Showing papers in "Applied physics in 1973"

Unified theory of Rayleigh-angle phenomena for acoustic beams at liquid-solid interfaces

Abstract: Various phenomena have been observed when a bounded acoustic beam is incident from a liquid onto the surface of a solid at or near the Rayleigh angle. These phenomena include: a shift of the reflected beam from the position predicted by geometrical acoustics, a null or minimum of intensity within the reflected beam, a 180° phase reversal of the field on either side of the null, a weak trailing field on only one side of the reflected beam and a frequency of least reflection when the solid is lossy. By carefully examining the reflection coefficient for angles in the vicinity of the Rayleight angle, and by taking into account the angular spectrum of plane waves that comprise a bounded beam, a model of the reflection process is developed that explains all of the observed phenomena. This model shows that the various critical-reflection effects result from the interference between a geometrically reflected field and the field of a leaky Rayleigh wave, which is excited by the incident beam. Moreover, this model resolves the conflict between various explanations made for these phenomena in the past; in particular, it is found that Schoch's classical description of a laterally displaced reflected beam is valid only for beams having a large width.

Fluorescence quenching in Nd:YAG

Abstract: We show that quenching of the Nd fluorescence is in principle not associated with the Nd3+ ion but with the host. The process is due to near-field electric dipole interaction between Nd pairs, and cross relaxation via the4I1 5/2 manifold. We present for the first time the complete fluorescence spectrum and level scheme of Nd∶YAG, and find that Nd∶YAG has an exceptional level configuration which boosts cross relaxation. Our results encourage the search for new Nd laser materials which have a slightly different position of the4I1 5/2 manifold so that higher Nd concentrations can be achieved for integrated-optics applications. Finally, we report on implications of energy migration which we found to be quite effective in Nd∶YAG.

Dielectric parameterization of raman lineshapes for GaP with a plasma of charge carriers

Abstract: We have studied the Raman lineshapes of several samples of GaP with appreciable carrier concentrations. There is no feature identifiable as a plasma resonance, but there are pronounced effects of interaction with the LO phonon resonance. For analysis we have developed a model along lines laid down by Barker and Loudon, employing Nyquist relations to calculate infrared fluctuations which scatter light. We introduce a response matrix α(ω) withseveral resonances; and we uncover some points which seem to be new, for coupled-mode scattering systems in general. In the GaP-plasma problem the data do not necessitate inclusion of the scattering amplitude from the plasma; we ascribe this to large plasma damping rates (ωτ≲1). This provides an account for the lack of any apparent plasma resonance in the scattering and for the modified appearance of the LO phonon, relative to the pure crystal. We emphasize that the following parameters suffice: Lorentz parameters measured in linear infrared experiments, the nonlinear parameterC from a visible-infrared mixing experiment, and the plasma frequency and damping fit to each sample. Beyond treatment of the plasma problem, the theory bears more generally on the conditions under which an LO Raman lineshape measures locally the shape of 〈E 2〉ω. Also it bears upon the analysis of polariton linewidths to infer the variation of the phonon damping Γ(ω).

Influence of Annealing on the Concentration Profiles of Boron Implantations in Silicon

Abstract: The influence of annealing on the concentration profiles of boron implanted into silicon with does of 1014 ions/cm2 up to 1016 ions/cm2 and an energy of 70 keV was studied. The concentration profiles were measured with Secondary Ion Mass Spectrometry (SIMS). The broadening of the concentration profiles during annealing can be described as a superposition of effects resulting from a relatively immobile and a mobile boron fraction. The properties of the immobile boron fraction were studied by measuring the influence of a boron implantation on the distribution of a homogeneous boron background dope. From these experiments it was concluded that the immobile boron fraction consists of boron precipitates. The properties of the mobile fraction were studied from concentration profiles that were obtained after annealing during different periods at the same temperature. It was found that during the initial stage of the annealing process a fast broadening of the profile occurs; this was assumed to be due to an interstitial type boron diffusion. After prolonged annealing the much slower substitutional type diffusion prevails, due to trapping of the interstitial boron atoms by vacancies. The reliability of the SIMS method, as applied to profile measurements, was checked for the high boron doses used in this investigation. Excessive boron precipitates, obtained after annealing of a high dose, such as 1016 ions/cm2 at about 1000°C, appear to give some increase of the ion yield.

