We investigate linear and nonlinear optical properties of standard human ovarian cancer cells (cell line: A2780cp) in vitro. Cells were treated by graphene quantum dots (GQDs) with two special concentrations. Nontoxicity of GQDs was examined in standard biological viability tests. Cancerous cells were fixed on a glass slide; then, interaction of light with biofilms was studied in linear and nonlinear regimes. Absorption spectra of untreated biofilms and biofilms with two different concentrations of GQDs was studied by UV-visible spectrophotometer. Optical behavior of biofilms in a linear regime of intensity (with low-intensity laser exposure) was reported using a simple optical setup. After that, we compared the attenuation of light in biofilm of cancerous cells with and without GQDs. Nonlinear behavior of these biofilms was investigated by a Z-scan setup using a continued wave He–Ne laser. Results showed that GQDs decreased the extinction coefficient and changed the sign and exact value of the nonlinear refractive index of malignant ovarian cells noticeably. The nonlinear refractive index of studied cells with no GQDs treatment was in the order of 10−8 (cm2/w) with a positive sign. This quantity changed to the same order of magnitude with a negative sign after GQDs treatment. Thus, GQDs can be used for cancer diagnosis under laser irradiation.
Colloidal nanoparticles are attractive optical materials for their low threshold nonlinear response and thus all-optical, nondestructive features which are important in biomedical optics and optical processing. We develop a theoretical scheme based on numerical solution of Nonlinear Schrödinger Equation and nonideal gas model of nonlinearity to investigate temporal analysis of optical bistability (OB) and modulation instability in colloidal nanoparticles. Our scheme determines the dependence of a nanosuspension system dynamic state on characteristic/control parameters including external feedback depth, nanosuspension length, and the initial density of nanoparticles as well as the optical input power. We show that these parameters are intensely correlated. We also indicate that the nonlinear response of nanosuspension may be saturated over a threshold of input power, and thus an unexpected procedure of system evolution toward stability rather than transition to chaos will occur. Consequently, provided that internal feedback is present inside the nanosuspension controlling chaos will be attainable by simply adjusting the optical input power as the control parameter in contrast to the other chaos control methods which require external injection. Finally, we propose an approach which gives a measure of switching time to optimize OB. The optimum results are obtained for the lowest taken values of characteristic/control parameters.
We report the experimental data of typical liquid crystals (6CHBT and w1680) in the nematic phase doped with and
without Sudan dyes. We investigated the effect of an ac-applied voltage on the nonlinear behavior of dye doped liquid
crystal (DDLC). The z-scan technique is used to measure the amplitude and the sign of the nonlinear refractive indices
DDLC. The amplitude of negative nonlinear refractive indices was
(~10-5cm2/W). The nonlinear absorption coefficient β of DDLC was measured by using open aperture z- scan technique. Also the optical limiting (OL) response of DDLC was
obtained. The novel effects on the far-field diffraction patterns of a Gaussian beam were depended on the external
applied field. The measurements were performed using a CW He:Ne laser and CW Nd:Yag laser tuned at 632.8 nm and
532 nm, respectively. Also Gaussian beam propagated through a thin cell (sample thickness =11.8 μm).
In this paper we present optical phase-conjugation based on the degenerate four-wave mixing (DFWM) arrangement in
photorefractive crystal. The 532nm beam from a low-power Nd:Yag laser was split to form two counter-propagating
pump beams and one probe beam in the DFWM geometry. Experiments were carried out by varying the parameters
(angle of separation between the forward-pump and the probe beam, writing beam intensities) that influence the phase-conjugate
beam reflectivity. High reflectivity optical phase-conjugation is hereby reported for low-power lasers. The
dependence of phase conjugate reflectivity on signal to pump ratio (m) and forward to backward pump ratio (q) have
been investigated experimentally
Optical bistability and switching are of great interest in the rapidly and developing field of photonics. Devices that
display this behavior could potentially play a major role in the development of optical communication systems and
computing. In this article we present experimental results concerning the optical bistability in ferroelectric of
photorefractive BaTiO3 crystal. Two laser beams were used to interact with the photorefractive crystal which resulted in
the bistability of the intensity of transmitted wave. This was achieved without the application of any optical resonator.
High contrast optical bistability is found experimentally in the pump-ratio dependence of the output intensity.
