摘要:

We present a simple and inexpensive computer code for free electron laser (FEL) operation that includes high gain and inhomogeneous broadening effects. The code is based on analytical formulae, obtained within the context of the theory of FEL approximants, requires negligible CPU time, and may run on small computers. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363780

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Probability distributions of the peak output power from planar microcavity dye lasers with pulsed excitation have been studied experimentally. Two microcavities were used, one operating possibly with a single mode and the other possibly with a number of modes. These expectations are based on the relative magnitude of the mode radius and the pump beam radius. In the former cavity an exponential‐like distribution was observed below threshold, which indicates single‐mode operation. In the latter cavity a single‐peaked distribution appeared even below threshold indicating multiple‐mode operation. These results are, respectively, in qualitative agreement with theoretical distributions for steady state. That the observed pulse width is large enough to apply steady state distribution equation is shown by calculating the characteristic transient time for the intensity distribution. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363782

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Linear electroabsorption (LEA) and linear electro‐optic (LEO) measurements are demonstrated using a model guest/host system consisting of disperse red 1 (DR1) doped in poly(methyl)methacrylate (PMMA). The LEA response is measured over a wavelength range of 300–700 nm. Electro‐optic measurements of the real and imaginary parts of the electric field‐induced Pockels coefficient are carried out at wavelengths near and far from the resonant absorption. A shift in the absorption maximum and change in the band shape of the LEA spectrum are related to the linear Stark effect and dipolar orientation. Expressions for the real and imaginary parts of the Pockels coefficient derived from the two experiments are provided. Induced dipolar order as a result of the contact poling process is investigated by the LEA measurement. Information concerning the relaxation of the induced dipolar order, investigated by the LEA measurement, is compared to the relaxation results obtained by using the second‐harmonic generation technique. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363783

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An analysis of the nonexponential behavior of the kinetics of the initial laser level for three‐micron generation (4I11/2) in an Er3+(45 at. %):YAlO3crystal under intense pump in the4S3/2level is performed. The observed nonexponential4I11/2decay can be satisfactorily described by the rate equation model which includes energy transfer processes inside the system of erbium ions, such as up‐conversion from4I13/2and4I11/2and cross‐relaxation from4S3/2and4I9/2provided only a small fraction (&bgr;21≊0.11) of the excitation from4I11/2level reaches the terminal laser level,4I13/2. The low value of &bgr;21and the observed reduction of the fluorescent lifetime of4I11/2with the increasing erbium doping could be related to the presence of accidental impurities. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363748

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Surface acoustic wave directional couplers have long been known in both microwave and integrated acoustic applications. Such couplers are ideal for integration in acoustical signal processing devices, such as modulators or switches. There are, however, very few publications concerning the frequency response of these devices. This article represents both experimental and theoretical studies on the frequency response of directional couplers, with and without a thin strip deposited in the gap between the main channels. The beam propagation method, used in integrated optics, was adapted for acoustical directional couplers. It enabled the analysis and prediction of the frequency response of these types of couplers. Calculations were performed for the channels and interdigital transducers in the frequency range of 50–90 MHz. By using proper dimensions of the couplers’ parameters, coupling efficiency for the higher part of the frequencies, in the receiver channel, was increased. This increase enables the selection of receiver frequencies and, therefore, a frequency channelizer could be developed. A thin strip between the main channels increases the coupling efficiency between the two channels and thereby reduces by about 30% the length of the coupler required for different frequency selections or conventional switches. This reduction makes it possible to obtain more compact devices with reduced losses. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363784

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Sets of electron‐molecule collision cross sections for H2O and NH3have been determined from a classical technique of electron swarm parameter unfolding. This deconvolution method is based on a simplex algorithm using a powerful multiterm Boltzmann equation analysis established in the framework of the classical hydrodynamic approximation. It is well adapted for the simulation of the different classes of swarm experiments (i.e., time resolved, time of flight, and steady state experiments). The sets of collision cross sections that exist in the literature are reviewed and analyzed. Fitted sets of cross sections are determined for H2O and NH3which exhibit features characteristic of polar molecules such as high rotational excitation collision cross sections. The hydrodynamic swarm parameters (i.e., drift velocity, longitudinal and transverse diffusion coefficients, ionization and attachment coefficients) calculated from the fitted sets are in excellent agreement with the measured ones. These sets are finally used to calculate the transport and reaction coefficients needed for discharge modeling in two cases of typical gas mixtures for which experimental swarm data are very sparse or nonexistent (i.e., flue gas mixtures and gas mixtures for rf plasma surface treatment). ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363785

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A theoretical and experimental investigation is made of the leakage power in microwave transmit–receive switches. The peak leakage power is shown to be independent of incident peak power but to depend on the rise time of the incident pulse. The plateau leakage power through the switch is also estimated and shown to be independent of incident peak power. The theoretical predictions for peak leakage power and plateau leakage power are compared and found to be in good agreement with experimental results. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363781

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The radial distribution of electron and ion fluxes to conducting and nonconducting walls in a planar inductively coupled plasma has been studied experimentally and theoretically. Measurements of electron and ion currents have been performed using electrostatic probe arrays. Radially resolved measurements of ion impact energies have been performed using an ion energy analyzer array. For conducting walls it is shown by calculations and measurements that electron and ion currents are not in balance locally but that diffusion is nonambipolar. The ion impact energies measured on a conducting surface show a significant radial variation in accord with our theoretical model. For nonconducting surfaces the ambipolar fluxes of electrons and ions result in the formation of a surface charge potential profile across the surface. Voltages of the order of several volts between the center and the periphery of the surface are measured. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363786

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An electron spin resonance (ESR) signal comprised of three resolved lines of equal 19.3 Gauss separation (3×19.3 G), but unequal amplitude, is observed in x‐irradiated amorphous silicon dioxide. The radical appears exclusively in silica samples which also exhibit the methyl radical, a familiar indicator of trace carbon and hydrogen contamination. The 3×19.3 G signal is observed to grow most rapidly versus irradiation dose when methyl radical concentration is near maximum. This evidence suggests that the ESR signal is due to a radiolytic, organic radical which evolves after the methyl radical and, like the methyl radical, is trapped and stabilized in the amorphous silica network. Experimental methods of radical generation are presented, followed by discussion of models for the chemical structure of the 3×19.3 G radical. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363787

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Ag ions were implanted in LiNbO3at energies of 25 keV and 3 MeV. Optical absorption spectra were measured in the visible range. A large absorption peak due to small colloidal Ag metal was observed at 460 and 510 nm for the as‐implanted sample at 3 MeV and 25 keV, respectively. Subsequently, the samples were heated in air up to 600 °C. The absorption peak moved toward longer wavelengths up to 560 nm when the sample was heated at high temperature. Small droplets of metallic Ag expelled from the implanted layer formed on the surface of the sample even when the samples were held at room temperature. The number and size of the droplets grew with time and their growth was accelerated when the samples were heated at high temperature. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363788

出版商:AIP    

年代:1996

数据来源: AIP