Strong Coupling Field Research Articles

Coupled atomic coherences induced by a standing wave

Atomic coherence effects with a strong standing-wave coupling field on a four-level system of hot Rb atoms are investigated. Amplitude modulation and phase modulation of the strong standing-wave field are coherently coupled in linear and nonlinear atomic polarizations in various multi-wave mixing processes. Such coupled atomic coherence effect leads to one-photon triple-bandpass filters in an electromagnetically induced transparency structure and two-photon bandgaps at two different wavelengths under two-photon resonance in the hot four-level Rb atoms. Such system can be useful for dispersion compensation in multi-channel WDM systems, all-optical switching and optical filters at multiple wavelengths.

Large splittings of the 4f shell of Ce3+ in garnets

Ab initio embedded cluster calculations on Ce(3+)-doped Y3Al5O12, Lu3Al5O12, Gd3Al5O12, Y3Ga5O12, Lu3Ga5O12, and Gd3Ga5O12, which do not make use of any adjustable parameter, support recent assignments of the seventh 4f level of Ce(3+) in garnets [Przybylińska et al., Appl. Phys. Lett., 2013, 102, 241112] and that the splitting of the 4f shell of Ce(3+) in these materials is slightly smaller than 4000 cm(-1) and much larger than the 2000-2500 cm(-1) commonly assumed in analyses of 5d → 4f emission bands. Why this wrong assumption has been working well so far is explained by the fact that the intensity of the emission to the seventh level of the 4f(1) configuration is found to be only one hundredth of the integrated intensity of the emissions to the other six levels, which group themselves into two sets of three individual levels separated by 2000-2500 cm(-1). The effective field splitting and the spin-orbit coupling splitting are found to be of the same size. From a strong field coupling point of view, the first six levels result from the interactions between (2)T(2u) and (2)T(1u) cubic levels and the higher, isolated seventh level comes directly from the cubic (2)A(2u). From a weak field coupling point of view, the first three levels result from the splitting of (2)F(5/2), the second three levels from the splitting of (2)F(7/2) and the seventh level from a strong, cubic field driven interaction between (2)F(7/2) and (2)F(5/2) components [Herrmann et al., J. Appl. Phys., 1966, 37, 1312].

Asymmetrical spectra due to atomic coherence of neighboring excited levels

In this paper, we propose to use two five-level systems to analyze asymmetrical transmitted spectra of probe field in traditional three-level Λ-type and ladder-type systems for electromagnetically induced transparency (EIT) and photonic band-gap in atoms with a strong coupling field. The five-level systems are constructed by choosing two additional levels adjoining to one of the upper or middle levels in a three-level Λ-type and ladder-type systems. Due to inhibited transition of the coupling laser to one of the two chosen levels, the asymmetrical absorptions at dressed states are obtained to be consistent with experimental observation in the original three-level systems.

Magnetic Susceptibility in Heavy Fermion Systems

Magnetic susceptibility in heavy fermion systems with degenerate f-orbitals is discussed. Especially, we confine ourselves to the case with strong spin-orbit coupling and strong crystalline field which lift the degeneracy to make a Kramers doublet the ground state. For this case, by assuming wide width of conduction band, we can derive a simple expression for the magnetic susceptibility, which is given by the product of the density of states of f-electrons and the enhancement factor due to the Coulomb repulsion between f-electrons.

Investigation of spin ordering in antiferromagnetic Fe1−xMnxPO4 with Mössbauer spectroscopy

We have investigated the spin ordering in Fe1−xMnxPO4, which is a possible cathode material for rechargeable lithium ion battery, with antiferromagnetic structure below Néel temperature (TN). The prepared Fe1−xMnxPO4 (x = 0.0, 0.1, and 0.3) samples have orthorhombic structures with space group of Pnma. These samples show the magnetic phase transition, caused by the strong crystalline field at the MO6 octahedral sites. According to the temperature dependence of magnetic susceptibility of Fe1−xMnxPO4, all samples show antiferromagnetic behaviors. The Néel temperature (TN) decreases from 114 K at x = 0.0 to 97 K at x = 0.3 with Mn concentrations. The magnetization of Fe1−xMnxPO4 decreases until the temperature reaches the spin-reorientation (TS) temperature, and then starts increasing as the temperature increases up to TN. The TS of the Fe1−xMnxPO4 were found to be 30, 27, and 24 K for x = 0.0, 0.1, and 0.3. In order to investigate the hyperfine interaction of Fe3+ ions in FeO6 octahedral sites, Mössbauer spectra of Fe1−xMnxPO4 have been taken at various temperatures from 4.2 to 295 K. The isomer shift (δ) values of the Fe1−xMnxPO4 were between 0.31 and 0.43 mm/s, indicating the high spin state of Fe3+ at all temperatures. The magnetic hyperfine field (Hhf) and electric quadrupole splitting (ΔEQ) values of Fe0.9Mn0.1PO4 at 4.2 K were determined to be Hhf = 498 kOe and ΔEQ = 2.1 mm/s. We have also observed the abrupt changes in Hhf and ΔEQ at 27 K for Fe0.9Mn0.1PO4, and decrease the value of TS of Fe1−xMnxPO4 with Mn concentrations. Our study suggests that these changes in Fe1−xMnxPO4 are originated from the strong electric crystalline field and spin-orbit coupling of FeO6 octahedral site.

