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Quantum Electronics and Laser Science Conference

Beyond inversionless gain to a demonstration of field-enhanced lasing

Peter B. Sellin, THOMAS W. MOSSBERG

Published Jun 7, 1996• 0 citations
OpenAlex

Abstract

Summary form only given. We experimentally demonstrate field-enhanced lasing, i.e., lasing made possible through an excitation-field-mediated boost in the gain normally realizable on a weakly inverted transition. The excitation field responsible for the boost in gain, the helper field couples the lasing transition to another transition in a cascade-type three-level atomic system. The gain boosting operative in our driven three-level-atom experiments derives from the same essential physics that gives rise to the gain that has recently attracted so much attention. In terms of achieving laser operation in new regimes, gain boosting may play much the same role as inversionless gain.

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Summary form only given.We provide additional insight into the process of resonant four-wave mixing via an analysis in the dressed states basis. As opposed to the common situation in lasing without inversion, both the excited and the ground state of the transition with enhanced coherent field generation are coupled to each other via external driving fields. For this reason we find more similarities to the well-understood process of light amplification in driven two-level systems. Initial gain does not need to arise from a spontaneous photon or a probe field but arises due to the coherence established directly by the strong external driving laser fields.

Conference on Lasers and Electro-Optics•Nov 27, 2002•0 citations
Summary form only given. We experimentally demonstrate field-enhanced lasing, i.e., lasing made possible through an excitation-field-mediated boost in the gain normally realizable on a weakly inverted transition. The excitation field responsible for the boost in gain, the helper field couples the lasing transition to another transition in a cascade-type three-level atomic system. The gain boosting operative in our driven three-level-atom experiments derives from the same essential physics that gives rise to the gain that has recently attracted so much attention. In terms of achieving laser operation in new regimes, gain boosting may play much the same role as inversionless gain.
We experimentally study the production of laser gain (phase-insensitive optical amplification) with and without atomic population inversion in a doubly driven three-level system in atomic barium. The external fields are found to create inversionless gain and to enhance gain available in the presence of inversion. Laser oscillation based on enhanced gain is observed. In analysis of the driven system, we identify an irreversible multiphoton process that is intrinsically supportive of gain in the absence of population inversion. \textcopyright{} 1996 The American Physical Society.
We show that continuous-wave, two colour excitation of three-level atoms opens new channels of irreversible population transfer between atomic levels. This process, which we describe as dynamically induced irreversibility, leads to unanticipated phenomena including the inversion of atomic transitions whose upper atomic level has no conventional source of irreversible population pumping. We also study the effect of excitation-field bandwidth on the gain exhibited by driven, three-level, V-type atomic systems. Gain, which may or may not be inversionless in the atomic-state basis, is produced through strong monochromatic driving of one atomic transition and weaker pumping of a coupled transition. It is found that monochromatic pumping frequently yields greater optical gain than incoherent (wide bandwidth) pumping. This is particularly true when system gain can be attributed to hidden inversions among the eigenstates (semi-classical dressed states) of the coupled atom+driving field quantum system. Last, we report the observation of continuous-wave lasing in a strongly driven barium cascade system and interpret its properties in terms of the models presented.
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.
Summary form only given.We provide additional insight into the process of resonant four-wave mixing via an analysis in the dressed states basis. As opposed to the common situation in lasing without inversion, both the excited and the ground state of the transition with enhanced coherent field generation are coupled to each other via external driving fields. For this reason we find more similarities to the well-understood process of light amplification in driven two-level systems. Initial gain does not need to arise from a spontaneous photon or a probe field but arises due to the coherence established directly by the strong external driving laser fields.