Internal collision double ionization of molecules driven by co-rotating two-color circularly polarized laser pulses

The double ionization process of molecules driven by co-rotating two-color circularly polarized fields is investigated with a three-dimensional classical ensemble model. Numerical results indicate that a considerable part of the sequential double ionization(DI) events of molecules occur through internal collision double ionization(ICD), and the ICD recollision mechanism is significantly different from that in non-sequential double ionization(NSDI). By analyzing the results of internuclear distances R = 5 a.u. and 2 a.u., these two recollision mechanisms are studied in depth. It is found that the dynamic behaviors of the recollision mechanisms of NSDI and ICD are similar. For NSDI, the motion range of electrons after the ionization is relatively large, and the electrons will return to the core after a period of time. In the ICD process,electrons will rotate around the parent ion before ionization, and the distance of the electron motion is relatively small. After a period of time, the electrons will come back to the core and collide with another electron. Furthermore, the molecular internuclear distance has a significant effect on the electron dynamic behavior of the two ionization mechanisms. This study will help to understand the multi-electron ionization process of complex systems.

Circularly Polarized Light-Enabled Chiral Nanomaterials:From Fabrication to Application

For decades,chiral nanomaterials have been extensively studied because of their extraordinary properties.Chiral nanostructures have attracted a lot of interest because of their potential applications including biosensing,asymmetric catalysis,optical devices,and negative index materials.Circularly polarized light(CPL)is the most attractive source for chirality owing to its high availability,and now it has been used as a chiral source for the preparation of chiral matter.In this review,the recent progress in the field of CPL-enabled chiral nanomaterials is summarized.Firstly,the recent advancements in the fabrication of chiral materials using circularly polarized light are described,focusing on the unique strategies.Secondly,an overview of the potential applications of chiral nanomaterials driven by CPL is provided,with a particular emphasis on biosensing,catalysis,and phototherapy.Finally,a perspective on the challenges in the field of CPL-enabled chiral nanomaterials is given.

A Compact Ultra-Wideband Circularly Polarized Antenna Array for Vehicular Communications

In this paper,a new compact ultrawideband(UWB)circularly polarized(CP)antenna array for vehicular communications is proposed.The antenna array consists of a 2×2 sequentially rotated T-shaped cross dipole,four parasitic elements,and a feeding network.By loading the T-shaped cross dipoles with parasitic rectangular elements with cut corners,the bandwidth can be expanded.On this basis,the radiation pattern can be improved by the topology with sequential rotation of four T-shaped cross-dipole antennas,and the axial ratio(AR)bandwidth of the antenna also can be further enhanced.In addition,due to the special topology that the vertical arms of all Tshaped cross dipoles are all oriented toward the center of the antenna array,the gain of proposed antenna is improved while the size of the antenna is almost the same as the traditional cross dipole.Simulated and measured results show that the proposed antenna has good CP characteristics,an impedance bandwidth for S11<-10 d B of about 106.1%(3.26:1,1.57-5.12 GHz)and the 3-d B AR bandwidth of about 104.1%(3.17:1,1.57-4.98 GHz),a wide 3-d B gain bandwidth of 73.3%as well as the peak gain of 8.6 d Bic at 3.5 GHz.The overall size of antenna is 0.56λ×0.56λ×0.12λ(λrefers to the wavelength of the lowest operating frequency in free space).The good performance of this compact UWB CP antenna array is promising for applications in vehicular communications.

High gain and circularly polarized substrate integrated waveguide cavity antenna array based on metasurface

Two substrate integrated waveguide(SIW) cavity antenna arrays based on metasurface are proposed in this paper. By rotating the metasurface element, circularly polarized and high gain antennas are achieved respectively. Firstly, multi-mode resonance theory is employed to broaden the bandwidth of the slot antenna. And then, an SIW cavity composed of 4×4 cornercut elements is added on the top of the slot antenna to achieve the circular polarization and improve the front-to-back ratio. Thirdly, the metasurface elements are sequentially rotated and a high gain antenna with 2-dBi enhancement on average in the operation band is obtained. Based on the two antenna units, two 2×2 antenna arrays are designed. The circularly polarized and high gain antenna arrays are both fabricated to verify the correctness. Furthermore, the novel wideband phase shifter is employed in the circularly polarized antenna to obtain an operating bandwidth of 38%(4.05 GHz–5.95 GHz)and AR bandwidth of 24.9%(4.4 GHz–5.65 GHz). The bandwidth of the high gain antenna can reach 42.7%(3.95 GHz–6.1 GHz) and with the gain enhancement of 2 dBi compared with that of the circularly polarized antenna. The gain remains steady in most of operating band within a variation of 1 dBi. It is remarkable that the rotating of the metasurface element has a great influence on the antenna performance, which provides a new explication for the multi-function antenna design.