Lasing without inversion with considering spontaneously generated coherence

We provide a four-level double-V type atomic system driven by two week probe fields and two strong coupling laser beams. In the condition of resonant four-wave mixing, the two probe fields can be amplified without population inversion. Due to the fact that the two excited states are close- lying upper levels of hyperfine structure, the spontaneously generated coherence (SGC) effect must be considered. Interestingly, the amplitude of gain is sufficiently enhanced with the same parameters as those in the case without considering SGC. In addition, we find that the probe gain is sensitive to the phase of two laser fields which interact with the same lower level. To be more specific, the amplitude of gain is modulated by the phase periodically but restricted by θ (the angle between two induced dipole moments). At the same time, we also analyze the influence of the coherence pumping (strong coupling fields) detuning.

Biomembrane derived porous carbon film supported Au nanoparticles for highly reproducible surface-enhanced Raman scattering

A surface-enhanced Raman scattering (SERS) substrate based on porous carbon film supported Au nanoparticles (NPs) has been successfully fabricated by using an eggshell membrane as template. The as-prepared substrate exhibited excellent sensitivity toward Rhodamine 6G (R6G) at a low concentration of 1 × 10−9 M and great reproducibility with a small relative standard deviation (RSD) (16.3%) in the intensity of the main Raman peaks of the R6G. The good SERS signals could be due to the strong electromagnetic field coupling induced by the densely assembled Au NPs and the absence of surfactant. The high reproducibility and sensitivity in SERS was also found in the detection of Sudan dye at a low concentration of 1 × 10−8 M with a RSD of less than 20%. The results not only provide a facile and green approach to an ultrasensitive SERS substrate but also represented a new strategy to utilize daily consumption waste and turned them into useful materials for inspection of the environment pollutants and food safety.

Substrates with Strong Photon-molecule Coupling Field that Enhances Protein Crystallization by Photochemical Reaction(<Special Issue>The Forefront of Protein Crystal Growth)

Substrates with Strong Photon-molecule Coupling Field that Enhances Protein Crystallization by Photochemical Reaction(<Special Issue>The Forefront of Protein Crystal Growth)

Proposed Coherent Trapping of a Population of Electrons in aC60Molecule Induced by Laser Excitation

This Letter demonstrates the possibility of generating coherent population trapping in C(60). Similar to a three-level Λ system, C(60) has a forbidden transition between the highest occupied molecular orbital (HOMO) (|a}) and the lowest unoccupied molecular orbital (LUMO) (|c}), but a dipole-allowed transition between HOMO and LUMO+1 (|b}) and between |b} and |c}. We employ two cw laser fields, one coupling and one probe. The strong coupling field is switched on first to resonantly excite the transition between |b} and |c}. After a delay, the probe is switched on; the coherent interaction between the coupling and probe fields traps the population in |a} and |c}. This forms a partially dark state in C(60), analogous to that in atomic vapors. Turning off the coupling field restores C(60)'s absorption. Pulsed lasers work as well. We use two pulses to steer the system into a dark state; when we send in a cw probe field, the electric polarization of C(60) plunges by five times, in comparison with the noncontrol case. This should be detectable experimentally.

Continuously tunable sub-half-wavelength localization via coherent control of spontaneous emission

We propose a continuously tunable method of sub-half-wavelength localization via the coherent control of the spontaneous emission of a four-level Y-type atomic system, which is coupled to three strong coupling fields including a standing-wave field together with a weak probe field. It is shown that the sub-half-wavelength atomic localization is realized for both resonance and off-resonance cases. Furthermore, by varying the probe detuning in succession, the positions of the two localization peaks are tuned continuously within a wide range of probe field frequencies, which provides convenience for the realization of sub-half-wavelength atomic localization experimentally.

