Nanosecond Pulsed Ablation Research Articles

The CellFX Percutaneous Electrode System for Nanosecond Pulsed Field Ablation.

The purpose of this study was to demonstrate the safety and performance of the CellFX Percutaneous Electrode for delivering nanosecond pulsed field ablation (nsPFA) energy to soft tissues. Three different porcine tissue types were treated, namely, liver, kidney, and skeletal muscle, at treatment levels of three times greater than clinical treatment levels. The histological characteristics of the ablation zone for each of these tissues compared with that of radiofrequency (RF) ablation on day 0 and 2 days post-treatment. Ablation zone dimensions were measured during gross necropsy after tetrazolium chloride staining and compared between the nsPFA and RF groups at 2 days post-ablation. The CellFX system successfully achieved ablation and necrosis of all treatment sites in all target tissues. No evidence of thermal effects or collagen degeneration was found at any of the nsPFA treatment sites. Overall systemic tolerability was evidenced by the absence of clinically significant changes in urinalysis and serum chemistry before and after treatments.

Ablating Myocardium Using Nanosecond Pulsed Electric Fields: Preclinical Assessment of Feasibility, Safety, and Durability.

Unlike conventional microsecond pulsed electrical fields that primarily target the cell membranes, nanosecond pulses are thought to primarily electroporate intracellular organelles. We conducted a comprehensive preclinical assessment of catheter-based endocardial nanosecond pulsed field ablation in swine. A novel endocardial nanosecond pulsed field ablation system was evaluated in a total of 25 swine. Using either a low-dose (5-second duration) or high-dose (15-second duration) strategy, thoracic veins and discrete atrial and ventricular sites were ablated. Predetermined survival periods were <1 (n=1), ≈2 (n=7), ≈7 (n=6), 14 (n=2), or ≈28 (n=9) days, and venous isolation was assessed before euthanasia. Safety assessments included evaluation of esophageal effects, phrenic nerve function, and changes in venous caliber. All tissues were subject to careful gross pathological and histopathologic examination. All (100%) veins (13 low-dose, 34 high-dose) were acutely isolated, and all reassessed veins (6 low-dose, 15 high-dose) were durably isolated. All examined vein lesions (10 low-dose, 22 high-dose) were transmural. Vein diameters (n=15) were not significantly changed. Of the animals assessed for phrenic palsy (n=9), 3 (33%) demonstrated only transient palsy. There were no differences between dosing strategies. Thirteen mitral isthmus lesions were analyzed, and all 13 (100%) were transmural (depth, 6.4±0.4 mm). Ventricular lesions were 14.7±4.5 mm wide and 7.1±1.3 mm deep, with high-dose lesions deeper than low-dose (7.9±1.2 versus 6.2±0.8 mm; P=0.007). The esophagus revealed nontransmural adventitial surface lesions in 5 of 5 (100%) animals euthanized early (2 days) post-ablation. In the 10 animals euthanized later (14-28 days), all animals demonstrated significant esophageal healing-8 with complete resolution, and 2 with only trace fibrosis. A novel, endocardial nanosecond pulsed field ablation system provides acute and durable venous isolation and linear lesions. Transient phrenic injury and nontransmural esophageal lesions can occur with worst-case assessments suggesting limits to pulsed field ablation tissue selectivity and the need for dedicated assessments during clinical studies.

Influence of water layer thickness on crater volume for nanosecond pulsed laser ablation of stainless steel

Under water laser ablation is a surface texturization method used to form micrometer-sized surface structures. Plasma confinement and cavitation bubble evolution play a critical role during the ablation process and their influence on material removal is strongly tied to liquid layer thickness. To influence the effects of these processes, such that material removal is at its maximum, an optimal layer thickness was found for various laser parameters. Specifically, for nanosecond pulsed laser ablation of stainless steel, however, the relation between layer thickness and volume removal is still unknown. Here, we show the relation between water layer thickness and removed material volume for a nanosecond pulsed laser. Results reveal that volume removal is at its maximum for a 1 mm water layer and drops by a factor of 2 when the layer thickness is increased to 2 mm. A further increase of layer thickness to 3 up to 10 mm shows a negligible effect on volume removal and removed volume amounts are shown to be similar to those obtained in ambient air in this water layer thickness range. This trend echo’s results obtained for nanosecond pulsed silicon ablation. The obtained results identify processing conditions which allow for faster and therefore more cost efficient texturization of stainless steel surfaces in the future.

