We discuss the unique possibilities stemming from exploiting the exotic properties of artificial metasurfaces designed for operation in the THz regime. We mainly focus on graphene based metasurfaces acting as modulators for the THz regime. Graphene exhibits unique optical properties particularly in the THz spectrum, where it predominantly exhibits a Drude-like response. Here we present that ultrafast modulation response in a graphene thin film absorber which can be assessed with use of a broadband THz time-domain-spectroscopic system (THz-TDS) in an IR pump-THz probe configuration. The simple scheme of the absorber can be used as a platform for ultrafast flat optics and metasurfaces.
In this article, a novel gas sensor platform has been studied. Several layers of graphene have been deposited on a SH-SAW, as a sensitive layer. Innovative methods of graphene solutions have been prepared in order to explore gas sensing applications. The real time detection measurement of the coated sensor under ethanol and humidity is presented. The adsorption of vapors leads to a frequency shift of 10.5 kHz and 22.7 kHz, at exposure of 100 ppm of ethanol and 6.22% of Relative Humidity, respectively. The experiments have been realized at room temperature; rapid response and recovery time were observed.
In this work, a systematic modeling study of polarization-induced internal field effects on the gain spectrum and threshold current density was performed. Two laser diodes of technological relevance: the In0.2Ga0.8N/GaN hexagonal nitride laser structures grown along the polar c-axis with internal field values up to 1.8MV/cm, and the In0.1Ga0.9As/Al0.15Ga0.85As (111)B laser structures with internal field values up to 100kV/cm were studied. The gain model is based on a self-consistent solution of Poisson-Schroedinger equations, and takes into account strain effects, free carrier screening, and the field dependence of gain and spontaneous emission rate.
In the nitride case, some of our main findings are: (a) assuming a laser structure with a single In0.2Ga0.8N/GaN quantum well (QW) and a modal gain Γg=30cm-1, the optimal QW width in terms of lowest current threshold is ≈3nm. (b) For a 3nm-wide QW and Γg=30cm-1, the presence of the internal field increases the threshold current over the zero-field value by at least a factor of three. This factor increases further for higher Γg's. (c) The optimal number of In0.2Ga0.8N/GaN QWs in the active region of a nitride laser with cavity losses of 30cm-1 is four, assuming homogeneous QW pumping.
In the arsenide case, however, our modeling shows that in some circumstances the internal field is beneficial and can lead to a substantial reduction of the threshold current, especially for cavities with low optical losses. This reduction was confirmed experimentally, by measuring systematically lower threshold current densities in In0.1Ga0.9As/Al0.15Ga0.85As (111)B laser diodes, compared to (100)-ones, carrying no internal field.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.