Sasi Kumar, P R; Nampoori, V P N; Vallabhan, C P G(IOP, 1994)
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Abstract:
Laser-induced photoelectric and photoemission optogalvanic effects in a Ne-Nd hollow cathode discharge have been studied using a continuous wave laser source. The potential barrier for photoinduced electron emission from the cathode decreases as the applied voltage is increased. Owing to secondary electron emission in the plasma, the photocurrent is greater than that without discharge. The multiplication of secondary electrons and the quantum efficiency are also investigated.
Sasi Kumar, P R; Nampoori, V P N; Vallabhan, C P G(Elsevier, August 1, 1995)
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Abstract:
The photoemission optogalvanic (POG) effect has been investigated in a neon-neodymium hollow cathode discharge using
cw laser excitation. Both positive and negative effects were observed. It was found that the amplitude of the POG signal was
unstable near the instability region of the discharge.
Sasi Kumar, P R; Nampoori, V P N; Vallabhan, C P G(IOP, 1993)
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Abstract:
A two-photon induced photoemission optogalvanic effect which brings about a change in the discharge voltage when a pulsed dye laser beam is focused on a tungsten electrode has been described. The experiment is performed with N2, NO2 and Ar discharges. The magnitude of the signal voltage is studied as a function of laser energy and discharge current. The effective quantum efficiency in the discharge is found to be larger than that in the vacuum condition.
Sasi Kumar, P R; Nampoori, V P N; Vallabhan, C P G(IOP, 1993)
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Abstract:
A two-photon induced photoemission optogalvanic effect which brings about a change in the discharge voltage when a pulsed dye laser beam is focused on a tungsten electrode has been described. The experiment is performed with N2, NO2 and Ar discharges. The magnitude of the signal voltage is studied as a function of laser energy and discharge current. The effective quantum efficiency in the discharge is found to be larger than that in the vacuum condition.
Ajith Prasad, K C; Nampoori, V P N; Vallabhan, C P G(Elsevier, 1996)
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Abstract:
Photoemission optogalvanaic (POG) effect has been observed by irradiating copper target electrode, in a nitrogen discharge cell using 1.06 μm and frequency doubled 532 nm Nd:YAG laser pulse. Measurement of the nature of the variation of POG signal strength with 532 nm laser fluence confirms the two photon induced photoelectric emission from copper. However, using 1.06 μm laser pulses thermally assisted photoemission is observed.
Shali, N B; Sugunan, S(Springer Netherlands, 2007)
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Abstract:
Lanthana modified sol-gel titania is prepared
through particulate sol-gel route and the physico-chemical
characterizations of the prepared systems were done using
X-Ray diffration, EDX, BET surface area-pore volume measurements
and TG-DTG analysis. Benzophenone was observed
to be the sole product in the TiO2 photocatalyzed
oxidation of benzhydrol in oxygen purged acetonitrile. The
influence of various parameters, like irradiation time, amount
of catalyst, concentration of the catalyst and other factors on
the photocatalytic oxidation has been investigated. The proposed
mechanism envisages the involvement of a superoxide
radical anion.
ZnO micro particles in the range 0.4-0.6 μm were synthesized by microwave irradiation
method. The XRD analysis reveals that the sample is in the wurtzite phase with orientation
along the (101) plane. SAED pattern of the sample reveals the single crystalline nature of
the micro grains. TEM images show the formation of cylindrical shaped ZnO micro
structures with hexagonal faces. The optical phonon modes were slightly shifted in the
Raman spectrum,attributed to the presence of various crystalline defects and laser induced
local heating at the grain boundaries. A broad transmission profile was observed in the
FTIR spectrum from 1550-3400 cm-1 which falls in the atmospheric transparency window
region. PL spectrum centered at 500 nm with a broad band in the region 420-570 nm
comprised of different emission peaks attributed to transition between defect levels.
Various emission levels in the sample were expliained with a band diagram
Description:
Journal of Optoelectronics and Biomedical Materials Vol. 4, Issue 1, January-March 2012, p. 1 - 7
Junaid, Bushiri M; Saji, Chacko; Vaidyan, V K(IOP Publishing LTD, October 20, 2006)
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Abstract:
SnO2 nanocrystalline thin films were deposited on glass substrates by the
spray pyrolysis technique in air atmosphere at 375, 400, 425, 450 and
500 ◦C substrate temperatures. The obtained films were characterized by
using XRD. The room temperature photoluminescence (PL) spectra of these
films have near band edge (NBE) and deep level emission under the
excitation of 325 nm radiation. NBE PL peak intensity decreased
consistently with temperatures for samples prepared at 400, 450 and 500 ◦C,
while a sudden reduction in intensity is observed for the sample prepared at
425 ◦C. A similar effect was observed for the optical transmittance spectra.