Direct laser interference patterning via scanning optics using the Michelson-Morley configuration

Direct Laser Interference Patterning (DLIP) is a promising method to realize patterns on surfaces, based on two or more beams, interference. Compared with the traditional direct laser writing approach, DLIP allows control of the features’ shape and size below the size of the laser beam. The standard configuration of a DLIP system is based on fixed optical elements and the movement of the sample via a motorized axis. This work proposes a new optical setup for two-beam DLIP. A Michelson-Morley interferometer was used, realizing the interference of a split beam. A nanosecond pulsed green laser was used to realize the interference phenomenon. The innovative concept combines the interferometer with an industrial scanner head for beam steering. The work explores possibility to use the galvanometric mirrors in DLIP to expand the process capabilities towards larger areas without moving the workpiece. Moreover, the concept is adaptable for different laser wavelengths and optical solutions permitting a degree of flexibility in the pattern period. An optical model is proposed for the first time to describe the design requirements and the pattern period for scanning optics. The developed prototype was used to pattern a biodegradable magnesium alloy with known difficulties for nanosecond pulse ablation. Two strategies namely point by point and continuous scanning were investigated. Periodic linear patterns were produced with periodicity equal to 23 µm and with a productivity up to 6.5 cm2/min.

Deep ablation and LIBS depth elemental profiling by combining nano- and microsecond laser pulses

A combination of nano- and microsecond pulses has been suggested for LIBS elemental profiling beyond 1 mm depth for metal coatings. Deep laser ablation and LIBS measurements have been compared for different laser pulse temporal shapes: single and double nanosecond pulses, free-run pulse and combined micro-nanosecond pulse. The deepest laser crater was produced by free-run pulse but plasma emissivity fell dramatically within the first few laser shots. Both single nanosecond pulse and double nanosecond pulse ablation provided crater with depth less than 0.6 mm which is not enough for a typical cladded coating thickness measurements. Nano- and microsecond laser pulses coupling resulted in deep crater formation (> 1.5 mm) but LIBS spectra with good signal-to-noise ratio can be still captured. The feasibility of LIBS depth profiling by coupled nano- (first) and microsecond (second) pulses has been demonstrated for 0.8–1.2 mm thick superalloy coatings measurements.

Au Nanoparticle-Decorated TiO&lt;sub&gt;2&lt;/sub&gt; Nanospheres Produced by Laser Reshaping in Water

Here, we demonstrate formation of spherical-shaped amorphous titania (TiO2) nanoparticles decorated with Au nanoclusters via nanosecond pulse ablation (7-ns, 532-nm wavelength) of commercially available TiO2 nanopowders dispersed in an aqueous solution of chloroauric acid (HAuCl4). Generation of such hybrid nanostructures was found to be caused by laser-induced remelting of the initial TiO2 nanoparticles, stimulated by Au nanoclusters that can adsorbed on their surface and boost light-to-heat conversion process in optically transparent titania. The morphology and chemical composition of the obtained hybrid nanomaterials were studied in detail via scanning electron microscopy, Raman spectroscopy and Energy Dispersive X-ray spectroscopy. The average size and number of Au nanoclusters reduced on the TiO2 nanoparticle surface was shown to be tuned by varying the initial nanoparticles/HAuCl4 concentration ratio. Spectroscopic measurements of single hybrid nanoparticles scattering, as well as the corresponding numerical calculations of electromagnetic fields structure near their surface indicate synthesized functional nanomaterials as extremely promising for numerous applications of modern optics, optoelectronics and nanophotonics, e.g., realization of advanced chemo-and biosensing platforms, as well as of new-generation solar cells.

