摘要:

The behavior of photoelectrons captured by traps and early stage latent image formation in undoped or Ir-doped AgCl grains was studied by photoconductivity-modulation techniques. Silver atoms were formed at the grain surface of undoped grains in ∼10−4s and near Ir ions of Ir-doped grains several seconds after exposure of the samples to a light pulse. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363953

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of scan size (scan length) and surface roughness on microscale friction was studied using atomic force/friction force microscopy. Three silicon specimens with different surface roughnesses were studied. Surface height and friction force plots were obtained simultaneously and friction mechanisms for the correlation between them were sought. The standard deviation of surface heights increases with the scan size initially and approaches a constant value at a scan length greater than the long wavelength limit of the roughness structure. Change in the value of the coefficient of friction at different scan lengths is random. In these measurements, the sampling interval is always lower than the correlation length which is believed to be responsible for the random variation in microscale friction with the scan size. The good correlation observed between the local change in friction force and the surface slope can be explained by a ratchet mechanism. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363954

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A multi-mode analysis of micro-cantilever dynamics is presented. We derive the power spectral density of the cantilever displacement due to a thermal noise source and predict the cantilevers’s fundamental resonant frequency and higher harmonics. The first mode in the multi-mode model is equivalent to the traditional single-mode model. Experimental results obtained with a silicon nitride cantilever at 300 K are in excellent qualitative agreement with the multi-mode model. The multi-mode model may be used to obtain accurate values of the cantilever properties such as the elastic modulus, effective mass, thickness and moment of inertia. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363955

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Using a point source formed by the sub-wavelength aperture of a near-field scanning optical microscope tip, we examine anomalies in the image contrast arising from the use of point source illumination as opposed to the more common collimated light geometry. For samples with predominately spatial index variations, the image contrast obtained using a point source is the reverse of what is normally expected from collimated light illumination at normal incidence. The point source image contrast is unusually large and has a strong dependence on the numerical aperture of the collection optics. We compare the measured contrast across two adjoining glasses of slightly different indices with the result of a two-dimensional model, and find that refraction at the index change boundary is the primary reason for the anomalous contrast. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364310

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Near-field optical (NFO) microscopes with an auxiliary gap width regulation (shear force, tunneling) may produce images that represent the path of the probe rather than optical properties of the sample. Experimental and theoretical evidence leads us to the conclusion that many NFO results reported in the past might have been affected or even dominated by the resulting artifact. The specifications derived from such results for the different types of NFO microscopes used therefore warrant reexamination. We show that the resolving power of aperture NFO microscopes, 30–50 nm, is of genuine NFO origin but can be heavily obscured by the artifact. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363956

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated the optical resolution of a scanning near-field optical microscope in reflection collection mode using an uncoated fiber tip. We demonstrate that the apparent resolution in the optical signal (better than 70 nm) is a topography-induced effect. We believe that the purely optical resolution is only of the order of &lgr;/2 and diffraction limited. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363957

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Single mode integrated-optical wide-band channel waveguides (SOWCWs) have been defined as a novel type of channel waveguides. The wavelength ranges (bandwidths) of both single mode operation in the channel waveguide and efficient junction-splitting using the same channel waveguides, that is for constant combining or splitting of light in integrated-optical devices like Y junctions, can easily comprise the entire visible wavelength region. In this case, the SOWCW is a real single mode white light channel waveguide. The optical bandwidths of both Rb↔K ion-exchanged channel waveguides in KTiOPO4(KTP) as an example of SOWCWs and Rb:KTP Y junctions in comparison with those of conventional titanium-indiffused channel waveguides and Y junctions inLiNbO3have been theoretically calculated and experimentally verified. The channel waveguide attenuation, the coupling efficiency to single mode fibers, and the splitting ratio of Y junctions, especially, show no significant wavelength dependence in the Rb:KTP case. Use of SOWCWs could open up new directions of integrated optics. As an example, the basic three-color-mixing device is chosen from a variety of possible applications in the field of integrated-optical color image generation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363958

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

p-i-nphotodiodes with integrated optical waveguides were successfully fabricated in the GaInAsP/InP material system. This integration leads to optoelectronical integrated circuits of significantly increased functionality, and it also offers the possibility to build high-speed detectors with high quantum efficiency. Butt-joint coupling between waveguide and photodiode was used allowing smallest detector sizes. Selective embedded growth of the photodiode layer stack was accomplished by metal-organic vapor-phase epitaxy on partially masked substrates. This technique was proven to be suitable for device fabrication. To study the influence of the lateral growth interface between waveguide and the photoabsorbing GaInAs material, the spacingdbetween interface andpregion of the photodiode was varied between 0 and 4 &mgr;m. The detector bandwidth is not limited by the electricalRCtime constant up to frequencies of 50 GHz for devices with an active area of 10×11 &mgr;m2. Best values for the quantum efficiency and the electrical 3 dB cutoff frequency of 65&percent; and 8 GHz are obtained. Both decrease strongly with increased spacingddue to an enhanced diffusion component and an increase of carriers trapping and recombination effects at the growth interface. This interpretation of the experimental data was well confirmed by a detailed analysis of the dynamic device behavior based on analytical calculations of the physical transport mechanisms. Consequently, for a redesigned photodiode the distancedhas to be minimized as far as possible. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363959

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The four-wave mixing in a slab waveguide is investigated theoretically by using the singular perturbation technique with multiple space scales. In order to apply the perturbation technique, we first introduce the perturbation parameter concerned with the nonlinear coefficients and the multiple space scales in the propagation direction. Substituting the expansion of the field and the multiple space scales into the Maxwell’s equation, we can get the governing equations to each order of the perturbation. From the solvability conditions to have nontrivial solutions for each perturbation solutions, it can be shown that the coupled-mode equations for four waves that are asymptotically correct in the limit of weak nonlinearity are obtained. The dependence of the coupling coefficient on the waveguide width and the field distribution of the phase conjugate wave are discussed numerically. We show that the coupling coefficients have the maximum for the optimum waveguide width. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363960

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In a discharge-pumped F2laser, time-resolved net-small-signal gain has been measured to study the population inversion by employing an oscillator-amplifier configuration. Characteristics of the gain and the fluorescence are studied under various conditions in two cases of He and Ne buffer gases. The peak of the net-small-signal gain in He/F2and Ne/F2show values of about 17&percent;/cm and 9&percent;/cm, respectively. The formation processes of the upper laser level F2(D′) are discussed on the basis of these experimental results. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364302

出版商:AIP    

年代:1997

数据来源: AIP