摘要:

A method is developed to describe the off‐equilibrium property of an open system by taking the difference between the forward and backward stochastic processes into account. Here the forward probability is concerned with an initially conditioned ensemble of fluctuations whereas the backward one is concerned with the finally conditioned ensemble of fluctuations described by the Bayes’ probability. An asymmetrical property between the correlation function of the forward process and that of the backward one is shown to be an experimentally useful measure of off‐equilibrium property. The above method is applied to the time series of stationary brain waves to find that the brain waves in both the active and meditative state of the brain are regarded as off‐equilibrium fluctuations. The violation of the principle of detailed balance results in the asymmetry between forward and backward conditional entropies.

ISSN:0021-8979    

DOI:10.1063/1.335303

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An electro‐optical technique has been developed to measure high‐frequency electric fields in free space. Electrically induced birefringence in an electro‐optical crystal is used to modulate a linearly polarized continuous‐wave laser beam. The modulation impressed on the laser beam contains both frequency and field intensity information. A way to use this technique as both a frequency and power meter is discussed. A proof‐of‐principle experiment has been carried out with a 3.1‐GHz magnetron source.

ISSN:0021-8979    

DOI:10.1063/1.335304

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A fast and simple algorithm is presented for calculating the effects of energy loss and scattering on electrons which pass through a converter foil. This algorithm is designed to be integrated into particle‐in‐cell codes for electron‐beam transport. The results of this algorithm for such quantities as energy and number transmission and reflection coefficients compare very favorably with results obtained from a more sophisticated Monte Carlo transport code for pertinent applications. The savings in time is appreciable: this algorithm is approximately 30 times faster than the more sophisticated code.

ISSN:0021-8979    

DOI:10.1063/1.335305

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Allowed and forbidden transitions of singlet helium from 2s1Stons1S,np1P, andnd1Dstates have been measured betweenn=8 and 31 by optogalvanic spectroscopy in a dc discharge positive column. The addition of neon in the discharge was found to increase the relative intensities of the forbidden transitions. For similar photon flux, the optogalvanic signal reaches a maximum atn=11 and decreases thereafter. Neutral collisional ionization of the excited states fromn=13 and above was found to be responsible for the increased ionization efficiency of the high Rydberg states.

ISSN:0021-8979    

DOI:10.1063/1.335462

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The study of asymmetrically self‐reversed lines emitted by inhomogeneous gas discharges has been made on the basis of an extension of the multiparameter method. A new procedure has been developed which makes it possible to determine the line broadening at the arc axis, its radial variation, and the ratio shift/width. An investigation is made into the effect of these quantities on the determination of the plasma temperature. The proposed method has been applied to high‐pressure mercury discharges operating on dc and ac (50 Hz) using the mercury line 5461 A˚. The pressure broadening in the impact approximation has been measured to be (1.43±0.11)×104mA˚ atm−1  K0.7; the corresponding line shift is towards the blue line wing.

ISSN:0021-8979    

DOI:10.1063/1.335306

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We present approximate analytical solutions of the Helmholtz equation for a slightly bent metallic rectangular waveguide with infinite aperture cylindrical mirrors. The low‐order, overmoded, low‐losses eigenmodes of the ‘‘cold resonator’’ are naturally expressed as products of cylindrical Gaussian–Hermite and trigonometric functions. In first order in perturbation theory, the correction to the attenuation constant is proportional to the straight waveguide attenuation constant. We show that &pgr; modes propagate with negligible losses in the far‐infrared region. These results are compatible with preliminary experimental data from the University of California, Santa Barbara Free Electron Laser experiment.

ISSN:0021-8979    

DOI:10.1063/1.335307

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The reflectivity of the surface polaritons incident normally on a grating of finite length is investigated without assuming that the amplitude of the grating is small. The maximum reflectivity is found to be essentially the same as that obtained from a small‐amplitude grating theory, but there is an upward shift in the center frequency of the band gap, with the shift increasing with the increase of the amplitude of the grating. A physical explanation for the shift of the band gap is provided.

ISSN:0021-8979    

DOI:10.1063/1.335308

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The light scattered out of multimode optical waveguides formed by ion exchange from molten salts of silver nitrate was measured in order to clarify the mechanism producing scattering loss. The angular distributions of the scattered light can be explained by the loss originating not only from surface roughness but also from silver ion concentration diffused in the glass. For a relatively thick waveguide of diffusion depth greater than 4.5 &mgr;m which was obtained by diffusion time longer than 7 h at 300 °C, it was found that the effect of bulk inhomogeneities is predominant in the air radiation. The correlation length in the direction of beam propogation was estimated to be the order of a wavelength of light.

ISSN:0021-8979    

DOI:10.1063/1.335309

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A detailed study of the output energy characteristics of the pulsed, optically pumped 4.3‐&mgr;m CO2laser is described. The predictions of a rate‐equation model representing the laser dynamics are shown to be in good agreement with experiment over a wide range of operating conditions. The factors which control the performance of the laser are identified, and the optimum operating conditions for maximum output energy are discussed. Output energies of 15 mJ/pulse and peak powers of 100 kW/pulse have been obtained from an 88‐cm‐long by 11‐cm2‐aperture discharge. Scalability of the pulse energy to several hundred mJ using available pump pulse energies is shown to be feasible.

ISSN:0021-8979    

DOI:10.1063/1.335310

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We report on the design and operation of an optimized version of aQ‐switched, mode‐locked, and cavity‐dumped ruby‐laser oscillator. The modulator window is much narrower than that assumed in conventional active mode‐lock theory, and is shown to yield much shorter pulses than the latter in cases where the number of round trips is restricted. To allow a high‐power pulse (≊1 GW) to evolve in the oscillator, and to allow simple synchronization to a (∼100 ns fixed delay) CO2laser, a limit of 23 round trips was chosen, but similar limits may be imposed by lasers having short‐gain duration as in an excimer laser. Details are given on the single spark gap switching element and Pockels cells, with an analysis of their expected switching speeds, in order to establish the effectiveness of the modulator, as compared to conventional sinusoidally driven active mode lockers. Single pulses of 50–70 mJ are reliably cavity‐dumped after only 100‐ns delay (23 round trips) with pulse length adjustable from 50–100 ps with ±5‐ps stability. Relative timing between the main (CO2) and probe (ruby) pulses allows a measurement accuracy of ±50 ps to be attained.

ISSN:0021-8979    

DOI:10.1063/1.335311

出版商:AIP    

年代:1985

数据来源: AIP