摘要:

Principles and fabrications of photo‐optical devices based on the photoinduced refractive index changes observed in amorphous chalcogenide films are described. In these devices, propagation of a light beam in optical waveguides constructed with amorphous As‐S films is controlled with blue‐ (and red‐) light illumination which can modify the refractive index of the films. The devices operate as single‐throw or double‐throw photo‐optical switches, having switching times ranging between 20 ms and 2 s.

ISSN:0021-8979    

DOI:10.1063/1.335312

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Steady‐state beam coupling is used to measure the concentration of empty traps, the sign of the dominant photocarrier, and the effective electro‐optic coefficient in seven crystals of BaTiO3. The measured value of the effective electro‐optic coefficient gives the product of the fractional poling of the crystal, the relative conductivity of the crystal, and the electro‐optic coefficient. Anomalously low beam coupling gain measured in an eighth crystal suggests that this crystal is nearly perfectly compensated; i.e., the photoconductivities due to electrons and holes are nearly equal.

ISSN:0021-8979    

DOI:10.1063/1.335313

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We report experimental and theoretical studies of the use of the photorefractive effect in the design of optical limiters. Preliminary results indicate extinction coefficients of at least 98–99% with 1 J/cm2transmitted before steady state is reached.

ISSN:0021-8979    

DOI:10.1063/1.335314

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A fundamental theory of nonlinear Rayleigh wave propagation is given here. Previously, the harmonic boundary value problem was solved by means of a direct iterative procedure. The nonlinear acoustic field could only be studied near the excitation transducer. The method could not explain the nonmonotonous behavior of curves giving the amplitude of various harmonics as a function of the propagation distance. In this paper, amplitude and phase relations of harmonics are calculated also in the far field. Anisotropy effect is demonstrated in the first numerical results obtained for various quartz crystal cuts.

ISSN:0021-8979    

DOI:10.1063/1.335315

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

As a continuous‐wave signal builds up in an energized laser dye solution, the lifetimes for the excited state of the molecules become shorter than their orientational relaxation time. Physical consequences of the phenomomenon are considered for two extreme situations—transmission through pure mobile and pure rigid media continua, respectively. The dye is treated as a linear oscillator and spectral properties are assumed to be unchanged between the media. Two problems are examined, namely signal propagation and the extraction of energy at apointinthemediumfor a number of configurations of pump and signal polarizations, transverse or longitudinal excitations. Signal gradients and steady‐state conversion efficiencies are presented algebraically and graphically. A mobile medium has one of the steepest gradients, the largest energy storage, and one of the highest conversion efficiencies. Nevertheless, performance of a transversely excited, single‐pass amplifier for the commonly used configuration where pump and signal are plane polarized and have a shared polarization axis (ConfigurationC) shows little difference between rigid or mobile media, according to this analysis. For a rigid ConfigurationC, only about 21% of the dye molecules carry most of the signal load, in contrast with a mobile medium where all molecules work equally, and such a restricted distribution undergoes rapid turnover of its excited state. Twisting of the signal plane of polarization in a dye amplifier is confirmed.

ISSN:0021-8979    

DOI:10.1063/1.335316

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We have constructed a micron wavelength acoustic microscope having a novel geometry which accentuates detail in acoustic imaging while providing ease in focusing, enhanced resolution, and the observation of third‐order nonlinear products (2F1‐F2). Convergent, acoustic beams generated by curved transducers provide very high power densities at the acoustic lens and focus. Oblique acoustic illumination of surfaces gives directionality to the image and the use of a second transducer position, removed from the specularly reflected beams, reduces undesired nonlinear interaction in the intervening liquid (water) medium. Increased resolution and sharper images are obtained by observing the second harmonic via the difference frequency (third‐order product 2F1‐F2) which falls back into the initial frequency range, ∼600 MHz. However, significant effects due to nonlinear interaction identified with the object have not yet been observed.

ISSN:0021-8979    

DOI:10.1063/1.335317

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The role of geometric factors in the operation of a modified design of the pyroelectric anemometer is examined. The two major variables were chip thicknessd(133 and 205 &mgr;m) and the separation between the heater and the measuring electrodes (25≤&Dgr;HE≤250 &mgr;m). The overall flow response varied as (flow) 0.48±0.02 for almost four orders of magnitude. No evidence of saturation was observed at either the high or low flow rates. One of the more interesting results obtained was the relative independence of the response at fixed flow rate on &Dgr;HEford=133 &mgr;m. Even ford=205 &mgr;m, the response was relatively independent of &Dgr;HE, though some variation was observed.

ISSN:0021-8979    

DOI:10.1063/1.335318

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A resistor‐capacitor analog heat transfer model is used to calculate the thermal pyroelectric anemometer (PA) response. This is compared to the data of Fredericketal. [J. Appl. Phys.57, 4936 (1985)] in the accompanying paper. Steady‐state gas flow conditions are assumed, and the calculations apply in the regime where the transit time of the gas over the device is much less than the time period of the heat input from the ac‐driven heater. Since the pyroelectric substrate is thin, the analysis is simplified to one dimension and excludes edge effects, heat losses due to the support, and thermal radiation. Further, no temperature difference is assumed at the interface between the gas and substrate, i.e., no temperature jump. The calculated dynamic response is in excellent agreement with measurements. However, the calculated level of response is 240  &mgr;V at a gas flow of 10 m/min, much lower than the 570  &mgr;V measured by Fredericketal.

ISSN:0021-8979    

DOI:10.1063/1.335319

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The evolution and distribution of temperature have been studied theoretically for an idealized model of a four‐ball wear‐test apparatus which can be used to study macroscopic effects of surfaces interacting under frictional conditions. The finite‐difference method was used to solve the coupled equations of heat generation, conduction, and cooling. Parameters were chosen to represent two types of material, a typical steel with relatively good thermal conductivity, and a ceramic with relatively poor thermal conductivity. Two values for the coefficients of friction were used to simulate dry and lubricated surfaces. A significant dependence on thermal conductivity was found.

ISSN:0021-8979    

DOI:10.1063/1.335320

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A Monte Carlo simulation technique has been used to model the cathode fall region of a glow discharge under the influence of a nonuniform electric field and a transverse magnetic field. It has been shown experimentally that a magnetic field can serve as an effective means for reducing the growth of discharge instabilities. The stabilization mechanism involves the dispersion of localized charged particle perturbations over the discharge area in a time less than that required for an instability to fully develop. The results of this paper provide a deeper insight into the magnetic stabilization technique, which has the potential of increasing the power output of a wide variety of gas lasers.

ISSN:0021-8979    

DOI:10.1063/1.335321

出版商:AIP    

年代:1985

数据来源: AIP