Abstract-Fibonacci terahertz imaging by silicon diffractive optics

D. Jokubauskis, L. Minkevičius, M. Karaliūnas, S. Indrišiūnas, I. Kašalynas, G. Račiukaitis, and G. Valušis

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-12-2795

Fibonacci or bifocal terahertz (THz) imaging is demonstrated experimentally employing a silicon diffractive zone plate in continuous wave mode. Images simultaneously recorded in two different planes are exhibited at 0.6 THz frequency with the spatial resolution of wavelength. Multifocus imaging operation of the Fibonacci lens is compared with a performance of the conventional silicon phase zone plate. Spatial profiles and focal depth features are discussed varying the frequency from 0.3 to 0.6 THz. Good agreement between experimental results and simulation data is revealed.

© 2018 Optical Society of America

Abstract-Terahertz multilevel phase Fresnel lenses fabricated by laser patterning of silicon

L. Minkevičius, S. Indrišiūnas, R. Šniaukas, B. Voisiat, V. Janonis, V. Tamošiūnas, I. Kašalynas, G. Račiukaitis, and G. Valušis

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-10-1875

Multilevel phase Fresnel lenses (MPFLs) with a high numerical aperture for 0.58 THz frequencies were developed. The components based on a monocrystalline silicon wafer are prepared by patterning by a high-speed industrial-scale laser direct writing (LDW) system. Two consistent series of the terahertz-MPFLs with phase quantization levels varying between 2 and the continuous kinoform shape for the focal lengths of 5 and 10 mm were produced employing inherent flexibility of the LDW fabrication process. The focusing performance was studied at the optimal 0.58 THz frequency using a Gaussian beam profile and scanning 2D intensity distribution with a terahertz detector along the optical axis. The efficiency of the terahertz-MPFL was found to be dependent of the number of subzones. The position and orientation angles of the patterned plane of the silicon wafer were considered to reduce the effect of standing waves formation in the experiment.

© 2017 Optical Society of America

Abstract-Selective thermal terahertz emission from GaAs and AlGaAs

K. Požela^1,a), E. Širmulis¹, I. Kašalynas¹, A. Šilėnas¹, J. Požela¹ and V. Jucienė¹
http://scitation.aip.org/content/aip/journal/apl/105/9/10.1063/1.4894539
1 Semiconductor Physics Institute, Center for Physical Sciences and Technology, Vilnius 01108, Lithuania
a) Electronic mail: kpozela@pfi.lt
Appl. Phys. Lett. 105, 091601 (2014); http://dx.doi.org/10.1063/1.48945

The selective thermally stimulated terahertz (THz) radiation emission from GaAs and AlGaAs alloys are experimentally observed at frequencies of coupled oscillations of free electron plasma and different branches of interface AlGaAs optical phonons. The effect of strong absorption of incident radiation with large oblique angle (26°) by heated GaAs and AlGaAs is revealed. The coherent THz radiation emission with the frequency of 7.6 THz from the heated high conductivity GaAs (n = 4 × 10¹⁸cm⁻³) layer is observed. The results are highly relevant to application in optoelectronic THz devices

Abstract-Focusing Performance of Terahertz Zone Plates with Integrated Cross-shape Apertures

• L. Minkevičius, 
• K. Madeikis, 
• B. Voisiat, 
• I. Kašalynas, 
• R. Venckevičius, 
• G. Račiukaitis, 
• V. Tamošiūnas, 
• G. Valušis

http://link.springer.com/article/10.1007/s10762-014-0086-8

Search of novel breakthrough concepts of room temperature compact terahertz (THz) imaging systems [1–3] remains as one of sensitive topics in THz photonics. As a rule, a particular attention is attributed to the development of compact THz sources and detectors, however, compact optic components – such as focusing lenses, mirrors, beam splitters, etc – as well plays important role in reducing size of the systems. Preferences here are usually given to inexpensive and relatively simple technology-based approaches, for instance, binary lenses [4], focusing elements of a combined design structures [5] or narrow-band laser-ablated filters [6]. These solutions can be found well-suited in THz heterodyne [7] and spectroscopic imaging [8] when only several specific spectral lines are used to record image, but still enabling to indentify an object under test. Very recently, terahertz zone plate with integrated resonant filters (TZP) was proposed and experimentally demonstrated for efficient radia.