Carmine Somma - Academia.edu (original) (raw)

Papers by Carmine Somma

EPJ Web of Conferences, 2019

The coupled lattice and charge dynamics connected with soft-mode excitations are mapped by nonlin... more The coupled lattice and charge dynamics connected with soft-mode excitations are mapped by nonlinear terahertz spectroscopy and ultrafast x-ray diffraction. Sub-picometer lattice displacements induce electron relocations over 100 pm in polycrystaline aspirin and ferroelectric ammonium sulfate (AS). In AS, the electron motions induce a macroscopic polarization switching.

Physical Review Letters, 2019

We demonstrate amplification of longitudinal optical (LO) phonons by polar-optical interaction wi... more We demonstrate amplification of longitudinal optical (LO) phonons by polar-optical interaction with an electron plasma in a GaAs structure coupled to a metallic metasurface using two-color two-dimensional spectroscopy. In a novel scheme, the metamaterial resonator enhances broadband terahertz fields, which generate coherent LO phonons and drive free electrons in the conduction band of GaAs. The time evolution of the LO phonon amplitude is monitored with mid-infrared pulses via the LO-phonon-induced Kerr nonlinearity of the sample, showing an amplification of the LO phonon amplitude by up to a factor of 10, in agreement with a theoretical estimate.

International Conference on Ultrafast Phenomena, 2016

The Journal of Chemical Physics, 2016

We present the first two-dimensional (2D) terahertz (THz) experiment with three phase-locked THz ... more We present the first two-dimensional (2D) terahertz (THz) experiment with three phase-locked THz pulses and a fully phase-resolved detection of the nonlinearly emitted field by electrooptic sampling. In a prototype experiment we study the ultrafast dynamics of nonlinear two-phonon and two-photon interband coherences in the narrow-gap semiconductor InSb. Due to the extraordinarily large optical interband dipole of InSb the experiments were performed in the strongly nonperturbative regime of light-matter interaction allowing for impulsive off-resonant excitation of both two-phonon coherences and two-photon interband coherences, the ultrafast dynamics of which is experimentally observed as a function of the waiting time in the three-pulse 2D experiment. Our novel three-pulse 2D THz spectroscopy paves the way for the detailed investigation of nonlinear quantum coherences in solids and holds potential for an extension to other systems.

Physical Review Letters, 2016

Physical Review B, 2015

We present an approach for controlling quantum coherences in condensed matter by interaction with... more We present an approach for controlling quantum coherences in condensed matter by interaction with a nonresonant optical control field. Coherent intersubband (IS) excitations of electrons in GaAs/AlGaAs quantum wells are manipulated by a strong nonresonant terahertz (THz) field as demonstrated by phase-resolved two-color two-dimensional spectroscopy. In the linear regime of IS response, we observe a THz-induced enhancement of the midinfrared (MIR) IS absorption and a dispersive perturbed free induction decay caused by a THz-induced blueshift of the IS polarization. In the regime of IS Rabi oscillations, the THz field causes pronounced phase shifts of the coherently emitted MIR field, while the IS Rabi frequency remains unaffected. Such behavior is accounted for by a full solution of the Maxwell-Bloch equations, treating the THz and MIR fields without approximations. Our control scheme paves the way for THz control of IS emitters and holds potential for an extension to other systems.

Optics Letters, 2015

Electric-field transients covering the extremely wide frequency range from 0.5 to 26 THz are gene... more Electric-field transients covering the extremely wide frequency range from 0.5 to 26 THz are generated in the organic nonlinear crystal 4-N,N-dimethylamino-4 0-N 0-methylstilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS). Parametric difference frequency mixing within the spectrum of 25-fs amplified pulses centered at 800 nm provides a highly stable broadband output with an electric-field amplitude of up to several hundred kilovolts/cm. The high stability of the terahertz pulse parameters allows for sensitive phase-resolved broadband spectroscopy of optically thick crystalline samples.

CLEO: 2015, 2015

Using fully phase-resolved two-dimensional terahertz spectroscopy we study coherent intersubband ... more Using fully phase-resolved two-dimensional terahertz spectroscopy we study coherent intersubband Rabi oscillations in GaAs quantum wells. A strong terahertz field modifies particularly the phase of the nonlinearly emitted field during the Rabi oscillation.

