Optical technique

Optical microscopy is extremely useful in providing a rapid view of a relatively large area of the specimen. It should be used as a starting point in most microscopic problem solving, to 

A major advantage of optical microscopy techniques is the ease of sample preparation. Thin fibers, films, or membranes can be placed directly in an appropriate iimnersion oil on a glass slide and information regarding the crystalline or dispersed phases, orientation, birefringence, etc., can be readily determined (Section 

A major advantage of optical microscopy techniques is the ease of sample preparation. Thin fibers, films, or membranes can be placed directly in an appropriate immersion oil on a glass slide and information regarding the crystalline or dispersed phases, orientation, birefringence, and so forth, can be readily determined (see Section 4.1.1). Sectioning (see Section 4.3.2) of thicker materials is routinely accomplished in very short times, on the order of 30 min or so, with steel or glass knives. Observations and measurements of spherulite sizes, local orientation in molded parts, and fiber orientation are also conducted with the optical microscope. Phase contrast and Nomarski techniques provide contrast in multiphase polymers. Small differences in refractive index are enough to make the dispersed phases distinct, so the 

A cost effective experimental setup for optical modulettion experiments, recently built in our laboratory. Is shown in Fig. 8 (57). Similar setup was recently reported by Tian et al. (58). Experiments performed with this system include photoreflectance (PR), electrolyte electroreflectance (EER), surface photovoltage spectroscopy (SPV), 1st. and 2nd. harmonics photoinduced current-voltage characteristics, spectral response and d.c. current-voltage characteristics. One can switch electronically between experiments and perform any number of techniques without moving the cell or removing the electrode from the electrolyte. A variable neutral 

NMR spectra were recorded on a Varian HA-100 spectrometer in an unlocked mode using an external oscillator and frequency counter to calibrate its sweep parameters. Samples were equilibrated in the magnetic field without spinning at ambient temperature (ca. 32 0) for nearly a day before each reorientation. The temperature was controlled with a precision of 0.2 with a Varian temperature-control unit. The samples were rotated by accurately known amounts with the aid of small aluminum sleeves 

Apparent viscosities were determined using a falling sphere method on samples that had been matured for more than a year. 

As in the NMR experiments the samples were magnetically oriented with the field direction perpendicular to the NMR tube axis. Crossed polarizers were mounted on the magnet for correlation of optical and viscometric data. After a rotation experiment was performed the sample was removed from the magnetic field and placed in a 25.0 0.02°C constant temperature bath. The velocity of the sphere falling along the axis of the NMR tube measured using a cathetometer and timer was used to calculate the Stokes law apparent viscosity. A Faxen correction (ll) of about 5 was applied to all data. 

The equations of motion for a memory-dependent nematic liquid undergoing reorientation in a magnetic field have recently been presented (lO). The equations were derived using the theory of micropolar continuum mechanics as introduced by Eringen (l2, 

In the special case when the memory can be neglected, the result is 

The value of using an extremely sophisticated sensor (the human eye) in the study of heated materials has been appreciated for some time. In the 

The video camera was able to produce 640 x 480 pixel images of an area ca. 2 x 2 mm, with the help of a microscope with an extra-long 

Detailed presentations of the theoretical framework for infrared and Raman spectroscopy can be found in many textbooks [1-6]. Here, we give only a few definitions for further comparison with INS. 

The transition between an initial state (po at energy Eq and a final state (pf) at Ef occurs at frequency roof = Ef — Eq and the intensity is proportional to the square amplitude of the transition matrix element (po M 9f p. Only vibrations generating a change of the dipole moment are infrared active. 

Normal Raman spectroscopy probes the variations of the polarizability tensor with respect to the degrees of freedom, in the ground electronic state. When an electrical field is applied to a system the electron distribution is modified and the sample acquires an induced dipole moment as the barycenters of the charges are displaced. The polarizability tensor [a] defines the correspondence between the incident electrical field E and the induced dipole moment M = [a]E. The polarizability tensor can be expanded in a Taylor series analogous to Equation (8.8)  

Because the interaction of photons with matter is quite complicated and depends strongly on the electronic structure, the various derivatives of the dipole moment and polarizability tensor cannot be estimated easily. Even calculations with the most advanced quantum methods are far from providing reliable estimations. Therefore, a major drawback of optical techniques is that intensities cannot be interpreted with confidence. 

