Self-confocal NIR-II fluorescence microscopy for multifunctional in vivo imaging

Fluorescence imaging in the second near-infrared window(NIR-II,900–1880 nm)with less scattering background in biological tissues has been combined with the confocal microscopic system for achieving deep in vivo imaging with high spatial resolution.However,the traditional NIR-IIfluorescence confocal microscope with separate excitation focus and detection pinhole makes it possess low confocal e±ciency,as well as di±cultly to adjust.Two types of upgraded NIR-IIfluorescence confocal microscopes,sharing the same pinhole by excitation and emission focus,leading to higher confocal e±ciency,are built in this work.One type is-ber-pinhole-based confocal microscope applicable to CW laser excitation.It is constructed forfluorescence intensity imaging with large depth,high stabilization and low cost,which could replace multiphotonfluorescence microscopy in some applications(e.g.,cerebrovascular and hepatocellular imaging).The other type is air-pinhole-based confocal microscope applicable to femtosecond(fs)laser excitation.It can be employed not only for NIR-IIfluorescence intensity imaging,but also for multi-channelfluorescence lifetime imaging to recognize different structures with similarfluorescence spectrum.Moreover,it can be facilely combined with multiphotonfluorescence microscopy.A single fs pulsed laser is utilized to achieve up-conversion(visible multiphotonfluorescence)and down-conversion(NIR-II one-photonfluorescence)excitation simultaneously,extending imaging spectral channels,and thus facilitates multi-structure and multi-functional observation.

High performance micromachining of sapphire by laser induced plasma assisted ablation(LIPAA)using GHz burst mode femtosecond pulses

GHz burst-mode femtosecond(fs)laser,which emits a series of pulse trains with extremely short intervals of several hundred picoseconds,provides distinct characteristics in materials processing as compared with the conventional irradiation scheme of fs laser(single-pulse mode).In this paper,we take advantage of the moderate pulse interval of 205 ps(4.88 GHz)in the burst pulse for high-quality and high-efficiency micromachining of single crystalline sapphire by laser induced plasma assisted ablation(LIPAA).Specifically,the preceding pulses in the burst generate plasma by ablation of copper placed behind the sapphire substrate,which interacts with the subsequent pulses to induce ablation at the rear surface of sapphire substrates.As a result,not only the ablation quality but also the ablation efficiency and the fabrication resolution are greatly improved compared to the other schemes including single-pulse mode fs laser direct ablation,single-pulse mode fs-LIPAA,and nanosecond-LIPAA.

Two-dimensional laser-induced periodic surface structures formed on crystalline silicon by GHz burst mode femtosecond laser pulses

Femtosecond laser pulses with GHz burst mode that consist of a series of trains of ultrashort laser pulses with a pulse interval of several hundred picoseconds offer distinct features in material processing that cannot be obtained by the conventional irradiation scheme of femtosecond laser pulses(single-pulse mode).However,most studies using the GHz burst mode femtosecond laser pulses focus on ablation of materials to achieve high-efficiency and high-quality material removal.In this study,we explore the ability of the GHz burst mode femtosecond laser processing to form laser-induced periodic surface structures(LIPSS)on silicon.It is well known that the direction of LIPSS formed by the single-pulse mode with linearly polarized laser pulses is typically perpendicular to the laser polarization direction.In contrast,we find that the GHz burst mode femtosecond laser(wavelength:1030 nm,intra-pulse duration:220 fs,intra-pulse interval time(intra-pulse repetition rate):205 ps(4.88 GHz),burst pulse repetition rate:200 kHz)creates unique two-dimensional(2D)LIPSS.We regard the formation mechanism of 2D LIPSS as the synergetic contribution of the electromagnetic mechanism and the hydrodynamic mechanism.Specifically,generation of hot spots with highly enhanced electric fields by the localized surface plasmon resonance of subsequent pulses in the bursts within the nanogrooves of one-dimensional LIPSS formed by the preceding pulses creates 2D LIPSS.Additionally,hydrodynamic instability including convection flow determines the final structure of 2D LIPSS.