SnO2 nonopowders were prepared by sol-gel method and exposed to different thermal decomposition. The XRD and
TEM analysis have been carried out. At higher temperature X-ray diffraction peaks are sharper with more intensified
peaks. AlsoTEM micrograph reveals that the grain size of nanopowders changed from 10 nm to 80 nm regarding to
different thermal treatment. The gas response shows characteristic dependence on dm (grain size). Responses to H2 and
LPG gas as a function of operation temperature in dry air for the analyzed sensors with different nano powders show that
smaller grain size are more sensitive to H2 and LPG gas.
Phase conjugation are optical devices that can generate a time-reversed replica of an incident electromagnetic wave. These devices play an important role in many optical system that require the transmission of optical waves through scattering media such as the atmosphere. Here we present four wave mixing configuration as one of the most important methods of generation and explanation of process of generation phase conjugation light the coupled equation was solved by three methods: undepleted pump approximation exact solution and two wave mixing approximation. Although exact solutions can be derived for four-wave mixing, the results are difficult to use because of the complicated transcendental equation involved. Solved the coupled equations and introduce an approximation in which two-wave mixing is the dominant process. In this approximation, we assume that the grating is dominated by a pair of waves. A comparative study of the diffraction efficiency as a function of fringe spacing, of some commonly used ferroelectric, non-ferroelectric crystals is presented.
In this paper the three dimensional Laplace equation was solved for a three layer photoreceptor with ti (i=1,2,3) thicknesses and dielectric εj(j =1,2,3) under suitable boundary conditions and the vertical component of electric field was obtained over the photoreceptor's photoconductive layer. Then, the behavior of the above equation was studied for different photoconductive layer's thicknesses and four thicknesses were chosen. For making the samples, the deposition of Al and formation Al2O3 in 2x10-5 - 5x10-7 mbar pressure, and coating of Se in 2x10-7 mbar pressure, 250 °C boat temperature and 95 °C substrate temperature in 120 min were carried out after the design and manufacture all of subsystems. In this way four samples were made by different photoconductive layer's thicknesses. Electrical measurements showed a resistance above 1012Ω in dark and about zero in light which these values suitable for development of electrostatic latent image. To consider the development field of made photoreceptors, the samples were mounted in Xerox machine and the operation of them observed. The sample with 60 μm photoconductive layer's thickness showed the best development and less background effects.
Photorefractive two-wave mixing and energy transfer in BaTiO3 are studied at three wavelengths using He-Cd, He-Ne and diode laser. The Photorefractive signal beam gain is measured as a function of the pump beam intensity, beam ratio intensity, spatial frequency of the grating, and angle between the grating vector and c axis of the crystal. The exponential gain coefficient is calculated from signal beam gain, and its dependence on the same parameters is studied. The dependence of the signal beam gain and exponential gain coefficient on spatial frequency are also evaluated theoretically and found to be in good agreement with the experimental data. Also, the signal beam gain is studied as a function of wavelength, and a very high value is obtained at 441.6nm. Diffraction efficiency of photorefractive gratings recorded in two-beam coupling configuration in crystal of BaTiO3 at multiple wavelengths is reported. We study the distortive effects in a thick PR hologram due to the angle between the two interfering beams and present our results on effect of spatial frequency on the diffraction efficiency. The behavior of crystal is compared at 441.6 nm, 632.8 nm and 780 nm using He-Cd, He-Ne and semiconductor diode lasers respectively. Value of diffraction efficiency of the crystal is higher at 441.6 nm as compared to other wavelengths. Figure-of-merit parameters such as the maximum change in the refractive index, the space charge field at saturation, the trap density of the charge carriers, and the photorefractive sensitivity of the crystals are calculated from the experimental data. Since the absorption in BaTiO3 varies strongly with wavelength, its influence has been included in the calculation of the figure-of-merit parameters.
Model calculation of second order susceptibilities for FA color centers in wide band gap materials are reported. The second order optical nonlinearity in crystals of alkali halide due to FA color centers evaluated theoretically. The density matrix formalism is employed and the equation of motion is solved by second order perturbation to evaluate the nonlinear optical susceptibilty for second harmonic generation as well as frequency mixing. It is found that the system shows large resonance-enhanced second order susceptibility (~10-16 mV-1) for color center concentration of ~1023 m-3. A scheme of phase matching in terms of anomalous dispersion of the centers and coherent length are discussed.
