Delivering Laser Pulses Research Articles

Rationally designed ultra-fast laser surface texturation of biocompatible temporal scaffolds

The aim of the current work is to create 2D silk fibroin and 3D calcium phosphate temporal cellular scaffolds with specifically enhanced porous topographical design by means of femtosecond laser-induced nano- and micro-scale hybrid surface structuring for application in muscle and bone tissue engineering. The created cellular matrices were ablated in a multistep manner using a Solstice Ace system, delivering laser pulses with pulse duration of 70 fs, at λ=800 nm and a focus spot of 25μm. The samples were positioned on a motorized XY translation stage perpendicular or in a variable angle in respect to the laser beam. Based on the previously performed comparative experimental study, optimal laser structuring conditions and raster patterns were chosen for further enhancement of muscular and Schwann cells environment. The most valuable contribution of the study presented is related to the optimization of the bioactivity properties of the studied cell matrices and their subsequent practical application in tissue engineering.

Soft monolithic infrared neural interface for simultaneous neurostimulation and electrophysiology

Controlling neuronal activity using implantable neural interfaces constitutes an important tool to understand and develop novel strategies against brain diseases. Infrared neurostimulation is a promising alternative to optogenetics for controlling the neuronal circuitry with high spatial resolution. However, bi-directional interfaces capable of simultaneously delivering infrared light and recording electrical signals from the brain with minimal inflammation have not yet been reported. Here, we have developed a soft fibre-based device using high-performance polymers which are >100-fold softer than conventional silica glass used in standard optical fibres. The developed implant is capable of stimulating the brain activity in localized cortical domains by delivering laser pulses in the 2 μm spectral region while recording electrophysiological signals. Action and local field potentials were recorded in vivo from the motor cortex and hippocampus in acute and chronic settings, respectively. Immunohistochemical analysis of the brain tissue indicated insignificant inflammatory response to the infrared pulses while the signal-to-noise ratio of recordings still remained high. Our neural interface constitutes a step forward in expanding infrared neurostimulation as a versatile approach for fundamental research and clinically translatable therapies.

High-power femtosecond regenerative amplifier based on Yb:CaYAlO4 dual-crystal configuration.

A thermal lens insensitive regenerative amplifier (RA) with a dual Yb:CaYAlO4 (Yb:CYA) crystal configuration for extending gain spectra is demonstrated for the first time, to the best of our knowledge. By orthogonalizing the orientation of two a-cut Yb:CYA crystals in one RA, the Q switched spectrum with a full width at half maximum of 15.4 nm is generated, which is 1.5 and 1.6 times of the Q switched spectral bandwidth with π- and σ-polarization, respectively. With chirped pulses injection, this RA can deliver laser pulses with an average power exceeding 10 W at the repetition rate of 20-800 kHz and pulse energy of 1.5 mJ at 1 kHz. This is the highest average power from the Yb:CYA RA to the best of our knowledge. Finally, compressed pulses of 163 fs with 92% overall efficiency are realized. Thanks to the heat insensitive cavity design and excellent thermodynamic properties of the Yb:CYA crystal, the output laser beam is close to the diffraction limit with an M2 value of 1.07 × 1.07.

Dual color, frequency, pulse duration and shape agile laser system for particle spectroscopy and manipulation.

A dual color, frequency and pulse duration agile laser system, capable of delivering laser pulses in arbitrary temporal profiles with ∼1 ns to ∼1 µs pulse duration, chirping rates of ∼27 MHz/ns with an achievable chirping range of several GHz across the pulse duration, and with energies ranging from a few nJ to hundreds of mJ per pulse has been developed. The flexibility and capability of this laser system provide a wide range of laser parameters that can be exploited to optimize operational conditions in various experiments ranging from laser diagnostics to spectroscopy and optical manipulation of matter. The developed system is successfully demonstrated to obtain coherent Rayleigh-Brillouin scattering (CRBS) in both single and dual color configuration, in an effort to expand the non-intrusive accessibility towards lower pressure regime for neutral gas and plasma diagnostics.

Guided propagation of extremely intense lasers in plasma via ion motion.

The upcoming 10-100 PW laser facilities may deliver laser pulses with unprecedented intensity of 10^{22}-10^{25}Wcm^{-2}. Such laser pulses interacting with ultrarelativistic electrons accelerated in plasma can trigger various nonlinear quantum electrodynamic processes. Usually, ion motion is expected to be ignorable since the laser intensities below 10^{25}Wcm^{-2} are underrelativistic for ions. Here, we find that ion motion becomes significant even with the intensity around 10^{22}Wcm^{-2} when electron cavitation is formed by the strong laser ponderomotive force. Due to the electron cavitation, guided laser propagation becomes impossible via usual plasma electron response to laser fields. However, we find that ion response to the laser fields may effectively guide laser propagation at such high intensity levels. The corresponding conditions of the required ion density distribution and laser power are presented and verified by three-dimensional particle-in-cell simulations.