Coin-structured tunable beam shaping assembly design for accelerator-based boron neutron capture therapy for tumors at different depths and sizes

In the past decade,boron neutron capture therapy utilizing an accelerator-based neutron source(ABNS)designed primarily for producing epithermal neutrons has been implemented in the treatment of brain tumors and other cancers.The specifications for designing an epithermal beam are primarily based on the IAEA-TECODC-1223 report,issued in 2001 for reactor neutron sources.Based on this report,the latest perspectives and clinical requirements,we designed an ABNS capable of adjusting the average neutron beam energy.The design was based on a 2.8 MeV,20 mA proton beam bombarding a lithium target to produce neutrons that were subsequently moderated and tuned through a tunable beam shaping assembly(BSA)which can modify the thicknesses and materials of the coin-shaped moderators,back reflectors,filters,and collimators.The simulation results demonstrated that epithermal neutron beams for deep seated tumor treatment,which were generated by utilizing magnesium fluoride with lengths ranging between 28 and 36 cm as the moderator,possessed a treatment depth of 5.6 cm although the neutron flux peak shifts from 4.5 to 1.0 keV.When utilizing a thinner moderator,a less accelerated beam power can meet the treatment requirements.However,higher powers reduced the treatment time.In contrast,employing a thick moderator can reduce the skin dose.In scenarios that required relatively low energy neutron beams,the removal of the thermal neutron filter can raise the thermal neutron flux at the beam port.And the depth of the dose rate peak could be adjusted between 0.25 and 2.20 cm by combining magnesium fluoride and polyethylene coins of different thicknesses.Hence,this device has a better adaptability for the treatment of superficial tumors.Overall,the tunable BSA provides greater flexibility for clinical treatment than common BSA designs that can only adjust the port size.

Edge enhanced depth perception with binocular meta-lens

The increasing popularity of the metaverse has led to a growing interest and market size in spatial computing from both academia and industry.Developing portable and accurate imaging and depth sensing systems is crucial for advancing next-generation virtual reality devices.This work demonstrates an intelligent,lightweight,and compact edge-enhanced depth perception system that utilizes a binocular meta-lens for spatial computing.The miniaturized system comprises a binocular meta-lens,a 532 nm filter,and a CMOS sensor.For disparity computation,we propose a stereo-matching neural network with a novel H-Module.The H-Module incorporates an attention mechanism into the Siamese network.The symmetric architecture,with cross-pixel interaction and cross-view interaction,enables a more comprehensive analysis of contextual information in stereo images.Based on spatial intensity discontinuity,the edge enhancement eliminates illposed regions in the image where ambiguous depth predictions may occur due to a lack of texture.With the assistance of deep learning,our edge-enhanced system provides prompt responses in less than 0.15 seconds.This edge-enhanced depth perception meta-lens imaging system will significantly contribute to accurate 3D scene modeling,machine vision,autonomous driving,and robotics development.

Liquid vortexes and flows induced by femtosecond laser ablation in liquid governing formation of circular and crisscross LIPSS

Orientations of laser induced periodic surface structures(LIPSS)are usually considered to be governed by the laser polarization state.In this work,we unveil that fluid dynamics induced by femtosecond(fs)laser ablation in liquid(fs-LAL)can easily break this polarization restriction to produce irregular circular-LIPSS(CLIPPS)and crisscross-LIPSS(CCLIPSS).Fs laser ablation of silicon in water shows formation of diverse LIPSS depending on ablation conditions.At a high power of 700 mW(repetition rate of 100 kHz,pulse duration of 457 fs and wavelength of 1045 nm),single/twin CLIPSS are produced at the bottom of macropores of several microns in diameter due to the formation of strong liquid vortexes and occurrence of the vortex shedding effect.Theoretical simulations validate our speculation about the formation of liquid vortex with an ultrahigh static pressure,which can induce the microstructure trenches and cracks at the sidewalls for fs-LAL of Si and tungsten(W)in water,respectively.At a low power of 50 mW,weak liquid vortexes are produced,which only give birth to curved LIPSS in the valleys of grooves.Consequently,it is deduced that liquid vortex plays a crucial role in the formation of macropores.Mountain-like microstructures induce complex fluid dynamics which can cause the formation of CCLIPSS on them.It is believed that liquid vortexes and fluid dynamics presented in this work open up new possibilities to diversify the morphologies of LIPSS formed by fs-LAL.

