Grid polarizers

The experiments described here were performed with a Digilab FTS40 Fourier transform instrument, with a liquid nitrogen-cooled Mercury Cadmium Telluride, (MCT), detector. The instrument is provided with a computer for data acquisition, storage and mathematical treatment. P-polarized incident light was obtained by means of an A1 wire-grid polarizer supported on a BaF2 substrate. 

Samples for infra-red absorption measurement were introduced between two rubbed nylon coated calcium fluoride substrates spaced 10 pm apart. To insure proper parallel alignment, samples were cooled at 0.02° C/minute from the isotropic to the Smectic C phase. The alignment was then checked using polarizing microscopy. Polarized IR spectra (32 scans per spectrum) were obtained using an FTIR spectrometer (IFS-66 Bruker, Pillerica, MA) equipped with a wire grid polarizer at a resolution of 2 cm"1. 

Infrared spectra were taken with a Michelson-Genzel type FTIR instrument (IR/98, IBM Instruments, Inc.) equipped with a liquid nitrogen cooled HgCdTe detector. The optical attachment arrangement is shown in Fig. 2-14. The infrared radiation was p-polarized using ERS-5 wire grid polarizer. 

Figure 9.3 Wire grid polarizer for infrared radiation.

As is shown in Figure 9.3, a wire grid polarizer will attenuate light polarized parallel to the conducting wires. This is a result of attenuation of the electric field oscillating... 

Upon leaving the monochromator, the light passes through an appropriate band pass filter to remove higher order diffractions, and is recollected and passes through a gold grid polarizer into the PEM. The major stress axis of the PEM is at 45 with respect to the plane of polarization transmitted by the polarizer. The sample is mounted directly behind the PEM in a standard, demountable and temperature controlled IR... 

The IR apparatus and dichroism methods used in this work have been previously described (11,12). In the differential dichroism experiment, the samples were stretched from both ends simultaneously at a true strain rate of approximately 30% per min. A motorized stretching jig was used which fits inside the instrument in the path of the common beam at a 45° angle. Wire grid polarizers were set at 45° in the reference and sample beams, and the instantaneous dichroic difference A A — AM — Aj was recorded with the instrument operating in constant, wave-number mode. 

Brewster polarizers are almost not used anymore in IR spectroscopy since their relatively big sizes represent a definite disadvantage. Nowadays they are practically replaced by the convenient grid polarizers. 

The infrared spectra were recorded on a Nicolet 7199 or a Nicolet 205 Fourier transform infrared spectrometer at a resolution of 2 cm l with a total number of scans of up to 128 for low-orientation samples. The infrared beam was polarized using a SPECAC gold wire-grid polarizer. Samples, rather than polarizer, were rotated 90° in order to obtain the two polarization measurements. The dichroic ratio was calculated from the measured absorbance at the maximum of the infrared band. 

A grid polarizer is the next object we need to consider. First we will define the Jones vectors for linear polarization at + 45° with respect to the y axis. These cases correspond to the situation shown in Fig. 8a. The required Jones vectors are... 

The reflective circular polarizer consists of a free-standing wire-grid polarizer parallel to and in front of a flat mirror. Half of the radiation is immediately reflected by the grid, while the other half, polarized in the orthogonal direction, is reflected by the flat mirror and delayed by X/A according to the spacing between the wire-grid polarizer and the mirror. 

Because of technological advances in this area, much higher efficiency polarizers and detector systems are available today than had been in recent years. One example of this is the commercial availability of infrared wire grid polarizers (Perkin Elmer) which is of higher efficiency in transmission and polarization than the former Brewster plate silver chloride polarizers. 

Type mission, adjust fire, fire for effect, immediate suppression. Method of target location grid, polar, shift from known point. 

FTIR experiments were carried out with a Bruker Vector 22 spectrometer equipped with a MCT detector. The electrochemical IR cell, fitted with a 60° CaF2 prismatic window, was provided with an inlet and an outlet for the solutions to allow the electrolyte exchange under potential control. For each spectmm, 128 interpherograms were collected at a resolution of 8 cm-1. Parallel (p) and perpendicular (s) polarized IR light were obtained from a BaF2-supported A1 grid polarizer. The spectra were represented as a ratio, R/R0, where R and Ra are the reflectances corresponding to the sample and reference spectra, respectively. 

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