Continuous oscillation of a (Sc, Nd) pentaphosphate laser with 4 milliwatts pump threshold

Abstract: We report on room temperature cw oscillation of a scandium neodymium pentaphosphate (Sc: NdP5O14) laser pumped with an argon laser. The threshold pump power is, to our knowledge, the lowest obtained so far at room temperature with any laser material.

Energy transfer and the complete level system of NdUP

Abstract: We report on the complete fluorescence spectrum (52 transitions) and the full level system of neodymium ultraphosphate (NdUP) single crystals. Below 30 K the actual linewidths are below 0.1 A indicating that there is one well defined site for all Nd ions which can be expected from a stoichiometric material. The position of the4I1 5/2 manifold does not allow for cross relaxation which explains the relatively long fluorescent lifetime of NdUP in spite of its high Nd-concentration. We find, however, lifetime shortening at high excitation rates which limits the optical gain of NdUP. We also find a very high rate of energy migration in NdUP which leads us to predict spontaneous single frequency oscillation for cw operation near threshold.

Planar leaky light-guides and couplers

Abstract: A quantitative theory of light propagation in a dielectric slab guide with general cladding media is presented. It is based on a plane wave which bounces in a zigzag fashion along the guide as a result of total or partial reflections at the two surfaces of the film. Two mechanisms are considered which contribute to the attenuation of the guide: losses due to absorption in the slab and cladding materials, and radiation losses if the guide is a leaky one. We point out the significance of the Goos-Hanchen effect for all questions relating to the power flow in the slab guide. The theory is illustrated by discussing dispersion and attenuation of guides with various low-index and high-index claddings, operating above and below cutoff. The low-index leaky guide is considered particularly in detail. Its high attenuation by leakage can be reduced to practically acceptable values (<1d B/cm) by increasing the film thickness to ≳ 40λ. One application of this guide is in the leaky wave coupler. This coupler may be viewed as a prism-film coupler simplified by omission of the gap. It offers a new approach to the problem of broad-band coupling to thin-film light guides.

Preparation and optical properties of single crystal thin films of bismuth substituted iron garnets for magneto-optic applications

Abstract: Single crystal thin films of Bi substituted iron garnets have been grown by the liquid phase epitaxy technique. The growth conditions and compositions are presented together with the segregation coefficients of Bi and Pb as a function of growth temperature. The Faraday rotation and optical absorption have been measured for wavelengths between 0.7 and 0.46 μm. The superior magneto-optic properties (Faraday rotations of up to ten times larger than that observed for Y3Fe5O12) make these epitaxial layers attractive for magneto-optic devices. The influence of Pb incorporation on the optical properties of the films is discussed. Compositions of Bi and Ga(Al) substituted Gd3Fe5O12, which exhibit a magnetic compensation temperature near room temperature and high Faraday rotation, have also been prepared. The magnetic switching behaviour as a function of temperature has been determined. It shows that these films are especially suited for thermomagnetic recording using an argon ion laser at a wavelength of 5145 A.

Ionized impurity scattering in degenerate In 2 O 3

Abstract: Thin films of In2O3 are prepared by the spraying method. The concentration of charge carriers is changed from about 8×1019 cm−3 to 5×1020 cm−3 by suitable doping with Sn. The optical effective mass is found to depend slightly on carrier concentration. Electrical and optical measurements indicate that electrons are scattered predominantly by charged impurity centres. Structural investigations show that grain boundary scattering can be neglected. The interpretation of the experimental results is mainly based on a paper by von Baltz and Escher, where analytical formulas for the imaginary part of the complex dielectric constant are given for the most important scattering mechanisms in (degenerate) semiconductors.

