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Fibre optic sugar sensor developed by ISP
Irregular
intensity fluctuations in the frequency doubled output
of a diode pumped multimode Nd?YAG laser with an
intracavity KTP crystal has been investigated for
sometime. Since the frequency doubled intensity is in
the green region the problem came to be known as the
"green problem ".In a recent work (Thomas
Kuruvilla and V M Nandakumaran, CHAOS, Vol. 9, No. 1, in
press) it was shown that an Nd:YAG laser operating in
two orthogonally polarized modes undergoes a sequence of
reverse period doubling bifurcation from chaos to
stability when the relative orientation between the KTP
and the Nd: YAG crystal is varied continuously. In the
chaotic regime there is a chaotic exchange of energy
between the two modes. As the relative orientation is
varied the energy exchange between the two orthogonally
polarized modes become periodic. The transition from
chaos to periodicity is also established by computing
the Lyapunov exponents.
Suppression and control of chaos in dynamical systems has been another area which has generated a lot of research in the last decade. Various methods have been employed to control chaos both numerically and experimentally. Recently Thomas Kuruvilla and V M Nandakumaran ( Phys Lett A, in press ) have numerically studied a mechanism to suppress chaos in semiconductor lasers with high frequency current modulation. Such semiconductor lasers are known to exhibit chaotic behaviour for certain range of parameter value. In numerical studies, semiconductor lasers are modeled by rate equations for the photon density and carrier density. The current modulation provides the third degree of freedom necessary for the observation of chaos.
This effectively introduces a coupling between two lasers characterized by a coupling constant
K. For small values of k both P1 and P2 are chaotic. However, as
K is varied output follow a sequence of period doubling bifurcation and passes through 8, 4, 2 ... cycles to attain a steady
PI and P2. Thus with appropriate values of the coupling constant
K, the chaos in either of the lasers could be suppressed. This is an interesting method to suppress chaos which could be experimentally
implemented. For details contact: Dr. V M Nandakumaran, International School of Photonics, Cochin University Of Science & Technology, Cochin-22.
News
from ISP labs
Optical
fibre based urine sugar sensor
A
group of researchers under the leadership of Dr. P.
Radhakrishnan has developed a urine sugar sensor using
optical fibre. This compact hand-held sensor works based
on the principle of evanescent wave generated in an
optical fibre.
The
device perfected by Dr. P Radhakrishnan and his student
Mr. Shelly John. M will make the analysis of sugar in
urine much simpler. Since the instrument makes use of
optical fibre measurement, the analysis can be included
under the category of instruments in the new field of
tele-medicine.
For
details contact: Dr. P Radhakrishnan, International
School of Photonics, Cochin University of Science of
Technology, Cochin- 682022, Tel: 0484 532848, 0484
620811.
Detection
of Energetic Photoelectrons from silver target
irradiated with pulsed laser
Metals are known to emit electrons when irradiated with
light of appropriate frequency. This phenomenon is known
as photoelectric effect and Einstein provided a simple
explanation for the photoelectric effect in which the
photons cause ejection of free electrons in the metal.
Invariably the energy of such electrons will be lower
than that of the photons. However when metal targets are
irradiated with high power laser pulses we do find an
extremely different kind of photoelectric effect. As
soon as the laser pulses are incident on the metal
target prompt electron emission does take place; but the
energy of such electrons are found to be several times
larger than the photon energy. Such energetic electron
emission has been measured when silver is irradiated
with focused Nd: YAG laser pulses at 1.06 micro meter
wavelength. Measurements with electrical probe show that
these electrons can have energies as high as 150 eV.
This is a clear example where the usual quantum concepts
are no longer valid. Classical electromagnetic theory
credits strong pondor motive force which when acting on
the electron can accelerate them to such high energies.
A recent paper published from ISP by Riju C Isac, Pramod
Gopinath, Geetha K Varier, C P Girijavallabhan and V P N
Nampoori (App. Phy. Lett. Vol.73, pp.163, 1998)
describes the characteristics of such electrons emitted
by silver target. Other workers in United States have
also found relativistic electron emission from targets
irradiated with femto second laser pulses. Scientists
from ISP have suggested that this is an excellent method
for producing ultra short pulses of electrons.
Mutagenic
effect of laser light on plants
The
International School of Photonics supports
interdisciplinary research. ISP in collaboration with
Bio technology department of CUSAT has recently studied
the mutagenic effect of laser radiation in faba bean (vicia
faba)and onion (Allium cepa). Studies conducted by
Dr.Padma Nambisan and her colleagues have revealed
stimulatory effect of laser light on growth and yield of
faba bean and onion. Laser radiation also causes
mutation resulting into aberrations in mitotic cell
divisions.
We
hear that
Complete
quantum teleportation using NMR
Quantum
Teleportation (QT) is an example of information processing
capability that is not possible with classical devices. In QT
quantum state of a system is transported from one location to
another without moving through the intervening space. Although
the spatial implementations of QT over macroscopic distances
have been achieved using optical systems, the final stage of
the teleportation procedure which attains the complete
recovery of original stage ? was omitted. Prof. Neilson and
his group at Log Alamos National Laboratory, USA report on
experimental implementation of full QT over inter atomic
distances using liquid ? state NMR. Quantum state of a carbon
molecule was teleported to a hydrogen molecule in a molecule
of trichloroethylene by exploiting the material phase
de-coherence of carbon molecule. Such a QT scheme may be used
as a surfeiting in larger quantum computations or
quantum communications, they claim.
