A simple and efficient protocol is developed for the in situ generation of highly monodisperse and small (2−3 nm) silver nanoparticles in poly(vinyl alcohol) film and the fabrication of their free-standing films. Efficient optical limiting with these nanoparticle-embedded polymer thin films is demonstrated.

We propose for the first time an E. coli bacteria sensor based on the evanescent field of the fundamental mode of a suspended-core terahertz fiber. The sensor is capable of E. coli detection at concentrations in the range of 10 4-10 9 cfu/ml. The polyethylene fiber features a 150 µm core suspended by three deeply sub-wavelength bridges in the center of a 5.1 mm-diameter cladding tube. The fiber core is biofunctionalized with T4 bacteriophages which bind and eventually destroy (lyse) their bacterial target. Using environmental SEM we demonstrate that E. coli is first captured by the phages on the fiber surface. After 25 minutes, most of the bacteria is infected by phages and then destroyed with ~1m-size fragments remaining bound to the fiber surface. The bacteria-binding and subsequent lysis unambiguously correlate with a strong increase of the fiber absorption. This signal allows the detection and quantification of bacteria concentration. Presented bacteria detection method is label-free and it does not rely on the presence of any bacterial "fingerprint" features in the THz spectrum. "Thin-film sensing with planar terahertz metamaterials: sensitivity and limitations," Opt. Express 16, 1786-1795 (2008).

Waveguide terahertz time-domain spectroscopy is used to demonstrate the narrowing of vibrational lines for a thin polycrystalline film of 1,2-dicyanobenzene in a parallel plate metal waveguide. When compared to corresponding linewidths for 1,2-dicyanobenzene in a pellet sample at room temperature, the linewidths for the waveguide film are found to be significantly sharper. For measurements near 77 K, a dramatic line narrowing is observed for the waveguide film, yielding linewidths as much as five times sharper than found in the pellet. These effects are attributed to much smaller inhomogeneous broadening in the waveguide film and result in a more informative spectrum. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2405884͔A standard method for measuring terahertz ͑THz͒ spectra of organic solids is to form a pellet that contains a small quantity of the target solid dispersed in a much larger quantity of a low absorbance host material such as polyethylene. A wide range of organic and bio-organic materials in the form of such pellets has been studied in the THz region, including explosives materials 1 and their by-products, 2 conjugated oligomers, 3 amino acids, 4 and DNA. 5 While much spectroscopic information can be obtained from pellet samples, in many cases their THz spectra exhibit broad line shapes due to intrinsic line broadening mechanisms, and to effects related to pellet preparation. 6 A promising method for investigating the THz properties of organic solids is through the use of THz waveguides. 7-9 For waveguide terahertz timedomain spectroscopy ͑THz-TDS͒ the parallel plate metal waveguide ͑PPWG͒ is particularly useful because of the nondispersive and low loss propagation for the transverse electromagnetic mode. 7,9 The high detection sensitivity that is possible with the PPWG has recently been demonstrated by the THz-TDS characterization of nanometer thick water layers. 9 In addition, the PPWG is easily opened, and the exposed flat inner surfaces are ideal for coating with a thin film of the investigated material.In this letter we demonstrate the application of a PPWG to the terahertz TDS characterization of a solid organic thin polycrystalline film. The material 1,2-dicyanobenzene ͑12DCB͒ is studied because of its relatively strong vibrational lines in the THz region. 10 The major finding of this study is that the THz spectrum of a waveguide polycrystalline film can display significantly sharper vibrational linewidths than found in the corresponding THz spectrum of the pellet. For measurements performed near 77 K, a dramatic line narrowing was observed for the waveguide film, yielding linewidths as much as five times sharper than found in the pellet sample. The line narrowing effect revealed additional vibrational structure in the waveguide film which is not apparent in the pellet. We attribute the line narrowing to a reduction of inhomogeneous broadening for the 12DCB polycrystalline film drop cast on the metal waveguide surface. We also demonstrate the high sensitivity of the waveguide techniq...

We have characterized the terahertz (THz) vibrational spectroscopy of organic polycrystalline thin films using the new experimental technique of waveguide terahertz time domain spectroscopy (waveguide THz-TDS). The organic materials used in this study are tetracyanoquinodimethane (TCNQ) and 1,3-dicyanobenzene (13DCB). For each material, a thin film is cast onto one of the inner surfaces of a metal parallel plate waveguide (PPWG), followed by measurement of the low-frequency vibrational spectrum using waveguide THz-TDS. The vibrational spectra of the waveguide films are compared to corresponding vibrational spectra of standard pellet samples made by dispersing the organic solid in transparent polyethylene. We show how the waveguide films produce significantly narrower THz vibrational line shapes and reveal additional spectral lines that are obscured by inhomogeneous broadening effects in the pellet samples. When TCNQ waveguide films are cooled to 77 K, vibrational line widths as sharp as 25-30 gigahertz (0.83-1.0 cm(-1)) at the full width at half-maximum are observed, which are among the narrowest far-infrared line widths measured for this material. The origin of the line-narrowing effect for the waveguide films is the suppression of inhomogeneous broadening due to the planar ordering of the film on the waveguide surface. The TCNQ waveguide films are further characterized using optical microscopic evaluation to understand how film morphology affects the THz vibrational spectrum. X-ray diffraction is used to determine the orientation of the polycrystalline TCNQ films on the PPWG surface and to qualitatively explain the different vibrational line strengths observed for the ordered waveguide film relative to the random pellet.