Time-resolved broadband analysis of slow-light propagation and superluminal transmission of electromagnetic waves in three-dimensional photonic crystals

A time-resolved analysis of the amplitude and phase of THz pulses propagating through three-dimensional photonic crystals is presented. Single-cycle pulses of THz radiation allow measurements over a wide frequency range, spanning more than an octave below, at and above the bandgap of strongly dispersive photonic crystals. Transmission data provide evidence for slow group velocities at the photonic band edges and for superluminal transmission at frequencies in the gap. Our experimental results are in good agreement with finite-difference-time-domain simulations.Comment: 7 pages, 11 figure

Low cost thermopile detectors for THz imaging and sensing

We evaluate 2 thermopile sensors as convenient detector options for a modern integrated THz imaging system. Both a commercial single pixel device and a 32 times 32 pixel FPA are utilized in a simple setup with a single optical element to achieve an outstanding resolution and SNR performance. Either a cryogenically cooled quantum cascade laser (QCL) or a room temperature electronic THz multiplier chain is used as source

Low cost thermopile detectors for THz imaging and sensing

We evaluate 2 thermopile sensors as convenient detector options for a modern integrated THz imaging system. Both a commercial single pixel device and a 32 times 32 pixel FPA are utilized in a simple setup with a single optical element to achieve an outstanding resolution and SNR performance. Either a cryogenically cooled quantum cascade laser (QCL) or a room temperature electronic THz multiplier chain is used as source

Optically switchable mirrors for surface plasmon polaritons propagating on semiconductor surfaces

6 págs.; 6 figs. ; PACS number s : 73.20.Mf, 42.79.Dj, 42.25.Bs, 78.68. mUsing terahertz time-domain spectroscopy measurements, we demonstrate optical switching of the transmission of terahertz surface plasmon polaritons (SPPs) propagating on an indium antimonide surface through Bragg scattering on grooves. The switching of the in-plane transmission of SPPs through the grooves is mediated by the modification of the stop-gap width due to changes of the surface plasmon characteristics, which are induced by the optical generation of charge carriers. The use of a semiconductor surface allows us to achieve switching at extremely low excitation powers. The experimental data can be quantitatively reproduced using rigorous numerical calculations for surfaces with varying dielectric function. Such an optically active device opens further possibilities for low-frequency surface plasmon optics. © 2006 The American Physical Society.Financial support from the European Union through the projects Interaction Grant No. HPRN-CT-2002-00206 and Metamorphose Grant No. NMP3-CT-2004-500252, and from the Deutsche Forschungsgemeinschaft. The work of J.G.R. was supported in part by the “Stichting voor Fundamenteel Onderzoek der Materie FOM,” which is financially supported by the “Nederlandse Organisatie voor Wetenschappelijk Onderzoek NWO.” The work of J.A.S.G. was supported in part by the Spanish Comunidad de Madrid Grants No. GR/MAT/0425/ 2004 and MICROSERES and MEC Grants No. FIS2006- 07894 and No. FIS2004-0108.Peer Reviewe

Transmission of THz radiation through InSb gratings of sub-wavelength apertures

We demonstrate the extraordinary transmission of terahertz THz radiation through gratings of subwavelength apertures structured in indium antimonide InSb. This transmission can be attributed to the tunneling of surface plasmons polaritons which are excited in semiconductors at THz frequencies. By thermally controlling the permittivity of the grating the transmittance increases by more than one order of magnitude. This increase might be associated to the larger the skin depth in InSb at low temperatures, nwhich gives rise to a larger effective size of the apertures

Observation of Bloch oscillations in a semiconductor superlattice

We investigate the polarization decay in biased superlattices with transient degenerate four-wave mixing. The signals have a strong periodic modulation in the field regime where the cw optical spectra show the transitions of a Wannier-Stark ladder. The period of the oscillations is in excellent agreement with Bloch oscillation theory. The oscillation period can be tuned over a large range by varying the electric bias field in the superlattice

Investigation of Bloch oscillations in a GaAs/AlGaAs superlattice by spectrally resolved four-wave mixing

We study Bloch oscillations (BO) in GaAs/AlGaAs superlattices with miniband widths of 19 and 38 meV at various lattice temperatures. In the time domain, we use transient degenerate four-wave mixing (FWM), while simultaneously monitoring the Wannier-Stark ladder (WSL) in the frequency domain by transmission spectroscopy. Spectrally resolved FWM measurements prove unambiguously that the oscillations in the decay of the FWM signal are due to quantum interference as expected for a wavepacket performing the BO

За кадры. 1957. № 18 (758)

День советской печатиВсесторонне освещать жизнь / Б. Титов, В. Ф. КуцепаленкоРассказывать о будущей работе / Л. С. Скрипов, Л. АверинаПопуляризировать лучший опыт / В. АндреевА что же делают кафедры? / А. ПетровИспользовать сатиру / А. ПеченкинЧитатели - нашей газете / А. Марус, Н. Петренко, ВолковаИтоги смотра стенных газет / В. АндреевНа первомайской демонстрацииУтро мая / А. НазаровВеликий подвиг советского народа / В. ОвчинниковБлагодарность от университетаГоворит декан факультета / В. ВладимировНа кафедре сопротивления материаловС конференции НСО / Р. УтцВесной / Н. Анастасье

Broadband terahertz and sub-terahertz CMOS modules for imaging and spectroscopy applications

Miniaturized, low cost and easy to use devices able to carry out analysis in the chemical or biomedical domains could extend the use of imaging and spectroscopic techniques, now widely exploited in the professional sector, to applications in the consumer market or in the domain of point-of-care diagnostics. While a number of advanced techniques based on infrared or optical radiation show great potential for use in highly sensitive biosensors, the use of another part of the electromagnetic spectrum, the so called terahertz band (100 GHz – 3 THz), promise the creation of new devices with the capability of carrying out spectroscopy and imaging at the same time, even on samples located in an opaque package. In this paper we present our results demonstrating the possibility to create a miniaturized terahertz imaging and spectroscopy system that can be mass produced at low cost using well-known and robust commercial technologies such as CMOS or 3D chip-scale packaging (3D-CSP). The presented device is able to produce and detect a broadband signal from 20 GHz to 280 GHz with a dynamic range of 44 dB at 140 GHz