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Generation of ultrahigh speed, ultrashort flat-top picosecond electrical pulses by laser pulse shaping and ultrafast electro-optics sampling
A novel method is proposed and demonstrated to generate ultrahigh speed, ultrashort flat-top picosecond electrical pulses by combining laser pulse shaping with ultrafast electro-optics sampling technique. Starting with high repetition rate laser pulses, a sequence of birefringent crystals is employed to produce optical pulses with flat-top temporal profile and tunable duration. Subsequent measurement of optical waveforms by an ultrafast photodetector yields high-speed, ultrashort flat-top picosecond electrical pulses. By using two sets of YVO4 crystals for laser pulse shaping, we report on the generation of 704 MHz, 48 picoseconds and 704 MHz, 88 picoseconds flat-top electrical pulses with 16-30 picoseconds rise or fall time. Lastly, to the best of our knowledge, these results are better than or comparable with the best performance using step recovery diodes and the direct electro-optics sampling technique.
Spectroscopic studies on diamond like carbon films synthesized by pulsed laser ablation
Hydrogen free Diamond like Carbon (DLC) thin films enriched with C-C sp{sup 3} bonding were grown on Si (111) substrates at laser pulse energies varying from 100 to 400 mJ (DLC-100, DLC-200, DLC-300, DLC-400), by Pulsed Laser Ablation (PLA) utilizing an Nd:YAG laser operating at fundamental wavelength. Structural, optical and morphological evolutions as a function of laser pulse energy were studied by micro Raman, UV-Vis spectroscopic studies and Atomic Force Microscopy (AFM), respectively. Raman spectra analysis provided critical clues for the variation in sp{sup 3} content and optical energy gap. The sp{sup 3} content was estimated using the FWHM of the G peak and found to be in the range of 62-69%. The trend of evolution of sp{sup 3} content matches well with the evolution of I{sub D}/I{sub G} ratio with pulse energy. UV-Vis absorption study of DLC films revealed the variation of optical energy gap with laser pulse energy (1.88 – 2.23 eV), which matches well with the evolution of G-Peak position of the Raman spectra. AFM study revealed that roughness, size and density of particulate in DLC films increase with laser pulse energy.
Manipulating mammalian cell by phase transformed titanium surface fabricated through ultra-short pulsed laser synthesis
Developing cell sensitive indicators on interacting substrates that allows specific cell manipulation by a combination of physical, chemical or mechanical cues is a challenge for current biomaterials. Hence, various fabrication approaches have been created on a variety of substrates to mimic or create cell specific cues. However, to achieve cell specific cues a multistep process or a post-chemical treatment is often necessitated. So, a simple approach without any chemical or biological treatment would go a long way in developing bio-functionalized substrates to effectively modulate cell adhesion and interaction. The present investigation is aimed to study the manipulative activity induced by phase transformed titanium surface. An ultra-short laser is used to fabricate the phase transformed titanium surface where a polymorphic titanium oxide phases with titanium monoxide (TiO), tri-titanium oxide (Ti{sub 3}O) and titanium dioxide (TiO{sub 2}) have been synthesized on commercially pure titanium. Control over oxide phase transformed area was demonstrated via a combination of laser scanning time (laser pulse interaction time) and laser pulse widths (laser pulse to pulse separation time). The interaction of phase transformed titanium surface with NIH3T3 fibroblasts and MC3T3-E1 osteoblast cells developed a new bio-functionalized platforms on titanium based biomaterials to modulate cell migration and adhesion. The synthesized phase transformed titanium surface on the whole appeared to induce directional cues for cell migration with unique preferential cell adhesion unseen by other fabrication approaches. The precise bio-functionalization controllability exhibited during fabrication offers perceptible edge for developing a variety of smart bio-medical devices, implants and cardiovascular stents where the need in supressing specific cell adhesion and proliferation is of great demand. - Highlights: • Generation of titanium oxide phase transformed surface by ultra-short pulsed laser synthesis is presented here. • Laser pulse to pulse separation time variation results in polymorphic titanium oxide phases. • The approach enables site specific mammalian cell adhesion and migration. • This method paves way for developing smart titanium based biomedical devices such as implants and biosensors.