---

Koroteev N I 1995 BioOARS—a novel nonlinear optical technique to study vibrational spectra of chiral biological molecules in solution Biospectroscopy 1 341-50... 

A comprehensive review of fast and ultrafast time-resolved optical techniques. 

Optical Techniques. The most important tool in a museum laboratory is the low power stereomicroscope. This instmment, usually used at magnifications of 3—50 x, has enough depth of field to be useful for the study of surface phenomena on many types of objects without the need for removal and preparation of a sample. The information thus obtained can relate to toohnarks and manufacturing techniques, wear patterns, the stmcture of corrosion, artificial patination techniques, the stmcture of paint layers, or previous restorations. Any art object coming into a museum laboratory is examined by this microscope (see Microscopy Surface and interface analysis). 

Structural Analysis. Some of the optical techniques are also used for stmctural analysis. Microscopic examinations of metallurgical cross sections or of sections through the paint layers of a painting are indeed stmctural examinations, as is ir reflectography. 

In addition to viscometers, optical devices such as microscopes and cameras can be used for defining and solving flow problems as weU as characterizing materials (3—5). Optical techniques allow the investigator to determine the physical stmcture of the material and visualize its flow processes. 

Instead of monitoring x-ray transmission, some instmments use visible light to monitor concentration (53). This optical technique is generally referred to as turbidimetry or photoextinction. Light is usually used for low particle concentrations and detection of low molecular weight particles. 

It was estabhshed ia 1945 that monolayers of saturated fatty acids have quite compHcated phase diagrams (13). However, the observation of the different phases has become possible only much more recendy owiag to improvements ia experimental optical techniques such as duorescence, polarized duorescence, and Brewster angle microscopies, and x-ray methods usiag synchrotron radiation, etc. Thus, it has become well accepted that Hpid monolayer stmctures are not merely soHd, Hquid expanded, Hquid condensed, etc, but that a faidy large number of phases and mesophases exist, as a variety of phase transitions between them (14,15). 

The majoiity of the various analyte measurements made in automated clinical chemistry analyzers involve optical techniques such as absorbance, reflectance, luminescence, and turbidimetric and nephelometric detection means. Some of these ate illustrated in Figure 3. The measurement of electrolytes such as sodium and potassium have generally been accomphshed by flame photometry or ion-selective electrode sensors (qv). However, the development of chromogenic ionophores permits these measurements to be done by absorbance photometry also. 

Adiabatic flame temperatures agree with values measured by optical techniques, when the combustion is essentially complete and when losses are known to be relatively small. Calculated temperatures and gas compositions are thus extremely useful and essential for assessing the combustion process and predicting the effects of variations in process parameters (4). Advances in computational techniques have made flame temperature and equifibrium gas composition calculations, and the prediction of thermodynamic properties, routine for any fuel-oxidizer system for which the enthalpies and heats of formation are available or can be estimated. 

McQueen, R.G., Hopson, J.W., and Fritz, J.N. (1982), Optical Technique for Determining Rarefaction Wave Velocities at Very High Pressures, Rev. Sci. Instrum. 53, 245-250. 

An optical detector with appropriate electronics and readout. Photomultiplier tubes supply good sensitivity for wavelengths in the visible range, and Ge, Si, or other photodiodes can be used in the near infrared range. Multichannel detectors like CCD or photodiode arrays can reduce measurement times, and a streak camera or nonlinear optical techniques can be used to record ps or sub-ps transients. 

Molecular ion mass interferences are not as prevalent for the simpler matrices, as is clear from the mass spectrum obtained for the Pechiney 11630 A1 standard sample by electron-gas SNMSd (Figure 4). For metals like high-purity Al, the use of the quadrupole mass spectrometer can be quite satisfiictory. The dopant elements are present in this standard at the level of several tens of ppm and are quite evident in the mass spectrum. While the detection limit on the order of one ppm is comparable to that obtained from optical techniques, the elemental coverage by SNMS is much more comprehensive. 

