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7Broadband THz emitters: from single chips to large-area devices
D. Lavrukhin1, A. Yachmenev1, N. Zenchenko1, R. Khabibullin1 Yu. Goncharov2, I. Spektor2, K. Zaytsev2, D. Ponomarev1*
1-Institute of Ultra High Frequency Semiconductor Electronics of the Russian Academy of Sciences,
Moscow, Russia
2- Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia
Modern THz spectroscopic and imaging setups require high-power THz generation, and, hence, an improvement of the THz-beam power becomes more and more challenging. The THz power enhancement in a broadband photoconductive antenna (PCA)-emitter is limited by a few factors [1,2]. On the one hand, both bias voltage and laser pump power should be increased. On the other hand, an increased electric field might cause an electrical breakdown of a semiconductor, while an intense laser pump might cause screening effects, thermal breakdown of a semiconductor, also affecting the carrier mobility, and thus decreasing the THz bandwidth. The very promising approach for the THz power boost is to resort from a single small-area emitter to a large-area PCA-emitter (LAPE), with the electrodes in form of a strip line array [3,4]. In this case, an increase in pump power is possible without any overheating or breakdown of the emitter. Unfortunately, LAPE usually requires a layer of masking metal to prevent destructive interference of THz waves from adjacent strips or the specific couplers of laser pump, such as an array of plano-convex microlenses, cylindrical micro-lenses, or diffractive optical elements, that severely complicates fabrication of LAPEs and reduces their cost efficiency.
We demonstrate both numerically and experimentally how the LAPE performance can be improved using an array of cylindrical near-field lenses made of sapphire fibers [5]. A judicious design of such high-refractive-index sapphire lenses allows strong confinement of a laser pump near the semiconductor surface, yielding an 8.5-fold THz power boost and + 9.3 dB in single-to-noise ratio [6].
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[2] A. Yachmenev, R. Khabibullin, D. Ponomarev, Recent advances in THz detectors based on semiconductor structures with quantum confinement: a review, J. Phys. D: Appl. Phys., 55(19), 193001 (2022).
[3] A. Dreyhaupt, S. Winnerl, T. Dekorsy, et al, High-intensity terahertz radiation from a microstructured large-area photoconductor, Appl. Phys. Lett., 86, 121114 (2005).
[4] M. Mittendorff, M. Xu, R. Dietz, et al, Large area photoconductive terahertz emitter for 1.55 ^m excitation based on an InGaAs heterostructure, Nanotech.24, 214007 (2013).
[5] D. Ponomarev, D. Lavrukhin, N. Zenchenko, et al, Boosting THz photoconductive antenna-emitter using optical light confinement behind a high refractive sapphire fiber-lens, Opt. Lett., 47(7), 1899 (2022).
[6] N. Zenchenko, D. Lavrukhin, R. Galiev, et al, Enhanced terahertz emission in a large-area photoconductive antenna through an array of tightly-packed sapphire fibers, Appl. Phys. Lett., 124(12), 121107 (2024).
