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Showing papers in "Applied Physics Letters in 1974"


Journal ArticleDOI
TL;DR: In this article, a double-barrier structure with a thin GaAs sandwiched between two GaAlas barriers has been shown to have resonance in the tunneling current at voltages near the quasistationary states of the potential well.
Abstract: Resonant tunneling of electrons has been observed in double‐barrier structures having a thin GaAs sandwiched between two GaAlas barriers. The resonance manifests itself as peaks or humps in the tunneling current at voltages near the quasistationary states of the potential well. The structures have been fabricated by molecular beam epitaxy which produces extremely smooth films and interfaces.

1,633 citations


Journal ArticleDOI
TL;DR: An explanation of the photovoltaic effect, based on the asymmetry of the lattice, is proposed in this paper, which accounts for the light-induced index changes in LiNbO3.
Abstract: Photocurrents in doped LiNbO3 crystals are shown to be due to a bulk photovoltaic effect with saturation voltages in excess of 1000 V (∼105 V/cm). This effect accounts for the light‐induced index changes in LiNbO3. An explanation of the photovoltaic effect, based on the asymmetry of the lattice, is proposed.

1,053 citations


Journal ArticleDOI
TL;DR: In this article, a single-mode low-loss waveguide which confine the guided light to within ∼1 μm of the surface has been constructed using a single transition metal (Ti, V, and Ni).
Abstract: Deposited films of transition metals (Ti, V, and Ni) have been diffused into LiNbO3 crystals to form low‐loss TE and TM mode optical waveguides Using Ti, single‐mode low‐loss waveguides which confine the guided light to within ∼1 μm of the surface have been constructed The choice of diffusion parameters allows independent control of important waveguide parameters

633 citations


Journal ArticleDOI
TL;DR: In this paper, the atomic numbers of the target and the bombarding energy were estimated and the predicted energy range where sputtering should be affected is consistent with observed anomalies in the measured yield.
Abstract: Spike effects may influence sputtering and disordering of ion‐bombarded solids in the case of a high density of energy deposition and long lifetime. We estimate both quantities and find very pronounced variations with the atomic numbers of the projectile ion and target and the bombarding energy. The predicted energy range where sputtering should be affected is consistent with observed anomalies in the measured yield.

392 citations


Journal ArticleDOI
TL;DR: In this article, a mechanically scanned acoustic microscope showing 10μm resolution was developed using single surface lenses, where an acoustic beam was focused with negligible spherical aberration in a water cell.
Abstract: This letter reports the development of a mechanically scanned acoustic microscope showing 10‐μm resolution. Using single‐surface lenses an acoustic beam is focused with negligible spherical aberration in a water cell. The image is formed by mechanically scanning an object through this focused beam in a raster pattern. Transmitted power is detected with a piezoelectric transducer, and this signal modulates the synchronized raster of a CRT display. By employing piezoelectric detection, sensitivities of 10−8 W/cm2 are obtained, yielding images of excellent clarity and contrast.

366 citations


Journal ArticleDOI
TL;DR: In this article, the authors report CuInSe2/CdS p−n heterojunction photovoltaic detectors which display uniform quantum efficiencies of up to ∼70% between 0.55 and 1.25 μ.
Abstract: We report CuInSe2/CdS p‐n heterojunction photovoltaic detectors which display uniform quantum efficiencies of up to ∼70% between 0.55 and 1.25 μ. Response times as short as 5 nsec have been observed. A weak electroluminescence (0.01% external quantum efficiency) peaking near 1.4 μ has also been observed at room temperature.

