The problem of glass relaxation under ambient conditions has intrigued scientists and the general public for centuries, most notably in the legend of flowing cathedral glass windows. Here we report quantitative measurement of glass relaxation at room temperature. We find that Corning® Gorilla® Glass shows measurable and reproducible relaxation at room temperature. Remarkably, this relaxation follows a stretched exponential decay rather than simple exponential relaxation, and the value of the stretching exponent (β=3/7) follows a theoretical prediction made by Phillips for homogeneous glasses.
We have applied techniques developed for IR waveguides to fabricate Ag/polystyrene (PS) -coated hollow glass waveguides (HGWs) for transmission of terahertz radiation. A loss of 0.95 dB/m at 119 microm (2.5 THz) was obtained for a 2 mm bore, 90 cm long Ag/PS HGW. We found that TE modes are supported in HGWs with thin PS films, while hybrid (HE) modes dominate when PS film thickness increases. The lowest losses are obtained for the thicker PS films and the propagation of the HE modes.
Cylindrical hollow-core metallic waveguides with an inner coating of polystyrene (PS) deposited over silver have losses less than 1dB/m for terahertz waves propagating in the HE11 mode. The thickness of the PS film determines whether the hybrid HE11 mode or the transverse TE01 mode exhibits the lowest loss. The mode selection is confirmed by studying mode profiles and transmission losses at 2.5 THz in waveguides with the dielectric coating thickness ranging from 0 to the optimum value of approximately 10 μm.
Propagation of terahertz waves in hollow metallic waveguides depends on the waveguide mode. Near-field scanning probe terahertz microscopy is applied to identify the mode structure and composition in dielectric-lined hollow metallic waveguides. Spatial profiles, relative amplitudes, and group velocities of three main waveguide modes are experimentally measured and matched to the HE 11 , HE 12 , and TE 11 modes. The combination of near-field microscopy with terahertz time-resolved spectroscopy opens the possibility of waveguide mode characterization in the terahertz band. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3126053͔Terahertz technology moves toward the component integration and it has become essential to develop terahertz waveguides with low transmission loss and small group velocity dispersion. Terahertz time-domain spectroscopy ͑terahertz-TDS͒ is potentially ideal for waveguide characterization. However, waveguide transmission spectra measured by terahertz TDS often contain periodic patterns, which are caused by the waveguide mode interference. 1 The loss and dispersion analysis in this case is difficult without knowledge of the waveguide mode composition.The mode structure and composition can be determined by imaging the output terahertz wave at the waveguide end. In particular, recently developed collection mode terahertz near-field microscopy has the potential to detect the output wave spatial profile. 2 The near-field technique is preferred because it gives the mode structure directly, contrary to the far-field imaging. In this letter, we discuss the application of terahertz near-field probe microscopy to determine the mode structure and composition in dielectric-lined hollow cylindrical metallic waveguides. [3][4][5] We consider a typical case of multimode propagation of a short terahertz pulse, when the output waveform becomes a superposition of all excited modes. By detecting the spatial distribution of the terahertz pulse field at the waveguide output, we attempt to determine profiles and relative weight of all excited modes experimentally. This knowledge is essential for the loss and dispersion characterization of individual modes and for waveguide design optimization.Identification of modes in the dielectric-lined hollow cylindrical metallic waveguides is of a particular interest because two modes have low-loss characteristics ͑1-3 dB/m at 2.5 THz͒. 4 The dominant mode is determined by the waveguide design ͑specifically, the dielectric layer thickness and the bore diameter͒. 6-9 The hybrid HE 11 mode is expected to be the lowest loss mode at ϳ1 -3 THz for a waveguide with a relatively thick ͑ϳ10 m͒ dielectric layer. However, the TE 01 mode with a doughnut shape electric field profile can be the dominant mode if the dielectric layer is thin ͑0-3 m͒. 4 Mode-specific dispersion characteristics in these waveguides have not been measured yet because several modes are often mixed in transmission experiments. 3,10 In the experimental setup a horizontally polarized broadband terahertz pulse ...
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