Triple-Band Circularly Polarized Dielectric Resonator Antenna (DRA) for Wireless Applications

This paper proposes a new dielectric resonator antenna(DRA)design that can generate circularly polarized(CP)triple-band signals.Atripleband CP DRA antenna fed by a probe feed system is achieved with metal strips structure on side of DRA structure.The design start with conventional rectangular DRA with F shaped metal strips on DRA structure alongside the feed.Then,the F metal strip is enhanced by extending the length of the metal strip to obtain wider impedance bandwidth.Further improvement on the antenna performance is observed by improvised the conventional DRA structure.The method of removing part of DRA bottom resulted to higher antenna gain with triple band CP.The primary features of the proposed DRA include wide impedance matching bandwidth(BW)and broadband circular polarization(CP).The primary features of the proposedDRAinclude wide impedance matching bandwidth(BW)and broadband circular polarization(CP).The CP BW values recorded by the proposed antenna were∼11.27%(3.3–3.65 GHz),12.18%(4.17–4.69 GHz),and 1.74%(6.44–6.55 GHz)for impedance-matching BW values of 35.4%(3.3–4.69 GHz),1.74%(5.36–5.44 GHz),and 1.85%(6.41–6.55 GHz)with peak gains of 6.8 dBic,7.6 dBic,and 8.5 dBic,respectively,in the lower,central,and upper bands.The prototype of the proposed antenna geometry was fabricated and measured.A good agreement was noted between the simulated and the measured results.

High-order harmonic generation of the cyclo[18]carbon molecule irradiated by circularly polarized laser pulse

High-order harmonic generation of the cyclo[18]carbon(C_(18) ) molecule under few-cycle circularly polarized laser pulse is studied by time-dependent density functional theory. Compared with the harmonic emission of the ring molecule C_(6)H_(6) having similar ionization potential, the C_(18) molecule has higher efficiency and cutoff energy than C_(6)H_(6) with the same laser field parameters. Further researches indicate that the harmonic efficiency and cutoff energy of the C_(18) molecule increase gradually with the increase of the laser intensity of the driving laser or decrease of the wavelength, both are larger than those of the C_(6)H_(6) molecule. Through the analysis of the time-dependent evolution of the electronic wave packets, it is also found that the higher efficiency of harmonic generation can be attributed to the larger spatial scale of the C_(18) molecule,which leads to a greater chance for the ionized electrons from one atom to recombine with others of the parent molecule.Selecting the suitable driving laser pulse, it is demonstrated that high-order harmonic generation in the C_(18) molecule has a wide range of applications in producing circularly polarized isolated attosecond pulse.

Self-powered circularly polarized light detector based on asymmetric chiral metamaterials

Circularly polarized light(CPL)has been given great attention because of its extensive application.While several devices for CPL detection have been studied,their performance is affected by the magnitude of photocurrent.In this paper,a self-powered photodetector based on hot electrons in chiral metamaterials is proposed and optimized.CPL can be distinguished by the direction of photocurrent without external bias owing to the interdigital electrodes with asymmetric chiral metamaterials.Distinguished by the direction of photocurrent,the device can easily detect the rotation direction of the CPL electric field,even if it only has a very weak responsivity.The responsivity of the proposed detector is near 1.9 mA/W at the wavelength of 1322 nm,which is enough to distinguish CPL.The detector we proposed has the potential for application in optical communication.

Scattering of Circularly Polarized Terahertz Waves on a Graphene Nanoantenna

We present a surface current method to model the graphene rectangular nanoantenna scattering in the terahertz band with Comsol. Compared with the equivalent thin slab method, the results obtained by the surface current method are more accurate and efficient. Then the electromagnetic scattering of circularly polarized terahertz waves on graphene nanoantennas is numerically analyzed by utilizing the surface current method. The depen- dences of the antenna resonant frequency with the circularly polarized wave on width and length are consistent with those for the linear polarized waves. These results are proved to be useful to design et^cient nanoantennas in terahertz wireless communications.

High-order harmonic generation of N2molecule in two-color circularly polarized laser fields

The generation of high-order harmonics and the attosecond pulse of the N2 molecule in two-color circularly polarized laser fields are investigated by the strong-field Lewenstein model. We show that the plateau of spectra is dramatically extended and a continuous harmonic spectrum with the bandwidth of 113 eV is obtained. When a static field is added to the x direction, the quantum path control is realized and a supercontinuum spectrum can be obtained, which is beneficial to obtain a shorter attosecond pulse. The underlying physical mechanism is well explained by the time-frequency analysis and the semi-classical three-step model with a finite initial transverse velocity. By superposing several orders of harmonics in the combination of two-color circularly polarized laser fields and a static field, an isolated attosecond pulse with a duration of 30 as can be generated.

