Optically Implemented Broadband Blueshift Switch in the Terahertz Regime

Cataloged from PDF version of article.We experimentally demonstrate, for the first time, an optically implemented blueshift tunable metamaterial in the terahertz (THz) regime. The design implies two potential resonance states, and the photoconductive semiconductor (silicon) settled in the critical region plays the role of intermediary for switching the resonator from mode 1 to mode 2. The observed tuning range of the fabricated device is as high as 26% (from 0.76 THz to 0.96 THz) through optical control to silicon. The realization of broadband blueshift tunable metamaterial offers opportunities for achieving switchable metamaterials with simultaneous redshift and blueshift tunability and cascade tunable devices. Our experimental approach is compatible with semiconductor technologies and can be used for other applications in the THz regime

High‐Operating‐Temperature Direct Ink Writing of Mesoscale Eutectic Architectures

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136318/1/adma201604778.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136318/2/adma201604778-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136318/3/adma201604778_am.pd

Enhancement of terahertz photoconductive antenna operation by optical nanoantennas

Photoconductive antennas are promising sources of terahertz radiation that is widely used for spectroscopy, characterization, and imaging of biological objects, deep space studies, scanning of surfaces, and detection of potentially hazardous substances. These antennas are compact and allow for generation of both ultrabroadband pulses and tunable continuous wave terahertz signals at room temperatures, with no need for high-power optical sources. However, such antennas have relatively low energy conversion efficiency of femtosecond laser pulses or two close pump wavelengths (photomixers) into the pulsed and continuous terahertz radiation, correspondingly. Recently, an approach to solving this problem that involves known methods of nanophotonics applied to terahertz photoconductive antennas and photomixers has been proposed. This approach comprises the use of optical nanoantennas for enhancing the absorption of pump laser radiation in the antenna gap, reducing the lifetime of photoexcited carriers, and improving the antenna thermal efficiency. This Review is intended to systematize the main results obtained by researchers in this promising field of hybrid optical-to-terahertz photoconductive antennas and photomixers. We summarize the main results on hybrid THz antennas, compare the approaches to their implementation, and offer further perspectives of their development including an application of all-dielectric nanoantennas instead of plasmonic ones

Structural and dynamics studies of small molecules and clusters via crossed beam scattering experiments

In order to perform in a more sophisticated manner, structural and dynamics studies of free clusters and molecules, a new experimental method was developed, based on the well known crossed-beam scattering technique combined with modern imaging technologies. This novel method facilitates measurements of differential collision cross-sections and double differential cross-sections and therefore gives valuable information on the dynamics of the colliding species and their structure. The investigation of simple collision systems (Ta+-Ne, N2, CO, C2H2) with this method were performed in the non-adiabatic regime (impulsive collisions) which is a not yet extensively explored region and where the colliding species can be treated as hard bodies. The measurements of the angular dependence of the differential crosssection reveal that the potential energy, which governs the ion-atom interaction, in the specific energy regime, exhibits a Coulombic repulsive behavior of the empirical Universal form. Moreover, the energy loss spectra recorded in ion-molecule collisions, indicate that energy is transferred both in rotational and vibrational degrees of freedom of the molecules. The simple hard-potential model was employed in the theoretical analysis of this inelastic process. By means of this model, we determined the equipotential surface, which characterize the interaction of the colliding species and subsequently the structure of the molecule in the specific collision energy. This novel experimental technique in conjunction with simple theoretical models is a promising new tool for static (structure) and dynamics (fragmentation, energy transfer, reactivity, etc.) studies of gas-phase molecules and clusters.Με στόχο την μελέτη της δομής και της δυναμικής μορίων και συστάδων (clusters) σε ελεύθερη κατάσταση, αναπτύχθηκε μία νέα πειραματική μέθοδος, η οποία συνδυάζει την γνωστή τεχνική σκέδασης κάθετων μοριακών δεσμών (crossed beam scattering experiments) με σύγχρονες τεχνικές απεικόνισης (imaging). Η μέθοδος αυτή δίνει την δυνατότητα μετρήσεων τόσο της διαφορικής ενεργού διατομής των σωματιδίων που λαμβάνουν μέρος στη κρούση, όσο και της διπλής διαφορικής ενεργού διατομής, παρέχοντας έτσι λεπτομερείς πληροφορίες για την δυναμική του συστήματος κρούσης που μελετάται και κατ’ επέκταση για την γεωμετρική δομή των σωματιδίων που λαμβάνουν μέρος σε αυτήν. Εφαρμόζοντας την μέθοδο σε πρότυπα συστήματα κρούσης μελετήθηκαν ο μηχανισμός ελαστικής σκέδασης (κρούση ιόντος-ατόμου, Ta+- Ne) και μηχανισμοί ανελαστικής σκέδασης (κρούση ιόντος-μορίου, Ta+-N2, CO και C2H2) στην όχι εκτενώς μελετημένη περιοχή μη-αδιαβατικών διαδικασιών (impulsive collisions). Από τα αποτελέσματα της μελέτης της ολικής γωνιακής κατανομής της σκέδασης, βρέθηκε ότι η δυναμική καμπύλη που χαρακτηρίζει την αλληλεπίδραση ιόντος-ατόμου, για τις σχετικά υψηλές ενέργειες όπου πραγματοποιήθηκαν τα πειράματα, είναι της μορφής ενός απωστικού δυναμικού Coulomb τύπου Universal. Επιπλέον, βρέθηκε ότι ο κύριος μηχανισμός που λαμβάνει χώρα κατά την κρούση ιόντος-μορίου είναι η μεταφορά ενέργειας στους εσωτερικούς βαθμούς ελευθερίας και μάλιστα με ιδιαίτερα μεγάλο ποσοστό μεταφοράς ενέργειας τόσο στην δόνηση όσο και στην περιστροφή του μορίου. Τα θεωρητικά μοντέλα κλασσικής φυσικής (το μοντέλο του παρατηρητή και το μοντέλο hard-potential) που εφαρμόστηκαν για την ερμηνεία του ανελαστικού μηχανισμού που παρατηρήθηκε κατά την κρούση ιόντος με μόριο, δείχνουν να αναπαράγουν αρκετά ικανοποιητικά τα πειραματικά αποτελέσματα. Βάση των μοντέλων αυτών προσδιορίστηκε η ισοδυναμική επιφάνεια αλληλεπίδρασης του εκάστοτε συστήματος κρούσης υποδεικνύοντας κατ’ επέκταση τη γεωμετρική δομή του μορίου που λαμβάνει μέρος στην αυτήν. Από την μελέτη και ερμηνεία της σκέδασης των σωματιδίων της πρωταρχικής μοριακής δέσμης ιόντων τανταλίου Ta+ που καταγράφτηκε κατά την κάθετη κρούση της με μία δευτερεύουσα δέσμη (ατόμων Ne ή μορίων N2, CO, C2H2) καταδεικνύεται ότι η νέα αυτή πειραματική μέθοδος σε συνδυασμό με απλά θεωρητικά μοντέλα μπορεί να δώσει αρκετά λεπτομερείς πληροφορίες τόσο για την δυναμική όσο και για την γεωμετρική δομή μορίων

