Showing papers on "Photon energy published in 1972"
TL;DR: In this paper, the optical absorption of benzene vapour has been measured with the spectral continuous synchrotron radiation from the electron accelerator DESY within the photon energy range of 6 to 35 eV, where excitations of all but the C 1s-electrons are expected to occur.
152 citations
01 Aug 1972
TL;DR: In this article, a model for the self-focusing mechanism in semiconductor lasers is analyzed and applied to the formation of lasing filaments in p-n junction devices, which is attributed to an increase of dielectric constant in the semiconductor in regions of high light intensity due to a depletion of injected carrier concentration.
Abstract: A model for the self-focusing mechanism in semiconductor lasers is analysed and applied to the formation of lasing filaments in p-n junction devices. The self-focusing is attributed to an increase of dielectric constant in the semiconductor in regions of high light intensity due to a depletion of the injected carrier concentration. Two mechanisms are postulated for the dependence of dielectric constant on carrier concentration; the free carrier effect and the band-to-band interaction. The band-to-band interaction is computed as a function of photon energy, and found to give the major contribution to a total dielectric constant perturbation of typically −0.05 at threshold. This agrees with experiment. A single-mode solution is obtained for the waveguide equation of an isolated filament or a set of coupled filaments. This shows that the filament width contracts with current. Expressions are obtained for the optical intensity distribution, for the guided wavelength, for the effect of carrier diffusion, and for the higher-order mode cut-offs. The calculated filament width at 300 K varies typically between 12 and 3 microns for currents from 1 to 60% above threshold; at 77 K the width is almost doubled. This agrees reasonably with experiment. In general the analysis shows that the strength of self-focusing in heterostructure lasers depends on the number of carriers injected at threshold per cm2 per micron thickness of the optical confinement region.
140 citations
TL;DR: In this paper, a surface-sensitive peak about 0.4 eV below the Fermi energy was identified as a surface state, which rapidly decays during gas adsorption.
Abstract: Photoelectron energy distributions from clean, polycrystalline tungsten reveal a surface-sensitive peak about 0.4 eV below the Fermi energy. This peak, which is identified as a surface state, rapidly decays during gas adsorption, and concomitant growth of a new peak at \ensuremath{\sim}2.5 eV below the Fermi energy is observed. Over the energy range of the surface-state peak, the strength of surface-state emission relative to bulk emission decreases with increasing photon energy. These results quantitatively substantiate existing field-emission data and qualitatively agree with model photoemission calculations.
109 citations
IBM1
TL;DR: In this article, the optical densities of states for Si, Ge, and GaAs obtained from ultraviolet photoemission energy distribution curves obtained at about 25 eV of photon energy were determined.
Abstract: We present experimental valence-band optical densities of states for Si, Ge, and GaAs obtained from ultraviolet photoemission energy distribution curves obtained at about 25 eV of photon energy. The width of the upper two valence bands of Si and the positions of several energy-band minima for the second and third valence bands of Ge and GaAs have been accurately determined. Comparing the above-mentioned band edges with theoretical calculations based on optical data, we find good agreement for Si and observe significant differences for Ge and GaAs.
97 citations
TL;DR: In this article, carbon dioxide in a helium buffer at room temperature was irradiated with a photon beam of wavelengths 1090 to 850 A. The authors observed that the phosphorescence yield is zero at threshold and increases smoothly to a maximum of ∼ 60% near 900 A. This was explained by postulating that the relevant potential surface crossings are outside the Franck-Condon region of CO2 absorption.
Abstract: Carbon dioxide in a helium buffer at room temperature was irradiated with a photon beam of wavelengths 1090 to 850 A. ``Phosphorescence'' from the CO(a 3Π ‐ X 1Σ) Cameron bands was observed. The phosphorescent yield is zero at threshold and increases smoothly to a maximum of ∼ 60% near 900 A. The smoothness of the percentage yield was an unexpected observation and is explained by postulating that the relevant potential surface crossings are outside the Franck‐Condon region of CO2 absorption. Approximate vibrational distributions have been determined and are also smooth functions of photon energy.
96 citations
TL;DR: In this paper, the absorption spectrum of atomic sodium in the photon energy region from 30 to 150 eV has been investigated and a great number of sharp absorption lines which can be attributed to the excitation of a 2p- or a 2s-electron has been detected.
Abstract: The absorption spectrum of atomic sodium in the photon energy region from 30 to 150 eV has been investigated. A great number of sharp absorption lines which can be attributed to the excitation of a 2p- or a 2s-electron has been detected. Simultaneous excitation of one 2p- and one 3s-electron gives rise to considerably strong broad and asymmetric absorption structures above the highest series limit (1P1) for the excitations of a single 2p-electron. Some of the assignments have been confirmed by Hartree-Fock calculations. The relative spectral dependence of the absorption cross-section in this energy range has been determined for the first time. The spectrum of free Na atoms has been compared with theLII, III spectrum of solid sodium.
