Kei. H Yang

Kei. H Yang
National Chiao Tung University | NCTU · Institute of Photonics System

PhD

About

89
Publications
10,287
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2,116
Citations
Citations since 2017
1 Research Item
216 Citations
2017201820192020202120222023010203040
2017201820192020202120222023010203040
2017201820192020202120222023010203040
2017201820192020202120222023010203040
Introduction

Publications

Publications (89)
Article
Full-text available
The analytical distribution of the electric field in a micro-lens made of polymer-stabilized blue phase liquid crystals (PS-BPLCs) between two electrodes has been derived, and ray bending and focusing for the o (ordinary) and e (extraordinary) rays caused by the field-induced extended Kerr effect on the PS-BPLC have also been calculated. Those calc...
Article
Full-text available
We have developed a simple optical method based on measurements of phase retardation versus out-of-plane cell rotation angle and data analyzed by extended Jones matrix method to obtain pretilt angles of inverse twisted nematic (ITN) and tilted homeotropic liquid crystal (LC) cells. In our Jones-matrix calculations, we have assumed a constant pretil...
Article
If the signal in a medical X-ray imaging detector is formed by integrating the scintillation (or electrical) pulses, rather than by counting them, the signal-to-noise ratio is reduced by a factor which depends on the pulse height distribution. Formulas are expanded from Swank's publication to derive the signal-to-noise ratio for any given optical o...
Article
In general, the optical properties of any general twisted nematic cells consist of two complementary effects: LC-birefringent and LC-director-twist effects. In this paper, electro-optical properties of ITN cells without chiral dopants with different pretilt angles have been investigated for the first time to differentiate the LC-birefringent effect...
Article
We have developed a simple optical method and analyzed data by extended Jones matrix method to obtain pretilt angles of invesed twist nematic (ITN) and tilted homeotropic liquid crystal (LC) cells. We have compared the measured pretilt angles of the ITN cell with those of an accompanying tilted homeotropic (ATH) cell. The results showed increasing...
Article
Display pixels of liquid-crystal-display televisions (LCD TVs) on thin-film-transistor (TFT) array are getting smaller. This paper introduced the method of voltage imaging technique, which developed and provides initial insight into the thin-film-transistor array flaw detection and measurement for ultra-high-definition (Ultra HD, UHD) LCD TV applic...
Article
Full-text available
We have developed a general approach to perform direct measurements of the pretilt angles from 0° to 75° in hybrid-aligned nematic (HAN) liquid-crystal cells whose cell gaps can also be accurately determined with the help of known pretilt angles. In this paper, we have used a Zeeman laser system to measure the angular-dependence phase retardation o...
Article
For the first time we report direct measurements on asymmetric pretilt angles of OCB cell (pi‐cell) with results in good agreement with the pretilt angles measured on accompanying tilted homogenous cells fabricated by using same material and processing steps. Our method has potential applications to monitor the changing in pretilt angles of fresh m...
Patent
Full-text available
An in-cell capacitive touch panel is disclosed. The present invention utilizes a sensing unit that comprises a sensing liquid crystal capacitor and three transistors to detect touch events. A first transistor is connected to a first gate line and the sensing liquid crystal capacitor and controlled by the first gate line to charge the sensing liquid...
Patent
Full-text available
A liquid crystal display panel includes a lower substrate, a printed circuit board, at least one connection unit and a plurality of readout lines. The connection unit is adapted to connect the printed circuit board to a periphery region of the lower substrate, and has a driver. The readout lines are extended from the lower substrate to the printed...
Article
Full-text available
Modern thin-film-transistor-driven twisted nematic (TN) products on the market require thin cell gaps below the value to satisfy the condition of the Gooch-Tarry first minimum in transmission for fast response times and wide viewing angles. For the first time to our knowledge, we have developed a simple experimental method based on a new configurat...
Article
We have utilized a transmission ratio (TR) between curtain-shaped (Curtain) Mura and non-Mura zones as a key parameter to characterize the optical appearance of Curtain Mura occurred on a 13.3-in TFT–TN panel (Mura sample) after bonding process to place silicon-based driver-IC chips on one of the panel substrates using anisotropic conductive film a...