Laser-printed plasmonic nanotextures with controlled porosity

We propose efficient approach for fabrication of various plasmonic nanostructures in the shape of the sub-micro rings and nanohillocks having tailored inner porosity. The fabrication approach combines the direct nanosecond-pulse ablation of the nitrogen-rich Au films covering glass or silicon substrates followed by a large-area etching with an Ar-ion beam. The average size of the nanopores inside the produced structures can be controlled via nitrogen doping level in the target metal films through tailoring the nitrogen gas concentration in the process of the film magnetron deposition, while the overall geometric shape of the produced plasmonic structures can be controlled by optimizing the thickness of the irradiated film as well as the laser irradiation parameters. Spherical-shape nanopores of variable size which depends on the initial nitrogen concentration in the irradiated film were directly revealed by preparing the cross-sectional cuts of the fabricated nanorings using focused ion beam milling. The proposed approach holds promise for easy-to-implement fast laser printing of the various nanostructures with the tailored porosity for chemo- and biosensing applications.

Laser-induced breakdown spectroscopy as a potential tool for autocarbonization detection in laserosteotomy.

In laserosteotomy, it is vital to avoid thermal damage of the surrounding tissue, such as carbonization, since carbonization does not only deteriorate the ablation efficiency but also prolongs the healing process. The state-of-the-art method to avoid carbonization is irrigation systems; however, it is difficult to determine the desired flow rate of the air and cooling water based on previous experiments without online monitoring of the bone surface. Lack of such feedback during the ablation process can cause carbonization in case of a possible error in the irrigation system or slow down the cutting process when irrigating with too much cooling water. The aim of this paper is to examine laser-induced breakdown spectroscopy as a potential tool for autocarbonization detection in laserosteotomy. By monitoring the laser-driven plasma generated during nanosecond pulse ablation of porcine bone samples, carbonization is hypothesized to be detectable. For this, the collected spectra were analyzed based on variation of a specific pair of emission line ratios in both groups of samples: normal and carbonized bone. The results confirmed a high accuracy of over 95% in classifying normal and carbonized bone.

Ion distribution and ablation depth measurements of a fs-ps laser-irradiated solid tin target

The ablation of solid tin surfaces by a 800-nanometer-wavelength laser is studied for a pulse length range from 500 fs to 4.5 ps and a fluence range spanning from 0.9 to 22 J/cm2. The ablation depth and volume are obtained employing a high-numerical-aperture optical microscope, while the ion yield and energy distributions are obtained from a set of Faraday cups set up under various angles. We found a slight increase of the ion yield for an increasing pulse length, while the ablation depth is slightly decreasing. The ablation volume remained constant as a function of pulse length. The ablation depth follows a two-region logarithmic dependence on the fluence, in agreement with the available literature and theory. In the examined fluence range, the ion yield angular distribution is sharply peaked along the target normal at low fluences but rapidly broadens with increasing fluence. The total ionization fraction increases monotonically with fluence to a 5%–6% maximum, which is substantially lower than the typical ionization fractions obtained with nanosecond-pulse ablation. The angular distribution of the ions does not depend on the laser pulse length within the measurement uncertainty. These results are of particular interest for the possible utilization of fs-ps laser systems in plasma sources of extreme ultraviolet light for nanolithography.

Laser induced breakdown spectroscopy with picosecond pulse train

Picosecond pulse train and nanosecond pulse were compared for laser ablation and laser induced breakdown spectroscopy (LIBS) measurements. A detailed study revealed that the picosecond pulse train ablation improved the quality of laser craters (symmetric crater walls and the absence of large redeposited droplets), which was explained by a smaller heat affected zone and suppression of melt splash. Greater plasma dimensions and brighter plasma emission were observed by gated imaging for picosecond pulse train compared to nanosecond pulse ablation. Increased intensity of atomic and ionic lines in gated and time integrated spectra provided better signal-to-noise ratio for picosecond pulse train sampling. Higher temperature and electron density were detected during first microsecond for the plasma induced by the picosecond pulse train. Improved shot-to-shot reproducibility for atomic/ionic line intensity in the case of picosecond pulse train LIBS was explained by more effective atomization of target material in plasma and better quality of laser craters. Improved precision and limits of detections were determined for picosecond pulse train LIBS due to better reproducibility of laser sampling and increased signal-to-noise ratio.

