C. V. Raman and the Discovery of the Raman Effect

Physics in Perspective (Impact Factor: 0.39). 11/2002; 4(4):399-420. DOI: 10.1007/s000160200002

ABSTRACT In 1928 the Indian physicist C. V. Raman (1888-1970) discovered the effect named after him virtually simultaneously with
the Russian physicists G. S. Landsberg (1890-1957) and L. I. Mandelstam (1879-1944). I first provide a biographical sketch
of Raman through his years in Calcutta (1907-1932) and Bangalore (after 1932). I then discuss his scientific work in acoustics,
astronomy, and optics up to 1928, including his views on Albert Einstein's light-quantum hypothesis and on Arthur Holly Compton's
discovery of the Compton effect, with particular reference to Compton's debate on it with William Duane in Toronto in 1924,
which Raman witnessed. I then examine Raman's discovery of the Raman effect and its reception among physicists. Finally, I
suggest reasons why Landsberg and Mandelstam did not share the Nobel Prize in Physics for 1930 with Raman.

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    ABSTRACT: Recent advances in solid-state lasers and high resolution charge-coupled devices have allowed Raman spectroscopy to emerge as a powerful tool in many applications, as for example in the fields of virology, pharmacology, forensic science, cosmetics, bioscience and nanotechnology. The goal of this research is to contribute even more to the wide spread of this technology by developing low-cost, portable Raman spectrometers, integrated on a chip. In particular the project aims at the fabrication of on-chip devices to be used for the detection of Raman signals from biological samples such as human skin and teeth. Such spectrometer systems comprise optics for delivering an excitation laser signal to, and collecting the resulting Raman signal from the specimen; a laser line filter; a laser suppression filter; the Raman spectrometer; and, for some applications, polarization splitters. The required light source and photodetectors were not studied in detail within the scope of this thesis. During the course of our research we opted to use silicon oxynitride as the core material for the integrated waveguide devices due to its low losses and excellent flexibility when used for waveguide design. In order to face one of the main challenges of our integrated approach, which is signal collection, we initially perform a study on the feasibility of using integrated waveguide probes as alternatives to commonly used fiber probes. We discuss the numerous advantages of integrated probes, in particular comparing their collection efficiency with those of large-core multi-mode and small-core single- and multimode fiber probes. We also investigate whether channel waveguides are the most efficient devices for collecting backscattered light using integrated optics, and we propose a new integrated optical device which enables focusing of the excitation light and confocal signal collection from a sample under study. The device that we propose makes use of two arrayed waveguide gratings in a confocal arrangement and has a collection efficiency which is an order of magnitude higher than that of a channel waveguide. Detailed designs of Raman spectrometers are presented for the applications targeted during our research: detection of water and natural moisturizing factor concentrations in the outermost layer of the skin, the stratum corneum, and the detection of early dental caries. We also present a novel arrayed waveguide grating layout on which we base the wavelength selection devices for the skin application. The novel layout makes use of identical bends in all the arrayed waveguides to avoid systematic phase errors arising from the use of different bends in the conventional layouts. Finally, we experimentally demonstrate the use of arrayed waveguide gratings to measure polarized Raman spectra from extracted human teeth exhibiting sites with early dental caries. The fabricated device which was designed for the specific application has a high spectral resolution of 0.2 nm and a free spectral range of 22 nm. The Raman spectra obtained with our device are compared with the measurements obtained using conventional bulk spectrometers, with which they are in excellent agreement. The measured depolarization ratios enable us to clearly distinguish between carious and sound dental regions with the same accuracy obtained using (much larger) conventional spectrometers.
    Sensors. 01/2012;
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    Notes and Records of The Royal Society - NOTES REC ROY SOC. 01/2004; 58(1):47-64.
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    ABSTRACT: Monolayers of molecules are capable of completely changing the nature of sur-faces and their interactions with the surroundings despite their almost negligible thickness. In the research presented in this doctoral thesis the surface specific technique Vibrational Sum Frequency Spectroscopy (VSFS) was combined with the Langmuir trough to investigate various manifestations of monolayers, such as biomimetic membranes, mono methyl branched long chain fatty acids in contact with air, and hydrophobic silane monolayers in contact with water. VSFS was applied to in situ studies of the oxidative degradation of Langmuir mon-olayers of 1,2-diacylphosphocholines with identical C-18 chains featuring various degrees of unsaturation. The monolayer area and vinyl CH signal intensity were probed at constant surface pressure to monitor the degradation. The rapid deg-radation of the unsaturated lipids in contact with the ambient air is attributed to oxidation of the C=C bonds mediated by reactive species in the air and can be inhibited by purging the compartment surrounding the monolayer with nitrogen. The molecular structure and order of Langmuir monolayers of 1,2-distearoyl-phosphocholine (18:0 PC) and their hydrating water were investigated at different surface pressures using VSFS. The monolayers are conformationally well ordered at all surface pressures and the signal intensity increases due to larger molecular number density at increasing surface pressures. Also, water signals with different vibrational frequencies are observed in different polarization combinations. Additionally, a selection of common phospholipids (18:0 PC, 18:0 PC-D83 and 18:0 PS) were Langmuir-Blodgett (LB) deposited on CaF2 substrates and the CH- and OH-stretching regions as well as lower wavenumber regions were probed using VSFS. The orientation of the conformationally well ordered aliphatic chains was determined to be approximately perpendicular to the sample surface. Monolayers of eicosanoic acid, its iso (19-MEA), and anteiso (18-MEA) analogues were investigated with VSFS, AFM imaging, and the Langmuir trough. The EA forms smooth, featureless monolayers when deposited on silica, while 19-MEA and 18-MEA form 10 -50 nm large domains with homogeneous size distribution. It was not possible to discriminate between the monolayers of racemic and chiral 18 MEA using any of the techniques employed The influence of the experimental geometry on the SF spectral shape and en-hancement at and near total internal reflection conditions (TIR) were systemati-cally investigated by comparing simulations with recorded data from a hydro-phobized silica / water interface. The data agree qualitatively, but not quantita-tively, with the simulations, and the reasons were critically discussed. The water structure next to ordered and disordered hydrophobic silane monolay-ers on silica was investigated using VSFS. The results indicate that the structure of water next to a well ordered hydrophobic monolayer, with the exception of the first layer of water molecules, is not much different from that in the isotropic bulk. This is in contrast to the previous notion where such monolayers were assumed to induce a more ordered interfacial water structure.
    09/2012; Chemical Science and Engineering, KTH Royal Institute of Technology., ISBN: 9789175014364

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