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arXiv:2111.03023 · Physical Review A

Toward lasing without inversion in the ultraviolet regime: Doppler-free three-photon coherence effects in mercury vapor

Benjamin Rein, Jochen M. Schmitt, Martin R. Sturm, R. Walser, Thomas Walther

Published Feb 24, 2022• 6 citations
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Abstract

Doppler-free three-photon coherence effects at a wavelength of $253.7\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ were observed in thermal mercury vapor. The experimental results are compared to simulations based on a detailed theoretical model reproducing the measured effects. Based on these results, we show by simulations that amplification without inversion in our setup is feasible, paving the way towards lasing without inversion in mercury.

DOI
10.1103/physreva.105.023722

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Doppler-free three-photon coherence effects at a wavelength of 253.7nm253.7\phantom{\rule{0.16em}{0ex}}\mathrm{nm}253.7nm were observed in thermal mercury vapor. The experimental results are compared to simulations based on a detailed theoretical model reproducing the measured effects. Based on these results, we show by simulations that amplification without inversion in our setup is feasible, paving the way towards lasing without inversion in mercury.
We investigate the feasibility of UV lasing without inversion at a wavelength of 253.7 nm utilizing interacting dark resonances in mercury vapor. Our theoretical analysis starts with radiation-damped optical Bloch equations for all relevant 13 atomic levels. These master equations are generalized by considering technical phase noise of the driving lasers. From the Doppler broadened complex susceptibility we obtain the stationary output power from semiclassical laser theory. The finite overlap of the driving Gaussian laser beams defines an ellipsoidal inhomogeneous gain distribution. Therefore, we evaluate the intra-cavity field inside a ring laser self-consistently with Fourier optics. This analysis confirms the feasibility of UV lasing and reveals its dependence on experimental parameters.
Abstract Lasing without inversion is a compelling method based on the generation of coherences between atomic levels in order to produce UV radiation. While the proof-of-principle of this scheme has been shown for several decades, so far no radiation at a significant shorter wavelength than the necessary drive fields has been observed. In a recent publication Rein et al (2022 Phys. Rev. A 105 023722) have made experimental progress towards this goal. In this paper, we investigate the necessary improvements to their setup and discuss the experimental steps taken to achieve those goals. Specifically, we report on the improvement with respect to the laser sources.
Summary form only given. We study a model for an incoherently pumped laser operating with a Doppler-broadened three-level system placed in a doubly resonant cavity and producing two laser fields, one of them without population inversion. Each laser field couples to only one of the transitions of the three-level medium. We have studied our model for parameters appropriate to two real atomic systems (i) a cascade scheme in atomic /sup 138/Ba looking for lasing with (without) inversion at /spl lambda//sub /spl beta//=554 nm (/spl lambda//sub /spl alpha//=821 nm), and (ii) a V-scheme in atomic /sup 85/Rb with ordinary lasing at /spl lambda//sub /spl alpha//=780 nm and lasing without inversion (LWI) at /spl lambda//sub /spl alpha//=4216 nm. These two cases are qualitatively different in that two-photon processes are responsible for inversionless gain in case (i) while LWI in case (ii) arises from one-photon processes. Moreover, the frequency up-conversion ratio is R=0.67 for the case of /sup 138/Ba and it is R=1.88 for the case of /sup 85/Rb. In spite of the fact that the frequencies of the two laser fields are relatively different, our results show that dual-wavelength lasing extends up to Doppler broadening values typical for optical transitions of atoms in a vapor cell. In case (i) /spl alpha/-lasing occurs without two-photon inversion only for approximately the lower half of the domain of Doppler-broadening values. However, in case (ii) one has LWI in all the domains. Some considerations for a practical realization of the dual-wavelength inversionless-conventional laser are discussed.
Three-level models of lasers without inversion in V and \ensuremath{\Lambda} configurations are studied in a realistic Doppler-broadened gas medium. The intensity of a generated coherent radiation is numerically calculated for a wide range of experimental parameters and the role of the laser cavity is fully taken into account. Different geometrical arrangements of the experiment are compared. Significant differences in lasing properties of the studied models are shown and discussed. An amplification mechanism based on the Doppler shift tuning to dressed-state inverted transitions is discussed.
We have studied an incoherently pumped laser operating with a Doppler-broadened three-level system placed in a doubly resonant cavity. This system generates two laser fields, one of them without population inversion. Both ladder and V-type three-level schemes are considered with a ratio $R={\ensuremath{\omega}}_{\ensuremath{\alpha}}/{\ensuremath{\omega}}_{\ensuremath{\beta}}$ of inversionless laser frequency ${\ensuremath{\omega}}_{\ensuremath{\alpha}}$ to ordinary laser frequency ${\ensuremath{\omega}}_{\ensuremath{\beta}}$ of R=0.67R=0.67R=0.67 and R=1.88,R=1.88,R=1.88, respectively. Dual-wavelength lasing extends up to Doppler-broadening values for optical transitions of atoms in a vapor cell. Some considerations for the practical realization of this dual-wavelength laser are discussed.