Photovoltaic performance and photocatalytic activity of facile synthesized graphene decorated TiO2 monohybrid using nanosecond pulsed ablation in liquid technique

We report the synthesis of graphene-TiO2 nanohybrid catalyst using different concentrations of deionized water suspended in graphene sheet as a medium in the ablation of titanium dioxide (TiO2) nanoparticles using an one-step pulsed laser ablation in liquid setup equipped with Nd-YAG laser (532nm wavelength) which was kept at a laser fluence of 320mJ/pulse, a pulse duration of 6ns and a frequency of 10Hz. The produced graphene-TiO2 nanohybrids obtained is active in both the ultraviolet and visible spectral regions as explained in the UV–vis absorption spectroscopy. This property is affiliated with improved crystallinity as shown in the X-ray diffraction technique and Raman spectroscopy. A perfect interaction between TiO2 nanoparticles and graphene sheets is confirmed by the bond formed between the surface carbon of graphene and oxygen in TiO2, which was obtained in the Fourier transform infrared analysis, Raman spectroscopy and X-ray photoelectron spectroscopy analysis. This is also confirmed with the morphology obtained from the transmission electron microscopic image of the nanohybrid. The prepared graphene-TiO2 nanohybrids were utilized as photo-catalyst and photo-anode in the degradation of methyl orange dye and dye sensitized solar cell, respectively. Improved crystallinity and reduced charge transfer resistance was observed in TiO2 nanoparticles hybridized with 3% graphene. This leads to an improvement in the photo-conversion efficiency of the dye sensitized solar cell from 0.60% to 3.80% and an enhancement in the removal of methyl orange pollutant from 89.10% to 99.60% when degraded under UV–vis solar spectrum.

Synergistic Combination of Electrolysis and Electroporation for Tissue Ablation.

Electrolysis, electrochemotherapy with reversible electroporation, nanosecond pulsed electric fields and irreversible electroporation are valuable non-thermal electricity based tissue ablation technologies. This paper reports results from the first large animal study of a new non-thermal tissue ablation technology that employs “Synergistic electrolysis and electroporation” (SEE). The goal of this pre-clinical study is to expand on earlier studies with small animals and use the pig liver to establish SEE treatment parameters of clinical utility. We examined two SEE methods. One of the methods employs multiple electrochemotherapy-type reversible electroporation magnitude pulses, designed in such a way that the charge delivered during the electroporation pulses generates the electrolytic products. The second SEE method combines the delivery of a small number of electrochemotherapy magnitude electroporation pulses with a low voltage electrolysis generating DC current in three different ways. We show that both methods can produce lesion with dimensions of clinical utility, without the need to inject drugs as in electrochemotherapy, faster than with conventional electrolysis and with lower electric fields than irreversible electroporation and nanosecond pulsed ablation.

Interferometric Analysis of 1064-nm Nanosecond Laser Induced Copper Plasma

This paper reports on the interferometric analysis of laser-induced plasma performed to investigate the spatial and temporal dynamics of a plasma column as a function of the time elapsed after laser-induced ablation on the surface of a copper target. The plasma was driven by focusing Q-switched Nd:YAG laser pulse ( λ = 1064 nm, τ = ~ 5 ns, and E=12. 5 mJ) onto a copper target and the interference patterns were constructed using a Nomarski interferometer. Phase information of the interference patterns was extracted using a fast Fourier-transform method. With the phase information obtained thus the spatial distribution of electron density was inferred from the Abel inversion equation. For the infrared nanosecond pulsed ablation regime, we observed that the resulting plasma expands preferentially toward the incoming laser beam at the early stage of plasma formation. The maximum plasma density was measured to be of the order of ~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . As time elapses, the rapid radial expansion of plasma plume and significant reduction of electron density were observed.

Direct Laser Interference Patterning of tetrahedral amorphous carbon films for tribological applications

In this work, the influence of surface topography and micro structural changes on the tribological properties of tetrahedral amorphous carbon coatings (ta-C) structured using a holographic technique the direct laser interference pattering (DLIP) is investigated. By utilizing a nanosecond pulsed UV-laser (wavelength 355nm), both ablation and graphitization thresholds were determined as a function of the pulse number. Incubation effects for the ablation threshold (~205mJcm−2) were found to be negligible. However, for the graphitization of the film thresholds varying from 47 to 74mJcm−2 were observed depending on the number of laser pulses utilized (from 1 to 30) and thus obtaining an incubation factor of 1.13. Using two- and three-beam interference setups, dot- and line-like periodic arrays were fabricated. The tribological performance of these patterns was investigated under reciprocating sliding with a ball on disk method under non-lubricated conditions showing that coefficient of friction can be reduced from~0.089 (un-patterned) to~0.055 patterned ta-C (~30% reduction). The results can be explained based on the reduction of surface contact area combined with high hardness as well as the good intrinsic tribological properties of the ta-C films.