Spannungsstufen in denU (T)-Übergangskurven undU (I)-Kennlinien stromtragender Zinn-Whisker

Abstract: The current induced phase transition from the superconducting to the normalconducting state is studied in whiskers of tin. Transition curves were taken byU(T)-measurements at steady currents as well as characteristic curves byU (I)-measurements at fixed temperatures. For larger current intensities these curves show voltage steps which increase linearly with current intensity. The onset of voltage reading appears at the critical current density, as predicted by theory. The step structures are, however, observed at current densities which are several times larger than the critical ones. The influence of a magnetic field on the location and the structure of the curves was measured and is compared to theoretical predictions. At temperatures close toTco whiskers are onedimensional with respect to the superconducting orderparameter because of their small diameters. Therefore, intermediate state pattern and flux flow are rejected as an explanation of the observed structures.

Goldanskii-Karyagin effect versus preferred orientations (texture)

Abstract: There are two main contributions influencing the relative line intensities in a hyperfine pattern of a polycrystalline material: 1) Lattice vibrational anisotropy-Goldanskii-Karyagin effect (GKE) and 2) preferred orientation of the crystallites (texture).

New developments in the surface analysis of solids

Abstract: In both fundamental and applied surface physics, it is essential to know as much as possible about the chemical composition of the outer atomic layers of solids. Rapid progress has recently been made in the development of analytical methods which could be used in surface analysis. All utilize some type of emission (photons, electrons, atoms, molecules, ions), caused by excitation of the surface states. Both the “excitation” and emission processes must meet certain basic requirements as regards information depth, form in which the information is obtained, sensitivity, changes in the surface layer during analysis, etc. The more important of the methods that qualify, namely Auger-Electron Spectroscopy (AES), photo-Electron Spectroscopy for Chemical Analysis (ESCA) and the static method of Secondary-Ion Mass Spectrometry (SIMS), are discussed and their potentialities and limitations illustrated by characteristic examples.

Intensity stabilization of dye laser radiation by saturated amplification

Abstract: A novel scheme is proposed for stabilizing the intensity of a fluctuating laser source, using a partly saturated high gain traveling wave laser amplifier with a nonsaturable absorber distributed in the amplifying medium. Calculations for homogeneously broadened laser gain band in an adiabatic approximation are presented, which indicate that the stabilization factor can be increased by several orders of magnitude with the help of the absorber. An experiment is reported in which a two-stage dye laser amplifier with inserted attenuator, pumped by a nitrogen laser, is used to amplify and stabilize the intensity of an ultra-narrowband repetitively pulsed dye laser. The output intensity changes by less than a factor of four when the input is changed over three orders of magnitude.

High-resolution spectroscopy with and frequency stabilization of a cw dye laser

Abstract: The hyperfine splittings of the Na D1 and D2 lines were investigated using a single mode cw dye laser. The light of the laser was scattered by the atoms of an atomic beam and the fluorescent light was observed as the frequency of the laser was tuned across the D lines. The Doppler width of the atomic beam was reduced to about 2.5 MHz so that the absorption width of the atoms of the beam was essentially determined by the natural width of the 32P1/2 and 32P3/2 levels, which is about 10 MHz. Since the linewidth observed for the hyperfine transitions was 30 MHz, most of the hyperfine components of the D1 and D2 lines could be resolved. In another experiment the frequency of the dye laser was locked to a hyperfine transition of the D1 line. The observed variation of the output frequency of the dye laser was less than ±1.5 MHz. In addition, the intensity of the dye laser was controlled to about 10−3, using an electro-optically variable transmission filter.

Formation of a periodic wave structure on the dry surface of a solid by TEA-CO 2 -laser pulses

Abstract: The formation of periodic wave patterns on surfaces of insulators and metals by means of TEA-CO2-laser pulses was observed. The wavelength of the patterns equals that of the laser radiation. The phenomenon is illustrated by samples of quartz glass and copper.

