YAG 2940 nm laser in debonding of porcelain laminate veneers: An in vitro study.

OBJECTIVE: To determine the effectiveness of different pulse durations (PD) and the water/air (W/A) cooling ratio of the Er:YAG 2940 nm laser that are required for debonding porcelain laminate veneers (PLV), by investigation of the needed time for PLV debonding (DT) and the changes in dental pulp temperature. MATERIALS AND METHODS: Thirty-six extracted noncarious human maxillary premolars were prepared for receiving PLV. Samples were randomly assigned to six different groups, based on PD and the W/A ratio: Groups A (50 µs, 1:1), B (50 µs, 3:3), C (100 µs, 1:1), D (100 µs, 3:3), E (300 µs, 1:1), and F (300 µs, 3:3). Veneers were debonded using laser irradiation by the same parameters (270 mJ, 15 Hz) with noncontact application mode. RESULTS: All 36 veneers were debonded. Samples of the 50 and 100 µs PDs showed significantly shorter DT (7.4-17 s) than that of the 300 µs which showed significantly the longest DT (104 s) among all other groups (p < .001). However, the highest elevation of pulp temperature was observed in Group E (300 µs, 1:1) which reached (3.4°C). CONCLUSION: Using the 50 or 100 µs PD of the Er:YAG laser was more efficient than 300 µs in reducing DT of PLVs with minimal change in pulp temperature. W/A cooling ratio had minimal influence on the DT of PLV.

Influence of Pulse Duration on X-ray Emission during Industrial Ultrafast Laser Processing.

Soft X-ray emissions during the processing of industrial materials with ultrafast lasers are of major interest, especially against the background of legal regulations. Potentially hazardous soft X-rays, with photon energies of >5 keV, originate from the fraction of hot electrons in plasma, the temperature of which depends on laser irradiance. The interaction of a laser with the plasma intensifies with growing plasma expansion during the laser pulse, and the fraction of hot electrons is therefore enhanced with increasing pulse duration. Hence, pulse duration is one of the dominant laser parameters that determines the soft X-ray emission. An existing analytical model, in which the fraction of hot electrons was treated as a constant, was therefore extended to include the influence of the duration of laser pulses on the fraction of hot electrons in the generated plasma. This extended model was validated with measurements of H (0.07) dose rates as a function of the pulse duration for a constant irradiance of about 3.5 × 1014 W/cm2, a laser wavelength of 800 nm, and a pulse repetition rate of 1 kHz, as well as for varying irradiance at the laser wavelength of 1030 nm and pulse repetition rates of 50 kHz and 200 kHz. The experimental data clearly verified the predictions of the model and confirmed that significantly decreased dose rates are generated with a decreasing pulse duration when the irradiance is kept constant.

Safety and efficacy for hair removal in dark skin types III and IV with a high-powered, combined wavelength (810, 940 and 1060 nm) diode laser: A single-site pilot study.

BACKGROUND: Previous studies have demonstrated the superior efficacy of a high-power diode laser (4800 W) with a wavelength of 810 nm over others with less power and the same wavelength, while also being safe and comfortable for the patient. However, the use of this laser is limited on dark skin. OBJECTIVES: This study aims to compare the efficacy, safety, and comfort of a 4800 W diode laser (810 nm) with that of the new Blend diode laser (810 nm, 940 nm, and 1064 nm). Furthermore, the study aims to demonstrate that the Blend diode laser delivers better results on darker skin. MATERIALS AND METHODS: A 810 nm diode laser was compared with the Blend diode laser (810, 940 and 1064 nm) (Primelase, Cocoon Medical). A side-by-side comparative study was carried out over three sessions involving fourteen participants with skin types III and IV, with evaluation of the results 6 months after treatment. The study was performed at the Tennessee Clinical Research Center, Nashville, Tennessee, USA. This evaluation was based on efficacy, safety, comfort, and participant satisfaction. RESULTS: Blend diode laser treatments were performed with fluences 40% (SE = 0.04%) higher than those of the 810 nm. Besides mild-to-moderate transient discomfort during the procedure, the Blend diode laser also produced an increased pricking sensation that was 1.8 points higher on a 10-point scale (p < 0.05), due to the higher fluence used. Hair reduction was 12% higher with the Blend diode laser, with a confidence level of 70%. Moreover, participants were more satisfied with the results of the Blend diode laser than with the diode laser (50% very satisfied vs. 36%, respectively). No long-term adverse effects were observed. CONCLUSIONS: The new Blend diode laser has been shown to be more effective and satisfactory than 810 nm diode laser on dark skin types III and IV, while also being safe and comfortable for participants.

