Laser Experiments Research Articles

Advances in Design and Fabrication of Micro-Structured Solid Targets for High-Power Laser-Matter Interaction

Accelerated particles have multiple applications in materials research, medicine, and the space industry. In contrast to classical particle accelerators, laser-driven acceleration at intensities greater than 1018 W/cm2, currently achieved at TW and PW laser facilities, allow for much larger electric field gradients at the laser focus point, several orders of magnitude higher than those found in conventional kilometer-sized accelerators. It has been demonstrated that target design becomes an important factor to consider in ultra-intense laser experiments. The energetic and spatial distribution of the accelerated particles strongly depends on the target configuration. Therefore, target engineering is one of the key approaches to optimizing energy transfer from the laser to the accelerated particles. This paper provides an overview of recent progress in 2D and 3D micro-structured solid targets, with an emphasis on fabrication procedures based on laser material processing. Recently, 3D laser lithography, which involves Two-Photon Absorption (TPA) effects in photopolymers, has been proposed as a technique for the high-resolution fabrication of 3D micro-structured targets. Additionally, laser surface nano-patterning followed by the replication of the patterns through molding, has been proposed and could become a cost-effective and reliable solution for intense laser experiments at high repetition rates. Recent works on numerical simulations have also been presented. Using particle-in-cell (PIC) simulation software, the importance of structured micro-target design in the energy absorption process of intense laser pulses—producing localized extreme temperatures and pressures—was demonstrated. Besides PIC simulations, the Finite-Difference Time-Domain (FDTD) numerical method offers the possibility to generate the specific data necessary for defining solid target material properties and designing their optical geometries with high accuracy. The prospects for the design and technological fabrication of 3D targets for ultra-intense laser facilities are also highlighted.

Numerical optimization of quantum vacuum signals

The identification of prospective scenarios for observing quantum vacuum signals in high-intensity laser experiments requires both accurate theoretical predictions and the exploration of high-dimensional parameter spaces. Numerical simulations address the first requirement, while optimization provides an efficient solution for the second one. In the present work, we put forward Bayesian optimization as a new and powerful means to optimize photonic quantum vacuum signals. We demonstrate its great potential on the example of the well-studied case of two-beam collisions. Apart from providing an ideal benchmark case, this immediately gives new physics results. Namely, Bayesian optimization allows us to find the optimal waist sizes for beams with elliptic cross sections, and to identify the specific physical process leading to a discernible signal in a coherent harmonic focusing configuration scenario. Published by the American Physical Society 2024

Solar Opacity Calculations: Recent Theoretical Advances Prompted by Laser and Z-Pinch Experiments

Solar Opacity Calculations: Recent Theoretical Advances Prompted by Laser and Z-Pinch Experiments

Total Ionizing Dose and Single-Event Effect Response of the AD524CDZ Instrumentation Amplifier

This manuscript focuses on studying the radiation response of the Commercial-off-the-shelf (COTS) AD524CDZ operational amplifier. Total Ionizing Dose (TID) effects were tested using low-dose 60Co irradiation. Single-Event Effect (SEE) sensitivity was studied on this operational amplifier using a 105 MeV proton beam. Additionally, further study of the SEE response was carried out using a Two-photon absorption laser to scan some sensitive sectors of the die. For this laser experiment, different gain setups and laser energies were employed to determine how the Single Event Transient (SET) response of the device was affected based on the test configuration. The results from the TID experiments revealed that the studied device remained functional after 100 krads (Si). Proton experiments revealed the studied device exhibited a high SET response with a maximum DC offset SET of about 1.5 V. Laser experiments demonstrated that there was a clear SET reduction when using 10× and 1000× gain setups.

Measurement bias in self-heating x-ray free electron laser experiments from diffraction studies of phase transformation in titanium

X-ray self-heating is a common by-product of X-ray Free Electron Laser (XFEL) techniques that can affect targets, optics, and other irradiated materials. Diagnosis of heating and induced changes in samples may be performed using the x-ray beam itself as a probe. However, the relationship between conditions created by and inferred from x-ray irradiation is unclear and may be highly dependent on the material system under consideration. Here, we report on a simple case study of a titanium foil irradiated, heated, and probed by a MHz XFEL pulse train at 18.1 keV delivered by the European XFEL using measured x-ray diffraction to determine temperature and finite element analysis to interpret the experimental data. We find a complex relationship between apparent temperatures and sample temperature distributions that must be accounted for to adequately interpret the data, including beam averaging effects, multivalued temperatures due to sample phase transitions, and jumps and gaps in the observable temperature near phase transformations. The results have implications for studies employing x-ray probing of systems with large temperature gradients, particularly where these gradients are produced by the beam itself. Finally, this study shows the potential complexity of studying nonlinear sample behavior, such as phase transformations, where biasing effects of temperature gradients can become paramount, precluding clear observation of true transformation conditions.