Article
Full-text available
We have proposed a sawtooth photonic crystal formed by Si-SiO<sub>2</sub> periodic layers designed on a planar medium as a polarizer. The polarizer can produce H-polarized light very efficiently because the frequency of E-polarized light is chosen at the photonic band gap but that of H-polarized light at the photonic conduction band. The best polar...
Article
A novel composite bump, Smart bump, structure has been successfully developed for chip-on-glass (COG) package using non-conductive adhesive film (NCF). We have successfully verified the low contact resistance and high reliabilities using Smart bump and COG NCF process for the packages of 17 “W, 12.1” and 2.4 “TFT-LCD modules. We have realized that...
Article
Full-text available
In this paper, we report the thermally induced light leakage in in-plane-switching liquid crystal displays (IPS LCDs) that have a built-in small-angle deviation (< 4 deg) between the polarization axis of a polarizer and the rubbing directions for liquid crystal (LC) alignment. We have found that the thermally induced light leakage depends strongly...
Article
Full-text available
A novel AGC-8D (asymmetric gate-coupled eight-domain) VA mode has been successfully developed to effectively reduce the 60-degree off-axis color difference (Δ u'v') of skin color to below 0.02. Compared to other published eight-domain VA modes, the AGC-8D HVA mode has also distinct advantages of higher panel transmittance, lower panel-manufacture c...
Article
For the first time, we have developed a field-sequential 3.5″ VGA zigzag TFT-driven OCB prototype that the splay-to-bend transition of the OCB LC was initiated by zigzag TFTs to enable a design of 64.5%-aperture ratio. We also optimize the light transmittance through the OCB LC medium to obtain a total panel transmittance of 15.2 % by a novel drivi...
Article
A novel low-cost and high contrast-ratio IPS (in-plane switching) LC mode, named Advanced Super Non-Organic Overcoat (AS-NOOC), has been successfully developed. Compared to the published AS-IPS mode, the AS-NOOC mode has the advantages of simpler process for lower manufacture cost by the elimination of a lithographic process step to form thick orga...
Article
Full-text available
— By using a new pixel design and a novel driving scheme that adds a bias electrode and a bias TFT to the ordinary pixel structure, a high-contrast-ratio and wide-viewing-angle LCD mode, refered to as the biased vertical-alignment (BVA) mode, has been sucessfully developed. Compared to the published data on the PVA and MVA modes, the BVA mode has a...
Article
Full-text available
A cost-effective wide-viewing-angle LCD mode, named Biased Vertical Alignment (BVA) mode, has been successfully developed by using a novel driving scheme and a new pixel design that adds a bias electrode and a bias TFT to the ordinary pixel structure. Compared to PVA and MVA modes, the BVA has a distinct advantage of lower manufacture cost due to t...
Article
In a previous publication, we have investigated the Advanced Super'-IPS (AS”-IPS) structure to obtain higher aperture ratio and low crosstalk. In this paper, we propose a novel electrode structure, named AS”-IPS, to reduce the thickness of the organic layer used in AS”-IPS for higher manufacture yield and lower manufacture cost.
Article
Full-text available
The growth rate of thin-film-transistor liquid crystal display (TFT-LCD) industries is faster than predicted due to the possible replacement of a cathode-ray tube television (CRT-TV) by a liquid crystal display television (LCD-TV). The in-plane switching (IPS) mode has been known as an excellent technology for realizing a wide viewing angle for LCD...
Article
Full-text available
We have measured intrinsic light leakage of VA and IPS LC cells between “ideal” crossed polarizers as a function of temperature. The measured intrinsic light leakage of VA LC cell were independent of temperature up to the nematic-to-isotropic transition temperature in comparison to a increasing light leakage as temperature increases in IPS LC cells...
