According to the World Health Organization, 31% of worldwide deaths are due to cardiovascular diseases (CVDs). The principal cause of death in 85% of the CVD cases are heart attack and stroke. About 795,000 people have a new or recurrent stroke annually in the U.S.A. alone. A study pointed out that 63% of stroke patients have at least one episode of cerebral hypoxia being able to cause coma, seizures, and even brain death. In previous work, we introduced a biocompatible, mechanically stable, and transparent nanocrystalline yttria-stabilized-zirconia (nc-YSZ) cranial implant to provide optical access to the brain. The nc-YSZ implant may facilitate the diagnosis and treatments of neurological disorders by imaging and laser-based techniques. In this study, we evaluate the scope of diffuse reflectance spectroscopy through the nc-YSZ cranial implant in the diagnosis of oxygen consumption in normal and hypoxic conditions (greater and less than 95%, respectively). We use the Monte Carlo method to assess the optical access provided by the implant to detect normal and decreased oxygen consumption. To emulate the brain tissue, we used a four-layer structure: skull, gray matter with an embedded blood vessel, white matter, and air at the top, structured in a numerical model with anisotropy as well as Rayleigh and Mie scattering. We analyze two scenarios, constant blood volume at variable oxyhemoglobin saturation, and constant oxyhemoglobin saturation at variable blood volume. We use light irradiation sources at 756 and 810 nm to compute light propagation in a semi-infinite medium and diffuse reflectance backward. The penetration depth and diffusely backscattered energy showed the feasibility of monitoring hypoxia episodes while blood flux in vessels decreases during a stroke with more accuracy when the volume of the blood vessel is reduced in a stroke.
Non-subjective, minimally-invasive, and quantifying techniques may support development and evaluation of a fibrosis regression treatment. The build-up of extracellular matrix in liver fibrosis may result on changes of the endogenous fluorescence of tissue. In this work, we evaluate the fluorescence excitation/emission matrix in the UV range for several bulk samples of murine hepatic tissue preserved in different media. Chemical changes on tissue, caused by formaldehyde preservation, alter the endogenous fluorescence spectra. To avoid these drawbacks, phosphate-buffered saline (PBS) or Iscove’s Modified Dulbecco’s Medium were used. PBS buffer showed to be the less harmful and cost-effective preservation medium to study the endogenous fluorescence in fibrotic tissue.
Non-subjective and early diagnostic technique for liver fibrosis may decrease morbidity in patients and reduce medical costs. Liver fibrosis results in changes in density and thermal properties of tissue. In this work, we evaluate numerically the feasibility of using the optical beam deflection method (OBDM) by means of a thermo-optic material in contact with liver tissue to quantitate changes in thermal conduction. We use the finite-difference method to model the heat transfer in liver and acrylic slab. The response required for thermal characterization for different fibrosis stages is assessed by calculating the deflection angle using ray trace analysis. Numerical study shows the potential of the OBDM for developing an optical-integrated sensor as non-subjective diagnostic technique for liver fibrosis.
We present a brief overview of using the effective refractive index of colloidal suspensions for characterizing
nanoparticles. We focus our analysis on the so-called nanofluids consisting of nanoparticles suspended in a homogenous
liquid matrix. Particular attention is paid to the role of the real part of the effective refractive index on sizing the
nanoparticles. We then discuss possible ways to measure the real part of the effective refractive index of nanofluids and
precautions needed.
In this work we utilize heat conduction measurements trough the photothermal beam deflection technique to characterize thermal properties of biological tissue. We design a heat flux sensor based on the phenomenon of photothermal laser beam deflection within a thermo-optic slab (acrylic), where the deflection is quantified by an optical fiber angle sensor. We analytically model the heat flux sensor response based on heat wave propagation theory that well agree with experimental data. We present heat conduction measurements on different tissues applying a heat pulse. Hence we obtain the thermal effusivity coefficient of bovine tendon and chicken liver and heart. It has been shown that thermal conduction depends on the tissue´s chemical composition as well on their structural arrangements, so any modification in tissue will affect on heat conduction rendering this method potentially useful as an auxiliary in biomedical studies. Nowadays there are several thermal effusivity and diffusivity measurement techniques with classic calorimetry (using thermistors) for research and industrial applications. However there are only few integrated optical devices already proposed, turning this optical technique in an innovative and alternative sensing system for thermal properties characterization.
