Sub-cycle slicing of phase-locked and intense mid-infrared transients

Abstract

We demonstrate sub-cycle manipulation of mid-infrared optical waveforms in the time domain. This goal is accomplished via efficient reflection at a semiconductor surface induced by femtosecond interband excitation. The ultrafast response of this process allows slicing of high-field multi-terahertz transients down to the single optical cycle. Ultrabroadband and phase-stable transients with peak amplitudes beyond 10 MV cm −1 are obtained, paving the way for efficient coherent control of light-matter interaction in the non-perturbative regime. The microscopic analysis of electron-hole plasma generation in germanium reveals a decisive role of two-photon absorption allowing efficient slicing up to midinfrared frequencies.

Tunability of the dielectric function of heavily doped germanium thin films for mid-infrared plasmonics

“…The detection is based on a lock-in scheme with mechanical modulation of the pump beam with a chopper wheel. The excitation fluence is kept at the moderate value of 500 µJ/cm 2 to minimize twophoton absorption that would directly create electronhole pairs at the L-point 61 . Figure 10-a sketches the pump-probe experiments in Ge.…”

XUV-driven plasma switch for THz: new spatio-temporal overlap tool for XUV–THz pump–probe experiments at FELs

“…The so-called plasma-switch, the transient change of optical constants in the visible (VIS) and near-infrared (NIR) spectral ranges by X-ray and XUV pulses, has been used for the temporal characterization of these pulses (Harmand et al, 2012;Gahl et al, 2008;Krupin et al, 2012;Riedel et al, 2013;Danailov et al, 2014). Transient changes of optical properties in the THz range, driven by femtosecond laser pulses, have been used for pickup of individual pulses from MHz trains at infrared free-electron lasers (FELs) (Schmidt et al, 2015) as well as for THz spectral shaping at table-top THz sources (Cartella et al, 2014;Mayer et al, 2014).…”

Terahertz shockwaves generated by a precise subcycle cut of the electric field

“…Generation of step-function field transients requires a new strategy for nonperturbative nonlinear optical interaction. To achieve ultrafast shaping of terahertz transients, we gate the reflectivity of a germanium (Ge) surface employed as an ultrafast active mirror [17]. A control pulse much shorter than one halfcycle of the terahertz field excites a dense electron-hole plasma, abruptly modifying the dielectric response of the semiconductor to behave like a metallic surface with high reflectivity.…”

“…A control pulse much shorter than one halfcycle of the terahertz field excites a dense electron-hole plasma, abruptly modifying the dielectric response of the semiconductor to behave like a metallic surface with high reflectivity. Previously, photoconductive switching has been applied to the generation of multicycle pulses from CO 2 -lasers [18,19], free electron lasers [20], and single-cycle pulses from phase-stable multicycle pulses in the mid-infrared [17]. Spectral shaping of strongly chirped terahertz transients also was achieved [21].…”

“…The reflected waveform shows a strong temporal asymmetry and is fundamentally different from the incident single cycle. Previous applications [17,21] of this technique are outperformed in rise time by the use of 8 fs short control pulses centered at a 600 nm wavelength. The nonlinear interaction between the terahertz waveform and the control pulse is mediated through a time-dependent electron-hole plasma acting as a dynamical nonlinearity, giving rise to a new kind of wave mixing outside the perturbative interaction regime.…”