A Review of Wideband Circularly Polarized Dielectric Resonator Antennas

This article presents a technical review of circularly polarized(CP) dielectric resonator antennas(DRA) for wideband applications.The primary objective of this review is,to highlight the techniques used by different researchers for generating circular polarization in DRA.First,a general idea of circular polarization and it advantages over linear polarization is presented,and then all the major developments made in the CP DRA are highlighted.The emphasis of the paper is on the wideband circularly polarized dielectric resonator antenna.The current state of the art and all the realizable features of the CP DRA are addressed comprehensively.Finally,some recommendations for future CP DRAs are given and the paper ends with concluding remarks.

Atomic high-order harmonic generation from a circularly polarized laser pulse

We demonstrate theoretically that the high-order harmonic of an atom can be generated by a circularly polarized laser pulse.The harmonic spectrum shows a clear cutoff with an energy Ip ＋ 2Up.In particular,the high-order harmonic generation comes from the multiple recombination of the ionized electron with non-zero initial velocity.These results are verified by the classical model theory and the time-frequency analysis of a harmonic spectrum.

Isolated attosecond pulse generation with few-cycle two-color counter-rotating circularly polarized laser pulses

Most of the schemes for generating isolated attosecond pulses（IAP） are sensitive to the carrier-envelope phase（CEP）of the driving lasers. We propose a scheme for generating IAP using two-color counter-rotating circularly polarized（TCCRCP） laser pulses. The results demonstrate that the dependence of the IAP generation on CEP stability is largely reduced in this scheme. IAP can be generated at most of CEPs. Therefore, the experiment requirements become lower.

Generation of Linear Isolated Sub-60 Attosecond Pulses by Combining a Circularly Polarized Pulse with an Elliptically Polarized Pulse

The two-color circularly polarized pulses scheme was proposed to generate isolated attosecond pulses in our previous work [Phys. Rev. A 87 （2013） 043406], while the polarization of the attosecond pulse was not investigated. We show a supplementary explanation of this scheme and present another scheme to generate linear isolated attosecond pulses by combining a circularly polarized pulse with an elliptically polarized pulse. High-order harmonic generation and quantum path control are investigated to compare these two schemes. Both schemes can obtain supercontinuum spectra plateau from about 200eV to 550eV, which belong to the water window region. It is found that the latter scheme can clearly eliminate the short quantum path and extend the harmonic plateau. A linear isolated attosecond pulse with a duration of sub-6Oas can be generated by superposing a bandwidth of 70eV.

Detecting Spin Bias with Circularly Polarized Light

We theoretically study the spin transport through a two-terminal quantum dot device under the influence of a symmetric spin bias and circularly polarized light. It is found that the combination of the circularly polarized light and the applied spin bias can result in a net charge current. The resultant charge current is large enough to be measured when properly choosing the system parameters. The resultant charge current can be used to deduce the spin bias due to the fact that there exists a simple linear relation between them. When the external circuit is open, a charge bias instead of a charge current can be induced, which is also measurable by present technologies. These findings indicate a new approach to detect the spin bias by using circularly polarized light.

A multi-frequency circularly polarized metasurface antenna array based on quarter-mode substrate integrated waveguide for sub-6 applications

A miniaturized multi-frequency circularly polarized array is designed in this paper.The antenna array is composed of three independent sub-arrays employing modified quarter-mode substrate ntegrated aveguide(QMSIW)to achieve three circularly polarized frequency bands.By introducing strip-slot,the impedance bandwidth of the antenna array is broadened while the dimension is decreased by 75%to realize miniaturization.Meanwhile,metasurface causes the impedance bandwidth of the sub-array to be further enhanced.Moreover,the metal vias are employed in the antenna array design to further achieve miniaturization.The antenna array is manufactured and measured to verify the design.Both the measured and simulated results display that the array achieves the impedance bandwidths of 10%,11.7%,and 14.8%and axial ratio bandwidths of 8.8%,8.0%,and 8.5%at 2.5,3.5,and 4.8 GHz,respectively.The gain is stable in the operating band within an uncertainty of 0.7 d Bi.The whole dimension is 0.92λ×0.63λ×0.04λ,whereλ_(0) is the wavelength at the lowest resonant frequency.Furthermore,the simple structure and miniaturization provides great convenience in sub-6 applications.

