摘要:

System functions of many linear physical systems or autocorrelation functions of their output signals are often a sum of relaxator terms with different relaxation times and amplitudes. In the time domain a superposition of exponential decayse−&ggr;tis observed, while in the frequency domain a sum of relaxator terms of structure 1/(&ggr;+i&ohgr;) is measured. Thus, the response is either the Laplace transform of the system function or its Stieltjes transform, respectively. In both cases it is the task of an analyst to gain the relaxation times and weights from the measured signal. An exact reconstruction of the system function is limited by the noise, measuring time, and number of points measured. In this paper procedures for the approximate reconstruction of the system function are introduced. The equivalence of most of them is shown and their properties are discussed. An expression for the limit of resolution is derived for a given signal‐to‐noise ratio. The results are applicable to experimental data from various physical systems. For illustration the autocorrelation function of the light scattered from polymer solutions and the response of photoconductors are used.

ISSN:0021-8979    

DOI:10.1063/1.348634

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have analyzed a linear radio‐frequency ion trap of finite length employing a four‐sectored hollow cylinder enclosed between two end caps. Solutions to Laplace’s equation determine the effective potential inside the trap due to the rf trapping field, the static confining potential from dc‐biased end caps, and the potential arising when a dc bias is present on the cylinder sectors. The finite length of a linear trap results in field distortion at the trap ends due to fringing effects. We have demonstrated that near the ends, the effective potential arising from the rf fields acts to propel ions out of the trap. We have further shown that the addition of a dc bias on two neighboring cylinder sectors generates an inhomogeneous field in the trap which produces a force on the ions along the trap’s long axis in a direction dependent on the sign of the bias. An exact analytic determination of the potential can be used to determine the profile of the trapped ion cloud.

ISSN:0021-8979    

DOI:10.1063/1.348635

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Cathodoluminescence (CL) scanning electron microscopy has been used to investigate the nature and distribution of defects involved in the infrared emission of GaAs:Te wafers. Spectral and CL‐contrast changes as a function of doping level have been found. Profiles of infrared CL intensity across the wafers show an inverted U shape.

ISSN:0021-8979    

DOI:10.1063/1.348636

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

It is demonstrated that frequency pulling by &Dgr;m=±1 hyperfine &sgr; transitions, here called Ramsey pulling, is a real calculable effect in atomic beam frequency standards. An analytic expression for the effects of Ramsey pulling is derived using perturbative techniques for the driving &sgr; transitions, while treating the primary &pgr; transitions exactly. It is shown that these Ramsey pulling effects are intrinsically different from Rabi pulling in origin, manifestation, and elimination. These predictions are compared to measurements performed on a cesium beam atomic frequency standard, giving good quantitative verification of the theory and a clear demonstration of the existence of these effects.

ISSN:0021-8979    

DOI:10.1063/1.348637

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Coherent anti‐Stokes Raman scattering (CARS) and spontaneous Raman spectroscopy have been used to obtain vibrational spectra of shock‐compressed and static high‐pressure fluid nitrogen, respectively. Vibrational frequencies were obtained from the CARS data using a semiclassical model for these spectra. Spontaneous Raman vibrational frequencies were determined by fitting data using a Lorentz‐shape line. A functional form was found for the dependence of the vibrational frequency on pressure and temperature to 40 GPa and 5000 K, respectively. By fitting the vibrational data to this form, a pressure scale based on the fluid nitrogen vibron has been calibrated for use at very high temperature. The nitrogen vibron pressure scale was used to determine the fluid‐&dgr; nitrogen phase boundary up to 20 GPa and 900 K.

ISSN:0021-8979    

DOI:10.1063/1.348638

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Two nonidentical spheres are immersed in a uniform external electric field. Induced multipoles through hexadecapole are found along the mutually perpendicular axes of the system. These multipoles are expressed directly in terms of the coefficients that appear in the infinite series representation of the potential.

ISSN:0021-8979    

DOI:10.1063/1.348639

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Stimulated emission on theP(43) andR(70) transitions of the BiF (A‐X,v’=1 tov‘=4) band was demonstrated, using the reaction of premixed FN3and Bi(CH3)3. The transient chemistry was thermally initiated by a pulsed CO2laser, using SF6as a sensitizer, while amplification was detected using an e´talon‐tuned pulsed dye laser probe and a sensitive cavity ringdown technique. The magnitude of the peak gain, estimated at 3.6×10−4/cm, was consistent with a negligible concentration of the terminal BiF(X,v‘=4) state, based on the calculated optical cross section and the peak concentration of the BiF (A,v’=1) state, as measured by absolute photometry.

ISSN:0021-8979    

DOI:10.1063/1.348640

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A novel taper‐formed three‐guide coupler is presented. Its unique power coupling characteristics are experimentally demonstrated. By virtue of adopting the taper‐formed waveguide, the severe restrictions imposed on the device fabrication process are greatly relaxed. This makes the coupler advantageous to application in a variety of integrated optics, such as power splitters and combiners, and as constituent elements of devices like optical isolators.

ISSN:0021-8979    

DOI:10.1063/1.348615

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A comprehensive kinetics and extraction model of electron‐beam‐excited xenon chloride lasers is used to examine the feasibility of constructing a megajoule‐class excimer laser. The ratio of small‐signal gain to absorption scales nearly logarithmically with pump rate over the range studied, 10 kW/cm3to 1 MW/cm3, and limits extraction efficiency to 20%–50%. Active volume dimensions are practically constrained to 1–2 m in length and to ∼2 m in width, with efficient extraction possible for pulse lengths of 2 &mgr;s or less. Single modules operating in the technologically conservative, low‐pump‐power (≤100 kW/cm3) regime should be capable of producing pulse energies of 40 kJ.

ISSN:0021-8979    

DOI:10.1063/1.348616

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

For TM‐polarized waves, a mode‐power measure is applied to characterize optical waveguides with a nonlinear self‐focusing substrate, producing a concise overview of the waveguiding properties at a given power for various designs. We also show how birefringence varies between the TE and TM modes as a function of the total power carried by the waveguide. Since our description is based on universal parameters, our results are applicable to different geometries of waveguide through simple scaling rules.

ISSN:0021-8979    

DOI:10.1063/1.348617

出版商:AIP    

年代:1991

数据来源: AIP