In the field of optical measurement, the inherent edge spectral leakage problem of the Fourier method significantly affects the accuracy of phase extraction. For the velocity measurement scenarios of inertial confinement fusion (ICF) research using a one-dimensional velocity interferometer system for any reflector (VISAR), this issue further undermines the reliability of velocity field calculations. To address this, a data processing method for VISAR image based on four-phase shifting and probability density function (PDF) compensation is proposed in this paper. This method first performs spatial phase-shifting on a single frame original VISAR image to obtain four phase-shifted images with successive phase differences ofπ/2. To compensate for phase-shifting errors introduced during the experimental measurement and phase-shifting process, the standard deviation of the PDF curve is taken as the objective function. An iterative compensation algorithm is employed to adjust the PDF of the wrapped phase to approximate the ideal distribution, thereby determining the compensation amount for phase-shifting errors. Subsequently, the least-squares method is applied to calculate the wrapped phase. Finally, the wrapped phase is unwrapped to obtain the phase distribution of the VISAR image, enabling velocity calculation. The verification results indicate that our method demonstrates robust performance across ideal simulated image, noisy synthetic image, and experimental VISAR image, which is superior to the Fourier method in suppressing edge spectral leakage, providing more reliable data for ICF diagnosis.

This paper proposes a new method for measuring film thickness that combines frequency-domain white-light interference and reflection spectroscopy.In addition to the film to be measured,this method considers air as a medium layer to construct a multilayer-film-structure model.The nonlinear phase is reconstructed using white-light frequency-domain interference fringes generated by the reflection of the multilayer film structure,and the film thickness is obtained via fitting.To solve the local optimal solution problem that occurs during fitting,the thickness obtained via reflection spectroscopy is used to limit the fitting range.In this study,theoretical derivation and numerical simulation are performed to examine the process of measuring the thickness of the film to be measured using a multilayer-film-structure model.Subsequently,a fiber-optic measuring system is constructed to verify the feasibility of this method by experimentally measuring the thickness of a single-layer silica film.

Diamond is a highly suitable material for X-ray detectors that can function effectively in harsh environments due to its unique properties, such as an ultrawide bandgap, high resistance to radiation, excellent carrier mobility, and remarkable chemical and thermal stability. However, the sensitivity of diamond X-ray detectors needs further improvement due to the relatively low X-ray absorption efficiency of diamond, and the exploration of single-crystal diamond array imaging remains unexplored. Herein, a 10×10 X-ray photodetector array was constructed from single-crystal diamond. To improve the sensitivity of the diamond X-ray detector, an asymmetric sandwich electrode structure was utilized. Additionally, trenches are created through laser cutting to prevent crosstalk between adjacent pixels. The diamond X-ray detector array shows exceptional performance, including a low detection limit of 4.9 nGy s-1, a sensitivity of 14.3 mC Gy-1 cm-2, and a light-dark current ratio of 18312, which are among the most favorable values ever reported for diamond X-ray detectors. Furthermore, these diamond X-ray detectors can operate at high temperatures up to 450 °C, making them suitable for development in harsh environments.

The phenomenon of mass ejection from shocked surface is a crucial issue in high-energy density physics and shock compression science. Ejecta from double-shock loaded metallic targets is important in some practical applications, but there are only a few research types on this aspect due to experimental difficulty. We proposed a new method of double-shock loading based on intense laser, that is, the laser is injected into a vacuum hohlraum to generate strong radiation and plasma jet simultaneously, and the target are respectively subjected to two shocks by these two different mechanisms. In the experiment, double-shock process was clearly observed by photonic Doppler velocimetry system, and the recompression of target due to the second shock was presented by x-ray photography. After the free surface was broken, the ejecta showed a unique multi-layer density structure for the first time. This work achieves effective double-shock loading with only one single laser pulse, which is valuable for understanding the metal damage under multiple shocks and the evolution of ejected materials. It also provides an experimental design for studying the material response in complex environments.

Giant electromagnetic pulses (EMPs) induced by high-power laser irradiating solid targets interfere with various experimental diagnoses and even damage equipment, so unveiling the evolution of EMPs inside the laser chamber is crucial for designing effective EMP shielding. In this work, the transmission characteristics of EMPs as a function of distances from the target chamber center (TCC) are studied using B-dot probes. The mean EMP amplitude generated by picosecond laser-target interaction reaches 561 kV m-1, 357 kV m-1, 395 kV m-1, and 341 kV m-1 at 0.32 m, 0.53 m, 0.76 m, and 1 m from TCC, which decreases dramatically from 0.32 m to 0.53 m. However, it shows a fluctuation from 0.53 m to 1 m. The temporal features of EMPs indicate that time-domain EMP signals near the target chamber wall have a wider full width at half maximum compared to that close to TCC, mainly due to the echo oscillation of electromagnetic waves inside the target chamber based on simulation and experimentation. The conclusions of this study will provide a new approach to mitigate strong electromagnetic pulses by decreasing the echo oscillation of electromagnetic waves inside the target chamber during laser coupling with targets.

