Optimization of photoconducting receivers for THz spectroscopy

Andrews, S. R.; Armitage, A.; Huggard, P. G.; Hussain, Amjad

doi:10.1088/0031-9155/47/21/305

Cited by 18 publications

(16 citation statements)

References 20 publications

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“…Using this assumption, we deduce an average THz power of 40 µW. To our knowledge, this value, supported by the large value of P/P probe , represents the strongest THz signal reported in the literature using a Ti:sapphire oscillator as a pump source (Cai et al 1997, Wu and Zhang 1997, McLaughlin et al 2000, Heyman et al 2001, Andrews et al 2002.…”

Section: Resultssupporting

confidence: 67%

A terahertz system using semi-large emitters: noise and performance characteristics

et al. 2002

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We have built a relatively simple, highly efficient, terahertz (THz) emission and detection system centred around a 15 fs Ti:sapphire laser. In the system, 200 mW of laser power is focused on a 120 µm diameter spot between two silverpaint electrodes on the surface of a semi-insulating GaAs crystal, kept at a temperature near 300 K, biased with a 50 kHz, ±400 V square wave. Using rapid delay scanning and lock-in detection at 50 kHz, we obtain probe laser quantum-noise limited signals using a standard electro-optic detection scheme with a 1 mm thick (110) oriented ZnTe crystal. The maximum THz-induced differential signal that we observe is P/P = 7 × 10 −3 , corresponding to a THz peak amplitude of 95 V cm −1 . The THz average power was measured to be about 40 µW, to our knowledge the highest power reported so far generated with Ti:sapphire oscillators as a pump source. The system uses off-the-shelf electronics and requires no microfabrication techniques.

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Section: Resultssupporting

confidence: 67%

A terahertz system using semi-large emitters: noise and performance characteristics

et al. 2002

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“…The average T-ray power in a focused beam has developed from nW to /JW levels, 140,141 with current systems achieving 30-40 fiW of average THz power. 142,143 The availability of high power, high repetition rate femtosecond laser sources has enabled PCAs to be driven into saturation, 144,145 and photoconductive substrates with high breakdown voltages permit large bias fields. 146 The maximum power emitted from a PCA depends on the photoconductive substrate and the coupling efficiency of the antenna.…”

Section: Photoconductive Antennasmentioning

confidence: 99%

“…150 High power PCAs were demonstrated initially on implanted silicon-on-sapphire and low-temperature-grown (LT) GaAs, 151 and since with semi-insulating GaAs, 143,144 ion-implanted GaAs and InGaAs. 142 Antenna design and coupling influences the efficiency, bandwidth and radiation pattern of T-ray emission. 141,152 Many antenna geometries have been explored, 141,153~160 however high power T-rays are still generated with coplanar strip lines and large aperture emitters.…”

Section: Photoconductive Antennasmentioning

confidence: 99%

T-Ray Sensing and Imaging

Mickan

Zhang

2003

Int. J. Hi. Spe. Ele. Syst.

110

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Terahertz (THz) radiation occupies part of the electromagnetic spectrum between the infrared and microwave bands. Until recently, technology at THz frequencies was underdeveloped compared to the rest of the electromagnetic spectrum, leaving a gap between millimeter waves and the far-infrared (FIR). In the past decade, interest in the THz gap has been increased by the development of ultrafast laser-based T-ray systems and their demonstration of diffraction-limited spatial resolution, picosecond temporal resolution, DC-THz spectral bandwidth and signal-to-noise ratios above 10 4 . This chapter reviews the development, the state of the art and the applications of T-ray spectrometers. Continuous-wave (CW) THz-frequency sources and detectors are briefly introduced in comparison to ultrafast pulsed THz systems. An emphasis is placed on experimental applications of T-rays to sensing and imaging, with a view to the continuing advance of technologies and applications in the THz band.

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“…6 Several attempts have been made to increase the THz emission efficiency by employing photoconductors with laterally structured emitter electrodes. 7,8 The driving forces for further developments of impulsive THz emitters are applications which require a large bandwidth and/or high THz electric field amplitudes. The performance of THz emitters based on photoconductors ͑PC͒ is limited by several conditions.…”

mentioning

confidence: 99%

High-intensity terahertz radiation from a microstructured large-area photoconductor

Dreyhaupt

Winnerl

Dekorsy

et al. 2005

Applied Physics Letters

343

206

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We present a planar large-area photoconducting emitter for impulsive generation of terahertz ͑THz͒ radiation. The device consists of an interdigitated electrode metal-semiconductor-metal ͑MSM͒ structure which is masked by a second metallization layer isolated from the MSM electrodes. The second layer blocks optical excitation in every second period of the MSM finger structure. Hence charge carriers are excited only in those periods of the MSM structure which exhibit a unidirectional electric field. Constructive interference of the THz emission from accelerated carriers leads to THz electric field amplitudes up to 85 V / cm when excited with fs optical pulses from a Ti:sapphire oscillator with an average power of 100 mW at a bias voltage of 65 V applied to the MSM structure. The proposed device structure has a large potential for large-area high-power THz emitters. 6 Several attempts have been made to increase the THz emission efficiency by employing photoconductors with laterally structured emitter electrodes. 7,8 The driving forces for further developments of impulsive THz emitters are applications which require a large bandwidth and/or high THz electric field amplitudes. The performance of THz emitters based on photoconductors ͑PC͒ is limited by several conditions. In order to achieve a high bandwidth the electric field applied to the PC should be high in the 100 kV/ cm range, i.e., close to the breakdown voltage of the PC. On the other hand the optically excited area should be large to prevent local heating of the PC with the exciting laser pulses which would have a detrimental effect on the carrier mobility and thus decrease the bandwidth. Therefore the solution of using pin-diodes has advantages over lateral electrical contacts to the PC, since in a pin-diode high electric fields exist in the whole area of the diode. Yet the acceleration of carriers in a pin-diode is perpendicular to the surface which results in a bad outcoupling efficiency of the dipole radiation with the main intensity being emitted parallel to the surface. Hence the acceleration of carriers in the plane of the PC would be favorable. However, large lateral electric fields applied over large areas, i.e., large electrode spacing, require pulsed high voltage sources in the kV range which one tries to avoid because of the electronic interference with sensitive electronic equipment in the laboratory. 9 Another limitation of PC emitters with lateral carrier excitation is the emission of the radiation via coupling to a microstructured dipole antenna, which typically exhibits a narrower bandwidth than the intrinsic carrier acceleration in the PC.Here we investigate the THz radiation from photoconductive MSM structures modified in a way to achieve unidirectional carrier acceleration on a large active area for high excitation powers. The emission is based on the intrinsic acceleration of carriers in the PC and hence does not require a narrow-band antenna. High electric fields of the order of 100 kV/ cm are achieved by convenient dc voltages of abo...

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Optimization of photoconducting receivers for THz spectroscopy

Cited by 18 publications

References 20 publications

A terahertz system using semi-large emitters: noise and performance characteristics

A terahertz system using semi-large emitters: noise and performance characteristics

T-Ray Sensing and Imaging

High-intensity terahertz radiation from a microstructured large-area photoconductor

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