摘要:

We characterize the performance of a built‐in hot filament broad beam ion source by mass spectrometry, energy analysis, and beam profile measurements. In the ion energy distribution we detect various peak structures which can be explained by the potential across the ion source and different charge transfer processes. Depending on the typical cross sections for these processes, differences between the energy distributions of the ion species are observed. The total ion current obtained with the source is determined by the ionization rate in the discharge and the current share directed toward the extraction grid system. The performance of the source is strongly dependent on the process gas used. We observe much broader energy distributions in oxygen and nitrogen than in argon. This broadening is explained by spatial inhomogeneities in the discharge region and can be reduced by a suitable setting of the source parameters. The main contribution to the ion flux is caused by species generated directly from the process gas, with important impurities from source materials appearing only with additional chemical reactions in oxygen. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362869

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This paper presents a detailed analysis of high‐load friction atomic force microscopy (AFM) images of layered structures in terms of a discrete stick‐slip model. It turned out that based on a geometric approach, the characteristics of slip behavior can be linked to the cantilever/sample spring anisotropy. In particular, the use of polar scans is emphasized to analyze and to quantify these characteristics. The measured stiffness as derived from the slip behavior is in correspondence with the stiffness inferred from static friction. It is concluded that the combined stiffness of substrate and cantilever is constant during an AFM scan in a given direction, which supports the simple stick‐slip model. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362870

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The generation of excimer radiation in mixtures of the rare‐gases Kr or Xe together with chlorine gas has been investigated by a dielectric barrier discharge. The characteristics of the emission spectra of the excimers formed, centered around 222 and 308 nm, were obtained for different gas mixtures and total gas pressures using an ultraviolet (UV) monochromator. The influence of the gas mixture, chlorine gas concentration, total gas pressure, and buffer gas dependence of the UV intensity has been investigated using chemical actinometry. Conversion efficiencies (from input electrical to output optical energy) as high as 15% can be achieved under optimal conditions. This low‐cost and high‐power excimer lamp system can provide an interesting alternative to conventional UV lamps for industrial large‐scale UV processes. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362871

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Strong stimulated cascade emission and coherent four‐wave parametric radiations are observed. By proper observation of the excitation spectra, the cascade emission and the coherent four‐wave mixing parametric processes can be identified. The effect of the buffer gas pressure on the intensity and the pulse compression of the emitted radiation were investigated. Cascade inversionless coherent radiation emission with absorption reduction and third order nonlinear susceptibility enhancement due to the presence of a strong internally generated field are discussed for the 4p–4sstrong emission observed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362872

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A model for quantitative analysis of microdisk laser emission spectra is presented. Conformal mapping is used to determine radial and azimuthal eigenvalues, eigenvectors, and cavityQcorresponding to leaky optical resonances in an optically transparent dielectric disk. The effects of gain and loss in a microcavity active medium are also included in the model. Our results compare well with experimental data obtained from an InGaAs/InGaAsP quantum well microdisk laser of radiusR=0.8 &mgr;m. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362873

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Germanosilicate glass waveguides were electrically poled using interdigitated electrodes. This poling resulted in a quasiphase‐matched second‐order susceptibility. Second‐harmonic light was observed. Measured intensities were one to two orders of magnitude smaller than expected based on previous electric‐field‐induced second‐harmonic (EFISH) generation studies with the same interdigitated electrodes. The dynamics of the EFISH signals were studied. Exponentially decaying signals suggest that through charge migration, via dielectric relaxation and electronic drift, a compromising field is established during the poling. This results in a weaker second‐order susceptibility. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362874

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Results of a study of laser‐induced synthesis of ZnSe from a stack of elemental layers are presented. The process is traced by real‐time, simultaneous measurement of both reflectivity and transmission of the irradiated thin films. Numerical solution of the thermal conductivity equation reveals that synthesis may develop at and above a well‐defined threshold temperature, which is set by the melting of selenium. Further, it is shown that the whole process comprises three independent successive steps: interlayer mixing (or alloying), chemical reaction (i.e., formation of an amorphous compound), and crystallization of that compound. Among other findings, this analysis shows that large atom transport velocities (in mm/s) are necessary to account for the extremely short duration of the mixing step. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362875

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The natural shape of a typical chemical oxygen‐iodine laser (COIL) beam is rectangular which means that the transverse cross section of the beam is rectangular. Such a rectangular beam can be split into two or more beams to carry out materials processing. The distance between such beams and the mode structure in the beams can affect the distribution of heat in the workpiece. This, in turn, affects the quality and efficiency of materials processing. A three‐dimensional quasi‐steady‐state thermal model is presented in this article, and an expression for the temperature distribution during laser heating with single or multiple COIL beams having rectangular spots is obtained. Calculations are carried out for single or two rectangular COIL beams. The depth of heating is found to increase when the distance between two beams is less than a certain value. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363555

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This work studies one‐dimensional and two‐dimensional heat transfer for short pulse lasers (<1 ps in duration) applied on metals using a two‐subsystem (i.e., electrons and phonons) temperature model. In this model laser energy is first deposited on the electrons, which then exchange energy with the lattice. Conduction of energy is by electron motion only and the lattice contributes to the scattering of electrons. The objectives of this study are (a) to analyze the effects of different parameters such as electron specific heat, lattice specific heat, electron–phonon coupling factor, and thermal relaxation time for the one‐dimensional electron and lattice temperature distributions using both hyperbolic and Fourier heat conduction formulations; (b) to examine two‐dimensional effects including the effects of laser beam radial variance, laser fluence, and laser power in addition to the above parameters; and (c) to solve the transient equation of radiative transfer to incorporate the wave nature of the radiative source for the one‐dimensional case. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362876

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A laser machining model for ceramics and glass ceramics is developed from the analytical treatment of a one‐dimensional vaporization problem with a distributed heat source. Analytical solutions are derived for evolution of the material system from an arbitrary initial state to a quasisteady state. The developed solutions are used to predict the behavior of high‐intensity Nd:YAG laser pulses (up to 107W/cm2, ms duration) on a typical ceramic or glass ceramic material. Predictions include the critical intensity required for vaporization of materialIc, the material removal &Dgr;M, and thickness of the affected residual surface layerSafter a single laser pulse of given shape and intensity. Predictions are compared with the numerical calculations from a commercially available software package. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362877

出版商:AIP    

年代:1996

数据来源: AIP