Hou Bi-Hui

Giant Birefringence of Lithium Niobate Crystals in the Terahertz Region

Terahertz time-domain spectroscopy (THz-TDS) is used to study the spectral response of lithium niobate crystals (LiNbO3) in the far infrared region. The optical constants are derived from the measured complex refractive index. A giant birefringence is observed in this material, and the average refractive-index difference between the ordinary wave and the extraordinary wave, no−ne, can reach up to about 1.6. Such a large birefringence is attributed to the different phonon modes of A1(z) and E(x,y). This unusual property makes LiNbO3 a promising material to be used as a functional material in the terahertz region, e.g. employed as wave-plates and polarization separators.

Photon-phonon resonance of PbB 4 O 7 crystal

We observed a photon-phonon resonance or polariton arises in PbB<inf>4</inf>O<inf>7</inf> crystal. We identified this resonance state is a phonon, ν<inf>TO</inf>=1.56THz and q=1930cm⁻¹, because the transmissivity T(ν<inf>p</inf>) is almost zero, the dielectric function ε(ν) satisfies the Lyddane-Sachs-Teller (LST) relation, and a split appears at 1.56THz in ν(k) curve.

Paramagnetic Anisotropy of CdGd2(WO4)4-δ Single Crystal

Abstract CdGd 2 (WO 4 ) 4-† single crystal was grown using the Czochralskis method. The crystal structure was tetragonal scheelite with lattice parameters a = b = 0.5203 nm and c = 1.1359 nm. There were vacancies of (WO 4 ) 2- , therefore, there were some Gd 2+ ions. Langevin paramagnetism and anisotropy were observed from the σ- T curves at room temperature. The susceptibility χ// was 3.5018 × 10 −3 , and χ was 3.4403 × 10 −2 . The anisotropy was also observed in the electron spin resonance (ESR) experiments. The anisotropic Lande factors were g // = 2.1333 and g ⊥ = 2.8411. The direction of easy magnetization was in the a-b plane. Anisotropic paramagnetic Curie constants C // and C ⊥ were not only related to macroscopic σ that was observed through the experiment, but were also related to J ⊥ and J //, which were the microscopic quantum numbers of the Gd 2+ and Gd 3+ ions. Based on the detailed analyses, the proportion of 36.8% of Gd 3+ ions to 63.2% of Gd 2+ ions in the Gd ions of the CdGd 2 (WO 4 ) 4-σ crystal was calculated, and δ was 0.638 in the single crystal.

ESR of dislocation defects in MgF2 crystals—with more than 130 line peaks

In this work, more than 130 line peaks in electron spin resonance (ESR) spectra have been discovered of the laser material MgF2 crystal in room-temperature experiments. A sample is cut from the shoulder part of the MgF2 crystal and another is from the MgF2:Co crystal. The samples were not treated by any irradiation. The same anisotropic ESR spectra of the two samples indicate that the dopant Co2+ introduces defects which induce the same multinuclear free radicals as in dislocations in the sample of MgF2. These paramagnetic solid multinuclear free radicals show good stability and their ESR spectra are found to be anisotropic. ESR signals are derived from three different types of multinuclear free radicals from a tentative simulation analysis. When the direction of the applied magnetic field is along the [100] or [010] orientation of the crystal, the magnetic field at which the ESR signals are detected ranges from 0.2294T to 0.4654T and the width of this range is 0.2362T (corresponding to an energy band of 0.233eV); the most narrow peak in the ESR spectra has a width ΔH about 1.28×10−3T. This width ΔH, equivalent to the energy difference of two neighbouring levels, is very small, only 1.85×10−7eV (or 1.46×10−3cm−1). This fact indicates that the ground state is highly degenerate and splits into nearly quasi-continuous energy levels like an energy band in an applied magnetic field. It may be served as a new starting point of solid laser exciter frequency modulation.

THz-ultraviolet spectra of KDP, NBP and PTB crystals

The ultraviolet-visible-infrared-THz transmission spectra of three oxide crystals, KH<inf>2</inf>PO<inf>4</inf>(KDP), Na<inf>5</inf>B<inf>2</inf>P<inf>3</inf>O<inf>13</inf>(NBP) and PbB<inf>4</inf>O<inf>7</inf> (PTB), have been studied. The band wide of the phonon absorption has been discussed. The maximal frequency ν<inf>LO</inf> is connected to the lightest cation ions, and the minimal frequency ν<inf>TO</inf> is connected to the heaviest cation ions for the three samples.

The reflectance and electrical properties of nanocrystalline metal Tm

The reflectance spectra R(λ) within 200nm–2500nm wavelength range of the two nanocrystalline bulk metal thulium(Tm) samples were studied. The reflectivities R(λ) of Sample 1 and Sample 2 reach their minima 2.383% at 256nm and 3.439% at 214nm respectively. These minima correspond to the plasma oscillations in nanocrystalline bulk metal Tm.