Femtosecond laser shockwave peening ablation in liquids for hierarchical micro/nanostructuring of brittle silicon and its biological application

This paper presents a new technique,termed femtosecond laser shock peening ablation in liquids(fs-LSPAL),which can realize simultaneous crack micro/nanomanufacturing and hierarchical micro/nanolaser ablation,giving rise to the formation of diverse multiscale hierarchical structures,such as macroporous ratcheted structures and enéchelon microfringes decorated with parabolic nanoripples.Through analysis of surface morphologies,many phenomena have been confirmed to take place during fs-LSPAL,including enéchelon cracks,nanostriation,ripple densification,crack branching,and selective formation of high spatial frequency laser-induced periodic surface structures of 100–200 nm in period.At a high laser power of 700 mW,fs-LSPAL at scanning speeds of 0.2 mm s^-1 and 1 mm s^-1 enables the generation of height-fluctuated and height-homogeneous hierarchical structures,respectively.The height-fluctuated structures can be used to induce‘colony’aggregates of embryonic EB3 stem cells.At 200 mW,fs-LSPAL at 1 mm s^-1 is capable of producing homogeneous tilt macroporous structures with cracked structures interleaved among them,which are the synergistic effects of bubble-induced light refraction/reflection ablation and cracks.As shown in this paper,the conventional laser ablation technique integrated with its self-driven unconventional cracking under extreme conditions expands the horizons of extreme manufacturing and offers more opportunities for complex surface structuring,which can potentially be used for biological applications.

Underwater persistent bubble-assisted femtosecond laser ablation for hierarchical micro/nanostructuring

In this study,we demonstrate a technique termed underwater persistent bubble assisted femtosecond laser ablation in liquids(UPB-fs-LAL)that can greatly expand the boundaries of surface micro/nanostructuring through laser ablation because of its capability to create concentric circular macrostructures with millimeter-scale tails on silicon substrates.Long-tailed macrostructures are composed of layered fan-shaped(central angles of 45°–141°)hierarchical micro/nanostructures,which are produced by fan-shaped beams refracted at the mobile bubble interface(.50°light tilt,referred to as the vertical incident direction)during UPB-fs-LAL line-by-line scanning.Marangoni flow generated during UPB-fs-LAL induces bubble movements.Fast scanning(e.g.1mms−1)allows a long bubble movement(as long as 2mm),while slow scanning(e.g.0.1mms−1)prevents bubble movements.When persistent bubbles grow considerably(e.g.hundreds of microns in diameter)due to incubation effects,they become sticky and can cause both gas-phase and liquidphase laser ablation in the central and peripheral regions of the persistent bubbles.This generates low/high/ultrahigh spatial frequency laser-induced periodic surface structures(LSFLs/HSFLs/UHSFLs)with periods of 550–900,100–200,40–100 nm,which produce complex hierarchical surface structures.A period of 40 nm,less than 1/25th of the laser wavelength(1030 nm),is the finest laser-induced periodic surface structures(LIPSS)ever created on silicon.The NIR-MIR reflectance/transmittance of fan-shaped hierarchical structures obtained by UPB-fs-LAL at a small line interval(5μm versus 10μm)is extremely low,due to both their extremely high light trapping capacity and absorbance characteristics,which are results of the structures’additional layers and much finer HSFLs.In the absence of persistent bubbles,only grooves covered with HSFLs with periods larger than 100 nm are produced,illustrating the unique attenuation abilities of laser properties(e.g.repetition rate,energy,incident angle,etc)by persistent bubbles with different curvatures.This research represents a straightforward and cost-effective approach to diversifying the achievable hierarchical micro/nanostructures for a multitude of applications.

Four-channel CWDM transmitter chip based on thin-film lithium niobate platform

Multi-lane integrated transmitter chips are key components in future compact optical modules to realize high-speed optical interconnects.Thin-film lithium niobate(TFLN)photonics have emerged as a promising platform for achieving high-performance chip-scale optical systems.Combining a coarse wavelength-division multiplexing(CWDM)devices using fabrication-tolerant angled multimode interferometer structure and high-performance electro-optical modulators,we demonstrate monolithic on-chip four-channel CWDM transmitter on the TFLN platform for the first time.The four-channel CWDM transmitter enables high-speed transmissions of 100 Gb/s data rate per wavelength channel(i.e.,an aggregated date rate of 400 Gb/s).

Enhanced ablation efficiency for silicon by femtosecond laser microprocessing with GHz bursts in MHz bursts(BiBurst)

Ultrashort laser pulses confine material processing to the laser-irradiated area by suppressing heat diffusion,resulting in precise ablation in diverse materials.However,challenges occur when high speed material removal and higher ablation efficiencies are required.Ultrafast burst mode laser ablation has been proposed as a successful method to overcome these limitations.Following this approach,we studied the influence of combining GHz bursts in MHz bursts,known as Bi Burst mode,on ablation efficiency of silicon.Bi Burst mode used in this study consists of multiple bursts happening at a repetition rate of 64 MHz,each of which contains multiple pulses with a repetition rate of 5 GHz.The obtained results show differences between Bi Burst mode and conventional single pulse mode laser ablation,with a remarkable increase in ablation efficiency for the Bi Burst mode,which under optimal conditions can ablate a volume4.5 times larger than the single pulse mode ablation while delivering the same total energy in the process.

