The Performance of Graphene-Enhanced THz Grating: Impact of the Gold Layer Imperfectness.

We report the performance of a graphene-enhanced THz grating fabricated by depositing a gold layer on the femtosecond micromachined SiO substrate. The morphology of the gold plated patterned substrate was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM), while the quality of the chemical vapor deposition (CVD) graphene was evaluated by Raman spectroscopy. The electromagnetic (EM) response of the metasurface comprising the graphene sheet and the gold plated substrate was studied by THz time domain spectroscopy in the 100 GHz-1 THz frequency range.

The Surface Photogalvanic and Photon Drag Effects in Ag/Pd Metal-Semiconductor Nanocomposite.

We performed the investigation of the polarization-sensitive photocurrent generated in silver-palladium metal-semiconductor nanocomposite films under irradiation with nanosecond laser pulses at the wavelength of 2600 nm. It is shown that in both the transverse and the longitudinal configuration, the surface photogalvanic (SPGE) and photon drag effects (PDE) contribute to the observed photocurrent. However, the temporal profile of the transverse photocurrent pulse is monopolar at any polarization and angle of incidence, while the temporal profile of the longitudinal photocurrent pulse depends on the polarization of the excitation beam.

Interaction of polarization-sensitive surface photocurrents in semitransparent CuSe/Se film.

We demonstrate that the transverse polarization-sensitive photoresponse of the CuSe/Se nanocomposite film deposited on a transparent substrate depends on whether the film is irradiated from the air side or substrate side. In particular, the nanosecond photocurrent pulse is either bipolar or unipolar pulse depending on which interface beam hits first. The observed phenomenon can be described in terms of the interplay between counter-propagating photocurrents generated at the air/nanocomposite and substrate/nanocomposite interfaces due to the surface photogalvanic effect.

Interplay of the photon drag and the surface photogalvanic effects in the metal-semiconductor nanocomposite.

Photon drag effect (PDE) and surface photogalvanic effect (SPGE) can be observed in centrosymmetric media and manifest themselves in photocurrents, the magnitude and polarity of which depend on wavevector and polarization of the excitation laser beam. PDE photocurrent originates from the transfer of the photon momentum to a free charge carrier, while SPGE photocurrent is due to diffuse scattering of the photoexcited carriers in the subsurface layer. However, despite the different underlying physical mechanisms, these photocurrents have almost indistinguishable dependencies on the polarization and the angle of incidence of the excitation laser beam.

Femtosecond Circular Photon Drag Effect in the Ag/Pd Nanocomposite.

We report on the observation of the helicity-dependent photoresponse of the 20-μm-thick silver-palladium (Ag/Pd) nanocomposite films. In the experiment, 120 fs pulses of Ti:S laser induced in the film an electric current perpendicular to the incidence plane. The photoinduced current is a linear function of the incident beam power, and its sign depends on the beam polarization and angle of incidence.