Symmetry breakdown in ground state dissociation of HD+

Experimental studies of the dissociation of the electronic ground state of HD+ following ionization of HD by fast proton impact indicate that the H++D(1s) dissociation channel is more likely than the H(1s)+D+ dissociation channel by about 7%. This isotopic symmetry breakdown is due to the finite nuclear mass correction to the Born-Oppenheimer approximation which makes the 1ssigma state 3.7 meV lower than the 2psigma state at the dissociation limit. The measured fractions of the two dissociation channels are in agreement with coupled-channels calculations of 1ssigma to 2psigma transitions.     

Non-adiabatic transitions at a continuum edge

We consider interaction of a single level with a broad, tending to semi-infinite continuum. In an example of two exactly solvable problems, we show that for time dependent quantum systems the probability of the irreversible transition from a discrete level to a continuum is strongly inhibited or even completely suppressed by the presence of a discrete adiabatic level near the continuum edge. Received 10 October 2002 Published online 4 March 2003 RID="a" ID="a"e-mail: Alain.Sarfati@lac.u-psud.fr     

Unusual one-way edge state in acoustic gyroscopic continuum

Unusual one-way edge states have been observed in composite structures composed of periodic lattices loaded with gyroscopes.Here, we provide a continuum-mechanics understanding to the one-way edge state by formulating surface state equations of acoustic gyroscopic mediums with Hermite mass density tensor. We discover that the unidirectional edge effect arises from nontrivial off-diagonal components of Hermite densities, which causes the symmetric breaking of surface wave propagation towards forward and backward directions. Theoretical predictions on the velocity and decay length of surface waves coincide excellently with numerical simulations. The unidirectional edge state in a two-interface gyroscopic medium is also analyzed.Due to the rotational symmetry in geometry, the unidirectional edge state on one interface is able to prevent itself from the coupling to surface waves on the other interface regardless of the slab thickness. With these anomalous effects, surface waves residing on gyroscopic mediums can flow around the edge defects without back-scatterings, or can be split into two beams of equal energy magnitudes. Our findings may make a bridge that would help to reach the design of non-reciprocal composite materials via an effective medium approach.     

Absorption edge of CdSb

Measurements of the absorption of CdSb near the absorption edge at temperatures of 300°, 200°, 80° and 15°K were carried out. The structure of the absorption edge was interpreted by means of indirect allowed transitions.     

Grating phase matching beyond a continuum edge

We show that fiber Bragg gratings can extend an optical continuum to spectral regions where continuum generation is very weak. Highly nonlinear fibers with Bragg grating resonances at 700, 750, and 800 nm were pumped with 70 fs pulses at 1580 nm and exhibited enhancement peaks up to 25 dB above the extremely weak continuum at these wavelengths, normally more than 40 dB below the average power in the continuum. We show that the grating peaks may be computed by treating the continuum pulse as an undepleted pump and including the grating dispersion as a phase-matching term.     

Absorption edge shift in lead-tin telluride

The absorption edge of lead-tin telluride was determined by means of transmission and photodiode spectral response measurements between 4 and 350K. It is found that degenerate material (P = 1 × 10¹⁸cm^-3) is characterized by a larger optical energy gap than nondegenerate material. A model suggested by Burstein was used to calculate the expected edge shift and compare it to the experimental results. The density of states effective mass for two samples was obtained by fitting the theoretical and the experimental results.     

Above threshold dissociation of vibrationally cold HD+ molecules

The experimental study of molecular dissociation of H2+ by intense laser pulses is complicated by the fact that the ions are initially produced in a wide range of vibrational states, each of which responds differently to the laser field. An electrostatic storage device has been used to radiatively cool HD+ ions enabling the observation of above threshold dissociation from the ground vibrational state by 40 fs laser pulses at 800 nm. At the highest intensities used, dissociation through the absorption of at least four photons is found to be the dominant process.     

Absorption edge of ultraheavily doped Si

The absorption edges of P- and As-ion implanted, laser-annealed thin SOS films have been measured between 1.5 and 3.5 eV. The strong increase in absorption reported by Jellison et al. for As-doped samples has been shown to be spurious. It has nevertheless been found that these edges shift towards the red by ～0.3 eV for either P or As doping of concentration N_i ? 2×10²¹ cm^?3. These shifts are discussed in terms of the perturbation produced by the impurities on the band structure.     

