摘要:

A relativistic electron beam of 150–300 keV, 1–2 kA, and 40–80 ns generated in a plasma‐filled diode is injected into a magnetized hydrogen plasma of density 1011–1014cm−3. Beam‐plasma interaction was observed to be strong when the plasma density in the diode and interaction region was &bartil;1012cm−3. The effective collision frequency was estimated to be around 10−2times the ion plasma frequency. The plasma heating levels of &bartil;1016eV cm−3 &mgr;s−1were inferred. The observed net current multiplication was explained by two‐stream instability.

ISSN:0021-8979    

DOI:10.1063/1.348523

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The photothermal deflection technique has been used to study thermal nonlinearity in samples of glasses doped with CdSxSe1−xmicrocrystals. The effect of the influence of probe beam absorption on deflection signal has been investigated from a theoretical point of view. Measurements have been performed showing the possibility of detecting very small changes of the probe beam absorption coefficient produced by the pump intensity.

ISSN:0021-8979    

DOI:10.1063/1.348524

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Noncritical phase‐matched second harmonic generation was measured in optically biaxial KNb1−xTaxO3mixed crystals in the orthorhombic phase. For Nd:YAG‐(1064 nm) the coefficientd31of the tensor of the nonlinear susceptibility was applied, while for the GaAs‐laser (905 nm) the coefficientd32was used. For both laser wavelengths the phase‐matching temperature decreases with increasing Ta‐concentration. Noncritical phase‐matching at room temperature can be reached with the GaAs‐laser for a Ta concentration of ≊9%. The corresponding value for the Nd:YAG laser is ≊14%.

ISSN:0021-8979    

DOI:10.1063/1.348525

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Optical phase conjugation by degenerate four‐wave mixing in samples of pristine and iodine‐doped polyphenylacetylene at ruby laser wavelength (694.3 nm) is reported here. The nonresonant values of the third‐order optical susceptibility &khgr;(3)are determined from the measurements of reflectivity of phase conjugate signals.

ISSN:0021-8979    

DOI:10.1063/1.348526

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The Alexandrite laser belongs to the class of vibronical lasers. The broad spectral laser gain of Alexandrite laser gain of Alexandrite suggests the possibility to generate femto‐second laser pulses with passive mode locking. Experiments showed, however, that a limit of pulsewidth shortening is reached near 10 ps. This effect is caused by the limited mode‐locking capability of the passive absorber. The results of eight different passive absorbers used to generate mode locking are presented. The effect of bandwidth narrowing of the laser emission spectrum of Alexandrite on pulsewidth and pulse‐train energy was measured for these absorbers. The dependence of laser output energy with the temperature on the active medium was also investigated.

ISSN:0021-8979    

DOI:10.1063/1.348527

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Ion implantation into Nd:YAG has been used to produce waveguides which are capable of supporting laser action. The refractive index profiles have been characterized as a function of ion dose and energy, implant temperature, and subsequent thermal annealing. Transmission losses down to 1.2 dB/cm have been obtained in the optimized waveguides. There is a temperature independent index enhancement of ∼0.15% in the electronic stopping (guiding) region. The nuclear collision damage is temperature dependent, and shows an initial index increase (∼0.3% for dose 1 × 1016ions/cm2), but a subsequent decrease of up to several percent, which forms an optical barrier, as has been observed in many other crystalline materials. The best mode confinement and attenuation is obtained by utilizing the low dose nuclear index enhancement produced by several equally spaced implants (multiple energy) to give a broad well with &Dgr;n∼0.25%. Several unusual features of the profiles are reported and discussed.

ISSN:0021-8979    

DOI:10.1063/1.348962

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The nozzle and the anode of the UCI (University of California, Irvine)z‐pinch facility were modified to study the influence of the anode‐cathode geometrical structure on the stability of the pinch and the x‐ray yield of the pinch. The anode was modified from a honey‐comb to a hollow cylinder with a 4‐cm diameter and a ∼3.5‐mm wall thickness, placed 2 cm below the cathode. The cavity in the center of the cathode was enlarged from 6‐mm diameter to 36 mm. The design of the cathode and the anode showed a marked improvement of the pinch stability over the previous design. Both zirconium and carbon‐carbon nozzle were used for the Kr and Nezpinches. After a few tens of shots the Zr nozzle was melted at the edge and the pinch degraded, while the carbon‐carbon nozzle did not sustain any damage for more than 300 shots. Some shots showed thedi/dtat the implosion is ∼5 times higher than thedi/dtat the beginning of the discharge, this has never been obtained at UCI before. This ratio of the initialdi/dtto pinchdi/dtis a measure of the pinch quality. By serendipity it was found that double gas puffzpinch increased the hard x‐ray (>1 keV) output by about an order of magnitude. The nozzle was then modified to allow double puff operation. A 3.4‐mm‐diam hole was opened at the center of the nozzle and a plunger was inserted from the top to control the mass of the gas entering the hole. The diagnostics includedi/dtcoil, soft, and hard x‐ray diodes. Soft and hard x‐ray emission are both enhanced by the double gas puffzpinch.

ISSN:0021-8979    

DOI:10.1063/1.348528

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A one‐dimensional kinetic model is developed for the flow of ions to a probe whose characteristic size is smaller than the ion gyroradius in drifting plasmas. Numerical solutions of the self‐consistent plasma‐sheath equations have been obtained for arbitrary external temperature and parallel plasma flow velocity. The ion current to the probe is obtained and the ratio of the upstream to downstream current is represented by the formR=exp[KUd], whereUdis the drift velocity in units of (Te/mi)0.5andKis constant depending on the type of source in the sheath‐transition region. Comparisons with other models are made.

ISSN:0021-8979    

DOI:10.1063/1.348529

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Ion flux and ion acceleration power have been measured at the electrode sheath in a capacitively coupled argon discharge driven at 13.56 MHz. Two independent methods have been used to evaluate the ion power. One method is based on measuring the ion current to an rf electrode and the dc component of the rf sheath voltage. The other method is based on measuring the discharge power as a function of the total discharge current. Measurements were performed at gas pressures between 3 mTorr and 3 Torr and at discharge powers between 10−2and 102W. Over the entire range of operation the ratio of the ion to discharge current varied between 1% and 3%, whereas the percentage of the ion power loss was between a fraction of a percent and 95% depending upon the total discharge power. The series equivalent resistance corresponding to the ion power loss was found experimentally and corresponds well with predictions based on a dynamic sheath model.

ISSN:0021-8979    

DOI:10.1063/1.348530

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The time evolution of measured plasma parameters, including the electron energy distribution function (EEDF), in the discharge and post‐discharge regime of a pulsed hydrogen magnetic multipole plasma is presented. The time necessary for the plasma to reach equilibrium has been established as 160 &mgr;s. The present results clarify the mechanisms which initiate the discharge. The decay rates of the charged‐particle density and energy in the post‐discharge have been measured. These measurements indicate that particle transport to the wall is the dominant loss mechanism for both charged‐particle density and energy. The time‐resolved EEDF is found to be non‐Maxwellian in the discharge and Maxwellian in the late post‐discharge.

ISSN:0021-8979    

DOI:10.1063/1.348531

出版商:AIP    

年代:1991

数据来源: AIP