摘要:

The discharge characteristics of an electrical circuit for uv preionization in TEA CO2laser are described. The suitable size of an electrode for uniform volumetric preionization of a laser gas is decided. The mechanisms of the ionization and the generated total initial electrons by uv photons are discussed. Moreover, both the effects of circuit parametersR,Lon the intensity of uv radiation and the endurance test of the electrode for repeated discharges are also described.

ISSN:0021-8979    

DOI:10.1063/1.327664

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Electric field dependence of the output polarization was investigated in the dye laser light amplifier, using the dimethyl sulfoxide (DMSO) solution of coumarin 30, which was found to have a large Kerr coefficient and a high resistivity. Output polarization was found to be determined by the Kerr effect of the solvent DMSO and the anisotropic gain due to the anisotropic orientation distribution of excited dye molecules. The nonlinear electric susceptibility ‖&khgr;xxxx−&khgr;zzxx‖ of DMSO was estimated to be 9.5×10−12cgs esu. The orientational distribution time constant &tgr;rfor coumarin 30 dissolved in DMSO was estimated to be about 1.3×10−9s.

ISSN:0021-8979    

DOI:10.1063/1.327665

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Degradation of Ga1−xAlxAs visible diode lasers in the 0.7‐&mgr;m wavelength region is investigated through room‐temperature life tests. A marked dependence of laser life on lasing wavelength is observed. In particular, degradation proceeds faster for shorter‐wavelength lasers. It is shown that the degradation of lasers radiating at wavelengths below 730 nm can mainly be attributed to the rapid formation of dark regions and dark‐line defects during aging. A notable improvement in life is obtained for these shorter‐wavelength lasers by Te doping of the active layer. On the other hand, degradation at above 740 nm results from enhanced facet oxidation due to high AlAs mole fractions in the active and cladding layers. This facet oxidation is effectively suppressed by facet coatings with SiO2films. As a result, stable operations, exceeding 4000 h, are achieved in the 740–770‐nm wavelength region.

ISSN:0021-8979    

DOI:10.1063/1.327666

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The effect of coherence between pump and signal beams on phase conjugation by degenerate four‐wave mixing is analyzed using a simple classical model. The influence this may have on practical applications is discussed.

ISSN:0021-8979    

DOI:10.1063/1.327667

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Room‐temperature low‐current‐threshold broad‐area Fabry‐Perot AlxGa1−xAs/AlyGa1−yAs double‐heterostructure (DH) lasers have been prepared by molecular‐beam epitaxy (MBE) covering the lasing emission wavelength from 8900 to 7200 A˚ (infrared to visible). In this emission range, the averaged pulsed current threshold densitiesJthare as low as those obtained by liquid‐phase epitaxy (LPE). At ∼8200 A˚, the wavelength at which DH lasers have also been prepared by metalorganic chemical‐vapor deposition (MO‐CVD), theJth’s of the MBE grown lasers are lower.

ISSN:0021-8979    

DOI:10.1063/1.327668

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The degenerate surface acoustic wave elastic convolver is analyzed by solving the nonlinear piezoelectric equations of motion subject to appropriate boundary conditions. The nonlinear equations are treated by a perturbation theory by assuming that the nonlinear stress and nonlinear electric displacement are small compared to the respective linear quantities. We obtain expressions for the open‐circuit voltage (V0) and short‐circuit current (I0) in terms of power (P(i)) in the incident waves and linear and nonlinear constants of the material. We also calculate the figure of meritM=Vrms0(P(1)P(2)/W2)−1/2(Wis the width of the incident acoustic beam) and the internal impedanceZ0=V0/I0. We obtain numerical values ofMandV0from an estimate of the nonlinear constants available in the existing literature and compare them with experiments.

ISSN:0021-8979    

DOI:10.1063/1.327669

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The effects of dilute additions of deuterium (D) and tritium (T) on the elastic moduli of single crystals of Nb and V were measured at room temperature. The coefficients &Dgr;C44/C44and &Dgr;C′/C′, per at.% isotope, are evaluated and compared with published data for H additions and previous measurements of D additions. The agreement among data from different laboratories is well within experimental error. The &Dgr;C′ effects in Nb are isotope dependent and closely related to the square root of the inverse mass. In the case of V, the &Dgr;C′ effect is the same for T and H but smaller for D, suggesting a possible change from tetrahedral to octahedral site occupancy with increasing isotope mass.

ISSN:0021-8979    

DOI:10.1063/1.327670

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A solution is derived for the elastic waves scattered by a thin inclusion. The solution is asymptotically valid as inclusion thickness tends to zero with the other dimensions and the frequency fixed. The method entails first approximating the total field in the inclusion in terms of the incident wave by enforcing the appropriate continuity conditions on traction and displacement across the interface, then using these displacements and strains in the volume integral that gives the scattered field. Expressions are derived for the far‐field angular distributions ofPandSwaves due to an incident planePwave, and plots are given for normalized differential cross sections of an oblate spheroidal tungsten carbide inclusion in a titanium matrix.

ISSN:0021-8979    

DOI:10.1063/1.327671

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

(Received 19 September 1979; accepted for publication 12 October 1979)A three‐dimensional heat transfer model for laser material processing with a moving Gaussian heat source is developed using finite difference numerical techniques. In order to develop the model, the process is physically defined as follows: A laser beam, having a defined power distribution, strikes the surface of an opaque substrate of infinite length but finite width and depth moving with a uniform velocity in the positivexdirection (along the length). The incident radiation is partly reflected and partly absorbed according to the value of the reflectivity. The reflectivity is considered to be zero at any surface point where the temperature exceeds the boiling point. This is because a ’’keyhole’’ is considered to have formed which will act as a black body. Some of the absorbed energy is lost by reradiation and convection from both the upper and lower surfaces while the rest is conducted into the substrate. That part of the incident radiant power which falls on a keyhole is considered to pass into the keyhole losing some power by absorption and reflection from the plasma within the keyhole as described by a Beer Lambert absorption coefficient. Matrix points within the keyhole are considered as part of the solid conduction network, but operating at fictitiously high temperatures. The convective heat transfer coefficient is enhanced to allow for a concentric gas jet on the upper surface as used for shielding in welding and surface treatment, but not cutting. The system is considered to be in a quasi‐steady‐state condition in that the thermal profile is considered steady relative to the position of the laser beam. The advantages of this method of calculation over others are discussed together with comparisons between the model predictions and experiments in laser welding, laser arc augmented welding, laser surface treatment, and laser glazing. The system is assumed to be in a quasi‐steady‐state condition after the keyhole initiation period which for most practical purposes may be considered instantaneous.

ISSN:0021-8979    

DOI:10.1063/1.327672

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The mechanical response of a metallic bar to pulses of 30‐MeV protons has been investigated. It was found that by making the pulse duration short in comparison with the periods of the low‐order harmonics of the bar resonant oscillations, vibration amplitudes of the order of 10−11cm could be measured. The required energy loss by the beam pulses amounted to about 10−5J, and very simple theoretical considerations suffice to relate quantitatively the deposition of energy in the bar with the amplitudes of its natural vibrational modes.

ISSN:0021-8979    

DOI:10.1063/1.327673

出版商:AIP    

年代:1980

数据来源: AIP