The ablation behavior of diamond/Cu composites by infrared nanosecond pulsed laser

This paper investigates the material removal behavior of diamond/Cu composites by multi-passes infrared nanosecond pulsed laser ablation, focusing on the formed surface cracks, periodic ripples, profile evolution and deposition. Combining nanosecond laser ablation experiments with simulations based on thermophysical properties is then undertaken to effectively reduce the maximum thermal stress and inhibit crack initiation and propagation. Three types of cracks were identified in nanosecond laser ablation, which were influenced by the diverse thermophysical properties of the material and the temperature gradient. The periodic ripples of 300–1800 nm on the sidewalls of the machined groove on diamond grains were induced when the laser fluence approached the ablation threshold, which did not even appear on the copper matrix as the thermal effects dominate. The groove profile showed a limited change as the ablation passes further increase to be over 40 due to the plasma shielding effect inside the groove, the laser defocusing phenomenon and the increased difficulty of sputtering the molten material. In addition, the different ablation mechanisms of diamond and copper resulted in the formation of overlapping deposition layers with changed surface characteristics at varying laser energy densities. The uneven island-like recast layer affected the uniformity of the ablated grooves, which was dependent on the material microstructure and accumulated laser energy.

Time resolved x-ray diffraction using the flexible imaging diffraction diagnostic for laser experiments (FIDDLE) at the National Ignition Facility (NIF): Preliminary assessment of diffraction precision.

The Flexible Imaging Diffraction Diagnostic for Laser Experiments (FIDDLE) is a new diagnostic at the National Ignition Facility (NIF) designed to observe in situ solid-solid phase changes at high pressures using time resolved x-ray diffraction. FIDDLE currently incorporates five Icarus ultrafast x-ray imager sensors that take 2ns snapshots and can be tuned to collect X-rays for tens of ns. The platform utilizes the laser power at NIF for both the laser drive and the generation of 10keV X-rays for ∼10ns using a Ge backlighter foil. We aim to use FIDDLE to observe diffraction at different times during compression to probe the kinetics of phase changes. Pb undergoes two solid-solid phase transitions during ramp compression: from face centered cubic (FCC) to hexagonal close packed (HCP) and HCP to body centered cubic (BCC). Results will be reported on some of the first shots using the FIDDLE diagnostic at NIF on ramp compressed Pb to a peak pressure of ∼110GPa and a single undriven CeO2 calibration shot. A discussion of the uncertainties in the observed diffraction is included.

Developing time-resolved x-ray diffraction diagnostics at the National Ignition Facility (invited).

As part of a program to measure phase transition timescales in materials under dynamic compression, we have designed new x-ray imaging diagnostics to record multiple x-ray diffraction measurements during a single laser-driven experiment. Our design places several ns-gated hybrid CMOS (hCMOS) sensors within a few cm of a laser-driven target. The sensors must be protected from an extremely harsh environment, including debris, electromagnetic pulses, and unconverted laser light. Another key challenge is reducing the x-ray background relative to the faint diffraction signal. Building on the success of our predecessor (Target Diffraction In Situ), we implemented a staged approach to platform development. First, we built a demonstration diagnostic (Gated Diffraction Development Diagnostic) with two hCMOS sensors to confirm we could adequately protect them from the harsh environment and also acquire acceptable diffraction data. This allowed the team to quickly assess the risks and address the most significant challenges. We also collected scientifically useful data during development. Leveraging what we learned, we recently developed a much more ambitious instrument (Flexible Imaging Diffraction Diagnostic for Laser Experiments) that can field up to eight hCMOS sensors in a flexible geometry and participate in back-to-back shots at the National Ignition Facility (NIF). The design also allows for future iterations, such as faster hCMOS sensors and an embedded x-ray streak camera. The enhanced capabilities of the new instrument required a much more complex design, and the unexpected issues encountered on the first few shots at NIF remind us that complexity has consequences. Our progress in addressing these challenges is described herein, as is our current focus on improving data quality by reducing x-ray background and quantifying the uncertainties of our diffraction measurements.

