High-resolution x-ray monochromatic imaging for laser plasma diagnostics based on toroidal crystal

Monochromatic x-ray imaging is an essential method for plasma diagnostics related to density information.Large-field high-resolution monochromatic imaging of a He-like iron(Fe XXV)Kαcharacteristic line(6.701 keV)for laser plasma diagnostics was achieved using a developed toroidal crystal x-ray imager.A high-index crystal orientation Ge(531)wafer with a Bragg angle of 75.37°and the toroidal substrate were selected to obtain sufficient diffraction efficiency and compensate for astigmatism under oblique incidence.A precise offline assembly method of the toroidal crystal imager based on energy substitution was proposed,and a spatial resolution of 3-7μm was obtained by toroidal crystal imaging of a 600 line-pairs/inch Au grid within an object field of view larger than 1.0 mm.The toroidal crystal x-ray imager has been successfully tested via side-on backlight imaging experiments of the sinusoidal modulation target and a 1000 line-pairs/inch Au grid with a linewidth of 5μm using an online alignment method based on dual positioning balls to indicate the target and backlighter.This paper describes the optical design,adjustment method,and experimental results of a toroidal crystal system in a laboratory and laser facility.

Optimized online filter stack spectrometer for ultrashort X-ray pulses

Currently,with the advent of high-repetition-rate laser-plasma experiments,the demand for online diagnosis for the X-ray spectrum is increasing because the laser-plasma-generated X-ray spectrum is very important for characterizing electron dynamics and applications.In this study,scintillators and silicon PIN(P-type–intrinsic-N-type semiconductor)diodes were used to construct a wideband online filter stack spectrometer.The X-ray sensor and filter arrangement was optimized using a genetic algorithm to minimize the condition number of the response matrix.Consequently,the unfolding error was significantly reduced based on numerical experiments.The detector responses were quantitatively calibrated by irradiating the scintillator and PIN diode with various nuclides and comparing the measuredγ-ray peaks.A prototype 15-channel spectrometer was developed by integrating an X-ray detector with front-and back-end electronics.The prototype spectrometer could record X-ray pulse signals at a repetition rate of 1 kHz.Furthermore,an optimized spectrometer was employed to record the real-time spectra of laser-driven bremsstrahlung sources.This optimized spectrometer offers a compact solution for spectrum diagnostics of ultrashort X-ray pulses,exhibiting improved accuracy in terms of spectrum measurements and repetition rates,and could be widely used in next-generation high-repetition-rate high-power laser facilities.

Optical design of a novel near-infrared phase contrast imaging(NI-PCI)diagnostic on the HL-2A tokamak

The optical design of near-infrared phase contrast imaging(NI-PCI)diagnosis on HL-2A is introduced in this paper.This scheme benefits from the great progress of near-infrared laser technology and is a broadening of traditional phase contrast technology.This diagnostic can work as a keen tool to measure plasma wavenumber spectra by inferring string-integrated plasma density fluctuations.Design of both the front optical path which is the path before the laser transmitting into the tokamak plasma and the rear optics which is the path after the laser passing through the plasma is detailed.The 1550 nm laser is chosen as the probe beam and highprecision optical components are designed to fit the laser beam,in which a phase plate with a 194-nm-deep silver groove is the key.Compared with the conventional 10.6μm laser-based PCI system on HL-2A,NI-PCI significantly overcomes the unwanted phase scintillation effect and promotes the measurement capability of high-wavenumber turbulence with an increased maximal measurable wavenumber from 15 cm^(-1)to 32.6 cm^(-1).

Random pinhole attenuator for high-power laser beams

The intensity attenuation of a high-power laser is a frequent task in the measurements of optical science.Laser intensity can be attenuated by inserting an optical element,such as a partial reflector,polarizer or absorption filter.These devices are,however,not always easily applicable,especially in the case of ultra-high-power lasers,because they can alter the characteristics of a laser beam or become easily damaged.In this study,we demonstrated that the intensity of a laser beam could be effectively attenuated using a random pinhole attenuator(RPA),a device with randomly distributed pinholes,without changing the beam properties.With this device,a multi-PW laser beam was successfully attenuated and the focused beam profile was measured without any alterations of its characteristics.In addition,it was confirmed that the temporal profile of a laser pulse,including the spectral phase,was preserved.Consequently,the RPA possesses significant potential for a wide range of applications.