High peak power Nd:YAG/Cr:YAG ceramic microchip laser with unstable resonator.

A doughnut mode microchip laser was demonstrated by introducing a monolithic ceramic Nd:YAG/Cr4+:YAG chip in an unstable resonator to deliver laser pulses with an energy of 13.2 mJ and a pulse width of 476 ps, corresponding to a record peak power of 27.7 MW. The laser beam quality was characterized by M2∼6 at 10 Hz repetition rate. No significant degradation or change of beam pattern, pulse width, and M2 was confirmed during energy scaling in the case of the unstable cavity, promising for further brightness improving. In comparison with a flat-flat cavity, pulse broadening and M2 increase was observed up to ∼1.2 ns and ∼10, respectively, during energy scaling up to 18 mJ due to the beam pattern degradation. The doughnut beam was observed to have an Airy disk at the focal point, which was suitable for laser induced breakdown in air. The measured breakdown threshold of doughnut beam was comparable to a near-Gaussian beam (M2=1.3).

Assembly process and optical performances for a golden laser spark-plug device

The low-stress Solderjet Bumping technique was employed to assemble the optical components of an increased-robustness laser spark-plug ignition device using the low melting alloys 96.5Sn3Ag0.5Cu and 80Au20Sn. A finite-element-method analysis, optical simulations, and a soldering parametrization test were performed to prove that different optical materials (sapphire, ECO-550, D-ZLaF52LA, TAC4, and N-SF11 glasses) could be fastened to the stainless steel body. The assembled spark-plug device featured a passively Q-switched Nd : YAG/Cr4 + : YAG composite ceramic medium and delivered laser pulses with energy variable between 2.40 and 4.70 mJ, with 0.8 ns duration, suitable for inducing air breakdown phenomenon and engine combustion.

High beam quality and high peak power Yb:YAG/Cr:YAG microchip laser.

The prospect for developing a passively Q-switched Yb:YAG/Cr:YAG monolithic microchip laser that operates at cryogenic temperature is theoretically analyzed. It is concluded that such a system has the potential to deliver laser pulses with improved energy and increased peak power in comparison with composite Yb:YAG/Cr:YAG or Nd:YAG/Cr:YAG devices that are operated at room temperature. Consequently, a cryogenically cooled Yb:YAG/Cr:YAG system is built and the emission performances are investigated. Laser pulses with 3.2 mJ energy, 6.1 MW peak power and high beam quality of M2 = 1.8 are achieved. By increasing the pump beam diameter, laser pulses with higher energy 32 mJ are obtained at 25 MW peak power with M2 = 5.4. To our knowledge, these are the best results obtained from passively Q-switched composite Yb:YAG/Cr:YAG monolithic microchip lasers.

A low-power laserwire profile monitor for H− beams: Design and experimental results

An instrument to non-destructively measure the transverse profile of an H−beam has been developed and tested at CERN’s new LINAC4. The vertical profile of the H−beam has been measured, at beam commissioning energies of 50, 80 and 107 MeV. The instrument consists of a laser-source which is coupled to an optical fibre, delivering laser pulses with hundreds Watts of peak power to the accelerator tunnel, where the laser beam is focused horizontally onto the H−beam. Due to photo-detachment, electrons are liberated from the ions and can be deflected by a weak dipole field onto a diamond detector. The beam profile is obtained by scanning the laser beam vertically across the H−beam and recording for each position the number of arriving electrons. The design, implementation and characterisation of the novel instrument shall be described and the measured beam profiles compared to profiles obtained with SEM-grids and wirescanners.

Imaging Artifacts in Continuous Scanning 2D LA-ICPMS Imaging Due to Nonsynchronization Issues.

Pulsed laser ablation (LA) devices in laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) imaging have become very advanced, delivering laser pulses with high temporal accuracy and stable energy density. However, unintentional imaging artifacts may be generated in 2D element maps when the LA repetition rate and the data acquisition parameters of ICPMS instruments with a sequential mass spectrometer (i.e., quadrupole filter or sector-field mass spectrometer) are desynchronized. This may potentially lead to interference patterns, visible as ripples in elemental images, and thus, compromised image quality. This paper describes the background of aliasing in continuous scanning mode through simulation experiments and ways to modulate the effect. The existence of this image degradation source is demonstrated experimentally via real-life imaging of a homogeneous glass standard.

