High Pulse Research Articles

Scaling of laboratory neutron sources based on laser wakefield-accelerated electrons using Monte Carlo simulations

Neutron sources based on laser-accelerated particles have attracted interest as they may provide a compact, cost-effective alternative to conventional sources. Recently, laser-driven neutron sources, based on ion acceleration, demonstrated neutron resonance spectroscopy, imaging and resonance imaging in first proof-of-principle experiments. To drive these sources efficiently with laser-accelerated ions, high laser pulse energies, in the range of tens to hundreds of Joules, with sub-ps pulse duration are needed. This requirement currently limits ion-based laser neutron sources to large-scale laser systems, which typically have maximum repetition rates in the order of a few shots per hour. In this paper, we investigate a potential path to circumvent these limitations by utilizing high repetition rate capable laser wakefield acceleration of electrons to drive a neutron source with high conversion efficiency. Monte Carlo simulations are performed to calculate neutron yields for various electron energies and converter materials, to determine optimal working parameters for an electron-based laser-driven neutron source. The results suggest that conversion efficiencies exceeding 25% can be achieved, depending on the electron energy and converter material. This electron-based approach could provide a neutron source with up to 1011\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{11}$$\\end{document}n/s with state-of-the-art laser sources (ELaser≲1J\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_{\ ext {Laser}} \\lesssim {1}\\,{\\rm J}$$\\end{document}, τLaser≲50fs\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au _{\ ext {Laser}} \\lesssim {50}\\,{\\rm fs}$$\\end{document}, ∼1kHz\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim {1}\\,\ extrm{kHz}$$\\end{document}).

Laser harmonic generation with independent control of frequency and orbital angular momentum

The non-linear optical process of laser harmonic generation (HG) enables the creation of high quality pulses of UV or even X-ray radiation, which have many potential uses at the frontiers of experimental science, ranging from lensless microscopy to ultrafast metrology and chiral science. Although many of the promising applications are enabled by generating harmonic modes with orbital angular momentum (OAM), independent control of the harmonic frequency and OAM level remains elusive. Here we show, through a theoretical approach, validated with 3D simulations, how unique 2-D harmonic progressions can be obtained, with both frequency and OAM level tuned independently, from tailored structured targets in both reflective and transmissive configurations. Through preferential selection of a subset of harmonic modes with a specific OAM value, a controlled frequency comb of circularly polarised harmonics can be produced. Our approach to describe HG, which simplifies both the theoretical predictions and the analysis of the harmonic spectrum, is directly applicable across the full range of HG mechanisms and can be readily applied to investigations of OAM harmonics in other processes, such as OAM cascades in Raman amplification, or the analysis of harmonic progressions in nonlinear optics.

Study on preparation and anti-sand erosion performance of thick DLC coating combined with FCVA deposition and HVP technology

To address the compatibility issues between the hardness and thickness of DLC coatings and to improve the erosion resistance of engine blades, a thick DLC coating was prepared using a combination of filter cathode vacuum arc (FCVA) deposition technology and high voltage pulse (HVP) technology. The prepared thick DLC coating exhibits low residual stress (1.79 ± 0.087 GPa) and high C-sp3 content (70.13 %), with a thickness and hardness of 18.46 μm and 51.07 ± 0.23 GPa, respectively. The results of anti-sand erosion tests indicate that the mass loss rates of DLC coating at the erosion angles of 45° and 90° are 4.44 × 10−3 mg/g and 1.99 × 10−2 mg/g, respectively. The good erosion resistance of thick DLC coatings is attributed to the consumption of residual impact energy by carbon cluster structures, which prevents the generation and propagation of cracks. Therefore, the thick and super-hard DLC coatings can be prepared by combining FCVA deposition technique with HVP technique, which has great potential applications in the aerospace industry.

Single-cycle, 643 mW average power terahertz source based on tilted pulse front in lithium niobate.

