摘要:

Multilambda Rabi cavities have been shown to be a viable solution for the reduction of cavity phase shift and other Doppler related effects in atomic beam frequency standards. For this reason they may be advisable to use in devices in which operations that are apt to measure or correct cavity phase shift are impossible or undesirable. These include short sealed (commercial) tubes, possibly some primary standards with vertical beam (because it is not easy to operate an atomic beam directed vertically down), and microgravity clocks. Analytical and numerical results are reported on particular cavity examples. They support the idea that a Ramsey cavity is not always the only solution for guiding microwaves in a beam standard. A comparison of line shapes between experimental results obtained with an atomic beam and numerical calculations is also reported. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366326

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

High-TcGdBa2Cu3O7−&dgr;superconductor bolometers with operation temperatures near 89 K, large receiving areas of0.95 mm2and very high detectivity have been made. The bolometers are supported by 0.62 &mgr;m thick silicon nitride membranes. A specially developed silicon-on-nitride layer was used to enable the epitaxial growth of the high-Tcsuperconductor. Using a gold black absorption layer an absorption efficiency for wavelengths between 70 and 200 &mgr;m of about 83&percent; has been established. The noise of the best devices is fully dominated by the intrinsic phonon noise of the thermal conductanceG,and not by the1/fnoise of the superconducting film. The temperature dependence of the noise and the resulting optimum bias temperature have been investigated. In the analysis the often neglected effect of electrothermal feedback has been taken into account. The minimum electrical noise equivalent power (NEP) of a bolometer with a time constant &tgr; of 95 ms is2.9 pW/Hz1/2which corresponds with an electrical detectivityD*of3.4×1010 cm Hz1/2/W.Similar bolometers with&tgr;=27 msandNEP=3.8 pW/Hz1/2were also made. No degradation of the bolometers could be observed after vibration tests, thermal cycling and half a year storage. Measurements of the noise of a Pr dopedYBa2Cu3O7−&dgr;film withTc=40 Kshow that with such films the performance of air bridge type high-Tcbolometers could be improved. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366327

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Laser concepts can be applied to a broad range of physical phenomena. One of the closest parallels occurs with the fluttering oscillations that are sometimes observed in the falling sheets of water associated with fountains, dams, and natural waterfalls. In many respects these fluid feedback oscillations are similar to the electromagnetic modes of typical lasers, and recognition of this similarity led to the interpretation of the waterfall behavior. Gain profiles for the waterfall oscillations are developed, and the relationship of experimental waterfall data to the laser-like models is considered in detail. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366328

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have theoretically investigated ultrafast surface-emitting second-harmonic (SH) generation from mode-locked laser pulses with arbitrary pulse shapes. The spatial dependence of the SH energy density per pulse is almost the same as the temporal profile of the SH power emitted from the entire surface per waveguide width for a long waveguide. For a sinc fundamental pulse, we have obtained, rich and unique, temporal, spatial, and spectral behavior of the second harmonic. We have found that both the temporal and spectral profiles of the emitted second harmonic depend on the location at the surface. These effects can be observed with lasers currently available, and used for auto correlation, in optical signal processing, optical communications, and practical frequency doubling of ultrafast optical pulses with an advantage of no broadening of the SH pulse. We have compared these results with those for a Gaussian fundamental pulse. After introducing saturation intensity to quantify the saturation regime, we have obtained quantitative expression on the second-harmonic intensity in terms of the pump and saturation intensities. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366329

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We consider the effective nonlinear susceptibility tensord(−2&ohgr;;&ohgr;,&ohgr;)for second harmonic generation in a nonlinear composite medium. We derive a simple expression for this susceptibility in terms of the position-dependent tensord, and three factors that describe the local field enhancement in a corresponding linear medium. The resulting expression can be used to calculate the local-field enhancement ofdin many geometries. In the dilute limit, the general expression reduces to a result previously derived. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366398

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Large-area film removal with lasers is a physical process of melting and vaporization of films. A mathematical model is developed to simulate the melting and vaporization of films under the irradiation of a chemical oxygen–iodine laser. The cross section of the film after laser scanning and the substrate surface temperature during laser irradiation are presented. There is an optimum laser power at which relatively wide films can be removed by maintaining low temperature at the substrate surface. The optimum laser power is associated with other process parameters. The results of film removal withTEM31andTEM00beams are compared, and the laser mode with more uniform intensity distribution is found to be more effective for large-area film removal. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366330

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

QuasistoichiometricLiNbO3was used as substrate for proton exchanged waveguides prepared by immersion in hot benzoic acid for different times and melt compositions. Both &agr;- and &bgr;-phase guides were investigated. Their basic properties were studied and compared with those of guides prepared under the same conditions on congruent substrates. For &agr;-phase guides on quasistoichiometric substrates, the values of the index jump and the effective diffusion coefficient are, respectively, 0.53 and 0.54 times those obtained on congruent substrates under the same conditions. Also, theird33coefficient for second harmonic generation is about 10&percent; greater, while the optical damage resistance is a factor of 5 smaller. On the other hand, the properties exhibited by &bgr;-phase guides depend very little on the substrate stoichiometry. The results are discussed in terms of the lithium deficiency generated during the exchange in comparison to that previously existing in the substrate used. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366331

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Laser-induced transient gratings (LITGs) at surfaces of absorbing materials were utilized to generate narrowband surface acoustic waves (SAWs). In these experiments, SAWs were excited thermoelastically by two crossed picosecond laser pulses and detected with an actively stabilized Michelson interferometer by measuring transient surface displacements in the sub-angstrom range in real time. In addition, coherent broadband SAW pulses with frequencies up to 350 MHz were excited by sharply focusing the laser beam with a cylindrical lens system onto the sample surface. The LITG experiments provide an extension of the frequency range achieved with the broadband SAW pulse technique. From the measurements of the dispersive SAW phase velocity for a 650 nm aluminum film on fused silica in the frequency range 10 MHz–1 GHz the density and elastic constants were determined by fitting the experimental data to the exact solution of the wave equations taking into account the boundary conditions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366332

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The product gas yields for a 30 mTorrC2H213.56 MHz glow discharge were measured using mass spectrometry. The volatile products areH2,C4H2,andC6H2.A reaction mechanism has been proposed that accounts quantitatively for the yields ofC4H2andC6H2,and film deposition rate, as a function of discharge power. The product gasesC4H2andC6H2are depleted at high rates in the plasma by electron collisional dissociation, and by reaction with H atoms andC2Hradicals. Under high power conditions suitable for diamondlike carbon deposition it is proposed that the film growth is dominated by the radicalsC4H3,C6H3,andC2H.These results are compared with the kinetics of methane rf glow discharges under similar conditions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366333

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Two-photon laser induced fluorescence measurement of H atom density in&percent;H2–&percent;N2gas mixture discharges has shown that the flux of H atom remains nearly constant over a wide range of gas compositions and pressures in three types of discharge devices. This unique feature is attributable to an efficient multiquantumN2vibrational energy transfer to the dissociation ofH2.This result shows that an appropriate choice of molecular gas mixtures can be used to extend the discharge operating conditions and device size scaling without compromising atom flux production. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366334

出版商:AIP    

年代:1997

数据来源: AIP