Article
Full-text available
The replacement of cathode ray tube (CRT) by thin-film-transistor liquid-crystal display (TFT-LCD) in TV applications requires the implementation of LC modes with wide viewing angles and excellent video display quality. Although the in-plane switching (IPS) mode has been known as an excellent technology for realizing wide viewing angles, it has a l...
Article
Full-text available
In thin-film-transistor liquid-crystal display (TFT-LCD), particularly pixel-electrode configuration of in-plane switching (IPS) mode, crosstalk caused by capacitive coupling between pixel electrodes and data lines could result in image degradation. We derived the capacitive coupling ratio (CCR) of the IPS cell and analyzed the CCR of three convent...
Article
Full-text available
— The TFT-LCD market is growing rapidly, and the replacement of CRT TV by LCD TV requires the implementation of LC modes with wide viewing angles and high brightness. The IPS mode is an excellent technology to realize wide viewing angles, but it has a low aperture ratio that has now been improved by Advanced Super-IPS (AS-IPS). In this paper, we pr...
Article
Full-text available
The IPS Mura related to array process is analyzed from its optical properties by examining enhanced macro and micro digital images using a novel DC ion-charging method. Image sticking and time-dependent flicker have been investigated by a bipolar DC voltage-stress method on three different IPS test-cell structures using a TN cell as a reference. Th...
Article
Full-text available
The technique used to align liquid crystals-rubbing the surface of a substrate on which a liquid crystal is subsequently deposited-has been perfected by the multibillion-dollar liquid-crystal display industry. However, it is widely recognized that a non-contact alignment technique would be highly desirable for future generations of large, high-reso...
Article
Full-text available
We have applied the simulated TFT-type circuit to direct drive a hardwired Si-based chip filled with the AFLC mixture by varying the values of storage capacitor and gate on-time. The results indicate that the gate on-time has to be comparable to or larger than the response time in order to fully switch the display. Adding a storage capacitor is eff...
Article
Full-text available
Low voltage and wide-viewing-angle single-domain and two-domain twisted nematic liquid crystal displays (TN-LCDs) can be achieved by using a single-layer twist discotic film with negative birefringence as a compensation film. The compensated TNs have also higher contrast ratio and less color-shifts over the uncompensated ones. The compensated t...
Article
Full-text available
A single-layer twist discotic film with negative birefringence is used to compensate either a single-domian (1D) TN or a two-domain (2D) TN with advantages of higher contrast ratio, wider viewing angles, lower operating voltage, faster response times, and lower color-shift over the uncompensated ones, respectively. The compensation on 2DTN has the...
Article
Full-text available
The dynamic evolution processes of fringe-field induced disclinations of vertically aligned LC light valves were directly imaged for the first time by using a CCD camera with 1 ms time resolution. Various switching patterns corresponding to different fringe fields, full off (dark) to full on (bright), interlaced column on and off to full on, checke...
Article
Full-text available
We have discovered that single evaporation of SiO2 can align liquid crytstal either homogeneously or homeotropically depending on the dielectric anisotropy of liquid crystal being positive or negative, respectively. Van der Waals potential taking into account the anisotropy of LC polarizabilities have been used to explain the alignment mechanism Th...
Article
Full-text available
For reflective liquid crystal displays, we report a band-shifted double twist nematic (BSDTN) mode that have advantages of achromatic spectral response, wider viewing angle, and faster switching than regular uncompensated normally-black twist nematic modes. Experimental results on a band-shifted twisted-film compensated twist nematic (BSTFTN) mode...
Article
Projectors that use LCOS lightvalves face special contrast requirements. Most configurations for reflective light valves employ tilted beam-dividing coatings that see both bright and dark polarization states. The optics must then be designed to eliminate polarization mixing at these coatings, which ordinarily arises when the S and P planes for diff...
Article
We have characterized the MLC00089 antiferroelectric liquid crystal (AFLC) mixture in terms of tilt angle, reflectance, and response time as a function of applied voltage. The derived highest contrast ratio was about 700 to 1. We also applied the simulated thin-film-transistor (TFT)-type circuit to direct drive a hardwired Si-based chip filled with...