We present the highest, to the best of our knowledge, average power from a laser-driven single-cycle THz source demonstrated so far, using optical rectification in the tilted pulse front geometry in cryogenically cooled lithium niobate, pumped by a commercially available 500 W ultrafast thin-disk ytterbium (Yb) amplifier. We study repetition rate-dependent effects in our setup at 100 and 40 kHz at this high average power, revealing different optimal fluence conditions for efficient conversion. The demonstrated sources with multi-100 mW average power at these high repetition rates combine high THz pulse energies and high repetition rate and are thus ideally suited for nonlinear THz spectroscopy experiments with significantly reduced measurement times. The presented result is a first benchmark for high average power THz time-domain spectroscopy systems for nonlinear spectroscopy, driven by very high average power ultrafast Yb lasers.

Highly Circularly Polarized Monochromatic High Harmonic Pulses via a Reflective Phase Retarder at 27.9 eV

Highly Circularly Polarized Monochromatic High Harmonic Pulses via a Reflective Phase Retarder at 27.9 eV

Evaluating perioperative stresses in children by noninvasive modalities using salivary cortisol and autonomic reactivity.

Salivary cortisol (SalC) and low to high pulse ratio (LHR) were used for evaluating perioperative stresses in children. Children aged 6months-16years having elective general (thoracic/abdominal) or minor (open/minimally invasive: MI) procedures underwent pulse monitoring during AM (08:00-12:00) and PM (17:00-21:00) saliva collections from the day before surgery (S-1) to 3days after surgery (S + 3). SalC/LHR were correlated with age, sex, caregiver attendance, operative time, and surgical site/approach using mixed model analysis and face/numeric pain rating scales (FRS/NRS). Mean ages (years): minor-open (n = 31) 4.7 ± 2.0, thoracic-open (n = 2) 8.7 ± 4.9, thoracic-MI (n = 6) 9.6 ± 6.1, abdominal-open (n = 14) 4.3 ± 4.1, and abdominal-MI (n = 32) 8.0 ± 5.0. Postoperative SalC increased rapidly and decreased to preoperative levels by S + 3 (p < 0.001). LHR increased slightly without decreasing (p = 0.038). SalC correlated positively with operative time (p = 0.036) and open surgery (p = 0.0057), and negatively with age (p < 0.0001) and caregiver attendance (p < 0.001). SalC correlated positively with FRS (n = 51) at S + 2(PM) (p = 0.023), S + 3(AM) (p < 0.001), S + 3(PM) (p = 0.012) and NRS (n = 34) at S + 1(AM) (p = 0.031), S + 3(AM) (p < 0.044). LHR positively correlated with age (p = 0.0072), female sex (p = 0.0047), and caregiver attendance (p = 0.0026). Postoperative SalC after robotic-assisted MI was significantly lower than after open surgery at S + 2(AM) (p = 0.020). SalC correlated with pain. Caregiver attendance effectively alleviated stress.

A method to resolve thermal and electronic contributions to the nolinear optical response

This paper presents the study and implementation of a modified Z-scan technique using a chopper to change the thermal load of the sample, while keeping the input peak irradiance constant. It was verified numerically and experimentally that by changing the frequency of the chopper and keeping the power of the laser beam constant, it is possible to vary the thermal load on the sample. This technique is illustrated under the study of the nonlinear optical (NLO) properties of nucleated Au–Pt metallic nanoparticles (NPs) by ion implantation. The nonlinear optical response was studied using the Z-scan. technique using a Ti:Sapphire laser with femtosecond pulses at a wavelength of 800 nm and a repetition rate of 76 MHz. By scanning the sample using the Z-scan technique it was It is possible to determine the refractive and absorbing contributions to the nonlinear response, in this case as a consequence of a high pulse repetition rate, cumulative pulse-to-pulse thermal effects occurred. Because of this, a modification of the Z-scan technique allowed to separate the resolution of the electronic and thermal contributions on the sample.