POWER RECYCLING OF BURST-MODE LASER PULSES FOR LASER PARTICLE INTERACTIONS
A number of laser-particle interaction experiments such as the laser assisted hydrogen ion beam stripping or X-/ -ray generations via inverse-Compton scattering involve light sources operating in a burst mode to match the tem-poral structure of the particle beam. To mitigate the laser power challenge, it is important to make the interaction inside an optical cavity to recycle the laser power. In many cases, conventional cavity locking techniques will not work since the burst normally has a very small duty factor and low repetition rate and it is impossible to gen-erate an effective control signal. This work reports on the development of a doubly-resonant optical cavity scheme and its locking techniques that enables a simultaneous resonance of two laser beams with different spectra and/or temporal structures. We demonstrate that such a cavity can be used to recycle burst-mode ultra-violet laser pulses with arbitrary burst lengths and repetition rates.
On the role of multiphoton light absorption in pulsed laser nanoablation of diamond
The rates of multipulse nanoablation of the diamond surface in air by pico- and nanosecond laser pulses that cause singlephoton, two-photon, three-photon and four-photon absorption in diamond are measured. In the experiments the radiation of ArF, KrF and Ti : Al{sub 2}O{sub 3} lasers and the second harmonic of the Yb : YAG laser was used. The power dependence of the material etching rate on the fluence of laser pulses was found. The power exponent of this dependence appeared to be twice lower than that found earlier for femtosecond pulses. We discuss the causes of the difference in the nanoablation regularities for 'short' and 'long' laser pulses.
Plasma mirror focal spot quality for glass and aluminum mirrors for laser pulses up to 20 ps
High-intensity short-pulse lasers are being pushed further as applications continue to demand higher laser intensities. Uses such as radiography and laser-driven particle acceleration require these higher intensities to produce the necessary x-ray and particle fluxes. Achieving these intensities, however, is limited by the damage threshold of costly optics and the complexity of target chambers. This is evidenced by the Advanced Radiographic Capability (ARC) short-pulse laser at the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory, producing four high-energy ≈1 kJ laser pulses at 30 ps pulse duration, being limited to an intensity of 10 18 W/cm 2 by the large focal spot size of ≈100 µm. Due to the setup complexity of NIF, changing the location of the final focusing parabola in order to improve the focal spot size is not an option. Therefore, this leads to the possible use of disposable ellipsoidal plasma mirrors (PMs) placed within the chamber, close to the target in an attempt to refocus the four ARC beams. However, the behavior of PMs at these relatively long pulse durations (tens of picoseconds) is not well characterized. The results from the COMET laser at the Jupiter Laser Facility carried out at 0.5 to 20 ps pulse durations on flat mirrors are presented as a necessary first step towards focusing curved mirrors. The findings show defocusing at longer pulse durations and higher intensities, with less degradation when using aluminum coated mirrors.
Advancing extreme pulsed lasers through measurements: summary of the pulsed laser metrology workshop
In this report we present consensus findings produced during the pulsed laser metrology (PLM) workshop (Boulder, CO, USA, August 2025). The workshop was a meeting of 35 scientists from private industry, academia, and U.S. government to compile a list of the metrology needs to support extreme pulsed laser development and implementation. We define ‘extreme pulsed lasers’ loosely as those with peak powers above 1 TW or multi-Joule pulse energies. Such lasers are being increasingly used and investigated for use in high energy particle acceleration, short wavelength radiation generation, laser-based fusion, etc. The rapid growth of these fields and the proliferation of extreme lasers for these applications, coupled with the extreme electric fields they generate and relative scarcity of such lasers, presents unique challenges to accuracy in their measurement. The PLM workshop was a two-day event designed to hear from users, developers, and researchers on the current state of optical metrology associated with these extreme pulsed lasers. The goal was to identify the most important measurement challenges limiting development and implementation of these lasers in practical applications. We report here the conclusions and recommendations of this workshop. The hope is that this document will become the first of many iterations which track the status of measurement needs supporting extreme pulsed lasers.