Microstructure and corrosion resistance of novel rare-earth-zirconia doped Y2O3 plasma-sprayed coating

Y2O3 coatings are widely applied in semiconductor etching machines to protect the inner walls of aluminum alloys. This study reports the preparation of yttria-based coatings on aluminum alloy substrates using atmospheric laminar plasma spraying (ALPS) methods. In this study, four yttria-based coatings were designed and tested for their thermal performance, plasma etching resistance, and resistance to laser ablation. The rare-earth-zirconia (RE-ZrO2) doped Y2O3 coating exhibited the best thermal insulation performance, with a thermal conductivity of approximately 0.6 W m−1 k−1 at 600 °C. Plasma etching experiments demonstrated that more rare-earth fluorides were generated on the surface of the RE-ZrO2 doped Y2O3 coating, which weakened the plasma energy. Finally, the lowest etching rate was achieved. Laser ablation experiments demonstrated that the depth of the ablation pit on the surface of the RE-ZrO2 doped Y2O3 coating was shallow, indicating good laser ablation resistance. These results indicate that rare-earth-doped yttria-based coatings provide excellent corrosion protection against plasma etching and laser ablation.

Numerical simulation and experiments of nano-second pulsed laser cleaning titanium alloy oxide film

Numerical simulation and experiments of nano-second pulsed laser cleaning titanium alloy oxide film

Machining damage in the fabrication of polycrystalline diamond micro end mill with laser and grinding combined processing method

The high hardness and wear resistance of polycrystalline diamond (PCD) micro tool make it widely used in precision machining of small parts of difficult-to-machine materials. The laser and grinding combined machining is an effective method to fabricate PCD micro tools, but the machining damage is difficult to control, which will reduce the cutting performance and tool life. Therefore, this paper aims to deeply study the damage forms and damage formation mechanisms during the fabrication process of PCD micro end mills, so as to improve the quality of the PCD micro mills. The laser and grinding combined machining experiments of PCD micro end mill are carried out, and the surface morphology characteristics and cutting edge of the mill are observed and analyzed. The influence of process parameters on the fabrication quality of PCD micro mill is investigated. The experimental results show that the high temperature of the laser is the main factor causing damage, which causes the melting and oxidation of the surface material, and further forms micro cracks, pits and oxidized attachments on the PCD mill. In addition, diamond phase transformation and excessive removal of cobalt-rich layer will also lead to graphitization and micro-grooves on the mill surface. For the grinding process, the cutting edge is fractured by the impact of the wheel, resulting in micro notches, micro pits and micro cracks. The intergranular crack expansion of PCD material and cleavage breakage of diamond particles are the main causes of micro cracks and micro pits on the mill surface. In addition, the chips will also scratch the tool surface to produce micro nicks and cause the chips coating on the rake face. The research results are helpful to further understand the damage mechanism of laser and grinding combined machining PCD mill, so as to improve the fabrication quality of micro tools.

Additively manufactured conformal cooling channels through topology optimization

Cooling channels play a critical role in various casting and molding processes, impacting both the cycle time and quality of the product. As additive manufacturing technologies become increasingly prevalent, conventional straight-drilled channels are being progressively substituted by intricate cooling lines that conform to the contours of the fabricated part. This transition can lead to a significant reduction of the solidification time and temperature gradients, consequently lowering the occurrence of part defects. However, designing such channels becomes challenging as geometric complexity and manufacturing constraints increase. In this work, we present a density-based topology optimization approach to generate conformal cooling channels in molds and dies inserts. To mitigate temperature variations, the objective function is penalized using the temperature standard deviation of the insert cavity surface. A density-gradient-based constraint is further utilized to reduce the generation of overhanging structures and promote manufacturability. In particular, the use of this constraint leads to the generation of channels characterized by a teardrop-shaped cross section. The cooling efficiency of a selected optimized design is confirmed through computations using a body-fitted solver. The geometry is subsequently manufactured by Laser Powder Bed Fusion (LPBF) and experiments are conducted to compare its performance in comparison to a design featuring straight-drilled channels. The results demonstrate that the optimized geometry significantly enhances the heat extraction rate and further leads to a 43% reduction of the cavity temperature standard deviation.