90 citations
TL;DR: In this paper, a phenomenological band-theoretic model for photoelectric emission which includes the effects of energy loss due to phonon scattering is developed, which is applicable near threshold when the optical absorption depth is large compared to the phonon scatter length of hot electrons, and is particularly useful for cesiated surfaces with positive electron affinity.
Abstract: A phenomenological band-theoretic model for photoelectric emission which includes the effects of energy loss due to phonon scattering is developed. The model is applicable near threshold when the optical absorption depth is large compared to the phonon scattering length of hot electrons, and is particularly useful for cesiated surfaces with positive electron affinity. It is shown that in the low-photon-energy range one must include the dispersion of the optical constants in the yield expression. Formulas are given for photoelectric yield and for energy distribution curves in the cases of direct, indirect, and nondirect volume transitions; direct transitions give the commonly observed cube law for yield near threshold, changing to linear and square laws at higher energy. The theory is illustrated on experimental data for the following cesiated single crystals: Si (indirect transitions), GaAs, GaSb, ${\mathrm{Ga}}_{0.6}$${\mathrm{In}}_{0.4}$As, and Ge (all direct transitions), and is shown to provide in each case an excellent fit over a range of at least ${10}^{3}$ in the yield (1 eV in photon energy). Its applicability to amorphous materials is discussed and illustrated on Ge. Information on hot-electron scattering lengths in the above materials is also extracted and the voltage dependence (due to barrier lowering) of the yield predicted by this model is given.
79 citations
TL;DR: In this paper, the optical constants n and k of magnetite have been determined in the photon energy region between 1 and 3 eV for temperatures between 77 and 300 K using reflectivity measurements.
65 citations
TL;DR: In this paper, the polarization of hard solar X-radiation (> 10 keV) is calculated on the assumption that electrons get a nonisotropic velocity distribution in the initial phase of a flare.
Abstract: The polarization of hard solar X-radiation (> 10 keV) is calculated on the assumption that electrons get a non-isotropic velocity distribution in the initial phase of a flare. The brems-strahlung generated by nonthermal electrons spiralling around magnetic field lines with discrete pitch angles is considerably polarized if observed at approximately right angles to the magnetic field. In the energy range from 10 to 50 keV the degree of polarization is not strongly dependent on the photon energy. For pitch-angle distributions of the form sin2α and cos2α, the polarization has opposite signs; it decreases appreciably at high photon energies. The observation of X-ray polarization will be useful in deducing the physical conditions in flares.
64 citations
TL;DR: In this article, the optical spectra of tetragonal HgI 2 single crystals were investigated at 4.2 K and 79 K in 2∼6 eV region of photon energy.
Abstract: The optical spectra of tetragonal HgI 2 single crystals were investigated at 4.2 K and 79 K in 2∼6 eV region of photon energy. The main part of the dichroic optical spectra is well described by the optical transition from three p -like valence bands, which are split due to spin orbit interaction and crystal field perturbation, to an s -like conduction band. The optical structures, which seem to be due to exciton series, were observed in the fundamental absorption edge for an ordinary light. The tail part of the absorption edge was well expressed by Urbach Rule.
56 citations
TL;DR: In this paper, the T matrix formalism of scattering theory was applied to derive general expressions for the absorption cross sections, the cross sections for resonance fluorescence and the emission quantum yields from large molecules in the statistical limit.
Abstract: In this paper we apply the T matrix formalism of scattering theory to derive general expressions for the absorption cross sections, the cross sections for resonance fluorescence and the emission quantum yields from large molecules in the statistical limit. In the simple case of an isolated molecular resonance both the absorption line shape and the photon scattering cross section exhibit a Lorentzian distribution on the photon energy, the emission quantum yields are distributed among the ground state vibronic levels according to their radiative widths and, most important, the emission quantum yields are independent of the photon energy and of the spectral width of the exciting light. We were able to derive general expressions for the resonance scattering from a pair of overlapping resonances, including radiative corrections to infinite order. The absorption cross section does not vanish in the region of destructive interference but assumes a finite value which depends on the radiative widths. A sharp maxim...
TL;DR: The absorption spectrum of naphthalene vapour has been photoelectrically recorded within the photon energy range from 5 to 30 eV using synchrotron radiation as discussed by the authors.
TL;DR: The photoionization absorption coefficients of helium, neon and argon have been measured by single beam photometry in the 60-230 eV photon energy range using a synchrotron radiation source and channel electron multiplier photodetection as discussed by the authors.
