The field intensity and polarization behaviour of an optically pumped laser is investigated in different operating conditions. For a linearly polarized pump field, a strong gain anisotropy is induced which favours generation of light with a polarization parallel to that of the pump field. Thus gain anisotropy can be counterbalanced by cavity-loss anisotropy only at low pumping field intensities, and the interplay between both types of anisotropy leads to polarization switching phenomena. In contrast to the case of the incoherently pumped laser, the decay rate for the magnetic dipole induced on the J = 1 level plays a minor role in determining the polarization dynamics. The influence of a longitudinal magnetic field or of modulation of the pump-field polarization orientation leads to new features and complex dynamic behaviour which includes full polarization (or vector) chaos.
Deflection of two-level atoms by a pulsed standing wave with a pulse duration of a few nanoseconds is studied by using the density matrix formalism. The effect of the limited coherence time of the pulsed laser field on the momentum distribution of the deflected atoms is investigated. In particular, we determine the coherence time at which the deflection by a pulsed standing wave differs significantly from the zero-relaxation case.
A process of photoionization of neutral atoms composing a Bose-Einstein condensate is examined theoretically. It is shown that the coherent nature of the initial atomic ensemble can lead to a relatively large phase-space density of the fermionic products (electrons and ions) and, hence, to photoionization rate suppression. This effect may serve as an experimental tool for investigation of collective interactions in a highly non-equilibrium coherent ensemble of charged fermions.
We study the polarization of the electric field in Fabry-Perot resonators which contain at least two optically birefringent elements. One of them is a frequency-doubling crystal, the other being either a passive and/or an active crystal. Using the Jones matrix technique, we review the polarization properties of the linear Fabry-Perot cavity and extend these results to V-shaped cavities. For these configurations, we derive the rate of conversion of the fundamental frequencies into the second harmonic and the sum frequencies. These conversion rates are interpreted as intensity-dependent losses for the rate equations of the fundamental modes which are derived.
Detected photons originating from classical light beams can be described either by means of photon statistics or by means of photocurrent statistics on a semiclassical basis. The statistical parameters of these two descriptions have, up to now, only been related to each other using vague, effective-time-constant arguments. We show that these relations are invalid for the general case of time-varying stochastic photon rates and arbitrary detector impulse responses and derive generally valid linking equations for the ensemble average, the shot noise variance and the excess noise variance of the photon statistics and the photocurrent statistics due to a random optical field. The derivations are based on a general definition of the time average that allows an elegant treatment in the Fourier domain.
This paper draws a comparison between atom optics and light optics, based on the observation that one can derive a Schrodinger equation for the slowly varying amplitude of the electromagnetic field in the paraxial approximation, the `optical Schrodinger equation'. A correction scheme between (monochromatic) light waves and matter waves is established and applied to cases of interest in atom or fibre optics. First the propagation in a periodic -potential is investigated, where well known effects, such as Bragg scattering or channelling are re-examined from a `matter wave versus light wave' point of view. In a second application the general theory is extended to axisymmetrical materials such as step-index fibres or graded-index fibres. In particular, a matter wave analogue of the so-called non-diffractive beams of electrodynamics is discussed.
We analyse the spatiotemporal dynamics of a broad-area two-level laser in the presence of a dressing field which is coupled to an adjacent transition. The dressing field induces Rabi splitting on one of the energy levels of the laser transition, which modifies the traditional scenario of pattern formation in two-level lasers. In particular, it is observed that phase rolls appear for any sign of the cavity detuning, and that two travelling-wave patterns with different wavenumbers can coexist near the threshold for a certain range of detuning values. Reciprocally, it can be seen that the spatial dynamics alters the standard framework of electromagnetically induced gain splitting.
We investigate the effects of the electron-hole spin dynamics on the polarization fluctuations in the light emitted from a vertical-cavity surface-emitting laser (VCSEL). The Langevin equations are derived based on a rate equation model including birefringence, dichroism and two carrier density pools separately coupled to right and left circular polarization. The results show that the carrier dynamics phase lock the polarization fluctuations to the laser mode. This is clearly seen in the difference between the fluctuations in ellipticity and the fluctuations in polarization direction. Separate measurements of the polarization fluctuations in ellipticity and in the polarization direction can therefore provide quantitative information on the nonlinear contribution of the carrier dynamics to polarization stability in VCSELs.
We show by coincidence measurements of photon pairs, produced by parametric downconversion and type II phase matching, that a polarization rotation can be determined with an angle uncertainty below the standard quantum limit.
Starting from a simple hexagonal pattern stabilized and selected with the spatial perturbation method in a wide-aperture CO2 laser, we observed the transition to a dodecagonal pattern via the doubling of the azimuthal spatial frequency by changing the cavity detuning. Further increasing the detuning induces more complicated patterns. such as double hexagons. The symmetry-breaking effect on the stabilized and selected patterns, introduced by a slight misalignment of a laser mirror, is observed. We also find that the complicated temporal instabilities of the unperturbed patterns are eliminated by the spatial perturbations. Numerical simulations, based on the Fox and Li theory for the held propagation inside the cavity, are able to reproduce the patterns with the simplest symmetry.