This paper present new optical configurations in speckle shear photography to measure in-plan displacement and the strain in real time using photorefractive (PR) crystals as recording medium. Speckle photography studies are made using a simple two-beam coupling configuration PR beam coupling in barium titanate crystals is characterized experimentally by measuring the signal beam gain and the exponential gain coefficient at 440 nm, 632.8 nm and 780 nm.
In speckle shear photography, a diffused object illuminated with two parallel narrow laser beams is imaged inside the crystal, and a pump beam is added at this plane. The speckle patterns due to each beam and the pump beam produce index gratings. When the object is deformed, the speckle patterns shift consequently. We now have four speckle fields two generated from the interaction of pump beam with the index gratings and two pertaining to deformed states directly transmitted through the crystal. Thus, the fields from respective points on the object interfere after passage through the crystal and produce the Young's fringe patterns. Due to strain, the fringes in each pattern are of different width and orientation, resulting in the generation of a moire pattern. The strain is obtained from the width and orientation of the fringes in the moire pattern. The experiments are conducted on a specimen with a notch, which is subjected to tensile loading. The above studies are carried out at three different laser wavelengths, namely, 441.6 nm, 632.8 nm and 780 nm and the results are compared.
The process of two-beam holographic coupling in optically anisotropic media is analyzed. We consider holographic media possessing birefringence, optically, and spatial modulation of these effects. In this paper energy transfer between two beams interfering in an electro-optic is analyzed as a function of the grating period of the recording hologram. The theory for two-beam coupling in Bi12SiO20 (BSO) with an external electric field and a moving grating is developed. We report high coefficients in a wide range of low spatial frequencies. Exponential gain coefficients of (Gamma) equals 7 cm-1 have been reached for high intensity beams ratio and moving gratings. These results have been compared with GaAs crystals.
A comparative study of the photorefractive response of some commonly used ferroelectric, nonferroelectric and semiconducting crystals is presented. The figure-of-merit parameters such as steady-state change in refractive index, response time and photorefractive sensitivity tare evaluated for crystals of BaTiO3, LiBnO3, BSO, GaAs and InP on the basis of Kukhtarev's theory, using input parameters form reported data. These parameters are calculated as a function of the grating period with and without an application of 10kV/cm electric field. The results indicate that the choice of the ideal material for a given application can be made only after a careful comparison of the figure-of-merit parameters as trade-offs exist among the various parameters for any material.
Photorefractive crystals offer several attractive features such as high resolution and in situ processing. As the images are erasable, these crystals are suitable for read-write applications and hence find potential use in speckle photography, image processing and holography. The BaTiO3 crystal as recording medium has been extensively used as a novelty filter for real-time in-plane displacement measurements employing two beam coupling configuration. This paper presents new optical configurations in speckle shear photography to measure in-plan displacement and the strain in real time using BaTiO3 crystal as recording medium. Speckle photography studies are made using a simple two-beam coupling configuration. In speckle shear photography, a diffused object illuminated with two parallel narrow laser beams is imaged inside the crystal, and a pump beam is added at this plane. The speckle patterns due to each beam and the pump beam produce index gratings. When the object is deformed, the speckle patterns shift consequently. We now have four speckle fields: two generated from the interaction of pump beam with the index gratings and two pertaining to deformed states directly transmitted through the crystal. Thus, the fields from respective points on the object interfere after passage through the crystal and produce the Young's fringe patterns. Due to strain, the fringes in each pattern are of different width and orientation, resulting in the generation of a moire pattern. The strain is obtained from the width and orientation of the fringes in the moire pattern. The experiments are conducted on a specimen with a notch, which is subjected to tensile loading. The in-plane displacement is measured separately in another experiment. Time evolution of the growth and the decay of the signal beam also is studied. The above studies are carried out at different laser wavelengths and the results are compared.
Photorefractive beam coupling in barium titanate crystals is characterized experimentally by measuring the signal beam gain and the exponential gain coefficient at 440 nm, 632.8 nm and 780 nm. The figure of merit parameters such as the change in refractive index, the space charge field and the trap density are estimated using Kukhtarev's theory. A comparative study at multiple wavelengths is presented. The signal beam gain is found to be maximum at 440 nm.
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