These effects can be explained on the basis of the change in population of
oxygen vacancies as indicated by the change in a values
Lyjo, Joseph K; Dayas, K R; Soniya, Damodar; Bindu, Krishnan; Krishnankutty, K; Nampoori, V P N; Radhakrishnan, P(Elsevier, December 15, 2008)
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Abstract:
The laser-induced luminescence studies of the rare earth titanates (R2Ti2O7) (R = La, Nd and Gd) using 355 nm radiation from an Nd:YAG laser are presented. These samples with submicron or nanometer size are prepared by the self-propagating high temperature synthesis (SHS) method and there is no known fluorescence shown by these rare earths in the visible region. Hence, the luminescence transitions shown by the La2Ti2O7 near 610 nm and Gd2Ti2O7 near 767 nm are quite interesting. Though La3+ ions with no 4f electrons have no electronic energy levels that can induce excitation and luminescence processes in the visible region, the presence of the Ti3+ ions leads to luminescence in this region.
Anantharaman, M R; Saravanan, S; Joseph, Mathai C; Venkatachalam, S; Avasthi, D K; Singh, F(Elsevier, November 15, 2005)
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Abstract:
Conjugated polymers in the form of thin films play an important role in the field of materials science due to their interesting properties. Polymer
thin films find extensive applications in the fabrication of devices, such as light emitting devices, rechargeable batteries, super capacitors, and
are used as intermetallic dielectrics and EMI shieldings. Polymer thin films prepared by plasma-polymerization are highly cross-linked, pinhole
free, and their permittivity lie in the ultra low k-regime. Electronic and photonic applications of plasma-polymerized thin films attracted the
attention of various researchers. Modification of polymer thin films by swift heavy ions is well established and ion irradiation of polymers can
induce irreversible changes in their structural, electrical, and optical properties. Polyaniline and polyfurfural thin films prepared by RF plasmapolymerization
were irradiated with 92MeV silicon ions for various fluences of 1×1011 ions cm−2, 1×1012 ions cm−2, and 1×1013 ions cm−2.
FTIR have been recorded on the pristine and silicon ion irradiated polymer thin films for structural evaluation. Photoluminescence (PL) spectra
were recorded for RF plasma-polymerized thin film samples before and after irradiation. In this paper the effect of swift heavy ions on the structural
and photoluminescence spectra of plasma-polymerized thin films are investigated.
Ravikumar, C D; Dr.Kuriakose, V C(Cochin University of Science and Technology, April , 2004)
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Abstract:
Determining the morphological parameters that describe galaxies has always
been a challenging task. The studies on the correlations between
different photometric as well as spectroscopic parameters of the galaxies
help in understanding their structure, properties of the stars and gas which
constitute the galaxy, the various physical and chemical processes which
determine the properties, and galaxy formation and evolution. In the last
few decades, the advent of Charge Coupled Devices (CCDs) and near infrared
arrays ha\·e provided quick and reliable digitized data acquisition,
in the optical and near infrared bands. This has provided an avalanche of
data, which can be processed using sophisticated image analysis techniques
to obtain information about the morphology of galaxies. The photometric
analysis performed in this thesis involve the extraction of structural
parameters of early type gala.xies imaged in the near infrared K (2.2ttm)
band, obtaining correlations between these, parameters and using them to
constrain the large scale properties of galaxi,~s.
Description:
Department of Physics, Cochin University of Science and
Technology
Nithyaja, B; Dr.Nampoori,V P N(Cochin University of Science and Technology, January , 2012)
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Abstract:
This thesis Entitled Photonic applications of biomaterials with special reference to biopolymers and microbes. A detailed investigation will be presented in the present thesis related to direct applications of biopolymers into some selected area of photonics and how the growth kinetics of an aerial bacterial colony on solid agar media was studied using laser induced fluorescence technique.
This chapter is an overview of the spectrum of biomaterials and their application to Photonics. The chapter discusses a wide range of biomaterials based photonics applications like efficient harvesting of solar energy, lowthreshold lasing, high-density data storage, optical switching, filtering and template for nano s tructures. The most extensively investigated photonics application in biology is Laser induced fluorescence technique. The importance of fluorescence studies in different biological and related fields are also mentioned in this chapter.
