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Techniques of Chiroptical Spectroscopy
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Nelu Grinberg, Harry G. Brittain, Sonia Rodriguez
The circular polarization in the infrared source is obtained by first linearly polarizing the light, and then by passing it through a photoelastic modulator. The linear polarizer is either a CaF2 crystal overlaid by a wire grid (producing the linear polarization through dichroism) or by a LiIO3 crystal polarizer. The optical element within the photoelastic modulator is made out of either CaF2 or ZnSe, chosen on the basis of the desired spectral range. The detector is usually a photovoltaic device capable of responding to infrared energy. The AC component within the detector output is discriminated and amplified by phase-sensitive detection, and the mean detector output is obtained to normalize the VCD signal. The ratio of the differential absorbance to the total absorbance is: gabs=2(aL−aR)/(aL+aR)
Highly polarised electroluminescence in low aspect ratio mesogenic molecules
Published in Liquid Crystals, 2019
Sa-Wook Kim, Dong-Myoung Lee, Jae-Hoon Kim, E-Joon Choi, Chang-Jae Yu
The linearly polarised (LP) PL and EL of the OLEDs were measured by a spectroradiometer (SR-UL1R from TOPCON). The LPPL and LPEL spectra were measured under a linear polariser at 0° and 90° with respect to the rubbing direction of the PEDOT:PSS. The PL quantum efficiency for the spin-coated compound on the rubbed alignment layer was measured using the spectrofluorometer (FP-8500 from JASCO). The current density-voltage-luminance (J-V-L) characteristics of the OLEDs were evaluated using a source meter (Keithley 2000 from Keithley Instruments) and spectroradiometer. The retardation of the EML was measured with photoelastic modulator (PEM) (PEM-100 from Hinds) and lock-in amplifier (SR830 form Stanford Research System) based on the PEM method [27]. Microscopic textures were observed under a polarising optical microscope (POM) (E600W POL from Nikon) with frame-grabbing system (SDC-450 from Samsung). All measurements were carried out in ambient environments after encapsulation.
Magnetooptical Analysis of the Subsurface Region in a Bearing Ring Subjected to Rolling Contact Fatigue
Published in Tribology Transactions, 2018
Yuri Kadin, Iacopo Bertelli, Andrei Kirilyuk
The MOKE setup is schematically presented in Fig. 4. An He-Ne laser beam (wavelength 632.8 nm) is sent through a polarizer (set at 0° from the vertical). The beam is focused by a lens on the surface of a sample at a small angle of incidence (θ is approximately 20.5° from the sample normal). Two magnets are located at the sides of the sample and can produce a magnetic field, up to 4 kG, parallel to its surface. The beam reflected from the surface (which has to be mirror-like polished to reflect the light) passes through a photoelastic modulator and analyzer (set at 45° from the vertical). The photoelastic modulator modulation frequency of 50 kHz serves as the reference for the lock-in amplifier. The light is then focused with a short focal distance lens on a photodetector. The main property to be measured in the magnetooptical experiment from the reflected beam is the so-called Kerr angle, ψk, which is the rotation of light polarization upon the reflection, proportional to the magnetization of material (ψk ∝ M). Applying a sweeping magnetic field to the sample, the magnetic behavior of material at the surface can be studied in terms of the curve relating the Kerr angle with the external magnetic field. In other words, we obtain a curve directly proportional to magnetic hysteresis of the sample, measured locally at the focused spot of the laser beam. The samples were placed on a mechanical unit, used to move the sample with respect to the laser beam with micrometer precision. It was thus possible to study the magnetic behavior of the material at different points at the surface.
Photoelastic modulator-based broadband mid-infrared Stokes polarimeter
Published in Journal of Modern Optics, 2018
William R. FitzGerald, Dennis K. Hore
Prior to discussing our broadband design in the next section, it will useful to introduce the concepts as they relate to a fixed wavelength in the infrared. A polarimeter based on two photoelastic modulators is capable of measuring all four elements of the Stokes vector in a single configuration, allowing rapid changes in polarization to be followed. The specific configuration considered here consists of a photoelastic modulator with retardation amplitude , resonance frequency , and static retardation , with its strain axis horizontal