摘要:

A novel concept for implementing a high‐resolution spatial light modulator using a thin slab of photorefractive LiNbO3crystal is described. This method uses the photovoltaic effect to impress phase information onto the crystal without the use of holography where coherent reference beams are required. Experimental demonstration as well as an analysis of the operation and performance of the device are given.

ISSN:0021-8979    

DOI:10.1063/1.348618

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A chromium‐ and neodymium‐codoped gadolinium scandium gallium garnet (Cr:Nd:GSGG) crystal was tested for pulsed‐ and continuous‐wave (cw) laser operations with a flashlamp and solar simulator as pumping sources. The crystal has been considered as a good candidate for a solar‐pumped laser because of its broad absorption bands over the solar spectrum. However, it was observed experimentally and theoretically that its cw laser operation is difficult at high pump powers because too many thermal lensing effects are induced. Only at low solar‐simulator beam intensities of up to 1500 solar constants (203 W/cm2) was cw laser operation lasting longer than 10 min achieved. For higher pump beam intensities of up to 2500 solar constants (338 W/cm2), a quasi‐cw‐laser operation was obtained with continuously chopped pumping with a duty cycle of 0.5 and a repetition rate of 13 Hz. The experimental result was compared with the calculated stability condition of the laser resonator for various pump powers and showed that the thermal focusing of the Cr:Nd:GSGG is 15–8 times greater than that of the neodymium‐doped yttrium aluminum garnet (Nd:YAG) laser for the pump beam intensities from 1000 to 3000 solar constants.

ISSN:0021-8979    

DOI:10.1063/1.348619

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Amorphous films having a component of the stoichiometric GeTe‐Sb2Te3pseudobinary alloy system, GeSb2Te4or Ge2Sb2Te5representatively, were found to have featuring characteristics for optical memory material presenting a large optical change and enabling high‐speed one‐beam data rewriting. The material films being sandwiched by heat‐conductive ZnS layers can be crystallized (low power) or reamorphized (high power) by laser irradiation of very short duration, less than 50 ns. The cooling speed of the sandwiched film is extremely high: more than 1010deg/s, which permits the molten material to convert to the amorphous state spontaneously; whereas, a low‐power pulse irradiation of the same duration changed the exposed portion into the crystalline state. The optical constant changes between the amorphous state and the crystalline state of them were measured to be large: from 4.7+i1.3 to 6.9+i2.6 and from 5.0+i1.3 to 6.5+i3.5, respectively. The crystallized portion was known to have a GeTe‐like fcc structure by an analytical experiment using transmission electron microscopy, differential scanning calorimetry, and x‐ray and electron diffraction methods. The high crystallization speed is ascribed to (1) the pseudobinary system which can form crystalline compositions without any phase separation, (2) the high symmetry of the fcc structure which is the nearest to the random amorphous structure, (3) the high‐energy difference between the amorphous state and the fcc crystal state.

ISSN:0021-8979    

DOI:10.1063/1.348620

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Waveguide structures for quantum well (QW) lasers are analyzed numerically by a straightforward 2×2 matrix approach. It is shown that this approach is capable of analyzing separate‐confinement heterostructure (SCH) waveguides, having any arbitrarily graded‐index (GRIN) profile in the waveguide layers and any number of QWs in the active layer, to any desired level of accuracy. Using this waveguide analysis, general GRIN‐SCH waveguide structures of QW lasers can be optimized for maximum confinement factors. It is estimated that the laser threshold current density can be reduced typically by 10% as a result of this waveguide optimization.

ISSN:0021-8979    

DOI:10.1063/1.348593

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

It is shown that the normal acceleration sensitivity of contoured quartz resonators with rectangular supports vanishes when the centers of the mode shape and support rectangle coincide. This result is a consequence of symmetry and applies to many other shapes. Since it is essentially impossible to realize this situation in practice, an analysis of the influence of an offset of the centers on the normal acceleration sensitivity is performed. The biasing deformation is determined by means of a variational approximation procedure using the variational principle with all natural conditions for anisotropic static flexure. The very important accompanying strains varying quadratically across the thickness are determined recursively, as in earlier work. The resulting flexural biasing states are employed in an existing perturbation equation along with the equivalent trapped‐energy‐mode shapes of the contoured resonators to calculate the normal acceleration sensitivities. It is shown that for small offsets the acceleration sensitivity increases linearly with offset, and orientations for which this effect is minimized are found.

ISSN:0021-8979    

DOI:10.1063/1.348594

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A general equation has been derived for computing the temperature distribution produced in a substrate heated by a high repetition rate pulsed laser. The theoretical predictions have been compared with experimental results obtained for etching of Mn‐Zn ferrite in KOH solution using a copper vapor laser. The effects of the laser power and substrate scan speed on the temperature distribution have been investigated, and the predicted melt‐zone boundaries have been compared with the experimentally observed width, depth, and shape of the etched grooves.

ISSN:0021-8979    

DOI:10.1063/1.348595

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Electron and ion avalanches have been recorded near a variety of insulators (plexiglas, teflon, high‐density polyethylene, low‐density polyethylene, polypropylene, delrin, polyvinyl chloride, and nylon) in nitrogen gas at pressures of 0.1, 0.2, and 0.3 MPa. With the exception of nylon, suppression of avalanches has been observed in the presence of insulators. In addition to electron and ion avalanches, simultaneous measurement of optical radiation associated with an electron avalanche was successfully carried out. Qualitative explanations have been provided for the suppression of avalanches near most insulators and an anomalous growth of avalanches near nylon insulators. Photoemission from nylon surfaces appears to be responsible for the enhanced growth of avalanches near nylon insulators. More precise measurements of optical radiation are needed to better understand the electron‐photon interactions near a solid insulator in a gaseous dielectric medium.

ISSN:0021-8979    

DOI:10.1063/1.348596

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The relative concentration of atomic fluroine was measured in a CF4rf glow discharge using the actinometric technique. The dependence of fluorine concentration on power, pressure and flow are presented and shown to be dependent upon reactor wall material and electrode material.

ISSN:0021-8979    

DOI:10.1063/1.348597

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The phenomenon of electric field induced (EFI) emission is examined in several diatomic and polyatomic molecules. The possibility of using this phenomenon as a diagnostic tool to measure, nonintrusively, the strength and direction of local electric fields in plasmas is discussed. An estimate of the EFI signal emitted in a typical application plasma is given. This yields a lower bound on the detector sensitivity necessary to exploit EFI emission in practical applications. It is concluded that, at present, the EFI signal could be measured by some very sensitive infrared detection schemes available. Current progress in infrared detector technology, if maintained, could result in the possibility of utilizing EFI emission on a more routine basis. This would allow measurement of electric fields in plasmas of species that are not suitable candidates for any of the other currently available schemes which measure such fields.

ISSN:0021-8979    

DOI:10.1063/1.348598

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A boundary‐layer model for a plane free‐burning high‐pressure gas‐discharge arc is given. For the dependence on the temperature, a rule given by Elenbaas [TheHighPressureMercuryVapourDischarge(North‐Holland, Amsterdam, 1951)]is used for the electrical conductivity and power‐law rules for the dynamic viscosity and the thermal conductivity. The specific heat is assumed to be constant. It is shown that a similarity transformation can be applied. The upward velocity increases with the square root of the core temperature. Graphs are given which show how the temperature rise in the arc depends upon the applied current.

ISSN:0021-8979    

DOI:10.1063/1.348599

出版商:AIP    

年代:1991

数据来源: AIP