Semiactive Car-Seat System for Rear-End Collisions

This study proposes and simulates a smart system that can be used in production car seats to decrease whiplash risk in rear-end crashes. A sliding seat incorporating a semiactively controlled magnetorheological (MR) damper model positioned under the seat-pan is simulated with a validated biofidelic human body model. Since this is the first study that demonstrates a computer controlled anti-whiplash car seat system to the best of the authors’ knowledge, a benchmark analysis is carried out to compare the proposed semiactive seat with a state-of-the-art passive anti-whiplash car seat using 23 different crash pulses, including the moderate and high severity crash pulses within the European New Car Assessment Program (EuroNCAP) whiplash risk assessment framework. The proposed semiactive design outperforms the passive seat design by further reducing the values of the critical EuroNCAP whiplash criteria, such as NIC and Nkm, together with the loads acting on the upper neck. The semiactive seat lowers the upper-neck shear force by an amount of 4 kg and 7 kg while lessening the NIC by 10% and 21% and Nkm by 9% and 56% for the EuroNCAP crash pulses, having a delta-V of 16 km/h and 24 km/h, respectively. The findings presented in this paper can aid in the design of car seats to further mitigate whiplash risk in rear-end crashes.

Efficient laser-driven proton acceleration from a petawatt contrast-enhanced second harmonic mixed-glass laser system

Efficient laser-driven plasma acceleration of ion beams requires precision control of the target–plasma profile, which is crucial to optimize the laser energy transfer. Along the laser propagation direction, this can be achieved by tailoring the temporal structure of the laser pulse. We show for the first time that frequency-doubling of a short pulse (hundreds-femtosecond range) petawatt-class mixed-glass laser system, which results in temporal intensity contrast enhancement, enables surface and volumetric laser–energy coupling, and the acceleration of proton beams from few-nanometer-thick foil targets. Experimentally, maximum ion energies and laser-to-proton energy conversion efficiencies were found to be both maximized at optimum laser and target conditions manifested when the normalized target density nearly equalizes the normalized laser vector potential, which is in agreement with theory and simulations. These signatures are recognized as a unique indication of the interaction between ultra-intense laser pulses with high temporal intensity contrast and ultra-thin nanometer-scale targets. Transverse modulations of accelerated proton beams in the form of bubble- and ring-like structures measured in the thinnest targets provide additional evidence of volumetric laser-driven particle acceleration regimes and transitional features in ultra-thin foil targets specific to laser–plasma interactions characterized by a high temporal intensity contrast. These results open avenues in the generation of high contrast laser pulses from short-pulse-femtosecond petawatt mixed-glass laser systems and demonstrate the feasibility of this technique for applications requiring high laser intensity contrast with high efficiency.

Coexistence of anti-KS and anti-TIF1-γ antibodies in clinically amyopathic dermatomyositis presenting with rapid progression of interstitial lung disease.

Polymyositis/Dermatomyositis (PM/DM) is an idiopathic inflammatory myopathy (IIM) manifesting mainly as symmetrical proximal muscle weakness and/or typical cutaneous features due to autoimmune mechanisms. Clinically amyopathic dermatomyositis (CADM) is a subset of DM that exhibits only the typical cutaneous features without any clinical muscle symptoms. Several autoantibodies have been found specifically in patients with PM/DM, including CADM patients. Anti-KS antibody is one of a group of anti-aminoacyl transfer RNA (ARS) antibodies that are mainly associated with fever, Raynaud's phenomenon, polyarthritis, and interstitial lung disease (ILD), whereas anti-TIF1-γantibody is frequently found in DM patients with malignancy. Here, we report a CADM patient having both anti-KS antibody and anti-TIF1-γantibody. This patient developed an acute exacerbation of ILD and was successfully treated with high dose corticosteroid pulse therapy together with immunosuppressive agents. Although earlier experience had indicated that the seminal characteristic of anti-KS-positive ILD was slowly developing disease onset with little or no progression over the clinical course, the present patient suffered rapidly progressive disease.

Design and optimization of handheld alloy analysis instrument based on microjoule high pulse repetition frequency LIBS.

We briefly describe the design of a handheld metal detection instrument based on microjoule high repetition frequency laser-induced breakdown spectroscopy. The instrument uses a Raspberry Pi as the control core and a laser with a frequency of 10kHz and a single pulse energy of 100 µJ as the excitation source. In addition, a mini-putter is built into the instrument to move the laser, allowing the ablation of the sample surface line area without external auxiliary equipment. The excitation-generated plasma radiation is collected by a simple optical path and transmitted directly to the spectrometer. We also constructed and trained a Backpropagation Artificial Neural Network (BP-ANN) model based on 12 different grades of alloys and transplanted the feedback process of the BP-ANN to the Raspberry Pi, which realized the rapid classification of the 12 alloys with >95% classification accuracy on the handheld instrument.