High-temperature multi-vacancy mediated diffusion of nitrogen in diamond: MD simulations and mid-IR laser experiments

Utilizing classical molecular dynamics with the precise machine-learning interatomic potential MTP, we investigated the high-temperature (3000–3500 K) dynamics of NV and N2V centers in the presence of additional free vacancies. We propose a novel mechanism for nitrogen diffusion in diamond, which involves the intermediate step of additional vacancies being absorbed by a NV center. The simulation results align with the experimentally observed transformations of NV centers into H1b and H1c in IaAB-diamond under 4.7-μm femtosecond-laser irradiation.

Baseline design of laser fusion research reactor with MW class laser facility

We propose a sub-ignition/burning reactor which is named the Laser-fusion Subcritical Power Reactor Engineering Method (L-Supreme). The reliabilities of L-Supreme in a MW class laser facility are assessed with respect to the following points: a reactor core, a target chamber, a target delivery system, an Exhaust Detritiation System (EDS), and neutron shielding. The Japan Establishment for Power-laser Community Harvest (J-EPoCH) would be applied as a MW class laser facility. A non-cryogenic glass balloon target filled with gaseous deuterium-tritium (DT) is contained in a target capsule. A chain-type magazine system might be used for a mass supply of the target capsules. Each target capsule is delivered to the center of a reactor core at 1 Hz. A batch of 10 000 laser shots would realize 0.22 MJ fusion power. The amount of tritium per batch is 1.51 × 1012 Bq. During laser experiments, unburned tritium is evacuated and transferred into an Exhaust Detritiation System (EDS). An evacuation rate of more than 0.1 m3 s−1 is required in order to recover less than 5000 Bq m−3 of the threshold of tritium concentration within 1 h. For safety, emergency situations such as tritium leakage in facilities are examined. The EDS works by internal circulation processes. Assuming leakage of tritium for a batch, an air circulation flow rate of 4100 Nm3 h−1 is required in an experimental hall for recovering less than 5000 Bq m−3 within 48 h. A primary and secondary neutron shield concept are proposed and would provide full neutron shielding. We conclude that it is possible to construct the L-Supreme system by marshalling current technologies.

Electrical design of the flexible imaging diffraction diagnostic for laser experiments (FIDDLE) at the National Ignition Facility (NIF)-Requirements, design, and performance.

The Flexible Imaging Diffraction Diagnostic for Laser Experiments (FIDDLE) is a newly developed diagnostic for imaging time resolved diffraction in experiments at the National Ignition Facility (NIF). It builds on the successes of its predecessor, the Gated Diffraction Development Diagnostic (G3D). The FIDDLE was designed to support eight Daedalus version 2 sensors (six more hCMOS sensors than any other hCMOS-based diagnostic in NIF to date) and an integrated streak camera. We will review the electrical requirements, design, and performance of the electrical subsystems that were created to support this large number of cameras in the FIDDLE. The analysis of the data that the FIDDLE is intended to collect relies heavily on the accurate and well-understood timing of each sensor. We report camera-to-camera timing jitter of less than 100ps rms and sensor integration times of 2.2ns FWHM in 2-2 timing mode. Additionally, diffraction experiments on the NIF produce electric fields (EMI) on the order of 1 kV/m, which have been observed to negatively impact the performance of some electrical components of the FIDDLE. We report on the results of testing hCMOS camera electronics in a similar EMI environment generated in an offline lab. We also summarize the use of a novel approach to using a vector network analyzer as an EMI leak detector to understand and reduce the negative impacts of EMI on the FIDDLE.

Investigation of laser-material interaction in picosecond single-point laser ablation of bronze

Comprehending the laser ablation mechanism is fundamental in determining how diverse laser parameters affect the quality of the ablation process. A finite difference model was developed in this study to investigate the ablation depth and temperature distribution in picosecond ablation process. The investigation involved conducting single-point laser experiments on bronze material using an ultrashort pulse laser with a pulse duration of 12 ps. The experiments were carried out with varying numbers of pulses, ranging from 1 to 80 pulses. The calculated depths of ablations were compared with experimental results. The variation of the ablation mechanism on the workpiece's surface during laser radiation was also investigated. The model established the laser-material interaction mechanisms under different incident pulses. The ionization temperature and ablated material temperature during laser processing are also determined. The results show that for the number of pulses higher than 10, the laser-material interaction changes from Multi-Photon Ionization to ablation, while in lower numbers, there are no effects of thermal damages adjacent to the laser points. The relationship between variations in the ablation depth and changes in the incidence angle was also investigated. As the incidence angle increases, the removal mechanism changes from MPI to the thermal.

