Ph. Jacquier

New manifestation of atomic parity violation in cesium: a chiral optical gain induced by linearly polarized 6S-7S excitation.

We have detected, by using stimulated emission, an atomic parity violation (APV) in the form of a chiral optical gain of a cesium vapor on the 7S-6P(3/2) transition, consecutive to linearly polarized 6S-7S excitation. We demonstrate the validity of this detection method of APV, by presenting a 9% accurate measurement of expected sign and magnitude. We stress several advantages of this new approach which fully exploits the cylindrical symmetry of the setup. Future measurements at the percent level will provide an important cross-check of an existing more precise result obtained by a different method.

Parity violation in forbidden transitions: Detection of the electroweak alignment or polarization in the upper state by stimulated emission

Abstract We present a new method for detecting the parity violation induced by weak neutral currents in a forbidden atomic transition such as the 6 S-7 S Cs transition. The 7 S atoms are produced by pulsed excitation and detected through the subsequent transient gain which appears at the 7 S-6 P frequency. A right-left asymmetry in this gain is expected as a result of parity violation, with possible amplification of this asymmetry when the vapor becomes optically thick. With respect to previous observation conditions, substantial improvement in signal/noise ratio is expected.

Experimental progress using nonlinear optics for precision measurements of the nuclear weak charge in the 6S-7S Cs transition

Abstract We report on the current status of our novel experiment designed for precision measurements of parity violation in the forbidden 6S–7S Cs transition. Pulsed 6S–7S excitation in a longitudinal E -field gives rise to large 7S–6P population inversion and subsequent transient amplification of a probe beam, as large as 100%. Dependence on the relative orientation of the excitation and probe polarizations is measured with a sensitive differential polarimeter. We present a calibration procedure circumventing all complications from nonlinear processes, which can thus be exploited to enhance the parity violating asymmetry.

Reaching the shot noise limit in the polarization measurement of individual nanosecond light pulses

Abstract Using a balanced dual-channel polarimeter and fast photodiodes coupled to low-noise charge integrators, we demonstrate precise polarization detection of individual light pulses in the nanosecond time-scale, with a noise very close to the shot noise limit. This result has important implications for various precision measurements such as atomic parity violation, squeezing at short time scales, and possibly parity violation with squeezed light.

High precision balanced mode polarimetry with a pulsed laser beam

Abstract We apply balanced mode polarimetry to study an amplifying atomic medium endowed with optical rotation and linear dichroism. The medium is prepared by pulsed excitation with a pump laser just before application of a collinear probe laser pulse. We discuss how displacements of the probe beam and small modifications of the angle of incidence, i.e. geometrical effects, can affect the measurements. We demonstrate double subtraction of such instrumental defects. First, we measure the difference between the two imbalances of the polarimeter corresponding to the amplified probe pulse and a consecutive unamplified reference pulse. Second, we insert and remove a half wave plate just in front of the polarimeter: this enables us to discriminate true polarisation effects from geometrical effects. Under such conditions the zero of the rotation of the plane of polarisation induced by the amplifying atomic medium acquires a real physical meaning with an accuracy better than 10 −6 rad. This result has important implications for future atomic parity violation measurements. Finally we consider near extinction polarimetry from the point of view of geometrical defects and suggest an adaptation of half wave plate switching as a possible way of improving measurements in the near extinction operation.

Prospects for forbidden-transition spectroscopy and parity violation measurements using a beam of cold stable or radioactive atoms

Abstract.Laser cooling and trapping offers the possibility of confining a sample of radioactive atoms in free space. Here, we address the question of how best to take advantage of cold atom properties to perform the observation of as highly forbidden a line as the 6S-7S Cs transition for achieving, in the longer term, atomic parity violation (APV) measurements in radioactive alkali isotopes. Another point at issue is whether one might do better with stable, cold atoms than with thermal atoms. To compensate for the large drawback of the small number of atoms available in a trap, one must take advantage of their low velocity. To lengthen the time of interaction with the excitation laser, we suggest choosing a geometry where the laser beam exciting the transition is colinear to a slow, cold atomic beam, either extracted from a trap or prepared by Zeeman slowing. We also suggest a new observable physical quantity manifesting APV, which presents several advantages: specificity, efficiency of detection, possibility of direct calibration by a parity conserving quantity of a similar nature. It is well adapted to a configuration where the cold atomic beam passes through two regions of transverse, crossed electric fields, leading both to differential measurements and to strong reduction of the contributions from the M1-Stark interference signals, potential sources of systematics in APV measurements. Our evaluation of signal-to-noise ratios shows that with available techniques, measurements of transition amplitudes, important as required tests of atomic theory, should be possible in 133Cs with a statistical precision of 10-3 and probably also in Fr isotopes for production rates of

Magnification of a tiny polarisation rotation by a dichroic plate in balanced mode polarimetry

\gtrsim 10^6

Absolute measurements of the photoionization cross section of the 5D52 Cs excited state and of the photodissociation cross section of Cs2 between 540 and 550 nm

Fr atoms s-1. For APV measurements to become realistic, some practical realization of the collimation of the atomic beam as well as multiple passages of the excitation beam matching the atomic beam looks essential.

Theory of transition probability saturation for photodissociation of Cs2 and photoionization of the 5D5/2 product atoms

Abstract We demonstrate the magnification of a small rotation angle of the linear polarisation of a laser beam measured with a balanced mode polarimeter. This is performed by a single-pass passive dichroic optical component placed between the sample inducing the rotation and the analyser. We show that in the shot-noise limit the signal-to-noise ratio is conserved while the angle is magnified by a factor K and the intensity attenuated by K 2 . Practical realisation is achieved using a dichroic plate for which K = −4.2. This amplification will be valuable for high precision measurements such as atomic Parity Violation tests.

Measurement of the radiative lifetime of the cesium 5D5/2 level using pulsed excitation and delayed probe absorption

Abstract We apply to two-photon resonant ionization of Cs via resonant dissociative states of Cs2 the technique of transition probability saturation. Our measurements are performed both with linear and circular polarization. Independently of the Cs2 density, they provide the first absolute determination of the photodissociation cross section averaged over the molecular states, σdis = (7.3 ± 1.1) X 10−18 cm2 at 550 nm, and of the photoionization cross section of the product atoms in the 5D 5 2 state, σion = (3.3 ± 0.5) X 10−17 cm2.