Optical Properties of Photobleached DAST Molecular Crystals in Terahertz Domain
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Optical Properties of Photobleached DAST Molecular Crystals in Terahertz Domain Igor Denisyuk 1 & Ilya Ozheredov 2,3 & Anton Sinko 2,3 & Maria Fokina 1 & Tamara Pogosian 1,4 & Iulia Ignateva 1 & Ngoc Diep Lai 4 & Isabelle Ledoux-Rak 4 Received: 27 September 2019 / Accepted: 21 January 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
Highly nonlinear optical 4-(4-dimethylaminostyryl)-1-methylpyridinium tosylate (DAST) crystals have been successfully grown. The photobleaching effect was demonstrated by irradiation with an UV light at 405 nm during 120 h. The UV-Vis and terahertz absorption spectra of DAST in crystalline states before and after photobleaching were measured and compared. Results of photobleaching modification of DAST monocrystal have been demonstrated with the help of differential interference contrast microscopy (DIC). A possible explanation of photobleaching effect has been suggested. Since absorption in the terahertz range of crystalline materials is associated with vibrational modes of the crystal lattice, we can conclude that photobleaching leads to its destruction. Taking into account the obvious change of crystalline spectra in the UV-Vis and terahertz frequency range and the absence of changes in the molecular spectra from irradiated DAST in ethanol solution, we can conclude that the photobleaching process may be a photoactivated destruction of chemical in DAST molecules. The photobleaching technique was proposed to implement quasi-phase matching (QPM) structures for efficient nonlinear conversion by optical rectification. Keywords Nonlinear optics . DAST crystals . Terahertz spectra . Photobleaching . Nonlinear grating
* Igor Denisyuk [email protected]
1
ITMO University, St. Petersburg, Russia
2
Lomonosov MSU, Moscow, Russia
3
ILIT RAS — Branch Of FSRC “Crystallography And Photonics” RAS, Shatura, Russia
4
Ecole Normale Superieure Paris-Saclay, Cachan, France
Journal of Infrared, Millimeter, and Terahertz Waves
1 Introduction Within the last 10 years, the field of terahertz science and technology has developed greatly. Many new and promising advances in the technology for generation, manipulation, and detection of terahertz (THz) radiation have been made. The most important task is development of the new materials and technology for terahertz generation and detection [1]. Optical rectification in electro-optical crystals has been demonstrated as the best technique for generating subpicosecond, broadband THz radiation [2]. Several groups in the world have examined different nonlinear materials for THz emission by optical rectification method. These materials include organic salts such as dimethyl amino 4-N-methylstilbazolium tosylate (DAST) [3]; inorganic electro-optical materials like LiTaO3; and semiconductors, such as GaAs and GaP. Among them, DAST is the most efficient THz material for optical rectification applications [4], due to its large electro-optics (EO) coefficient and a low dielectric constant (ε = 5.2), giving rise to a high mod
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