A narrowband single-mode dye laser

Abstract: The linewidth of a cw-single-mode tunable dye laser has been investigated. It was found that the linewidth is determined by microscopic velocity fluctuations of the turbulent flow within the dye cell of the laser and by fluctuations of the pump power. The linewidth is further influenced by mechanical disturbances and by temperature fluctuations of the dye solution. The results of the investigations made it possible to achieve a reduction of the velocity fluctuations. It is shown that under adequate operating conditions the free-running dye laser has a linewidth of 2 MHz.

Limits of sensitivity of laser spectrometers

Abstract: Theoretical considerations are given on the sensitivity of laser spectrometers in which the molecular transition is observed by a photoelectric detector, a photoconductive detector, or a diode. It is shown that the single-pass absorption spectrometer has extremely high sensitivity at a relatively high gas pressure and with optimum laser power. The holeburning spectrometer is less sensitive, though in offers much higher resolution of the homogeneous width at a low gas pressure. The nonlinear fluorescence method is characterized by both high resolution and high sensitivity, provided the fluorescence from the laser-excited level can be observed. The minimum detectable number of absorbing molecules is calculated to be 102 to 106 depending on the parameters of the spectrometer. Thus a concentration of absorbing molecules lower than 10−12 is expected to be detectable in some cases.

Mode-locked lasers and ultrashort light pulses

Abstract: This article reviews some aspects of the generation of very short optical pulses using mode-locked lasers, with the emphasis laid on pulsed laser systems. Active and passive mode-locking is discussed, and the problem of measuring ultrashort light pulses is considered. A survey of some commonly used sources and techniques for the generation of ultrashort light pulses follows. The paper concludes with a short account of limitations in the generation and propagation of these pulses.

Ideal laser amplifier as a phase measuring system of a microscopic radiation field

Abstract: A measuring system is described for the phase determination of a microscopic radiation field. The essential element of this system is a Q-switched Nd:YAG laser which serves as an ideal laser amplifier with a high amplification of approximately 1010, having insignificant quantum noise. The result for a phase measurement of several photons (about five) is presented.

Theory of electrodynamic levitation with a continuous sheet track — Part I

Abstract: Exact analytical expressions for forces on moving rectangular current-carrying coils above and below an infinite conducting sheet track of arbitrary thickness are developed. These general expressions for the lift and drag forces acting on the excitation coils as functions of speed are investigated for normal flux, null flux and brake flux systems and discussed with the aid of numerical calculations. A concise parameter study is also made. The system velocity characteristics with constant load (technologically more relevant) are given for the first time for normal and null flux systems.

Hollow-cathode transverse discharge He−Ne and He−Cd+ lasers

Abstract: An all-metal hollow-cathode laser tube consisting of a perforated cylindrical cathode surrounded by a coaxial cylindrical anode has been operated as a He−Ne laser at 0.6328, 1.15 and 3.39 μm, and as a He−Cd laser at red, green and blue visible wavelengths, using both de and pulsed-plus-dc excitation. Laser oscillation in He−Zn, Ne−Cd, Xe−Cd and Ar−Cd mixtures has also been obtained. The hollow-cathode discharge consists primarily of an intense cathode glow inside the cathode cylinder, giving a quiet, stable, low-voltage, positive-resistance discharge. Results for the He−Ne and He−Cd laser output versus partial and total pressures and discharge currents are presented. The unoptimized laser performance for the He−Ne case approaches but does not yet equal the conventional positive-column case, while the He−Cd performance for the charge-transfer-pumped green 5378A line appears particularly promising.

Unified theory of total reflection phenomena at a dielectric interface

Abstract: By utilizing a rigorous plane-wave representation, we investigate the basic wave mechanism that is responsible for both the lateral (Goos-Hanchen) shift of a gaussian light beam incident from a denser medium upon the interface to a rarer medium, and the weak radiance that accompanies the reflected beam. We thus find that the complete reflected field contains a geometric-optics component, whose domain is given by the mirror reflection of the incident beam, as well as a lateral-wave component which occupies a much larger domain. Our results show that the near field of the lateral-wave component interferes with the geometric-optics component and thereby produces the Goos-Hanchen shift of the reflected beam. The intermediate and far fields of the lateral-wave, on the other hand, are responsible for the weak radiance that trails the reflected beam. By demonstrating that both the beam shift and the trailing radiance represent two facets of the same wave process, the lateral-wave field is shown to provide a unified interpretation of two effects that have previously been regarded as separate phenomena. The dependence of these effects on beam width, angle of incidence, and polarization are also considered.

