摘要:

Measurements of the refractive index of thermally grown oxide after annealing reveal that the density relaxation of the oxide is well described by a stretched exponential decay function. The experiments of two‐step oxidation show that oxygen diffusivity in the oxide exponentially decreases with the oxide density. The relation between the oxide density and the refractive index is well expressed by a simple power relation rather than the Lorenz–Lorenz formula.

ISSN:0021-8979    

DOI:10.1063/1.345563

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Time domain scattering parameters of a two port are found for a ‘‘quasi‐Debye’’‐like lossy dielectric. Exact solutions are found for the zeroth‐ and round‐tripS11parameter and the one‐way‐tripS21parameter. Numerical examples are presented for a hypothetical material.

ISSN:0021-8979    

DOI:10.1063/1.345564

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effects of random field errors on the propagation of a relativistic electron beam through a wiggler magnet are analyzed both theoretically and numerically. Both helical and planar wiggler configurations are studied, with and without the effects of transverse focusing forces. Theoretical expressions are derived for the random electron motion for (i) individual realizations of field errors and for (ii) ensembles of statistically identical wigglers. These results are then confirmed through three‐dimensional particle simulations of electron‐beam transport including the effects of finite emittance. In addition to producing a random walk of the beam centroid, the field errors lead to significant variations in the parallel beam energy. Asymptotically, the variance of the parallel beam energy scales asz1/2, wherezis the axial propagation distance. Although transverse beam focusing reduces the asymptotic scaling of the rms centroid displacement fromz3/2toz1/2, transverse focusing is not effective in reducing the parallel energy variation (the variance of the parallel beam energy is only reduced by a factor of &sqrt;2). Statistically, the variance of the parallel beam energy may be interpreted as an effective parallel energy spread due to field errors. In order to maintain the wave–particle resonance in small‐signal free‐electron lasers, it is desirable for this effective energy spread to be small compared to the intrinsic efficiency. As an example, in the low‐gain regime (assuming a helical wiggler in the strong‐wiggler limit), this requirement implies that the normalized rms field error must satisfy &dgr;Bˆrms<1/(2&pgr;N3/2), whereNis the number of wiggler periods.

ISSN:0021-8979    

DOI:10.1063/1.345565

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Optical polarization bistability induced by transverse‐magnetic‐ (TM) wave injection is thought from experimental results to originate from simultaneous generation of the oscillation of the transverse‐electric wave (TE oscillation) and the amplification of the transverse‐magnetic wave (TM amplification). In order to prove authenticity of this assertion, we use rate equations that include a term of the TM mode and an equation of the transmittance of the laser cavity. The calculations show that the carrier density is kept constant in the low‐TM‐photon‐density region while it varies in the high‐TM‐photon‐density region. It is also shown that the constant gain is divided into both TM amplification and TE oscillation in the former region. The transmittance changes only in the latter region since the refractive index varies with the carrier density. The bistability appears between these two regions. Calculated light output versus light input characteristics show good agreement with the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.345535

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A description of bandwidth‐limiting tuning filters is introduced into a semiclassical model for synchronously pumped mode‐locked dye lasers. The finite phase memory of the molecular wave functions is included as are the isotropic molecular distribution and the finite vibrational relaxation times. The new set of equations has been solved numerically using the best available values for the various parameters. The results have been compared with experimental data obtained using a rhodamine 6G dye laser, which is synchronously pumped using an acousto‐optically mode‐locked argon laser. Tuning element effects have been studied using two‐ and three‐plate birefringent filters and a tuning wedge, and the experimental results agree with the numerical solutions.

ISSN:0021-8979    

DOI:10.1063/1.345536

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Polysilynes, a new class of amorphous alkyl silicon network polymers, undergo a novel photo-oxidative crosslinking reaction associated with up to a 15% decrease in refractive index related to the loss of SiSi bonding. We describe the fabrication and initial measurements of waveguides formed with this index imaging technique in poly(cyclohexylsilyne) films on both SiO2and poly(methyl methacrylate)-coated silicon wafers. Measurements of multimode guides show typical propagation losses of 0.68 dB/cm at 633 nm. Results indicate the polyalkylsilynes show promise as self-developing, planar optical waveguide media.

ISSN:0021-8979    

DOI:10.1063/1.345537

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Fluorescence spectra and rise as well as decay curves of 1‐ethylpyrene (EPy) in poly(methyl methacrylate) films changed using a XeCl (308‐nm) excimer laser as an ablation source. This phenomenon was observed not only for the ablated area but also for the masked region of about 20 &mgr;m around the ablated area and was attributed to the change of the dispersion condition of EPy. Effects of laser ablation upon properties of polymer films were elucidated by analyzing fluorescence dynamics using a microscope and under a total internal reflection condition.

ISSN:0021-8979    

DOI:10.1063/1.345538

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have conducted measurements of the linear electro‐optic coefficient (r41) and electrogyratory coefficient (&eegr;41) in Bi12TiO20at 633 nm. A precise knowledge of these coefficients is important for evaluating the holographic recording properties of this photorefractive material. We have employed both transverse and longitudinal electric field geometries. For each geometry, we present the results of dc as well as ac techniques. Based on these results we findr41=5.75±0.10 pm/V and ‖&eegr;41‖≤0.30±0.05 pm/V. We critically examine our measurements and discuss their relative accuracy. Our findings are compared to those previously reported by other investigators.

ISSN:0021-8979    

DOI:10.1063/1.345539

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The amplitude of the photoacoustic signal is measured as a function of chopping frequency for thin benzophenone polycrystalline samples in the temperature range 100–300 K. Analysis of experimental results, obtained by rear surface illumination, allows us to determine the thermal diffusivity of benzophenone crystals in the whole temperature range.

ISSN:0021-8979    

DOI:10.1063/1.346094

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Recently we reported a far field theory of transverse acoustic waves radiated from an interdigital transducer deposited on a singly rotated quartz crystal. This was done by an approximation called the local decoupling approach, allowing us to consider electrical effects as forcing fields for the mechanical motion. The present analysis demonstrates that this approximation is not valid in predicting the complete spectrum of acoustic waves. It is shown that near the cutoff frequency the bulk wave may be converted into a surface wave of Bleustein–Gulyaev type in the free surface case, and that a surface metallization reinforces the strength of this conversion. Velocity of surface waves are determined by means of the effective permittivity function and correct radiation diagrams are plotted in the far field.

ISSN:0021-8979    

DOI:10.1063/1.345518

出版商:AIP    

年代:1990

数据来源: AIP