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Journal of Physics B Atomic Molecular and Optical Physics

On identifying critical parameters in an amplification without inversion setup in mercury *

Daniel Preißler, Noah Eizenhöfer, Jens Gumm, Thomas Walther

Published Dec 5, 2022• 1 citation
Publisher

Abstract

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.

DOI
10.1088/1361-6455/aca8de

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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.
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.
Lasers and masers typically require population inversion. But with phase coherent atoms (phasers), we get lasing without inversion (e.g. 10% of the atoms excited). However, in recent work we found that it is possible to get coherent light emitted with no atoms excited, via Quantum Amplification of Superradiant Emission of Radiation (QASER). In particular, we found that by utilizing collective superradiant emission, we can generate coherent light at high frequency in the UV or x-ray bands by driving the atomic system with lower frequency source. Here, we present a simple analysis based on near-resonant QASER operation and on a multi-photon Hamiltonian obtained by, e.g. a canonical transformation.
This review paper is devoted to amplification and lasing without population inversion involving atomic transitions in gas media. We start by discussing the main motivation in inversionless lasing research, namely, the generation of short-wavelength laser light. Then, we review the basic physics of inversionless lasing in two-level and, eventually, in three- and multilevel atomic configurations. Finally, we summarize the current state of the art of LWI experiments and indicate the main difficulties with respect to short-wavelength laser generation.
The most commonly used lasers operate with population inversion. This requires an incoherent pumping power (from lamps, electrical discharges, etc.) that rapidly scales with the frequency of the generated laser radiation. In practice, this is the main obstacle for the operation in the continuous-wave regime of short-wavelength lasers in the UV, X-rays, etc. But lasers can also operate without population inversion using atomic coherences excited in the laser medium by coherent pumping with another laser. We present in this paper a short review of the field of lasing without inversion (LWI). In particular, we summarize the basic physics of LWI in the framework of both semiclassical theory and quantumjump formalism to describe light-matter interaction. We also review the experimental state-of-the-art in LWI. Most proof-of-principle demonstrations of LWI have used atomic vapours, so far. But recently gain without inversion (a pre-requisite for lasing) has been observed also in a technologically relevant medium: semiconductor nanostructures that can be tailored to have “artificial atom” electron states.