Non-linear Optical Effects in Magnetic Nanofluids
Chintamani Pai1, H. Muthurajan2, Nooris Momin1, M. Shalini1, S. Radha1*
1
Department of Physics,University of Mumbai, Santracruz, Mumbai-400098, India.
2 National Centre for Nanoscience & Nanotechnology, University of Mumbai, Santacruz,Mumbai-400098, India.
*
Corresponding author’s e-mail:radhasri12@gmail.com, Tel.: +91-9820926830
Abstract
Introduction
Light scattering studies in ferrofluids have
been reported by various researchers [1]. This has
potential applications in optical limiters, optical
switches, filters and sensors. Laser beam passing
through the ferrofluid establishes refractive index [2].
This causes the laser beam to undergo self diffraction.
Far field diffraction patterns show change in external
magnetic field due to aggregation of particles along the
direction of magnetic field. Our study involves intensity
dependence, effect of magnetic field, particle size and
dispersion medium on the formation of diffraction
patterns and estimation of non-linear refractive index.
Change in refractive index occurs due to local heating
by the laser beam given by,
 n(r,z,t) 
 n(r,z,t) 
 n(r,z,t) 
T  
c  
H
 T 
 c 
 H 
n(r,z,t)  
This determines self-focusing
defocusing of the incident laser beam.
or
Fig. 1 and fig. 2 show laser beam transmission
and diffraction patterns in presence of magnetic field.
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Transmission
Keywords: magnetic nanoparticles, magnetic fluid, self
diffraction, spatial phase modulation, non-linear effect.
Results and Discussions
Current Pulse (mA)
Non-linear optical effects are observed by passing HeNe laser beam through magnetic nanofluids of Fe3O4 and
Fe2O3. Self diffraction patterns are seen showing
variations with parameters like magnetic field, laser beam
intensity, size of nanoparticles and dispersion medium. Inhouse instrumentation software is developed for control,
data acquisition and image processing.
(1)
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Time (second)
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Time (second)
Fig. 1: Current pulse generating magnetic field and
corresponding transmitted laser intensity.
Fig. 2: Self diffraction patterns in magnetic field
(Fe3O4 40 nm 30 mg/ ml of hexane)
Patterns evolve at millisecond scale with change in
shape, size, apparent rotation and number of rings.
Presence of magnetic field induces instabilities in
magnetic nanofluid causing the dynamics of diffraction
patterns.
self-
Experimental set-up
Experimental setup includes He-Ne Gaussian
laser (10 mW, 632 nm) passed through samples
containing magnetic nanofluids. Magnetic field (max.
1.7 kG) is applied perpendicular to the direction of
beam. The chemically synthesized magnetic nanofluids
have been characterized by XRD, microscopic and
spectroscopic techniques. Computer code in Visual
Basic is developed by authors to generate time varying
pulses of magnetic field. Separate modules are
developed for data acquisition and image processing.
Acknowledgement
Authors acknowledge Dr. A. Misra, Prof. D. Kothari,
Dr. M. Press, Prof. R. Nagarajan, Prof. D. Mathur, Prof.
S. Manoharan (DoP, UM-DAE, TIFR, NCNNUM,
Mumbai).
References
[1] J.Philip, J. M. Laskar, “Optical Properties and
Applications of Ferrofluids”, J. Nanofluids, 1, 1, 2012,
pp. 3-20.
[2] T. Du, W. Luo, “Nonlinear Optical Effects in
Ferrofluids Induced by Temperature and Concentration
Cross Coupling”, App. Phys. Lett., 72, 3, 1998, pp. 272274.