Multi-energy four-channel Kirkpatrick–Baez microscope for X-ray imaging diagnostics at the Shenguang-II laser facility

A four-channel Kirkpatrick Baez microscope working at multiple energy bands is developed for multiframe X-ray imaging diagnostics at the Shenguang-II laser facility. The response to the multiple energy bands is realized by coating the double-periodic multilayers on the reflected surfaces of the microscope. Because of the limited size of the microstrips in the X-ray framing camera, the image separation is controlled by the coni- cal angle of the reference cores during microscope assembly. This study describes the optical and multilayer design, assembly, and aligmnent of the developed microscope. The microscope achieves a spatial resolution of 4 5 gin in the laboratory and 10 20 ~tm at Shenguang-II laser facility within a 300 tim field of view. The versatile nature of the developed microscope enables the multiple microscopes currently installed in the laser facility to be replaced with a single, multipurpose microscope.

High-power non-perturbative laser delivery diagnostics at the final focus of 100-TW-class laser pulses

Controlling the delivery of multi-terawatt and petawatt laser pulses to final focus,both in position and angle,is critical to many laser applications such as optical guiding,laser–plasma acceleration,and laser-produced secondary radiation.We present an online,non-destructive laser diagnostic,capable of measuring the transverse position and pointing angle at focus.The diagnostic is based on a unique double-surface-coated wedged-mirror design for the final steering optic in the laser line,producing a witness beam highly correlated with the main beam.By propagating low-power kilohertz pulses to focus,we observed spectra of focus position and pointing angle fluctuations dominated by frequencies below 70 Hz.The setup was also used to characterize the excellent position and pointing angle correlation of the 1 Hz high-power laser pulses to this low-power kilohertz pulse train,opening a promising path to fast non-perturbative feedback concepts even on few-hertz-class high-power laser systems.

Impact of temporal modulations on laser-induced damage of fused silica at 351 nm

Laser-induced damage(LID)on high-power laser facilities is one of the limiting factors for the increase in power and energy.Inertial confinement fusion(ICF)facilities such as Laser Mégajoule or the National Ignition Facility use spectral broadening of the laser pulse that may induce power modulations because of frequency modulation to amplitude modulation conversion.In this paper,we study the impact of low and fast power modulations of laser pulses both experimentally and numerically.The MELBA experimental testbed was used to shape a wide variety of laser pulses and to study their impact on LID.A 1D Lagrangian hydrodynamic code was used to understand the impact of different power profiles on LID.

Data Processing and Acquisition System for the HT-7 Multipulse Thomson Scattering Diagnostic

This article describes the data processing and acquisition system for the HT-7 mul-tipulse Thomson scattering diagnostic. An eight-pulse laser is used in the Thomson scattering system to obtain electron temperature profiles at eight different times throughout an entire plasma discharge. The major components of the diagnostic system consist of a multipulse Nd-glass laser, a photodetector's subsystem, a calibration set and a CAMAC data processing and acquisition system. The data processing software along with LeCroy 2250L will perform the data acquisition. In order to simplify the operation and extend the capability of its compatibility with other math softwares, the processing software has been improved by the authors. The new software based on the VC++ easily utilizes some math softwares to calculate the electron temperature. The new software is simpler and more operational than the old one.

Optical path design of phase contrast imaging on HL-2A tokamak

A phase contrast imaging（PCI） diagnostic has recently been developed on HL-2 A tokamak. It can diagnose plasma density fluctuations with maximum wave number of 15 cm^（-1） and wave number resolution of 2 cm^（-1）. The time resolution reaches 2 μs. A 10.6 μm CO_2 laser is expanded to a beam with a diameter of 30 mm and injected into the plasma as an incident beam,injecting into plasma. The emerging scattered and unscattered beams are contrasted by a phase plate. The ideas of optical path design are presented in this paper, together with the parameters of the main optical components. The whole optical path of PCI is not only carefully designed, but also constructed on HL-2 A. First calibration results show the ability of this system to catch plasma turbulence in a wide frequency domain.