355 citations


Journal ArticleDOI
TL;DR: In this article, the authors showed that the density-squared signal dependence becomes linear due to coherent mixing with an intense solvent Raman mode or the third-order background signal, which is useful for biological compounds where background fluorescence is a problem for conventional spontaneous Raman studies.
Abstract: Coherent anti‐Stokes Raman spectroscopy offers significant advantages over standard incoherent Raman spectroscopy. The advantages include 105 improvement in conversion efficiency, spectral and spatial discrimination against fluorescence, low incident average power, and no requirement for a monochromator. The potential disadvantages of signal scaling as power cubed and requirement for a high peak power tunable laser source are largely overcome by presently available tunable laser sources. The method appears particularly useful for investigating biological compounds where background fluorescence is a problem for conventional spontaneous Raman studies. We show that for low concentrations, the density‐squared signal dependence becomes linear due to coherent mixing with an intense solvent Raman mode or the third‐order background signal.

334 citations


Journal ArticleDOI
TL;DR: In this article, a TeO2 noncollinear acousto-optic filter with large angular aperture is described, where the momentum mismatch caused by the angular deviation of the incident light from the matching condition in a non-linear interaction can be compensated by angular change of optical birefringence.
Abstract: A new type of noncollinear acousto‐optic filter with large angular aperture is described. By an appropriate choice of acoustic wave propagation direction, the momentum mismatch caused by the angular deviation of the incident light from the matching condition in a noncollinear interaction can be compensated by the angular change of optical birefringence. A TeO2 noncollinear acousto‐optic filter was constructed that had a half‐power bandwidth of 40 A at an f/4 (±7°) aperture. Tuning from 700 to 450 nm is obtained by changing the acoustic frequency from about 100 to 180 MHz. About 95% maximum transmission is obtained with an electrical power density of 1 W/cm2 applied to the transducer.

267 citations


Journal ArticleDOI
TL;DR: In this paper, permanent reversible changes of the refractive index of pure and doped LiNbO3 have been obtained by multiphoton absorption, which can be read nondestructively, eliminating the need for fixing processes while maintaining the versatility of optical erasure.
Abstract: Permanent reversible changes of the refractive index of pure and doped LiNbO3 have been obtained by multiphoton absorption. Greatly increased sensitivity over the linear process enables holograms to be recorded even in high‐purity LiNbO3, with a diffraction efficiency of 25% with less than 0.4 J/cm2. These holograms can be read nondestructively, eliminating the need for fixing processes while the versatility of optical erasure is maintained.

264 citations


Journal ArticleDOI
TL;DR: In this paper, a phase matched nonlinear mixing in a silica fiber optical waveguide using the dispersion of the guide modes to compensate for bulk dispersion was observed, which is useful as a probe of waveguide properties and for the study of the nonlinearities of the medium.
Abstract: We have observed phase‐matched nonlinear mixing in a silica fiber optical waveguide using the dispersion of the guide modes to compensate for bulk dispersion. A tunable dye laser signal is mixed with a fixed‐frequency pump wave to generate output in specific waveguide modes at different frequencies. The technique is useful as a probe of waveguide properties and for the study of the nonlinearities of the medium.

261 citations


Journal ArticleDOI
TL;DR: In this paper, the refractive indices of AlGa1−xAs samples prepared by liquid-phase epitaxy were determined from accurate double-beam reflectance measurements, and they were obtained for AlAs mole fractions between 0 ≤ x ≤ 0.38 in the spectral range 1.2-1.8 eV.
Abstract: The refractive indices of AlxGa1−xAs samples prepared by liquid‐phase epitaxy were determined from accurate double‐beam reflectance measurements. The variation of the refractive index with photon energy at room temperature was obtained for AlAs mole fractions between 0 ≤ x ≤ 0.38 in the spectral range 1.2–1.8 eV.

Journal ArticleDOI
TL;DR: In this article, the gain medium and saturable absorber are placed in a single free-flowing dye stream located near the center of the resonator, and peak pulse powers of several kilowatts are obtained by acousto-optically dumping the mode-locked pulses from the optical cavity at repetition rates up to 105 pps.
Abstract: Subpicosecond pulses (0.5–1.0 psec) have been generated by passive mode locking of a composite medium dye laser. Both the gain medium and saturable absorber are placed in a single free‐flowing dye stream located near the center of the resonator. Peak pulse powers of several kilowatts have been obtained by acousto‐optically dumping the mode‐locked pulses from the optical cavity at repetition rates up to 105 pps.