To find a way to control the electron-bunching process and the bunch-emitting directions when an ultraintense, linearly polarized laser pulse interacts with a nanoscale target, we explored the mechanisms for the periodical generation of relativistic attosecond electron bunches. By comparing the simulation results of three different target geometries, the results show that for nanofoil target, limiting the transverse target size to a small value and increasing the longitudinal size to a certain extent is an effective way to improve the total electron quantity in a single bunch. Then the subfemtosecond electronic dynamics when an ultrashort ultraintense laser grazing propagates along a nanofoil target was analyzed through particle-in-cell simulations and semiclassical analyses, which shows the detailed dynamics of the electron acceleration, radiation, and bunching process in the laser field. The analyses also show that the charge separation field produced by the ions plays a key role in the generation of electron bunches, which can be used to control the quantity of the corresponding attosecond radiation bunches by adjusting the length of the nanofoil target.

The axiparabola is a novel reflective element proposed in recent years, which can generate a long focal line with high peak intensity, and has important applications in laser plasma accelerators. The off-axis design of an axiparabola has the advantage of separating the focus from incident rays. However, an off-axis axiparabola designed by the current method always produces a curved focal line. In this paper, we propose a new method to design its surface by combining geometric optics design and diffraction optics correction, which can effectively convert a curved focal line into a straight foal line. We reveal that the geometric optics design inevitably introduces an inclined wavefront, which leads to the bending of the focal line. To compensate for the tilt wavefront, we use an annealing algorithm to further correct the surface through diffraction integral operation. We also carry out numerical simulation verification based on scalar diffraction theory, which proves that the surface of this off-axis mirror designed by this method can always obtain a straight focal line. This new method has wide applicability in an axiparabola with any off-axis angle.

Objective Terahertz (THz) waves offer a distinctive diagnostic method for detecting high energy density matter. However, realizing the THz time-domain spectral (THz-TDS) diagnosis of matter states under extreme conditions in large high-energy density devices remains a significant obstacle. To address this requirement, we designed and implemented an optical pump-THz single-shot detection system driven by a strong femtosecond laser. The system possesses the capability of THz single-shot detection under extreme conditions and diagnosis of irreversible processes with extreme transience using THz-TDS diagnosis under intense laser pumping. Methods We developed an integrated optically pumped terahertz (THz) single-shot detection system that utilizes a 45 TW Ti: sapphire femtosecond laser with a pulse width of 30 fs, central wavelength of 800 nm, and spot diameter of approximately 38 mm. The laser pulses were initially directed to realize second harmonic generation (SHG) via KDP crystals and then separated into fundamental and SHG using a dichroic mirror (DM). The SHG was reflected into the pump time-delay line (TD2) and focused by a lens to ensure complete pumping of the target object with a focus size of approximately 2 mm in diameter consistent with the THz focus size. Meanwhile, the fundamental frequency laser transmitted by the DM was divided by the beam splitting mirror (BS) with 90% of the energy used as the driving laser of the lithium niobate wafer. An intense THz pulse was generated by collinear optical rectification effect, and an off-axis parabolic mirror (OAP) was utilized to focus it onto the target object. The THz pulses transmitted through the target object were focused by the OAP and reflected by indium tin oxide (ITO) to reach the surface of the ZnTe crystal. Moreover, 10% of the transmitted energy of the THz probe laser was directed into the time-delay line (TD1) incident with the surface normal of the reflective echelon at 14 degrees and encoded time information into a one-dimensional space. The outgoing laser was spatiotemporal coincident with the THz on the surface of the ZnTe crystal. Finally, the orthogonal detection scheme was utilized to probe the THz waveform. Results and Discussions We present the design and implementation of an intense-field optical pump-THz time-domain spectroscopy single-shot detection system for measuring the irreversible non-equilibrium transient processes in high-energy and low-repetition-rate pumps of large laser devices. The system employs a reflective echelon and orthogonal detection scheme to detect pulses generated through the collinear optical rectification of a lithium niobate wafer with a diameter of 3 inch. The system consists of a THz generation-intense laser pumping module and a THz time-domain spectral single-shot detection module integrated into separate optical breadboards. The former can be placed in a vacuum chamber, and the latter in an atmospheric environment, making it easy to move and install and suitable for different laser-device application scenarios. The THz pulses have an energy of 7 mu J at 800 nm 1 J laser energy, can be easily adjusted, and have a detection capability of a 30 nm free-standing gold foils transmission spectrum at room temperature. We verify that the waveform obtained by the single-shot detection is the same as that obtained by traditional scanning. Based on this device, the variation of conductivity in the THz band of 30 nm free-standing gold foils with pumping delay measured under the 0.8 MJ/kg laser energy density of a 400 nm pump contributes to the further understanding of the generation and evolution of the warm dense state of gold. Conclusions With the advent of intense femtosecond lasers, it has become possible to investigate the state of matter in extreme conditions. The maturation of THz time-domain spectroscopy technology also provides a new tool for diagnosing extreme non-equilibrium states. To meet the demands of THz emission and state diagnosis under such extreme conditions, an intense-field optical pump-THz time-domain spectroscopy single-shot detection system with a simple THz path was designed and fabricated. The system was employed to measure the transient THz conductivity of 30 nm thick free-standing gold foils pumped by a 400 nm laser pulse. The obtained results serve as a potent platform for further exploration of irreversible processes including extreme condition THz emission-detection and the diagnosis of non-equilibrium states of matter under extreme conditions.