The dynamics of Al/Pt reactive multilayer ignition via pulsed-laser irradiation
Reactive multilayers consisting of alternating layers of Al and Pt were irradiated by single laser pulses ranging from 100 μs to 100 ms in duration, resulting in the initiation of rapid, self-propagating reactions. The threshold intensities for ignition vary with the focused laser beam diameter, bilayer thickness, and pulse length and are affected by solid state reactions and conduction of heat away from the irradiated regions. High-speed photography was used to observe ignition dynamics during irradiation and elucidate the effects of heat transfer into a multilayer foil. For an increasing laser pulse length, the ignition process transitioned from a more uniform to a less uniform temperature profile within the laser-heated zone. A more uniform temperature profile is attributed to rapid heating rates and heat localization for shorter laser pulses, and a less uniform temperature profile is due to slower heating of reactants and conduction during irradiation by longer laser pulses. Finite element simulations of laser heating using measured threshold intensities indicate that micron-scale ignition of Al/Pt occurs at low temperatures, below the melting point of both reactants.
Decay of a laser beam under stimulated temperature scattering in toluene as a result of two-photon pump absorption and nonsteady-state laser pulse interaction with matter
The decay of the pump-beam spatial structure under conditions of stimulated temperature scattering of a pulsed laser beam in toluene as a result of two-photon absorption of pump radiation and time-dependent interaction of a laser pulse with a medium is considered. (paper)
Optoacoustic Effects in Pentaerythritol Tetranitrate with Ultrafine Aluminum-Particle Inclusions under Pulsed-Laser Action
Results of studying optoacoustic characteristics of pentaerythritol tetranitrate (PETN) specimens with inclusions of ultrafine aluminum particles (100 nm) are presented. Regularities of the increase of extinction coefficient k{sub ef} and signal amplitude U on a piezodetector by increasing laser-pulse fluence H have been established. Estimates have been made, and it has been concluded that, during a laser pulse, heating of aluminum inclusions and a shell surrounding it occurs up to a gasification temperature and appear craters on a specimen’s surface appear at H > 0.1 J/cm{sup 2}.
Features of Pulsed Laser Annealing of BC{sub 3} Films on a Sapphire Substrate
The morphology, chemical composition, microstructure, and electrical properties of BC{sub 3} thin films subjected to melting by a nanosecond laser pulse are investigated. The original films have been created by pulsed laser codeposition of B and C onto a sapphire substrate at 150 and 350°C. Morphological changes in the films depended on their initial structural state. However, a “frozen” structure of both films after irradiation corresponded to the B-saturated graphite-like phase, the local composition of which varied due to the formation of inclusions of amorphous boron carbide. Before and after irradiation, the films exhibited a slightly decreasing dependence of the surface resistance with increasing temperature from 4.2 to 330 K. After laser irradiation, the films resistance has decreased by a factor of ~2.6.
Laser pulse shaping for additive manufacturing
A system for additive manufacturing uses a pulsed laser beam with one or more low flux components on the order of kW/cm2, and one or more high flux components on the order of MW/cm2 during the duration of the pulse. The pulsed laser beam is directed onto the powder particles on the substrate thereby melting the powder particles and melting the substrate at the interface layer between the powder and the substrate such that the powder particles bond to the substrate. This is accomplished by using low power (and low cost) lasers to do the majority of the energy transfer, and using high power (and higher cost) lasers to complete the melting process, overcoming the kinetics of powder agglomeration through surface tension forces by partially melting the powder-substrate interface layer before surface tension can take effect on the molten powder particles.