Electromagnetically induced grating in an atomic system with a static magnetic field

We study the electromagnetically induced grating in an Fe=0↔Fg=1 transition interacting with a weak probe, a strong standing-wave coupling field and a static magnetic field. With a standing-wave coupling field, the phase modulation effectively diffracts a weak probe light into the first-order direction by applying a static magnetic field. Moreover, the diffraction pattern of probe beam could be dynamically tuned by manipulating the magnetic field, and the high efficiency of phase grating can be obtained by choosing the proper parameters.

Low moment NiCr radio frequency magnetic films for multiferroic heterostructures with strong magnetoelectric coupling

Magnetic/piezoelectric multiferroic heterostructures with a magnetic thin film on a piezoelectric slab provides a great opportunity to achieve a strong converse magnetoelectric coupling with great potential for voltage tunable magnetic devices. Efforts have been made in developing highly magnetostrictive RF magnetic materials with low magnetization using magnetic/piezoelectric heterostructures to generate large electric-field induced effective magnetic fields. In this work, we report on NiCr films having low magnetization and relatively large magnetostriction. Strong converse magnetoelectric coupling and large electric field tunable ferromagnetic resonance (FMR) bandwidths are achieved in layered NiCr/lead zirconate titanate (PZT) and NiCr/lead zinc niobate lead titanate (PZN-PT) multiferroic heterostructures. A large electric field induced effective magnetic field of 260 Oe for NiCr/PZT and 756 Oe for NiCr/PZN-PT was observed, corresponding to a giant magnetoelectric coupling coefficient of 13 Oe cm/kV in NiCr/PZT and 75.6 Oe cm/kV in NiCr/PZN-PT multiferroic heterostructures. A high voltage tunable FMR frequency range was observed, with fmax/fmin being 124 and 325% for NiCr/PZT and NiCr/PZN-PT. The strong converse magnetoelectric coupling of NiCr/PZT and NiCr/PZN-PT heterostructures provide great opportunities for electric field tunable RF magnetic devices.

Generation of multipartite continuous-variable entanglement via atomic spin wave

We present a proof-of-principle way to generate nondegenerate multipartite continuous-variable entanglements via atomic spin wave induced by the strong coupling and probe fields in the Lambda-type electromagnetically induced transparency configuration in an atomic ensemble. Quantum correlated/anti-correlated and entangled Stokes and anti-Stokes fields, simultaneously produced through scattering the applied laser fields off the atomic spin wave, can be achieved. This method can, in principle, be extended to flexibly and conveniently create multicolor multipartite entangled narrow-band fields to any desired order with long correlation time, which may find promising applications in quantum information processing and quantum networks.

Theoretical investigation of optical spectra and covalent effect of Cr4+ in Y2Ti2O7 and Y2Sn2O7

In this work, the complete matrix of optical spectral levels in trigonal symmetry of 3d2 (3d8) ions are established on basis of strong field coupling mechanism by using two spin–orbit coupling parameters model. The contribution of the spin–orbit coupling of ligand to the optical spectra has been included in these formulas. As an application, the optical spectra of Cr4+ in Y2Ti2O7 and Y2Sn2O7 have been studied by the complete diagonalization (energy matrix) method. The covalent effect has been studied and the difficulty about Dq parameter in explanation of optical spectra of Cr-doped Y2Ti2O7 and Y2Sn2O7 is removed. The theoretical results are in good agreement with observed data.

Photoinduced diffraction grating in hybrid artificial molecule

Photoinduced diffraction grating is theoretically investigated in a three-level ladder-type hybrid artificial molecule comprised of a semiconductor quantum dot (SQD) and a metal nanoparticle (MNP). The SQD and the MNP are coupled via the Coulomb interaction. The probe absorption vanishes under the action of a strong coupling field, indicating an effect of electromagnetically induced transparency (EIT). Based on this EIT effect, diffraction grating is achievable when a standing-wave coupling field is applied. It turns out that the efficiency of diffraction grating is greatly improved due to the existence of the MNP. Furthermore, the diffraction efficiency can be controlled by tuning the interaction strength between the SQD and the MNP. Nearly pure phase grating is obtained, showing high transmissivity and high diffraction efficiency up to 33%.

The three-photon resonant nondegenerate six-wave mixing via quantum interference in the middle level

We study the quantum interference in three-photon resonant nondegenerate six-wave mixing (NSWM) of a five-level system in which the middle level of six-wave mixing and other levels are coupled by a strong laser field. The coupling field-dependence of the NSWM signal intensity, and the spectrum of the NSWM with a coupling field, are discussed. We find that in the presence of a strong coupling field, the three-photon resonant NSWM spectrum exhibits Autler-Townes splitting, which reflects the levels of the dressed states. It also leads to either suppression or enhancement of the NSWM signal. Due to the enhancement of NSWM signal caused by quantum interference, the dressed state created by a coupling field can replace the atom intrinsic level and serve as the middle level of three-photon resonance. Thus the middle level of three-photon resonance can be controlled by a coupling field.