Experimental Study of Fuel-Air Mixing and Dilution Jets on Outlet Temperature Distribution in a Small Gas Turbine Combustor

Experimental analysis was conducted to study the impact of fuel-air mixing and dilution jet on the temperature distribution in a small gas turbine combustor using various optical diagnostic techniques.The strength and velocity of the swirler at the venturi exit were adjusted to modify the fuel-air mixture,which is presumed to dominate the heat release of the main combustion zone.Additionally,the dilution hole configuration,including the number and size of the holes,was varied to investigate the dilution effect on outlet temperature distribution.Various optical diagnostic techniques,such as particle image velocimetry,planar Mie scattering,and OH~*chemiluminescence,were used to measure the flow field,fuel spray distribution,and flame structure,respectively.A reduction in swirling strength led to a decrease in the average flow rate in the throat,which improved the structure and symmetry of the axial vortex system in the sleeve,enhanced the mixing of fuel and gas in the dome swirling air,and ultimately,improved the temperature uniformity of the heat release zone.Compared to larger and sparse dilution jets,smaller and dense dilution jets tended to generate hot spots shifted towards the radial middle area.

Photothermal damage prediction of laser interstitial thermotherapy

An improved scattering optical model was developed under cylindrical coordinate to simulate the thermal effect of diffusing applicator in laser interstitial thermotherapy （LITT）. The thermal damage was calculated by finite element method （FEM） using Pennes bio-heat transfer equation and Arrhenius injury integral formula. The numerical results showed that the scattering can considerably influence the evaluation of the lesion area, and the relationship between application powers or time and resulting tissue thermal damage was nonlinear. Although usually applying relatively low power can avoid tissue charring, rather higher power is recommended because it is indispensable to achieve necessary damage threshold and the therapy time can be shortened. OCIS codes： 000.4430, 350.5340, 140.3330.

Laser technology in Poland： 2013-2016

This paper presents the state of art of laser technologies in Poland. A list of primary laser technology development centers is included. The involvement of Polish scientists in the development of lasers and fourth generation synchrotron light sources as well as their applications is discussed. The development of laser applications in medical therapy and diagnostics, material micro- and macro-processing as well as environmental monitoring and protection, safety, and security is presented.

Diagnostic value of confocal laser endomicroscopy in primary bile reflux gastritis

Objective To evaluate the accuracy of confocal laser endomicroscopy(CLE)in primary bile reflux gastritis(BRG).Methods From November 10 to December 15,2015,55 patients undergoing CLE examination and preliminarily diagnosed as BRG with traditional white-light endoscopy were enrolled.CLE score standard was designed.Dixon pathologic score was considered as

Deep Neural Network-Based Generation of Planar CH Distribution through Flame Chemiluminescence in Premixed Turbulent Flame

Flame front structure is one of the most fundamental characteristics and, hence, vital for understanding combustion processes. Measuring flame front structure in turbulent flames usually needs laser-based diagnostic techniques, mostly planar laser-induced fluorescence (PLIF). The equipment of PLIF, burdened with lasers, is often too sophisticated to be configured in harsh environments. Here, to shed the burden, we propose a deep neural network-based method to generate the structures of flame fronts using line-of-sight CH* chemiluminescence that can be obtained without the use of lasers. A conditional generative adversarial network (CGAN) was trained by simultaneously recording CH-PLIF and chemiluminescence images of turbulent premixed methane/air flames. Two distinct generators of the C-GAN, namely Resnet and U-net, were evaluated. The former net performs better in this study in terms of both generating snap-shot images and statistics over multiple images. For chemiluminescence imaging, the selection of the camera’s gate width produces a trade-off between the signal-to-noise (SNR) ratio and the temporal resolution. The trained C-GAN model can generate CH-PLIF images from the chemiluminescence images with an accuracy of over 91% at a Reynolds number of 5000, and the flame surface density at a higher Reynolds number of 10,000 can also be effectively estimated by the model. This new method has the potential to achieve the flame characteristics without the use of laser and significantly simplify the diagnosing system, also with the potential for high-speed flame diagnostics.

High-resolution Mo KαX-ray monochromatic backlight imaging using a toroidal crystal

Curved crystal imaging is an important means of plasma diagnosis.Due to the short wavelengths of high-energy X rays and the fixed lattice constant of the spherical crystal,it is difficult to apply the spherical crystal in high-energy X-ray imaging.In this study,we have developed a high-energy,high-resolution X-ray imager based on a toroidal crystal that can effectively correct astigmatism.We prepared a Ge<511>toroidal crystal for backlighting Mo Kα1 characteristic lines(∼17.48 keV)and verified its high-resolution imaging ability in high-energy X-ray region,achieving a spatial resolution of 5–10μm in a field of view larger than 1.0 mm.

