High-frequency EPR of Ho3+ ion in the LaF3 crystal

The nonlinear phase shift and nonlinear damping of spin-electromagnetic waves were theoretically studied for the first time in sub-terahertz frequency range in infinite homogeneous longitudinal magnetized multiferroics. The research was based on the solution of the Ginzburg-Landau equation. It is shown that the saturation of the phase shift occurs due to the nonlinear damping if the nonlinear damping coefficients exceed v1=108 s-1 and v2=109 s-1.

In this paper, the design and analysis of a transmission-type linear-to-circular polarization converter (LCPC) operating in the sub-terahertz frequency range is presented. The proposed structure features a simple and compact geometry. The proposed LCPC consists of four layers of fused silica with a horizontally oriented gold strip printed on the top layer of substrate. The design achieves a wide 3-dB axial ratio bandwidth (ARBW) of 52.6%(154−164GHz) under normal incidence and maintains polarization conversion performance for oblique incidence angles up to 10°. The equivalent circuit model (ECM) of the proposed LCPC validates its working as the results of ECM and full wave solver are in close agreement to each other. Furthermore, the converter exhibits an extinction ratio exceeding 15 dB within the 160−255GHz frequency band and achieves a transmission efficiency greater than 75 % across 154−254GHZ frequency range. The working of proposed LCPC is also validated through an ECM. These results demonstrate the suitability of the proposed LCPC for high-performance terahertz applications requiring efficient and broadband circular polarization.

In this paper, we have discussed a new approach for measuring the dielectric permittivity of crystalline and nanocomposite materials at subTHz frequency range. The proposed approach's idea is based on the interferometric method, where the shifts in the interference fringes are received by introducing the wedge from the epoxy risen in one arm of the interferometer. All the measuring processes are controlled by means of the LabVIEW programming language. The proposed method was experimentally verified on the Fused Silica and BK-7 glasses. The received values of dielectric permittivity are in good agreement with the one from the literature.

Terahertz applications have been extensively studied during the last decade since they allow not only increasing the bandwidth of telecom systems but also the detection of many organic molecules in solid and liquid phase, including hazardous materials such as explosives. In this contribution, we present a device that allows generating frequencies in the Terahertz domain through the heterodyning of signals emitted by two distributed feedback lasers made by ion exchange on a erbium-ytterbium co-doped glass. Thanks to the intrinsic thermal stability of the glass substrate, the slow dynamic of the amplifier medium and since the laser pairs are integrated on a single chip and identically pumped by the same sources, stable frequencies have been generated in the millimeter and sub-Terahertz frequency range, without any thermal or electrical control loop being implemented.

The evolution of the electron energy distribution function in the plasma channel created in air by the third harmonic of the Ti:Sa-laser pulse of femtosecond duration is studied. It is shown that strong nonequilibrium of such a plasma leads to the possibility to use the channel for guiding and amplification of few-cycle electromagnetic pulses in subterahertz frequency range at the time of relaxation of the energy spectrum in air determined by the vibrational excitation of the nitrogen molecules. The refractive index and the gain factor as a function of time, electron concentration and frequency of the amplifying radiation are obtained. The propagation of few-cycle radio-frequency pulses through the amplifying medium is analyzed.

Magnetic and dielectric resonances in the sub-terahertz (sub-THz) frequency range are observed in pure and Al-substituted hexagonal barium ferrite. A resonator based on magnetic excitations has been fabricated and its performance characteristics have been studied. The possible use of the resonator at sub-THz frequencies has been demonstrated. The resonator exhibited a loaded Q-factor of 150-330 in the frequency range 97-108 GHz. Dielectric resonances in a single-crystal barium hexaferrite are observed in the frequency range 75-110 GHz. The modes excited by circularly polarized electromagnetic waves show nonreciprocal propagation characteristics. The dielectric resonances may occur at a much higher frequency than ferromagnetic resonance. It is shown that degeneracy in the dielectric modes is lifted with an applied magnetic field H and that the modes can be tuned by 10 GHz or more with H. Data on frequencies of the modes versus H shows hysteresis. Theoretical predictions on H-tuning characteristics of the principal dielectric E11δ mode are in agreement with the data. The dielectric modes are of importance for the realization of low-loss devices, including resonators, isolators and phase shifters.

We present experiments on 2D photonic crystal waveguides for fluid sensing applications. Using a standard machining process, photonic crystal waveguides for the sub-terahertz (0.1 THz) frequency range are fabricated. The insertion of fluids into the active region of the crystal leads to a change of the photonic band gap properties. We present results for different non-polar liquids, which are in the good agreement with simulations.

Currently, the increasing interest of researchers is attracted by the theoretical and practical problems of mastering the sub-terahertz and terahertz frequency range. Electronic devices operating in these ranges find effective applications in various fields of science and technology: aerospace equipment, security systems, spectroscopy, medicine, biology and many others. The purpose of this work is to focus on a frequency multiplication device that allows using basic sources of relatively low frequency generation to enter the terahertz frequency range. The results of recent years obtained both on the basis of solid-state effects and with the help of vacuum electronics, in particular, magnetron-type devices, which are characterized by compactness, high resistance to radiation loads, mechanical influences, which is important for on-board equipment, are considered. It is known that at high frequencies, vacuum devices require super-precision manufacturing of decelerating systems. This is essentially the main difficulty. The article proposes a new approach based on the hypothesis of P.L. Kapitsa, which allows to significantly simplify the anode structure of a magnetron multiplier with an acceptable level of output parameters. The achievements of recent years in the field of creating sub-terahertz and terahertz frequency multipliers, mainly for on-board equipment of mobile platforms, taking into account the requirements of aerospace systems, first of all, are noted.

