The image shows fast object detection and data analysis of high-power high-repetition-rate laserplasma experiment using neural networks. In the petawatt, Hz laser system at the Center for Advanced Laser Applications, Munich, object detection networks are used to rapidly process and visualize various diagnostic data from each frame of the laser’s output images, including electron energy spectra, plasma wave, and laser damage.
Helical laser beams, due to their unique ?eld structure, are ideal optical drivers for producing monoenergetic, pellet-like electron bunches. In contrast to regular laser beams, their ?eld structure close to the axis of the beam is dominated by longitudinal electric and magnetic ?elds. The bunches are generated as a result of two synergetic e?ects that take place when such a beam is re?ected o? a mirror: the longitudinal electric ?eld accelerates electrons after extracting them from the mirror surface; while the magnetic ?eld con?nes them into the central region, allowing for acceleration within the laser over a long duration.
The cover image illustrates the photonic quasicrystal fiber (PQF), which is also named quasiperiodic photonic crystal fiber. The five insets surrounding the PQF end-face provide a simultaneous display of three typical structures and two representative potential applications of PQF. The three white-circled insets (top-left, right, and bottom-left) represent the Stampfli-type, Penrose-type, and Sunflower-type structures, respectively. The two blue-circled insets (left and bottom-right) show applications of the supercontinuum generation and orbital angular momentum mode propagation, respectively.
By harnessing Tamm plasmon coupling, spintronics THz radiation not only achieved a 264% enhancement but guaranteed nearly lossless (~4%) THz transmission. This approach provides the compatible optical structure design and the low energy consumption for ultrafast opto-spintronics devices.
A snapshot full-polarization hyperspectral imaging method based on convolutional neural network (CNN) reconstruction is proposed. In the imaging system, a quarter-wave plate is combined with a liquid crystal tunable filter to encode full-polarization information. Meanwhile, the liquid crystal tunable filter flexibly selects spectral bands of interest. Finally, a CMOS detector captures the total light intensity image after full-polarization encoding. In the reconstructed model, a two-layer CNN reconstructs four full-polarization images from one full-polarization encoded image. The cover image shows the main components of both the full-polarization hyperspectral imaging system and the CNN reconstruction model.
A wideband sensitive needle ultrasound sensor based on a polarized PVDF-TrFE copolymer piezoelectric film has been developed, which is capable of providin
A wideband sensitive needle ultrasound sensor based on a polarized PVDF-TrFE copolymer piezoelectric film has been developed, which is capable of providing a noise equivalent pressure of 14 Pa and a uniform frequency response ranging from 1 to 25 MHz. Its high sensitivity (1.6 μV / Pa) and compact size were achieved by capitalizing on the large electromechanical coupling coefficient of PVDF-TrFE and minimizing parasitic capacitance in a two-stage amplifier structure. The detection sensitivity of the newly designed sensor outperformed commercially available hydrophones with an equivalent sensing element area by a factor of 9. The sensor has been successfully integrated into a light scanning optoacoustic microscopy (OAM) system with a limited working space. Submicrometer resolution images were subsequently attained from living mice without employing signal averaging. The miniature sensor design can readily be integrated into various OAM systems and further facilitate multimodal imaging system implementations.show less
Photoacoustic imaging (PAI), recognized as a promising biomedical imaging modality for preclinical and clinical studies, uniquely combines the advantages
Photoacoustic imaging (PAI), recognized as a promising biomedical imaging modality for preclinical and clinical studies, uniquely combines the advantages of optical and ultrasound imaging. Despite PAI’s great potential to provide valuable biological information, its wide application has been hindered by technical limitations, such as hardware restrictions or lack of the biometric information required for image reconstruction. We first analyze the limitations of PAI and categorize them by seven key challenges: limited detection, low-dosage light delivery, inaccurate quantification, limited numerical reconstruction, tissue heterogeneity, imperfect image segmentation/classification, and others. Then, because deep learning (DL) has increasingly demonstrated its ability to overcome the physical limitations of imaging modalities, we review DL studies from the past five years that address each of the seven challenges in PAI. Finally, we discuss the promise of future research directions in DL-enhanced PAI.show less
The laser-induced damage threshold (LIDT) of plate laser beam splitter (PLBS) coatings is closely related to the subsurface absorption defects of the subs
The laser-induced damage threshold (LIDT) of plate laser beam splitter (PLBS) coatings is closely related to the subsurface absorption defects of the substrate. Herein, a two-step deposition temperature method is proposed to understand the effect of substrate subsurface impurity defects on the LIDT of PLBS coatings. Firstly, BK7 substrates are heat-treated at three different temperatures. The surface morphology and subsurface impurity defect distribution of the substrate before and after the heat treatment are compared. Then, a PLBS coating consisting of alternating HfO2–Al2O3 mixture and SiO2 layers is designed to achieve a beam-splitting ratio (transmittance to reflectance, s-polarized light) of approximately 50:50 at 1053 nm and an angle of incidence of 45°, and it is prepared under four different deposition processes. The experimental and simulation results show that the subsurface impurity defects of the substrate migrate to the surface and accumulate on the surface during the heat treatment, and become absorption defect sources or nodule defect seeds in the coating, reducing the LIDT of the coating. The higher the heat treatment temperature, the more evident the migration and accumulation of impurity defects. A lower deposition temperature (at which the coating can be fully oxidized) helps to improve the LIDT of the PLBS coating. When the deposition temperature is 140°C, the LIDT (s-polarized light, wavelength: 1064 nm, pulse width: 9 ns, incident angle: 45°) of the PLBS coating is 26.2 J/cm2, which is approximately 6.7 times that of the PLBS coating deposited at 200°C. We believe that the investigation into the laser damage mechanism of PLBS coatings will help to improve the LIDT of coatings with partial or high transmittance at laser wavelengths.show less
