THz saturable absorption in turbostratic multilayer graphene on silicon carbide

Abstract

We investigated the room-temperature Terahertz (THz) response as saturable absorber of turbostratic multilayer graphene grown on the carbon-face of silicon carbide. By employing an open-aperture z-scan method and a 2.9 THz quantum cascade laser as source, a 10% enhancement of transparency is observed. The saturation intensity is several W/cm2, mostly attributed to the Pauli blocking effect in the intrinsic graphene layers. A visible increase of the modulation depth as a function of the number of graphene sheets was recorded as consequence of the low nonsaturable losses. The latter in turn revealed that crystalline disorder is the main limitation to larger modulations, demonstrating that the THz nonlinear absorption properties of turbostratic graphene can be engineered via a proper control of the crystalline disorder and the layers number.

Terahertz saturable absorbers from liquid phase exfoliation of graphite

“…The α S coefficient is the largest reported to date for any spectral range172528. The saturation intensity values are in agreement with what achieved in the far-IR30 in presence of optical pulses much longer (2 μs) than the demarcation time scale set by the carrier-phonon scattering time (∼150 fs as derived by pump-probe)2066. Under the above experimental conditions charge carrier distribution develops into quasi-equilibrium within the optical pulse duration.…”

“…To investigate the THz-induced non-linear absorption properties of GSAs we use the open-aperture z -scan technique30. The 3.5 THz radiation generated by a QCL (single-plasmon waveguide)7 is focused at normal incidence, by using two closely positioned convergent lenses with 3 cm focal length f (Fig.…”

“…Mode-locked lasers exploiting graphene SAs (GSAs) have been demonstrated at frequencies from the visible to the IR242526272829. To the best of our knowledge, the only reported THz SA using multi-layer graphene grown on the carbon-face of silicon carbide30 showed a maximum absorption modulation∼10%, too low to alter the intra-cavity field of existing THz QCLs30. Furthermore, its intracavity integration within the 10–14 μm active region of THz semiconductor sources is hindered by the device architecture/material geometry6.…”

Coherent absorption of light by graphene and other optically conducting surfaces in realistic on-substrate configurations

“…The system consisted in multilayer graphene grown via chemical vapor deposition (CVD) on the carbon-terminated surface of an insulating silicon carbide substrate (4H-SiC (000-1)); more details on the growth parameters are reported elsewhere. 18 The graphene is composed of 30 ± 5 electronically decoupled layers, as confirmed by the single-Lorentzian shape of the 2D peak in the Raman spectrum (Fig. 4(a)).…”

“…A technique for nondestructive wafer scale diagnosis of optically conducting surfaces is hence enabled. This technique has a remarkable potential for instance when considering multilayer graphene sheets, whose thickness determination is necessary for applications in optics [17][18][19][20] and electronics. [21][22][23] Currently, several methods are used for estimating the multilayer graphene thickness.…”