Physics
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The Physics department is committed to education and research in physics, the study of the fundamental universal laws that govern the behavior of matter and energy, and the exploration of the consequences and applications of those laws. Our department is widely known for its excellent teaching and student mentoring. Our department plays an important role in the university’s Core Curriculum. We have strong academic programs with several options for undergraduate physics majors, leading to the B.S. degree, as well as graduate curricula leading to the M.S. and Ph.D. degrees. Our research groups span a variety of fields within physics. Our principal concentrations are in Astrophysics, Relativity, Gravitation and Cosmology, Condensed Matter Physics, Lasers and Optics, Physics Education, Solar Physics, and the Space Science and Engineering Lab.
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Item Dielectric, NMR and X-ray diffraction study of Cs1-x(NH4)xH2PO4(1998) Meschia, S. C.; Lanceros-Mendez, S.; Zidansek, Aleksander; Schmidt, V. Hugo; Larson, R.Mixed crystals Cs1−x(NH4)xH2PO4 of the ferroelectric CsH2PO4 (CDP) and the antiferroelectric (NH4)H2PO4 were grown with x=0.2 (CADP0.2) in solution. The structural properties of the crystal were analyzed by means of x-ray diffraction. Dielectric measurements at several temperatures and frequencies have been performed along the three crystallographic axes in this sample and also in the fully deuterated CADP0.2 sample (DCADP0.2). NMR experiments were also performed.Item Phase coexistence in proton glass(1998) Schmidt, V. HugoPhase coexistence results from quenched structural randomness and frustrated interactions. The nature of this randomness and the frustrated interactions in proton glass are explained. The six types of ordered domains and corresponding ferroelectric and antiferroelectric phases are described, as well as the disordered paraelectric and proton glass phases. Experimental evidence for phase coexistence is presented. Parameters are introduced which describe the volume fractions of phases, and the overall amount of coexistence. This last parameter provides the basis for locating the nominal phase boundaries, and for an expression which describes the sharpness of any of the five smeared-out phase transitions which occur in proton glass crystals.Item Optical properties of RbTiOAsO4 single crystal(1998) Tu, Chi-Shun; Yeh, Y.-L.; Katiyar, R. S.; Guo, Ruqian; Schmidt, V. Hugo; Chien, R.-M.; Guo, Ruyan; Bhalla, A.S.Rubidium titanyl arsenate (RbTiOAsO4) belongs to the family of nonlinear optical crystals with the general formula M1+TiOX5+O4, where M = K, Rb, Tl, Cs and X = P, As. [1–6] The high damage threshold and broad angular acceptance have made such crystals attractive materials for frequency doubling of Nd-based lasers at λ=1.064 and 1.32 µm, and for optical parametric oscillators (OPO). In addition, the ion exchange properties also make them one of the best candidates for waveguide applications. Potassium titanyl phosphate, KTiOPO4 (KTP), is the most popular among such materials and has been used successfully in different applications. However, the orthophosphate absorption at ∼4.3 and ∼3.5 µm in KTP severely limits the oscillator output power. In contrast, RTA has a broad infrared transparency (∼0.35-5.3 µm) and exhibits no overtone absorption between 3 and 5 µm. [4] This makes the RTA crystal a potential candidate for nonlinear optical applications. At room temperature, KTP-type crystals have an orthorhombic structure with non- centrosymmetric point group C2v (mm2) and space group Pna2 (Z=8). The crystal framework is a three-dimensional structure made from corner-linked TiO6 octahedra and PO4 tetrahedra. Four oxygen ions of the TiO6 belong to PO4 tetrahedral groups which link the TiO6 groups. In our earlier Raman results, a slight softening was exhibited by several LO and TO vibrational modes of RTA. [1,2] However, there is no typical soft mode observed in the lowfrequency modes of the Raman spectra. This motivated usto carryoutBrillouinscatteringmeasurements tolook for softening in the acoustic modes. We report here both the temperature-dependent acoustic phonon spectra and wavelength- dependent refractive indices. The Cauchy equations [n(λ) = A + B/λ2 + C/λ4] of nx, ny and nz are obtained. In particular, the first direct evidence for acoustic phonon soft mode is presented.Item Temperature dependent Raman spectra of Rb1-x(ND4)xD2AsO4 mixed crystals(1998) Tu, Chi-Shun; Gao, S.-S.; Jaw, R.-J.; Hwa, L.-G.; Schmidt, V. Hugo; Brandt, Dan; Chien, R.