Femtosecond terahertz time-domain spectroscopy at 36 kHz scan rate using an acousto-optic delay

Abstract

We present a rapid-scan, time-domain terahertz spectrometer employing femtosecond Er:fiber technology and an acousto-optic delay with attosecond precision, enabling scanning of terahertz transients over a 12.4-ps time window at a waveform refresh rate of 36 kHz, and a signal-to-noise ratio of 1. or spin currents [10]. Whereas the repeatable nature of these phenomena allows for stroboscopic sampling of the THz field in a laboratory environment, many industrial or biological applications require real-time acquisition of singular events at kHz scan rates, facilitating rapid DNA analysis [11], spectroscopy of biomolecules [12,13], environmental gas sensing [2,14], drugs and explosives testing [2,14,15] or imaging applications [16]. Hence, numerous strategies towards replacing mechanical delays by faster, more precise and more robust concepts have

Yellow‐Colored Electro‐Optic Crystals as Intense Terahertz Wave Sources

“…The previously reported yellow‐colored organic THz crystals 2‐cyclooctylamino‐5‐nitropyridine (COANP) and BNA have a remarkably different chemical structure compared with benchmark organic electro‐optic crystals. COANP and BNA crystals are nonionic crystals that consist of molecules with one aromatic ring in the push–pull π‐conjugated bridge, while most benchmark organic electro‐optic crystals (ionic or nonionic) are based on chromophores that consist of two aromatic rings, with electron‐donor and ‐acceptor groups at the opposite end of each ring . In this work, the phenolic pyridinium OHP cation was chosen as the molecular cation.…”

“…Organic electro‐optic crystals are highly interesting materials for intense broadband terahertz (THz) wave generation with an extremely high optical‐to‐THz conversion efficiency . Using nonlinear optical conversion processes, such as optical rectification and difference frequency generation, organic electro‐optic crystals can generate very large THz electric fields exceeding 10 MV m −1 .…”

“…Organic electro‐optic crystals are highly interesting materials for intense broadband terahertz (THz) wave generation with an extremely high optical‐to‐THz conversion efficiency . Using nonlinear optical conversion processes, such as optical rectification and difference frequency generation, organic electro‐optic crystals can generate very large THz electric fields exceeding 10 MV m −1 . Compared with well‐known inorganic counterparts (e.g., ZnTe and GaP) for collinear interaction, organic crystals primarily exhibit a higher figure of merit (FOM) for THz wave generation due to the considerably larger optical nonlinearity combined with good phase‐matching possibilities .…”

“…Benchmark electro‐optic organic crystals used previously as efficient THz sources have been primarily based on red‐ or orange‐colored nonlinear optical chromophores. This is because, in general, the microscopic optical nonlinearity of push–pull‐type chromophores increases with increasing the π‐conjugation length and the strength of electron donor and acceptor groups, based among others on the decreased bandgap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the chromophore.…”

“…Compared with red‐ or orange‐colored chromophores used in benchmark organic electro‐optic crystals, such as DAST 4‐(4‐( N,N ‐dimethylamino)styryl)‐1‐methylpyridinium 4‐methylbenzenesulfonate), DSTMS 4‐(4‐( N,N ‐dimethylamino)styryl)‐1‐methylpyridinium 2,4,6‐trimethylbenzenesulfonate), OH1 (2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile), and HMQ‐T (2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium 4‐methylbenzenesulfonate), yellow‐colored chromophores possess significantly different absorption and refraction properties. Therefore, using yellow‐colored chromophores may provide various advantages for intense THz wave generation, e.g., different and even better phase‐matching possibilities when pumped at different wavelengths in diverse configurations along with the wider transparency range.…”