Light scattering irradiance

The combination of atomic force microscopy (AFM) and Raman spectroscopy is another approach to attain high spatial resolution. AFM also employs a sharp tip close to a sample surface. When the tip is made of metal and light is irradiated onto the tip and surface, Raman scattering is largely enhanced. In this way, a spatial resolution of 15 nm is achieved [2]. 

Figure 7.3 shows the two-beam photon-force measurement system using a coaxial illumination photon force measurement system. Two microparticles dispersed in a liquid are optically trapped by two focused near-infrared beams ( 1 pm spot size) of a CW Nd YAG laser under an optical microscope (1064 nm, 1.2 MWcm , lOOX oil-immersion objective, NA = 1.4). The particles are positioned sufficiently far from the surface of a glass slide in order to neglect the interaction between the particles and the substrate. Green and red beams from a green LD laser (532 nm, 21 kWcm ) and a He-Ne laser (632.8 nm, 21 kW cm ) are introduced coaxially into the microscope and slightly focused onto each microparticle as an illumination light (the irradiated area was about 3 pm in diameter). The sizes of the illumination areas for the green and red beams are almost the same as the diameter of the microparticles (see Figure 7.4). The back scattered light from the surface of each microparticle is...

Figure 10.7 The phase diagram (a) and the glass transition temperatures (b) of a PSC/PVME mixture obtained, respectively, by light scattering and differential scanning calorimetry (DSC). Irradiation experiments were performed in the miscible region at 127 C indicated by (X) in the figure of trans-cinnamic acid-labeled polystyrene/poly(vinyl methyl ether) blends.

If a processing apparatus is constructed in such a way that the X-ray beam can irradiate the sample, it can most probably be mounted in the beamline. Suitable chambers allow for a change of sample temperature, humidity, strain, pressure, etc. Melts may be sheared during irradiation. Fibers can be spun in the beam. Several methods may be combined (SAXS, WAXS, calorimetry, light scattering) by utilization of sophisticated sample chambers. 

The signal generation principle of Raman is inelastic molecular light scattering, in contrast to resonant energy absorption/emission in IR spectroscopy. During the measurement, the sample is irradiated with intense monochromatic radiation. While most of this radiation is transmitted, refracted or reflected, a small amount is scattered at the molecules. 

Figure 3. Change in light scattering intensity (Rjo ) upon photo-irradiation of the micelle of 2a. [2] = M. AABS at 450 nm...

The scattering functions S, and S2 are particularly useful for interpreting experimental data. For incident light polarized parallel to the scattering plane, typically chosen to be the horizontal plane for which = 90°, the ratio of the scattered irradiance to the incident irradiance is given by... 

When the size parameter x is sufficiently small, that is, when the particle is small compared with the wavelength of light, only the leading term in the normal mode expansion for the spherical harmonic functions is needed. In this case Eq. (76) reduces to Rayleigh s result, Eq. (47), for the ratio of the scattered irradiance to the incident irradiance. 

Although the irradiance of the scattered light is of major interest to the experimentalist, there are several other aspects of light scattering that should be included in this review. These include cross-sections, radiation pressure, and electromagnetic energy absorption. The latter two phenomena can be related to cross-sections. 

Laser Raman spectroscopy uses a light scattering process where a specimen is irradiated monochromatically with a laser. The visible light that has passed into the specimen causes the photons of the same wavelength to be scattered elastically, while... 

By interposing various polarizers between particle and detector and recording the resulting irradiances in a manner identical to that discussed for a plane wave in Section 2.11, we obtain the Stokes parameters of the light scattered by... 

If unpolarized light of irradiance /, is incident on one or more particles, the Stokes parameters of the scattered light are... 

Thus, the scattered light is also polarized perpendicular to the scattering plane. We denote by i the scattered irradiance per unit incident irradiance given that the incident light is polarized perpendicular to the scattering plane ... 

If the incident light is unpolarized with irradiance /, the scattered irradiance Is is... 

The scattered irradiances per unit incident irradiance (dimensionless irradi-ances) for incident light parallel and perpendicular to the scattering plane are (omitting k2r2)... 

Angular light scattering measurements are sometimes classified as either absolute or relative. In an absolute measurement 7s//(, which is directly related to the differential scattering cross section (13.2), is determined in a relative measurement the irradiance is referred to some arbitrary scattering angle, say 10°, so that (assuming azimuthal symmetry)... 

The simplest, and probably most obvious, way to measure scattering matrix elements is with a conventional nephelometer (Fig. 13.5) and various optical elements fore and aft of the scattering medium. Recall that we introduced Stokes parameters in Section 2.11 by way of a series of conceptual measurements of differences between irradiances with different polarizers in the beam. Although we did not specify the origin of the beam, it could be light scattered in any direction. Combinations of scattering matrix elements can therefore be extracted from these kinds of measurements. There are now, however, two beams—incident and scattered—and many possible pairs of optical elements these are discussed below. 

Changes in molar mass of irradiated polymers were measured by viscosity, gel permeation chromatography, osmometry and light scattering. G (scission) and G (cross-link) values can be derived from gel contents if cross-linking predominates (3) and a GPC technique requiring only 50 mg of polymer, which could be in the form of powder, was developed for this purpose (4). 

Electron microscopy provides direct evidence that the polymerized dispersions still contain spherical liposomes (Fig. 20). Laser light scattering measurements also demonstrate the presence of vesicles in the irradiated dispersions16). The size distribution of vesicles is not significantly altered by polymerization 13) (Fig. 21) as confirmed by gel filtration before and after irradiation of vesicles of (7). 

Fig. 3. Mukiparameter light scatter and DNA assay. Burkitt lymphoma cells induced into apoptosis by irradiation with 4 Gy were analyzed for forward light scatter (FSC) and propidium iodide fluorescence (FL2). Region , viable cells Region 2, apoptotic cells.

Experimental. All photodimerizations were carried out in a stainless steel fixed volume cell (1.75 cm ID with a 1.0 cm path length) with sapphire windows under the irradiation of a Hanovia medium pressure mercury lamp filtered through water and Pyrex for a 13.5 hour exposure. The cell and lamp assembly have been described previously (31). For selected runs a custom built 0.9 mL variable-volume pump was connected to the cell and the pressure was varied to determine the exact location of the phase boundary, based on light scattering measured in a Cary 2290 UV-Vis spectrophotometer (Varian Inst.). The spectrophotometer was also used to measure the concentrations of the monomeric cyclohexenone before and after reaction. 

---