Design of an Optimized Terahertz Time-Domain Spectroscopy System Pumped by a 30 W Yb:KGW Source at a 100 kHz Repetition Rate with 245 fs Pulse Duration

Ytterbium laser sources are state-of-the-art systems that are increasingly replacing Ti:Sapphire lasers in most applications requiring high repetition rate pulse trains. However, extending these laser sources to THz Time-Domain Spectroscopy (THz-TDS) poses several challenges not encountered in conventional, lower-power systems. These challenges include pump rejection, thermal lensing in nonlinear media, and pulse durations exceeding 100 fs, which consequently limit the detection bandwidth in TDS applications. In this article, we describe our design of a THz-TDS beamline that seeks to address these issues. We report on the effectiveness of temperature controlling the Gallium Phosphide (GaP) used to generate the THz radiation and its impact on increasing the generation efficiency and aiding pump rejection while avoiding thermal distortions of the residual pump laser beam. We detail our approach to pump rejection, which can be implemented with off-the-shelf products and minimal customization. Finally, we describe our solution based on a commercial optical parametric amplifier to obtain a temporally compressed probe pulse of 55 fs duration. Our study will prove useful to the increasing number of laboratories seeking to move from the high-energy, low-power THz time-domain spectroscopy systems based on Ti:Sapphire lasers, to medium-energy, high-power systems driven by Yb-doped lasers.

Generation of high-energy self-mode-locked pulses in a Tm-doped fiber laser

The incorporation of a material-based or artificial saturable absorber into a fiber laser cavity imposes a limitation on energy enhancement owing to its low damage threshold and high environmental sensitivity. To address this issue, one promising alternative approach is the utilization of the self-mode-locking technique. Here, we present a robust self-mode-locked Tm-doped fiber laser with high pulse energy emission. A simple and compact fiber laser structure is realized by utilizing a section of a Tm-doped fiber, serving both as a gain medium and a saturable absorber. Thus, the operational stability is enhanced, especially under high-energy conditions. Furthermore, the realization of high-energy pulses is accomplished through the integration of dispersion management technique. Experimental results reveal that the maximum single-pulse energy increases from 34.8 pJ to 120.2 nJ as the round-trip group delay dispersion decreases from −0.43 to −12.40 ps2. The proposed self-mode-locked Tm-doped fiber laser under high-energy operation exhibits remarkable performance. Our results provide a simple approach to obtaining a mid-infrared laser source with high pulse energy and hold significant potential for advancing high-energy laser systems.

Effect of the electrode spacing on dynamic fracture behavior of red sandstone under high-voltage pulse discharge

High voltage pulse technology has broad application prospects in the field of rock fragmentation. Electrical breakdown experiments of red sandstone under the action of high-voltage pulse discharge (HVPD) at different electrode spacings were conducted. The current waveform was recorded using a Rogowski coil. The fracture process on the specimen surface was observed by using an ultra-high-speed camera. The stress wave generated by HVPD was obtained. The experimental results show that both the peak values of the current wave and the stress wave decrease with the increase of the electrode spacing. The surface fracture of the specimen is dominated by transverse fractures parallel to the electrode axis, accompanied by shorter vertical fractures that are perpendicular to the electrode axis. The numerical model is further established to elucidate the three-dimensional fracture process and mechanism of the specimens, and the influence of the electrode spacing on the degree of fracturing is expounded.

Colloidal Titanium Nitride Nanoparticles by Laser Ablation in Solvents for Plasmonic Applications.

