Wyniki wyszukiwania - Biblioteka Nauki

1

Dielectric relaxation behaviour of liquid crystals with opposite orientation of -COO ester group in molecular core

100%

Rutkowska J. , Perkowski P. , Piecek W. , Raszewski Z. , Kędzierski J.

|

tom Vol. 16, No. 3

262-266

EN

Dielectric measurements were performed for two smectogens, being structurally analogous with the opposite space orientation of the -COO ester group in the molecular core, using a HP4192A impedance analyser. Gold coated electrode cells of different thicknesses were used. Temperature dependences of the relaxation frequency fR and the inverse of the dielectric strength Δ ε '⊥⁻¹ obtained by fitting experimental values of perpendicular components, i.e., the real ε '⊥ and the imaginary ε "⊥ parts of the complex dielectric permittivity to the Cole-Cole equation as well as the investigation of modification of relaxation processes under bias were determined for the SmC*, SmA*, and N* phases of studied compounds. One can conclude, on the basis of the above results, that dielectric relaxation processes observed by us in the studied compounds are similar to those of the soft and Goldstone mode typically observed by others in the SmC*, SmA*, and N* phases. It is concluded from a comparison of their properties with other related compounds that the link between the biphenyl moiety and –COO ester group is closely related to the stability of smectic phases.

2

Technical aspects of dielectric spectroscopy measurements of liquid crystals

86%

Perkowski P. , Łada D. , Ogrodnik K. , Rutkowska J. , Piecek W. , Raszewski Z.

|

tom Vol. 16, No. 3

271-276

EN

The dielectric spectroscopy measurements were performed for antiferroelectric liquid crystalline mixture. For this purpose, the cells with ITO electrodes were prepared. It was found that it is not possible to detect some important relaxation modes in Sm A*, Sm C*, and Sm CA* phases. The own cell mode (related to cell properties, i.e., capacity and resistivity) covers the dielectric response of liquid crystalline medium. Dielectric measurements in cells with gold electrodes were done to show all possible relaxations in antiferroelectric liquid crystals (Lcs).

3

Dielectric measurements of new antiferroelectric liquid crystals

72%

Perkowski P. , Ogrodnik K. , Łada D. , Piecek W. , Rutkowska J. , Raszewski Z. , Żurowska M. , Dąbrowski R. , Sun X.

|

tom Vol. 16, No. 3

277-280

EN

Three new pure antiferroelectric materials, synthesized at the Military University of Technology (MUT), were investigated by dielectric means. Clear relaxation modes were detected, i.e., Soft, Goldstone, low frequency in-phase (PL) as well high frequency anti-phase (PH) modes for paraelectric Sm A* phase, ferroelectric Sm C* phase and antiferroelectric Sm CA* phase, respectively. Additionally, a high relaxation mode in Sm CA* was found. The relaxation frequencies fR of the observed modes were calculated from Cole-Cole diagrams.

4

Transparent laser damage resistant nematic liquid crystal cell “LCNP3”

58%

Raszewski Z. , Piecek W. , Jaroszewicz L. , Dąbrowski R. , Nowinowski-Kruszelnicki E. , Soms L. , Olifierczuk M. , Kędzierski J. , Morawiak P. , Mazur R. , Miszczyk E. , Mrukiewicz M. , Kowiorski K.

|

2014

|

tom Vol. 22, No. 3

196-200

EN

There exists the problem in diagnostics of dense plasma (so-called Thomson diagnostics). For this purpose the plasma is illuminated by series of high energy laser pulses. The energy of each separate pulse is as large as 3 J, so it is impossible to generate a burst of such pulses by a single laser. In this situation, the pulses are generated by several independent lasers operating sequentially, and these pulses are to be directed along the same optical path. To form an optical path with ʎ = 1.064 μm and absolute value of the laser pulse energy of 3 J, a special refractive index matched twisted Nematic Liquid Crystal Cell of type LCNP3, with switching on time ƮON smaller than 3 μs was applied.

5

Refractive index matched half-wave plate with a nematic liquid crystal for three-dimensional laser metrology applications

58%

Piecek W. , Jaroszewicz L. R. , Miszczyk E. , Raszewski Z. , Mrukiewicz M. , Perkowski P. , Nowinowski-Kruszelnicki E. , Zieliński J. , Olifierczuk M. , Kędzierski J. , Sun X. W. , Garbat K. , Kowiorski K. , Morawiak P. , Mazur R. , Tkaczyk J.

|

tom Vol. 24, No. 4

169--182

EN

There exists a need in a quality and accuracy of a three-dimensional laser metrology operating in numerically controlled automatic machines. For this purpose, one sends three laser beams mutually perpendicular. These three beams of the wavelength λ = 0.6328 μm are generated by the same laser and are directed along three independent, orthogonal, mutually perpendicular, optical paths with a given light polarization plain. Using these beams, constituting the frame of coordinates, three independent laser rangefinders are able to determine spatial coordinates of a working tool or a work piece. To form these optical pulses, a special refractive index matched Half-Wave Plate with nematic Liquid Crystal (LCHWP) was applied. The presented half-wave plate is based on a single Twisted Nematic (TN) cell (with the twist angle φ = π/2) of a rather high cell gap d ~15 μm filled with a newly developed High-Birefringence Nematic Liquid Crystal Mixture (HBLCM) of optical anisotropy as high as ∆n ~0.40 at λ = 0.6328 μm, where the Mauguin limit above 5.00 ~ ∆nd >> λ/2 = 0.32 is fulfilled.

6

Measurement of elastic constants of nematic liquid crystals with use of hybrid in-plane-switched cell

58%

Nowinowski-Kruszelnicki E. , Kędzierski J. , Raszewski Z. , Jaroszewicz L. , Kojdecki M. A. , Piecek W. , Perkowski P. , Olifierczuk M. , Miszczyk E. , Ogrosnik K. , Morawiak P.

|

tom Vol. 20, No. 3

255-259

EN

A new method for quick and pretty accurate measurements of splay, twist and bend elastic constants of nematic liquid crystals is experimentally verified. The main concept relies on exploiting only the electric field and determining magnitudes of nematic elastic constants from threshold fields for Freedericksz transitions in only one hybrid in-plane-switched cell. In such cell the deformations of an investigated liquid crystal are controlled by three separated pairs of electrodes confining measurement domains. In two of them inter-digital electrodes are mounted on one cell cover. Splay, twist and bend elastic constants can be measured by a proper choice of electrodes' configuration together with orienting cover coatings (without applying magnetic fields). In this paper, we describe layout of our cells and results of experimental tests by using different liquid crystals: 5CB and 6CHBT (with positive dielectric anisotropy), Demus' esters (with negative dielectric anisotropy) and new liquid crystals mixtures produced in our university.