Pulsed laser ejection of single-crystalline III-V solar cells from GaAs substrates
The best III-V solar cells start out as single-crystalline multilayers on GaAs substrates. Separating these multilayers from their growth substrate enables higher performance and wafer reuse, which are both critical for terrestrial III-V solar cell viability. Here, we remove rigidly bonded, 16 mm 2 x 3.5μm thick devices from a GaAs substrate using an unfocused Nd:YAG laser pulse. The pulse is absorbed by a low-bandgap, lattice-matched layer below the device, driving an ablation event that ejected the crystalline multilayer from the substrate. Minutes of selective wet-chemical etching and device finishing yield a 0.1 cm 2 device with a 17.4% power conversion efficiency and open-circuit voltage of 1.07 V, using AM1.5 direct with no anti-reflection coating. We show that the performance is comparable to similar cells produced via conventional processes. We discuss unique process characteristics, such as the potential to separate wafer-sized solar cells per laser pulse.
Nanocrystalline and Polyicosahedral Structure of a Nanospike Generated on Metal Surface Irradiated by a Single Femtosecond Laser Pulse
Short pulse laser irradiation of metal targets can trigger a cascade of highly nonequilibrium processes leading to the formation of unique surface structures of interest to various practical applications. In this paper, we report the results of a large-scale atomistic simulation predicting the generation of a ~200 nm long frozen nanospike on the surface of a Ag target irradiated by a femtosecond laser pulse. The simulation provides detailed information on the mechanisms responsible for the formation of the nanospike and the processes that define its complex nanostructure. The competing contributions of the epitaxial regrowth of the solid part of the target and the homogeneous nucleation of new crystallites triggered by the strong undercooling of the liquid regions are found to produce a remarkable variability of the structural motifs coexisting in different regions of the frozen nanospike. The homogeneous solidification, in particular, proceeds along two distinct paths selected at the nucleation stage and produces markedly different nanostructures in different parts of the nanospike, namely, nanograins with mixed fcc/hcp structure and a continuous network of pentagonal twinned structural elements arranged into a polyicosahedral structure.
Investigation of Proton Beam-Driven Fusion Reactions Generated by an Ultra-Short Petawatt-Scale Laser Pulse
We present results from a pitcher-catcher experiment utilizing a proton beam generated with nanostructured targets at a petawatt-class, short-pulse laser facility to induce proton-boron fusion reactions in a secondary target. A 45-fs laser pulse with either 400 nm wavelength and 7 J energy, or 800 nm and 14 J, and an intensity of up to 5 × 10 21 W/cm 2 was used to irradiate either thin foil targets or near-solid density, nanostructured targets made of boron nitride (BN) nanotubes. In particular, for 800 nm wavelength irradiation, a BN nanotube target created a proton beam with about five times higher maximum energy and about ten times more protons than a foil target. This proton beam was used to irradiate a thick plate made of boron nitride placed in close proximity to trigger 11 B (p, α) 2α fusion reactions. A suite of diagnostics consisting of Thomson parabola ion spectrometers, postshot nuclear activation measurements, neutron time-of-flight detectors, and differentially filtered solid-state nuclear track detectors were used to measure both the primary proton spectrum and the fusion products. From the primary proton spectrum, we calculated (p, n) and (α,n) reactions in the catcher and compare with our measurements. The nuclear activation results agree quantitatively and neutron signals agree qualitatively with the calculations, giving confidence that primary particle distributions can be obtained from such measurements. These results provide new insights for measuring the ion distributions inside of proton-boron fusion targets.
Broad bandwidth high reflection coatings for petawatt class lasers: Femtosecond pulse laser damage tests and measurement of group delay dispersion.
Abstract not provided.
Broad bandwidth high reflection coatings for petawatt class lasers: Femtosecond pulse laser damage tests and measurement of group delay dispersion.
Abstract not provided.