High order harmonics generation by relativistically circularly polarized laser-solid interaction

Coherent extreme ultra-violet (XUV) and soft X-ray light with attosecond duration enable the time-resolved study of electron dynamics in a completely new regime. High order harmonic generation (HHG) from the highly nonlinear process of relativistically intense laser interactions with solid-density plasma offers a very new way to generate such a light source. In this paper, we study the HHG by a relativistically circularly polarized femtosecond laser interacting with solid-density plasma. The experiment is carried out by using a 200 TW Ti:sapphire laser system at the Laboratory for Laser Plasmas in Shanghai Jiao Tong University, China. The laser system can deliver laser pulses at 800 nm with a pulse duration (full width at half maximum, FWHM) of 25 fs and repetition rate of 10 Hz. The circularly polarized laser beam with an energy of 460 mJ is used in the experiment and focused by an F/4 off-axis parabolic mirror at an incidence angle of 40 with respect to the glass target. The focal spot diameter is 6 m (FWHM) with 25% energy enclosed, giving a calculated peak intensity of 1.61019 W/cm2. We detect high order harmonics by a flat-field spectrometer. The experimental results show that high order harmonic radiation can also be efficiently generated by a circularly polarized laser at a lager incidence angle, which provides a straightforward way to obtain a circularly polarized XUV light source. Different plasma density scale lengths are obtained by introducing a prepulse with different delays. We study the dependence of HHG efficiency on plasma density scale length by the circularly polarized laser, and find an optimal density scale length to exist. The influence of laser polarization and plasma density scale length on HHG are studied by two-dimensional (2D) PIC simulations. The good agreement is found between the 2D PIC simulations and experimental results. We plan to measure the polarization characteristics of high order harmonic produced by the interaction of circularly polarized lasers with solid target in the future. It is expected to obtain a compact coherent circularly polarized XUV light source, which can be used to study the ultra-fast dynamic process of magnetic materials.

O208 Evidence by direct current stimulation (tDCS) of cerebellum involvement in pain perception and modulation in humans

Objective cerebellum is involved in a wide number of integrative functions; its role in pain processing has been scarcely investigated. We tried to clarify this aspect using transcranial cerebellar direct current stimulation (tcDCS) and studying changes in perceptive threshold (PT), pain intensity (VAS) and laser evoked potentials (LEPs) responses (N1 and N2/P2). Materials and methods Fifteen subjects were studied before and after anodal, cathodal and sham tcDCS. LEPs were obtained using a Nd:YAP laser; signals were amplified, band pass filtered. The left hand dorsum was stimulated by laser pulses with short duration (5 ms) and small diameter spots (5 mm). VAS was evaluated by delivering laser pulses at two different intensities, respectively two and three times the pain threshold (PT). Results Cathodal polarization dampened the PT and increased the VAS score, while the anodal one had opposite effects ( p p Discussion tcDCS modulates pain perception and its cortical correlates. As it is effective on N1 and N2/P2 components and these responses are generated by parallel and partially segregated spinal pathways reaching different cortical targets, we speculate that the cerebellum modulates the activity of both somatosensory and cingulate cortices, interfering with the sensory-discriminative as well as emotional dimensions of pain. Conclusions Present findings prove Cerebellum involvement in pain processing and prompt further investigations on tcDCS employments as novel therapeutic tool in chronic pain patients.

Thin-disk multipass amplifier for fs pulses delivering 400 W of average and 2.0 GW of peak power for linear polarization as well as 235 W and 1.2 GW for radial polarization

We report on an Yb:YAG thin-disk multipass amplifier delivering linearly polarized laser pulses with a pulse duration of 885 fs at an average output power of 400 W and a repetition rate of 200 kHz, corresponding to a peak power of 2.0 GW. This is the highest average output power reported for thin-disk multipass amplifiers delivering pulses with peak powers in excess of 1 GW and it confirms the suitability of thin-disk multipass amplifiers to reach high average output and peak powers at the same time. The amplifier was seeded by a regenerative amplifier delivering laser pulses with a pulse duration of 805 fs and an average power of 40 W. We investigated the influence of self-phase-modulation on the amplified beam and compared it to results with lower peak intensities at a repetition rate of 800 kHz. Furthermore, we report on the amplification of a radially polarized beam leading to 235 W of average output power and 1.2 GW of peak power (at a pulse duration of 888 fs). To the best of our knowledge, this is the highest average output power demonstrated so far for radially polarized GW peak-level laser pulses.

