Nonperturbative Interband Response of a Bulk InSb Semiconductor Driven Off Resonantly by Terahertz Electromagnetic Few-Cycle Pulses

Abstract

Intense multi-THz pulses are used to study the coherent nonlinear response of bulk InSb by means of field-resolved four-wave mixing spectroscopy. At amplitudes above 5 MV/cm the signals show a clear temporal substructure which is unexpected in perturbative nonlinear optics. Simulations based on a two-level quantum system demonstrate that in spite of the strongly off-resonant character of the excitation the high-field pulses drive the interband resonances into a non-perturbative regime of Rabi flopping.PACS numbers: 42.65. Re, 78.47.nj, Semiconductors form a uniquely well-defined laboratory to explore novel limits of nonlinear optics. A key parameter for interaction of a coherent light field with an electronic transition is given by the Rabi frequency Ω R = µE/ . E is the electric field strength and µ the transition dipole moment. When the dephasing rate is negligible compared to Ω R , coherent Rabi flopping governs the dynamics of electronic systems [1]. If the detuning of the driving electromagnetic field is smaller than Ω R the response of a system cannot be described by the perturbative approach which usually depicts offresonant nonlinear optics. This non-perturbative excitation regime provides access to many fascinating quantum effects in semiconductors such as Rabi splitting, selfinduced transparency and generation of high harmonics [2][3][4][5][6][7][8]. In particular, sufficiently intense and ultrashort laser pulses have been exploited to implement ultimate scenarios in which the duration of the light pulse, the Rabi cycle and the oscillation period of the carrier wave all become comparable in size [9]. Under such conditions, a detailed insight into the nonlinear optical interaction calls for complete phase and amplitude resolution of all interacting light fields. However, in most of the cases, the lack of phase-stable laser pulses and fast detectors does not allow for capturing sub-cycle polarization dynamics of a system. The development of ultraintense THz laser systems generating phase-stable transients with field amplitudes above 1 MV/cm [10][11][12] paves the way towards a coherent spectroscopy of extreme nonlinearities in condensed matter systems with absolute sampling of amplitude and phase. Recent experiments performed with high-field multi-THz pulses have demonstrated a high potential of this approach [13][14][15][16]. However, the regime of an offresonant excitation of Rabi flopping has remained almost unexplored due to the lack of sufficiently intense and phase-locked pulses. The latest breakthrough in generation and field-resolved detection of multi-THz pulses with peak fields up to 100 MV/cm [17,18] opens up the possibility to explore this highly non-perturbative regime.

Coherent Excitation of Optical Phonons in GaAs by Broadband Terahertz Pulses

“…THz wave technologies have been providing a powerful tool to access and manipulate variety of material properties including molecular vibration12, lattice and electronic dynamics345, coherent antiferromagnetic spin wave6, and so on789. THz reflection and transmission spectroscopy reveals THz interaction with phonons1011, and THz waves emitted by coherent phonons has been studied and used as THz source12131415.…”

Focus: Phase-resolved nonlinear terahertz spectroscopy—From charge dynamics in solids to molecular excitations in liquids

“…5,6,39,[80][81][82][83][84][85] Intersubband (IS) transitions in lowdimensional, in particular quasi-2D semiconductor nanostructures 5,6,80 as well as electronic interband transitions in the semiconductor InSb, 82,83 epitaxial multi-layer graphene, 39,84,85 and the ferroelectric material 81 LiNbO 3 were investigated. All 2D THz experiments on interband transitions were performed in the non-perturbative regime, where the strength of lightmatter interaction is comparable to or even larger than electronic couplings in the material.…”

Electric and magnetic terahertz nonlinearities resolved on the sub-cycle scale

“…In the first part of this article, we report on the coherent nonlinear THz response of an interband polarization in the narrowband semiconductor InSb, studied by means of fieldresolved four-wave mixing (FWM) spectroscopy [32]. The carrier frequency of the THz driving field is set well below the interband resonance.…”