Imaging three-dimensional, subcellular structures with high axial resolution has always been the core purpose of fluorescence microscopy. However, trade-o
Imaging three-dimensional, subcellular structures with high axial resolution has always been the core purpose of fluorescence microscopy. However, trade-offs exist between axial resolution and other important technical indicators, such as temporal resolution, optical power density, and imaging process complexity. We report a new imaging modality, fluorescence interference structured illumination microscopy (FI-SIM), which is based on three-dimensional structured illumination microscopy for wide-field lateral imaging and fluorescence interference for axial reconstruction. FI-SIM can acquire images quickly within the order of hundreds of milliseconds and exhibit even 30 nm axial resolution in half the wavelength depth range without z-axis scanning. Moreover, the relatively low laser power density relaxes the requirements for dyes and enables a wide range of applications for observing fixed and live subcellular structures.show less
This work presents a brief review of our recent research on a novel anti-resonant mechanism named “Core-Anti-Resonant Reflection (CARR)”, which leads to a broadband terahertz (THz) spectrum outp
This work presents a brief review of our recent research on a novel anti-resonant mechanism named “Core-Anti-Resonant Reflection (CARR)”, which leads to a broadband terahertz (THz) spectrum output with periodic dips at resonant frequencies after its transmission along a hollow-core tubular structure (e.g., a paper tube). The CARR theory relies only on parameters of the tube core (e.g., the inner diameter) rather than the cladding, thus being distinct from existing principles such as the traditional Anti-Resonant Reflection inside Optical Waveguides (ARROW). We have demonstrated that diverse tubular structures, including cylindrical, polyhedral, spiral, meshy and notched hollow tubes with either transparent or opaque cladding materials, as well as a thick-walled hole, could indeed become CARR-type resonators. Based on this CARR effect, we have also performed various applications, such as the pressure sensing with paper-folded THz cavities, force/magnetic-driven chiral polarization modulations, and single-pulse measurements of the angular dispersion of THz beams, etc. In future studies, the proposed CARR method is promising to make breakthroughs in multiple fields by means of being extended to more kinds of tubular entities for enhancing their interactions with light waves in an anti-resonance manner.show less
Entangled photon pairs are crucial resources for quantum information processing protocols. Via the process of spontaneous parametric down-conversion (SPDC), we can generate these photon pairs us
Entangled photon pairs are crucial resources for quantum information processing protocols. Via the process of spontaneous parametric down-conversion (SPDC), we can generate these photon pairs using bulk nonlinear crystals. Traditionally, the crystal is designed to satisfy specific type of phase-matching condition. Here, we report controllable transitions among different types of phase-matching in a single periodically poled potassium titanyl phosphate (PPKTP) crystal. By carefully selecting pump conditions, we can satisfy different phase-matching conditions. This allows us to observe first-order type-II, fifth-order type-I, third-order type-0, and fifth-order type-II SPDCs. The temperature-dependent spectra of our source were also analyzed in detail. Finally, we discussed the possibility of observing more than nine SPDCs in this crystal. Our work not only deepens the understanding of the physics behind phase-matching conditions, but also offers the potential for a highly versatile entangled biphoton source for quantum information research.show less
Large-aperture pulse compression grating (PCG) is a critical component in generating an ultra-high-intensity, ultra-short-pulse laser, however, the size of PCG manufactured by transmission holog
Large-aperture pulse compression grating (PCG) is a critical component in generating an ultra-high-intensity, ultra-short-pulse laser, however, the size of PCG manufactured by transmission holographic exposure is limited to large-scale high-quality materials. The reflective method is a potential way for solving the size limitation, but there is still no successful precedent due to the lack of scientific specifications and advanced processing technology of exposure mirrors. In this paper, an analytical model is developed to clarify the specifications of mirrors and advanced processing technology is adopted to control the spatial frequency errors. Hereafter, we have successfully fabricated a multilayer dielectric (MLD) grating of 200 mm × 150 mm by using off-axis reflective exposure system with Φ300 mm. This demonstration proves that PCGs can be manufactured by using reflection holographic exposure method and shows the potential for manufacturing of meters-level gratings used in 100 Pettwatt class high-power laser.show less
We propose a spatially-chirped quasi-phase-matching (QPM) scheme that enables ultrabroadband second-harmonic-generation (SHG) by using fan-out QPM grating to frequency convert a spatially-chirpe
We propose a spatially-chirped quasi-phase-matching (QPM) scheme that enables ultrabroadband second-harmonic-generation (SHG) by using fan-out QPM grating to frequency convert a spatially-chirped fundamental wave. A ‘zero-dispersion’ 4f system maps the spectral contents of ultrabroadband fundamental onto different spatial coordinates in the Fourier plane, where the fundamental is quasi-monochromatic locally in picosecond duration, fundamentally canceling high-order phase mismatch. A fan-out QPM grating characterized by a linear variation of the poling period along transverse direction exactly supports the QPM of spatially-chirped beam. We theoretically demonstrate the SHG of an 810-nm, 12.1-fs pulse into a 405-nm, 10.2-fs pulse with a conversion efficiency of 77%.show less