Abstract 5387: Exploring effects of nanosecond and microsecond pulsed electric field ablation in a rat orthotopic hepatocellular carcinoma model

Abstract Hepatocellular carcinoma (HCC) is the third most common cancer in the world. A diagnosis of HCC carries a guarded prognosis, especially when metastasis is documented. Reliable, curative treatment for very early, early, and intermediate stages is still an inconsistent ideal. Nanosecond (ns), or microsecond (μs) pulsed electric fields (PEFs) that produce irreversible electroporation (IRE) could be used to ablate local tumor masses through minimal invasive or open surgery delivery. Both nsPEFs and μsPEFs induce permanent permeabilization of cells resulting in cell death without any thermal effect. NsPEFs can also impact intracellular organelles and induce apoptosis. Previous studies indicated under certain condition, there was a protective tumor response following nsPEFs treatment in mouse subcutaneous HCC model. In these studies, we specifically test the efficacy of nsPEFs and μsPEFs in an orthotopic HCC rat tumor model. N1S1 cells stably transfected with luciferase were used to generate tumors. Orthotropic insertion of transfected N1S1 HCC cells in Sprague Dawley rat livers was used as the model. Different pulses numbers, rise times and pulse durations were applied. The effect on treated tumor tissue suggests that a single treatment of 500 or 1000 100ns pulses with either slow (50ns) or fast (10ns) rise times and 50 kV/cm can eliminate HCC tumors. Continuous delivery of eighty 100μs microsecond pulses at 2.5 kV/cm dramatically reverses lesion enlargement. 1000 pulses of 100 ns PEFs with fast rise times provoke an innate immune response. Immune responses in this orthotopic HCC model are still under investigation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5387. doi:1538-7445.AM2012-5387

Comparison of Pd plasmas produced at 532nm and 1064nm by a Nd:YAG laser ablation

A comparison between the laser ablation of a palladium target in vacuum, by using 1064 nm and 532 nm Nd:YAG laser wavelengths, with an intensity of about 109 W/cm2, is reported. Nanosecond pulsed ablation produces high non-isotropic emission of neutrals and ions. For both wavelengths, mass quadrupole spectrometry and time-of-flight measurements allow estimation of the atomic and ionic species emitted from the plasma and of their energy distributions. Ions show Coulomb–Boltzmann-shifted distributions depending on their charge state. Surface profiles of the ablated craters permitted to study the ablation threshold and yields of palladium in vacuum vs. the laser fluence. The plasma temperature and density was evaluated by the experimental data. A special regard is given to the ion acceleration process occurring inside the plasma, due to the high electrical field generated inside the plasma.

Nickel plasma produced by 532-nm and 1064-nm pulsed laser ablation

A comparison between laser ablation of nickel in vacuum by using 532-and 1064-nm Nd:YAG (Yttrium Aluminium Garnet) laser wavelengths, with an intensity of 5 × 109 W/cm2, is reported. Nanosecond pulsed ablation produces high nonisotropic emission of neutrals and ionic species. For 532-nm laser irradiation, mass quadrupole spectrometry, coupled to electrostatic ion deflection and time-of-flight measurements, allows estimation of the energy distributions of the emitted species from plasma. For 1064-nm laser ablation, a cylindrical electrostatic ion analyzer permits one to measure the yield and the charge state of the emitted ions and reconstruct the ion energy and charge state distributions. Neutrals show typical Boltzmann-like distributions, while ions show Coulomb-Boltzmann-shifted distributions depending on their charge state. Surface profiles of the ablated craters permitted study of the ablation threshold and yields of nickel in vacuum versus the laser fluence. The plasma temperature was evaluated using experimental data. Special regard is given to the ion acceleration process occurring inside the plasma due to the high electrical field generated at nonequilibrium plasma conditions and the angular distribution of the emitted species.

