摘要:

The design of high‐Tcsuperconducting bolometers for applications such as infrared imaging arrays is discussed. The dependence of bolometer sensitivity on excess voltage noise in the thermometer is a function of the detector area and thus of the wavelength to be detected. Measurements of the voltage noise in thin films of YBa2Cu3O7−&dgr;on Si, Si3N4, and sapphire substrates are used to predict the performance of different bolometer architectures. Useful opportunities exist for bolometers made on both Si and Si3N4membranes. A readout scheme for two‐dimensional arrays of bolometers is also described in which real‐time signal integration is performed on the chip.

ISSN:0021-8979    

DOI:10.1063/1.351063

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An attractive‐mode atomic force microscope is described in which the cantilever is held orthogonally with respect to the sample. The technique utilizes a linear differential optical detection scheme for the cantilever vibrations. In this design, the cantilever end is not bent to form a tip. This geometry substantially reduces the possibility of spontaneous jump‐to‐contact of the tip onto the sample, allowing the tip/sample separation to be set essentially to any desired value. Relatively large‐ and small‐scale results are presented on imaging a smear of red blood cells, demonstrating the resolution and sensitivity.

ISSN:0021-8979    

DOI:10.1063/1.351064

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A relativistic electron beam of 175 keV, 6 kA, and 40 ns is injected into neutral argon and air in the pressure range of 0.1–20 Torr. The peak beam transport up to 100 cm is found to be maximum, 75% of the input beam current, around 0.3 Torr. The plasma heating level of &bartil;5×1022eV/m3&mgr;s is inferred from the net current signals.

ISSN:0021-8979    

DOI:10.1063/1.351065

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Photoelectrons from a metal surface irradiated by a pulsed ultraviolet laser were accelerated to relativistic energy to obtain a very cold and relatively high‐current electron beam. Typical values of the transverse velocity component &bgr;⊥/&bgr;∥were measured to be less than 8×10−3, which leads to a spread of the parallel energy component &Dgr;&ggr;∥ /&ggr;∥of 1×10−4or less. Propagation characteristics in a longitudinal guiding magnetic field were investigated. A nonadiabatic factor was defined to estimate the conservation of the magnetic moment of the electrons moving along the magnetic flux, and this was shown experimentally to be reasonable. Spacial controllability of the cross section of this electron beam was demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.351066

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The optical transmission loss in dielectric waveguide bends is investigated using the finite‐difference time‐domain approach. An absorbing boundary condition, applied to reduce the size of the mesh, is proven to work very well for the waveguide structure. The desired modes are excited using the solution of a one‐dimensional waveguide structure. The bending loss is then obtained using the methods of overlap integral and least‐square fit. The structures of multiple‐bend waveguides are analyzed. It is shown that the coupling between neighboring bends leads to direct transmission to the waveguide section on the aligned plane in addition to the transmission through the zigzag path. The bending loss in nonplanar laser arrays is investigated in detail. The possibility of having a shallow groove depth laser array is then discussed. Lateral lasing is prohibited by the radiation loss due to the bend. It is observed that the optical coupling between neighboring emitters is enhanced by the shallow groove depth, implying that phase‐locked array modes can be obtained.

ISSN:0021-8979    

DOI:10.1063/1.351369

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Data are presented demonstrating the continuous (cw) room‐temperature (23 °C) operation of planar index‐guided ‘‘buried‐mesa’’ AlxGa1−xAs‐In0.5(AlyGa1−y)0.5P‐ In0.5Ga0.5P heterostructure visible‐spectrum laser diodes. The planar ‘‘mesa’’ structure is formed by ‘‘wet’’ oxidation (H2O vapor+N2carrier gas, 550 °C) of the AlxGa1−xAs on the composite AlxGa1−xAs‐In0.5(AlyGa1−y)0.5P upper confining layer (outside of the active stripes). The oxidation process results in a ∼0.5‐&mgr;m‐thick native oxide located (in depth) within ∼3000 A˚ of the active layer in the region outside of the laser stripes themselves. The oxide possesses excellent current‐confinement properties and a low refractive index (n≊1.60), resulting in relatively low‐threshold laser operation for narrow‐stripe devices. In addition, these devices exhibit transverse‐mode confinement and small beam astigmatism because of the refractive index step provided by the deep native oxide.

ISSN:0021-8979    

DOI:10.1063/1.351067

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A novel physical concept termed ‘‘spatiotemporal mode’’ is presented for ultrashort optical pulse‐beam propagation in a saturable Kerr‐law nonlinear medium. The mathematical structure of the mode with spherical symmetry is described analytically. Dispersion characteristics are calculated and compared with those of the conventional spatial modes in planar and cylindrical dielectric waveguides. Nonvanishing cutoff frequency is obtained even for the fundamental mode.

ISSN:0021-8979    

DOI:10.1063/1.351068

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Fabry–Perot microcavities are analyzed in terms of their light emission characteristics. The analysis considers full output coupling, and we calculate both spontaneous and stimulated emission dependencies on cavity length, mirror design, and spectral characteristics. The cavities correspond to vertical‐cavity surface‐emitting lasers in the AlAs‐GaAs‐InGaAs material system, and a GaAs cavity with Bragg mirrors of CaF2/ZnSe. We show that considerable gain enhancement depends on the degree of coherence in the spontaneous emission, the microcavity length, and the Bragg reflector design.

ISSN:0021-8979    

DOI:10.1063/1.351069

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

First‐ and second‐order reflection effects in oblique incidence surface acoustic wave gratings are examined. A general formulation usable for both metallic and same material grooved overlays is provided. The existence of several important effects, particularly a reflection effect at the second harmonic of the grating and a velocity shift at the first harmonic for grooved gratings, are demonstrated, and the behavior of these effects as a function of incidence angle is examined. For angles of incidence of interest in the production of reflective array compressors, these effects are analyzed as a function of metallization ratio.  

ISSN:0021-8979    

DOI:10.1063/1.351070

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A previous investigation [B. G. Martin, J. Appl. Phys.66, 1931 (1989)] showed that acoustical symmetric multilayer (ASM) structures could be used as antireflection (AR) coatings. In the present investigation, we consider the AR properties of stacked ASMs, which offer a practical means for achieving graded impedance structures for virtually any gradient profile.

ISSN:0021-8979    

DOI:10.1063/1.351393

出版商:AIP    

年代:1992

数据来源: AIP