摘要:

When radiation undergoes total internal reflection at a solid–gas interface, an exponentially decaying wave, known as the evanescent wave, propagates into the gas. If the incident radiation is amplitude modulated and the gas has an absorption at the wavelength of the radiation, the optoacoustic effect can be produced by absorption of energy from the evanescent wave. Experiments with 10.6 &mgr; radiation internally reflected in an NaCl prism show the amplitude of the optoacoustic signal (in SF6) to be linearly proportional to the product of the square of the electric field amplitude and the penetration depth of the evanescent wave as given by Fresnel’s equations. The amplitude of the optoacoustic signal in a 100‐&mgr;l detection cell is found to increase linearly with the mole fraction of SF6in He over the range from 10−5to 10−2.

ISSN:0021-8979    

DOI:10.1063/1.332678

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The heterodyne performance of Ge photoconductors doped with shallow impurities was investigated using optically pumped far infrared lasers. Two lasers operating on the 67‐&mgr;m NH3Raman line generated difference frequencies from 0–100 MHz. An additional frequency point at 1.155 GHz was produced with two methanol‐isotope lasers at 118 &mgr;m. For three detectors with different doping levels IF bandwidths of 141, 63, and 8 MHz were measured using local oscillator powers of a few milliwatts. The detector gain and quantum efficiency were calculated from shot noise measurements. For impedance matched operation the calculated noise equivalent power (NEP) values are 2×10−18W Hz−1for the fastest detector and 6.5×10−19W Hz−1for the slowest detector.

ISSN:0021-8979    

DOI:10.1063/1.332679

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We report the absolute conversion efficiency &xgr;xfrom the incident laser light energy to x‐ray photons for laser‐produced plasmas. Potential x‐ray backlighting (radiography) line sources having photon energies from 1.4 to 8.6 keV are studied as a function of laser wavelength, pulsewidth, and intensity. The laser intensity and pulsewidth range from 1014to 1016W/cm2, 100 ps to 2 ns and include incident wavelengths of 1.06, 0.53, and 0.35 &mgr;m. We found thatK‐shell x‐ray line emission &xgr;x: (1) decreases with increasing x‐ray energy, (2) decreases with increasing laser intensity, (3) decreases rapidly with pulselength, and (4) moderately increases with decreasing laser wavelength. On the contrary, for Au Mband emission, at a fixed laser intensity and pulsewidth, &xgr;xsignificantly increases (∼25×) upon decreasing the laser wavelength from 1.06 to 0.35 &mgr;m.

ISSN:0021-8979    

DOI:10.1063/1.332680

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Magnetically insulated ion diodes with a cryogenically refrigerated anode are proposed and their characteristics are examined. Proton beams of 7 A/cm2and deuteron beams of 5 A/cm2, with energy of about 80 keV are extracted from a refrigerated H2O or D2O anode with good reproducibility and reasonable repetition rate.

ISSN:0021-8979    

DOI:10.1063/1.332681

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Recent experiments have demonstrated that the finite rate of vibrational relaxation in the formation of KrF affects the saturation characteristics of the KrF(B) state during extraction of laser light. We have assembled a collisional radiative model using calculated EinsteinAcoefficients for the lowest twenty KrF states and an approximate calculation of the rate of vibrational energy transfer between KrF and a buffer gas. The model describes the flow of excitation through the vibrational levels of KrF, and demonstrates the effects of vibrational relaxation on KrF(B) saturation and spectra. The results of these calculations agree qualitatively with the published experimental results. In addition, we find that, due to the relaxation kinetics of KrF, Kr2F, a major absorber, is not truly saturable.

ISSN:0021-8979    

DOI:10.1063/1.332682

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

It is shown that the nonlinear ‘‘Hall’’ force generated in a conducting sphere placed in an oscillatory (ac) magnetic field has a nonzero curl. It, therefore, drives a poloidal current which has a steady (dc) component and a second harmonic component. A general analytic expression for the dc toroidal magnetic field generated by the Hall current is obtained for the weakly nonlinear case: &ohgr;ce/&ngr; ≪1, where &ohgr;ce=eB/mis the electron cyclotron frequency in the ac magnetic field and &ngr; is the effective collision frequency. The dc magnetic field is evaluated numerically (using the general analytic formulae) for the special case where the applied ac magnetic field is uniform.

ISSN:0021-8979    

DOI:10.1063/1.332683

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A laser method for accelerating electrons is described, based on the inverse Cherenkov effect in a gas. The laser fields are in the form of a cylindrical cone of plane waves on whose axis travel the electrons, with the cone angle and the gas refraction index such that each electron sees constant fields in time. Expressions are obtained relating the overall energy transfer to total laser power and wavelength, and to gas index and interaction length. With laser powers now available, energy increments of tens of GeV are possible. For comparative purposes, a related alternative scheme involving electrons in vacuum and evanescent laser fields is also analyzed. It is found that the method applies particularly well to adding energy to the electron bunches produced by large microwave accelerators, as collision effects are less troublesome at high injection energies.

ISSN:0021-8979    

DOI:10.1063/1.332684

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A wiggler‐free free electron laser operating in a waveguide is analyzed by using a single particle treatment. The use of either a TE or a TM mode is shown to enhance the gain for a resonant frequency much higher than the cyclotron frequency. It is demonstrated that a source of a submillimeter radiation, based on this analysis, may have output power comparable to that of a wiggler‐type free electron laser.

ISSN:0021-8979    

DOI:10.1063/1.332662

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Temporal resolution in fast photonic tubes, e.g., streak tubes, frame tubes, and photodiodes, is enhanced by using a high electric field at the photocathode. However, at relatively high irradiance, the tube performance is degraded in both temporal and spatial resolution. It is generally assumed that the degradation is due to space charge. It is well known that space charge depresses the electric field in the immediate region of the cathode. For zero initial‐energy electrons, the electric field at the photocathode decreases with increasing space charge and becomes zero when the full space‐charge‐limit current is extracted from the cathode; however, photoelectrons from real cathodes have finite energy distributions that can change the polarity of the cathode field from accelerating to retarding at high irradiance. By utilizing appropriate photoelectron energy distribution functions, we will first calculate the electric field at the cathode‐grid region for high irradiance and then examine the perturbing effects upon the resolution in the photonic tube.

ISSN:0021-8979    

DOI:10.1063/1.332663

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A new class of gain guiding laser with a tapered‐stripe structure has been developed which exhibits a linear dependence of light output on cw current, a stable single‐lobe far‐field pattern along the junction at the power level of more than 10 mW, and an amount of astigmatism below 20 &mgr;m. It is also shown that a thin active layer thickness is desirable to achieve a stable lateral mode. The main feature of the tapered‐stripe structure is that it offers an additional degree of freedom in controlling the beam spot size and the radius of curvature of the phase front separately, by varying the widths as well as the length of the tapered stripe.

ISSN:0021-8979    

DOI:10.1063/1.332664

出版商:AIP    

年代:1983

数据来源: AIP