In conclusion RAIRS, which affords high spectral resolution, is a very versatile nondestructive optical technique which does not depend on a vacuum environment. Vibrational spectra also serve as characteristic fingerprints for adsorbate molecules, adsorption configurations, and structures on metallic and dielectric substrates. Extension to include dielectric substrates opened new fields of application in polymer and biochemical research. 

Fig. 7. Optical density of solid Coo on Suprasil based on two different optical techniques (+, ). For comparison, the solution spectrum for Coo dissolved in decalin (small dots) is shown. The inset is a plot of the electron loss function -7m[(l + e)] vs E shown for comparison (HREELS) [78].

Given the advanced state of wave-profile detectors, it seems safe to recognize that the descriptions given by such an apparatus provide a necessary, but overly restricted, picture. As is described in later chapters of this book, shock-compressed matter displays a far more complex face when probed with electrical, magnetic, or optical techniques and when chemical changes are considered. It appears that realistic descriptive pictures require probing matter with a full array of modern probes. The recovery experiment in which samples are preserved for post-shock analysis appears critical for the development of a more detailed defective solid scientific description. 

Dial-indicator methods (i.e., reverse-dial indicator and the two variations of the rim-and-face method) use the same type of dial indicators and mounting equipment. However, the number of indicators and their orientations on the shaft are different. The optical technique does not use this device to make measurements, but uses laser transmitters and sensors. 

See, e.g., K. Seki, Photoclecrron spectroscopy of polymers, in Optical Techniques to Characterize Polymer Systems (Ed. H. Bassler), Elsevier, Amsterdam 1989, Chapter 4. 

While electron or ion beam techniques can only be applied under ultra-high vacuum, optical techniques have no specific requirements concerning sample environment and are generally easier to use. The surface information which can be obtained is, however, quite different and mostly does not contain direct chemical information. While with infra-red attenuated total reflection spectroscopy (IR-ATR) a deep surface area with a typical depth of some micrometers is investigated, other techniques like phase-measurement interference microscopy (PMIM) have, due to interference effects, a much better surface sensitivity. PMIM is a very quick technique for surface roughness and homogeneity inspection with subnanometer resolution. 

Seki K (1989) Photoelectron spectroscopy. In Bassler H (ed) Optical technique to characterize polymer systems, Elsevier, Amsterdam p 115... 

Laser Doppler Vibrometry (LDV) is a sensitive laser optical technique well suited for noncontact dynamic response measurements of microscopic structures. Up to now, this technology has integrated the micro-scanning function for... 

Previous data have concerned rmconfined flame configurations driven by velocity perturbations. These cases are less dependent on the geometry because sound generation is not modified by reflection from boundaries. It is also easier to examine rmconfined flames with optical techniques. However, in many applications, combustion takes place in confined environments and sound radiation takes place from the combustor inlet or exhaust sections. The presence of bormdaries has two main effects ... 

B.N. Shivashankara, W.C. Strahle, and J.C. Handley. Evaluation of combustion noise scaling laws by an optical technique. AIAA., 13 623-627,1975. 

The surface forces apparatus (SEA) can measure the interaction forces between two surfaces through a liquid [10,11]. The SEA consists of two curved, molecularly smooth mica surfaces made from sheets with a thickness of a few micrometers. These sheets are glued to quartz cylindrical lenses ( 10-mm radius of curvature) and mounted with then-axes perpendicular to each other. The distance is measured by a Fabry-Perot optical technique using multiple beam interference fringes. The distance resolution is 1-2 A and the force sensitivity is about 10 nN. With the SEA many fundamental interactions between surfaces in aqueous solutions and nonaqueous liquids have been identified and quantified. These include the van der Waals and electrostatic double-layer forces, oscillatory forces, repulsive hydration forces, attractive hydrophobic forces, steric interactions involving polymeric systems, and capillary and adhesion forces. Although cleaved mica is the most commonly used substrate material in the SEA, it can also be coated with thin films of materials with different chemical and physical properties [12]. 

---