Ultra-compact post-compressor on-shot wavefront measurement for beam correction at PHELIX

In order to reach the highest intensities,modern laser systems use adaptive optics to control their beam quality.Ideally,the focal spot is optimized after the compression stage of the system in order to avoid spatio-temporal couplings.This also requires a wavefront sensor after the compressor,which should be able to measure the wavefront on-shot.At PHELIX,we have developed an ultra-compact post-compressor beam diagnostic due to strict space constraints,measuring the wavefront over the full aperture of 28 cm.This system features all-reflective imaging beam transport and a high dynamic range in order to measure the wavefront in alignment mode as well as on shot.

Spectral broadening for multi-Joule pulse compression in the APOLLON Long Focal Area facility

Spectral-broadening of the APOLLON PW-class laser pulses using a thin-film compression technique within the longfocal-area interaction chamber of the APOLLON laser facility is reported,demonstrating the delivery of the full energy pulse to the target interaction area.The laser pulse at 7 J passing through large aperture,thin glass wafers is spectrally broadened to a bandwidth that is compatible with a 15-fs pulse,indicating also the possibility to achieve sub-10-fs pulses using 14 J.Placing the post-compressor near the interaction makes for an economical method to produce the shortest pulses by limiting the need for high damage,broadband optics close to the final target rather than throughout the entire laser transport system.

Innovative single-shot 2D pulse front tilt diagnostic

The presence of pulse front tilt(PFT),caused by angular dispersion(AD)in femtosecond laser pulses,could degrade the performance of the laser system and/or impact the experimental yields.We present a single-shot diagnostic capable of measuring the AD in the x–y plane by adopting an intensity mask.It can be applied to stretched pulses,making it ideal for diagnosing the AD along the amplification chain of a high-power laser system,and to ultrashort pulses exiting from an optical compressor.In this way,it can help in properly characterizing a laser pulse before it is delivered to the target area.In this Letter,we present experimental evidence of AD retrieval for different compression configurations,supported by theoretical analysis.

Photoacoustic image reconstruction based on Bayesian compressive sensing algorithm

The photoacoustic tomography （PAT） method, based on compressive sensing （CS） theory, requires that, for the CS reconstruction, the desired image should have a sparse representation in a known transform domain. However, the sparsity of photoacoustic signals is destroyed because noises always exist. Therefore, the original sparse signal cannot be effectively recovered using the general reconstruction algorithm. In this study, Bayesian compressive sensing （BCS） is employed to obtain highly sparse representations of photoacoustic images based on a set of noisy CS measurements. Results of simulation demonstrate that the BCS-reconstructed image can achieve superior performance than other state-of-the-art CS-reconstruction algorithms.

Serum peptidome profiling for identifying pathological patterns in patients with primary nephrotic syndrome

Background Renal biopsy is necessary for diagnosing the pathological changes of primary nephrotic syndrome （NS）. However, it is invasive, time-consuming and can not be performed frequent on the same patient. Thus, development of a non-invasive and rapid diagnostic method may improve clinical patient management. Methods Proteomic tool magnetic bead-based matrix-assisted laser desorption/ionization time-of-flight mass spectrometry （MB-based MALDI TOF MS） was applied to serum to determine peptidome patterns that are characteristic of different pathological changes. Results Serum specimen from 114 patients with NS （62 were minimal change disease （MCD）, 30 were membranous nephropathy （MN）, and 22 were focal segmental glomerulosclerosis （FSGS）） and 60 normal individuals were analyzed using MB-based MALDI TOF MS. The peptidome pattern was generated by genetic algorithms using a training set of 31 MCD, 15 MN, 11 FSGS and 30 normal individuals and was validated by an independent testing set of the remaining samples. The serum peptidome pattern, based on a panel of 14 peaks, accurately recognized samples from MCD, MN, FSGS and healthy control with sensitivities of 93.5%, 86.7%, 63.6% and 90.0%, and specificities of 98.2%, 94.4%, 100% and 89.5%, respectively. Moreover, one peptide from peptidome pattern was identified by liquid chromatography tandem mass spectrometry （LC MS/MS） as fibrinogen A. Conclusion Detection of the serum peptidome pattern is a rapid, non-invasive, high-throughout, and reproducible method for identifying the pathological patterns of patients with nephrotic syndrome.