A. Prodell

Search for photon regeneration in a magnetic field

We have searched for the regeneration of photons propagating in a transverse magnetic field. Such an effect would reveal the existence of light scalar or pseudoscalar particles such as the axion that couple to two photons. We obtain for this coupling the limitgaγγ<(1.3×106 GeV)−1, provided the axion massma≲10−3 eV.

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.

First measurement of the magnetic birefringence of helium gas

Abstract Using a sensitive ellipsometer we have measured the Cotton-Mouton constant of helium at 514.5 nm. We have found that, at 1 atm and 0°C,C CM (He) = (3.5 ± 0.7) × 10 -20 G -2 cm -1 . Our experimental value is compatible within the errors with previous theoretical calculations.

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.

Coherent production/detection of light scalars/pseudoscalars and QED vacuum polarization

We searched for light scalars/pseudoscalars (e.g., axions) that couple to two photons using three different techniques: (1) Optical rotation, where a polarized laser beam enters a dipole magnetic field region. The production of scalars/pseudoscalars has an effect the rotation of the polarization which is detected by an analyzer system giving a limit [ital g][sub [alpha][gamma][gamma]][lt]3.6[times]10[sup [minus]7] GeV[sup [minus]1], for [ital m][sub [ital a]][lt]10[sup [minus]3] eV. (2) Photon regeneration experiment, where the particles are generated in one magnet by the polarized laser beam, travel through a wall and reconvert back to the original photons inside another magnet where they are detected by a photomultiplier, giving a limit to [ital g][sub [alpha][gamma][gamma]][lt]6.7[times]10[sup [minus]7] GeV[sup [minus]1] for the same mass range as above. (3) Finally we searched for scalars/pseudoscalars coming from the sun, looking at the back of a dipole magnet pointing at the setting sun, with an x-ray detector. The limit obtained this way is [ital g][sub [alpha][gamma][gamma]][lt]3.7[times]10[sup [minus]9] GeV[sup [minus]1], provided [ital m][sub [ital a]][lt]0.1 eV.

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.