The diffraction dissociation of deuterons on the diffused edge nuclei

The dependence of the cross-sections of various diffraction processes on the diffuseness of nuclear edge is calculated at the interaction of high-energy deuterons with nuclei. The immonotonous dependence of the deuteron dissociation cross-section on the mass number, conditioned by the influence of the nuclear edge diffuseness, is shown.     

Discussion on the dissociation of fast HD+2 ions traversing thin foils

the discussion is on the following experimental results: The energy distribution of the H+ and D+ fragments resulting from the dissociation of HD+2 molecular ions at energy 1.497 7 MeV has been measured using the Coulomb explosion technique. The spectra were used to determine the binding energy of HD+2 and its structure. There existed differences between the spectral structures for proton and for deuteron.     

Absorption and electroabsorption near the indirect edge of GaSe

Absorption and electroabsorption spectra have been measured near the indirect edge of the layer semiconductor GaSe. The experimental structures observed at 1.5 K are ascribed to the indirect excitonic transition with emission of different phonons. The determination of the threshold energy of the no-phonon indirect absorption process affords the energies of the phonons involved in the indirect transition to be derived.     

Quantum dissociation of an edge of a Luttinger liquid

In a Luttinger liquid phase of one-dimensional molecular matter the strength of zero-point motion can be characterized by dimensionless De Boer's number quantifying the interplay of quantum fluctuations and two-body interactions. Selecting the latter in the Morse form we show that dissociation of the Luttinger liquid is a process initiated at the system edge. The latter becomes unstable against quantum fluctuations at a value of De Boer's number which is smaller than that of the bulk instability which parallels the classical phenomenon of surface melting.     

Absorption edge shift: Internal electric field model

The shift of the optical absorption edge caused by defect-induced electric fields through Redfield's internal Franz-Keldysh mechanism is discussed for semiconductors and insulators.     

分子吸收池在水中布里渊散射边缘探测技术中的应用

在用边缘探测技术测量水中的布里渊散射信号方法中,碘分子吸收池作为边缘滤波器探测水中的布里渊散射频移,2个相同的溴分子吸收池,一个作为带阻滤波器吸收瑞利散射信号,另一个用于激光器的稳频,提高了布里渊频移的探测精度.     

Absorption edge and photoconductivity of CuPbAsS3 Single crystals

Absorption curves of CuPbAsS₃ have been measured in the temperature range 90÷300 K. Their analysis leads to conclusion that the absorption edge of CuPbAsS₃ is due to allowed indirect electronic transitions between the valence and conduction band extrema. The forbidden-gap width, its temperature dependence and energies of three interacting phonons have been determined. The temperature shift of the photoconductivity band is in agreement with that of the forbidden gap in CuPbAsS₃.Leninovo nám. 565, Pardubice, Czechoslovakia.The authors are indebted to Dr. Vl. Syneek and Mrs V. Míková from the Institute of Solid State Physics, Czechosl. Acad. Sci., Prague for advice and help in orientation of prepared crystals.     

Absorption edge shift in ZnO thin films at high carrier densities

The optical absorption edge has been measured as a function of carrier concentration for thin films of zinc oxide prepared by organometallic chemical vapour deposition and reactive R.F. magnetron sputtering. Large shifts of the absorption edge have been observed which are only a function of the carrier concentration. Below n = 3 × 10¹⁹ cm^-3 the shifts are well described by the Burstein-Moss model. For carrier concentrations between 3–5 ×10¹⁹cm^-3, the shift decreases very rapidly, finally increasing again with further increases in the carrier density. These effects are consistent with a merging of the donor band with the conduction band following a semiconductor-metal transition.     

Absorption edge effects on the temperature dependence of threshold currents in GaAS laser diodes

The loss α, governing the threshold current in GaAs laser diodes is attributed to absorptive transitions involving tail states rather than free carriers.The determination of α from lasing photon energy and absorption edge data for compensated and uncompensated material yield a temperature dependence of α which can account for the temperature dependence of threshold currents observed experimentally.