Laser without inversion in a Δ -configuration three-level system with cyclic transition

In the case of incoherent pumping, laser without population inversion in a resonant three-level Δ -configuration system is investigated. By taking the strong coupling field limit, we obtain the approximate steady-state analytical solution of populations and imaginary part of coherences within the dressed-state regime, and discuss the condition of the generating of laser without inversion and the dependences of population distribution and system gain on Rabi frequency of the probe and coherence fields. The results show that the resonant three-level Δ-configuration system is always in the state of no population inversion, and laser without inversion occurs if one of the two fields is strong. When one of the two fields is much stronger than the other one, the gain without inversion is independent of the two Rabi frequencies.

Phase-controlled all-optical switching based on coherent population oscillation in a two-level system

We theoretically propose a scheme of phase-controlled all-optical switching due to the effect of degenerate four-wave mixing (FWM) and coherent population oscillation (CPO) in a two-level system driven by a strong coupling field and two weak symmetrically detuned fields. The results show that the phase of the FWM field can be utilized to switch between constructive and destructive interference, which can lead to the transmission or attenuation of the probe field and thus switch the field on or off. We also find the intensity of the coupling field and the propagation distance have great influence on the performance of the switching. In our scheme, due to the quick response in semiconductor systems, a fast all-optical switching can be realized at low light level.

Highly Reproducible Surface‐Enhanced Raman Scattering on a Capillarity‐Assisted Gold Nanoparticle Assembly

AbstractA facile method based on capillarity‐assisted assembly is used to fabricate high‐performance surface‐enhanced Raman scattering (SERS) substrates employing clean Au nanoparticles (NPs). This method is better than micro‐channel way because the former may supply large‐area uniform assembly and overcome the uneven radial distribution. Such densely‐arranged assembly of Au NPs exhibits high reproducibility and large Raman enhancement factors of 3 × 1010, arising from strong electromagnetic field coupling induced by adjacent Au NPs. The spot‐to‐spot SERS signals show that the relative standard deviation (RSD) in the intensity of the main Raman vibration modes (1310, 1361, 1509, 1650 cm−1) of Rhodamine 6G at a concentration of 1 × 10−10 M are consistently less than 20%, demonstrating good spatial uniformity and reproducibility. The SERS signals of sudan dye at a 1 × 10−8 M concentration also shows high reproducibility with a low RSD of <20%. Further, the assembly substrate is stable, retaining excellent uniformity and sensitivity after storage for months. This assembly strategy integrating the advantages of low‐cost production, high sensitivity, and reproducibility would significantly facilitate practical SERS detection.

Electron spin diffusion and transport in graphene

We investigate the spin diffusion and transport in a graphene monolayer on SiO${}_{2}$ substrate by means of the microscopic kinetic spin Bloch equation approach. The substrate causes a strong Rashba spin-orbit coupling field $~0.15$ meV, which might be accounted for by the impurities initially present in the substrate or even the substrate-induced structure distortion. By surface chemical doping with Au atoms, this Rashba spin-orbit coupling is further strengthened as the adatoms can distort the graphene lattice from ${\mathit{sp}}^{2}$ to ${\mathit{sp}}^{3}$ bonding structure. By fitting the Au doping dependence of spin relaxation from Pi et al.[Phys. Rev. Lett. 104, 187201 (2010)], the Rashba spin-orbit coupling coefficient is found to increase approximately linearly from 0.15 to 0.23 meV with the increase of Au density. With this strong spin-orbit coupling, the spin diffusion or transport length is comparable with the experimental values. In the strong scattering limit (dominated by the electron-impurity scattering in our study), the spin diffusion is uniquely determined by the Rashba spin-orbit coupling strength and insensitive to the temperature, electron density, as well as scattering. With the presence of an electric field along the spin injection direction, the spin transport length can be modulated by either the electric field or the electron density. It is shown that the spin diffusion and transport show an anisotropy with respect to the polarization direction of injected spins. The spin diffusion or transport lengths with the injected spins polarized in the plane defined by the spin-injection direction and the direction perpendicular to the graphene are identical, but longer than that with the injected spins polarized vertical to this plane. This anisotropy differs from the one given by the two-component drift-diffusion model, which indicates equal spin diffusion or transport lengths when the injected spins are polarized in the graphene plane and relatively shorter lengths when the injected spins are polarized perpendicular to the graphene plane.