This activity revolves around the amplified laser chain (50 fs, 1 kHz, 5 mJ/pulse) which makes it possible to obtain peak optical powers of around 100 GW. By focusing these optical pulses, we obtain electric fields strong enough to ionize the air. This plasma is a centro-symmetric medium in which the non-linear effect of order 3 (Kerr effect) is preponderant. Consequently, the spatial and temporal superposition of a pulse centered 800 nm and another centered at 400 nm allows the generation of a THz pulse by Kerr effect (ωred+ωred-ωblue=ΩTHz).
The objective is to study the physical mechanisms involved in this generation process, or the impact of certain experimental parameters on the quality of THz pulses.
In parallel, we will discuss the development of innovative THz plasma sources. The aim is to enrich the photo-generated plasma by adding charged particles brought by external plasma in order to improve/modify the characteristics of the generated THz pulse. Encouraging preliminary results allow us to envisage the development of THz sources whose intrinsic characteristics (pulse duration, polarization, amplitude...) are parameterized by the physical properties of the external plasma (charge density, nature of the gas, plasma temperature...). Such THz sources would be of great interest for the development of "agile" spectroscopy systems, for example. It is therefore also possible to diagnose an external plasma by observing the THz pulse generated inside it. To assist us in these studies, we have initiated collaboration with the GREMI laboratory in Orleans.
Integrated THz devices
We are pursuing the development and characterization of fast GaAs and high conversion efficiency photo-switches and their circuits (coll. Institut Néel, Quantum Coherence group). The design of photo-switches is based on nano-photonics and plasmonics. The fabricated devices will have to allow the generation of picosecond electrical signals using very low optical energies (~ pJ/ Pulse), to control the operation of an electronic circuit with quantum properties (2D electron gas) while maintaining the circuit at 100 mK (this temperature is necessary to ensure a sufficiently long coherence time of the electrons).
In the long term, we wish to be able to generate electrical signals with variable parameters according to the function that the quantum circuit will have to perform. Amplitudes from 10 to 300 mV, durations from 2 to 50 p and shapes (Lorentzian, square) will be sought. The design and characterization of such devices is based on cross-disciplinary skills in the laboratory (optics, semiconductor and RF). The technological realization of the components is outsourced, in particular to the PTA in Grenoble.
This research axis is supported by the ANR STEPforQUBITS project (Generic PAA 2019).