HAL (Le Centre pour la Communication Scientifique Directe), 2015
In this paper, we present the results of the terahertz measurements of liquid crystal (LC) ferroe... more In this paper, we present the results of the terahertz measurements of liquid crystal (LC) ferroelectric BaTiO 3 nanoparticles (nps) suspensions in the range of frequency from 0.3 up to 3.0 THz. Two different sol-gel methods and the harvesting technique were used to fabricate the nanoparticles. Five LC materials served as hosts for the suspensions: two single compounds: 6CHBT and 2,3′,5′-trifluoro-4-(4-pentylcyclohexyl)-4′-(trifluoromethoxy)-1,1′-biphenyl, and three mixtures: 1867, 2037 and 2020. We characterise, for the first time, the refractive indices and absorption parameters of suspensions with harvested nps in the terahertz range and show how the process of the nps' preparation affects their response. We observed the increase of birefringence for few LC suspensions in comparison with the pure LCs. The highest increase of birefringence was for 2020 suspension with one kind of ferroelectric nps. On the other hand in most cases the addition of ferroelectric nps to LC causes the increase of its absorption in the THz range. The measurements of LCs terahertz properties by using time-pulsed spectrometer were performed.
ABSTRACT A novel mechanism of photorefractivity in nematic liquid crystal (LC) cells is presented... more ABSTRACT A novel mechanism of photorefractivity in nematic liquid crystal (LC) cells is presented. Dynamic photorefractivity is based on temporal quasiperiodic modules excitation in the liquid crystal layer by applied external alternating electric field and their reorientation due to the charges induced by interference optical field on a surface of photoconducting orienting layer.
A simple model describing location of Raman-Nath index grating photoexcited in a planar cell with... more A simple model describing location of Raman-Nath index grating photoexcited in a planar cell with photoconductive orienting layers is proposed. We believe that index grating vector is parallel to cell boundaries. One of the most important features resulting from this model is that the index grating spacing equals to projection of the exciting optical grating spacing on cell boundaries. The experimental study was carried out with 9 micrometer thick planar cell filled with nematic liquid crystal 6CHBT, activated by anthraquinone dyes. DC or square-wave AC field has been applied to the cell. Holographic gratings were recorded by two (signal + pump) or three (signal + 2 pumps) coherent p-polarized beams from He-Ne laser operating at 632.8 nm. The crossing angle between signal and pump beams and the sample tilting angle were chosen to satisfy "angular resonance". The tilting angle varied from 20° to 45°, high diffraction orders were observed up to angle 77°. Calculations on the basis of our model and experimental results are in good agreement. We also discuss and present explanation of the observed effects in geometry with 2 pump beams.
Induced by nanosecond pulses of second harmonic generation from Nd:YAG laser the hydrodynamical i... more Induced by nanosecond pulses of second harmonic generation from Nd:YAG laser the hydrodynamical instabilities in planar- and twist-oriented layers of the nematic 6CHBT doped with anthraquinone dyes under dc electric field in the region above the Freedericksz threshold were revealed. The dependence of diffraction efficiency on voltage is characterized by the two maxima which are corresponding to the two types
ABSTRACT An influence of material constants such as elastic constants, electric permittivity cons... more ABSTRACT An influence of material constants such as elastic constants, electric permittivity constants, refractive indices, viscosity and concentration of optical dopants on the performance of STN displays are discussed. It is shown that mixtures containing as main components isothiocyanato and borodioxane compounds are speedily operating liquid crystalline materials and a high multiplexing level in this mode is obtained.
... and J. PARKAb Institute of Electronics, Belarus National Academy of Sciences, Lagoiski Trakt... more ... and J. PARKAb Institute of Electronics, Belarus National Academy of Sciences, Lagoiski Trakt 22, 220090 Minsk, Belarus, e-mail: [email protected] and ... reflectivity in DFWM as R = I4 /[3, the signal beam 110 (image Ii) gain in DTWM as g = 11 /110 = [om /1;, and the ...
In this paper we present the results of the terahertz measurements of liquid crystal ferroelectri... more In this paper we present the results of the terahertz measurements of liquid crystal ferroelectric BaTiO 3 nanoparticles suspensions in the range of frequency from 0.3 up to 3.0 THz. Two different sol-gel methods and the harvesting technique were used to fabricate the nanoparticles. Five liquid crystal materials served as hosts for the suspensions: two single compounds: 6CHBT and 2,3',5'-trifluoro-4-(4-pentylcyclohexyl)-4'-(trifluoromethoxy)-1,1'-biphenyl, and three mixtures: 1867, 2037 and 2020. We characterize, for the first time, the refractive indices and absorption parameters of suspensions with harvested nanoparticles in the terahertz range and show how the process of the nanoparticles' preparation affects their response. We observed the increase of birefringence for few liquid crystal suspensions in comparison with the pure liquid crystals. The highest increase of birefringence was for 2020 suspension with one kind of ferroelectric nanoparticles. On the other hand in the most cases the addition of ferroelectric nanoparticles to liquid crystal causes the increase of its absorption in the THz range. The measurements of liquid crystals terahertz properties by using Time-Pulsed Spectrometer were performed.
