Self-phase locking in lasers with homogeneously broadened emission lines

It is shown by numerical analysis based on Lamb's equations of motion, that standing-wave lasers with purely homogeneously broadened emission lines exhibit regular multimode oscillations. Specifically, modes lying far from the line centre are quenched due to mode competition, and the amplitudes of the oscillating modes approach steady-state values. The stabilization of the amplitudes is normally accompanied, or followed, by an evolution of the phases towards a phase-locked regime, where the relative phases _n = 2 _n – _{n + 1} – _{n – 1} [ _n phase in then ^th mode, defined by (6)] attain either the value 0 or ± . The build-up times for the relative phases are found to vary over a wide range.     

Stability analysis of a bidirectional homogeneously broadened ring laser

We study the stability of steady state solutions of a resonantly tuned bidirectional homogeneously broadened ring laser retaining the complete longitudinal spatial dependence. We prove that in two limits, the stable steady states are only weakly stable since the relaxation rates are very large. This implies a high sensitivity to any kind of perturbation which will easily induce a transition from one direction of propagation to the other one. We also analyze a popular approximation which uses a truncated harmonic expansion and the adiabatic elimination of the polarization. When the adiabatic elimination is justified, we show that the harmonic truncation does not further limit the range of applicability of the stability analysis.     

均匀加宽注入锁定环形激光器的半经典理论—小信号分析

本文用拉姆(Lamb)的半经典理论分析了在小信号情况下均匀加宽注入锁定环形激光器的单模运转问题.     

Mode instabilities in a homogeneously broadened ring laser

A nonperturbative theory of a homogeneously broadened ring laser is presented after incorporating spatial hole-burning effects arising due to mutual interference of two counterpropagating cavity modes. It is shown that under suitable conditions the continuous-wave unidirectional lasing mode becomes unstable due to Hopf bifurcations. The time-periodic state associated with these bifurcations corresponds to self-induced pulsations either in one direction or in both directions.     

Power characteristics of homogeneously broadened index-antiguided waveguide lasers

A model is reported that describes a bidirectional homogeneously broadened index-antiguided (IAG) slab laser having arbitrary single-pass gain and distributed losses. Maximum extraction efficiency and corresponding optimum output coupling are determined for various values of unsaturated gain and loss per pass. A method is proposed to determine the intrinsic laser parameters from output power measurements.     

Stability of a detuned single mode homogeneously broadened ring laser

We study analytically the influence of detuning on the properties of a homogeneously broadened single mode ring laser. In the good cavity domain the stationary output is stable. In the bad cavity domain the stationary output becomes unstable via a Hopf bifurcation. Near line center this Hopf bifurcation is subcritical, leading to unstable small amplitude oscillations. Far from line center this Hopf bifurcation is supercritical and leads to stable small amplitude output.     

Effects of nonlinear mode coupling on the chaotic dynamics of multimode lasers

The dynamics of individual modes of a cw multimode dye laser in a 2-mirror configuration has been studied theoretically and experimentally. Numerical solutions of the laser rate equations including nonlinear mode coupling exhibit chaotic and stochastic behavior in the regime of high and low power, respectively. Chaotic behavior due to mode coupling has been observed in the operating regime well above threshold. The mode dynamics in this case is characterized by a chaotic attractor with low dimension between 2 and 3. With decreasing laser power the dimension increases, suggesting stochastic behavior due to quantum noise in the limit of the laser threshold.On leave at 1. Institut für Experimentalphysik, Universität Hamburg, Fed. Rep. Germany     

Collision induced and resonantly enhanced extra resonances in four-wave mixing in inhomogeneously broadened four level systems

Role of collisions in inducing and enhancing extra resonances in non-linear generation by four-wave mixing in inhomogeneously broadened four level systems is studied. It is shown that collision induced three and two-photon resonances can be enhanced further by tuning to exact one photon (non-absorbing) transitions between unpopulated upper levels. In addition we also find existence of collision induced interference dip at the three-photon resonance that arises due to complete cancellation of signal at the line center.     

