BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:Nonlinear terahertz spectroscopy on liquid water DTSTART;VALUE=DATE-TIME:20220707T124500Z DTEND;VALUE=DATE-TIME:20220707T133000Z DTSTAMP;VALUE=DATE-TIME:20260618T042530Z UID:indico-contribution-88-743@events.ncbj.gov.pl DESCRIPTION:Speakers: F. Novelli (Department of Physical Chemistry II\, Ru hr University Bochum\, 44780 Bochum\, DE)\nWater is one of the most studie d and least understood liquids[1]. While several anomalies in the thermody namic\, macroscopic properties of water are well documented[2]\, on the mi croscopic scale this special liquid is characterized by a dynamic\, tetrah edral network of hydrogen bonded (HB) molecules rearranging on the picosec ond timescale[3]. Thus\, terahertz (THz) spectroscopy is uniquely suited t o probe the dynamics of the HB water network. \n\nThe first results detail ing the nonlinear response of water in the THz frequency range are recent\ , and the molecular interpretation is a matter of ongoing discussion. Tcyp kin et al.[4\,5]\, Ghalgaoui et al.[6]\, and Novelli et al.[7–10] all fo und that the third-order nonlinear response of water in the THz range has a similar magnitude\, but proposed different explanations. The transient r esponse of liquid water was assigned to cascaded second-order anharmonicit y of the intramolecular O–H stretching modes[4]\; to the field-induced i rreversible ionization of water molecules[6]\; or to the resonant excitati on of molecular reorientations[8]. \n\nWe performed a series of non-linear experiments at ~1 and 12.3 THz on liquid water at user facilities[7–10] . By comparing results obtained on a static sample and a free-flowing wate r jet at 12.3 THz\, we were able to disentangle the distinct contributions by thermal\, acoustic\, and nonlinear optical effects[9]. Recently\, we s howed that the non-linear response of water at ~1 THz depends weakly on th e temperature of the bulk liquid[10]. Based on these observations\, we sug gest that the THz fields could be reorienting the hydrogen-bonded water mo lecules in the liquid phase\, as originally proposed in ref.[8]. \n\n[1] P . Ball\, Nature. 452 (2008) 291–292. \n[2] P. Gallo\,et al. Pettersson\, Water: A Tale of Two Liquids\, Chem. Rev. 116 (2016) 7463–7500. \n[3] F . Novelli\, B. Guchhait\, M. Havenith\, Materials (Basel). 13 (2020) 1311. \n[4] A. Tcypkin\,et al.\, Phys. Rev. Appl. 15 (2021) 054009.\n[5] A.N. Tc ypkin\, et al.\, Opt. Express. 27 (2019) 10419. \n[6] A. Ghalgaoui\, et al .\, J. Phys. Chem. Lett. 11 (2020) 7717–7722.\n[7] F. Novelli\, et al.\, Appl. Sci. 10 (2020) 5290. \n[8] F. Novelli\, et al.\, J. Phys. Chem. B. 124 (2020) 4989–5001. \n[9] F. Novelli\, et al.\, Phys. Chem. Chem. Phys . 24 (2022) 653–665. \n[10] F. Novelli\, et al.\, Temperature-independen t non-linear terahertz transmission by liquid water\, (2022). https://doi .org/10.48550/arxiv.2206.03998.\n\nhttps://events.ncbj.gov.pl/event/75/con tributions/743/ LOCATION:Novotel Warszawa Centrum Róża URL:https://events.ncbj.gov.pl/event/75/contributions/743/ END:VEVENT BEGIN:VEVENT SUMMARY:Detection of short-pulse terahertz radiation with field-effect tra nsistors DTSTART;VALUE=DATE-TIME:20220707T120000Z DTEND;VALUE=DATE-TIME:20220707T124500Z DTSTAMP;VALUE=DATE-TIME:20260618T042530Z UID:indico-contribution-88-813@events.ncbj.gov.pl DESCRIPTION:Speakers: Alvydas Lisauskas (Institute of Applied Electrodynam ics and Telecommunications\, Vilnius University\, Vilnius\, 10257\, Lithua nia\; CENTERA Laboratories\, Institute of High Pressure Physics PAS\, War saw\, 01-142\, Poland)\nDuring the last decade\, field-effect-transistor-b ased terahertz detectors (TeraFETs) have been developed to the competitive technology which enables a variety of new applications in the THz frequen cy range [1]. Among the achieved state-of-the-art performance [2] TeraFETs can also exhibit a strong nonlinear response to intense THz radiation pul ses [3]. We show that the character of nonlinearity can be tuned by gate-t o-source voltage from super-linear to saturation. We support this statemen t by experimental findings on TeraFETs fabricated in CMOS and GaN MMIC tec hnologies using two different systems: a free-electron laser with ~20 ps T Hz pulses and a few THz cycle emission derived from a femtosecond Ti:Sapph ire laser excited photoconductive emitter. Furthermore\, the existence of a superlinear response regime can be supported using large-signal circuit modeling of antenna-coupled devices. This phenomenon can be employed both for THz autocorrelation measurement and to study the build-up time of rect ified signal [4].\n\n[1] G. Valušis\, et al. MDPI Sensors 21.12\, 4092 (2 021). \n[2] E. Javadi\, et al. MDPI Sensors 21.9 2909 (2021). \n[3] K. Ika mas\, I. Nevinskas\, A. Krotkus\, and A. Lisauskas\, Sensors 18\, 3735 (20 18). \n[4] A. Lisauskas et al.\, APL Photonics 3\, 051705 (2018).\n\nhttps ://events.ncbj.gov.pl/event/75/contributions/813/ LOCATION:Novotel Warszawa Centrum Róża URL:https://events.ncbj.gov.pl/event/75/contributions/813/ END:VEVENT END:VCALENDAR