Backscattered light

Let us first consider the case where the laser beam is emitted through the telescope. The outgoing beam undergoes a tilt deflection through the turbulent atmosphere as does the backscattered light. The round trip time to the mesosphere is 0.6 ms at zenith. It is much shorter than the tilt coherence time ... 

Figure 19. The polychromatic LGS. The laser beam is tilted on its way to the mesosphere, where it produces a spectmm spanning from the UV to the infrared. The optical path of the backscattered light depends on the wavelength.

In the case of a single lifetime with no interference from ambient or backscattered light only a single frequency is necessary to determine the lifetime of the luminescence. Determination of the phase and modulation at multiple frequencies is necessary to characterize complex decays in fiberoptic sensors. 

We note that since Q involves the scattering coefficients, the radiation pressure force has resonance or near-resonance behavior. This first was observed and analyzed by Ashkin and Dziedzic (1977) in their study of microparticle levitation by radiation pressure. They made additional measurements (Ashkin and Dziedzic, 1981) of the laser power required to levitate a microdroplet, and Fig. 19 presents their data for a silicone droplet. The morphological resonance spectrum for the 180° backscattered light shows well-defined peaks at wavelengths corresponding to frequencies close to natural frequencies of the sphere. The laser power shows the same resonance structures in reverse, that is, when the scattered intensity is high the laser power required to levitate the droplet is low. 

It seems relevant to remind that this technique is based on recording the backscattered light (usually helium) ions occurred as a result of their interaction with the matter of a solid layered specimen (for more detail, see Ref. 124). Experimental data are presented as plots of intensity, /, against energy, E, of the beam of backscattered ions (Fig. 2.15). 

IwASAKA Y., Hayashida S., and Ono A., Increased backscattered light from the stratospheric aerosol layer after Mt. El Chichon eruption laser radar measurements at Nagoya (35 N, 137 E). Geophys. Res. Lett. , 10, 440-442 (1983). 

A technique of special interest to the pharmaceutical and other industries is FBRM. It is an on-line instrument that can give information on parameters such as particle size , surface area, filtration rate and flocculationSi- It is used in crystallisation, filtration and drying applications. It works by scanning a laser beam in a circular motion over a surface at high speed. Light is back scattered by the particles and picked up by a detector. The duration of time that it takes for the backscattered light to return to the detector is called chord... 

Figure 15. Diffuse reflectance distributions used to measure tissue absorption and scattering properties non-invasively. (a,b) principle of the technique, showing light entering a point on the tissue surface and the measured radial distribution of the diffusely reflected (backscattered) light that depends on the tissue absorption and scattering properties, (c) external surface probe (courtesy Dr M. Patterson, Hamilton, Canada), (d) endoscopic probe (courtesy Dr R. Bays and colleagues, Lausanne, Switzerland) in this case the distribution is measured along the probe from light input at the end, with the probe placed flat on the tissue (e.g. esophagus) surface.

Dharmarajan and Brouwers (1987) described the use of an instrument, the atomizing trace gas monitoring system [total combustible gas (TCG) analyzer], equipped with ion-specific electrodes for measuring airborne HCl and HF. A lidar system, based on measnring backscattered light from a short pnlse of laser radiation, has been reported for determining hydrogen chloride in incinerator ship plnmes (Weitkamp 1985). 

Intravenous fiberoptic catheters are utilized in monitoring SvOj in the pulmonary artery and can be used to indicate the effectiveness of the cardiopulmonary system during cardiac surgery and in the ICU. Several problems limit the wide clinical application of intravascular fiberoptic oximeters. These include the dependence of the individual red and infrared backscattered light intensities and their ratio on hematocrit (especially for SvOj below 80%), blood flow, motion artifacts due to catheter tip whipping against the blood vessel wall, blood temperature, and pH. 

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