Interferometer assemblies

The interferometer assembly has been modified to provide acoustic isolation from both building vibrations and airborne noise (7). These improvements have greatly enhanced the signal to noise. The spectra presented here show a signal to noise ratio in excess of 500 for silica samples and in excess of 100 for the alumina samples the differences are due to different sample porosities. No smoothing of the spectra has been performed, and all spectra reported are direct reproductions of the plotter output from the spectrometer. 

The total optical path difference between the two arms of the interferometer, for a sample length of about 50 mm, is of the order of 10 mm or less, minimizing the systematic error due to laser frequency fluctuations. To reduce the thermal effects on the interferometer assembly, the interferometer support plate is stabilized to a temperature slightly higher than room temperature and insulated from air currents by a polystyrene foam shield. The temperature variation of the interferometer support is kept below 0.1 K. 

Figure 2. Simplified diagram of the optical layout of the FTIR spectrometer and A are apertures, P and P are polarizers, and the area inside the dashed box the actual interferometer assembly...

Israelachvili and coworkers [64,69], Tirrell and coworkers [61-63,70], and other researchers employed the SFA to measure molecular level adhesion and deformation of self-assembled monolayers and polymers. The pull-off force (FJ, and the contact radius (a versus P) are measured. The contact radius, the local radius of curvature, and the distance between the surfaces are measured using the optical interferometer in the SFA. The primary advantage of using the SFA is its ability to study the interfacial adhesion between thin films of relatively high... 

Figure 18. ISTROG Interferometer. The high improvement on the accuracy of contrast measurements with such devices mainly results from the efficient spatial filtering and the spatial stability of the recombining assembly.

Nealey and coworkers [75,76,146] took a similar approach and applied lithographically defined self-assembled monolayers as substrates to direct the orientation of block copolymer thin films. After EUV interferometic lithography on octadecyltrichlorosilane (OTS) or phenylethyltrichlorosilane (PETS) monolayers, PS-fr-PMMA block copolymers were deposited and annealed on the substrates. Due to the selective wetting of PS and PMMA on the unexposed and exposed regions, respectively, they were able to obtain large areas of perpendicular lamella when the commensurate condition was fulfilled. 

Fig. 13.17 Working principle of the MEMS-based FDNMR spectrometer. The sample (S) sits within an RE excitation coU (C), which modulates the NMR signal at the mechanical resonance frequency of a resonator made up of the detector magnet (D) and sihcon beam (O). The detector magnet sits within an annular magnet (R) and the entire assembly is within the pole piece of an external field magnet (M). Detector magnet motion is measured using a fiber optic interferometer (F)...

An FTIR spectrometer contains a single beam optical assembly with, as an essential component, an interferometer - often of the Michelson type - located between the source and the sample (Figure 10.7c). It consists of three active components a moving mirror, a fixed mirror and a beam-splitter. 

Figure 10.8 The optical assembly of a Fourier transform apparatus, (a) 90° Michelson interferometer with below, some details of the beam-splitter (b) the optical diagram of a single beam spectrophotometer (picture of Shimadzu model 8300). A low power He/Ne laser is used as an internal standard (632.8 nm) in order to locate with precision the position of the mobile mirror by an interference method (this second sinusoidal interferogram which follows the same optical pathway, is used by the software to determine the optical path difference).

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