Titanium nitride (TiN) is a candidate material for several plasmonic applications, and pulsed laser ablation in liquids (PLAL) represents a rapid, scalable, and environmentally friendly approach for the large-scale production of nanomaterials with customized properties. In this work, the nanosecond PLAL process is developed, and we provide a concise understanding of the process parameters, such as the solvent and the laser fluence and pulse wavelength, to the size and structure of the produced TiN nanoparticles (NPs). TiN films of a 0.6 μm thickness developed by direct-current (DC) magnetron sputtering were used as the ablation targets. All laser process parameters lead to the fabrication of spherical NPs, while the laser pulse fluence was used to control the NPs' size. High laser pulse fluence values result in larger TiN NPs (diameter around 42 nm for 5 mJ and 25 nm for 1 mJ), as measured from scanning electron microscopy (SEM). On the other hand, the wavelength of the laser pulse does not affect the mean size of the TiN NPs (24, 26, and 25 nm for 355, 532, and 1064 nm wavelengths, respectively). However, the wavelength plays a vital role in the quality of the produced TiN NPs. Shorter wavelengths result in NPs with fewer defects, as indicated by Raman spectra and XPS analysis. The solvent type also significantly affects the size of the NPs. In aqueous solutions, strong oxidation of the NPs is evident, while organic solvents such as acetone, carbides, and oxides cover the TiN NPs.

Controllable Double‐Emulsion Droplet Manipulation Actuated by a Triboelectric Nanogenerator

AbstractElectrically controlled droplet manipulation is attractive for lots of applications ranging from material synthesis and drug delivery. However, the present techniques using bulky and expensive power supplies to generate high‐voltage electrical signals are easy to cause electrode electrolysis, bubble formation in buffer solution, and are incapable for point‐of‐care testing. Herein, a novel and portable electrical method for self‐powered emulsion droplet core coalescence and release based on triboelectric nanogenerator (TENG) is presented. The electrical signal with a 2.25 kV open‐voltage and a 35 µA short‐circuit current can be conveniently generated via frictional electrification effect, and the harmful electrochemical reaction in solutions can be avoided. The high transient pulse voltage and stable sinusoidal signal between two electrodes in microfluidic device can generate a strong electric field, which causes apparent Maxwell electrical stresses at droplet interfaces and subsequently promotes the core coalescence and release of double‐emulsions. By adjusting the voltage magnitude, the core coalescence and release behaviors of double‐emulsion droplets can be controllably achieved, followed by the synthesis copper‐based metal–organic framework (Cu‐MOF) nanoparticles. Thus, this portable, effective and self‐powered droplet manipulation technique can be attractive for those droplet‐based applications.

In-band pumped, Q-switched thulium-doped fiber laser system delivering 140 W and 7 mJ pulse energy.

We report on a highly efficient, in-band pumped, Q-switched, Tm-doped, rod-type master oscillator power amplifier (MOPA) system delivering up to 140 W average output power and 7 mJ pulse energy with a slope efficiency of 77% at 20 kHz repetition rate. The amplifier is pumped with Raman-shifted fiber lasers centered at 1692 nm. This in-band pump scheme for Tm-doped fiber lasers can significantly mitigate their quantum defect-related heat load limitations. At the same time, this pump wavelength yields a similar amount of storable and extractable energy to the state-of-the-art pumping at 793 nm. This approach has allowed for the development of highly efficient Tm-doped fiber laser systems combining a high average power and a high output pulse energy.

Development Of An Endoscopic, Absorption Corrected And Calibrated OH Laser Induced Fluorescence Probe System for High Pressure Combustion Diagnostics

We present the design and preliminary results of an endoscopic OH laser-induced fluorescence (LIF) system that is capable of acquiring 1D-line measurements in high pressure combustion processes within large-scale test facilities. The system can be exploited to acquire line-of-sight OH-chemiluminescence images and absorption corrected absolute OH-species concentration from which additionally temperature distribution can be extracted in case of lean mixtures in chemical equilibrium. Different critical components, such as light guides for high power UV laser pulses and flexible UV image guides, were first tested and characterized in a laboratory setup. Optimization regarding pulse energy and beam quality led to the selection of an 1m long hollow core fiber for laser light delivery as a central element for the experimental setup despite high losses caused by bending the fiber. The image transfer is accomplished by a 7m long flexible UV image bundle, which is preferred to the use of a rigid borescope in harsh environments. We designed the endoscopic UV optics using readily available parts and achieved an approximated image resolution of 21.6 line pairs/mm. Additionally, post-processing methods, such as flat-field correction, can improve the image quality substantially and remove the pixilation effect of the fiber bundle structure nearly completely. To validate the complete system, probe-based qualitative OH-LIF measurements were performed in a well-known laminar flame of a matrix burner, which serves as a mock-up for anticipated applications in an industrial test environment with a technology readiness level (TRL) greater than 4. The final step consists of the integration of the miniaturized optics into a cooled probe system which protects the sensitive optics against the harsh environment of an aero-engine sector combustor. For this purpose, two probe systems were designed to include, on the one hand, the endoscope optics together with the fiber image bundle end tip and, on the other hand, the laser emitting and receiving system for performing an absorption measurement needed to quantify the recorded LIF signal.