This tutorial paper is based on lectures delivered by G M Stephan at PELS'97. The idea was to tell the students about the methodology used by the authors to understand and to quantitatively compute the flips observed between two polarization states in a single-frequency He-Ne laser. The study is limited to this phenomenon. Contents are: introduction, quasi-isotropic lasers and polarization flips; the passive Fabry-Perot interferometer, an illustrative example; a vectorial description of a two energy-level system with magnetic degeneracy; two useful tools: adiabatic elimination of fast variables and use of Lyapunov exponents to study the stability of a solution; medium polarization in the adiabatic approximation; the laser equations for the field.These contents are organized for people coming into the field: rather than being too general, we have preferred to focus on limited and well defined examples from which other cases can be studied.
We describe an ongoing experiment to measure parity violation in atomic caesium, based on detection by stimulated emission. Our goal is to measure to 1% a left-right asymmetry of 10(-6) to rest electroweak theory and look for new physics beyond the Standard Model. The Cs highly forbidden transition, 6S(1/2)-7S(1/2), is excited in a vapour (5-10 mtorr) by a pump laser pulse in a longitudinal electric field (E) over right arrow(l) (2 kV cm(-1)). The PV asymmetry resulting from the weak interaction during optical excitation is converted into an anisotropy in the gain of a probe laser pulse which stimulates the allowed transition 7S(1/2)-6P(3/2), and manifests itself as a tiny (E) over right arrow(l)-odd rotation of the probe's linear polarization. Differential polarimetry allows dark-field detection of the rotation angle with a baseline defined to better than 10(-6) and discrimination between true and pseudo-rotation. Lineshape-independent angle calibration is performed using a parity-conserving (E) over right arrow(l)-even anisotropy. To isolate the parity-violating effect, we exploit the symmetry of revolution of the experiment by (i) rotating pump and probe linear polarizations around the beam axis and (ii) reversing (E) over right arrow(l) in a cylindrically symmetric cell. After describing the apparatus and data acquisition procedure, we summarize the current experimental status and short-term prospects.
We propose a scheme for the generation of even and odd coherent states in the motion a cavity mirror. it is based on the atom-field and field-mirror interactions.
Nonlinear polarization phenomena in a single-longitudinal-mode class-A gas laser are studied at the transition from isotropic to strongly anisotropic cavity conditions. The effects of competition between active-medium and empty-cavity anisotropies, leading to spontaneous pulsations and polarization multistability, are considered at different eigenstates of these anisotropies. Spontaneous polarization symmetry breaking is discussed. A classification of lasers with respect to their values of the cavity anisotropy is suggested.
Weakly vectorial lasers with intracavity wave retardation plates can exhibit a rich variety of unusual dynamic polarization characteristics. For example, the output of an external-cavity semiconductor laser with an intracavity quarter-wave plate shows polarization self-modulations alternating between TE and TM modes at a fundamental frequency corresponding to twice the cavity round-trip time and at odd harmonics of this fundamental frequency. Higher-order harmonics greater than the 30th harmonic at frequencies above 5 GHz have been observed, which is much higher than the relaxation-oscillation frequency of the laser. As the pumping level is increased, the period-doubling route to chaos and hysteresis behaviour associated with higher harmonic bifurcations and multiple stable states has also been observed. These experimental results as well as preliminary numerical simulation results are summarized on the basis of a fairly simple model. Apart from possible applications, these results raise interesting questions about the fundamental polarization and nonlinear dynamic characteristics of such lasers. Some of these general issues are discussed.
Recently, Bishop and co-workers (1996 Phys. Rev. A 54 R4657) applied the coupled-cluster method to study the ground state of the Jaynes-Cummings model without the rotating-wave approximation and reported strong evidence for a second-order quantum phase transition which was believed to be caused by spontaneous breaking of the parity symmetry of the system. In the present work we have re-investigated this conjecture via examining the nature of the exact (numerical) ground state of the system. Our analysis has indicated that the ground state has definite positive parity and there is no spontaneous breaking of the parity symmetry of the system.
We propose a new type of accessible source of ultra-short pulses based on the phenomenon of collective coherent recombination (superradiance) of electrons and holes in semiconductor heterostructures. We find and analyse a novel regime of ultra-fast operation of quantum-well semiconductor lasers in which a quasiperiodic sequence of femtosecond superradiant pulses is emitted under continuous pumping. According to our calculations for AlGaAs-GaAs heterostructures, the coherent optical pulses of duration greater than or similar to 30 fs and peak intensity greater than or similar to 100 MW cm(-2) can be generated in a low-Q cavity of length similar to 30-100 mu m.