Optimal pulse configuration for peripheral inductive nerve stimulation.

Peripheral magnetic stimulation is a promising technique for several applications like rehabilitation or diagnose of neuronal pathways. However, most available magnetic stimulation devices are designed for transcranial stimulation and require high-power, expensive hardware. Modern technology such as rectangular pulses allows to adapt parameters like pulse shape and duration in order to reduce the required energy. Nevertheless, the effect of different temporal electromagnetic field shapes on neuronal structures is not yet fully understood. We created a simulation environment to find out how peripheral nerves are affected by induced magnetic fields and what pulse shapes have the lowest energy requirements. Using the electric field distribution of afigure-of-8coil together with an axon model in saline solution, we calculated the potential along the axon and determined the required threshold current to elicit an action potential. Further, for the purpose of selective stimulation, we investigated different axon diameters. Our results show that rectangular pulses have the lowest thresholds at a pulse duration of 20µs. For sinusoidal coil currents, the optimal pulse duration was found to be 40µs. Most importantly, with an asymmetric rectangular pulse, the coil current could be reduced from 2.3 kA (cosine shaped pulse) to 600 A. In summary, our results indicate that for magnetic nerve stimulation the use of rectangular pulse shapes holds the potential to reduce the required coil current by a factor of 4, which would be a massive improvement.

Molecular Emissions from Stretched Excitation Pulse in Nanosecond Phase-Selective Laser-Induced Breakdown Spectroscopy of TiO2 Nanoaerosols.

In phase-selective laser-induced breakdown spectroscopy (PS-LIBS), gas-borne nanoparticles are irradiated with laser pulses (∼2.4 GW/cm2) resulting in breakdown of the nanoparticle phase but not the surrounding gas phase. In this work, the effect of excitation laser-pulse duration and energy on the intensity and duration of TiO2-nanoparticle PS-LIBS emission signal is investigated. Laser pulses from a frequency-doubled neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (532 nm) are stretched from 8 ns (full width at half maximum, FWHM) up to ∼30 ns at fixed pulse energy using combinations of two optical cavities. The intensity of the titanium atomic emissions at around 500 nm wavelength increases by ∼60%, with the stretched pulse and emissions at around 482 nm, attributed to TiO, enhanced over 10 times. While the atomic emissions rise with the stretched laser pulse and decay around 20 ns after the end of the laser pulse, the TiO emissions reach their peak intensity at about 20 ns later and last longer. At low laser energy (i.e., 1 mJ/pulse, or 80 MW/cm2), the TiO emissions dominate, but their increase with laser energy is lower compared to the atomic emissions. The origin of the 482 nm emission is explored by examining several different aerosol setups, including Ti-O, Ti-N, and Ti-O-N from a spark particle generator and Ti-O-N-C-H aerosol from flame synthesis. The 482 nm emissions are attributed to electronically excited TiO, likely resulting from the reaction of excited titanium atoms with surrounding oxidizing (carbonaceous and/or radical) species. The effects of pulse length are attributed to the shift of absorption from the initial interaction with the particle to the prolonged interaction with the plasma through inverse bremsstrahlung.

Stone Retropulsion Caused by the Pulse-Duration Adjustable Holmium Laser: Analysis of the Whole-Process Dynamics with a Modified Method.

Introduction: Stone retropulsion was shown to be impacted by pulse duration during holmium laser lithotripsy, although the whole process of retropulsion was troublesome to study. We developed a modified method to analyze retropulsion using a smartphone and video tracking software. Materials and Methods: A holmium laser system was incorporated with a short (200 µseconds) and long pulse-duration (LP) (800 µseconds), and a 272-µm core fiber was attached. A cross-sectional V-shaped rail was submerged in a tank, on which artificial stones were displaced linearly after lasering. Different combinations of pulse energy, frequency, and pulse duration were tested for at least 4 seconds. An iPhone 11 capable of high-definition videoing and video tracking software was used to analyze the stone's displacement and velocity. Results: For most settings, the displacement-time graph resembled logarithmic growth and the velocity peaked within the first second after lasering. Higher energy or frequency translated into greater displacement, accompanied by earlier and faster velocity peaks. When the laser power was constant, the short pulse-duration at the fourth second after lasering was much larger in 0.5 J × 40 Hz than 1.0 J × 20 Hz under the short pulse-duration (SP) (13.17 ± 0.92 mm vs 6.90 ± 1.98 mm, p < 0.05), but this discrepancy was offset by the LP. The largest stone displacement and velocity were observed in 0.5 J × 40 Hz SP. Conclusion: The pulse duration plays a dominant role in determining the stone retropulsion and velocity, and a long pulse decreases retropulsion and velocity. Given a constant power, the variable combination of frequency and pulse energy contributes to significantly different retropulsion with a short pulse rather than a long pulse. The modified method offers a feasible solution for the study of stone retropulsion by laser lithotripsy.

