摘要:

Electronic cooling for improving the signal‐to‐noise (S/N) performance of sensors was applied to the mechanically resonant Hughes rotating gravity gradiometer (RGG). An 8.3‐dB improvement in theS/Nwas obtained. The electronic cooling technique uses a negative feedback damping circuit between the two RGG transducers. The feedback circuit is electrically equivalent to a high‐impedance resistor cooled to cryogenic temperatures.

ISSN:0021-8979    

DOI:10.1063/1.325699

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We measured the damage threshold of 10.6‐&mgr;m light incident on glass microballoon laser fusion targets. The threshold is several dozen microjoules, depending on target size and laser pulse width, and the damage mechanism appears to be thermal heating and rupture. Perforating glass microballoons proves to be a useful alignment verification technique.

ISSN:0021-8979    

DOI:10.1063/1.325620

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Spectral effects and nonlinearities that characterize illumination of dc discharges by low‐intensity light and illumination of gas cells by high‐intensity lasers are described. The similarities suggest an analogy between both cases. This analogy can be used to deepen the understanding of the low‐intensity EM radiation interaction with gas discharges and as a possible tool for further study of gas breakdown by high‐intensity lasers, including further investigation of the ’’effective photon’’ concept.

ISSN:0021-8979    

DOI:10.1063/1.325693

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An integral equation method is developed for the computer modeling of the magnetic fields produced by color television deflection yokes. Saddle or toroidal yokes with either radial or nonradial winding distributions can be analyzed using this new technique. The integral equation method is shown to yield magnetic field calculations that are at least as accurate as those produced by conventional finite‐difference analysis. In most cases computer algorithms using the integral equation approach have been found to be more computationally efficient than existing finite‐difference programs.

ISSN:0021-8979    

DOI:10.1063/1.325687

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The magnetic field in an imploding wire array is studied. After the initial explosion of the wires the array starts imploding. The process can be considered quasistatic electromagnetically and the assumption of perfect conduction is made. Under these conditions the driving magnetostatic forces generated by the wires need to be calculated in a series of snapshots, which are stages of the magnetohydrodynamics process. For that purpose a Green’s function technique is developed to solve for the magnetostatic field generated by an array of perfectly conducting wires of arbitraryx‐ycross section, carrying current in thezdirection. The wires are enclosed in an outer cylinder, inside of which they are arranged with angular periodicity. This outer cylinder carries all the returning current, and ideally does not permit any magnetic lines to escape from its enclosure. The resulting equations for the magnetic vector potential (A=A?,∇2A=0 in vacuum,A=0 on the outer cylinder,A=const≠0 on the inner conductors) are implicitly solved by writing the potential as a linear superposition of point (zlines) current densities around the boundaries of the inner conductors. The point current densities are determined by imposition of the boundary conditions. For the case of small round wires not overlapping and sufficiently far from the center, an explicit solution is found in the form of an angular Fourier series, having as expansion parameter the ratio between the radius of the inner conductors and the distance to the center, times the number of wires periodically arranged. For the general case the problem is discretized by considering the boundary of each of the inner conductors as a connected set of segments of either circumferences or straight lines, each segment carrying a different amount of current. This procedure yields a set ofNlinear equations withNunknowns; theNunknowns are the currents carried by each of theNsegments by which the boundary is approximated. Knowledge of these currents solves the problem completely because with them and using the Green’s function and its complex derivative, the vector potential and magnetic field, respectively, can be obtained anywhere in the region of interest. In particular the magnitude of the magnetic field just on the boundary of each of the inner conductors is related to the magnitude of the segment currents through a proportionality constant. An algorithm to solve the linear equations is discussed and representative cases shown. The method is seen to be accurate and fast.

ISSN:0021-8979    

DOI:10.1063/1.325707

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The generation of far‐infrared radiation by frequency mixing has been studied for the case of phase matching by means of the noncollinearity of the generating beams. An exact theoretical treatment has been performed for the case where the laser beams propagate linearly in the sample and for the case where the laser beams follow a zigzag path resulting from multiple internal reflections; the profile of each laser beam entering the sample is taken realistically to be a truncated Gaussian; sample absorption of the generating and generated radiations is taken into account. Previous treatments for the two geometries were approximate; in addition, square profile beams were assumed and the effect of absorption was neglected. Measurements have been made on insulating GaAs; the effects of sample length and sample absorption have been investigated. In contrast to previous work where two separate lasers were used, a single TEA CO2laser has been modified to provide both generating beams, resulting in a more consistent temporal overlap of the pulses in the two beams. Furthermore, an SF6saturable absorption cell has been used to select a single longitudinal mode, thereby eliminating the fine structure in pulses of one beam and making the overlap of the pulses from the two beams tractable. The coherence of the generated radiation was measured. The ratio of the theoretical prediction to the experimental results is a factor of ∼6, in comparison with the smallest factor of ∼400 for previous work with pulsed lasers, indicating the significance of the improvements in the experiment and the theory.

ISSN:0021-8979    

DOI:10.1063/1.325661

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

First‐ and third‐derivative signals of saturated absorption in iodine 127 molecular vapor are detected by using a frequency‐modulated 190‐cm‐long 633‐nm He‐Ne laser with a Fox‐Smith–type resonator and an iodine absorption cell which is set outside of the resonator. Aiming to stabilize the laser with unmodulated output, a retroreflector‐type optical modulator is added to the above system, and the first‐derivative signal is obtained by external modulation. Comparing the obtained signal with those obtained by the frequency‐modulated laser, possibilities to detect the third‐derivative signal by using the optical modulator and to stabilize the unmodulated laser are found.

ISSN:0021-8979    

DOI:10.1063/1.325676

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The scattering of a two‐dimensional Gaussian beam wave by a perfectly conducting or dielectric cylinder centered off both the beam axis and the beam waist is treated by the Fourier‐series‐expansion method. The incident‐beam fields are expanded in a Fourier series with respect to the polar angle in a cylindrical coordinate, and the expansion coefficients are numerically evaluated. Several scattering patterns are obtained by the use of these expansion coefficients, and the dependence of the scattering characteristics on the offset of the incident‐beam wave is examined.

ISSN:0021-8979    

DOI:10.1063/1.325627

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

It is shown that a pair of counterrotating fused‐quartz plates may be used to vary the phase between the second harmonic and the square of the fundamental in two‐crystal optical interference techniques. The advantages are simplicity of design and ease of use.

ISSN:0021-8979    

DOI:10.1063/1.325637

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The theory of linear and stimulated free‐electron lasers using the Smith‐Purcell effect is presented. These lasers depend upon the resonant interaction of an electron beam with the longitudinal field of a surface‐harmonic wave on a diffraction grating. Detailed design criteria for the linear Smith‐Purcell‐effect laser are determined. Numerical estimates show that infrared lasers are feasible at beam currents smaller than 1 A and that single‐mode operation may be achieved. Saturation estimates determine the power output in the range 102W. An expression for the gain of the stimulated Smith‐Purcell laser is derived. The frequency up‐conversion factor for the stimulated interaction may be very large. Its possible use as a soft x‐ray laser is limited by the available intensity of the pump wave.

ISSN:0021-8979    

DOI:10.1063/1.325642

出版商:AIP    

年代:1979

数据来源: AIP