Abstract-Compact solutions for spectroscopic solid-state-based terahertz imaging systems

Rimvydas Venckevičius,  Linas Minkevičius,  Antanas Reklaitis, Vincas Tamošiūnas,  Irmantas Kašalyns,  Domas Jokubauskis,  Dalius Seliuta,  Bogdan Voisiat,  Gediminas Račiukaitis,  Gintaras Valušis,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10383/103830S/Compact-solutions-for-spectroscopic-solid-state-based-terahertz-imaging-systems/10.1117/12.2273353.short

Convenience in use of room-temperature terahertz (THz) imaging systems, reduction of their dimensions and presence of on-chip solutions remains one of prime interests for direct implementation aims. Solid-state-based solutions in miniaturization of spectroscopic THz imaging systems including novel semiconductor nanostructures bias-free emitters, diffractive THz optics components and their on-chip integration with THz detectors are discussed. In particular, pulsed optoelectronic terahertz emitter based on a δ-doped p-i-n-i GaAs/AlxGa1−xAs heterostructure was studied and it is demonstrated that the heterostructure can serve as efficient antenna- and bias-free surface emitter. Diffractive optics elements – Fresnel zone plates –with integrated band-pass filters were simulated employing Finite-difference time domain method. Structures were fabricated using the laser direct writing and investigated using electronic THz sources and an optically pumped terahertz laser. Advantages of on-chip integration of diffractive optics and bow-tie-shaped InGaAs-based terahertz detectors are revealed via detection enhancement. Bow-tie diodes properties in frequency scale and detection sensitivity are considered and compared for different materials. Homodyne detection and imaging of low-absorbing objects at 0.6 THz are demonstrated and discussed.

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Abstract-Theoretical analysis of conditions for observation of plasma oscillations in semiconductors from pulsed terahertz emission

Antanas Reklaitis^1,a)

1 Semiconductor Physics Institute, Center for Physical Sciences and Technology, A. Goshtauto 11, Vilnius 01108, Lithuania
http://scitation.aip.org/content/aip/journal/jap/116/8/10.1063/1.4894163
a) Electronic address: reklaitis@pfi.lt.
J. Appl. Phys. 116, 083107 (2014); http://dx.doi.org/10.1063/1.4894163

Oscillations of electron-hole plasma generated by femtosecond optical pulse in freestandingsemiconductor are studied using hydrodynamic model and Monte Carlo simulations. The conditions required for the observation of coherent plasma oscillations in THz emission fromsemiconductor are determined. It is shown that several conditions have to be fulfilled in order to observe coherent plasma oscillations. First, the intensity of the optical pulse must exceed some threshold value. Second, the optical absorption depth must exceed the thickness of the built-in electric field region. Third, the generation of electron-hole pairs with uniform illumination is required, i.e., the laser beam with the flattop intensity profile has to be used. It is found that the duration of the optical pulse does not play a vital role in the development of plasma oscillations.