Terahertz Phonon Mode Engineering of Highly Efficient Organic Terahertz Generators. (3rd March 2017)

• Record Type: Journal Article
• Authors: Lee, Seung‐Heon; Kang, Bong Joo; Yoo, Ba‐Wool; Lee, Seung‐Chul; Lee, Seung‐Jun; Jazbinsek, Mojca; Yun, Hoseop; Rotermund, Fabian; Kwon, O‐Pil
• Is Part Of: Advanced functional materials. Volume 27:Number 14(2017)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-03-03
• Subjects: electrooptics -- nonlinear optics -- organic crystals -- terahertz waves; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adfm.201605583
• Languages: English
• ISSNs: 1616-301X

Abstract

Abstract : For terahertz (THz) wave generators based on organic electrooptic crystals, their intrinsic phonon modes are playing an essential role in THz generation characteristics. Here, this study proposes an effective design strategy for THz phonon mode engineering of organic electrooptic salt crystals for efficient optical‐to‐THz frequency conversion. To reduce phonon‐mode intensity, strongly electronegative trifluoromethyl group acting as strong hydrogen‐bond acceptor is incorporated into molecular anions. New 2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium 4‐(trifluoromethyl)benzenesulfonate (HMQ‐4TFS) crystals exhibit a relatively small absorption coefficient in the THz spectral range between 0.5 and 4 THz, which is attributed to suppressed molecular vibrations due to strong hydrogen bonds involving the 4TFS anion. In addition, HMQ‐4TFS crystals possess a very large macroscopic optical nonlinearity, comparable (or even higher) to benchmark stilbazolium crystals. Based on the low‐intensity THz phonon modes and the large optical nonlinearity, a 0.37 mm thick HMQ‐4TFS crystal pumped with 150 fs infrared laser pulses facilitates very efficient THz wave generation by optical rectification, delivering 23 times higher peak‐to‐peak THz electric field than the widely used standard inorganic ZnTe crystal (1.0 mm thick) and a broader spectral bandwidth. Therefore, strongly electronegative groups introduced into molecular salt electrooptic crystals provide a very promising design strategy of THz phonon mode engineering for developing intense broadband THz sources. Abstract : New organic electrooptic quinolinium salt crystals exhibit high optical‐to‐THz conversion efficiency due to large optical nonlinearity and lower THz absorption, achieved by suppressing the THz vibrational modes by introduction of strongly electronegative groups acting as strong hydrogen‐bond acceptor sites into molecular anions.