Peter L. Hagelstein

NEW PHYSICAL EFFECTS IN METAL DEUTERIDES

Following the initial claims of 1989, the body of research on anomalous effects in metal deuterides has grown to include thousands of papers on a wide spectrum of topics. DoE, to facilitate their review of this set of research, has asked for the preparation of the following summary. The entire body of research is not addressed. Rather, a subset of research from two areas is presented: selected issues associated with excess heat production in deuterated metals, and a brief discussion of some aspects of nuclear emissions from deuterated metals.

Amplification in Ni-like Nb at 204.2 Å pumped by a table-top laser

We identified for the first time the 3d94d1S − 3d94p1P line in Ni-like Nb at 204.2 Å that was predicted to show gain. When pumped with a train of pulses containing less than 1 J per pulse, significant emission was recorded at 204.2 Å following the second and the third pulses. We measured the small signal gain coefficient per Joule of incident laser energy to be 1.49±0.42 cm−1 J−1 for this laser transition, which is higher by several orders of magnitude than that reported for other collisional laser systems in this wavelength range.

Application of escape probability to line transfer in laser-produced plasmas

The application of an escape probability method to treat transfer of optically thick lines in laser‐produced plasmas in plane‐parallel geometry is described. The escape probability calculated is valid in a plasma with any locally linear velocity profile. It reduces to the standard result for a static plasma and to the result of Sobolev [Sov. Astron. Astrophys. J. 1, 678 (1957)] for large ion velocity gradients. As examples, escape probability is applied to model the effect of optically thick line trapping in both exploding foil and ablating massive slab targets. Compared to detailed numerical calculations for the line transfer in these targets, the escape probability gives quite accurate estimates. This can be understood in terms of the large Doppler shifts in the line profiles that are generated by the ion velocity in the plasmas.

Whispering-gallery laser resonators. I. Diffraction of whispering-gallery modes

Whispering-gallery optics for use at soft X-ray and extreme ultraviolet wavelengths are examined for their potential applications in laser resonators. An examination is made of beam divergence at the exit of a whispering gallery resonator. The properties of whispering-gallery eigenmodes are reviewed, and the features of their Fourier transforms discussed. The Fraunhofer approximation is then used to describe the farfield pattern resulting from the diffraction of a whispering-gallery eigenmode. Explicit formulas are given for the farfield beamwidth and the Rayleigh distance. For modes of high order the results can be understood in terms of geometrical optics. >

Importance of barrier layers in thermal diodes for energy conversion

Very high thermal to electric conversion efficiencies have been reported previously with thermal diode structures in which a thin n-type emitter layer is formed on the hot side of a thick near-intrinsic thermoelectric semiconductor. The figure of merit derived from direct measurements of electrical parameters and heat flow is increased by as much as a factor of eight. The question of what physical mechanisms are involved has been of interest since the initial observations of the effect. We have conjectured that the short-circuit current injection in these experiments is due to a second-order thermionic injection mechanism. More recently, we proposed that the open-circuit voltage comes about due to the presence of a p-type blocking layer between the emitter and the near-intrinsic bulk region. The experiments reported here show that a p-type blocking layer is required for the effect, and the dependence of conversion efficiency on the blocking layer concentration and width is studied. The results are general...

Whispering-gallery laser resonators. II. Analysis of mirrors with nonuniform curvature

For pt.I see ibid., vol.27, p.1069-77 (1991). Although the whispering-gallery mirror shows great promise for use at short wavelengths, undesired beam divergence at the mirror exit can be a significant issue in the design of laser resonators. This problem can be alleviated by appropriate choice of the mirror geometry: elongated mirror shapes can give reduced beam divergence without requiring too large an overall size. It is shown that, for circular geometries, beam propagation along the mirror surface is conventionally described in terms of normal modes. Elliptical mirrors are shown to admit a similar analysis, thereby providing a convenient prototype for the elongated geometries of interest. They are found to offer a substantial, though ultimately limited, reduction of beam divergence. >

Energy conversion using diode-like structures

An experimental study of diode structures with the basic configuration ohmic/n*/n/intrinsic/ohmic shows a significant enhancement of heat to electricity conversion performance compared to the initial thermoelectric material (n). Direct electrical and thermal measurements indicate a conversion efficiency that is as high as 40% of the ideal Carnot cycle limit.

NEARLY ISOTROPIC PHOTONIC BANDGAP STRUCTURES IN TWO DIMENSIONS

It is suggested that a material with a novel spatial dielectric distribution can exhibit a bandgap that is approximately independent of propagation angle. This independence is accomplished by development of the dielectric constant from reflection vectors of equal strength that are ideally equispaced in angle.

Shape and stability dependence of passively mode‐locked pulses on absorber relaxation time

The dependence of the saturable absorber mode‐locked pulse shape upon the relaxation time of the absorber is determined when the laser gain is assumed constant. The pulses are found to be asymmetric with a slowly rising edge and a more rapidly decaying edge. The mode‐locked pulse width is a weak function of absorber relaxation time TA, becoming broader with increasing TA. Furthermore, the pulses are found to experience a delay in traversing the absorber which lengthens the cavity transit time. The growth of perturbations introduced into the steady state is shown to be bounded, indicating that stable mode‐locked operation is possible even in cases where TA is comparable to or greater than the width of the steady‐state pulse.

Investigations of whisper gallery mirrors for extreme ultraviolet (EUV) and soft X-rays

The authors have examined optical constants and predicted reflectivities of candidate surface coatings for whisper gallery mirrors (WGMs) in the extreme ultraviolet. The spectral regime near 100-150 AA has been identified in the literature as particularly promising due to the high WGM reflectivities of the noble metals in the vicinity of their Cooper minima in this regime. The authors confirm this basic result using newer EUV optical data, and they have sought candidate surface materials which would extend the range over which WGMs may be used to longer wavelengths. It is found that substantial WGM reflectivities are predicted for a variety of elements in the EUV, and that TE peak reflection is larger than TM peak reflection by on the order of 10%; however, most of the elements which do reflect well have surfaces which are vulnerable to oxygen contamination. >