**Le 30 mars 2018 - 11 h - salle 172 - bâtiment P5 bis**

*GHz-THz-MIR Sources and Nonlinearities*

Intersubband lasers, such as Quantum Cascade Lasers, are the prime sources for coherent radiation in the Mid-Infrared (MIR). All gases and bio-materials of increasingly interest for both basic science and applications, have strong absorption signatures in the GHz-THz-MIR range [1]. Detection of mixes of different gases with high sensitivity require a narrow laser linewidth, which can be influenced by the linewidth enhancement (α-factor). The α-factor of intersubband lasers was initially expected to be zero. However, values ranging from -0.5 to 3 have been found experimentally. This talk starts with a general Nonequilibrium Green’s Functions (NEGF) approach suitable for both interband and intersubband optics and shows a connection with previous density matrix approaches. Next, the equations are simplified in the intersubband case to a limit that resembles the usual two-level atom approach typically used in Quantum Optics and the nonzero α-factor is explained [2]. Luminescence is one of the most important characterisation tools of semiconductor materials and devices. Recently, a very efficient analytical set of equations has been applied to explain optical properties of dilute semiconductor materials, with an emphasis on the evolution of peak luminescence gain with temperature and its relation to sample quality and it will be explained here and presented as a numerical characterization tools, notably useful for materials for the MIR and NIR ranges [3-6]. Evolving from the MIR to the THz and GHz ranges, the talk introduces a concept to study nonlinear optics through controllable nonlinearities in semiconductor superlattices. A predictive NEGF approach is used to deliver input to a relaxation-rate approximation approach leading to fully analytical expressions for the nonlinear polarization at arbitrary orders. [7-8]. These results open the possibility of extending the whole field of nonlinear optics to the GHZ-THz range and the possibility of designing materials and devices for a large number of applications, including spectroscopy of biomolecules, which typically have strong GHz-THz resonances.

REFERENCES

[1] M.F. Pereira, Opt Quant Electron 47, 815–820 (2015).

[2] M.F. Pereira, Applied Physics Letters 109, 222102 (2016).

[3] C. I. Oriaku and M. F. Pereira, J. Opt. Soc. Am. B 34, 321-328 (2017).

[4] X. Yang, C.I. Oriaku, J.P. Zubelli and M.F. Pereira, Opt Quant Electron 49, 93 (2017).

[5] C. I. Oriaku, T. J. Spencer, X. Yang, J. P. Zubelli and M. F. Pereira, J. Nanophoton. 1, 026005 (2017).

[6] M.F. Pereira, Materials, 11(1), 2 (2018).

[7] M.F. Pereira, D. Winge and A. Wacker, J.P. Zubelli, A.S. Rodrigues, V. Anfertev and V. Vaks, , Phys. Rev. B 96, 045306 (2017).

[8] M.F. Pereira, V. Anfertev, J.P. Zubelli and V. Vaks, J. Nanophoton 11 (4), 046022 (2017).