Additive and interfacial control for efficient perovskite light-emitting diodes with reduced trap densities

Metal halide perovskite semiconductors show excellent optoelectronic properties including tunable bandgaps[1,2],narrow emission bandwidths[3]and high luminescence quantum efficiencies[4],making them an ideal candidate for light-emitting diode(LED)applications.Perovskite LEDs(PeLEDs)have attracted considerable attention since the initial report of room-temperature electroluminescence(EL)from halide perovskites in 2014[5].

At wavelength coherent scatterometry microscope using high-order harmonics for EUV mask inspection

In this review,we describe our research on the development of the 13.5 nm coherent microscope using high-order harmonics for the mask inspection of extreme ultraviolet(EUV)lithography.EUV lithography is a game-changing piece of technology for high-volume manufacturing of commercial semiconductors.Many top manufacturers apply EUV technology for fabricating the most critical layers of 7 nm chips.Fabrication and inspection of defect-free masks,however,still remain critical issues in EUV technology.Thus,in our pursuit for a resolution,we have developed the coherent EUV scatterometry microscope(CSM)system with a synchrotron radiation(SR)source to establish the actinic metrology,along with inspection algorithms.The intensity and phase images of patterned EUV masks were reconstructed from diffraction patterns using ptychography algorithms.To expedite the practical application of the CSM,we have also developed a standalone CSM,based on high-order harmonic generation,as an alternative to the SR-CSM.Since the application of a coherent 13.5 nm harmonic enabled the production of a high contrast diffraction pattern,diffraction patterns of sub-100 ns size defects in a 2D periodic pattern mask could be observed.Reconstruction of intensity and phase images from diffraction patterns were also performed for a periodic line-and-space structure,an aperiodic angle edge structure,as well as a cross pattern in an EUV mask.

Quantification methodologies on organization and morphology features of fiber-like structures:A review

Among all the structural formations,fiber-like structure is one of the most common modalities in organisms that undertake essential functions.Alterations in spatial organization of fibrous structures can refiect information of physiological and pathological activities,which is of significance in both researches and clinical applications.Hence,the quantification of subtle changes in fiber-like structures is potentiallymeaningful in studying structure-function relationships,disease progression,carcinoma staging and engineered tissue remodeling.In this study,we examined a wide range of methodologies that quantify organizational and morphological features of fibrous structures,including orientation,alignment,waviness and thickness.Each method was demonstrated with specific applications.Finally,perspectives of future quantification analysis techniques were explored.

GHz bursts in MHz burst(BiBurst) enabling high-speed femtosecond laser ablation of silicon due to prevention of air ionization

For the practical use of femtosecond laser ablation, inputs of higher laser intensity are preferred to attain high-throughput material removal. However, the use of higher laser intensities for increasing ablation rates can have detrimental effects on ablation quality due to excess heat generation and air ionization. This paper employs ablation using BiBurst femtosecond laser pulses, which consist of multiple bursts(2 and 5 bursts) at a repetition rate of 64 MHz, each containing multiple intra-pulses(2–20 pulses) at an ultrafast repetition rate of 4.88 GHz, to overcome these conflicting conditions. Ablation of silicon substrates using the BiBurst mode with 5 burst pulses and 20 intra-pulses successfully prevents air breakdown at packet energies higher than the pulse energy inducing the air ionization by the conventional femtosecond laser pulse irradiation(single-pulse mode). As a result, ablation speed can be enhanced by a factor of23 without deteriorating the ablation quality compared to that by the single-pulse mode ablation under the conditions where the air ionization is avoided.

Ultra-high extinction ratio optical pulse generation with a thin film lithium niobate modulator for distributed acoustic sensing

We experimentally demonstrate ultra-high extinction ratio(ER)optical pulse modulation with an electro-optical modulator(EOM)on thin film lithium niobate(TFLN)and its application for fiber optic distributed acoustic sensing(DAS).An interface carrier effect leading to a relaxation-tail response of TFLN EOM is discovered,which can be well addressed by a small compensation component following the main driving signal.An ultrahigh ER>50 dB is achieved by canceling out the tailed response during pulse modulation using the EOM based on a cascaded Mach–Zehnder interferometer(MZI)structure.The modulated optical_(√)pulses are then utilized as a probe light for a DAS system,showing a sensitivity up to-62.9 dB·rad∕Hz~2(7 pε/Hz)for 2-km single-mode sensing fiber.Spatial crosstalk suppression of 24.9 dB along the fiber is also obtained when the ER is improved from 20 dB to 50 dB,clearly revealing its importance to the sensing performance.