Description:
International School of Photonics, Cochin University of Science and Technology
Poly(6-tert-butyl-3,4-dihydro-2H-1,3-benzoxazine) was synthesized by
thermally activated cationic ring opening polymerization. The structure of the
polymer was confirmed by spectral and thermal studies. The highest occupied
molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were
estimated using cyclic voltammetry and optical absorption. Modulated photocurrent
measurement technique was employed to study the spectral and field dependence of
photocurrent. Photocurrent of the order of 1.5 micro A/m2 was obtained for polymer at a
biasing electric field of 40 V/mico m.
Preethy Menon, C; Dr. Jacob, Philip(Cochin University of Science & Technology, September , 2001)
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Abstract:
This thesis presents in detail. the theoretical developments and calculations
which are used for the simultaneous determination of thermal parameters, namely thermal diffusivity (a). thermal effusivity (e), thermal conductivity (K) and heat
capacity (cr ) employing photopyroelectric technique. In our calculations. we have
assumed that the pyroelectric detector is supported on a copper backing. so that there
will be sufficient heat exchange between the heated pyroelectric detector and the
backing so that the signal fluctuations are reduced to a minimum. Since the PPE
signal depends on the properties of the detector that are also temperature dependent.
a careful temperature calibration of the system need to be carried out. APPE cell has
been fabricated for the measurements that can be used to measure the thermal
properties of solid samples from ~ 90 K to ~ 350 K. The cell has been calibrated
using standard samples and the accuracy of the technique is found to be of the order
of± 1%.In this thesis, we have taken up work n photopyroelectric investigation of
thermal parameters of ferroelectric crystals such as Glycine phosphite
(NH3CH2COOH3P03), Triglycine sulfate and Thiourea as well as mixed valence
perovskites samples such as Lead doped Lanthanum Manganate (Lal_xPb~Mn03)
Calcium doped (Lal_xCaxMnOJ) and Nickel doped Lanthanum Stroncium Cobaltate
(Lao~Sro5Ni,Col_x03).The three ferroelectric crystals are prepared by the slow
evaporation technique and the mixed valence perovskites by solid state reaction
technique.Mixed valence perovskites, with the general formula RI_xA~Mn03 (R = La.
Nd or Pr and A = Ba, Ca, Sr or Pb) have been materials of intense experimental and
theoretical studies over the past few years. These materials show . colossal
magneloresis/ance' (CMR) in samples with 0.2 < x < 0.5 in such a doping region,
resistivity exhibits a peak at T = T p' the metal - insulator transition temperature. The system exhibits metallic characteristics with d %T > Oabove Tp (wherep is the
resistivity) and insulating characteristics with d % T < 0 above T p. Despite
intensive investigations on the CMR phenomena and associated electrical properties.
not much work has been done on the variation of thermal properties of these
samples. We have been quite successful in finding out the nature of anomaly
associated with thermal properties when the sample undergoes M-I transition.The ferroelectric crystal showing para-ferroelectric phase transitions -
Glycine phosphite. Thiourea and Triglycine sulfate - are studied in detail in order to
see how well the PPE technique enables one to measure the thermal parameters
during phase transitions. It is seen that the phase transition gets clearly reflected in
the variation of thermal parameters. The anisotropy in thermal transport along
different crystallographic directions are explained in terms of the elastic anisotropy
and lattice contribution to the thermal conductivity. Interesting new results have
been obtained on the above samples and are presented in three different chapters of
the thesis.In summary. we have carried investigations of the variations of the thermal
parameters during phase transitions employing photopyroelectric technique. The
results obtained on different systems are important not only in understanding the
physics behind the transitions but also in establishing the potentiality of the PPE
tool. The full potential of PPE technique for the investigation of optical and thermal
properties of materials still remains to be taken advantage of by workers in this field.
Description:
Department of Instrumentation,
Cochin University of Science and Technology
Annieta, Philip K; Lyjo, Joseph K; Litty, Irimpan; Radhakrishnan, P; Nampoori, V P N(Department of Photonics, 2004)
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Abstract:
Laser induced photoacoustic (PA) technique is used in the study of photostability of polymethyl
methacrylate (PMMA) films doped with Rhodamine 6G -Rhodamine B dye system. Energy transfer from a donor
molecule to an acceptor molecule in a dye mixture affects the output of the dye system. Details of investigations on
the role of laser power, modulation frequency and the irradiation wavelength on the photosensitivity of the dye
mixture doped PMMA films are presented.