Electrical properties of cadmium and zinc doped CuInS2

The electrical resistivity and mobility of Cd and Zn doped CuInS₂ single crystals grown by a Bridgman technique have been investigated. Crystals annealed in Cd or Zn vapor at high temperatures (～ 800°C) exhibit degenerate behaviour while those crystals annealed at more moderate temperatures (～650°C) show ionized impurity conduction with a shallow activation energy on the order of 0.004 eV. Resistivities as low as 0.15 Ω-cm and mobilities as high as 90 cm²/v-sec have been observed.     

Bayesian approach to non-Gaussian field statistics for diffusive broadband terahertz pulses

We develop a closed-form expression for the probability distribution function for the field components of a diffusive broadband wave propagating through a random medium. We consider each spectral component to provide an individual observation of a random variable, the configurationally averaged spectral intensity. Since the intensity determines the variance of the field distribution at each frequency, this random variable serves as the Bayesian prior that determines the form of the non-Gaussian field statistics. This model agrees well with experimental results.     

Two-element dielectric antenna serially excited by optical wavelength multiplexing

A single pulsed laser beam containing multiple wavelengths (wavelength multiplexing) is employed to activate two semiconductor antennas in series. The dielectric nature of the semiconductors permits serial cascading of the antenna elements. Recently observed nonlinear characteristics of the radiated field as a function of the free carrier accelerating (bias) voltage are used to minimize the small interactions between elements. We demonstrate that the temporal electromagnetic radiation distribution of two serial antennas is sensitive to the three-dimensional pattern of the optical excitation source. One can, in turn, vary this distribution continuously by optical means to reconfigure the array.     

Improving the electrong-2 measurement

The measurement and calculation of the anomalous magnetic moment of the electron currently provides the most stringent test of QED. In the past, one of the limitations in the experiment has been the small inhomogeneous component of the magnetic field which has been used to detect the magnet resonances of the trapped electron. We have developed a technique which allows us to reduce this inhomogeneous field by as much as two orders of magnitude and have demonstrated the technique with a factor of fifteen reduction, virtually eliminating the broadening of the magnetic lines in our geonium atom.     

Terahertz imaging with compressed sensing and phase retrieval

We describe a novel, high-speed pulsed terahertz (THz) Fourier imaging system based on compressed sensing (CS), a new signal processing theory, which allows image reconstruction with fewer samples than traditionally required. Using CS, we successfully reconstruct a 64 x 64 image of an object with pixel size 1.4 mm using a randomly chosen subset of the 4096 pixels, which defines the image in the Fourier plane, and observe improved reconstruction quality when we apply phase correction. For our chosen image, only about 12% of the pixels are required for reassembling the image. In combination with phase retrieval, our system has the capability to reconstruct images with only a small subset of Fourier amplitude measurements and thus has potential application in THz imaging with cw sources.     

Gas sensing using terahertz time-domain spectroscopy

Received: 25 February 1998     

The scattering of electrons by atomic hydrogen

A method is presented which reduces the problem to the scattering of a single electron in an equivalent potential. The complexities of the electron-electron interaction are embodied in this potential. An exact expression is given for the potential, and various approximation methods are discussed. The adiabatic approxmation is investigated and the imaginary part of the potential is examined.     

Atomic ionization by ultra—strong laser fields

The problem of multi-photon ionization of hydrogen by ultra-strong electromagnetic fields is solved in the limit where the field energy is greater than the Coulomb energy. The transition rate goes to zero as the reciprocal of the field strength.