The use of refractometers to investigate the nature of liquids is very common. Here it is shown that surface relief diffraction gratings can be used to measure the refractive index of liquids. Calibration plots showing the relation between first order intensity as a function of refractive index are shown. We also developed a microfluidic device behaving as a grating which is used as refractometer where a very small amount of liquid (microliters) is used.
The use of electronic Relative Humidity (RH) sensors is widespread. However, when spark-free methods in explosive areas are needed optical RH methods could be employed. Here we present the application of the Mach-Zehnder (MZ) interferometer to study the response of thin films to changes in RH. These films could be used as the sensor element in RH instruments. As an example three types of films have been studied: poly(vinyl alcohol), an Interpenetrated Polymer Hydrogel (IPH) and gelatin. The configuration to study the polymer’s response consists of a climatic chamber where the MZ interferometer is immersed. The thin film is inserted in one arm. When humidity or water vapor increases the film thickness increases and its refractive index decreases. These phenomena will cause the shifting or lateral movement of the interference pattern. By sampling the interference pattern with a fixed point sensor it is possible to find a plot relating light intensity as a function of RH. These plots characterize the material. Several thin films parameters have been studied like Molecular Weight (MW) of poly(vinyl alcohol); thicknesses, hardness, and polymer ratio of an IPH and finally gelatin hardness.
Here we present a refractometer for liquids based on a sinusoidal relief grating immersed in a small cuvette. He – Ne light is sent to the cuvette + grating device where it is diffracted. Zero, +1 and -1 orders appear. It is possible to calibrate the device by measuring +1 order intensity, when different liquids with known refractive index are poured in the cuvette. A theoretical study has been developed that supports the experimental results.
A lens containing a liquid medium and having at least one elastic membrane as one of its components is known as an elastic membrane lens (EML). The elastic membrane may have a constant or variable thickness. The optical properties of the EML change by modifying the profile of its elastic membrane(s). The EML formed of elastic constant thickness membrane(s) have been studied extensively. However, EML information using elastic membrane of variable thickness is limited. In this work, we present simulation results of the mechanical and optical behavior of two EML with variable thickness membranes (convex-plane membranes). The profile of its surfaces were modified by liquid medium volume increases. The model of the convex-plane membranes, as well as the simulation of its mechanical behavior, were performed using Solidworks® software; and surface’s points of the deformed elastic lens were obtained. Experimental stress-strain data, obtained from a silicone rubber simple tensile test, according to ASTM D638 norm, were used in the simulation. Algebraic expressions, (Schwarzschild formula, up to four deformation coefficients, in a cylindrical coordinate system (r, z)), of the meridional profiles of the first and second surfaces of the deformed convex-plane membranes, were obtained using the results from Solidworks® and a program in the software Mathematica®. The optical performance of the EML was obtained by simulation using the software OSLO® and the algebraic expressions obtained in Mathematica®.
Gelatin thin films inserted in a Mach – Zehnder interferometer were used to monitor Relative Humidity (RH). When RH
varied, gelatin film thickness and refractive index also changed. As a result interference pattern moved horizontally. A
fixed detector, with a pinhole in front of it, was placed at the interference pattern. It sampled the pattern when it moved.
These intensity values were used to find a calibration plot relating intensity as a function of RH.
This paper describes a simple method of measuring refractive indices of liquids with a small hollow prism. When a He-Ne laser beam is sent to the liquid filled prism it is angularly deviated or deflected. If different liquids are injected in the prism, one at a time, the angular position of the emerging beam changes. These angular positions are detected by an optical fiber that samples a small area of the Gaussian beam cross section. A calibration curve relating intensity as a function of the liquid refractive index is obtained.
Here we present two optofluidic configurations: a spectrometer and a beam aligner. The spectrometer has a compound element that consists of an optofluidic lens and a relief blazed diffraction grating. When light traverses the two optical elements it is focused and diffracted. At the focal length a spectrum is present. This spectrum can be collected by a CCD and information sent to a computer for analysis. Regarding the beam aligner it is made with two hollow prisms oriented 90° to each other. By changing the liquid inside the prisms an X-Y movement can be performed to align the beam.
Usually optofluidic lenses are spherical (ball lenses), plano - concave or plano - convex. Here we present a method to
fabricate non - ball small microfluidic lenses in the bulk of a polymer. The cavity of these lenses can be filled with a
liquid by means of a syringe. Liquids present different refractive index thus the lens focal distance can be changed at
will. An optical characterization study and an application in the measurements of liquids refractive index are shown.
Arrays of microfluidic lenses were also fabricated.
In this work we present a different method to reduce shot noise in phase imaging from digital holograms. An averaging
process of phase images reconstructed with different reconstruction algorithms of the complex amplitude of a phase
object in digital holographic microscopy. We obtain an improved phase image reaching a 29% of shot noise reduction.
We use a single object complex amplitude that is needed to perform our proposal. Also show the corresponding
simulations and experimental results. As phase sample test we used a micro-thin film step surface made at home of 100
nm high of TiO2 on a glass substrate of 4.7 mm thickness, our system was calibrated and traceable to an Atomic Force
Here we show a method to make compound optofluidic lenses with sizes of some millimeters. These lenses could have
several chambers which combined could help to decrease aberrations. Liquids used in the lenses are ionic liquids. We
present an optical characterization study of some of these liquids. A two cell compound lens is show.