An original idea of hydrostatic pressure monitoring based on a new kind of anisotropic fibers wit... more An original idea of hydrostatic pressure monitoring based on a new kind of anisotropic fibers with a liquid crystalline core is presented. The liquid crystalline-core optical fiber giving a possibility of birefringence control unite the unique advantages of liquid crystals and quality of fiber technology what can be used for continuous pressure monitoring. Preliminary results of experimental studies of light
Induced by nanosecond pulses of second harmonic generation from Nd:YAG laser the hydrodynamical i... more Induced by nanosecond pulses of second harmonic generation from Nd:YAG laser the hydrodynamical instabilities in planar- and twist-oriented layers of the nematic 6CHBT doped with anthraquinone dyes under dc electric field in the region above the Freedericksz threshold were revealed. The dependence of diffraction efficiency on voltage is characterized by the two maxima which are corresponding to the two types
ABSTRACT Dynamic optical data storage and other applications in the field of optical data process... more ABSTRACT Dynamic optical data storage and other applications in the field of optical data processing would be possible due to devel-opment of suitable nonlinear optical materials. The experimental investigations of the orientation photorefractive effect in nematic liquid crystals have been presented. The investigations showed that the orientational optical sensitivity of liquid crystals can be greatly enhanced by an external electric and optical applied field. The photorefractive volume space charge field in the LC cell is the result of charge generation in the bright regions of interference pattern and charge transportation.
works on terahertz (Thz) technology have been conducted for over three decades while research on ... more works on terahertz (Thz) technology have been conducted for over three decades while research on the use of liquid crystals in the Thz range lasted only a decade. In the paper, the results of spectral measurements of lC in the Thz range are presented. selected properties of a commercially available lC compound with the symbol 5CB and two lC mixtures called 1832B and 1825 are described. Using available literature, several devices, which modulate the Thz radiation, were selected and discussed. In these devices, liquid crystals were used as tunable elements.
HAL (Le Centre pour la Communication Scientifique Directe), 2015
In this paper, we present the results of the terahertz measurements of liquid crystal (LC) ferroe... more In this paper, we present the results of the terahertz measurements of liquid crystal (LC) ferroelectric BaTiO 3 nanoparticles (nps) suspensions in the range of frequency from 0.3 up to 3.0 THz. Two different sol-gel methods and the harvesting technique were used to fabricate the nanoparticles. Five LC materials served as hosts for the suspensions: two single compounds: 6CHBT and 2,3′,5′-trifluoro-4-(4-pentylcyclohexyl)-4′-(trifluoromethoxy)-1,1′-biphenyl, and three mixtures: 1867, 2037 and 2020. We characterise, for the first time, the refractive indices and absorption parameters of suspensions with harvested nps in the terahertz range and show how the process of the nps' preparation affects their response. We observed the increase of birefringence for few LC suspensions in comparison with the pure LCs. The highest increase of birefringence was for 2020 suspension with one kind of ferroelectric nps. On the other hand in most cases the addition of ferroelectric nps to LC causes the increase of its absorption in the THz range. The measurements of LCs terahertz properties by using time-pulsed spectrometer were performed.
ABSTRACT A novel mechanism of photorefractivity in nematic liquid crystal (LC) cells is presented... more ABSTRACT A novel mechanism of photorefractivity in nematic liquid crystal (LC) cells is presented. Dynamic photorefractivity is based on temporal quasiperiodic modules excitation in the liquid crystal layer by applied external alternating electric field and their reorientation due to the charges induced by interference optical field on a surface of photoconducting orienting layer.
A simple model describing location of Raman-Nath index grating photoexcited in a planar cell with... more A simple model describing location of Raman-Nath index grating photoexcited in a planar cell with photoconductive orienting layers is proposed. We believe that index grating vector is parallel to cell boundaries. One of the most important features resulting from this model is that the index grating spacing equals to projection of the exciting optical grating spacing on cell boundaries. The experimental study was carried out with 9 micrometer thick planar cell filled with nematic liquid crystal 6CHBT, activated by anthraquinone dyes. DC or square-wave AC field has been applied to the cell. Holographic gratings were recorded by two (signal + pump) or three (signal + 2 pumps) coherent p-polarized beams from He-Ne laser operating at 632.8 nm. The crossing angle between signal and pump beams and the sample tilting angle were chosen to satisfy "angular resonance". The tilting angle varied from 20° to 45°, high diffraction orders were observed up to angle 77°. Calculations on the basis of our model and experimental results are in good agreement. We also discuss and present explanation of the observed effects in geometry with 2 pump beams.
