Rotating polarization imaging in turbid media.

It is shown experimentally that one can image an object embedded in a turbid medium by probing the medium with light with a rotating linear polarization. This method permits the ballistic photons to be isolated from the large background of photons that have been multiply scattered by optically dense anisotropic scatterers. This technique achieves a good signal-to-noise ratio even with a low-power continuous laser, leading to images with a diffraction-limited resolution comparable with that obtained in optically homogeneous media.

Supermirror phase anisotropy measurement.

The high sensitivity of the eigenstates of a large-finesse passive Fabry-Perot cavity is used to measure the residual anisotropy of supermirrors at strictly normal incidence. An experimental demonstration leads to the measurement of phase retardances of the order of 10(-6) rad.

Angular Goos-Hänchen effect in curved dielectric microstructures.

A macroscopic angular Goos-Hänchen effect at total reflection on curved interfaces is studied experimentally. The results are compared with the complex-angular-momentum model of quasi-critical scattering. An extremum in angular deflection, which has not yet been predicted by any theory other than exact Mie scattering computations, is identified at low size parameters.

Optical-activity measurements with bihelicoidal laser eigenstates.

A novel, doubly differential method for the measurement of optical activity that uses the so-called bihelicoidal eigenstates of a laser is demonstrated. An experimental realization is presented, and prospects are discussed.

Jones matrices of a quarter-wave plate for Gaussian beams.

The Jones matrix of a quarter-wave plate is studied theoretically and experimentally, taking into account internal reflections, the ellipsoid of the indices, geometric defects, the tilt angle, and the characteristics of the incident Gaussian beam. The influence of the different parameters is isolated, and large discrepancies are observed with respect to results obtained from the Jones matrix that are usually given in textbooks. It is shown that the effective Jones matrix of the plate does not depend on the longitudinal position of the plate on the Gaussian beam but only on the beam-waist size. This leads to a method of characterization of the defects of a quarter-wave plate that is more precise than the usual methods. Different procedures to optimize the efficiency of a given plate are discussed, taking the plate defects into account. In all cases, a good agreement between experiments and theory is obtained.

Ring-laser gyro with spatially resolved eigenstates.

The spatial resolution of laser eigenstates is applied to ring geometry. A bidirectional optical diode based on the Faraday effect and nonreciprocal intracavity losses is theoretically and experimentally investigated. This novel optical diode combined with spatial separation provides a biased gyro with no lock-in band.

Differential absorption measurement of methane with two spatially resolved laser lines.

Simultaneous and independent lasing on two different atomic lines is achieved with spatial resolution of laser eigenstates in conjunction with intracavity frequency selection. A sensitivity of 0.3 part in 10(6) meter in the differential detection of methane in 1 atm of air is experimentally demonstrated with this novel dual-wavelength laser. Monitoring the output intensities of the two orthogonally polarized eigenstates permits absolute measurement of methane concentration.

Dynamics of circularly polarized eigenstates in lasers with nonweak atomic coupling.

It is shown theoretically and experimentally that the two circularly polarized eigenstates of a laser oscillating on a nonweak atomic coupling transition exhibit two types of vectorial bistability. A rotation and an inhibition mechanism are isolated, depending on the eigenfrequency difference of the two eigenstates. For both mechanisms, the evolution of the hysteresis loop with this frequency difference shows good agreement with a phenomenological Landau's potential model.

Jones matrices of a tilted plate for Gaussian beams.

The Jones matrix of a tilted plate is theoretically and experimentally described, taking into account the contribution of the successive internal reflections of the incident fundamental TEM(00) Gaussian beam. This induces variations of up to 10% of the transmission coefficients of the Jones matrix with angle of incidence. The consequence of the influences on the walkoff and the internal interference effects of the characteristics ofthe plate and of the incident beam, especially its mode size and its radius of curvature, leads to important different variations of the Jones matrix. of such a plate however, we show that for a given Gaussian beam the Jones matrix of the plate does not depend on its position along the beam propagation axis, in spite of the variations of mode size and radius of curvature whose effects compensate mutually. The Jones matrix of such a plate used in a laser cavity containing a diffracting aperture is also investigated. In every case, good agreement is observed between theory and experiment.

Measurement of residual reflectivities using the two eigenstates of a passive cavity.

A sensitive differential method is described for isolating from other losses the residual reflectivity of an antireflection coating deposited on a quarterwave plate. Insertion of such a plate into a passive cavity reveals two eigenstates related to its axis, which may be by nature simultaneously resonant and antiresonant. The ratio between the two corresponding output intensities depends on the residual reflectivity of the plate and is moreover enhanced by the resonator. A residual reflectivity resolution of 10 ppm with a relatively low cavity finesse of 70 is achieved, and the possibility of measuring separately the losses from the coating and the substrate, using a half-coated quarterwave plate, is developed. We discuss the performances of our experimental setup and possible improvements and extensions of the method, in particular to isotropic components.

Twofold critical geometry for lasers.

Use of a twofold critical cavity is proposed to obtain a symmetrical saturated absorption peak on a symmetrical background. The experimental verification is performed on the CH(4)3.39-microm system. This geometry is expected to provide optical frequency standards with better reproducibility.

Spatial-asymmetry distribution of a saturated-absorption peak.

The amount of asymmetry of saturated-absorption peaks observed outside a cavity with two collinearly counter-propagating Gaussian beams is analyzed at different points in the cross section of the probe beam. Although the total beam exhibits a quasi-symmetric line shape, a spatial distribution of asymmetries with different amounts and signs is obtained versus the distance to the beam axis. A simple model taking account of pure focusing and defocusing effects induced by a saturated Gaussian beam leads to agreement between experiment and theory for the 5944-A neon line in the case of saturated-absorption spectroscopy.

Frequency stabilization and tunability of lasers; use of mobile dips and peaks.

Frequency stabilization possibilities using mobile resonances are investigated. A stability measurement is given for two high power magnetic Lamb dip stabilized lasers. These mobile resonances lead to unmodulated frequency lasers with tunability possibilities interesting for continuous dye lasers.