Steady state behaviour in atomic three-level lambda and ladder systems with incoherent population pumping

The steady state in three-level lambda and ladder systems is studied. It is well-known that in a lambda system this steady state is the coherent population trapping state, independent of the presence of spontaneous emission. In contrast, the steady state in a ladder system is in general not stable against radiative decay and exhibits a minimum in the population of the ground state. It is shown that incoherent population pumping destroys the stability of the coherent population trapping state in the lambda system and suppresses a previously discovered sharp dip in the steady state response. In the ladder system the observed minimum disappears in the presence of an incoherent pump on the upper transition.Comment: 4 pages, RevTex, 5 figures, to appear in Phys. Rev.

Role of inhomogeneous broadening in lasing without inversion in ladder systems

We study the effect of Doppler broadening on the inversionless gain that can be realized in a ladder configuration. The gain is calculated when the strong coherent pump and the weak probe are either copropagating or counterpropagating. The results indicate that the counterpropagating situation is the optimal one for obtaining maximum amplification, since for identical Doppler broadening, the counterpropagating geometry yields higher amplification than the copropagating geometry. The effect of Doppler broadening on electromagnetically induced transparency in the same atomic system is also briefly discussed

Parity-time symmetry breaking in optically coupled semiconductor lasers

We experimentally demonstrate the realization of a parity-time (PT) symmetry breaking in optically coupled semiconductor lasers (SCLs). The two SCLs are identical except for a detuning between their optical emission frequencies. This detuning is analogous to the gain-loss parameter found in optical PT systems. To model the coupled SCLs, we employ the standard rate equations describing the electric field and carrier inversion of each SCL, and show that, under certain conditions, the rate equations reduce to the canonical, two-site PT- symmetric model. This model captures the global behavior of the laser intensity as the system parameters are varied. Overall, we find that this bulk system (coupled SCLs) provides an excellent test-bed to probe the characteristics of PT-breaking transitions, including the effects of time delay

Effects of quantum noise on the nonlinear dynamics of a semiconductor laser subject to two spectrally ltered, time-delayed optical feedbacks

We report on a theoretical and computational investigation of the complex dynamics that arise in a semiconductor laser that is subject to two external, time-delayed, filtered optical feedbacks with special attention to the effect of quantum noise. In particular, we focus on the dynamics of the instantaneous optical frequency (wavelength) and its behavior for a wide range of feedback strengths and filter parameters. In the case of two intermediate filter bandwidths, the most significant results are that in the presence of noise, the feedback strengths required for the onset of chaos in a period doubling route are higher than in the absence of noise. We find that the inclusion of noise changes the dominant frequency of the wavelength oscillations, and that certain attractors do not survive in the presence of noise for a range of filter parameters. The results are interpreted by use of a combination of phase portraits, rf spectra, and first return maps

Lasing without inversion in the absence of a coherent coupling field

We analyze the inversionless gain in a three-level ladder system by replacing the usual coherent coupling field with an incoherent field. Surprisingly, it is found that one can obtain inversionless amplification of a weak probe even in the absence of a coherent field in the model. We conclude that gain is determined by the ensemble average of the product of the two-photon coherence and the "effective Rabi frequency" of the field. Thus, even though the incoherent pump reduces the two-photon coherence, gain can be restored by choosing sufficiently high strengths of the incoherent field

Deriving spectroscopic information from intensity-intensity correlations

We present a very simple theoretical framework for extracting spectroscopic data on an atom via stochastic probing with a fluctuating laser source. By exploiting the fact that the linear susceptibility contains all the atomic structure information in it, we show that the power spectrum of the fluctuations in the intensity radiated from an atomic sample provides the relevant, atomic-level information. The analysis we present is very general and can be applied to a wide variety of atomic and molecular systems