摘要:

Single‐crystal fibers have been grown from high‐purity 1.5 wt&percent; Nd2O3 : Y2O3powder mixtures, and short lengths of the fiber in dielectric mirror resonators have been evaluated as lasers at both 1.07‐ and 1.35‐&mgr;m wavelength. The laser transition cross sections were approximately equal at the two wavelengths, and they were about two‐thirds the cross section of Nd : YAG at 1.31 &mgr;m. The fluorescence lifetime of the laser samples was 340 &mgr;sec. Loss in the material was approximately 3&percent; per cm. The absorption spectrum from 0.7 to 1.0 &mgr;m and fluorescence spectra for the 4F3/2→4I9/2, 4F3/2→4I11/2, and 4F3/2→4I13/2manifolds of Nd3+in Y2O3, taken with fiber samples, are reproduced in detail. The resultant energy levels are given. With a Kr laser operating at 0.7525 &mgr;m as the end pump, minimum observed laser threshold was 0.57 mW absorbed pump power for a 100‐&mgr;m‐diam 2.5‐mm‐long fiber operating cw in room‐temperature air at 1.07 &mgr;m. The lasers operated in one or two transverse modes and had active linewidths of approximately 2 A˚.

ISSN:0021-8979    

DOI:10.1063/1.325112

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The paper concerns a simplified analysis of the problem of the power extraction from the multipass cavity of the cw gasdynamic laser. Analytical formulas for the laser output and the resonator efficiency are given relating them to the cavity geometric features, cavity losses, number of the cavity passes, and gain and population inversion of a flowing optically activated medium. The analysis is oriented toward application of the obtained results for a rapid estimation of the power characteristics of a CO2(or N2O)/N2/(additives) cw gasdynamic lasers. The interaction between gain and radiation field is treated in terms of the rate‐equation formalism.

ISSN:0021-8979    

DOI:10.1063/1.325113

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The intensity of light scattered by surface acoustic waves (SAW) on internal reflection has been calculated for the geometry where the incident and scattered light are in a plane perpendicular to the SAW wave vector. The calculation was carried out for an arbitrary piezoelectric crystal having a free or metallized surface. Measurements on ay‐cut LiNbO3crystal and az‐propagating SAW give good agreement with the theory.

ISSN:0021-8979    

DOI:10.1063/1.325114

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The bulk‐wave properties of lead molybdate are well known in relation to its applicability as an acousto‐optic material. Some new results about its acoustic surface wave propagation properties are reported here, and potential applications of the light diffraction by acoustic surface waves propagating on lead molybdate are studied.

ISSN:0021-8979    

DOI:10.1063/1.325115

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The theory of the photoacoustic effect is extended to include the contribution of mechanical vibration of the sample. Coupled equations for thermal and acoustic waves are solved in both sample and gas. It is shown that the pressure signal in the gas may be significantly affected by acoustic coupling in the sample, and experimental confirmation of this extended theory is given. The results of the fully coupled treatment are shown to be accurately reproduced by an extension of the Rosencwaig piston model: the pistonlike motion of the gas boundary layer adjoining the sample is superimposed on the mechanical vibration of the sample surface to give a composite piston displacement which then produces the pressure signal in the gas. The composite‐piston model provides relatively simple algebraic results applicable to many cases of physical interest.

ISSN:0021-8979    

DOI:10.1063/1.325116

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Theory for the absorption/amplification coefficient of acoustic waves in nonparabolic degenerate semiconductors is developed using the modified collision term. Ionized impurity scattering is considered to be the sole mechanism of scattering of electrons. It is noted that an increase either in the nonparabolicity factor or in the electron concentration leads to a decrease in the threshold value of the drift velocity of electrons.

ISSN:0021-8979    

DOI:10.1063/1.325117

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The method of analyzing the activation of fracture mechanisms under the influence of generalized forces is described, leading to a generalized approach to the problem of time‐ and temperature‐dependent fracture processes. The analysis of complex fracture mechanisms of the type necessary for the simultaneous fracture of two phases is discussed. Fracture processes are described in terms of a network of events that can occur both sequentially and simultaneously.

ISSN:0021-8979    

DOI:10.1063/1.325118

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Experiments are performed with a single‐stage magnetic fluid rotary feed‐through seal to determine the influence of shaft rotation, seal fluid inventory, seal clearance, magnetic field intensity, and magnetic field distribution on the maximum seal capacity or burst pressure. For small magnetic fluid inventories, the seal exhibits very low static capacity, a maximum capacity near 20 Hz, and a slowly decreasing capacity for higher shaft speeds. For larger inventories, the effect of motion is small. Under a constant inventory condition, the larger clearance seals are less sensitive to shaft motion than the smaller clearance seals. As the seal clearance is increased, inevitable fluid loss due to rotation becomes more pronounced and the seal becomes weaker. For decreased magnetic field intensity in the gap, the seal capacity exhibits increased sensitivity to shaft speed. Several hypotheses are proposed to explain the observed behavior. Certain design‐related implications are discussed.

ISSN:0021-8979    

DOI:10.1063/1.325119

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The theoretical analysis of a two‐dimensional jet of ideal fluid impinging normally upon a void has been made and compared with experimental observations. Using a scaled‐up water model with a fixed‐jet Reynolds number of 750, general features of the flow such as streamline positions and fluid velocities are in good agreement with theoretical predictions. Moreover, theoretical limitations on the void‐space opening ratioh/wfor a given jet spacing ratios/wcovering a range from 0 to 2 correlate well with the onset of irregularities in the observed flow pattern. Finally, experimental precautions are outlined necessary to minimize fluid instabilities and concurrent fluid flux into the void space.

ISSN:0021-8979    

DOI:10.1063/1.325120

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The stopping cross sections of acetaldehyde, ethylene oxide, propylene oxide, and vinyl methyl ether for 0.3–2.0-MeV accelerated He+ions have been measured with probable random errors of 0.5–0.9&percent;. The stopping cross sections of the three-membered ring-structure compounds ethylene oxide and propylene oxide were found to be lower than those of their double-bonded isomers, but higher than those of isomers calculated from single-bonded alcohols.

ISSN:0021-8979    

DOI:10.1063/1.325121

出版商:AIP    

年代:1978

数据来源: AIP