摘要:

A recently developed class of digital filters known as morphological pseudoconvolutions is applied to scanning tunneling microscopy (STM) images. These filters use a nonlinear branch of image processing known as morphology to improve the characteristics of both moving mean and moving median filters. They filter equally in both thexandydirections, so as not to introduce artifacts, and they have an adjustable parameter that allows the user to restore the observed image completely as the parameter tends to infinity. Very few assumptions are made concerning image and noise content; only the shape of typical data is taken into account. These filters are shown to outperform, both visually and in the mean‐square‐error sense, previously introduced Wiener filtering techniques. The filters are compared on typical STM‐type images, using both modeled and actual data. The technique is general, and has been shown to perform very well on all types of STM and atomic force microscopy images.

ISSN:0021-8979    

DOI:10.1063/1.351233

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The wavelength shifts of theR1 andR2 fluorescence lines of alexandrite (BeAl2O4:Cr+3) have been experimentally calibrated against the ruby‐fluorescence scale as a function of both hydrostatic and nonhydrostatic pressures between 0 and 50 GPa, and simultaneously as a function of temperatures between 290 and 550 K. The results can be expressed in nm as &lgr;(R1)=680.26(±0.01)+8.7×10−3(±0.3) (T−273)+0.292(±0.003)P+1.3(±0.1)×10−3 P2and &lgr;(R2)=678.63 (±0.01)+7.8×10−3(±0.2)(T−273)+0.031 (±0.003)P+0.8(±0.1)×10−3 P2, with pressurePin GPa and temperatureTin K. Notably, we find that the pressure–temperature cross derivative of the fluorescence wavelength shifts are negligible for both ruby and alexandrite.

ISSN:0021-8979    

DOI:10.1063/1.351234

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The details of the autoresonance acceleration scheme suggested recently are being investigated below. The eikonal perturbation analysis is presented as well as some numerical results on the finite current effects. An electron cyclotron maser as well as a peniotron‐like interactions are discussed for the acceleration with a circularly polarized TE21mode in a round waveguide. Experimental data, resulting from an improvement of the axial magnetic field, showing acceleration to 200 keV out of the expected 250 keV, are reported.

ISSN:0021-8979    

DOI:10.1063/1.351235

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Canonical aberration theory has been applied to analyze the aberration structure of both electrostatic and magnetic multipoles. It is shown rigorously that for 2N‐pole magnetic multipoles withN=even, there is no axially symmetric aberration of any order, while for all the other cases of electromagnetic multipoles, there is always an axially symmetric aberration of the order of 2N−3. The method used is general in nature and can be applied to obtain detailed formulas of higher‐order aberrations of multipoles and also to study their off‐axis aberrations.  

ISSN:0021-8979    

DOI:10.1063/1.351236

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A comparison is made between the second‐order polarizabilities of nitropyridine derivatives determined with two different methods: electric‐field‐induced second‐harmonic generation (EFISH) and a solvatochromic method. Both techniques yield the same values within the experimental errors, showing that the main contribution of the microscopic nonlinearity arises from a single intramolecular charge‐transfer transition. Based on the quantum‐mechanical two‐level model, the solvatochromic method also yields important molecular parameters, such as transition and excited‐state dipole moments. The second‐order polarizabilities determined with the EFISH method are shown to follow the theoretical two‐level dispersion.

ISSN:0021-8979    

DOI:10.1063/1.351237

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An electron‐beam pumped XeF(C‐A) laser has been operated as an injection controlled oscillator. The electron‐beam pump rate was 290 kW/cm3and the pulse length was 600 ns. An etalon controlled dye laser was used as the injection source and reduced the free‐running laser linewidth from 16 to 0.003 nm. The intrinsic laser efficiency of the injection controlled XeF(C‐A) excimer was 1.8% with a specific output energy of 3 J/l, exceeding the free‐running performance.

ISSN:0021-8979    

DOI:10.1063/1.351216

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Characteristics of the fission‐fragment excited helium/argon laser operating on the 1.79‐&mgr;m (3d[1/2]0,10−4p[3/2]1,2argon transition are presented. Laser output occurs for approximately 80% of the 0.9 to 3 ms full width at half maximum thermal neutron pump pulse. Output power efficiency optimizes for a total gas pressure of 760 Torr and argon concentration of 0.3% to 2.0%. Power efficiency was 1.4%±0.4% for instantaneous pump rates of 45 to 230 W/cm3. The small signal gain and saturation intensity for instantaneous pump rates of 30 to 90 W/cm3are 0.55% to 1.05%/cm and 70 to 110 W/cm2, respectively. The laser threshold as a function of helium pressure and argon concentration will be presented. The advantages of fission‐fragment excitation in predominantly helium gas mixtures will be discussed.

ISSN:0021-8979    

DOI:10.1063/1.351217

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A new thin‐film optical testing method is described for both thickness and sound velocity of transparent films on opaque substrates with laser picosecond acoustics using the optical pump‐probe technique. The theory of excitation and detection of ultrasonic stress pulses for this geometry is presented in detail together with experimental results for sputtered thin films of silica of thickness 200 nm–2 &mgr;m on amorphous germanium substrates. Reflectance variations, measured as a function of pump‐probe delay time, are characterized by echoes and beating oscillations superimposed on periodic steplike changes. These effects are modeled as a sum of an echo contribution from the stress‐induced modulation of the substrate reflectance, an interference contribution from the light reflected by the moving stress pulse in the transparent film, a contribution from the modulation of the light on transmission through this stress pulse, and a contribution from the stress‐induced ultrafast vibrations of the film interfaces of order 10−3nm. The latter contribution arises from thin‐film interference effects that represent a novel detection mechanism for surface vibrations in the picosecond regime. Sound velocity and thickness are derived from the data to an accuracy of a few percent, and the photoelastic constant of the transparent film is determined.

ISSN:0021-8979    

DOI:10.1063/1.351218

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A study of the operation of the XeF(B‐X) laser under low‐electron‐beam pump rate and high‐energy loading is reported. Measurements have been performed at pump rates of 36, 44, and 66 kW/cm3with laser output pulse lengths greater than 4 &mgr;s in duration and energy loadings up to 280 J/l. Intrinsic laser efficiencies of 2.0% at 66 kW/cm3, 1.7% at 44 kW/cm3, and 1.5% at 36 kW/cm3were measured in optimized NF3, Xe, Ne mixtures. Under optimum conditions specific output energies as high as 5.6 J/l were measured. Gain and absorption were also measured.

ISSN:0021-8979    

DOI:10.1063/1.351193

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Holograms are recorded by laser‐assisted oxidation of thin tellurium films in air. The process of recording is characterizedinsituby measuring the evolution of a self‐diffracted beam of a cw Ar+laser. Stationary diffraction efficiency is shown to be independent both on the recording beam power and on the grating period. Amplitude holograms are obtained with an efficiency of 3.2% at a spatial period of 3 &mgr;m.

ISSN:0021-8979    

DOI:10.1063/1.351370

出版商:AIP    

年代:1992

数据来源: AIP