Advances in Atomic Time Scale Imaging with a Fine Intrinsic Spatial Resolution

Atomic time scale imaging,opening a new era for studying dynamics in microcosmos,is presently attracting immense research interest on the global level due to its powerful ability.On the atom level,physics,chemistry,and biology are identical for researching atom motion and atomic state change.The light possesses twoness,the information carrier and the research resource.The most fundamental principle of this imaging is that light records the event-modulated light field by itself,so-called all-optical imaging.This paper can answer what is the essential standard to develop and evaluate atomic time scale imaging,what is the optimal imaging system,and what are the typical techniques to implement this imaging,up to now.At present,the best record in the experiment,made by multistage optical parametric amplification(MOPA),is realizing 50-fs resolved optical imaging with a spatial resolution of~83 lp/mm at an effective framing rate of 15×10^(12)fps for recording an ultrafast optical lattice with its rotating speed up to 13.5×10^(12)rad/s.

Interface-enhanced thermoelectric output power in CrN/SrTiO_(3-x) heterostructure

Thermoelectric devices enable direct conversion between thermal and electrical energy.Recent studies have indicated that the thin film/substrate heterostructure is effective in achieving high thermoelectric performance via decoupling the Seebeck coefficient and electrical conductivity otherwise adversely inter-dependent in homogenous bulk materials.However,the mechanism underlying the thin film/substrate heterostructure thermoelectricity remains unclear.In addition,the power output of the thin film/substrate heterostructure is limited to the nanowatt scale to date,falling short of the practical application requirement.Here,we fabricated the CrN/SrTiO_(3-x) heterostructures with high thermoelectric output power and outstanding thermal stability.By varying the CrN film thickness and the reduction degree of CrN/SrTiO_(3-x) substrate,the optimized power output and the power density have respectively reached 276μWand 10^(8) mW/cm^(2) for the 30 nm CrN film on a highly reduced surface of CrN/SrTiO_(3-x) under a temperature difference of 300 K.The performance enhancement is attributed to the CrN/CrN/SrTiO_(3-x) heterointerface,corroborated by the band bending as revealed by the scanning Kelvin probe microscopy.These results will stimulate further research efforts towards interface thermoelectrics.

Recent advances in generation of terahertz vortex beams andtheir applications

Last decade has witnessed a rapid development of the generation of terahertz(THz)vortex beams as well as their wide applications,mainly due to their unique combination characteristics of regular THz radiation and orbital angular momentum(OAM).Here we have reviewed the ways to generate THz vortex beams by two representative scenarios,i.e.,THz wavefront modulation via specific devices,and direct excitation of the helicity of THz vortex beams.The former is similar to those wavefront engineering devices in the optical and infrared(IR)domain,but just with suitable THz materials,while the latter is newly-developed in THz regime and some of the physical mechanisms still have not been explained explicitly enough though,which would provide both challenges and opportunities for THz vortex beam generation.As for their applications,thanks to the recent development of THz optics and singular optics,THz vortex beams have potentials to open doors towards a myriad of practice applications in many fields.Besides,some representative potential applications are evaluated such as THz wireless communication,THz super-resolution imaging,manipulating chiral matters,accelerating electron bunches,and detecting astrophysical sources.

Spectral polarization-encoding of broadband laser pulses by optical rotatory dispersion and its applications in spectral manipulation

We propose a kind of spectral polarization-encoding(SPE)for broadband light pulses,which is realized by inducing optical rotatory dispersion(ORD),and decoded by compensating ORD.Combining with polarization-sensitive devices,SPE can not only work to control polarization-dependent transmission for central wavelength or bandwidth-tunable filtering,but also can be used for broadband regenerative or multi-pass amplification with a polarization-dependent gain medium to improve output bandwidth.SPE is entirely passive thus very simple to be designed and aligned.By using an ORD crystal with a good transmission beyond 3-μm mid-infrared region,e.g.,Ag Ga S_(2),SPE promises to be applied for the wavelength tuning lasers in mid-infrared region,where the tunning devices are rather under developed compared with those in visible and near-infrared region.

High-spatial-resolution ultrafast framing imaging at 15 trillion frames per second by optical parametric amplification

We report a framing imaging based on noncollinear optical parametric amplification(NCOPA),named FINCOPA,which applies NCOPA for the first time to single-shot ultrafast optical imaging.In an experiment targeting a laser-induced air plasma grating,FINCOPA achieved 50 fs-resolved optical imaging with a spatial resolution of^83 lp∕mm and an effective frame rate of 10 trillion frames per second(Tfps).It has also successfully visualized an ultrafast rotating optical field with an effective frame rate of 15 Tfps.FINCOPA has simultaneously a femtosecond-level temporal resolution and frame interval and a micrometer-level spatial resolution.Combining outstanding spatial and temporal resolutions with an ultrahigh frame rate,FINCOPA will contribute to high-spatiotemporal resolution observations of ultrafast transient events,such as atomic or molecular dynamics in photonic materials,plasma physics,and laser inertial-confinement fusion.

