Browsing by Author "El-Ganainy, R."
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Item Open Access Non-Hermitian matter-wave mixing in Bose-Einstein condensates : Dissipation-induced amplification(American Physical Society, 2017) Wüster, Sebastian; El-Ganainy, R.We investigate the nonlinear scattering dynamics in interacting atomic Bose-Einstein condensates under non-Hermitian dissipative conditions. We show that, by carefully engineering a momentum-dependent atomic loss profile, one can achieve matter-wave amplification through four-wave mixing in a quasi-one-dimensional nearly-free-space setup - a process that is forbidden in the counterpart Hermitian systems due to energy mismatch. Additionally, we show that similar effects lead to rich nonlinear dynamics in higher dimensions. Finally, we propose a physical realization for selectively tailoring the momentum-dependent atomic dissipation. Our strategy is based on a two-step process: (i) exciting atoms to narrow Rydberg or metastable excited states, and (ii) introducing loss through recoil; all while leaving the bulk condensate intact due to protection by quantum interference.Item Open Access Quasi PT-symmetric design for single-mode high-power edge-emitting semiconductor lasers(IEEE - Institute of Electrical and Electronics Engineers, 2023-09-04) Olyaeefar, Babak; Şeker, Enes; Şengül, Serdar; Dadashi, Khalil; Teimourpour, M. H.; El-Ganainy, R.; Demir, AbdullahLarge-area lasers are utilized for generating higher optical powers. However, enlarged cross-sections for increased current injection lead to the introduction of high-order modes, decreased beam qualities, and limited applicability. Available mode filtering approaches such as adiabatic amplifiers, tapered designs, laterally inhomogeneous structures, and refractive index modulations mostly adversely affect the fundamental mode and require added steps and complexities in the fabrication. As a novel concept in quantum mechanics, PT-symmetric (PTS) designs have found their only experimental validation in optical devices. They have shown capabilities in high-order mode filtering by inducing selective modal losses on the coupled higher-order mode from a pumped main potential to a lossy partner potential. Again, these systems require precise adjustments to avoid affecting the fundamental mode. Here, we introduce the quasi-PTS concept, with reduced operational sensitivity, to selectively force loss on the high-order mode while keeping the fundamental mode intact. This design is based on adjusting the width of the passive partner to support the higher-order mode of the main potential as its first mode. We present experimental evidence for an electrically pumped, large-area edge-emitting laser with high-power emission above 400mW and high beam qualities below 1.2. Beyond prior proof-of-concept investigations, this study provides the first unambiguous demonstration of PTS applicability in designing laser geometries with industrial output power levels and emission characteristics.Item Open Access Single-mode quasi PT-symmetric laser with high power emission(Springer Nature, 2023-06-16) Şeker, Enes; Olyaeefar, Babak; Dadashi, Khalil; Şengül, Serdar; Teimourpour, M. H.; El-Ganainy, R.; Demir, AbdullahLarge-area lasers are practical for generating high output powers. However, this often comes at the expense of lower beam quality due to the introduction of higher-order modes. Here, we experimentally demonstrate a new type of electrically pumped, large-area edge-emitting lasers that exhibit a high power emission (∼0.4 W) and a high-quality beam (M2∼1.25). These favorable operational characteristics are enabled by establishing a quasi PT-symmetry between the second-order mode of a large area two-mode laser cavity and that of a single-mode auxiliary partner cavity, i.e., by implementing a partial isospectrality between the two coupled cavities. This in turn enlarges the effective volume of the higher-order modes. As a result, a selective pump applied via current injection into the main laser cavity can provide a stronger modal gain to the fundamental mode, and thus lead to lasing in the single mode regime after filtering out higher order transverse modes. The reported experimental results confirm this intuitive picture and are in good agreement with both theoretical and numerical analysis. Above all, the employed material platform and fabrication process are compatible with the industrial standards of semiconductor lasers. This work provides the first clear demonstration, beyond previous proof-of-concept studies, of the utility of PT-symmetry in building laser geometries with enhanced performance and, at the same time, useful output power levels and emission characteristics. © 2023, The Author(s).