Article
Single-domain nematic liquid crystal (LC) devices based on either the polarization-rotation or the birefringent effect or both are investigated for reflective spatial light modulators (SLMs). We evaluate each LC mode in terms of its contrast ratio, optical efficiency, operating voltage and its tolerance in cell-gap. We study the hybrid-aligned, the...
Article
Full-text available
A polarizing microscope is used to measure the electro-optic properties of nematic light valves on a spatial, spectral, and time-resolved basis. Under the quiescent uniform twist approximation(8), the response of the liquid crystal (LC) layer can be broadly characterized by a universal polarization conversion efficiency (PCE) function (essentially...
Article
Projection display in today's market is dominated by cathode ray tubes (CRTs). Further progress in this mature CRT projector technology will be slow and evolutionary. Liquid crystal based projection displays have gained rapid acceptance in the business market. New technologies are being developed on several fronts: (1) active matrix built from poly...
Article
A prototype reflective spatial light modulator (SLM) system has been developed for writing megabit pages of data into a holographic medium at a rate of 12 pages per minute. The SLM is based upon a crystalline-silicon reflective active-matrix array with integrated data drivers, using liquid crystal (LC) electro-optics and a personal computer system...
Article
Full-text available
A prototype 28-in.-diagonal desktop data monitor capable of displaying 2048 × 2048-pixel images has been designed, built, and evaluated. The monitor uses optical projection technology. A reflective, crystalline silicon active-matrix light valve using liquid crystal electro-optics and a digital electronic interface architecture is described. This re...
Article
Full-text available
Projectors that use reflective light valves must employ beam splitters or analogous components to separate bright-state light from dark-state light, since both states must propagate in the space above the light valve. Polarization ray tracing shows that beam splitters will not usually achieve high rejection of dark-state light when the beam has the...
Article
Full-text available
Single-domain nematic liquid crystal (LC) devices based on the polarization-rotation effect, the birefringent effect, or both have been investigated for reflective spatial light modulators (SLMs) which use a polarizing beam splitter to separate the input light beam from its orthogonal output beam. We have evaluated each LC mode in terms of its cont...
Article
Full-text available
The twisted nematic liquid crystal phase grating, using patterned alignment with opposite twist angles for reflective spatial light modulators, is analyzed with respect to operating mode, diffraction efficiency and operating voltage including the effect of disclination lines between opposite twist domains. In general, the high-field difflactive...
Article
Full-text available
A mirror structure for reflective Si based light valves was fabricated using chemical mechanical polishing and a thin 150 nm Al(Cu)/Ti mirror to minimize hillock formation. The use of chemical-mechanical polishing planarization resulted in only a 1% loss in reflectivity from topography under the mirrors. The reflectivity for pixel sizes from 7.5–40...
Article
Single-domain nematic liquid crystal (LC) devices based on either the polarization-rotation or the birefringent effect or both have been investigated for reflective spatial light modulators (SLMs) which use a polarized beam splitter to separate the input light beam from its orthogonal output beam. We have evaluated each LC mode in terms of its cont...
Article
— A mirror structure for reflective Si-based light valves was fabricated using chemical-mechanical polishing and a thin 150-nm Al(Cu)/Ti mirror to minimize hillock formation. The use of chemical-mechanical polishing planarization resulted in only a 1% loss in reflectivity from topography under the mirrors. The reflectivity for pixel sizes from 7.5...
Article
The twist nematic liquid crystal diffracting grating using patterned alignment with opposite twist angle for reflective SLM have been analyzed in terms of operation mode, diffraction efficiency, and operation voltage. In general, the normally white modes have higher operating voltages, but faster response time than normally black modes which have b...
Article
Full-text available
A model has been developed to account for the occurrence of flickers and image-stickings in TN or two-domain TN cells aligned by polyimide (PI) films with one of the films subjected to uv radiations prior to rubbings. The probability of flickers and image-stickings is proportional to the imbalance in the charge densities trapped on the two interfac...
