Robert L. Peterson

Analysis of response of pyroelectric optical detectors

Several configurations of pyroelectric optical‐radiation detectors are mathematically modeled to determine their frequency response and current response to step‐function heat inputs. Included in the analysis are heat losses by conduction and reradiation, effects of absorptive coatings, and an experimentally observed nonuniformity of polarization through the thickness of polymer pyroelectric films. Roll‐off of the frequency response at both low and high frequencies is carefully examined. Curve fitting to response data allows a quantitative determination of the pyroelectric coefficient and the degree of nonuniformity of the polarization. The thermal conductivities of gold blacks used as absorbers are determined from the high‐frequency data together with independent measurements of the black thicknesses and densities. The total emissivity of evaporated nickel films sometimes used as absorbers can be estimated from the low‐frequency data. The difference in response to optical and electrical heat inputs is exa...

Effects of poling conditions on responsivity and uniformity of polarization of PVF2 pyroelectric detectors

A large number of pyroelectric detectors, fabricated from commercially available PVF2 and poled under a variety of conditions of voltage, temperature, and time have been evaluated for responsivity and uniformity of polarization in the direction of the poling field. Results show that uniformity of polarization (a requirement for flat frequency response) can be achieved and responsivities as high as 2.9 μA/W can be obtained.

Analysis of threshold curves for superconducting interferometers

Threshold curves for multijunction superconducting interferometers have been calculated previously, showing general agreement with observed features, especially in symmetric cases. We here add some more details to the analysis, paying particular attention to the effects of asymmetries in coupling, inductance, or critical currents. Feed‐loop inductance and flux quantization in the feed loop can be important. A changing lobe pattern over many periods, asymmetries within a period, shifting patterns between runs spanning a warm‐up, and sudden changes in pattern because of noise in the environment are all quantitatively explainable on the basis of this model. By use of a single ’’calibration curve’’, the inductance for symmetric two‐ or three‐junction interferometers can be obtained immediately.

Generation of Harmonics and Subharmonics of the Josephson Oscillation

The observation of harmonics and subharmonics of the Josephson oscillation is shown to be in agreement with a rather simple model of the junction. The generation of harmonics provides an explanation of induced steps in the current‐voltage characteristic which occur at submultiples of the usual induced step voltages. The subharmonic oscillation is seen to be a relaxation‐like process which can be easily understood in terms of a mechanical analog.

The polarization of PVF and PVF2 pyroelectrics

Abstract Through detailed investigations of the modulation frequency response of pyroelectric detectors, nonuniform polarizations have been shown to exist in polyvinylfluoride and polyvinylidene fluoride plastics. The nonuniform polarization is also confirmed by measurements using multilayer structures. The direction and magnitude of the gradients in polarization are dependent on the magnitude and polarity of the poling voltage. The gradients in the polarization for PVF and PVF2 are opposite in direction. Using structures that allow for poling to 2 × 106 V/cm uniform polarizations, the highest responsivities and improved frequency responses were obtained.

Picosecond applications of Josephson junctions

The behavior of simple superconducting circuits in the picosecond regime is described in a comprehensive way, with primary emphasis being given to the step function and pulse responses of these circuits. Topics receiving detailed discussion include Josephson-junction modeling with both the microscopic and shunted-junction models. Limitations of the shunted-junction model are explored by comparing it with experimental results and with the microscopic model. An approximate evaluation is given of the important dynamical properties of junctions made with the dominant fabrication technology (Pb-alloy systems), as a function of tunneling barrier thickness. Rounding out the device aspects of the discussion, we describe in detail the properties of superconducting microstrip transmission lines, with an emphasis on their high-speed behavior. Turning to simple circuits we review experimental results on the measurement of picosecond regime transient signals. The concept of turn-on delay is analyzed anew, providing simplified and extended results. Details of concepts for pulse height and pulsewidth measurements are explored, leading to the conclusion that the time resolution of superconducting circuits is limited to approximately the period of one plasma oscillation. With present Pb-alloy fabrication technology this limit is 2 ps.

A superconducting sampler for Josephson logic circuits

A method is described for automating a technique which is used to sample transition duration (rise time) in superconducting logic circuits. The method is based on measuring the time at which a biased Josephson junction switches under the influence of an applied signal. The system transition duration is limited primarily by time jitter which is estimated to be 7 ps. Transition durations of as little as 9 ps have been observed.

Picosecond pulses from Josephson junctions: Phenomenological and microscopic analyses

A Josephson junction modeled by the phenomenological current relation together with internal resistance can exhibit pulses in the voltage across the junction when driven by an oscillating current source. These pulses occur singly, in pairs, triplets, etc. with a repetition rate equal to twice the driving frequency. The inclusion of capacitance and inductance generally degrades the pulse characteristics, but attainable values for tunnel junctions are tolerable, with typical parameter values, the pulses have picosecond widths. The phenomenological model becomes suspect on such time scales, however, because typical gap frequencies are just under 1012Hz. Preliminary studies based on the microscopic tunnel-junction theory nevertheless show results qualitatively similar to those of the Phenomenological model. The effects of resistor noise and current noise have also been studied. It is concluded that well developed ps voltage pulses can be created in physical Josephson junctions.

Magnetization of anisotropic superconducting grains

A critical‐state calculation of the magnetization of hard type‐II superconducting grains having anisotropic critical‐current densities is given. The analysis shows how the critical‐current densities should be deduced from magnetization measurements for various grain morphologies. A universal curve of the magnetization hysteresis versus one of the grain dimensions is presented, showing that the hysteresis does not change linearly with grain size. Applications to single crystals and to bulk materials are made.

Voltage and current expressions for a two‐junction superconducting interferometer

The average voltage and circulating current of a superconducting interferometer containing two Josephson junctions (a dc SQUID) are calculated analytically, in various approximations, as functions of bias current and applied magnetic field or control current. The results are useful in calculations of the noise characteristics of the dc SQUID, as well as in other applications.