Ultrashort-pulse fiber ring lasers

Received: 18 February 1997/Revised version: 22 April 1997     

Sub-half-wavelength atom localization via bichromatic phase control of spontaneous emission

We show that the bichromatic phase control of the spontaneous emission spectrum leads to the sub-half-wavelength atom localization. We consider a three-level Λ-type atom interacting with a bichromatic coupling field and a bichromatic probe field with equal frequency difference. One component of the bichromatic coupling field is a standing-wave field with position dependent Rabi frequency. When the spontaneous emitted photons are detected, the atom is localized in either of the two half-wavelength regions with 50% probability by the variation of the difference between the relative phases of the two bichromatic fields.     

A dense collection of two-level atoms embedded in a dielectric medium in a ring cavity

The hysteresis behavior of a dense collection of two-level atoms embedded in a linear dielectric medium in an optical cavity is investigated theoretically in terms of a parametric formulation method under the thin-sample approximation. The relation of the output intensity to the input intensity is obtained in an explicit formula. The numerical results show that the hysteresis behavior and the cavity transmission are different from those in vacuum because of the local-field enhancement and the local cooperative decay effect. Received: 27 June 2000 / Revised version: 11 September 2000 / Published online: 10 January 2001     

Three-wave and four-wave forward mixing in photorefractive materials

An amplification mechanism relying mainly on the real part of the arising space charge field in the presence of two strong pump beams is described. The dependence of amplification on frequency detuning, applied electric field and pump beam ratio are investigated in the undepleted beam approximation.     

Optical bistability in gaussian inhomogeneously broadened ring lasers with saturable absorber

The optical bistability (OB) in Gaussian inhomogeneously broadened ring lasers with saturable absorber (LSA) in both resonance and out-of-resonance is theoretically analyzed in the rate-equation approximation based on the dual two-level model. The OB effect may appear for appropriate sets of LSA control parameter values which can be displayed in phase diagrams. The characteristics of the OB curves as well as their stability behavior are analytically and numerically studied in detail. The influence of the control parameters, including detuning, are investigated and displayed in the figures. A brief comparison with the Lorentzian case is given as well. Paper submitted by authors in English April 20, 1999.     

Dynamics of refractive-index changes and two-beam coupling in resonant media

The dynamics of light-induced change in the refractive index of a resonant medium are examined. For illumination with weak fields, the two relevant relaxation times are T ₁, the population lifetime and T ₂, the dipole-dephasing time. The response time of the index change is determined by the slower relaxation time of the medium which is usually the time T ₁ taken by the excited system to relax back to its thermal equilibrium value. Illumination with two beams of the same frequency that intersect within the medium leads to the formation of a volume grating in the medium that is spatially local. Hence there is no exchange of energy between the beams that write the grating, each beam merely reducing the absorption experienced by the other beam. Illumination with a moving, spatially periodic intensity pattern leads to gain for one beam and additional absorption for the other beam as they propagate through the medium. A complete set of coupled equations describing the intensities and phases of the beams undergoing non-degenerate two-wave mixing in the resonant media is derived using third-order perturbation theory, and the solutions are studied numerically. In particular, the two-beam coupling constant for intensity is shown to depend on the frequency difference between the two beams and on the pressure-induced collisional relaxations in the system.     

cw Injection phase locking in homogeneously broadened media

A theory of cw injection phase locking in homogeneously broadened media is investigated using density matrix formalism to derive the interactions of three coherent fields with a two levels system. This powerful formalism leads to analytical expressions of the complex gain for each wave propagating inside the amplifier medium. Studies of the minimum signal intensity for single-frequency operation and power output are related.     

Phase transition to superradiance in a multicomponent system

Abtract The study deals with the ground-state energy transition of a multicomponent atomic system from its normal state to the superradiant state when interacting with a multimode quantized electromagnetic field. The threshold conditions are determined.Alexander-von-Humboldt awardee     

Soliton-shaped nonlinear waves of space charge in photorefractive materials

A new type of nonlinear waves of space charge in photorefractive media is presented. These waves have a sech-shaped envelope which makes them similar to solitons. The conditions for their experimental observation are discussed.