Multiple-frequency terahertz pulsed sensing of dielectric films

Cunningham, J. E.; Wood, C.; Davies, A. G.; Tiang, C. K.; Tosch, P.; Evans, David A.; Linfield, E. H.; Hunter, I.C.; Missous, M.

doi:10.1063/1.2174101

Cited by 24 publications

(12 citation statements)

References 4 publications

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“…To increase sensitivity, filter structures are fabricated in the waveguide, the resonant frequency of which is sensitively dependent on the local dielectric environment in its proximity. By monitoring the detuning of the filter when overlaid materials are deposited, one can determine an unknown dielectric's permittivity at the filter frequency (provided the thickness can also be measured, which is a limitation of this technique) [9]. Several filter geometries have been studied for this application, including bandpass [10], ring resonators [11], and bandstop filters [12].…”

Section: On-chip Pulsed Terahertz Systemsmentioning

confidence: 99%

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Terahertz time domain spectroscopy - present and future modalities

Cunningham

Wood

Burnett

et al. 2007

2007 IEEE/MTT-S International Microwave Symposium

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We overview and compare free-space and onchip terahertz time-domain spectroscopy systems. Example spectroscopic applications are given for both types of system: vibrational spectroscopy of crystalline compounds for freespace systems, and assay of dielectric films for on-chip systems.Index Terms -Submillimeter wave imaging, Submillimeter wave propagation.I. THz TIME DOMAIN SPECTROSCOPY Terahertz time domain spectroscopy (THz-TDS) allows the optical properties of materials to be extracted in the frequency range -50 GHz to 30 THz. A typical system is shown in Fig. 1. It comprises a visible continuous-wave laser pumping a Ti:sapphire oscillator, which emits sub-100 fs duration pulses of near-infrared (NIR) radiation at a centre frequency of -800 nm, and at a repetition rate of -80 MHz. The laser pulse-train is split into two: one part is focused onto a semiconductor surface; low-temperaturegrown gallium arsenide (LT-GaAs) is widely chosen as this semiconductor since it has high carrier mobility and short (sub-picosecond) photoconductive carrier lifetime [1]. The photoexcited carriers (electrons and holes), generated at the semiconductor surface, are accelerated in the bias field created by a lateral antenna. This results in a transient dipole which radiates pulses with a broad spectral content extending well over 1 THz [2]. The THz pulses are then collected and collimated using off-axis parabolic mirrors, before being focused to a (diffraction-limited) spot size of a few hundred microns at the sample position. The frequency range of the pulses can be maximized by collecting them from the front surface of the LT-GaAs wafer, which reduces the effect of absorption within the GaAs substrate. When combined with a suitably fast laser system for excitation (-10 fs), this extends the usable bandwidth of the system to above 25 THz [3].After passing THz pulses through, or reflecting them from, the sample surface, the modified THz pulses are collected and collimated, before being focused onto a detection crystal. The second NIR beam is given a variable time-delay using a retroreflector mounted on a linear translation stage, and is also focused onto the detection crystal. Two different methods of detection can be employed. The first, photoconductive detection, uses a similar scheme to the emitter, based on an antenna deposited on LT-GaAs; the incident THz radiation acts as a bias field for the carriers generated by the second NIR beam beam strip-line off-axis splitter antenna parabolics Fig. 1. Schematic of typical THz-TDS system, showing the paths of the NIR (dark grey lines) and THz (light grey)beams. Electrooptic detection is achieved using a ZnTe crystal, Wollaston prism, and photodiodes as described in the text.at the detector, and the resulting current is measured as a function of time delay applied to the NIR beam. In this way, it is possible to map the time-evolution of the electric field which constitutes the THz pulse. A second detection mechanism exploits the ac Pockels effect in an electro-optic crystal such as zinc ...

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Section: On-chip Pulsed Terahertz Systemsmentioning

confidence: 99%

“…We have performed measurements of overlaid dielectric material using a dual bandstop-filter systems (full geometry is given in [9]), recording the frequency shift of each filter when different 1698 K.X,'.] GaP detector -incident pulse transmitted pulse thicknesses of dielectric material are deposited (see Fig.…”

Section: On-chip Pulsed Terahertz Systemsmentioning

confidence: 99%

Terahertz time domain spectroscopy - present and future modalities

Cunningham

Wood

Burnett

et al. 2007

2007 IEEE/MTT-S International Microwave Symposium

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“…Such TFMSLs may be regarded as the terahertz counterpart to conventional larger microstriplines used in microwave integrated circuits. They are now increasingly used as sensing elements for biomolecule detection at THz frequencies [56][57][58][59]. For TFMSLs, BCB is a very popular dielectric material, since in addition to having a relatively low dielectric loss tangent, it provides also chemical robustness.…”

Section: Application Examples: Thz Waveguide Probe-tip and Antenna Dmentioning

confidence: 99%

Coherent and ultrafast optoelectronics in III–V semiconductor compounds

Först

Nagel

Awad

et al. 2007

Physica Status Solidi (b)

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PACS 63. 22.+m, 71.55.Eq, 72.20.Jv, 78.47.+p III -V compound semiconductors offer a fascinating multitude of phenomena which have become accessible via ultrafast time-resolved spectroscopy. Coherent vibronic and electronic dynamics are prepared by excitation with taylored femtosecond laser pulses. The analysis of their temporal dephasing or decay provides deep insights into the interaction between electronic and vibronic degrees of freedem and the surrounding bath in high purity quantum structures. In contrast to coherent electronic or vibronic states, deliberately introduced growth defects can be used to drastically shorten the lifetime of optically excited carriers. Sub-picosecond carrier lifetimes open the possibility to realize ultrafast saturable absorbers and optoelectronic transducer elements. They are particularly important as key elements in THz technology, such as efficient THz emitters, detectors, and for on-chip THz technology. This paper summarizes the most distinguished results relevant in the context of ultrafast optoelectronics and THz technology obtained in close collaboration with the Paul-Drude-Institute Berlin over the past decade.

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“…Introduction: Optoelectronic on-chip terahertz (THz) sub-systems (also transceivers) bear great potential, especially within spectroscopy/ biosensing [1] and dielectric-material characterisation [2]. Opticallydriven THz spectrometers on the basis of coplanar waveguides (CPWs) [3] and microstrip lines [4] have been successfully demonstrated in the past.…”

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confidence: 99%

Continuous-wave single-sampling-point characterisation of optoelectronic on-chip terahertz transceiver

et al. 2009

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Fast electro-optic modulation of the terahertz phase, single-samplingpoint lock-in detection and the use of interdigitated-finger photomixers improve the dynamic range of the transceiver by several orders of magnitude compared with standard chopping techniques. This allowed the frequency range of the continuous-wave on-chip terahertz transceiver to be extended beyond 1THz, which is roughly a factor of five improvement compared to previous reports.

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Multiple-frequency terahertz pulsed sensing of dielectric films

Abstract: A tunable universal terahertz filter using artificial dielectrics based on parallel-plate waveguides Appl. Phys. Lett. 97, 131106 (2010); 10.1063/1.3495994Electromagnetic simulation of terahertz frequency range filters for genetic sensing

Cited by 24 publications

References 4 publications

Terahertz time domain spectroscopy - present and future modalities

Terahertz time domain spectroscopy - present and future modalities

Coherent and ultrafast optoelectronics in III–V semiconductor compounds

Continuous-wave single-sampling-point characterisation of optoelectronic on-chip terahertz transceiver

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