| Electric-Field Effects in ESR Spectrum of Low-Spin Center Ni3+ in KTaO3 Crystals (Preprint) |
APR 2007 |
7 pages |
| Authors:
L. S. Sochava; S. A. Basun; V. E. Bursian; A. G. Razdobarin; Dean R. Evans; RUSSIAN ACADEMY OF SCIENCES SAINT PETERSBURG IOFFE PHYSICAL-TECHNICAL INST
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 | Electric-field effects in ESR spectrum of low-spin (S=1/2) tetragonal center Ni3+ was studied in KTaO3 single crystals. Orientation of the centers as well as splitting of the resonance lines was found resulting from the external E-field interaction with the electric dipole moment of the center. The value of the dipole moment was determined to be p=103D=21.4 eAngstrom. An analysis of the experimental results allowed us to make a reasonable choice ... |
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| Liquid Crystal Bragg Gratings: Dynamic Optical Elements for Spatial Light Modulators (Preprint) |
JAN 2007 |
18 pages |
| Authors:
Richard L. Sutherland; Vincent P. Tondiglia; Lalgudi V. Natarajan; Jeremy M. Wofford; Stephen Siwecki; Gary Cook; Dean R. Evans; Pamela F. Lloyd; Timothy J. Bunning; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH SURVIVABILITY AND SENSOR MATERIALS DIV/HARDENED MATERIALS
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| Bragg gratings yield a single diffracted order when irradiated by a coherent beam at the appropriate Bragg angle. In many cases, nearly all of the energy of the incident beam can be coupled to the diffracted beam. Hence these gratings can form many useful optical elements, and this has been realized in 1-D, 2-D, and 3-D photonic crystals. Bragg gratings made with liquid crystals offer the added dimension of dynamic ... |
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| Contra-Directional Two-Beam Coupling for Variable Rear Reflectivities in LiNbO3:Fe (Preprint) |
AUG 2006 |
17 pages |
| Authors:
Dean R. Evans; Gary Cook; Mohammad Saleh; Gerald Landis; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS AND MANUFACTURING DIRECTORATE
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| 1. Coating the rear c-surface, we are able to produce a controlled range of rear reflectivity on a photorefractive LiNb03 crystal. 2. The contra-directional two-beam coupling does not vary significantly with reduced rear reflection. This agrees with theoretical calculation. 3. The time response of two beam coupling increases with reduced reflectivity. 4. Future work will produce similar work on other types of photorefractive crystals. |
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| Self-Pumped Photorefractive Reflection Gratings in Fe:KNbO3 (Preprint) |
AUG 2006 |
41 pages |
| Authors:
Gary Gook; Mohammad Saleh; Dean R. Evans; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH SURVIVABILITY AND SENSOR MATERIALS DIV/HARDENED MATERIALS
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| High gain confirmed in off-axis geometries for Fe:KNbO3 Mismatch between theory and experiment for mid-range crystal angles, especially for the a-c plane* Large apparent variation in the effective trap density with crystal angle* Modified theory gives a good fit to experimental data* Mechanism for trap density anistropy is uncertain, but may be due to stochastic layering of impurities during crystal growth*, or from the Franz-Keldysh Effect |
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| Photovoltaic Field-Induced Self-Phase Modulation in Liquid Crystal Cells (Preprint) |
JAN 2006 |
12 pages |
| Authors:
Jennifer L. Carns; Gary Cook; Mohammad A. Saleh; Svetlana V. Serak; Nelson V. Tabiryan; Sergei A. Basun; Dean R. Evans; ANTEON CORP DAYTON OH
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| We show that photovoltaic fields generated internally in LiNbO3:Fe substrates are capable of efficiently reorienting liquid crystal molecules leading to new concepts of optically addressable light modulators. Using an arrangement consisting of a liquid crystal layer in contact with one or more LiNbO3:Fe photovoltaic substrates, we observe spatial filtering due to self-phase modulation in a planar oriented cell. The LiNbO3:Fe substrates are arranged such that light propagates along the +c ... |
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| A New Type of Potassium Niobate Crystal: Utilizing the Potassium Sites (Preprint) |
JAN 2006 |
18 pages |
| Authors:
Dean R. Evans; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH STRUCTURAL MATERIALS BRANCH/NONMETALLIC MATERIALS DIV
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| Darker regions (perturbed Fe- FeNb near a AgK) in the crystal exhibit strong contra-directional-TBC. There is a similar affect for interchanging NiNb for FeNb and RbK for AgK. AuK should work as well, but there's no evidence yet. The presence of Ag changes the local environment, perturbing the other impurities (i.e. Oh-), and the phonon/Raman modes are strongly affected. Ag was then purposely used as a codopant KNbO3:Fe, Ag and ... |
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| Self-Pumped Photorefractive Gratings in Fe:KNbO3 (Preprint) |
JAN 2006 |
16 pages |
| Authors:
Dean R. Evans; G. Gook; J. L. Carns; M. A. Saleh; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH SURVIVABILITY AND SENSOR MATERIALS DIV/HARDENED MATERIALS
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| *High gain confirmed in off-axis geometries for Fe:KNbO3; *Mismatch between theory and experiment for mid-range crystal angles, especially for the a-c plane; *Large apparent variation in the effective trap density with crystal angle; *Modified theory gives a good fit to experimental data; *Mechanism for trap density anisotropy is unclear. |
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| Self-Activated Liquid Crystal Cells Using Photovoltaic Substrates (Postprint) |
JAN 2006 |
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| Authors:
Jennifer L. Carns; Gary Cook; Mohammad A. Saleh; Svetlana V. Serak; Nelson V. Tabiryan; Dean R. Evans; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS AND MANUFACTURING DIRECTORATE
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 | We show that photovoltaic fields are capable of efficiently reorienting liquid crystals, leading to new concepts of optically addressable light modulators. Using an arrangement consisting of a liquid-crystal layer between LiNbO3:Fe photovoltaic substrates, we observed spatial filtering due to self-phase modulation in a planar oriented cell and nonlinear transmission between crossed polarizers in a twist-oriented cell. These processes do not require an external electric field. The substrates are arranged such ... |
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