Photochemical Action Plots Map Orthogonal Reactivity in Photochemical Release Systems.

The wavelength-by-wavelength resolved photoreactivity of two photo-caged carboxylic acids, i. e. 7-(diethylamino)-coumarin- and 3-perylene-modified substrates, is investigated via photochemical action plots. The observed wavelength-dependent reactivity of the chromophores is contrasted with their absorption profile. The photochemical action plots reveal a remarkable mismatch between the maximum reactivity and the absorbance. Through the action plot data, the study is able to uncover photochemical reactivity maxima at longer and shorter wavelengths, where the molar absorptivity of the chromophores is strongly reduced. Finally, the laser experiments are translated to light emitting diode (LED)irradiation and show efficient visible-light-induced release in a near fully wavelength-orthogonal, sequence-independent fashion (λLED1=405nm, λLED2=505nm) with both chromophores in the same reaction solution. The herein pioneered wavelength orthogonal release systems open an avenue for releasing two different molecular cargos with visible light in a fully orthogonal fashion.

Isofield plasma expansion in kJ petawatt laser-driven ion acceleration with a tailored fast electron temperature

Kilojoule-class relativistic intensity lasers, having multi-picosecond (ps) pulse durations, enable efficient ion acceleration in the interaction with thin foil targets. The foil plasma expands under the laser energy input over picoseconds where fast electrons keep increasing their effective temperature, while they convert a part of the energy into fast ions through generation of a sheath electric field. The temporal evolution of the sheath electric field is the key to understanding the efficient ion acceleration seen in kJ-class laser experiments. Here, we extend the non-isothermal plasma expansion model by introducing a temporal function of the effective temperature of fast electrons to obtain the sheath electric field in the expanding plasma. We theoretically derived that when the effective temperature of fast electrons increases in proportional to the square of the time, the strength of the sheath electric field is kept constant without depletion during the expansion. This ‘isofield’ expansion is confirmed by a quasi-one-dimensional particle-in-cell simulation. The isofield expansion results in a high energy ion acceleration with a small expansion length, which is favorable for realizing an efficient ion acceleration with less lateral energy loss in multi-dimensional situations.

Saturation Level of Ion Weibel Instability and Isotropization Length Scale in Electron-Ion Weibel-Mediated Shocks

Abstract Ion Weibel instability is considered to be the dominant physics for the dissipation in high-Mach number astrophysical shocks such as supernova remnant shocks and gamma-ray burst shocks. We study the instability dependence on various parameters using theory and particle-in-cell simulations. We demonstrate that electron physics determines the saturation level of the Weibel-generated magnetic field, even though the instability is driven by the ions. We discuss the application to astrophysical and laboratory laser experiment environments to clarify the roles of the ion Weibel instability. We develop a model for the isotropization length scale in Weibel-mediated shocks and compare its value to other characteristic length scales of each system. We find that electron heating to near equipartition is crucial for the formation of ultra-relativistic Weibel-mediated shocks. On the other hand, our results imply that non-relativistic shocks in typical interstellar medium are not purely mediated by the Weibel instability.

Acceleration of flow-focused liquid jets in the presence of a strong electric field

This paper investigates the acceleration of flow-focused micro-jets under an applied external electric field. Such thin and fast jets are needed, for example, to deliver protein crystals in X-ray free electron laser experiments. This contribution focuses on analysing the acceleration of liquid jets produced from 50 % vol water and ethanol mixture. Such jets are focused with nitrogen gas and are subjected to 0 - 7 kV electric potential between a submerged electrode and an external electrode downstream of the nozzle. To gain insights into jet geometric properties an automatic image recognition and computer vision algorithm is utilised on already published data. Jet velocities and acceleration calculated for two jetting regimes show that application of external electric field accelerates the jets up to four orders of magnitude larger than the conventional micro-jets.