The long-focal-depth mirror is a novel reflective element proposed in recent years. Due to the advantages of negligible dependence on wavelength and high damage threshold, it is suitable to focus ultra-short laser pulses with broadband spectra and high intensity with a focal depth of centimeter scale. To the best of our knowledge, the focusing properties of this mirror has been only studied under low numerical aperture (NA). In this paper, we extend it to the case of high NA and it is proved that an accelerating superluminal laser focus can be always generated by this extension, in which the degree of acceleration increases with the increase of NA. And the velocity of laser focus increases approximately linearly from c to 1.6c for NA=0.707. Due to its properties of tight focusing, the Richards-Wolf integrals have been used to study the intensity distribution of each polarization component for different kinds of incident light. And these are linearly polarized light, radially polarized light, azimuthally polarized light, linearly polarized light with spiral phase, and linearly polarized light with ultrashort pulses. From comparisons of numerical results, the intensity distributions are obviously different for different kind of incident light, and accelerating superluminal laser focus with special structure (such as the hollow conical beam) can be produced under appropriate condition. We believe this study can expand the fields of application for the long-focal-depth mirror.

X-ray detectors have numerous applications in medical imaging, industrial inspection, and crystal structure analysis. Gallium oxide (Ga2O3) shows potential as a material for high-performance X-ray detectors due to its wide bandgap, relatively high mass attenuation coefficient, and resistance to radiation damage. In this study, we present Sn-doped Ga2O3 microwire detectors for solar-blind and X-ray detection. The developed detectors exhibit a switching ratio of 1.66 × 102 under X-ray irradiation and can operate stably from room temperature to 623 K, which is one of the highest reported operating temperatures for Ga2O3 X-ray detectors to date. These findings offer a promising new direction for the design of Ga2O3-based X-ray detectors.

Luminescent solar concentrators (LSCs) are attractive for the easy operation and high compatibility with building integrated photovoltaics due to their low cost, large-scale and applicability. However, underutilized sunlight in visible wavelengths often impedes the advance of LSCs. Here, we demonstrate an orange-emitting carbon nanodots-based LSC (O-CDs) with excitation concentrated in the visible wavelengths. The orange-emitting carbon nanodots (O-CDs) with highly localized excitonic emission are prepared via atomic condensation of doped pyrrolic nitrogen, delivering a high photoluminescence quantum yield of 80 % and a suitable Stokes shift with absorption spectrum situated in the visible region. The O-CDs are embedded in polyvinylpyrrolidone to obtain a highly transparent, stable and environmentally friendly O-CDs-based LSC. Thanks to efficient utilization of solar radiation in visible areas and well match between the emission of O-CDs and the response bands of photovoltaic cells, the O-CDs-based LSC reveals an optical conversion efficiency of 5.17 %, superior to that of most carbon nanodots-based LSCs. These results provide an effective strategy to develop carbon-based luminescent concentrated materials for architectural integrated photovoltaic technology.