Assessment of the precision and accuracy of thorium (232Th) and uranium (238U) measured by quadrupole based inductively coupled plasma-mass spectrometry using liquid nebulization, nanosecond and femtosecond laser ablation

The precision and accuracy of the 238U/232Th ratio were evaluated from liquid nebulization and direct solid sampling repetitive pulsed laser ablation. Nanosecond and femtosecond pulsed lasers at 266 nm wavelength were utilized for the ablation studies. The ICP-MS and sampling parameters were optimized for each procedure; flow rates, gases, laser energy and other parameters were optimized for the particular sampling approach and therefore will not be the same. The work is not a comparison per se but represents performance metrics for three optimized sampling modalities. As expected, nanosecond pulsed ablation provided the greatest inaccuracy (>30%) from the nominal 238U/232Th bulk ratio. This deviation from bulk ratio is attributed to incomplete vaporization of large particle agglomerates produced by nanosecond laser ablation. Femtosecond pulsed ablation provided inaccuracy (∼1–3%) approaching that of liquid nebulization (∼1%). In terms of temporal relative standard deviation (TRSD) and relative standard deviation (RSD), liquid nebulization provided the best precision for the 238U/232Th ratio (TRSD ∼3–5%, RSD ∼0.2–0.6%), femtosecond laser ablation (TRSD ∼5–12%, RSD ∼1%) and nanosecond laser ablation (TRSD ∼25–48%, RSD ∼9–12%). Laser ablation requires less sample to achieve these performance metrics, in some cases less than a factor of 100-times depending on the entrainment and transport efficiency.

Characterization of laser-generated silicon plasma

A study of visible laser ablation of silicon, in vacuum, by using 3 ns Nd:YAG laser radiation is reported. Nanosecond pulsed ablation, at an intensity of the order of 10 10 W/cm 2, produces high non-isotropic emission of neutrals and ionic species. Mass quadrupole spectrometry, coupled to electrostatic ion deflection, allows estimation of the energy distributions of the emitted species from plasma. Neutrals show typical Boltzmann-like distributions while ions show Coulomb–Boltzmann-shifted distributions depending on their charge state. Time-of-flight measurements were also performed by using an ion collector consisting of a collimated Faraday cup placed along the normal to the target surface. Surface profiles of the craters, created by the laser radiation absorption, permitted to study the ablation threshold and ablation yields of silicon in vacuum. The plasma fractional ionization, temperature and density were evaluated by the experimental data. A special regard is given to the ion acceleration process occurring inside the plasma due to the high electrical field generated at the non-equilibrium plasma conditions. The angular distribution of the neutral and ion species is discussed.

Metal particles produced by laser ablation for ICP–MS measurements

Pulsed laser ablation (266 nm) was used to generate metal particles of Zn and Al alloys using femtosecond (150 fs) and nanosecond (4 ns) laser pulses with identical fluences of 50 J cm −2. Characterization of particles and correlation with inductively coupled plasma mass spectrometer (ICP–MS) performance was investigated. Particles produced by nanosecond laser ablation were mainly primary particles with irregular shape and hard agglomerates (without internal voids). Particles produced by femtosecond laser ablation consisted of spherical primary particles and soft agglomerates formed from numerous small particles. Examination of the craters by white light interferometric microscopy showed that there is a rim of material surrounding the craters formed after nanosecond laser ablation. The determination of the crater volume by white light interferometric microscopy, considering the rim of material surrounding ablation craters, revealed that the volume ratio (fs/ns) of the craters on the selected samples was approximately 9 (Zn), 7 (NIST627 alloy) and 5 (NIST1711 alloy) times more ablated mass with femtosecond pulsed ablation compared to nanosecond pulsed ablation. In addition, an increase of Al concentration from 0 to 5% in Zn base alloys caused a large increase in the diameter of the particles, up to 65% while using nanosecond laser pulses. When the ablated particles were carried in argon into an ICP–MS, the Zn and Al signals intensities were greater by factors of ∼50 and ∼12 for fs versus ns ablation. Femtosecond pulsed ablation also reduced temporal fluctuations in the 66Zn transient signal by a factor of 10 compared to nanosecond laser pulses.