Hofstadter spectrum in electric and magnetic fields

The problem of Bloch electrons in two dimensions subjected to magnetic and intense electric fields is investigated. Magnetic translations, electric evolution, and energy translation operators are used to specify the solutions of the Schrödinger equation. For rational values of the magnetic flux quanta per unit cell and commensurate orientations of the electric field relative to the original lattice, an extended superlattice can be defined and a complete set of mutually commuting space-time symmetry operators is obtained. Dynamics of the system is governed by a finite difference equation that exactly includes the effects of: an arbitrary periodic potential, an electric field orientated in a commensurable direction of the lattice, and coupling between Landau levels. A weak periodic potential broadens each Landau level in a series of minibands, separated by the corresponding minigaps. The addition of the electric field induces a series of avoided and exact crossing of the quasienergies, for sufficiently strong electric field the spectrum evolves into equally spaced discreet levels, in this “magnetic Stark ladder” the energy separation is an integer multiple of hE/aB, with a the lattice parameter.     

Disorder broadening of alloy Auger spectra

Auger spectroscopy promises the means to separate initial and final state contributions to the disorder broadening of core XPS spectra in disordered alloys. Auger disorder broadening, deduced from recent ab initio results, is predicted to be greater than XPS disorder broadening for Cu₅₀Pd₅₀ and Ag₅₀Pd₅₀ alloys. Simulations are used to assess whether this effect is observable experimentally despite the greater lifetime broadening of Auger spectra. A number of cases where narrow core–core–core Auger transitions should allow clear experimental identification of this effect are identified. The prospects for determining environment-resolved Auger spectra using APECS have been investigated.     

Stark broadening in the Sb III spectrum

The shapes of nine doubly ionized antimony (Sb III) spectral lines have been obtained in the laboratory helium plasma at 17 500 K electron temperature and electron density of . Measured line profiles are of a Voigt type. At the mentioned plasma conditions the Stark broadening has been found as the dominant mechanism in the Sb III line shapes formation. Using a deconvolution procedure the Lorentz (Stark) FWHM (Full-Width at Half of the Maximal intensity, W) have been obtained. Our measured Sb III Stark widths are the first data in the literature. The modified version of the linear, low-pressure, pulsed arc was used as a plasma source operated in helium with antimony atoms, as impurities. They were evaporated from the thin antimony layer, deposited on the silver cylindrical plates, located in the homogenous part of the discharge. This plasma source ensures good conditions for the generation of the doubly ionized antimony atoms in the helium plasma due to atomic processes concerning helium metastables.     

Line broadening of the EPR absorption spectrum of ruby

Experimental evidence is given that the EPR absorption spectrum of diluted ruby is about 100% homogeneously broadened when observed with the external field H perpendicular to the ruby crystal axis, while it is inhomogeneously broadened, with well defined spin packets, when observed with H parallel to the ruby crystal axis. Relation to ENDOR and spin-echo experiments is discussed.     

Turbulence-induced square-root broadening of the Raman fiber laser output spectrum

The output characteristics of the conventional one-stage Raman fiber laser (RFL) are described in an optical wave turbulence formalism. Simple analytical expressions describing RFL output power and its spectral shape are presented, and square-root law for the output spectrum broadening law has been discovered. The indications of the turbulent-like spectral broadening in other types of cw fiber lasers and propagation phenomena in fibers are also discussed.     

Pressure broadening and shift in the millimeter-wave spectrum of formaldehyde

Helium, hydrogen, and self-broadening have been measured at room temperature for 12 lines of formaldehyde between 100 and 300 GHz. The self-broadening parameters ranged from 20 to 30 MHz/Torr, with typical accuracies of 0.5–0.8 MHz/Torr. For all measured lines the helium and hydrogen broadening parameters were 2.5 and 5.5 MHz/Torr, respectively, to within the experimental accuracy, typically 0.25 MHz/Torr. Pressure shifts of up to 2.5 MHz/Torr were observed in self-broadening, with estimated errors of 0.25–0.50 MHz/Torr. No significant lineshifts were seen in the foreign gas broadening measurements.The observed widths and shifts are compared with those calculated from three models of molecular collisions: Anderson's pressure broadening theory, a similar semiclassical theory of Rabitz and Gordon, and a hard-sphere, sudden approximation model of Thaddeus.     

Solid state broadening effects in the Auger spectrum of xenon

The M_4,5N_4,5 Auger spectrum has been measured at high resolution from solid xenon. Comparison with the gas phase data shows that considerable broadening of the Auger lines occurs in the solid. Electron energy loss data is also reported for solid xenon.     