AbstractPhotodetectors play a crucial role in converting light signals into electrical signals and have significant applications in various fields such as communications, imaging, and sensing. However, the fabrication of a photodetector is a complex process that involves precise control of surface preparation, lithography, and deposition techniques. Here the study demonstrates that GaN/Ga2O3 heterojunctions can be fabricated utilizing laser processing to transform the surface of GaN into Ga2O3. The GaN/Ga2O3 heterojunctions exhibit good reproducibility, uniformity, and ability to operate under zero bias, with a responsivity of 110.22 mA W−1, a detection rate of 5.56 × 1011 jones, and an external quantum efficiency of 42.34%. Moreover, an 8 × 8 photodetector array based on GaN/Ga2O3 heterojunction is fabricated via laser writing and is demonstrated to have ultraviolet imaging capabilities. This report presents the pioneering fabrication of a photodetector array using laser writing. The findings offer a versatile and scalable approach for the production of large‐area heterojunction photodetector arrays.

In order to establish a compact all-optical Thomson scattering source, experimental studies were conducted on the 45 TW Ti: sapphire laser facility. By including a steel wafer, mixed gas, and plasma mirror into a double-exit jet, several mechanisms, such as shock-assisted ionization injection, ionization injection, and driving laser reflection, were integrated into one source. So, the source of complexity was remarkably reduced. Electron bunches with central energy fluctuating from 90 to 160 MeV can be produced. Plasma mirrors were used to reflect the driving laser. The scattering of the reflected laser on the electron bunches led to the generation of X-ray photons. Through comparing the X-ray spots under different experimental conditions, it is confirmed that the X-ray photons are generated by Thomson scattering. For further application, the energy spectra and source size of the Thomson scattering source were measured. The unfolded spectrum contains a large amount of low-energy photons besides a peak near 67 keV. Through importing the electron energy spectrum into the Monte Carlo simulation code, the different contributions of the photons with small and large emitting angles can be used to explain the origin of the unfolded spectrum. The maximum photon energy extended to about 500 keV. The total photon production was 10 7 /pulse. The FWHM source size was about 12 μ m.

Laser-driven flyer has been studied for decades as it promises to possess many applications such as in measuring the equation of state (EOS) under ultrahigh pressure, investigating the material dynamic properties under high strain rate, simulating the high-speed impact for aircraft protection, and igniting explosives. However, the planarity and integrity of flyers are determined by indirect velocity lnterferometer system for any reflector (VISAR) or witness slab results due to its high speed and small dimension. For further and wide applications, it is very important to obtain direct experimental proof of the flyer gesture and configuration. Thus, the acceleration and gesture investigation of aluminum flyer driven by laser plasma are studied on Xingguang-III laser facility. The X-ray radiography is achieved by a picosecond laser irradiating the copper wire target. The shadowgraph of flyer and plasma are realized by the incidence of a bunch of infrared laser through the flyer flight path. In additon, photon Doppler velocimetry is employed to measure the flyer velocity simultaneously. The radiography, shadowgraph and velocity of typical small aluminum flyer are obtained. By optimizing the thickness of both CH ablation layer and vacuum gap, the flyer is slowly accelerated via consecutive stress wave produced by plasma colliding. The aluminum flyer has a thickness of 20 μm and diameter of about 500 μm. The whole flyer remains the integrated shape after a great angle of rotation due to uneven plasma loading. The flight distance is about 400 μm, giving an average velocity of 2.2 km/s. The planarity of the flyer is good except a little bend on the two sides due to side rarefaction of plasma. The study verifies that the laser plasma collision can generate a sub-millimeter-diameter metal flyer with integrated shape and a velocity of several kilo-meters per second, showing that it possesses the promising applications in measuring the EOS and igniting explosive .

The metal–nonmetal transition is of fundamental interest in contemporary physics. We present a combination of the optical reflectivity measurement of an expanded gold fluid produced by gold L-band x-rays from a Hohlraum and the corresponding ab initio calculations to study the metal–nonmetal transition. The averaged density and temperature of the reflective layer are derived from 1D radiation hydrodynamic simulations constrained by matching the expansion velocity obtained from the fringe shift. A sharp change in time-resolved reflectivity occurs at one third of the initial density, near where the metal–nonmetal transition is predicted to occur. The reflectivity calculated based on the Helmholtz equations with the dielectric function from the density functional theory calculations is compared with the experimental measurement. Disagreement of reflectivity between calculation and measurement probably originates from the energy shift of the dielectric function due to the inaccurate Kohn–Sham eigenvalue. More accurate methods on calculating the dielectric function are still needed to improve the calculated reflectivity.

