Dejiao Hu

Determination of magneto-optical constant of Fe films with weak measurements

In this letter, a detecting method for the magneto-optical constant is presented by using weak measurements. The photonic spin Hall effect (PSHE), which manifests itself as spin-dependent splitting, is introduced to characterize the magneto-optical constant, and a propagation model to describe the quantitative relation between the magneto-optical constant and the PSHE is established. According to the amplified shift of the PSHE detected by weak measurements, we determinate the magneto-optical constant of the Fe film sample. The Kerr rotation is measured via the standard polarimetry method to verify the rationality and feasibility of our method. These findings may provide possible applications in magnetic physics research.

Anomalous reflection in the ultra-thin nano-strip antenna induced by incident field and displacement current phase matching

Recently, ultra-thin nano-strip antenna (thinner than skin depth) has attracted extensive attention as a key structure unit of metasurface. It can be used to realize anomalous enhanced reflection and absorption, as well as suppressed transmission, which has been used in photonic devices. However, there is still a lack of clear analysis to explain systematically these phenomena. In this paper, we present the concept of phase matching between the displacement current and the incident field, which initially leads to the anomalous scattering property of a single ultra-thin nano-strip antenna. Base on the property of a single nano-strip, we study the coupling of multi-nano-strip antennas and demonstrate that the randomized and periodic array of nano-strips have the same anomalous reflection spectrum. The phase matching is also reflected in the theoretic model, from which the reflection and transmission formulas for nano-strip array are derived. The formulas successfully predict the thickness influence on the reflection spectra of a periodic array. Our results can promote the development of ultra-thin nano-strip based metasurfaces.

Pure magnetic resonances controlled by the relative azimuth angle between meta-atoms

A plasmonic molecule showing strong magnetic resonance modes and flexible tunability is proposed. The molecule is composed of two elements, a crescent shaped metallic disk and a smaller one embedded in the cavity of the larger one. The cavity and gap formed by these two elements enable the molecule to support magnetic resonances in the visible and near infrared spectral region, while electric resonances are much weaker to be detected. We show that by changing the relative orientation angle of these two meta-atoms, the resonance wavelength can be changed from the visible to near infrared without modification of the size of the molecule. Anti-crossings and crossings of resonance energy levels, which stem from the coupling effect, are analyzed. When resonating magnetically, the local electric field enhancement at the crescent tip can reach up to hundreds of times with high spatial confinement, which renders the molecule promising applications in many fields.

Cl-assisted highly efficient synthesis of FePd3 alloys encapsulated in graphite papers: a two stage CVD approach

Recently it has been shown that FePd alloys can be encapsulated in graphitic carbon based systems for a better particle dispersion through addition of dichloro-cyclooctadiene palladium to ferrocene. Here we propose an advanced two-stage method which allows the synthesis of very thick deposits of planar rolled-like graphite structures filled with FePd3 alloys as dominant product in the entire reactor. The first stage is used to pyrolyze the Pd-containing hydrocarbon on the top of Si/SiO2 substrates for Pd deposition while the second stage is used for the evaporation and pyrolysis of the Fe-containing precursor (ferrocene) for the FePd alloy formation and encapsulation. Annealing studies also show that no changes in the unit cell of the FePd3 structure are found even after tens of hours at 600–650 °C under Ar/H2 flow. Instead a change in the encapsulated particle shape and spatial arrangement is found. The samples are characterized in detail through scanning and transmission electron microscopy, energy dispersive X-rays, Raman spectroscopy, thermogravimetric analyses, X-ray diffraction and room-temperature magnetometry.

Optoplasmonic probe to realize scanning near-field Raman microscopy

Tip-enhanced Raman spectroscopy (TERS) is a powerful scanning probe technique for Raman detections in nanotechnology to date. However, limited by the physical principles of a nanosize tapered metal (or metal-coated) probe used in a TERS device, only far-field without near-field Raman signal can be collected by the TERS with the metal probe. This makes conventional TERS lower in efficiency and cannot be a real near-field Raman microscopy. In this paper, we propose a simple and realizable optoplasmonic probe model, which is composed of a dielectric microsphere and a metal nanobowtie, to realize an ideal scanning near-field Raman microscopy (SNRM). Using finite-difference time-domain (FDTD) method, calculation results of electric field distributions of the proposed probe demonstrate that the probe provides three outstanding characteristics, including strong enhancement of local electric field, nanoscale distributions of the produced electric filed, and collection enhancement of emitted energy with wide wavelength range in near field. These characteristics of the probe resolve the detecting restrictions of metal probes and provide a real near-field scanning method. Therefore, a potentially novel SNRM can be expected to extend Raman application range greatly.