Article
Iso-contrast curves as a function of viewing angle between eight gray levels in sequence have been investigated for two-domain twisted nematic liquid crystal displays. The optimal twist angle has been found to be approximately 80°. The two-domain 80°-twisted nematic LCD shows a large viewing zone of ± 45° in the vertical and ± 60° in the horizontal...
Article
Full-text available
Optical second-harmonic generation and ellipsometry were used to study molecular alignment in an interfacial region and the deviation of the layer normal from the surface-rubbing axis in the smectic-A phase of a ferroelectric liquid crystal. The results can be well explained by the surface electroclinic effect.
Article
Full-text available
A 1-in-wide, 577-dot/in, and 4:1 multiplex ferroelectric-liquid-crystal (FLC) shutter array has been fabricated and tested for optical performance. The array has a cell gap of 2.8 μm and is surface stabilized with an FLC material of high spontaneous polarization (140 nC/cm<sup>2</sup>) and fast switching time (16 μs) at room temperature. It is capa...
Article
Full-text available
Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies
Article
Full-text available
Based on the 4×4 matrix method for inhomogeneous uniaxial media by Berreman [J. Opt. Soc. Am. 62, 502 (1972); 63, 1374 (1973)] and by Wöhler et al. [J. Opt. Soc. Am. A 5, 1554 (1988)], a simple method to eliminate the Fabry–Perot effect caused by optical discontinuities at the input and output interfaces has been developed. It facilitates an easy c...
Article
Full-text available
Recent experimental results indicate that bistability is difficult to achieve in surface‐stabilized ferroelectric liquid‐crystal devices with high spontaneous polarization (P s ) materials. We formulated the basic equations to analyze the bistability as a function of the conductivity and thickness of the alignment layers using P s as a parameter. I...
Article
Full-text available
The transmissive Fabry–Perot interference peaks of a filled twisted nematic (TN) cell as a function of wavelength, from 400 to 600 nm and from 1100 to 2000 nm, have been used for the determination of the cell gap. Theoretical formulations have been developed to calculate the effective indices of refraction including the dispersive effect, as well a...
Article
Full-text available
A simulated thin‐film transistor (TFT) circuit has been built to drive the twisted nematic (TN) cell for the measurements of charge retention and the transmission versus peak voltage applied to the drain electrode of the simulated TFT using the gate pulse width as a parameter. The established rule that the transmission of the TN cell depends only o...
Article
The transient ionic current in a ferroelectric liquid crystal (FLC) cell was measured as a function of applied voltage at different temperatures. The measured current shows a delay peak which decays rapidly to a steady-state value. The steady-state current exhibits a thermal activated behavior with an activation energy of 0.94 eV, and depends expon...
Article
Full-text available
The bistability of surface-stabilized ferroelectric liquid crystal (FLC) devices using ion-free FLC mixtures has been analyzed as a function of the spontaneous polarization, the thickness of the insulating alignment layer, and the percentage of chiral dopants in the achiral host. A memory time that scales with the rotational viscosity of the FLC wa...
Article
Based on a collective switching model coupled to a simplified continuity equation for impurity ions, the internal electric field and light transmission of a surface‐stabilized (SS), layer‐tilted ferroelectric liquid‐crystal (FLC) cell with insulating alignment layers have been calculated as a function of time, under bipolar voltage pulses. The pola...
Article
Using an electro‐optical method, we have determined the director tilt angle, the layer‐tilt angle, and the quiescent‐state azimuthal angles of a surface‐stabilized ferroelectric liquid‐crystal (SSFLC) cell as a function of temperature in the smectic C phase. The method is based on a collective switching of the director’s conical motion due to the i...
Article
In order to determine the empty cell gap of a liquid‐crystal (LC) cell to better than 1% accuracy, the empty LC cell has been modeled as an optical medium consisting of seven layers with an air gap representing the true cell gap in the middle layer. The given index of refraction and thickness for each layer, optical reflections as a function of wav...
