Natural linewidth of a two-level two-photon laser

Berthold Burghardt, M. Dubke, Wolfgang Jitschin +1 more

Jacques Arnaud

Ning Lu

A quantum theory of a two-photon laser is developed by making use of the antinormal-ordering Q function. Starting from the microscopic atom-field interaction Hamiltonian for cascade three-level atoms and including saturable absorbers, we first present a master equation for the field-density operator, and then transform the master equation into a Fokker-Planck equation for the Q function. The Q-function approach enables us to study the two-photon laser analytically, obtaining simple expressions for nonlinear gain, mean photon number, frequency pulling, natural linewidth, and photon-number variance in a unified method. We find that the field in a two-photon laser will build up from a vacuum without triggering if its linear gain is larger than the cavity loss. Also hysteresis can occur in the two-photon laser even without triggering. With an overall two-photon resonance, the normalized photon-number variance approaches a common value 11/8 well above ``threshold,'' independent of the one-photon detuning. We compare these results with previous results obtained from an effective interaction Hamiltonian. We find that the domain of validity of the effective Hamiltonian for the photon-number variance is much smaller than that for the mean photon number. Well above ``threshold'' the effective Hamiltonian overestimates both the natural linewidth and the photon-number variance.

Jozsef S. Bakos, Gagik P. Djotyan, G. Demeter +1 more

We propose a scheme of transient laser manipulation and cooling of two-level quantum systems with narrow natural linewidths by a sequence of counterpropagating laser pulses with special frequency chirping. Interaction with a large number of laser pulses within the decay time decreases drastically the cooling time of such systems. \textcopyright{} 1996 The American Physical Society.

Seyedeh Hamideh Kazemi, Mohammad Mahmoudi

We study the influence of laser profile on the linewidth of the optical spectrum of multi-photon resonance phenomena. First, we investigate the dependence of the absorption spectrum on the laser profile in a two-level system. Thanks to the Laguerre–Gaussian field, the linewidth of the one-photon optical pumping and two-photon absorption peaks are explicitly narrower than that obtained with a Gaussian field. In the next section, it is shown that, compared to the Gaussian fields, the Laguerre–Gaussian ones reduce the linewidth of the optical spectrum in the coherent population trapping. Interestingly, it turns out that the use of a Laguerre–Gaussian beam makes the linewidth of the spectrum narrower as compared with a Gaussian one in Doppler-broadened electromagnetically induced transparency. Moreover, we study the effect of the laser profile on the Autler–Townes doublet structure in the absorption spectrum for a laser-driven four-level atomic system. We also consider the different values of the Laguerre–Gaussian mode beam waist, and, perhaps more remarkably, we find that for the small waist values, the Autler–Townes doublet can be removed and a prominent narrow central peak appears in the absorption spectrum. Finally, we investigate the effect of the laser profile on the linewidth of the sub-natural three-photon absorption peak of double dark resonance. The differences in the linewidth are quite large, offering potential applications in metrology and isotope separation methods. Our results can be used for super ultra-high resolution laser spectroscopy and to improve the resolution of the technology of isotope/isomer separation and photo-biology even at essential overlap of the spectra of the different particles.

B. Nikolaus, D. Z. Zhang, P. E. Toschek