Improving the wear and heat resistance of niobium substrate via reactive electrospark treatment using fusible AlCaSiY electrode

Protective coatings with a heterophase layered structure were obtained by reactive electrospark treatment (EST) of niobium substrate with a fusible AlCaSiY electrode. The effect of the frequency–energy modes of EST on the phase composition, structure and properties of the coatings was studied. A combination of high discharge current values (400A) and long pulses (100 μs) yields a double-layer coating with the total thickness of 80 μm, which consists of the (Al) matrix strengthened with Nb2CaAl20 particles and a hard (10 GPa) NbAl3 layer. The results of pin-on-plate tribological testing revealed that this structure made it possible to reduce the coefficient of friction from 0.42 to 0.24 and increase wear resistance 3.5-fold compared to those of niobium. Oxidative annealing of Nb plates in air at 700 °C causes their fracture due to the formation of Nb2O5. Indeed, oxidative annealing of the samples subjected to EST leads to in situ formation of a dense Ca12Al10Si4O35-oxide based near surface layer that inhibits oxygen diffusion into the bulk, thus suppressing Nb2O5 formation. Mass gain of the sample having a protective coating after 300-min isothermal exposure was 2.54 mg/cm2, which is 3.6-fold lower than that for the Nb substrate (9.04 mg/cm2).

Effects of pulse shape on pitch sensitivity of cochlear implant users

Contemporary cochlear implants (CIs) use cathodic-leading symmetric biphasic (C-BP) pulses for electrical stimulation. It remains unclear whether asymmetric pulses emphasizing the anodic or cathodic phase may improve spectral and temporal coding with CIs. This study tested place- and temporal-pitch sensitivity with C-BP, anodic-centered triphasic (A-TP), and cathodic-centered triphasic (C-TP) pulse trains on apical, middle, and basal electrodes in 10 implanted ears. Virtual channel ranking (VCR) thresholds (for place-pitch sensitivity) were measured at both a low and a high pulse rate of 99 (Experiment 1) and 1000 (Experiment 2) pulses per second (pps), and amplitude modulation frequency ranking (AMFR) thresholds (for temporal-pitch sensitivity) were measured at a 1000-pps pulse rate in Experiment 3. All stimuli were presented in monopolar mode. Results of all experiments showed that detection thresholds, most comfortable levels (MCLs), VCR thresholds, and AMFR thresholds were higher on more basal electrodes. C-BP pulses had longer active phase duration and thus lower detection thresholds and MCLs than A-TP and C-TP pulses. Compared to C-TP pulses, A-TP pulses had lower detection thresholds at the 99-pps but not the 1000-pps pulse rate, and had lower MCLs at both pulse rates. A-TP pulses led to lower VCR thresholds than C-BP pulses, and in turn than C-TP pulses, at the 1000-pps pulse rate. However, pulse shape did not affect VCR thresholds at the 99-pps pulse rate (possibly due to the fixed temporal pitch) or AMFR thresholds at the 1000-pps pulse rate (where the overall high performance may have reduced the changes with different pulse shapes). Notably, stronger polarity effect on VCR thresholds (or more improvement in VCR with A-TP than with C-TP pulses) at the 1000-pps pulse rate was associated with stronger polarity effect on detection thresholds at the 99-pps pulse rate (consistent with more degeneration of auditory nerve peripheral processes). The results suggest that A-TP pulses may improve place-pitch sensitivity or spectral coding for CI users, especially in situations with peripheral process degeneration.