Disorder induced core photoelectron linewidth broadening in AgPd alloys

High resolution core level photoelectron spectra for a series of Ag_xPd_1−x alloys have been measured and reveal a large “disorder broadening” effect. A comparison of measurements of this effect for three alloy systems, Ag_xPd_1−x, Cu_xPd_1−x and Cu_xZn_1−x, with results of ab initio calculations is presented. Poor agreement is obtained and possible reasons for this observation are discussed.     

Revision on the calculation of optically pumped FIR laser spectrum with Doppler broadening and pressure broadening effects

By means of iteration method and also taking into account Doppler broadening and pressure braodening effect of IR pumping laser, the output power density of optically pumped NH₃ molecules FIR laser is calculated by solving density matrix equations of three-level system. The results of theoretical calculation shows that, in comparison with the FIR laser under the assumption of ideal monochromatic IR pumping, the output power density of FIR laser in the case of Doppler broadening and pressure broadening IR pumping decreases much more. Meanwhile, via the revision of Doppler broadening and pressure broadening effect, the theoretical value of optimum operating gas pressure reduces, which is in better agreement with the experimental value. Further study shows that the revision of Doppler broadening effect is more fit for the conventional FIR laser with a 2m sample tuble and the revision of pressure broadening effect is much more suitable for the miniature FIR laser with a short sample tube of 5 to 20cm in length.Supported by the National Natural Sciences Foundation of P.R.China and the NSF of Guangdong Province.     

Collisional broadening and shifting of OCS rotational spectrum lines

Broadening and shifting of carbonyl sulfide (OCS) rotational spectrum lines by pressure of N₂, O₂ and OCS were accurately studied in the frequency range 24–850 GHz at room temperature using a spectrometer with radio-acoustic detection of absorption. Rotational dependences of collisional widths of OCS spectrum lines were determined by a simple empirical polynomial fit of experimental data. Experimental uncertainties were analyzed. Results of supplementary test measurements of self-broadening of rotational OCS lines in the ν₂ excited vibrational state and carbon monoxide (CO) lines in the ground vibrational state are presented. Comparison of the obtained results with previously known measurements and theoretical calculations is given. The performed work allows for the first time development of accurate gaseous etalon of absorption for atmospheric applications and laboratory use, covering continuously the whole millimeter- and submillimeter-wave range.     

Argon and nitrogen broadening in the pure rotational spectrum of HCl

The Ar- and N₂-broadened linewidths have been measured for the first four pure rotational transitions of HCl. The spectra were taken by means of a Fourier transform spectrometer working in the range 10–100 cm⁻¹ with an apodized resolution of 0.05 cm⁻¹. The results obtained generally agree with those of other authors. Comparison is also made with the most recent results of various theoretical calculations.     

Real-time full spectrum fitting of beam-based Doppler broadening data

A full spectrum fitting code, developed and used by the Bath positron group to compute the fractions of positrons annihilated from surface, defect and bulk states as a function of incident positron energy, is described. To date, the most useful application of the code has been in studies of ion-implanted silicon, being particularly useful in the observation of the formation of oxygen-divacancy complexes. The advantages and limitations of the code are discussed.     

水汽分子对CO_2谱线加宽的影响

报道了以高分辨力连续可调谐中红外差频激光为探测光源,结合可调长光程怀特池,利用直接吸收的方法探测了CO2的10011←10002带R支以及部分P支在室温下的水汽加宽吸收光谱。在2422cm-1到2457cm-1范围内共有26条吸收谱线被探测到,采用Voigt线型对吸收谱线进行拟合,得到了CO2光谱的水汽加宽系数,结果显示CO2的水汽加宽系数平均比干燥空气的加宽系数大52%。利用实验测得的CO2的水汽加宽系数与HITRAN04数据库中CO2谱线的线位置、线强和干燥的空气加宽系数进行比较,分析了在实际大气中(海平面,10km光程)不存在水汽和存在水汽(含有2.0kPa水汽)时该波段CO2的大气透过率,结果表明潮湿空气与干燥空气之间的最大透过率差约为0.5‰。     

Fixed points of the dissipative Hofstadter model

The phase diagram of a dissipative particle in a periodic potential and a magnetic field is studied in the weak barrier limit and in the tight binding regime. For the case of half flux per plaquette, and for a wide range of values of the dissipation, the physics of the model is determined by a nontrivial fixed point. A combination of exact and variational results is used to characterize this fixed point. Finally, it is also argued that there is an intermediate energy scale that separates the weak coupling physics from the tight binding solution.