Raman backscattering

Raman backscattering occurs at twice the wave vector of the incident light, 2fcp = 4nn/Xp, where Xp is the wavelength of the light and n the... 

Raman backscattering measurements were performed in the wave number range between 200 and 4300 cm. Besides the well known phonon modes that are located between 200 and 800 cm additional lines were observed at wave numbers ranging from 2800 to 3150 cm" (see spectrum (a) in Fig. 1). At higher wave numbers Raman lines were not observed. 

Figure 1. Raman backscattering spectra of single crystal ZnO before (a) and after hydrogen effusion (b). The measurements were performed using the 488 nm line of an Ar laser and a laser power of 190 mW. Background data were subtracted.

In summary, Raman backscattering measurements showed the presence of C-Hx and N-H local vibrational modes in single crystal ZnO. Heating the specimens to temperatures of up to 950 °C caused hydrogen out diffusion. After dehydrogenation the local vibrational modes disappeared indicating that they are related to the presence of H. From H effusion measurements the... 

Raman backscattering spectra were recorded at room temperature using Fourier spectrometer Excalibur 4100 supplied with the FT-Raman accessory... 

Fig. 5. Top left Laser-induced Raman backscatter (381 nm) and two fluorescence return signals (414, 482 nm) measured during an overflight over an oleyl alcohol slick and adjacent clean sea areas bottom left the simultaneously obtained passive microwave L-band data top right same lidar sensor, Raman backscatter (381 nm) and fluorescence return signal at 500 nm during an overflight over a Murban cmde oil spill and adjacent clean sea areas bottom right same passive microwave sensor, over an artificial oil spill in the New York Bight.

With regard to the Lidar measurements, the presence of an OLA slick at the ocean surface caused a decrease in both the Raman backscatter at 381 nm and of the fluorescent bands at 414 and 482 nm, while in the presence of a thick cmde oil spill the Raman depression at 381 nm was accompanied by a simultaneous increase in the longer wavelength bands. During the same overflights a dramatic decrease in the passive microwave L-band signals was observed in the presence of an OLA slick (Blume et al. 1983), while in the presence of a cmde oil spill an increase in the same band is encountered. Unfortunately, a verification of the latter conclusions is still... 

Fig. 4. 12-channel imaging airborne laser fluorosensor signature of spilled crude oil (all data rectified). The channel 2 (344 nanometres) shows the suppression of the laser-induced water Raman backscatter signal through the strongly absorbing oil film. This information can be used for thickness estimation... 

F. E. Hoge, R.N. Swift Airborne simultaneous spectroscopic detection of laser-induced water Raman backscatter and fluorescence from chlorophyll a and other naturally occuring pigments. Appl. Opt. 20, 3197 (1981)... 

Figure 1.23 Raman backscattering spectrum of as-grown single-costal ZnO after background subtraction. The sample was irradiated with the 488 nm line of an Ar laser and a power of 190 mW. The solid line represents a least-square fitofsixGaussian lines to the data. The dashed lines indicate the individual local vibrational modes. The peak positions are indicated in the plot.

Hoge, EE. and Swift, R.N. (1983). Airborne detection of oceanic turbidity cell structure using depth-resolved laser-induced water Raman backscatter. Appl. Optics, 22, 3778-3786. 

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