Three-dimensional remodeling of collagen fibers within cervical tissues in pregnancy

The cervix is a collagen-rich connective tissue that must remain closed during pregnancy while undergoing progressive remodeling in preparation for delivery,which begins before the onset of the preterm labor process.Therefore,it is important to resolve the changes of collagen flbers during cervical remodeling for the prevention of preterm labor.Herein,we assessed the spatial organization of collagen flbers in a three-dimensional(3D)context within cervical tissues of mice on day 3,9,12,15 and 18 of gestation.We found that the 3D directional variance,a novel metric of alignment,was higher on day 9 than that on day 3 and then gradually decreased from day 9 to day 18.Compared with two-dimensional(2D)approach,a higher sensitivity was achieved from 3D analysis,highlighting the importance of truly 3D quantification.Moreover,the depthdependent variation of 3D directional variance was investigated.By combining multiple 3D directional variance-derived metrics,a high level of classification accuracy was acquired in distinguishing different periods of pregnancy.These results demonstrate that 3D directional variance is sensitive to remodeling of collagen fibers within cervical tissues,shedding new light on highly-sensitive,early detection of preterm birth(PTB).

Waveguide-integrated optical modulators with two-dimensional materials

Waveguide-integrated optical modulators are indispensable for on-chip optical interconnects and optical computing.To cope with the ever-increasing amount of data being generated and consumed,ultrafast waveguide-integrated optical modulators with low energy consumption are highly demanded.In recent years,two-dimensional(2D)materials have attracted a lot of attention and have provided tremendous opportunities for the development of high-performance waveguide-integrated optical modulators because of their extraordinary optoelectronic properties and versatile compatibility.This paper reviews the state-of-the-art waveguide-integrated optical modulators with 2D materials,providing researchers with the developing trends in the field and allowing them to identify existing challenges and promising potential solutions.First,the concept and fundamental mechanisms of optical modulation with 2D materials are summarized.Second,a review of waveguide-integrated optical modulators employing electro-optic,all-optic,and thermo-optic effects is provided.Finally,the challenges and perspectives of waveguide-integrated modulators with 2D materials are discussed.

Fundamentals and applications of photonic waveguides with bound states in the continuum

Photonic waveguides are the most fundamental element for photonic integrated circuits(PICs).Waveguide properties,such as propagation loss,modal areas,nonlinear coefficients,etc.,directly determine the functionalities and performance of PICs.Recently,the emerging waveguides with bound states in the continuum(BICs)have opened new opportunities for PICs because of their special properties in resonance and radiation.Here,we review the recent progress of PICs composed of waveguides with BICs.First,fundamentals including background physics and design rules of a BIC-based waveguide will be introduced.Next,two types of BIC-based waveguide structures,including shallowly etched dielectric and hybrid waveguides,will be presented.Lastly,the challenges and opportunities of PICs with BICs will be discussed.

Lipid droplets imaging with three-photon microscopy

Lipid droplets(LDs)participate in many physiological processes,the abnormality of which will cause chronic diseases and pathologies such as diabetes and obesity.It is crucial to monitor the distribution of LDs at high spatial resolution and large depth.Herein,we carried three-photon imaging of LDs in fat liver.Owing to the large three-photon absorption cross-section of the luminogen named NAP-CF_(3)(1:67×10^(-79) cm^(6) s^(2)),three-photon fluorescence fat liver imaging reached the largest depth of 80μm.Fat liver diagnosis was successfully carried out with excellent performance,providing great potential for LDs-associated pathologies research.

Fabrication of Mie-resonant silicon nanoparticles using laser annealing for surface-enhanced fluorescence spectroscopy

Silicon nanostructures with unique Mie resonances have garnered considerable attention in the field of nanophotonics.Here,we present a simple and efficient method for the fabrication of silicon(Si)nanoparticle substrates using continuous-wave(CW)laser annealing.The resulting silicon nanoparticles exhibit Mie resonances in the visible region,and their resonant wavelengths can be precisely controlled.Notably,laser-annealed silicon nanoparticle substrates show a 60-fold enhancement in fluorescence.This tunable and fluorescence-enhancing silicon nanoparticle platform has tremendous potential for highly sensitive fluorescence sensing and biomedical imaging applications.