High spatial-resolution biological tissue imaging in the second near-infrared region via optical parametric amplification pumped by an ultrafast vortex pulse [Invited]

Applying an ultrafast vortex laser as the pump,optical parametric amplification can be used for spiral phase-contrast imaging with high gain,wide spatial bandwidth,and high imaging contrast.Our experiments show that this design has realized the 1064 nm spiral phase-contrast idler imaging of biological tissues(frog egg cells and onion epidermis)with a spatial resolution at several microns level and a superior imaging contrast to both the traditional bright-or dark-field imaging under a weak illumination of 7 nW/cm^(2).This work provides a powerful way for biological tissue imaging in the second near-infrared region.

Absolute Configuration of the Phenylpropanoid Isolated from Peperomia tetraphylla

A recently identified phenylpropanoid isolated from Peperomia tetraphylla was synthesized in enantiopure forms using an aldol condensation of enantiopure （R）-N-acetyl 4-phenyl-oxazolidin-2-one as the key step. With the aid of the single crystal X-ray crystallographic analysis of the synthetic sample, the configuration for the natural product was unambiguously established. Corrected/updated ^13C NMR and optical rotation are also presented.

Review and Prospect of Single-Shot Ultrafast Optical Imaging by Active Detection

In the recent decade,single-shot ultrafast optical imaging by active detection,called single-shot active ultrafast optical imaging(SS-AUOI)here,has made great progress,e.g.,with a temporal resolution of 50 fs and a frame rate beyond 10 trillion frames per second.Now,it has become indispensable for charactering the nonrepeatable and difficult-to-reproduce events and revealing the underlying physical,chemical,and biological mechanisms.On the basis of this delightful status,we would like to make a review of SS-AUOI.On the basis of a brief introduction of SS-AUOI,our review starts with discussing its characteristics and then focuses on the survey and prospect of SS-AUOI technology.

Generation and imaging of a tunable ultrafast intensity-rotating optical field with a cycle down to femtosecond region

A tunable ultrafast intensity-rotating optical field is generated by overlapping a pair of 20Hz,800 nm chirped pulses with a Michelson interferometer(MI).Its rotating rate can be up to 10 trillion radians per second(Trad/s),which can be flexibly tuned with a mirror in the MI.Besides,its fold rotational symmetry structure is also changeable by controlling the difference from the topological charges of the pulse pair.Experimentally,we have successfully developed a twopetal lattice with a tunable rotating speed from 3.9 Trad/s up to 11.9 Trad/s,which is confirmed by our single-shot ultrafast frame imager based on noncollinear optical-parametric amplification with its highest frame rate of 15 trillion frames per second(Tfps).This work is carried out at a low repetition rate.Therefore,it can be applied at relativistic,even ultrarelativistic,intensities,which usually operate in low repetition rate ultrashort and ultraintense laser systems.We believe that it may have application in laser-plasma-based accelerators,strong terahertz radiations and celestial phenomena.

Role of the carrier gas flow rate in monolayer MoS2 growth by modified chemical vapor deposition

Monolayer molybdenum disulfide （MoS2） has attracted much attention because of the variety of potential applications. However, its controlled growth is still a great challenge. Here, we report a modified chemical vapor deposition method to grow monolayer MoS2. We observed that the quality of the MoS2 crystals could be greatly improved by tuning the carrier gas flow rate during the heating stage. This subtle modification prevents the uncontrollable reaction between the precursors, a critical factor for the growth of high-quality monolayer MoS2. Based on an optimized gas flow rate, the MoS2 coverage and flake size can be controlled by adjusting the growth time.

Single-shot terahertz polarization detection based on terahertz time-domain spectroscopy

This paper presents a novel design for single-shot terahertz polarization detection based on terahertz time-domain spectroscopy(THz-TDS).Its validity has been confirmed by comparing its detection results with those of the THz common-path spectral interferometer through two separate measurements for the orthogonal components.Our results also show that its detection signal-to-noise ratios(SNRs)are obviously superior to those of the 45°optical bias THz-TDS by electro-optical sampling due to its operation on common-path spectral interference rather than the polarization-sensitive intensity modulation.The setup works without need of any optical scan,which does not only save time,but also efficiently avoids the disturbances from the fluctuations of the system and environment.Its single-shot mode allows it to work well for the applications with poor or no repeatability.

High-gain amplification for femtosecond optical vortex with mode-control regenerative cavity

Ultra-intense femtosecond vortex pulses can provide an opportunity to investigate the new phenomena with orbital angular momentum(OAM)involved in extreme cases.This paper reports a high gain optical vortex amplifier for intense femtosecond vortex pulses generation.Traditional regeneration amplifiers can offer high gain for Gaussian mode pulses but cannot amplify optical vortex pulses while maintaining the phase singularity because of mode competition.Here,we present a regeneration amplifier with a ring-shaped pump.By controlling the radius of the pump,the system can realize the motivation of the Laguerre–Gaussian[LG0,1(−1)]mode and the suppression of the Gaussian mode.Without seeds,the amplifier has a donut-shaped output containing two opposite OAM states simultaneously,as our prediction by simulation.If seeded by a pulse of a topologic charge of 1 or−1,the system will output an amplified LG0,1(−1)mode pulse with the same topologic charge as the seed.To our knowledge,this amplifier can offer the highest gain as 1.45×106 for optical vortex amplification.Finally,we obtain a 1.8 mJ,51 fs compressed optical vortex seeded from a 2 nJ optical vortex.