Interdigitated terahertz emitters

Acuna, Guillermo P.; Buersgens, F.; Lang, C.; Handloser, Matthias; Guggenmos, Alexander; Kersting, R.

doi:10.1049/el:20082905

Cited by 11 publications

(10 citation statements)

References 8 publications

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“…A much simpler technique is preparing an interdigitated electrode pattern similar to the one illustrated in Fig. 1, but instead of evaporating a second metallization layer, trenches are etched into every second gap between the electrodes [68]. In the trenches the bias field is weaker, resulting in THz wavelets that weaken, but do not cancel the contributions from the non-etched areas.…”

Section: Fabrication Techniques For Scalable Microstructured Antennasmentioning

confidence: 99%

Scalable Microstructured Photoconductive Terahertz Emitters

Winnerl

2011

J Infrared Milli Terahz Waves

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The development of scalable emitters for pulsed broadband terahertz (THz) radiation is reviewed. Their large active area in the 1 -100 mm 2 range allows for using the full power of state-of-the-art femtosecond lasers for excitation of charge carriers. Large fields for acceleration of the photogenerated carriers are achieved at moderate voltages by interdigitated electrodes. This results in efficient emission of single-cycle THz waves. THz field amplitudes in the range of 300 V/cm and 17 kV/cm are reached for excitation with 10 nJ pulses from Ti:sapphire oscillators and for excitation with 5 μJ pulses from amplified lasers, respectively. The corresponding efficiencies for conversion of near-infrared to THz radiation are 2.5×10 -4 (oscillator excitation) and 2×10 -3 (amplifier excitation). In this article the principle of operation of scalable emitters is explained and different technical realizations are described. We demonstrate that the scalable concept provides freedom for designing optimized antenna patterns for different polarization modes. In particular emitters for linearly, radially and azimuthally polarized radiation are discussed. The success story of photoconductive THz emitters is closely linked to the development of mode-locked Ti: sapphire lasers. GaAs is an ideal photoconductive material for THz emitters excited with Ti: sapphire lasers, which are widely used in research laboratories. For many applications, especially in industrial environments, however, fiber-based lasers are strongly preferred due to their lower cost, compactness and extremely stable operation. Designing photoconductive emitters on InGaAs materials, which have a low enough energy gap for excitation with fiber lasers, is challenging due to the electrical properties of the materials. We discuss why the challenges are even larger for microstructured THz emitters as compared to conventional photoconductive antennas and present first results of emitters suitable for excitation with ytterbium-based fiber lasers. Furthermore an alternative concept, namely the lateral photo-Dember emitter, is presented. Due to the strong THz output scalable emitters are well suited for THz systems with fast data acquisition. Here the application of scalable emitters in THz spectrometers without mechanical delay stages, providing THz spectra with 1 GHz spectral resolution and a signal-to-noise ratio of 37 dB within 1 s, is

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Section: Fabrication Techniques For Scalable Microstructured Antennasmentioning

confidence: 99%

Scalable Microstructured Photoconductive Terahertz Emitters

Winnerl

2011

J Infrared Milli Terahz Waves

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“…1,2 These structures prevent carrier excitation in every second spacing by additional metallization 1,2 or by etching of the substrate. 3,4 Hereby the excited elementary terahertz waves interfere constructively in the far field. These emitter designs combine the advantages of high bias fields and large active areas.…”

Section: Terahertz Emission From a Large-area Gainasn Emittermentioning

confidence: 99%

Terahertz emission from a large-area GaInAsN emitter

Peter

Winnerl

Schneider

et al. 2008

Applied Physics Letters

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A large-area interdigitated terahertz emitter based on molecular-beam epitaxy grown GaInAsN with an additional AlGaAs heterostructure is investigated as a terahertz source for excitation wavelengths between 1.1 and 1.5 mu m. The optical and electrical properties of the emitter material exhibit absorption up to a wavelength of 1.5 mu m and have a resistivity of 550 k Omega cm. Terahertz waves were detected by electro-optical sampling with a bandwidth exceeding 2 THz. Best performance is found for excitation wavelengths below 1.35 mu m. Furthermore the emission properties for several excitation powers are investigated, showing a linear increase in terahertz emission

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“…Drawbacks of these sources are the lack of longterm stability, scalability and the low conversion efficiencies from the optical to the THz regime. Further research led to the development of large-area photoconductive emitters [8][9][10], which exhibit one order of magnitude larger conversion efficiency compared to the first sources. Furthermore, recently it has been shown that, with an improved excitation geometry, conversion efficiencies up to 2 × 10 23 are possible [11].…”

mentioning

confidence: 99%

Large-area laser-driven terahertz emitters

et al. 2010

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Intense terahertz emitters are one of the most important components of terahertz (THz) time-domain spectroscopy systems. In this presented report, the development of THz emitters over the last two decades is reviewed, and an outlook for future THz emitters is given. The physical principle behind the THz generation process is discussed for two types of emitters: state-of-the-art large-area photoconductive emitters are compared to THz emitters based on the photo-Dember effect. The latter do not require an external bias voltage. This passive character of the photo-Dember emitters has several advantages which are outlined.The first photoconductive switch with electromagnetic waves in the picosecond regime was shown by Auston in 1984 [1]. The frequent employment of these 'Auston switches' then became established with the wide availability of femtosecond lasers such as the Kerr-lens modelocked titanium:sapphire in the 1990s. The most commonly used THz sources were subsequently based on either photoconductive switches [2] or the emission from semiconductor surfaces [3], in both cases irradiated with femtosecond laser beams. To date, these two methods introduced 20 years ago are still commonly employed for generating, by optical excitation, THz radiation in the frequency range 0.2-5 THz [4,5]. Advances have also been made in the generation of THz radiation via optical rectification or difference frequency mixing [6,7], but these will not be discussed further in this Letter.Typically, the peak frequency of photoconductive sources or bare semiconductor surfaces lies around 1 THz, and the spectral coverage is limited to 3 THz. Drawbacks of these sources are the lack of longterm stability, scalability and the low conversion efficiencies from the optical to the THz regime. Further research led to the development of large-area photoconductive emitters [8-10], which exhibit one order of magnitude larger conversion efficiency compared to the first sources. Furthermore, recently it has been shown that, with an improved excitation geometry, conversion efficiencies up to 2 × 10 23 are possible [11]. A new concept for the generation of intense THz radiation is based on the lateral photo-Dember effect [12]. Inspired by the large-area photoconductive emitters, these new emitters allow scalability, but do not require an external bias voltage.The common feature of these THz generation methods is the emission of electromagnetic radiation from accelerated carriers in semiconductors such as gallium arsenide (GaAs) or indium gallium arsenide (InGaAs) [13]. Free carriers -electrons and holes -are generated at the surface of the semiconductor by femtosecond pulses with a photon energy above the gap energy of the semiconductor. For conventional photoconductive switches, electrodes deposited on the substrate material are externally biased and hence an electric field exists between the electrodes. The accelerating electric field E ext is given by the externally applied voltage U ext divided by the electrode spacing d. After photoexcitation, a ti...

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Interdigitated terahertz emitters

Cited by 11 publications

References 8 publications

Scalable Microstructured Photoconductive Terahertz Emitters

Scalable Microstructured Photoconductive Terahertz Emitters

Terahertz emission from a large-area GaInAsN emitter

Large-area laser-driven terahertz emitters

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