Single-shot terahertz time-domain spectrometer using 1550 nm probe pulses and diversity electro-optic sampling.

Classical terahertz spectroscopy usually requires the use of Fourier transform or Time-Domain Spectrometers. However, these classical techniques become impractical when using recent high peak power terahertz sources - based on intense lasers or accelerators - which operate at low repetition rate. We present and test the design of a novel Time-Domain Spectrometer, that is capable of recording a whole terahertz spectrum at each shot of the source, and that uses a 1550 nm probe fiber laser. Single-shot operation is obtained using chirped-pulse electro-optic sampling in Gallium Arsenide, and high bandwidth is obtained by using the recently introduced Diversity Electro-Optic Sampling (DEOS) method. We present the first real-time measurements of THz spectra at the TeraFERMI Coherent Transition Radiation source. The system achieves 2.5 THz bandwidth with a maximum dynamic range reaching up to 25 dB. By reducing the required measurement time from minutes to a split-second, this strategy dramatically expands the application range of high power low-repetition rate THz sources.

Terahertz Tuning of Dirac Plasmons in Bi_{2}Se_{3} Topological Insulator.

Light can be strongly confined in subwavelength spatial regions through the interaction with plasmons, the collective electronic modes appearing in metals and semiconductors. This confinement, which is particularly important in the terahertz spectral region, amplifies light-matter interaction and provides a powerful mechanism for efficiently generating nonlinear optical phenomena. These effects are particularly relevant in graphene and topological insulators, where massless Dirac fermions show a naturally nonlinear optical behavior in the terahertz range. The strong interaction scenario has been considered so far from the point of view of light. In this Letter, we investigate instead the effect of strong interaction on the plasmon itself. In particular, we will show that Dirac plasmons in Bi_{2}Se_{3} topological insulator are strongly renormalized when excited by high-intensity terahertz radiation by displaying a huge red-shift down to 60% of its characteristic frequency. This opens the road towards tunable terahertz nonlinear optical devices based on topological insulators.

Coherent THz Emission Enhanced by Coherent Synchrotron Radiation Wakefield.

We demonstrate that emission of coherent transition radiation by a ∼1 GeV energy-electron beam passing through an Al foil is enhanced in intensity and extended in frequency spectral range, by the energy correlation established along the beam by coherent synchrotron radiation wakefield, in the presence of a proper electron optics in the beam delivery system. Analytical and numerical models, based on experimental electron beam parameters collected at the FERMI free electron laser (FEL), predict transition radiation with two intensity peaks at ∼0.3 THz and ∼1.5 THz, and extending up to 8.5 THz with intensity above 20 dB w.r.t. the main peak. Up to 80-µJ pulse energy integrated over the full bandwidth is expected at the source, and in agreement with experimental pulse energy measurements. By virtue of its implementation in an FEL beam dump line, this work promises dissemination of user-oriented multi-THz beamlines parasitic and self-synchronized to EUV and x-ray FELs.

Voided urinary cytology in bladder cancer: is it time to review the indications?

OBJECTIVES: The sensitivity of voided urinary cytology has been reported as very low. In this study, we investigated the sensitivity and clinical utility of voided urinary cytology in the detection of various grades and stages of transitional cell carcinoma (TCC) of the bladder compared with the urinary nuclear matrix protein-22 (NMP-22) qualitative assay. METHODS: From March 2004 to April 2006, all patients with TCC of the bladder receiving follow-up care and those presenting with gross hematuria were enrolled in this prospective study. These patients underwent urinary cytologic examination and NMP-22 qualitative assay. The diagnosis, determined from the cystoscopy findings and biopsy findings of the suspicious lesion, was accepted as the reference standard. RESULTS: A total of 196 patients were enrolled in this study, of whom 127 patients had previously been diagnosed with bladder TCC and 69 were presenting for investigation of gross hematuria. A total of 52 cases of bladder TCC were diagnosed. The overall sensitivity of voided urine cytology and NMP-22 assay was 21.1% and 67.3%, respectively (P <0.001). The sensitivity of urinary cytology and urinary NMP-22 for well-differentiated tumors was 9.5% and 52.4%, respectively, and was 18.1% and 77.3%, respectively (P <0.001), in moderately differentiated tumors. The overall specificity of urinary cytology for TCC of the bladder was 98.6% and was greater than the specificity of NMP-22 (80.5%). CONCLUSIONS: The results of our study suggest that urinary cytology has a very low sensitivity and can be omitted in favor of NMP-22 in the follow-up of low-grade superficial bladder TCC.