Optical back-scattering

The mixing process of pesticide dispersion in a spray tank mounted on a tractor was monitored using optical back-scattering probes mounted in the tank [89]. A granulated powder was fully dispersed in 20 s whereas a powder product took 4 min. 

---

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...

In Raman measurements [57], the 514-nm line of an Ar+ laser, the 325-nm line of a He-Cd laser, and the 244-nm line of an intracavity frequency-doubled Ar+ laser were employed. The incident laser beam was directed onto the sample surface under the back-scattering geometry, and the samples were kept at room temperature. In the 514-nm excitation, the scattered light was collected and dispersed in a SPEX 1403 double monochromator and detected with a photomultiplier. The laser output power was 300 mW. In the 325- and 244-nm excitations, the scattered light was collected with fused silica optics and was analyzed with a UV-enhanced CCD camera, using a Renishaw micro-Raman system 1000 spectrometer modified for use at 325 and 244 nm, respectively. A laser output of 10 mW was used, which resulted in an incident power at the sample of approximately 1.5 mW. The spectral resolution was approximately 2 cm k That no photoalteration of the samples occurred during the UV laser irradiation was ensured by confirming that the visible Raman spectra were unaltered after the UV Raman measurements. 

Figure 1.4 Comparison of the application ranges of techniques that are sensitive to nearsurface strains. Minimum detection limits are plotted against depth resolution of the measurement. XRD X-ray diffraction DOR differential optical reflectometry. RBS Rutherford back scattering MEIS medium energy ion scattering TEM transmission electron microscopy...

The Sccmning Electron Microscope (SEM) is a standard imaging technique based on electron back-scattering from the sample surface. It analyses the surfaces of solid objects, producing images with the resolution which is about order of magnitude better than that of optical microscopy (typically 10 nm). The SEM avoids the problem of thin samples (TEM) but the SEM observation requires the deposition of a thin conductive metal film on the sample surface to prevent sample charging. 

Figure 2.4 Different types of interactions of electrons with a solid 1, X-ray or optical photons 2, back-scattered electrons 3, secondary electrons 4, coherent elastic scattering 5, inelastic scattering 6, incoherent elastic scattering.

An interesting modification of this technique is the fibre-optic dynamic anemometer (FODA)143. A length of fibre-optic cable carries the laser beam to the interior of the dispersion. Back-scattered light, with its Doppler frequency shift, is returned to the detector along with reflected light and, again, the resulting beat frequency pattern is analysed. Since only a very small volume around... 

Figure 1. Diagram of the optical arrangement for back-scattering at 6 = 175.5° used in photon correlation spectroscopy...

The necessity of immobilisation for many of the above-mentioned technologies can significantly limit their application. Recently free-solution, label-free molecular interactions were investigated with back-scattering interferometry (BSI) in an optical train composed of a helium-neon laser, a microfluidic channel and a position sensor.56 Molecular binding interactions between proteins, ions and protein as well as small molecules and protein could be monitored without labelling or immobilising any of the interaction partners. 

Naqui et. al. [153] describe a phase Doppler technique, for measuring particle velocity and statistcal information about particle size of irregular particles, based on a phase shift signal. The technique works on near back-scatter which leads to a robust set-up under conditions of limited optical access. Preliminary measurements in a crystallizer were presented and good agreement with TSI Aerodynamic particle sizer was found. 

---