Stellar coronagraphs using circular phase masks are promising concepts dedicated to the image suppression of an
observed bright star in order to enhance the substellar mass companions present in its vicinity, typically 2 λ/D
angular separation. These concepts include a focal plane phase mask which introduces a phase delay on a part
of the stellar image. With an adequate choice of the mask parameters (thickness, diameter), the light going
through the mask and the light going outside the mask will interfere destructively inside the geometric pupil in
the following pupil plane. The light rejected outside this re-imaged pupil will be blocked by a Lyot stop.
Typically, the mask physical size is about λF, where F denotes the f-number of the optical system, and the mask
thickness depends on the required phase shifting. The contrast provided by these concepts is highly related to
the quality of thickness profile of the phase mask and therefore, severe manufacturing tolerances are necessary to
reach the theoretical performance of the corresponding coronagraphic system. In 2007, we designed a Roddier
& Roddier phase mask with a 65 μm diameter and ordered it to GEPI of Paris Observatory which manufactured
it using ion etching process. A roughness of 0.8 nm rms and a transition width of 1% of the mask diameter were
measured with a profilometer for this mask showing the good quality of the mask (N'Diaye et al. 2010).
We pursue our efforts to design and manufacture high quality masks in collaboration with the firm SILIOS. Several
tests of manufacturing procedures are currently realized to reach the best trade-off between mask roughness and
mask transition width. These values, measured in our laboratory with a profilometer, allow us to determine the
best configuration for fabrication. In addition, by knowing the mask profile, we can estimate theoretically the
performance that can be reached.
Stellar coronagraphy is a key technology for current and future instruments for exoplanet imaging and spectroscopy,
both on the ground and in space. We pursue the research on coronagraphs based on circular phase masks
and report in this paper on recent advances in terms of the trade between spectral bandwidth and
achievable contrast. Circular phase masks combined with colored apodizations prove to be promising options in
such coronagraphic systems to reach high contrast gains within the search area over a wide band of wavelengths.
We describe a fast method for measuring the refractive-index dispersion of transparent and absorbing liquid solutions.
The method is based on measuring the reflectance spectra of an optical beam of white light in an internal reflection
configuration near the critical angle defined by the refractive indices of the incident medium (a glass prism) and that of
the solvent, which is assumed to be transparent. From a few reflectance spectra taken near the critical angle with the pure
solvent and the solution, the dispersion of the contribution to the refractive index of the solute (the sample) can be
obtained. We present results with solutions of Rodamine 6G dissolved in distilled water and in methanol showing the
feasibility of the proposed method.
In this paper, we propose a method to determine refractive index changes and its dispersion of diluted solutions by
analyzing the refraction of light by a hollow prism containing the medium to be characterized. The system uses a double
prism refractometer to compensate the dispersion of the medium and the output beam is analyzed with a
spectrophotometer resulting in a faster measurement with a simple setup. The system was calibrated using solutions of
sucrose in water. We present experimental results of the characterization and monitoring of water oxidation as an
example of potential applications.
It has been observed in the literature, developments about characterization of several materials for gas sensing
application; simultaneously, also it has been observed that only some of them show a procedure of design for the
implementation of these materials in a device or an optical system. In consequence, appears differences between the
predicted by theory and the experiments. For that reason, the present work proposes a new approach for the design of
optical-integrated (OI) sensors. We show the advances in the design of an OI sensor for ammonia detection (NH3), using
tungsten trioxide (WO3) as sensitive material. We considered a model that incorporates the concepts of the kinetic of gas adsorption on solids, the effects of the real and imaginary part of the refractive index in the redistribution of the optical
field, and the influence of the photo and thermochromism, before and during the sensing mechanism. Although the work
has not been concluded, we can affirm that the concepts incorporated in this proposal, must be considered as critical
parameters in the design of an OI sensor or an optical fiber (FO) sensor.
We propose a simple technique to determine the distance to an object from two passive photometric measurements. The technique offers the possibility of developing fast and inexpensive passive optical range sensors for different applications.