High intensity laser is an efficient method for shock generator to study the dynamic fragmentation of materials, in which the direct drive is widely utilized. The continuum phase plate is used for smoothing the focal spot of the laser, but the loading region is usually smaller than the designed value. In this work, we study an experimental technique for investigating the dynamic fragmentation of metal via indirectly driving a high-intensity laser. Firstly, the radiation distributions on the sample for four different hohlraums each with a diameter of 2 mm but different length are simulated via the IRAD software, in which the proper hohlraum with a diameter of 2 mm and a height of 2 mm is selected for the experiments. Secondly, the peak temperatures and radiation waves under different laser energy and pulse durations are measured. The peak temperature decreases simultaneously as the laser energy decreases. In addition, the loading shock waves under a peak temperature of 140 eV and different radiation waves are estimated via the hydrodynamic simulation. It is revealed that a peak pressure of several tens of gigapascals is acquired and the peak pressure is greatly increased when the 10 μm CH layer is placed on the sample. In the end, the dynamic fragmentation process via indirect drive is investigated by using the high energy X-ray radiography and photonic Doppler velocimetry. The radiograph is a snapshot at 600 ns and shows a typical result of the spall process. The first layer is measured to be 0.06 mm thick and 0.3 mm away from the unperturbed free surface. It is also exhibited that the hohlraum is expanded to a large extent but is not broken up. The jump-up velocity and time of spall are measured to be 0.65 km/s and 131 ns, respectively. The average velocity of the first layer is estimated to be (0.63 ± 0.1) km/s, obtained via the distance of 0.3 mm divided by the time difference of 469 ns (600 ns minus 131 ns). The one-dimensional loading region is 2 mm, and the flatness is better than 5 %. This work provides a reference for designing new hohlraum, shock wave loading technique and dynamic fragmentation process.

In this paper, the generation of relativistic electron mirrors (REMs) and the reflection of an ultra-short laser off this mirrors are discussed, applying two-dimensional particle-in-cell (2D-PIC) simulations. REMs with ultra-high acceleration and expanding velocity can be produced from a solid nanofoil illuminated normally by an ultra-intense femtosecond laser pulse with a sharp rising edge. Chirped attosecond pulse can be produced through the reflection of a counter-propagating probe laser off the accelerating REM. In the electron moving frame, the plasma frequency of the REM keeps decreasing due to its rapidly expanding. The laser frequency, on the contrary, keeps increasing due to the acceleration of REM and the relativistic Doppler shift from the lab frame to the electron moving frame. Within an ultra-short time interval, the two frequencies will be equal in the electron moving frame, which leads the resonance between laser and REM. The reflected radiation near this interval and the corresponding spectra will be amplified due to the resonance. Through adjusting the arriving time of the probe laser, certain part of the reflected field could be selectively amplified or depressed, leading to the selectively adjusting of the corresponding spectra.

We investigated the dynamic fragmentation of laser shock-loaded tin to gain insights on the underlying mechanism of this process. In the experiments, tin samples were shock-loaded by nanosecond laser over sequential pressures ranging from 7 GPa to 43 GPa. Integrated diagnostic techniques, including four-frame optical transverse shadowgraph imaging system, soft recovery, and photonic Doppler velocimetry (PDV), were employed. They provide the shape of the ejecta in the dynamic fragmentation process, the recovered ejecta, as well as the loading parameters. These experimental results were compared with those obtained using one-dimensional Lagrangian hydrodynamics simulation. The crossed results over sequential pressures allowed us to gain better insights on the different dynamic fragmentation processes of spall fracture and micro-spalling, which can help develop reliable models for dynamic fragmentation of triangular-wave shocking metals.

Ab initio simulations based on quantum molecular dynamics have been performed to study the electrical and optical properties of expanded gold fluids from one to a sixth of the normal solid density and with temperatures varying from 5000 to 20 000 K. With decreasing density, the dynamic conductivity evolves from the characteristic of a metal to that of a nonmetal. The DC conductivity is given by fitting the dynamic conductivity using the Drude or Drude-Smith model. According to the shift of the central peak of dynamic conductivity, the change of the slope of DC conductivity with respect to temperature, and the appearance of the disconnected network in the charge density distribution, the metal-nonmetal transition of expanded gold fluids occurs in the vicinity of one-third of the normal solid density. In addition, as the density decreases, the localization of 6s and 5d states is observed in the density of states.

Positron production by picosecond laser-driven electrons has been studied via simulations. The laser parameters were chosen according to a typical 100 J/1 ps laser system, such as the XingGuang III laser. A near-critical density plasma was used to accelerate electrons. Then the positrons were generated by these electrons interacting with a high-Z converter. Particle-in-cell simulations of laser-plasma interaction indicate that the picosecond laser-accelerated electrons have a temperature up to 12 MeV with a beam charge of 800 nC (>5 MeV). The positron generation was simulated by a Monte Carlo toolkit. The simulation results show that with an optimal converter thickness the generated positron beam has a yield of 5 × 1010 that is over one order of magnitude higher than that from direct laser-solid interaction.