Effect of Pulse Duration and Direction on Plasticity Induced by 5 Hz Repetitive Transcranial Magnetic Stimulation in Correlation With Neuronal Depolarization.

Introduction: High frequency repetitive transcranial magnetic stimulation applied to the motor cortex causes an increase in the amplitude of motor evoked potentials (MEPs) that persists after stimulation. Here, we focus on the aftereffects generated by high frequency controllable pulse TMS (cTMS) with different directions, intensities, and pulse durations. Objectives: To investigate the influence of pulse duration, direction, and amplitude in correlation to induced depolarization on the excitatory plastic aftereffects of 5 Hz repetitive transcranial magnetic stimulation (rTMS) using bidirectional cTMS pulses. Methods: We stimulated the hand motor cortex with 5 Hz rTMS applying 1,200 bidirectional pulses with the main component durations of 80, 100, and 120 µs using a controllable pulse stimulator TMS (cTMS). Fourteen healthy subjects were investigated in nine sessions with 80% resting motor threshold (RMT) for posterior-anterior (PA) and 80 and 90% RMT anterior-posterior (AP) induced current direction. We used a model approximating neuronal membranes as a linear first order low-pass filter to estimate the strength-duration time constant and to simulate the membrane polarization produced by each waveform. Results: PA and AP 5 Hz rTMS at 80% RMT produced no significant excitation. An exploratory analysis indicated that 90% RMT AP stimulation with 100 and 120 µs pulses but not 80 µs pulses led to significant excitation. We found a positive correlation between the plastic outcome of each session and the simulated peak neural membrane depolarization for time constants >100 µs. This correlation was strongest for neural elements that are depolarized by the main phase of the AP pulse, suggesting the effects were dependent on pulse direction. Conclusions: Among the tested conditions, only 5 Hz rTMS with higher intensity and wider pulses appeared to produce excitatory aftereffects. This correlated with the greater depolarization of neural elements with time constants slower than the directly activated neural elements responsible for producing the motor output (e.g., somatic or dendritic membrane). Significance: Higher intensities and wider pulses seem to be more efficient in inducing excitation. If confirmed, this observation could lead to better results in future clinical studies performed with wider pulses.

Effect of Different Pulse Durations on the Efficacy of Long-Pulsed Alexandrite-Assisted Hair Removal; A Split-Face Comparison Study.

Introduction: Laser-assisted hair removal is widely used by a large number of patients complaining of unwanted hair. However, little is known about the effect of varying the pulse duration on clinical results and side effects. This study aimed to investigate the effectiveness of hair removal using an alexandrite laser with different pulse durations. Methods: Fifty female patients with facial hirsutism were subjected to a hair removal procedure with an alexandrite laser, using 3 and 10 milliseconds pulse durations on each side of the face every 5 weeks for three sessions. Photographs were taken and hair counts were checked before the treatment and one month postoperatively. Results: one month after the laser treatment, the clearance rate was 56% with both 3 and 10 milliseconds pulse durations. There was not any significant difference in clinical efficacy or the side effect profile. Conclusion: Using a 755 nm alexandrite laser for hair removal is an effective and safe method for delaying hair regrowth and this delay is not markedly different by increasing the pulse duration from 3 to 10 milliseconds.

Surface Roughness Analysis of H13 Steel during Electrical Discharge Machining Process Using Cu-TiC Sintered Electrode.

In electrical discharge machining (EDM), the machined surface quality can be affected by the excessive temperature generation during the machining process. To achieve a longer life of the finished part, the machined surface quality plays a key role in maintaining its overall integrity. Surface roughness is an important quality evaluation of a material's surface that has considerable influence on mechanical performance of the material. Herein, a sintered cermet tooltip with 75% copper and 25% titanium carbide was used as tool electrode for processing H13 steel. The experiments have been performed to investigate the effects of EDM parameters on the machined surface roughness. The findings show that, as the pulse current, pulse length, and pulse interval are increased, the surface roughness tends to rise. The most significant determinant for surface roughness was found to be pulse current. A semi-empirical surface roughness model was created using the characteristics of the EDM technique. Buckingham's theorem was used to develop a semi-empirical surface roughness prediction model. The semi-empirical model's predictions were in good agreement with the experimental studies, and the built empirical model based on physical features of the cermet tooltip was tested using dimensional analysis.