-M.In the mixed ferroelectric (FE)-antiferroelectric (AFE) systemA1−x(ND4)xD2BO4 [A=Rb(orK,Cs)andB=As (or P)], there is competition between the FE and the AFE orderings, each characterized by specific configurations of the acid deuterons. [1–8] The random distribution of the Rb and ND4 ions is the main source to produce frustration which can increase local structural competition such that the long-range order of electric dipole disappears. Instead of a typical sharp FE or AFE phase transition, the phase coexistence becomes a characteristic in this type of mixed compounds. By a group theoretical analysis for the KDP-type structure (which contains two molecular units in a primitive unit cell); at zero wavevector, the vibrational modes in the tetragonal symmetry (space group I¯ 42d − D12 2d) can be decomposed into the following irreducible representations: Γvib = 4A1(R) + 5A2(Silent) + 6B1(R) + 6B2(R,IR) + 12E(R,IR). [9] The symmetry species A1, B1, B2 and E are Raman active. The situation in the mixed system D*RADA-x is more complicated than one in the parent crystals, because some Rb (or ND4) ions have been substituted by ND4 (or Rb) ions. In this case, the selection rule of the free AsO4 group is expected to be broken much easily than in the pure crystal. In the recent years, many measurements in D*RADAx system have been achieved on ferroelectric-side crystals x = 0.1, 0.10 and 0.28. [2–5] However, only a few experiments were done on antiferroelectric-side compounds (x ≥0.50).[6,7]A complete understanding for this mixed system is still lacking. This motivated us to carry out the polarized Raman scattering on D*RADA-0.55, 0.69 and 1.0. Here, we pay special attention to the stretching mode ν1 (near 755 cm−1) and the in-plane bending mode δ(O-D) (near 825 cm−1).Item Dielectric, NMR and x-ray diffraction study of pseudo-one-dimensional Cs1-x(NH4)xH2PO4(1999) Meschia, S. C.; Lanceros-Mendez, S.; Zidansek, Aleksander; Schmidt, V. Hugo; Larsen, R.Mixed crystals Cs1−x (NH4) x H2PO4 of the ferroelectric CsH2PO4 (CDP) and the antiferroelectric NH4H2PO4 were grown with x = 0.2 (CADP0.2) in solution. The structural properties of the crystal were analyzed by means of X-ray diffraction. Dielectric measurements at several temperatures and frequencies have been performed along the three crystallographic axes in this sample and also in the fully deuterated CADP0.2 sample (DCADP0.2). Dielectric and NMR experiments in a powdered sample were also performed. The shift of the transition temperature as a function of x and deuteration, and the changes in the properties of the different phases together with, the thermally-activated conductivity found in the paraelectric phase will be discussed and related with the several relaxation mechanisms measured in the NMR experiments.Item Dynamical model for phase coexistence in proton glass(1998-02) Schmidt, V. HugoItem Piezoelectric polymer actuators for active vibration isolation in space applications(1999) Bohannan, G; Schmidt, V. Hugo; Brandt, Dan; Mooibroek, MA lightweight actuator for active vibration isolation in space applications is being developed to replace the heavy electromagnetic systems now in use. The actuator has a low effective spring constant that provides for passive vibration damping down to sub-Hertz frequencies while allowing the isolated experiment to follow the near-dc bias motion of the spacecraft. The actuator is currently optimized for the vibration level of the Space Shuttle and assembled from a pair of bimorphs in a leaf-spring configuration. Changing the size and number of sheets used in construction can vary electromechanical properties. Passive damping has been demonstrated in one and two-dimensional tests. For large (greater than a few kilograms) suspended masses, the system is underdamped and relative velocity feedback must be used to remove the resonance. Real-time control of the resonance frequency is achieved by controlling the voltage applied to the actuator with feedback from a displacement sensor. A folded pendulum seismic monitoring device was adapted for use as a one-dimensional low frequency test platform and has obtained accurate measurements of the effective spring constant and damping coefficient. Single-degree-of-freedom active feedback testing is also being conducted using this device. Two-dimensional (three-degree-of-freedom) passive damping tests were conducted on NASA's KC-135 Reduced Gravity Platform in March 1998.Item Piezoelectric polymer actuator and material properties(1996) Schmidt, V. Hugo; Brandt, Dan; Holloway, F; Vinogradov, A. M.; Rosenberg, DThis paper presents the construction and performance of a PVF/sub 2/ [poly(vinylidene fluoride), (CH/sub 2/CF/sub 2/),] thin film piezoelectric actuator. In addition, the paper discusses the methods used to characterize the viscoelastic properties of the actuator material.Item An electret accelerometer for use in active vibration control systems(1996-08) Meschia, Steven C. L.; Schmidt, V. Hugo; Taubner, SAn electret accelerometer was designed which can easily be integrated with piezoelectric actuators in order to actively control sub-audio vibrations.Item Dielectric permittivity in paraelectric/ferroelectric coexistence region in several proton glasses(1995) Howell, Francis L.; Fundaun, I. L.; Stadler, S.; Meschia, Steven C. L.; Tu, Chi-Shun; Schmidt, V. HugoWe present results for the complex permittivities of several proton glasses of the form M/sub 1-x/(NZ/sub 4/)/sub x/Z/sub 2/AO/sub 4/, where M=Rb, Z=H or D, and A=As or P. All measurements were made perpendicular to the ferroelectric axis, so no effects of domain wall motion occurred. Phase coexistence was apparent in all species. The phosphate glasses exhibited a much narrower coexistence composition range than the arsenate glasses.