Induced by nanosecond pulses of second harmonic generation from Nd:YAG laser the hydrodynamical i... more Induced by nanosecond pulses of second harmonic generation from Nd:YAG laser the hydrodynamical instabilities in planar- and twist-oriented layers of the nematic 6CHBT doped with anthraquinone dyes under dc electric field in the region above the Freedericksz threshold were revealed. The dependence of diffraction efficiency on voltage is characterized by the two maxima which are corresponding to the two types
ABSTRACT An influence of material constants such as elastic constants, electric permittivity cons... more ABSTRACT An influence of material constants such as elastic constants, electric permittivity constants, refractive indices, viscosity and concentration of optical dopants on the performance of STN displays are discussed. It is shown that mixtures containing as main components isothiocyanato and borodioxane compounds are speedily operating liquid crystalline materials and a high multiplexing level in this mode is obtained.
... and J. PARKAb Institute of Electronics, Belarus National Academy of Sciences, Lagoiski Trakt... more ... and J. PARKAb Institute of Electronics, Belarus National Academy of Sciences, Lagoiski Trakt 22, 220090 Minsk, Belarus, e-mail: [email protected] and ... reflectivity in DFWM as R = I4 /[3, the signal beam 110 (image Ii) gain in DTWM as g = 11 /110 = [om /1;, and the ...
In this paper we present the results of the terahertz measurements of liquid crystal ferroelectri... more In this paper we present the results of the terahertz measurements of liquid crystal ferroelectric BaTiO 3 nanoparticles suspensions in the range of frequency from 0.3 up to 3.0 THz. Two different sol-gel methods and the harvesting technique were used to fabricate the nanoparticles. Five liquid crystal materials served as hosts for the suspensions: two single compounds: 6CHBT and 2,3',5'-trifluoro-4-(4-pentylcyclohexyl)-4'-(trifluoromethoxy)-1,1'-biphenyl, and three mixtures: 1867, 2037 and 2020. We characterize, for the first time, the refractive indices and absorption parameters of suspensions with harvested nanoparticles in the terahertz range and show how the process of the nanoparticles' preparation affects their response. We observed the increase of birefringence for few liquid crystal suspensions in comparison with the pure liquid crystals. The highest increase of birefringence was for 2020 suspension with one kind of ferroelectric nanoparticles. On the other hand in the most cases the addition of ferroelectric nanoparticles to liquid crystal causes the increase of its absorption in the THz range. The measurements of liquid crystals terahertz properties by using Time-Pulsed Spectrometer were performed.
An original idea of hydrostatic pressure monitoring based on a new kind of anisotropic fibers wit... more An original idea of hydrostatic pressure monitoring based on a new kind of anisotropic fibers with a liquid crystalline core is presented. The liquid crystalline-core optical fiber giving a possibility of birefringence control unite the unique advantages of liquid crystals and quality of fiber technology what can be used for continuous pressure monitoring. Preliminary results of experimental studies of light
Induced by nanosecond pulses of second harmonic generation from Nd:YAG laser the hydrodynamical i... more Induced by nanosecond pulses of second harmonic generation from Nd:YAG laser the hydrodynamical instabilities in planar- and twist-oriented layers of the nematic 6CHBT doped with anthraquinone dyes under dc electric field in the region above the Freedericksz threshold were revealed. The dependence of diffraction efficiency on voltage is characterized by the two maxima which are corresponding to the two types
ABSTRACT Dynamic optical data storage and other applications in the field of optical data process... more ABSTRACT Dynamic optical data storage and other applications in the field of optical data processing would be possible due to devel-opment of suitable nonlinear optical materials. The experimental investigations of the orientation photorefractive effect in nematic liquid crystals have been presented. The investigations showed that the orientational optical sensitivity of liquid crystals can be greatly enhanced by an external electric and optical applied field. The photorefractive volume space charge field in the LC cell is the result of charge generation in the bright regions of interference pattern and charge transportation.
works on terahertz (Thz) technology have been conducted for over three decades while research on ... more works on terahertz (Thz) technology have been conducted for over three decades while research on the use of liquid crystals in the Thz range lasted only a decade. In the paper, the results of spectral measurements of lC in the Thz range are presented. selected properties of a commercially available lC compound with the symbol 5CB and two lC mixtures called 1832B and 1825 are described. Using available literature, several devices, which modulate the Thz radiation, were selected and discussed. In these devices, liquid crystals were used as tunable elements.
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Papers by Janusz Parka