High-frequency dielectric relaxation of liquid crystals: THz time-domain spectroscopy of liquid crystal colloids

Oh‐e, Masahito; Yokoyama, Hiroshi; Koeberg, Mattijs; Hendry, Euan; Bonn, Mischa

doi:10.1364/oe.14.011433

Cited by 25 publications

(12 citation statements)

References 30 publications

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“…In the "on-state" the THz wave propagates through the device, while in the "off-state" the THz wave is blocked. The device uses the THz birefringence of the LC in the presence of an electric field [19][20][21][22][23][24][25]. Figure 1 shows a schematic of the device.…”

mentioning

confidence: 99%

Electrically Tunable Terahertz Notch Filters

Vieweg

Born

Al-Naib

et al. 2012

J Infrared Milli Terahz Waves

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In this letter we present a switchable THz notch filter. The filter contains a liquid crystal layer that acts as a half wave retarder in one state and as an isotropic layer in the other state. The device combines three unique properties: it can be switched electrically, it provides a filter depth of 35 dB at 350 GHz and it can be tuned over wide frequency range from 350 GHz to 700 GHz. Keywords Liquid crystals . Switchable terahertz devices . BirefringenceIn recent years terahertz technology has experienced a tremendous development [1, 2]. Many applications for THz systems are presently discussed. They range from nondestructive testing [3][4][5] and process monitoring in the industry [5, 6] to free-space communications with THz carrier waves [7][8][9].Besides sources and detectors, a mature THz technology also requires devices to guide and manipulate THz waves. Among them are reflectors [10,11], waveguides [12, 13], splitters [14], lenses [15], filters [16] and modulators [17, 18]. Modulators and switches could be based on liquid crystals (LCs) the dielectric THz properties of which have recently been characterized with high precision [19-25]. First devices have been demonstrated by Pan et al., including THz phase shifters [26, 27] and polarizers [28]. Wilk et al. reported on a LC based switchable THz Bragg structure [29] and Ghattan et al. presented an on-off switch for sub-THz-waves, which was based on a two-dimensional photonic crystal infiltrated by LCs [30]. A THz device, which combines liquid crystals with an artificial medium, was reported by Khoo et al. [31] and Chen et al. presented a magnetically tunable Lyot filter [32].In this paper we report on the fabrication of an electrically tunable liquid crystal filter which uses the THz birefringence of LCs. It provides a high filter depth and is electrically tunable over a broad frequency range. The filter consists of a 2.4 mm thick liquid crystal layer, which is sandwiched between two 710 μm thick fused silica windows (Fig. 1). As a

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mentioning

confidence: 99%

Electrically Tunable Terahertz Notch Filters

Vieweg

Born

Al-Naib

et al. 2012

J Infrared Milli Terahz Waves

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“…This is due to the steric hindrance between the different groups. [26] 3.2 THz absorption spectrum THz absorption spectrum and the intensity of 5CB calculated using B3LYP/6-311++G** function are shown in Figure 2, where the experimental result of (14,15,16) 113.5213 A (15,16,17) 113.2678 Vieweg et al [22,23] and their calculated data using BVP86/def2-SVP function are collected also. In order to identify the different data, the absorption curves of different results are shifted in the intensity.…”

Section: Molecular Geometrymentioning

confidence: 99%

“…high chemical stability and pronounced sensitivity in electric fields, 5CB presents potential applications in designing or fabricating functional devices in THz range. [7] Furthermore, some research group has also focused on the molecular properties of 5CB in THz region, [13][14][15][16][17] but the relationship between molecular structure and its characteristics on THz region is still not clear. For example, the peaks and absorption bands of THz spectra were just assigned simply in their works.…”

Section: Introductionmentioning

confidence: 99%

Molecular vibration mode assignment of nematic liquid crystal 5CB on Terahertz spectra

Chen

Jiang

et al. 2015

Liquid Crystals

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2015): Molecular vibration mode assignment of nematic liquid crystal 5CB on Terahertz spectra, Liquid Crystals, Using DFT/B3LYP/6-311++G** method, the molecular structure and absorption spectra in terahertz (THz) range of liquid crystal 5CB are investigated. In a frequency range 0-15 THz, an assignment of the vibrational modes corresponding to absorption frequencies is performed using potential energy distribution for the first time. It is found that the cyano group radical (-CN) do actively take part in the strongest THz absorption of 1.743, 3.942, 5.169 and 14.769 THz in different vibration modes. The results suggest that the strong polar group should be avoided in designing liquid crystal molecule and mixtures in order to reduce the absorption intensity in THz range.

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“…This report was followed by several papers published by Prof. Pan's group on 5CB, 6CB, 7CB, 8CB [20][21][22][23][24][25], PCH5 [20,22], E7 [26,27], and a ferroelectric liquid crystal [28]. THz data on 5CB have also been presented by Bonn et al [29]. Using different spectroscopy techniques, Takanishi et al and Nishizawa et al studied P-8-PIMB and MBBA, respectively [30,31].…”

Section: State Of the Artmentioning

confidence: 99%

Liquid Crystals and their Applications in the THz Frequency Range

Vieweg

Jansen

Koch

2012

Terahertz Spectroscopy and Imaging

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We present a survey through the study of liquid crystals with terahertz time domain spectroscopy. The macroscopic dielectric properties such as the refractive index and the absorption coefficient for both ordinary and extraordinary polarization of various liquid crystals are presented and the underlying physical mechanisms are discussed. Furthermore, we deduce the microscopic characteristics such as the order parameter and the polarizabilities from the measured data.

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High-frequency dielectric relaxation of liquid crystals: THz time-domain spectroscopy of liquid crystal colloids

Cited by 25 publications

References 30 publications

Electrically Tunable Terahertz Notch Filters

Electrically Tunable Terahertz Notch Filters

Molecular vibration mode assignment of nematic liquid crystal 5CB on Terahertz spectra

Liquid Crystals and their Applications in the THz Frequency Range

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