Article
We have used simple optical methods to determine, simultaneously, the layer-tilt, pretilt, quiescent state azimuthal, and tilt angles of surface-stabilized ferroelectric liquid crystal (SSFLC) devices as a function of temperature. In a SSFLC cell aligned by rubbed polymer films, the measured pretilt angles are small and the layer-tilt angle is, in...
Conference Paper
Based on a collective switching model and a layer-tilted free-energy model with surface interactions, the authors have determined the cone, the layer-tilt, the quiescent state azimuthal angles, the director twist angles at quiescent states, and the ratio of polar to nonpolar interaction coefficients of surface-stabilized ferroelectric liquid crysta...
Article
Continuous bipolar switching of layer-tilted states in ferroelectric liquid crystals (FLC) can be explained by a collective mode including the interaction of the external field with the spontaneous polarization and the dielectric anisotropy of the FLC medium. A domain-nucleation model is more suitable to account for the switch-on starting from a qu...
Article
Full-text available
Experimental results on the electro‐optical behavior of uniform layer‐tilted ferroelectric liquid crystals (FLCs) are reported for the first time. The special arrangement of the uniform layer‐tilted state, with the spontaneous polarization parallel to the cell substrates, responds equally to either polarity of the electric field without a storage e...
Article
The phase retardation‐extremum method offers a fast and simple way to measure the pretilt angle of nematic liquid crystal (NLC) cells. Due to optical absorption of the dissolved dyes, such a method is not suitable to measure the pretilt angle of a guest‐host (GH) NLC cell. We have obtained a simple and fast method to determine the pretilt angle of...
Article
A simple optical imaging method is developed for quick evaluation of wafer surface quality and warpage. Surface irregularities 50-100 angstroms deep can be detected by this method. The detection limit is about 270m for the radius of curvature. The sense of curvature can be ambiguously determined by image contrast and image size. The principle of th...
Article
The possibility of increasing the degree of multiplexing of twisted nematic cells has been investigated by taking the following factors into consideration: unequal elastic constants and arbitrary dielectric anisotropy for the liquid crystal medium, and a general anisotropic interfacial potential. It can be shown that the achievable degree of multip...
Article
Full-text available
The image formation and the resolution of a self‐contained electrophoretic x‐ray imager have been investigated. The electrophoretic suspension contained pigments and counterions, ionic surfactants, and extraneous charges. Rate equations have been formulated to describe the transport properties of the ionic surfactants from the low to high field reg...
Article
Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies
Article
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The integrated birefringence of a surfactant (C 1 6 H 3 3 NH 2 )‐aligned methoxybenzylidene butylaniline cell as a function of applied magnetic field (up to 100 kG) has been measured. The Oseen and Frank elastic continuum theory and a generalized torque balance equation at the interface have been utilized for the calculation to fit the measured dat...
Article
A general formula for calculating the Freedericksz transition of twisted nematic liquid crystal cells has been derived by taking into consideration the following factors: unequal elastic constants and arbitrary dielectric anisotropy for the liquid crystal medium, and a general form of the anisotropic liquid crystal‐to‐substrate interfacial potentia...
Article
Based on the Oseen and Frank elastic continuum theory of nematic liquid crystals and on a generalized torque balance equation at the liquid crystal-to-substrate interface, static deformations of a semi-infinite liquid crystal (LC) medium and a homogeneous LC cell have been investigated using the anisotropic LC-to-substrate anchoring energy C as a p...
Article
Full-text available
Based on the Oseen and Frank elastic continuum theory of nematic liquid crystals, and on a generalized torque balance equation at the interface, the magnitude and the gradient of the tilt angle of liquid crystal molecules at the interface have been calculated in a homogeneous cell as a function of applied voltage and liquid crystal‐to‐wall anchorin...
Conference Paper
The feasibility of an x-ray imaging device based on photoconductive control of an electrophoretic display has been explored. Contrast ratios of 18 to 1 and resolutions of 8 line pairs/mm have been measured. The radiation to reflectance transfer characteristic is non-linear, with substantially less sensitivity to small exposures. Radiation exposures...