We describe a fast and accurate method for the measurement of refractive index spectra of absorbing layers from transmittance spectra at two angles of incidence. The method is less sensitive to surface conditions than other photometric techniques.
We propose a simple technique for determining the refractive indices of highly absorbing materials. This method uses two transmittance measurements at oblique incidence. A theoretical analysis of the proposed method is presented. The refractive index of water was experimentally determined with a relative error ranging from 0.12% to 1.3%. We discuss the extension of this method to spectroscopic measurements.
We present the design of an innovating integrated planar structure adapted for intensity or phase measurements. It is based on the evanescent prism decoupling of the optical signal from a waveguide used as the sensing element. The device is formed by successive thin film sputtering deposition. A TiO2 crystalline layer forms the gas sensing element from which light is coupled out by a planar high refractive index prism. We experimentally validate the structure.
In this work we present experimental findings in the field of laser matter interaction on the topic of laser induced oxidation and crystalline structure change. It has been shown in the past few years that lasers can be used to induce both oxidization of metals as well changes the crystal in the crystalline structure of the metal oxide. Conventional theory has proven to be mildly successful in predicting these effects with a thermal model; drawing its influence from the traditional method of inducing material change by baking the metal. We reformed a scan of varying values of laser intensity and accumulated fluence. We will show evidence of an increase in the oxygen content in Ti and W thin films irradiated by a frequency doubled Nd:YAG laser source with a pulse duration of 4 ns and per pulse energies of 26 to 60 μJ (peak intensities of 1.7 x 107 to 3.8 x 107W/cm2). We will also show that other effects, that may include crystalline structure change, are also occurring.
Titanium oxide thin films were obtained by reactive dc-magnetron sputtering. A target of titanium (Lesker; 99.9% pure) and a mixture of argon and oxygen gases were used to deposit titanium oxide films onto silicon and glass substrates. The substrate temperature was varied between 200 and 400°C. Optical constants have been determined by spectroscopic ellipsometry and by using the optical transmittance data from UV-Vis spectrometry. The effect of substrate temperature on the optical properties is analyzed. Results indicate an increase in the refractive index of the films with substrate temperature, which is attributed to changes in the oxygen content, density and degree of crystallization of the films.
We propose and study a novel optoelectronic device for thermal characterization of materials. It is based on monitoring the photothermal deflection of a laser beam within a slab of a thermo-optic material in thermal contact with the material under study. An optical angle sensor is used to measure the laser deflection providing a simple and compact experimental arrangement. We demonstrate the principle of operation of the sensor and simple procedure that can be used to measure thermal effusivity of liquids. The proposed device could be implemented into a compact sensor head for remote measurements using electrical and fiber optic links.
We present a theoretical study of an erbium-doped optical fiber operating in the superluminescent regime. Experimental results for different pump power levels and fiber length show that the theoretical model could render useful information for predicting parameters such as total output power, spectral bandwidth and optimum fiber length to achieve the superluminescent regime. These types of sources could have direct application in wavelength multiplexed arrangements of fiber sensor, fiber gyroscopes or in general, in any sensors in which a broad wavelength and stable light source is required.
We present different glass ion-exchanged waveguide polarizer configurations using an electro-optic polymer (conjugated PMMA-DR1) overlay. The polarizer function is accomplished by modifying the propagation constant of a guided mode by changing the birefringence induced in the polymer by a poling process. A TE pass polarizer with an extinction ratio of 39 dB, has been realized using a corona poling. Further developments require a better control of the poling process. A TE polarizer structure using poling in the vertical direction have also been tested. A TM polarizer with planar metallic electrodes for poling is presented. Design considerations and fabrication results are presented.
We report on a new type of glass ion-exchanged waveguide TE polarizer using an electro-optic polymer (conjugated PMMA-DR1) overlay. The polarization function is assured by poling the polymer in the vertical direction using a Corona process. An extinction ratio of 39 dB is obtained at the wavelength of (lambda) equals 1.3 micrometer. The insertion losses of the device are in order of 7 dB. The performance of the polarizer are investigated. Our experimental investigations show a polarization efficiency over than 40 dB.
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