Joseph Thomas Rogers

Measurement of the magnetic birefringence of neon gas

We constructed a sensitive ellipsometer to study extremely small ellipticities that are acquired by laser light when it traverses a multipass optical cavity in a 9-m-long superconducting magnet. This setup was used to measure the Cotton–Mouton constant (CCM) of neon at 514.5 nm. We find for 760 Torr (1 atm) and 25°C that CCM(Ne) = (5.5 ± 0.3) × 10−20 G−2 cm−1.

Anomalous rf magnetoresistance in copper at 4 K

We have measured the effect of a magnetic field on the surface resistance of polycrystalline Cu at f=1.2 GHz and at 4.4 K; under these conditions the surface resistance is well into the anomalous skin effect regime but has not reached its limiting value. We find that the transverse and longitudinal magnetoresistance are an order of magnitude smaller than the dc magnetoresistance and depend quadratically on the field. At low fields we observe a decrease in surface resistance with increasing field which can be interpreted as a size effect of the rf surface current, but is also typical of superconductors.

Analysis of a microwave cavity detector coupled to a noisy amplifier

Abstract In a class of detectors for light pseudocscalar particles, a microwave cavity traps photons produced by the interaction of the particles with a strong magnetic field. The cavity strongly influences the signal and noise properties of the amplifier coupled to its output. We present the theory of a noisy amplifier coupled to a microwave cavity, along with experimental data for a cryogenic GaAsFET amplifier. The signal-to-noise ratio of the cavity-amplifier system is determined, and applications to the measurement of amplifier parameters are discussed.

L- and S-band low-noise cryogenic GaAs FET amplifiers

The authors present the results of the construction and testing of three cryogenic low-noise GaAs FET amplifiers, based on a National Radio Astronomy Observatory design, to be used in a detector for the axion, a hypothetical particle. The amplifiers are centered on 1.1 GHz, and 2.4 GHz, have a gain of approximately 30 dB in bandwidths of 300 MHz, 225 MHz, and 310 MHz, and have minimum noise temperatures of 7.8 K, 8 K, and 15 K, respectively. >

Improved Limits from the Galactic Axion Search

Cold, light axions are a leading candidate for the composition of dark matter in the galactic halo. An experiment designed to detect the microwave conversion signal from galactic axions has searched the frequency range 1.1–2.5 GHz. The updated limits on axion density and coupling are presented, and improvements for a possible second-generation experiment are discussed.

Anomalous rf magnetoresistance in copper at 4/degree/K

We have measured the effect of a magnetic field on the surface resistance of polycrystalline Cu at f = 1.2 GHz and at 4.4/degree/K; under these conditions the surface resistance is well into the anomalous skin effect regime but has not reached its limiting value. We find that the transverse and longitudinal magnetoresistance are an order of magnitude smaller than the DC magnetoresistance and depend quadratically on the field. At low fields we observe a decrease in surface resistance with increasing field which can be interpreted as a size effect of the TF surface current. 17 refs., 4 figs., 1 tab.

An Experimental Search for Galactic Axions

Several groups in the United States and elsewhere have proposed building detectors sensitive to axions of the Dine-Fischler Srednicki (DFS) type that may have condensed into the galactic halo. These detectors are based on the principle, due to Sikivie [1], of conversion of axions to microwave photons in a magnetic field. We describe the device built by a Rochester-Brookhaven-Fermilab collaboration*, its sensitivity, and the motivation from astrophysics for attempting to observe axions.