P190 Cerebellar direct current stimulation modulates pain perception in humans

Question The cerebellum is involved in a wide number of integrative functions, but its role in pain perception and nociceptive processing is poorly understood. We evaluated the effects of transcranial cerebellar direct current stimulation (tcDCS) by studying the changes in perceptive threshold (PT), pain intensity (VAS) and laser evoked potentials (LEPs) variables (amplitude and latency of both N1 and N2/P2 responses). Methods Fifteen subjects were studied before and after anodal, cathodal and sham tcDCS. LEPs were obtained using a Nd:YAP laser (wavelength 1.04 μm, pulse 164 duration 2–20 ms, maximum energy 7 J). The laser beam was transmitted from the generator to the stimulating probe via a 10 m length optical fibre; signals were then amplified, band pass filtered (0.1–200 Hz, time analysis 1000 ms). The dorsum of the left hand was stimulated by laser pulses (individual variability: 3.89–15.75 J/cm2) with short duration (5 ms) and small diameter spots (5 mm). VAS was evaluated by delivering laser pulses at two different intensities, respectively two and three times the PT. Results Cathodal polarization dampened the PT and increased the VAS score, while the anodal one had opposite effects. Conclusions TcDCS modulates pain perception and its cortical correlates. As it is effective on N1 and N2/P2 components and these responses are generated by parallel and partially segregated spinal pathways reaching different cortical targets, we speculate that the cerebellum modulates the activity of both somatosensory and cingulate cortices, thus interfering with the sensory-discriminative and emotional dimensions of pain. Present findings prompt investigation of the tsDCS as a novel, safe therapeutic tool in chronic pain patients. Download : Download high-res image (428KB) Download : Download full-size image

5. Cerebellar direct current stimulation modulates pain perception and its neural correlates in humans

The cerebellum is involved in a number of integrative functions, but its role in pain perception and nociceptive processing is poorly understood. We evaluated the effects of transcranial cerebellar direct current stimulation (tcDCS) by studying changes in perceptive threshold (PT), pain intensity (VAS) and laser evoked potentials (LEPs). Twenty-five subjects were studied before and after anodal, cathodal and sham tcDCS. LEPs were obtained using a Nd:YAP laser. VAS was evaluated by delivering laser pulses at two different intensities, respectively two and three times the PT. Cathodal polarization dampened the perceptive threshold and increased the VAS score, while anodal one had opposite effects (p < 0.001, two-way repeated measures ANOVA, “time” × “stimulation”). Cathodal tcDCS increased LEPs amplitudes and decreased their latencies, whereas anodal polarization elicited opposite effects (p < 0.0001). Motor thresholds assessed through transcranial magnetic stimulation were not affected by tcDCS. tcDCS modulates pain perception and its cortical correlates. As it is effective on N1 and N2/P2 components, we speculate that the cerebellum modulates the activity of both somatosensory and cingulate cortices, thus interfering with the sensory-discriminative and affective-emotional dimensions of pain. Our findings prompt investigation of the tsDCS as a novel and safe therapeutic tool in pain syndromes.

Extending ultra-short pulse laser texturing over large area

Surface texturing by Ultra-Short Pulses Laser (UPL) for industrial applications passes through the use of both fast beam scanning systems and high repetition rate, high average power P, UPL. Nevertheless unwanted thermal effects are expected when P exceeds some tens of W. An interesting strategy for a reliable heat management would consists in texturing with a low fluence values (slightly higher than the ablation threshold) and utilising a Polygon Scanner Heads delivering laser pulses with unrepeated speed.Here we show for the first time that with relatively low fluence it is possible over stainless steel, to obtain surface texturing by utilising a 2MHz femtosecond laser jointly with a polygonal scanner head in a relatively low fluence regime (0.11Jcm−2). Different surface textures (Ripples, micro grooves and spikes) can be obtained varying the scan speed from 90ms−1 to 25ms−1. In particular, spikes formation process has been shown and optimised at 25ms−1 and a full morphology characterization by SEM has been carried out. Reflectance measurements with integrating sphere are presented to compare reference surface with high scan rate textures. In the best case we show a black surface with reflectance value<5%.