We present a method to make liquid lenses. It is based on the microfluidic method to make emulsions. An emulsion is a
mixture of two immiscible liquids, where one liquid (the dispersed phase) is dispersed in the form of small droplets in
another liquid that forms a continuous phase. The presence of a surfactant is necessary for the long term stability of
emulsions. To make liquid lenses we have used capillaries. Through them we inject some microliters of a liquid. The
result is that a spherical micro-lens is formed. These lenses can focus light or form images. We have tested the lenses
through image forming techniques and compared the results with the ones given by an optical design program.
To study the radiation emitted by the human skin, the emissivity of its surface must be known. We present a new approach to measure the emissivity of the human skin in vivo. Our method is based on the calculation of the difference of two infrared images: one acquired before projecting a CO2 laser beam on the surface of the skin and the other after such projection. The difference image contains the radiation reflected by the skin, which is used to calculate the emissivity, making use of Kirchhoff's law and the Helmholtz reciprocity relation. With our method, noncontact measurements are achieved, and the determination of the skin temperature is not needed, which has been an inconvenience for other methods. We show that it is possible to make determinations of the emissivity at specific wavelengths. Last, our results confirm that the human skin obeys Lambert's law of diffuse reflection and that it behaves almost like a blackbody at a wavelength of 10.6 µm.
By using two optical fibers and a capillary it is possible to measure the refractive index of liquids. Light
leaving a fiber is sent transversally to a capillary that behaves as a cylindrical lens when liquids are
inserted in it. Focused light is collected by a second fiber and sent to a detector.
We present a mathematical model of the surface relief formation suffered by photographic emulsions when an intensity pattern is recorded. Traditional explanations consider that this relief is due to silver compounds, but mainly to a mass transfer process in presence of tension forces. According to this description, the model considers diffusion and smoothing processes. Main parameters of the model were obtained by fitting simulated profiles to measured profiles for different micro-optical elements. The error between simulated and measured profiles ranged from 2.6% to 7.3%. Results obtained with this model reinforce the hypothesis of the surface relief formation. This model may be useful in numerical simulations of surface relief micro optical elements.
Large-mode-area photonic crystal fibers with a limited number of air channels in the cladding are investigated theoretically and experimentally. An impact of the relative hole diameter on single-mode operation, the fiber transmission, and bending loss is addressed in detail.
A holographic lens is recorded superimposing two beams with orthogonal linear polarizations on an azobenzene polymer film. The polarization pattern on the interference plane induces two modulations in the media: the volume and the surface modulation. The spatial frequency of the surface relief is twice the one for the volumetric modulation resulting in a holographic lens with two different focal lengths. Additionally, because of the modulated anisotropy induced in the medium, the polarization at the longer focus distance is orthogonal to the polarization at the shorter one. We propose this polarization element to send or detect information in two planes simultaneously or separately by using an analyzer behind the holographic lens.
Refracting surfaces of spherical and rod microlenses have been made with the melting method. Size of spherical lenses ranged between tens of microns to hundreds of them. Length of rod lenses ranged between hundreds of microns to about some millimeters. Diameter of these last lenses ranged between hundreds of microns to about 1.2 mm. The testing of the refracting surfaces has been done by means of a Scanning Electron Microscope and an Atomic Force Microscope. An USAF test target has been used to find the resolution of the lenses. Theoretical behavior of the lenses has been obtained through ray tracing. Applications of the microlenses in combination with VCSELs and in other field are presented.
Polarization holographic gratings in azopolymers are due to three photoinduced effects: linear anisotropy, circular anisotropy, and surface relief. In our polymers the surface relief grating is with doubled frequency with respect to the volume anisotropic grating. A theoretical analysis is presented and compared with experimental data.
Microlenses, microlens arrays and diffraction gratings can be made by using polymer materials. These elements can work
with mid-infrared light. The influence of some fabrication process variables in the fmal parameters of the elements is
analyzed. The surface shapes of the fabricated elements were investigated by a surface analyzer and an interference
microscope. The ability of microlenses to focus mid-infrared light and to form infrared images and a diffraction efficiency
study of the gratings are shown.
Mid-infrared optical microelements, like lenses or array of them, can be used to couple light or to form images. We present simple methods to fabricate mid-infrared microlenses and other optical elements by means of irradiation of a polymer substrate with CO2 laser or by the melting method. Application of these methods can lead to a mass production, low cost mid-infrared elements. It is analyzed the influence of some fabrication process variables in the final parameters of the elements. The quality of the microlenses was characterized by direct measurement of their surface profile through mechanical (surface analyzer) and optical (interference) methods. Capability of microelements to form infrared images is shown.
A photographic method using silver halide emulsions as photoresist medium has been used for the fabrication of relief blazed diffractive elements. The fabrication method comprises the design of half tone masks in the computer and the recording of a reduced image of the mask on the emulsion. After development a thin film of aluminum is laid over the emulsion to obtain a high reflective zone plate.
The use of photopolymer films to record information by optical methods is described. The final result in such thin polymer films is its surface modulation that develops under the sole action of light and does not require any chemical treatment. The relief generating process permits the fabrication of diffractive and refractive optical elements that work in transmission or in reflexion. This last mode is achieved when a metal thin film is overcoated on its surface. Low spatial frequency gratings, microlenses and micromirrors were made. Several diffractive elements using computer generated holograms were also fabricated.
In this article are reported the results when four polymeric
materials were used to record interference patterns. Radiation
(10.6 ,im) used in the recording and reading steps came from a CO2
laser. To read the recorded patterns a thin film of aluminium was
evaporated over them. It is shownthe behavior of the diffraction
efficiency for the recorded interference gratings.