摘要:

Nd3+incorporation in CaF2layers grown by molecular‐beam epitaxy on CaF2substrates is investigated by making use of the photoluminescence lines associated with Nd3+centers involving one or several Nd3+ions. It is shown that the substrate crystal orientation has no effect on the aggregation state of Nd3+while the growth temperature greatly influences the formation of Nd3+aggregate centers. An optimum growth temperature around 500 °C is determined, leading to CaF2layers of good crystal quality in which the main emission, related to single Nd3+centers, is optimized. The results have been obtained for Nd3+concentrations as high as 3.6 wt % Nd and growth rates in the range of 0.2–1 &mgr;m/h.

ISSN:0003-6951    

DOI:10.1063/1.105665

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of chlorine doping on photostructural defect states in amorphous selenium films (∼100 &mgr;m) has been studied using the thermally stimulated discharge current technique. Chlorine doping in amorphous selenium results in the shift of deep photostructural defect states C+3and C−1to relatively shallower levels, i.e., from 1.6 and 1.7 eV in pure films to 1.4 and 1.5 eV in chlorine‐doped films for electrons and holes, respectively. These effects have been explained in terms of the enhancement in the conductivity of amorphous selenium and increase in the mobility of electrons and holes on chlorine doping.

ISSN:0003-6951    

DOI:10.1063/1.105666

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report on the first example that applies coherent anti‐Stokes Raman scattering (CARS) to real time diagnostics of detonation products from a solid explosive. The supersonically expanding gaseous products, from the detonation of either lead azide pellets or powders, are studied, using broadband CARS. The density, and the rotational and vibrational temperatures of ground electronic state N2molecules, N2(X), are monitored as a function of time at a fixed distance, 3.3 cm, from the azide surface. The rotational temperature is low, around 200–300 K, while the vibrational temperature is around 2000 K for delays of 8–12 &mgr;s, following the initiation of detonation. The density of N2(X), during this time interval, increases from ∼1×1017to 1×1018cm−3.

ISSN:0003-6951    

DOI:10.1063/1.105667

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A LMA (LaMgAl11O19) microchip laser close coupled to the fiber output of a laser diode has been tested. For a 1‐mm‐thick cavity and a 6×1020cm−3Nd concentration, an output power of 35 mW has been obtained, leading to an optical efficiency of 12%. The laser proved to be very stable with an intrinsic noise of 0.6% and an output power variation of only 5% for a 15 °C temperature change of the pump laser diode. Even near threshold two longitudinal modes were observed. The half divergence of this microchip laser was found to be 5±1 mrad.

ISSN:0003-6951    

DOI:10.1063/1.105668

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The gain‐current characteristics of undoped GaInP (660‐nm) bulk lasers have been calculated over a range of temperatures. The calculations use parabolic bands with strictkselection and include band‐gap narrowing and lifetime broadening due to carrier‐carrier interactions at high densities. The broadening lifetime &tgr; has been implemented as a constant value of 10−13s and as a carrier‐dependent value proportional ton−1/3. Using &tgr;=10−13s, our calculations for GaInP at room temperature give a value for the differential gain &bgr; of 0.026 cm−1(A cm−2 &mgr;m−1)−1and a value for the transparency currentJ0of 4.4 kA cm−2 &mgr;m−1. These are in close agreement with experimental results. Results for GaAs at room temperature are also given.

ISSN:0003-6951    

DOI:10.1063/1.105669

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We propose and demonstrate novel surface‐normal multiple‐quantum‐well reflection modulators which are operable at high intensities while maintaining high contrast (greater than 10) by exploiting resonant tunneling between adjacent wells. At the resonant tunneling field, the lifetime of the excited (highly absorbing) state is dramatically shortened, thus minimizing carrier‐density‐dependent saturation effects. Moreover, we show that even in a Fabry–Perot cavity, device deterioration due to saturation is greatly reduced.

ISSN:0003-6951    

DOI:10.1063/1.106395

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Previous reports of harmonically driven mode‐locked semiconductor lasers have indicated that the intensity correlation between adjacent pulses has a contrast ratio of two, rather than three as expected for mode‐locked pulses. We show that this reduced contrast ratio is a result of pulse instabilities in harmonically driven mode‐locked lasers. By setting the rf drive frequency to the stable operating condition, stable pulses with a contrast ratio of three have been obtained.

ISSN:0003-6951    

DOI:10.1063/1.105670

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A noncontact, nondestructive, laser‐based method for remote monitoring of material grain size is described. A surface acoustic wave surge, generated in the material under test by a short, high‐power laser pulse, is detected optically. The leading‐edge rise time of the acoustic signal is found to relate to the material grain size through frequency‐dependent scattering. In assuming a Rayleigh scattering model, a good correlation with metallurgical measurements is obtained in steel specimens.

ISSN:0003-6951    

DOI:10.1063/1.105671

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have performed computer simulations of simultaneous and sequential ion bombardment and epitaxial growth. In agreement with recent reflection high‐energy electron diffraction (RHEED) measurements on Si, we observe ion‐induced RHEED oscillations, a cancellation of RHEED oscillations during simultaneous equal‐rate ion bombardment and growth, and a reversal of growth‐induced roughening by subsequent ion bombardment. Comparison between simulations and measurements indicate that a model of the ion/surface interaction characterized by the creation of mobile vacancies with minimal preferential sputtering is sufficient to simulate all the RHEED measurements.

ISSN:0003-6951    

DOI:10.1063/1.105648

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The imaging resolution of an atomic force microscope operating in contact with a Langmuir–Blodgett (LB) film is predicted as a function of applied force, tip radius, adhesive force, and tip and film properties. The elastic modulus and the hardness of the LB film were measured using a nanoindenter and the imaging resolution is predicted using both a simple Hertzian elastic analysis and one that includes adhesive forces between the tip and the sample. For a small applied force (<1 nN) the resolution improves sharply as the tip radius and the adhesive force decrease. The onset of inelastic deformation, however, limits the resolution of the sharpest tips.

ISSN:0003-6951    

DOI:10.1063/1.105649

出版商:AIP    

年代:1991

数据来源: AIP