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- ItemRotational quantum beat lasing without inversion(Washington, DC : OSA, 2020) Richter, Maria; Lytova, Marianna; Morales, Felipe; Haessler, Stefan; Smirnova, Olga; Spanner, Michael; Ivanov, MishaIn standard lasers, light amplification requires population inversion between an upper and a lower state to break the reciprocity between absorption and stimulated emission. However, in a medium prepared in a specific superposition state, quantum interference may fully suppress absorption while leaving stimulated emission intact, opening the possibility of lasing without inversion. Here we show that lasing without inversion arises naturally during propagation of intense femtosecond laser pulses in air. It is triggered by the combination of molecular ionization and molecular alignment, both unavoidable in intense light fields. The effect could enable inversionless amplification of broadband radiation in many molecular gases, opening unusual opportunities for remote sensing. © 2020 Optical Society of America
- ItemNon-instantaneous third-order optical response of gases in low-frequency fields(Washington, DC : Soc., 2022) Morales, Felipe; Richter, Maria; Ivanov, Misha; Husakou, AntonIt is commonly assumed that for low-intensity short optical pulses far from resonance, the third-order optical nonlinear response is instantaneous. We solve the three-dimensional time-dependent Schrödinger equation for the hydrogen atom and show that this is not the case: the polarization is not simply proportional to the cube of the electric field even at low intensities. We analyze the fundamental-frequency and third-harmonic nonlinear susceptibilities of hydrogen, investigate their dependence on intensity, and find that the delays in the Kerr response rapidly approach the femtosecond time-scale at higher intensities, while the delays in the third harmonic generation remain much lower. We also propose an experimental scheme to detect and characterize the above effects.