Article
Full-text available
We report the construction and operation of a self‐contained electrophoretic x‐ray image cell which, between two transparent‐electrode coated glass plates, has an electrophoretic liquid in direct contact with radioconductive amorphous selenium. The image cell has a built‐in memory which holds the x‐ray image after a transitory x‐ray exposure. The x...
Article
Full-text available
We have observed 5d‐to‐5d energy transfer from trivalent Tm to Nd in YF 3 and LuF 3 and Nd to Ce in YF 3 . In a YF 3  : 5 mol% Tm : 1 mol% Nd sample, the probability of energy transfer from Tm<sup>3+</sup> to Nd<sup>3+</sup> was determined to be 0.94. The 5d‐to‐5d energy transfer has the possibility of broadening the optical pumping bands of the Li...
Article
Full-text available
We have measured the vacuum-uv excitation spectra of interconfiguration (5d14fn-1 to 4fn) and intraconfiguration (4fn to 4fn) transitions of Nd-, Er-, and Tm-doped LaF3, YF3, LuF3, and LiYF4. In Nddoped samples the observed vacuum-uv excitation spectra of interconfiguration transitions differ completely from those of intraconfiguration transitions....
Article
Full-text available
Broad‐band uv flurescence is reported for LaF 2  : Ce<sup>3+</sup> (2760–3120 Å) and LuF 3  : Ce<sup>3+</sup> (2880–3220 Å). The five‐peak excitation spectrum expected for the 5d state of Ce<sup>3+</sup> in a noncubic crystal field is observed. The fluorescence quantum yields for LaF 3  : 1% Ce<sup>3+</sup> and LuF 3  : 0.1% Ce<sup>3+</sup> are 0.9...
Article
Full-text available
Broad‐band vacuum ultraviolet (VUV) fluorescence has been observed in Nd<sup>3+</sup>‐, Er<sup>3+</sup>‐, and Tm<sup>3+</sup>‐doped LaF 3 , YF 3 , LiYF 4 , and LuF 3 by electron‐beam and VUV excitation. The VUV excitation spectra indicate a large Stokes shift (≳5000 cm<sup>-1</sup>) and a high fluorescence quantum yield of 0.8. The threshold power...
Article
Full-text available
We have investigated the problem of coupling light emitting diodes to contemporary low-loss multimode optical fibers (NA ~ 0.14) for optical communications. We have calculated the maximum coupled light power and the coupling efficiencies for a disk geometry and a strip geometry with and without a lens. In our calculations, we assumed that the homos...
Article
Full-text available
We report the use of a dual‐frequency dye laser system to generate continuously tunable far‐infrared radiation over the frequency range from 20 to 190 cm<sup>-1</sup>. We have investigated both collinear (forward and backward) and noncollinear phase matching in LiNbO 3 over most of this frequency range and forward collinear phase matching in ZnO, Z...
Article
Full-text available
With the help of the lattice momentum, phase‐matched optical generation of coherent phonons with frequencies higher than 50 GHz appears feasible. We have considered two cases: (i) direct conversion of millimeter or submillimeter photons in a piezoelectric superlattice, (ii) optical mixing of two laser beams in a nonpiezoelectric superlattice.
Article
Full-text available
We have observed far‐infrared radiation generated by picosecond pulses in LiNbO 3 with several different phase‐matching conditions. The output spectra, analyzed by a far‐infrared Michelson interferometer and by a Fabry‐Perot interferometer, agree well with theoretical calculations. The laser pulsewidth deduced from these measurements was about 2 ps...
Article
Full-text available
Far-infrared radiation generated from the difference frequency between two temperature-tuned ruby lasers operated on the R1 and R2 transitions has been observed. This radiation is continuously tunable over the frequency range 20-38 cm-1. Lithium niobate was used as a mixing crystal. The expected frequencies of the far-infrared radiation were measur...
Article
An improved direct charge readout electron radiography apparatus of the type having an upper electrode receiving differentially-absorbed X-radiation, a lower electrode including a plurality of parallel transparent, conductive strips overlaid with a layer of photoconductive material; and means for scanning a beam of light through the transparent str...

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