The present paper is a detailed account of the study of the methylene molecule trapped in matrices at 4.2 °K by electron paramagnetic resonance spectroscopy. The methylene is generated by photolysis of its diazirine precursor dissolved in the matrix material. Besides verifying that the methylene ground electronic state was a spin triplet, the first observation of the EPR spectrum revealed that the molecule was nonlinear. Through assumptions concerning the amounts of spectral averaging owing to molecular motion and the relationship of the zero‐field splitting parameters D and E with each other through an s–p hybrid model of the electronic structure, other workers showed the bond angle to be substantially bent. This was later confirmed by ourselves and others with a measurement of the isotropic carbon‐13 hyperfine interaction. Using 90.5% carbon‐13 enrichment in the present work, a more precise determination of the isotropic carbon‐13 hyperfine interaction was found to be 239 MHz. The increased resolution a...

X‐band EPR spectra of a single crystal of Gd++‐doped NH4Pr (SO4)2 · 4 H2O (APST) are recorded in the temperature range 4.2 to 410 K. The angular variation of the EPR line positions indicates the presence of two magnetically‐inequivalent Gd3+ ions. The orientations of their principal axes are determined. The Gd3+ spin‐Hamiltonian parameters are evaluated using a rigorous least‐squares‐fitting procedure. The superposition model is applied to calculate the values of the zero‐field splitting parameters b, b of Gd3+, and those of the intrinsic parameters b2 and b4. The temperature variation of the EPR spectra reveals the occurrences of two first‐order phase transitions in APST crystal at 266 and 155K.

Synthetic single crystals of chromium-and lithium-doped forsterite, namely, (Cr,Li): Mg2SiO4, are studied using electron paramagnetic resonance spectroscopy. It is revealed that, apart from the known centers Cr3+(M1) and Cr3+(M2) (with local symmetries Ci and Cs, respectively), these crystals involve two new types of centers with C1 symmetry, namely, Cr3+(M1)′ and Cr3+(M2)′ centers. The standard parameters D and E in a zero magnetic field [zero-field splitting (ZFS) parameters expressed in GHz] and principal components of the g tensor are determined as follows: D=31.35, E=8.28, and g=(1.9797, 1.9801, 1.9759) for Cr3+(M1)′ centers and D=15.171, E=2.283, and g=(1.9747, 1.9769, 1.9710) for Cr3+(M2)′ centers. It is found that the lowsymmetric effect of misalignment of the principal axes of the ZFS and g tensors most clearly manifests itself (i.e., its magnitude reaches 19°) in the case of Cr3+(M2)′ centers. The structural models Cr3+(M1)-Li+(M2) and Cr3+(M2)-Li+(M1) are proposed for the Cr3+(M1)′ and Cr3+(M2)′ centers, respectively. The concentrations of both centers are determined. It is demonstrated that, upon the formation of Cr3+-Li+ ion pairs, the M1 position for chromium appears to be two times more preferable than the M2 position. Reasoning from the results obtained, the R1 line (the 2E → 4A2 transition) observed in the luminescence spectra of (Cr,Li): Mg2SiO4 crystals in the vicinity of 699.6 nm is assigned to the Cr3+(M1)′ center.

Synthesis and catalytic properties of crystalline, microporous vanadium silicates with MEL structure

EPR spectra of Ho3+ impurity ions were recorded in single crystals of yttrium aluminum garnet (Y3Al5O12) in the frequency range of 114-170 GHz, at a temperature of 4.2 K. The measurement results indicate the substitution of Ho3+ ions for Y3+ ions in the dodecahedral position with D2 local symmetry. The magnitude of the g-factor, the hyperfine structure constant, and the energy interval between the main and the first excited nondegenerate sublevels of the main multiplet 5I8 are determined. Weak satellite signals have also been registered, the origin of which is associated with the formation of antisite defects in the environment of Ho3+ paramagnetic centers.

Synthesis, structural, and spectroscopic characterization of the linear cationic complex [LCr(III)(mu-[dmg)(3)Zn(II))Cr(III)L](2+) (1) in which L = 1,4,7-trimethyl-1,4,7-triazacyclononane and dmg is the dimethylglyoximato anion are reported. The Cr...Cr distance of 1 is 7 A. SQUID magnetic susceptibility measurements reveal the presence of long-range exchange interaction of the Cr(III) terminal ions, mediated by the diamagnetic Zn(II)(dmg)(3) "bridging ligand" (J(0) = -4.4 cm(-1), H(ex) = -2J(0)S(1)S(2), S(i) = 3/2). Multifrequency EPR measurements (S-, X-, Q-band) on frozen solutions were used to establish the intramolecular nature of the exchange coupling and to determine the zero-field splitting (ZFS) parameters and the anisotropic contributions of spin coupling. An effective spin Hamiltonian description was applied for interpretation of the spectra originating from the S(t) = 2 total spin manifold which included up to fourth-order terms for the ZFS. By the help of alternative simulations with the full coupling matrix for two spins S(i) = 3/2 (16 x 16) it could be shown that the higher-order terms in the effective description owe their origin to multiplet mixing due to competing single-ion ZFS (the absolute value of D(i) = 0.2 cm(-1)) and isotropic exchange interaction. The magnetic anisotropy related to dimer properties could be readily explained by dipolar coupling (j(z) = -0.012 cm(-1)). Implications for the interpretation of other integer-spin EPR spectra are discussed.

Multi-frequency, high-field EPR as a powerful tool to accurately determine zero-field splitting in high-spin transition metal coordination complexes