CLEO: 2014, 2014

ABSTRACT We study the nonlinear terahertz response of LiNbO3 using 2D spectroscopy. Dissecting th... more ABSTRACT We study the nonlinear terahertz response of LiNbO3 using 2D spectroscopy. Dissecting the nonlinear response into different orders in the electric field shows a strong shift current and higher harmonics of the THz fundamental.

19th International Conference on Ultrafast Phenomena, 2014

ABSTRACT The response of a LiNbO3 crystal to THz pulses in the nonperturbative regime is studied ... more ABSTRACT The response of a LiNbO3 crystal to THz pulses in the nonperturbative regime is studied by two-dimensional spectroscopy. Phase-resolved detection allows for separating the THz bulk photovoltaic effect from other nonlinear contributions.

Physical Review Letters, 2014

The terahertz (THz) response of the ferroelectric prototype material lithium niobate (LiNbO 3) is... more The terahertz (THz) response of the ferroelectric prototype material lithium niobate (LiNbO 3) is studied in the nonperturbative regime of light-matter interaction. Applying two-dimensional THz spectroscopy with few-cycle pulses of an amplitude E ≈ 100 kV=cm and a center frequency of 2 THz, we dissect the overall nonlinear response into different orders in the electric field. The underlying nonlinear current is of interband character and consists of a strong low-frequency shift current (SC) and higher harmonics of the THz fundamental. The SC component originates from the lack of inversion symmetry and the strong interband decoherence for long electron trajectories in k space as shown by theoretical calculations.

The work presented in this thesis is motivated by three interconnected objectives: to study new c... more The work presented in this thesis is motivated by three interconnected objectives: to study new coherent sources of high-field ultra-broadband terahertz (THz) pulses for multi-octave THz spectroscopy, to develop novel techniques in the frequency range 0.1-30 THz capable of accessing single and multiple quantum coherences off-resonantly under nonperturbative conditions and to understand their dynamics on their fundamental ultrafast time scale. For the first time, the coherent generation of ultrashort MV/cm field pulses with a spectral content covering the frequency range 0.1-30 THz continuously is demonstrated in the organic crystal DSTMS by non-phase-matched difference frequency mixing within the broad spectrum of femtosecond near infrared pulses. Coherent multidimensional terahertz spectroscopy (CMTS) has developed into an important technique for, e.g, driving low-energy excitations in both bulk and nanostructured semiconductors and monitoring their coherent dynamics. A novel CMTS technique employing three phase-locked inter-delayed THz pulses is implemented. It relies on a collinear interaction of the pulses with a sample, so that different contributions to the nonlinear signal are emitted in the same direction, and thus can be measured all at once. Phase-resolved detection by electro-optic sampling allows for measuring amplitude and absolute phase of the nonlinear signal, thereby enabling to investigate the evolution of coherent interactions between quantum excitations in real time. In CMTS, the nonlinear signal is dissected into the distinct nonlinear contributions in the corresponding multidimensional frequency domain. This novel technique is applied to study the nonlinear off-resonant response of two undoped bulk semiconductors, the wide-bandgap ferroelectric lithium niobate (LiNbO3, Eg = 1000 THz) and the narrow-bandgap indium antimonide (InSb, Eg = 40 THz), in the nonperturbative regime. In LiNbO3, the nonlinear signal is generated by a femtosecond nonlinear shift current (SC), which is a distinctive characteristic of the bulk photovoltaic effect. The SC stems from the lack of inversion symmetry and the ultrafast dephasing of the field-induced interband coherent polarization due to a sufficiently high decoherence rate, which enables tunneling of electrons from the valence to the conduction band. In InSb, the nonlinear signal is caused by the coherent response on both the two-phonon and two-photon interband excitations. The impulsive generation of the two-phonon coherent polarization is enhanced by the large interband transition dipole of InSb, resulting in much larger polarization amplitudes than in the regime of linear response. In the future, CMTS could be applied for example to gain further insight in magnetic multi-quantum coherences of materials with long range magnetic order. Furthermore this novel concept can be easily implemented into two-colour nonlinear spectroscopic experiments.