An
atomic dimmer switch
Doron
Meshulach and Yaron Silberag of Weizmann Institute show how
absorption of light by atoms can be controlled using the phase
of light incident on them. This new technique of "
coherent control" for manipulating the internal quantum
dynamics of atoms and molecules employs the coherence
properties of light rather than the intensity or colour.
When
an atom is subjected to intense laser light, nonlinear
absorption takes place using two or more photons. Nonlinear
optical effects are sharper when light is compressed into a
short, intense pulse. The group at Weizmann Institute was able
to control light absorption using multiphoton absorption from
two arms of an interferometer. By manipulating phases, any
particular resonant frequency in the spectrum can be made to
vanish, there by reducing the absorption at that frequency to
naught
Atomic
interferometer and the origin of quantum mechanical
complementarity
The
principle of complementarily refers to the ability of quantum
mechanical entities to behave like particles or waves under
different experimental conditions. For example, in the famous
double slit experiment, a single electron can apparently pass
through both apertures simultaneously, forming an interference
pattern. But if 'which way' detector is employed to determine
the particles' path, the interference pattern is destroyed.
This is usually explained in terms of Heisenberg's uncertainty
principle, in which acquisition of spatial information
increases the uncertainty in the particle momentum, thus
destroying the interference. A group of researchers from
University of Kanstanz, Germany have another explanation for
the phenomena deduced using the results obtained from their
studies using atom interferometer. They found that in an atom
interferometer, the "back action" of the path
detection on atoms' momentum is too small to explain the
disappearance of the interference pattern. They attributed it,
instead, to correlation between the "which ? way detector
" and the motion.
Conference
news
National
Seminar on High Power Lasers and Their Applications.
Feb 27-28, 1999
For details, contact Dr. P Radhakrishnan, International School
of Photonics, Cochin University of Science & Technology,
Cochin? 682022.
Some
of the recent publications from ISP
1.
An optical fiber based evanescent wave sensor to monitor the
deposition rate of thin films. Deepa Jose, M Shelly John, P
Radhakrishnan , V P N Nampoori and C P G Vallabhan, Thin Solid
Filims (325) 1998.
2.
A force sensor using polarization maintaining fiber, M Shelly
John, S Bindu, P Radhakrishnan, V P N Nampoori and C P G
Vallabhan, Comm Instr. January-March 6 (1998)
3.
A fiber optic sensor to measure glucose concentration, M
Shelly John, P Radhakrishnan, V P N Nampoori and C P G
Vallabhan Comm. in Instr. vol.6, No.1 April-June(1998)
4.
Influence of ambient gas on the temperature and density of
laser produced carbon plasma, S S Harilal, C V Bindu, V .P N
Nampoori and C P G Vallabhan, Appl. Phys. Lett. 72 167 (1998).
5.
Time evolution of electron density and temperature of laser
produced plasmas from YBa2Cu3O7, S S Harilal, C V Bindu, V P N
Nampoori and C P G Vallabhan, Appl.Phys. B 66 633 (1998)
6.
Electron density and temperature measurements of laser induced
YBa2Cu3O7 plasma, S S Harilal, C V Bindu, V P N Nampoori and C
P G Vallabhan, Applied Spectroscopy ( in press) 1998.
7.
Dynamics of laser produced silver plasma under film deposition
conditions studied using optical emission spectroscopy , Riju
C Issac, K Vasudevan Pillai, S S Harilal, Geetha K Varier, C V
Bindu, Pramod Gopinath, P Radhakrishnan, V P N Nampoori and C
P G Vallabhan, Appl. Surf. Sci. 125, 227 (1998)
8.
Twin peak distribution of electron emission profile and impact
ionization of ambient molecule during laser ablation of silver
target,, Riju C Issac, Pramod Gopinath, Geetha K Varier, V P N
Nampoori, C P G Vallabhan, Appl. Phys. Lett. 73 (1998) 163.
9.
Collective diffusion of laser produced plasma from the multi
component YBa2Cu3O7 target in air,Riju C Issac, Geetha K
Varier, S S Harilal, V P N Nampoori, C P G Vallabhan, Appl.
Phys B, (in press) 1998.
10.
Prompt electron emission and collisional ionization of ambient
gas during laser ablation of silver target, Riju C Issac,
Geetha K Varier, Pramod Gopinath, S S Harilal, V P N Nampoori,
C P G Vallabhan, Appl. Phys. A, (in press) 1998.
11.
Ionic temporal profile from laser produced silver plasma at
the plasma ambient boundary in low pressure nitrogen gas, Riju
C Issac, Geetha K Varier, Pramod Gopinath, V P N Nampoori, C P
G Vallabhan, J. Appl. Phys (in press)
12.
Studies of nonlinear absorption and aggregation in aqueous
solution Rhodamine 6G using a transient thermal lens
technique, C V Bindu, S S Harilal, V P N Nampoori, C P G
Vallabhan, J. Appl. Phys. 32 (1999) 1-5
13.
A fiber optic evanescent wave sensor for monitoring the rate
of pulsed laser deposition of metal thin films, M Shelly John,
PRadhakrishnan, V P N Nampoori and C P G Vallabhan, Meas. Sci.
Technol. 10 (1999) N17- N20
Editor:
Dr. V P N Nampoori
Layout & graphics: B. Aneesh and Nibu
Online version: B.Aneesh
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