Journal ArticleDOI
TL;DR: In this paper, a model on the preionization requirements for initiating a volume-stabilized glow discharge is proposed and a minimum required preionized electron density of ∼ 104 cm−3 is predicted for a typical CO2 TEA laser discharge and is consistent with experimental observations.
Abstract: A model on the preionization requirements for initiating a volume‐stabilized glow discharge is proposed. The basic requirement of the model is that the preionized electron density be large enough to cause appreciable spatial overlap of the primary avalanches and consequent smoothing of space‐charge field gradients at the stage when streamer formation would otherwise occur. A minimum required preionization electron density of ∼ 104 cm−3 is predicted for a typical CO2 TEA laser discharge and is consistent with experimental observations.

Journal ArticleDOI
TL;DR: In this paper, the fabrication and evaluation of corrugation grating filters with reflectivities better than 75% and bandwidths less than 2 A was reported, using standard interferometric and ionbeam machining techniques and evaluated with a tunable dye laser.
Abstract: The fabrication and evaluation of corrugation grating filters with reflectivities better than 75% and bandwidths less that 2 A is reported. Grating filters were fabricated on glass waveguides using standard interferometric and ion‐beam machining techniques and evaluated with a tunable dye laser. Measured and calculated filter responses are found to be in excellent agreement. Tolerances for realizing ideal filter performances are given.

Journal ArticleDOI
TL;DR: In this article, the magnitude and sign (positive) of the molecular hyperpolarizability γ have been determined for several mixtures of nitrobenzene and benzene.
Abstract: The magnitude and sign (positive) of the molecular hyperpolarizability γ has been determined for several mixtures of nitrobenzene and benzene. This has allowed the testing of the adequacy of Onsager's local field factors, which are found to be valid. By comparing γ of nitrobenzene with that of nitromethane, we find that the delocalized conjugated electrons are an order of magnitude more effective in contributing to γ than are the localized nonconjugated electrons.

Journal ArticleDOI
TL;DR: Transparent heat-mirror films of TiO2/Ag/TiO2 on glass with a visible transmission of 84% and an infrared reflectivity of 98-99% have been fabricated by rf sputtering as mentioned in this paper.
Abstract: Transparent heat‐mirror films of TiO2/Ag/TiO2 on glass with a visible transmission of 84% (at 0.5 μm) and an infrared reflectivity of 98–99% (at 10 μm) have been fabricated by rf sputtering. Initial tests indicate that the films are thermally stable in air at 200°C and inert to water attack. Because of their excellent optical properties and apparent stability, these transparent heat‐mirror films offer great promise for use in solar‐thermal power conversion and as transparent thermal insulators.

Journal ArticleDOI
TL;DR: In this paper, the authors simulated the structure of thin amorphous films grown from a vapor and showed that structural anisotropy and voids are a natural occurrence of the deposition process.
Abstract: We have computer simulated the structure of thin amorphous films grown from a vapor. Our hard‐sphere model shows that structural anisotropy and voids are a natural occurrence of the deposition process. The amount of unfilled space (voids) and the anisotropy have been studied as a function of the angle of incidence of the vapor stream upon the substrate.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the contact angle θ of water on silicon and on very thin layers of silicon dioxide grown on silicon, and showed that the interaction energy between water and the solid surface depends strongly on the oxide thickness.
Abstract: We have measured the contact angle θ of water on silicon and on very thin layers of silicon dioxide grown on silicon. The silicon is hydrophobic and θ is near 90°. Oxides thicker than 30 A are hydrophilic and θ is near 0°. For intermediate thicknesses, θ varies smoothly between these limits. Our results show that the interaction energy between water and the solid surface depends strongly on the oxide thickness. Consideration of different possible interactions leads us to conclude that this is due to corresponding changes in the structure or composition of the oxide surface.