Circularly Polarized Absorption Property of Tetra-4[4'-(2-methylbutoxy)benzoyloxy]phenyl Porphyrin by Introducing Optical Pendant Groups

Tetra-4[4'-(2-methylbutoxy)benzoyloxy]phenyl porphyrin [T(MBBP)P] has been synthesized and its solid film has strong CD absorption effect.

A Compact Flexible Circularly Polarized Implantable Antenna for Biotelemetry Applications

With the help of in-body antennas,the wireless communication among the implantable medical devices(IMDs)and exterior monitoring equipment,the telemetry system has brought us many benefits.Thus,a very thin-profile circularly polarized(CP)in-body antenna,functioning in ISM band at 2.45 GHz,is proposed.A tapered coplanar waveguide(CPW)method is used to excite the antenna.The radiator contains a pentagonal shape with five horizontal slits inside to obtain a circular polarization behavior.A bendable Roger Duroid RT5880 material(εr=2.2,tanδ=0.0009)with a typical 0.25 mm-thickness is used as a substrate.The proposed antenna has a total volume of 21×13×0.25 mm3.The antenna covers up a bandwidth of 2.38 to 2.53 GHz(150 MHz)in vacuum,while in skin tissue it covers 1.56 to 2.72 GHz(1.16 GHz)and in the muscle tissue covers 2.16 to 3.17 GHz(1.01 GHz).GHz).The flexion analysis in the x and y axes was also performed in simulation as the proposed antenna works with a wider bandwidth in the skin and muscle tissue.The simulation and the curved antenna measurements turned out to be in good agreement.The impedance bandwidth of−10 dB and the axis ratio bandwidth of 3 dB(AR)are measured on the skin and imitative gel of the pig at 27.78%and 35.5%,13.5%and 4.9%,respectively,at a frequency of 2.45 GHz.The simulations revealed that the specific absorption rate(SAR)in the skin is 0.634 and 0.914 W/kg in muscle on 1g-tissue.The recommended SAR values are below the limits set by the federal communications commission(FCC).Finally,the proposed low-profile implantable antenna has achieved very compact size,flexibility,lower SAR values,high gain,higher impedance and axis ratio bandwidths in the skin and muscle tissues of the human body.This antenna is smaller in size and a good applicant for application in medical implants.

Effects of initial electronic state on vortex patterns in counter-rotating circularly polarized attosecond pulses

We theoretically investigate the effects of different electronic states as the initial state on the vortex patterns in photoelectron momentum distributions(PMDs)from numerical solutions of the two-dimensional(2D)time-dependent Schrodinger equation(TDSE)of He^(+)with a pair of counter-rotating circularly polarized attosecond pulses.It is found that the number of spiral arms in vortex patterns is equal to the number of the absorbed photons when the initial state is the ground state.However,the number of spiral arms in vortex patterns is always two more than the number of the absorbed photons when the initial state is the excited state.This sensitivity is attributed to the initial electron density distribution.In addition,we have demonstrated the PMDs for different initial electronic states with the same wavelengths and analyzed their corresponding physical mechanisms.It is illustrated that the method presented can be employed to effectively control the distribution of the electron vortices.

Semi-integer harmonic generation from an argon atom by bichromatic counter-rotating circularly polarized laser field

We theoretically investigated the properties of the high-order harmonic generation from an argon atom by bichromatic counter-rotating circularly polarized(BCCP)laser field.The harmonic emission processes have been illustrated by numerically solving the two-dimensional time-dependent Schr¨odinger equation of an atom in intense laser fields.It is found that with the decrease of the right-circularly polarized laser wavelength,the harmonic spectra are gradually splitting and the harmonic orders move towards the higher frequency.Meanwhile,the integer and semi-integer harmonic emission will be generated when the frequency ratios of right-and left-circularly polarized lasers are semi-integer.The emission mechanism of the semi-integer-order harmonics has been investigated by using the rules of photon absorption and emission.

Role of potential on high-order harmonic generation from atoms irradiated by bichromatic counter-rotating circularly polarized laser fields

We investigate high-order harmonic generation from atoms irradiated by bichromatic counter-rotating circularly polarized laser pulses by numerically solving the time-dependent Schrödinger equation.It is found that the minimum energy position of the harmonic spectrum and the non-integer order optical radiation are greatly discrepant for different atomic potentials.By analyzing the quantum trajectory of the harmonic emission,discrepancies among the harmonic spectra from different potentials can be attributed to the action of the potential on the ionized electrons.In addition,based on the influence of the driving light intensity on the overall intensity and ellipticity of higher order harmonics,the physical conditions for generating a high-intensity circularly polarized harmonic can be obtained.