摘要:

Scattering of the evanescent light by a finite‐size SiO2probe is calculated using a point matching method in order to improve the efficiency collecting the near‐field optical signal. The scattered‐light patterns can be classified into three categories. Category 1 is where the probe tip radius is very small (<&lgr;/13). Category 3 is where the probe radius is very large (≳&lgr;/6). Category 2 is the intermediate case (&lgr;/13<radius<&lgr;/6). When the radius is in category 1, the scattered light is able to be treated as a field radiated by the point dipole induced by the evanescent light at the probe tip. When the tip radius is in category 2 (&lgr;/13<radius<&lgr;/6), in order to obtain the angular distribution of the scattered light, the induced multipoles should be calculated, considering the probe radius and the incident angle. When the tip radius is in category 3 (radius ≳&lgr;/6), the scattered light becomes larger in the parallel direction to a prism surface due to the forward scattering of the evanescent light. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363519

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Consistently obtaining super‐resolution with scanning near‐field optical microscopy depends almost entirely on the ability to manufacture reproducibly probes with aperture sizes smaller than 100 nm. The probe fabrication process usually involves heating an optical fiber using a CO2laser and melt‐drawing the glass to produce a taper. A number of variables ultimately define the taper shape but the actual effects these parameters have are still not clear. In this work, the physics behind the taper formation is examined in detail for the first time and equations describing the initial taper profile and the final aperture size are derived in terms of the experimental conditions. It is shown that the taper shape is primarily determined by the laser spot size. The pulling force, although important, has a lower significance. Continuum mechanics and Stefan’s law are used to show that the aperture size is closely related to the radius of the fiber at the start of the hard pull and the fiber temperature at that time. Further comparisons of experimental data with the expected taper profile exposes the heating effect of the CO2laser. Further analysis is given using a form of Mie theory which describes the interaction of electromagnetic fields with cylindrical structures. These results give many significant insights into the fabrication process and the formation of the aperture. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363521

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Diagnosis and evaluation have been carried out of the ion beam and anode plasma produced in a ‘‘point pinch diode.’’ From the measurement of a highly resolved Thomson‐parabola mass spectrometer, the ions accelerated in the diode gap contain (a) protons, (b) highly ionized carbon and oxygen ions, and (c) singly ionized medium mass ions such as carbon, oxygen, CO+2, OH+, H2O+. Time‐integrated x‐ray and particle pinhole images show the spot size of the electron beam on the plasma to be less than 0.5 mm in diameter, in which fine structures are found with size less than 0.1 mm. AK&agr; satellite line of Al Vis observed with a crystal spectrograph, which indicates the existence of Al4+in the plasma. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363522

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A detailed theoretical analysis with numerical calculations was conducted to study the frequency spectrum resulting from the application of a sinusoidal phase modulation to a two‐beam interferometer illuminated by a low‐coherence source with a Gaussian spectral profile. Results of these calculations show behavior of the frequency components which was unexpected from earlier derivations of the frequency spectrum. The results of the calculations have been experimentally confirmed using an all‐fiber interferometer illuminated by a source with a Gaussian spectral profile. The results will be useful for the signal processing of tandem interferometers for ‘‘white light’’ interferometry in the field of optical sensing. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363523

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This report discusses the properties of a 13‐keV submicrometer x‐ray beam exiting from a waveguide. Waveguides for this spectral regime can be constructed by enclosing a low‐absorbing material between highly absorbant metals. Best performance is found for about 0.1 &mgr;m guiding layer thickness. Measurements of the photon beam size close to the exit and of the intensity distribution far from the exit will be presented. From these data one derives a beam size at the exit which is identical to the guiding layer thickness. This number being in the submicrometer range offers interesting perspectives for microscopy experiments in the hard x‐ray range. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363524

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We discuss a buried oxide layer forming a current aperture in a vertical‐cavity surface‐emitting laser. The current spreading under the oxide current aperture leads to high threshold and dual‐longitudinal‐wavelength characteristics. One is the as‐grown cavity resonance and the other is the resonance wavelength under the oxide layer. This structure exhibits ≳30 dB side‐mode suppression throughout its operating range. Meanwhile, a single‐longitudinal‐wavelength laser with a minimized current spreading has a low threshold current of 85 &mgr;A and several nonlasing modes. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363525

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The operating peak energy of a porous silicon (PS) cavity can be completely controlled over a wide range of 1.5–2.2 eV, using a PS‐based Fabry–Perot resonator composed of a light‐emitting active PS layer and two high‐reflectivity mirrors. When the PS devices are excited by a uv laser, quite narrow spectra (10–40 meV in full width at half‐maximum) are observed without any significant signs of side mode. The central photon energy is precisely and continuously tuned simply by changing the anodization parameters. The key issues of the controlled device operation are adjustment of the optical thickness of the active PS layer to an appropriate value and fabrication of the quarter‐wavelength multilayered PS mirror with a high reflectivity. The spectral qualities of the emitted light are also discussed by theoretical analyses on the basis of a simplified model. These results suggest that the PS devices operate as sharp band‐pass optical filter and the PS materials are available for novel silicon‐based microphotonics. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363526

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The stimulated emission cross section &sgr;pfor the 1060 nm transition of Nd3+in lead borate and bismuth borate glasses has been determined from fluorescence measurements. The compositional dependence of &sgr;p, which has been evaluated using radiative transition probability, refractive index of the host glass, effective fluorescence linewidth, and position of the band, with PbO/Bi2O3content is investigated. The &sgr;pvalues of the 1060 nm band of Nd3+for lead borate and bismuth borate glasses are found to be in the range 2.6–5.7×10−20cm2at 298 K and 3.0–6.3×10−20cm2at 4.2 K. The &sgr;pvalues are comparatively large suggesting the possible utilization of these materials in laser applications. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363520

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This study analyzes the dependence of third‐order susceptibilities at 532 nm ofn‐type ZnSe crystals in relation to free carrier concentration and annealing temperatures. The nonlinear optical absorption and the efficiency of degenerate four‐wave mixing of ZnSe are investigated. We find that the magnitude of the nonlinear absorption decreases with the electron concentration and annealing temperature increase, while the nonlinear refractive index increases slightly. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363527

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The operation of output coupler, input coupler, surface emitting amplifier, and surface emitting distributed feedback laser formed on a thin‐film dielectric waveguide depends on guided–guided and guided–radiated wave couplings. The characteristics of these devices are treated for the transverse electric mode for wave interactions caused by a suitable relief grating formed on the film–cover interface. Design criteria are deduced and optimization procedures are indicated with illustrative numerical examples. The device characteristics are insensitive to small changes in the physical parameters. Surface emitting amplifier with a uniform near‐field pattern and surface emitting distributed feedback laser operating in a single mode are investigated. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363528

出版商:AIP    

年代:1996

数据来源: AIP