Journal ArticleDOI
TL;DR: In this paper, proximity-imaging techniques are used to observe TSFE from single domain and multidomain single crystals of LiNbO3 and the mechanism responsible for this emission is discussed.
Abstract: Proximity‐imaging techniques are used to observe thermally stimulated field emission (TSFE) from single‐domain and multidomain single crystals of LiNbO3. Experimental results are reported and the mechanism responsible for this emission is discussed.

Journal ArticleDOI
TL;DR: In this article, a thin highly doped layer at the surface of a semiconductor was used to increase the surface field of a Schottky barrier and reduce the barrier height by an amount insensitive to applied bias.
Abstract: A thin highly doped layer at the surface of a semiconductor has been used to increase the surface field of a Schottky barrier and reduce the barrier height by an amount insensitive to applied bias. The effective barrier height of Ni–Si barriers of this type made using ion‐implantation techniques has been reduced by an amount in the range 0–0.2 eV without significant degradation of the reverse characteristic.

Journal ArticleDOI
TL;DR: In this article, the electron affinity of heat-cleaned GaN and semi-insulating GaN was derived from photoemissive yield measurements on degenerate n−type and semi−incoarse GaN for heatcleaned and cesiated surfaces.
Abstract: Photoemissive yield measurements were performed on degenerate n‐type and semi‐insulating GaN for heat‐cleaned and for cesiated surfaces. The photoemissive threshold for heat‐cleaned n‐type material occurs at 4.1 eV, while that for semi‐insulating material is beyond 5.5 eV, the experimental spectral range. From these measurements an upper and a lower limit of the electron affinity of heat‐cleaned GaN is derived, namely 4.1 > χ > 2.1 eV. The threshold for cesiated surfaces on both materials is lowered to 1.5 eV, and the photoyield curve exhibits a second threshold at about 3.4 eV. The occurrence of negative electron affinity is suggested for cesiated semi‐insulating GaN.

Journal ArticleDOI
TL;DR: In this paper, low-loss LiNbxTa1−xO3 optical waveguides have been made by a simple diffusion technique and demonstrated over 80% base band electro-optic modulation with frequency capabilities extending to the microwave range.
Abstract: Low‐loss LiNbxTa1−xO3 optical waveguides have been made by a simple diffusion technique. They are used to demonstrate over 80% base band electro‐optic modulation with frequency capabilities extending to the microwave range. Voltages below 5 V and drive powers below 2/10 mW/MHz are required.

Journal ArticleDOI
TL;DR: In this paper, the growth of platinum silicide layers has been observed using Rutherford backscattering, and it is possible to deduce that Si is the diffusing species with the reaction occurring at either the Pt2Si−Pt, PtSi-Pt2Si, or PtSi•Pt interfaces.
Abstract: The growth of platinum silicide layers has been observed using Rutherford backscattering. By simultaneous observation of the relative movement of the Pt2Si and PtSi interfaces, it is possible to deduce that Si is the diffusing species with the reaction occurring at either the Pt2Si–Pt, PtSi–Pt2Si, or PtSi–Pt interfaces. Activation energies for the growth of the Pt2Si and PtSi layers are 1.6 eV. It is possible to interact Pt with Si by means of Ar ion bombardment; however, the reacted layer acts as a barrier to Si diffusion.

Journal ArticleDOI
TL;DR: In this paper, the existence of two distinct stable regimes of optical levitation for solid spheres, one located above the beam focus, the other below it, was discovered and a particle can be switched back and forth between these regimes.
Abstract: Stable optical levitation of transparent hollow dielectric spheres has been demonstrated using TEM01 mode laser beams. The levitation of solid dielectric spheres has been made much more stable using highly convergent TEM00 mode beams. We have discovered the existence of two distinct stable regimes of levitation for solid spheres, one located above the beam focus, the other below it. A particle can be switched back and forth between these regimes. Three separate stable regimes are also possible.