74. Cerebellum and pain: A transcranial direct current stimulation (tDCS) study

The cerebellum is involved in a wide number of integrative functions, but its role in pain experience is poorly understood. We evaluated the effects of transcranial cerebellar direct current stimulation (tcDCS) by studying the changes in the perceptive threshold, pain intensity (VAS:0-10) and laser evoked potentials (LEPs) variables. Twenty-five subjects were studied before and after anodal, cathodal and sham tcDCS. LEPs were obtained using a Nd:YAP laser and recorded from the dorsum of the left hand. VAS was evaluated by delivering laser pulses at different intensities, respectively two and three times the perceptive threshold. Cathodal polarization dampened significantly the perceptive threshold and increased the VAS score, while the anodal one had opposite effects (p < 0.001, two-way repeated measures ANOVA, “time” × “stimulation”). Cathodal tcDCS increased the N1 and N2/P2 amplitudes and decreased their latencies, whereas anodal tcDCS elicited opposite effects (p < 0.0001). tcDCS modulates pain perception and its cortical correlates. As it influences both N1 and N2/P2 components, we speculate that the cerebellum modulates the activity of both somatosensory and cingulate cortices. Present findings prompt investigation of the cerebellar direct current polarization as a novel and safe therapeutic tool in chronic pain patients.

Cerebellar direct current stimulation modulates pain perception and its neural correlates in humans

The cerebellum is involved in a number of integrative functions, but its role in pain perception and nociceptive processing is poorly understood. We evaluated the effects of transcranial cerebellar direct current stimulation (tcDCS) by studying changes in perceptive threshold (PT), pain intensity (VAS) and laser evoked potentials (LEPs). Twenty-five subjects were studied before and after anodal, cathodal and sham tcDCS. LEPs were obtained using a Nd:YAP laser. VAS was evaluated by delivering laser pulses at two different intensities, respectively two and three times the PT. Cathodal polarization dampened the perceptive threshold and increased the VAS score, while anodal one had opposite effects (p tcDCS modulates pain perception and its cortical correlates. As it is effective on N1 and N2/P2 components, we speculate that the cerebellum modulates the activity of both somatosensory and cingulate cortices, thus interfering with the sensory-discriminative and affective-emotional dimensions of pain. Our findings prompt investigation of the tsDCS as a novel and safe therapeutic tool in pain syndromes.

Cerebellar direct current stimulation modulates pain perception in humans.

The cerebellum is involved in a wide number of integrative functions, but its role in pain experience and in the nociceptive information processing is poorly understood. In healthy volunteers we evaluated the effects of transcranial cerebellar direct current stimulation (tcDCS) by studying the changes in the perceptive threshold, pain intensity at given stimulation intensities (VAS:0-10) and laser evoked potentials (LEPs) variables (N1 and N2/P2 amplitudes and latencies). Fifteen subjects were studied before and after anodal, cathodal and sham tcDCS. LEPs were obtained using a neodymium:yttrium-aluminium-perovskite (Nd:YAP) laser and recorded from the dorsum of the left hand. VAS was evaluated by delivering laser pulses at two different intensities, respectively two and three times the perceptive threshold. Cathodal polarization dampened significantly the perceptive threshold and increased the VAS score, while the anodal one had opposite effects. Cathodal tcDCS increased significantly the N1 and N2/P2 amplitudes and decreased their latencies, whereas anodal tcDCS elicited opposite effects. Motor thresholds assessed through transcranial magnetic stimulation were not affected by cerebellar stimulation. tcDCS modulates pain perception and its cortical correlates. Since it is effective on both N1 and N2/P2 components, we speculate that the cerebellum engagement in pain processing modulates the activity of both somatosensory and cingulate cortices. Present findings prompt investigation of the cerebellar direct current polarization as a possible novel and safe therapeutic tool in chronic pain patients.

Scaling and passively Q-switch operation of a Nd:YAG laser pumped laterally through a YAG prism

Abstract We report on scaling of a laser configuration in which a YAG prism is used to couple the pump beam from a fiber-coupled diode laser directly into a Nd:YAG medium. Several resonator geometries have been investigated. In free generation regime laser pulses at 1.06 μm with energy of 22.1 mJ for the pump energy of 44.6 mJ were obtained from a 10.0 mm long, 1.0-at% Nd:YAG single crystal that had the high-reflectivity mirror coated directly on one of the laser crystal surface. The slope efficiency was 0.51. A similar uncoated Nd:YAG crystal placed in a plane–plane resonator delivered laser pulses with 17.8 mJ energy under the pump with 45.4 mJ energy, at 0.40 slope efficiency. Further, a passively Q-switched Nd:YAG/Cr 4+ :YAG composite ceramic laser pumped through a YAG prism has been built. Using a Cr 4+ :YAG saturable absorber of 0.85 initial transmission the device delivered laser pulses with 0.29 mJ energy and 11 ns duration. The output performances are compared to those obtained in a classical end-pumping scheme.