Abstract: The photoionization absorption coefficients of helium, neon and argon have been measured by single beam photometry in the 60-230 eV photon energy range using a synchrotron radiation source and channel electron multiplier photodetection. The accuracy of most of the data is +or-3% rising to +or-5% for a few cases in helium. Agreement with theory is typically better than 20% for photon energies up to 150 eV with greater discrepancies at higher energies especially for helium and argon.
TL;DR: The dielectric constants of MoTe2 and WSe2 have been measured over the photon energy range 0.5 to 3.8 eV and derived direct optical band gap energies compared with the measured activation energies of intrinsic electrical conduction.
Abstract: The dielectric constants of (2H) MoTe2 und (2H) WSe2 have been measured over the photon energy range 0.5 to 3.8 eV and the derived direct optical band gap energies compared with the measured activation energies of intrinsic electrical conduction. A systematic excitonic description of the MoSe2, MoTe2, and WSe2 spectra is given, together with an outline development of the band structures of these compounds.
TL;DR: The efficiency of vacuum u.v. for producing single‐strand breaks in DNA was determined by using the supertwisted RF‐DNA of bacteriophage φX174 to demonstrate that in this energy range only a small fraction of the ionizations leads to strand breakage in DNA.
Abstract: — The efficiency of vacuum u.v. for producing single-strand breaks in DNA was determined for wavelengths between 58 and 254 nm (corresponding to photon energies of 21·2 and 4·9 eV, respectively) by using the supertwisted RF-DNA of bacteriophage φX174. The cross-section for production of single-strand breaks increases continuously by about 5 orders of magnitude between 5 and 10 eV photon energy, whereas from 11 to 21 eV the number of strand breaks produced per unit of incident radiation energy is approximately constant. Thus, absorption of a 10-eV photon causes DNA strand breaks with maximum efficiency. In addition, the number of electrons liberated from DNA by photons below 10 eV is one or two orders of magnitude higher than the frequency of strand breaks, demonstrating that in this energy range only a small fraction of the ionizations leads to strand breakage in DNA.
TL;DR: The photoelectron angular distribution parameter β for the 3p shell of argon has been measured over a range of photon energies in this article, and the results are in good agreement with the Hartree-Fock calculation of Manson and Kennedy.
TL;DR: The surface photovoltage inversion effect has been observed in ZnO single crystals, manifested as a pronounced increase in the surface barrier height under sub-bandgap illumination as mentioned in this paper.
TL;DR: In this paper, a simple and exactly soluble model for exciton-LO phonon interactions, with no free parameters, was exploited to study optical absorption below the fundamental edge in polar semiconductors.
TL;DR: In this article, a stochastic superposition of the individual Cu and Ni metal spectra is proposed to explain the wide structures in the transition metal spectrum as a predominantly atomic effect.
Abstract: CuNi alloy films have been investigated in the vicinity of the onset of 3p electron absorption in the photon energy range 50 to 90 eV. The spectra obtained can be described as a stoichiometric superposition of the individual Cu and Ni metal spectra. Any rearrangement of the states due to an alloy interaction is of no great influence. This result is in general agreement with results on soft X-ray emission, uv and X-ray photoelectric emission. It is in contradiction to the rigid band model and supports more recent alloy theories such as the coherent-potential approximation. This result, moreover, supports the interpretation of the wide structures in the transition metal spectra as a predominantly atomic effect.
Dunne Schichten einer CuNi-Legierung wurden in der Umgebung der Absorption der 3p-Elektronen im Photonenenergiebereich 50 bis 90 eV untersucht. Die Spektren konnen als stochiometrische Superposition der Spektren von Cu und Ni beschrieben werden. Veranderungen der Zustande durch die Legierungsbildung sind ohne merklichen Einflus. Dieses Ergebnis zeigt die gleiche Tendenz wie Rontgenemissionsmessungen im weichen Rontgengebiet und Photoelektronenuntersuchungen im UV− und Rontgengebiet. Es steht im Widerspruch zum „rigid-band-model” und unterstutzt neuere Theorien wie die „coherentpotential approximation”. Daruber hinaus spricht dieses Ergebnis fur eine atomare Deutung der breiten Maxima in den Spektren der Ubergangsmetalle.
Patent•
10 Jul 1972TL;DR: In this article, a solid-satte semiconductor constant photon energy source and circuits therefor, including a temperature-compensating circuit and a light-sensing control element circuit, are discussed.
Abstract: The disclosure herein relates to a solid-satte semiconductor constant photon energy source and circuits therefor, including a temperature-compensating circuit and a light-sensing control element circuit.
TL;DR: A Compton polarimeter for measuring the linear polarization of resonantly scattered neutron-capture γ-rays in the energy region 4-9 MeV is described in this paper. But the performance of this system as a function of photon energy for perfectly polarized radiation is given.