Lifetime measurements using stepwise excitation by two pulsed dye lasers

Abstract: The 42D level of sodium was populated in a stepwise excitation process involving two pulsed dye lasers. The lifetime of the 42D level was derived from the decay of the fluorescence intensity.

Properties and laser oscillation of the (Nd, Y) pentaphosphate system

Abstract: We report on fluorescence and other properties of the system (Nd, Y)P5O14. With a single crystal of 1.32 mm length containing approximately one atomic percent yttrium we obtained pulsed laser oscillation at 1.05 microns wavelength with peak powers exceeding 200 Watts.

Deviations from the Stefan Boltzmann law at low temperatures

Abstract: The total radiation energy in a cavity is studied in the limit of small volume and temperature. The validity of refined high-temperature expansions is examined. For the cube-shaped cavity with edge lengthL complete results covering the range 0≦LT<∞ are presented.

Photoluminescence ofn-GaAs at transparent Schottky contacts

Abstract: Near-bandgap photoluminescence at 300 K of a Se-dopedn-GaAs crystal withn=4.8·1016 cm−3 was measured at a transparent CrAu−GaAs Schottky contact. The dependence of the luminescence intensity on the applied reverse voltage was recorded. Both the doping concentration and absorption coefficients above bandgap are determined.

An internal friction study of the vanadium-deuterium system

Abstract: The internal friction of deuterium-doped vanadium has been investigated in the temperature range from 65 to 350 K. At low deuterium concentrations (≦0.18 at.−%) a relaxation effect has been observed near 90 K; its activation energy and its limiting relaxation tiem are 0.17 eV and 2×10−12 sec, respectively. A second internal friction peak (precipitation peak) appears in more heavily doped samples; the position of this second peak shifts to higher temperatures as the deuterium content is increased. Possible mechanisms for the two peaks are discussed. The phase diagram of the vanadium-deuterium system at low temperatures has been deduced from the correlation between the deuterium concentration and the position of the precipitation peak.

Nachwirkungsmechanismen in Ferriten

Abstract: In ferrites a large number of after-effects are found, with time constants between nano-seconds and years. In this review the after-effects due to ion-and electron motion will be treated. One finds: 1) single-ion effects in combination with lattice deformations, e.g. Mn3+; 2) ion effects caused by mobile vacancies, e.g. Co2+; 3) effects due to electron transfer: a) Co2+−Co3+ b) Me2+−Fe3+, in combination with Me4+ and vacancies. c) Me4+−Fe2+, with Me=Si, Ti (photomagnetic effect).

Controlled decay of electrically induced deformations in nematic liquid crystals

Abstract: The transient behavior of electrically induced deformations of parallel oriented nematic liquid crystal layers was investigated. The nematic material used was a mixture of disubstituted benzoyloxybenzoic acid esters the dielectric anisotropy of which is positive at dc and low frequencies, and changes sign in the kHz range. The decay time of a deformation induced by a low frequency field can be considerably reduced by switching the frequency to the range where the dielectric anisotropy is negative. This effect becomes even more pronounced for higher viscosities.

An integrated optical system for the vacuum ultraviolet region

Abstract: We use a 0.5 m Seya-Namioka monochromator and two gold plated cylindrical mirrors to set up an optical system which produces a collimated beam of plane polarized, monochromatic radiation in the vacuum ultraviolet region. The two mirrors compensate for the astigmatism of the Seya-Namioka monochromator, thereby increasing the spectral resolution drastically. The degree of linear polarization is about 0.97–1.00 in the spectral region of 6–11.5 eV.