Comparative Assessment of Affinity-Based Techniques for Oriented Antibody Immobilization towards Immunosensor Performance Optimization

Immunosensor sensitivity and stability depend on a number of parameters such as the orientation, the surface density, and the antigen-binding efficiency of antibodies following their immobilization onto functionalized surfaces. A number of techniques have been developed to improve the performance of an immunosensor that targets one or both of the parameters mentioned above. Herein, two widely employed techniques are compared for the first time, which do not require any complex engineering of neither the antibodies nor the surfaces onto which the former get immobilized. To optimize the different surface functionalization protocols and compare their efficiency, a model antibody-antigen system was employed that resembles the complex matrices immunosensors are frequently faced with in real conditions. The obtained results reveal that protein A/G is much more efficient in increasing antibody loading onto the surfaces in comparison to boronate ester chemistry. Despite the fact, therefore, that both contribute towards the orientation-specific immobilization of antibodies and hence enhance their antigen-binding efficiency, it is the increased antibody surface density attained with the use of protein A/G that plays a critical role in achieving maximal antigen recognition

Nonlinear imaging and THz diagnostic tools in the service of cultural heritage

We present the use of novel nonlinear imaging, terahertz time-domain spectroscopy and imaging as powerful diagnostic tools for studies of works of art. It is shown that nonlinear imaging offers precise in-depth information, while terahertz imaging can reveal hidden objects and uncover information on highly absorbing organic compounds whose visualization is difficult in other parts of the spectrumThe authors acknowledge Ms. K. Melessanaki for her expert assistance in the preparation of samples. This work was supported by the EU Marie Curie Excellence Grant “MULTIRAD” MEXT-CT-2006-042683. The EU FP7 Program “LASERLABEUROPE” (grant n◦ 228334) is also acknowledgedPostprint (published version

Functionalization of gold screen printed electrodes with bacterial photosynthetic reaction centers by laser printing technology for mediatorless herbicide biosensing

The development of an amperometric biosensor for herbicide detection, using bacterial reaction centers (RC) as biorecognition element, is presented. RC immobilization on gold screen printed electrodes was achieved by LIFT, a powerful physisorption-based immobilization technique that enhances the intimate contact between the protein and the electrode surface. As a result, stable photocurrents driven by direct electron transfer at the donor side were observed, both in the presence and in the absence of a quinone substrate in solution. The addition of quinone UQ(0) increased the photocurrents, while the UQ(0)-free system showed higher sensitivity to the herbicide terbutryn, a model inhibitor, acting as photocurrent attenuator. In spite of its simple design, the performances achieved by our mediatorless device are comparable or superior to those reported for analogous RC-based photoelectrochemical cells, in terms of both terbutryn sensing and photocurrent generation