TL;DR: In this article, the differential cross section of the reaction γ D→ π 0 D has been measured at constant momentum transfer for photon energy ranging from 220 MeV to 500 MeV.
TL;DR: In this paper, general expressions for the spectral distribution and attenuation of the intensity and exposure-rate of bremsstrahlung generated in a thick plane absorbing target by electrons of constant medium energy are derived in terms of intensity-photon energy distribution of the radiation at its point of origin, on the assumption that electron penetration of the target is given by the Thomson-Whiddington relation.
Abstract: General expressions for the spectral distribution and the attenuation of the intensity and exposure-rate of bremsstrahlung generated in a thick plane absorbing target by electrons of constant medium energy are derived in terms of the intensity-photon energy distribution of the radiation at its point of origin, on the assumption that electron penetration of the target is given by the Thomson-Whiddington relation. Comparison of computed exposure-rate attenuation curves with published experimental results shows that agreement is sensitive to the form assumed for the variation with bremsstrahlung energy of the coefficient B of the differential radiative cross section of the target nucleus, and that significantly better agreement is obtained when this is assumed to decrease with increasing photon energy, rather than remain constant, in general agreement with the predictions of Bethe and Heitler (1934). It is concluded that the reasonable agreement shown with the results of computations based upon the Kulenkampff-Kramers expression for radiation intensity leaving the target is fortuitous, being the result of the near-cancellation of errors arising from (i) the neglect of target absorption, and (ii) the assumption of a constant value for B.
TL;DR: In this article, the optical properties of AuCr and AuV alloy systems were investigated through a photon energy range 0.6 eV to 4 eV using an ellipsometric technique on bulk specimens.
Abstract: The optical properties of AuCr and AuV alloy systems have been investigated through a photon energy range 0.6 eV to 4 eV using an ellipsometric technique on bulk specimens. In the infrared region nearly Drude type absorptions is observed with collision frequency dependent on both concentration and impurity. The movement of the absorption edge on alloying is found to lie between the predictions of the rigid band model and of Friedel's work. Both parts of the main absorption edge are consistent with the assumption that they are associated with transitions from the d band to the Fermi level. In the case of AuCr extra absorption bands were detected compared with pure Au and these were interpreted in terms of virtual energy levels in the region of 1.2 eV from the Fermi level.
TL;DR: In this paper, an analysis of the spectral distribution of quantum yield and the applicability of the Einstein equation in the near beyond threshold region were made out for photoemission and compared with data on photoconductivity, and photoionization processes in molecular crystals at photon energy larger than the bandgap energy were discussed.
Abstract: An analysis has been made out for the spectral distribution of quantum yield and for the applicability of the Einstein equation in the near beyond-threshold region. Results obtained for photoemission have been compared with data on photoconductivity. Photoionization processes in molecular crystals at photon energy larger than the bandgap energy are discussed also.
[Russian text Ignored].
TL;DR: In this article, a new type of resonance has been found in the absorption as a function of magnetic field, independent of the photon energy, attributed to the variation in the carrier transfer between valleys which are not equivalent with respect to the magnetic field.
Abstract: Phonon-cyclotron resonance in the free-carrier magnetoabsorption of $n$-type PbTe has been studied. The results observed for the many-valley conduction band with an anisotropic effective mass in each valley depend on the orientation of magnetic field relative to the crystal axes, and resonances are observable with polarization of radiation either longitudinal or transverse relative to the magnetic field. The results interpreted with the help of a theory provide a determination of the anisotropic effective mass and the energy of longitudinal-optical phonons. A new type of resonance has been found in the absorption as a function of magnetic field, independent of the photon energy. The effect has been observed only with radiation of longitudinal polarization. It is attributed to the variation in the carrier transfer between valleys which are not equivalent with respect to the magnetic field. The "carrier-transfer resonance" may be useful for the study of anisotropic carrier absorption in individual valleys.
TL;DR: In this article, weak impurity lines appear on sweeping the field with laser wavelenghts where photon energy is insufficient to cause transitions from the ground state to any of the excited states if the impurities.
01 Jan 1972
TL;DR: In this article, the width and energy of the occupied and unoccupied 5d-bands have been determined as well as the energy relative to the Fermi level of the bottom of the valence band.
Abstract: Photoemission measurements have been made on samarium and erbium in the photon energy range 4 to 21 eV. The photoelectron energy distributions are dominated by electron emission from valence band states whereas emission from 4f-states is unimportant. The width and energy of the occupied and unoccupied 5d-bands has been determined as well as the energy relative to the Fermi level of the bottom of the valence band. A model for the unscattered yield is presented allowing a determination of the hot electron scattering length for some rare-earths using available optical and photoemission data.