Journal ArticleDOI
TL;DR: In this paper, a technique is described by which light entering a thin film is ''trapped'' in the sense of having to traverse the film a number of times, and it is shown that the use of this technique in silicon provides a solar cell with good carrier collection efficiencies even with Si only ∼2 μm thick and with ∼10nsec lifetime.
Abstract: A technique is described by which light entering a thin film is ``trapped'' in the sense of having to traverse the film a number of times. It is shown that the use of this technique in silicon provides a solar cell with good carrier collection efficiencies even with Si only ∼2 μm thick and with ∼10‐nsec lifetime.

Journal ArticleDOI
TL;DR: In this article, a single heterojunction (SH) GaAs/GaAlAs diodes using distributed feedback (DFB) was used for single-input single-out (SISO) laser operation.
Abstract: Laser operation utilizing distributed feedback (DFB) in single heterojunction (SH) GaAs/GaAlAs diodes is reported. Laser wavelengths ranging from 8430 to 8560 A were observed in various samples depending on grating period. The threshold current densities required were comparable to those of normal SH diodes.

Journal ArticleDOI
TL;DR: In this paper, a model for the incipient stages of intrinsic dielectric breakdown was proposed for a wideband gap insulator with a low hole mobility, and the model predicted an intrinsic breakdown voltage which approached a lower limit of V = 9+φ for very thin films, where φ is the cathode contact barrier in volts.
Abstract: A mechanism describing the incipient stages of intrinsic dielectric breakdown is formulated for the case of a wide‐band‐gap insulator with a low hole mobility. Dielectric instability results from the tunnel injection of electrons from the cathode contact and the subsequent impact ionization and field distortion which lead to dielectric breakdown. The model, evaluated for the parameters of SiO2, predicts an intrinsic breakdown voltage which approaches a lower limit of V=9+φ for very thin films, where φ is the cathode contact barrier in volts. As a result, both the electric field at breakdown and the critical current density increase rapidly as the film thickness is reduced below 200 A.

Journal ArticleDOI
TL;DR: In this article, the alignment of nematics and smectics on substrates where an obliquely evaporated thin film has been previously deposited is discussed, and it is shown that the surface anchoring energy is substantially larger than with the traditional rubbing technique.
Abstract: We discuss the alignment of nematics and smectics on substrates where an obliquely evaporated thin film has been previously deposited. In the planar samples, the surface anchoring energy is substantially larger than with the traditional rubbing technique. We can also uniformly align the liquid crystals obliquely, in particular by coating the evaporated film by a surfactant.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the pressure environment at the back surface of various sample thicknesses and compared the results with numerical calculations obtained from a one-dimensional radiation hydrodynamics computer code.
Abstract: Laser‐induced stress waves in iron samples were analyzed by measuring the pressure environment at the back surface of various sample thicknesses. These results were compared with numerical calculations obtained from a one‐dimensional radiation hydrodynamics computer code. The experiments were conducted in an air environment under ambient conditions and the metal surfaces were confined by transparent overlays. Peak pressures exceeding 50 kbar were measured with quartz pressure transducers at a laser power density of about 109 W/cm2. Computer predictions agreed favorably with the experimental results and indicated that peak pressures exceeding 100 kbar could be generated by appropriate modifications in the laser environment and target overlay configuration.

Journal ArticleDOI
TL;DR: In this article, a new scheme for electro-optical tuning of tunable lasers is described, which achieves tuning rates and tuning ranges in cw dye lasers nearly 100 times greater than those previously reported using a comparable-sized electrooptical crystal.
Abstract: A new scheme for electro‐optical tuning of tunable lasers is described. Tuning rates and tuning ranges in cw dye lasers nearly 100 times greater than those previously reported using a comparable‐sized electro‐optical crystal have been achieved using this method.