Thomas, Baby; Nampoori, V P N(Solid State Communications, 1992)
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Abstract:
A method of preparation of strontium sulphide phosphors doped
with europium is given. Nitrogen laser excited fluorescence emission
spectra of these phosphors in the visible region are recorded. A band
with line structure in the region 350-430 nm and a new broad band at
460 nm are observed. The splitting pattern for the 6p levels of Eu 2+ are
given.
Sasi Kumar, P R; Nampoori, V P N; Vallabhan, C P G(Springer, May , 1994)
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Abstract:
The changes in emission characteristics of a neon hollow cathode discharge by resonant laser excitation of 1s 5→2p 2 and 1s 5→2p 4 transition have been studied by simultaneously monitoring the optogalvanic effect and the laser induced fluorescence. It has been observed that resonant excitation causes substantial variation in the relative intensities of lines in the emission spectrum of neon discharge.
V P N Nampoori; Radhakrishnan, P; Girijavallabhan, C P; Shelly John, M(Measurement Science and Technology, UK, November 12, 1998)
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Abstract:
A novel sensing technique for the in situ monitoring of the rate of pulsed laser
deposition (PLD) of metal thin films has been developed. This optical fibre based sensor
works on the principle of the evanescent wave penetration of waveguide modes into the
uncladded portion of a multimode fibre. The utility of this optical fibre sensor is
demonstrated in the case of PLD of silver thin films obtained by a Q-switched Nd:YAG laser
which is used to irradiate a silver target at the required conditions for the preparation of thin
films. This paper describes the performance and characteristics of the sensor and shows how
the device can be used as an effective tool for the monitoring of the deposition rate of silver
thin films. The fibre optic sensor is very simple, inexpensive and highly sensitive compared
with existing techniques for thin film deposition rate measurements.
Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Indian Journal of Physics, 1992)
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Abstract:
A simple fiber optic concentration sensor based on the coupling of light f rom one
fiber to another through a solution is discussed. The operational characteristics of the sensor are
illustrated by taking the solutions of potassium permanganate and fast green dye as samples.The extrinsic type sensor described here shows linearity at lower concentrations.
Riju C, Issac; Bindhu, C V; Harilal, S S; Geetha K, Varier; Nampoori, V P N; Vallabhan, C P G(World Scientific Publishing Company, 1996)
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Abstract:
Pulsed photoacoustic studies in solution of C60 in toluene have been made using the 532 nm radiation from a frequency doubled Nd:YAG laser. Though C60 is found to exhibit the phenomenon of optical limiting, the results on photoacoustic measurements do not give any indication of multiphoton transitions as suggested in some of the earlier works. Results of photoacoustic measurements show that excited state absorption is the dominant process responsible for optical limiting while phenomena like nonlinear scattering may contribute to a lesser extent.
James, Joseph; Ananthakrishnan, T R; Nampoori, V P N; Rudra Warier, M K; Karanjikar, N P; Kamat, M J(World Scientific Publishing Company, 1995)
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Abstract:
The effect of Ce3+ on the fluorescence emission from CaS:Ce3+ phosphor is studied using X-ray excitation. Apart from the emission in the visible region, the phosphor also shows fluorescence emission in the ultraviolet region. Variation in wavelengths and intensities of these emissions due to change in dopant concentration is also analysed.
Sasi Kumar, P R; Ambadi, B; Nampoori, V P N; Vallabhan, C P G(Springer, February , 1993)
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Abstract:
Doppler limited high resolution spectrum in the wavelength region 17224 to 17236 cm−1 of the first positive system (B 3Π g −A 3Σ u + ) of the N2 molecule is recorded by optogalvanic spectroscopic technique using a single mode ring dye laser. It is observed that the intensity and line width of the rotational line increase with the discharge current. Dependence of the collision broadening coefficient on the current was also evaluated.
Bindhu, C V; Harilal, S S; Riju C, Issac; Nampoori, V P N; Vallabhan, C P G(World Scientific Puhlishing Company, 1996)
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Abstract:
Pulsed photoacoustic technique which is found to be a very convenient and accurate method, is used for the determination of absolute fluorescence quantum yield of laser dye rhodamine B. Concentration and power dependence of quantum yield of rhodamine B in methanol for excitation at 532 nm is reported here. Results show that a rapid decrease in quantum yield as the concentration is increased and finally it reaches the limit corresponding to fluorescence quenching.
Harilal, S S; Riju C, Issac; Bindhu, C V; Geetha K, Varier; Nampoori, V P N; Vallabhan, C P G(World Scientific Publishing Company, 1995)
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Abstract:
Pulsed photoacoustic measurements have been carried out in liquid CS2 using 532 nm radiation from a frequency doubled Nd:YAG laser. Variation of signal amplitude with laser fluence clearly indicates the role of multiphoton processes in the generation of photoacoustic effect. It is also shown that four photon induced dissociation and five photon induced ionization are likely processes in CS2 and 532 nm radiation.
Bindhu, C V; Harilal, S S; Riju C, Issac; Geetha K, Varier; Nampoori, V P N; Vallabhan, C P G(World Scientific Publishing Company, 1995)
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Abstract:
Measurement of thermal lensing signal as a function of laser power made in Rhodamine B solutions in methanol give clear evidence of two photon absorption process within certain concentration ranges when 488 nm Ar+ laser beam is used as the pump source. Only one photon process is found to occur when 514 nm and 476 nm beams are used as the pump.