Design of ultra-thin metallic grating based circular polarizer in the near infrared

The circular polarizers were mostly made of meta-atom based chiral metamaterials (CMMs). Here we propose an ultra-thin metallic grating based circular polarizer, which can convert any polarization into circular polarization. The circular polarizer consists of two layers: an ultra-thin metallic grating embedded in the substrate and a silicon grating on the substrate surface. The ultra-thin metallic grating, which is thinner than the skin depth and was shown to hold anomalous resonant reflection for transverse magnetic (TM) wave, functions as a quarter-wave plate. We show that the ultra-thin metallic grating based quarter-wave plate can transmit circular polarized wave when the incident linear polarized wave is oriented properly. The silicon grating acts as a linear polarizer which restricts the polarization of the light that reaches the metallic grating. Unlike some of the CMMs, our structure is independent of the incident polarization state. Moreover, the fabrication of our circular polarizer is easier than other double-layer-CMMs, in which the relative position between the two layers must be precisely controlled. Our structure can find its application integrated photonic devices.

Surface plasmons leaky radiation of the flat metal

Surface plasmons have been widely investigated in many fields due to the unique property. ATR (attenuated totalreflection) is the common method to excite surface plasmons. We derive the Fano-type analysis to present the reflection spectrum of ATR configuration derived from the three-layer Fresnel reflection equation, which are asymmetric curves resulted from interference between direct reflectance and surface plasmons leaky radiation. In the fitting progress, we obtain the relationship between surface plasmons leaky radiation and metal thickness. When the metal thickness is greater than 25nm, surface plasmons leaky radiation rate is less than 0.07. We also compare the ATR and grating coupler excitement mechanism, which provide a reference to evaluate their application.

Angular-momentum-dependent splitting of light through metal nanohole

We numerically study the splitting of light beam which carries orbital angular momentum (OAM) through single metal nano-scale hole. A light beam carrying with OAM has a helical phase distribution in the transverse plane, where the electric field has the form: E(r,θ)=E0exp(lθ), and l is the topological charge which denotes the value of OAM. The circular polarization state is corresponding to the spin angular momentum (SAM), where s=+1 represents the left-handed polarization and s=-1 the right-handed polarization. Simulation results show l dependent splitting of beam through nano metal hole. When l is odd, the transmitted far field splits while no splitting happens when l is even. This phenomenon is attributed to the interaction between OAM beam and plasmonic mode of metal nano-hole. It is revealed that different OAM beam can excite different transverse mode in the metal cavity, which means the interaction should obey an OAM section rule. We show that even l can excite transverse mode with zero total AM and odd l can excite transverse mode with non-zero total AM within the hole. Orbital-spin conversion is also revealed in the free wave/plasmon interaction.

Enhancement of light absorption in organic solar cells by using plasmonic gratings

Organic solar cells show a commercially viable future duo to their inherent advantages, such as light weight, flexibility, and so on. Recently, a lot of progress has been made in every domain of organic solar cells. Among these, plasmonic light trapping is regarded as a promising light management technology for improving the light absorption in organic active layer. In this work, we numerically investigate the light enhancement in organic solar cell by embedding metal gratings as electrodes, including the anode and cathode. The absorption enhancement mechanism is analyzed, and the effects of grating parameters and incident angle are also investigated systematically. The results show the plasmonic gratings, especially the bottom grating, have an obvious improvement for light harvesting in organic layer, and an optical enhancement factor about 100% is obtained.

Polarization state control using metal nanograting

A special kind of metal nanograting which has excellent performance on polarization state controlling, is fabricated by means of interference lithography, reactive ion etching (RIE) and two-time-evaporation coating with metal. The MNG can produce angle-free elliptically polarized light via rolling the direction of grating, so it will have wide and convenient applications in the systems which need flexible polarization orientation. We fabricate the MNG and test its performances on polarization state controlling, then we simulate the process with software.