In this work we present an experimental proposal for an efficient optical pressure sensor based on a Variable Liquid Lens
(VLL) and a modified Point Diffraction Interferometer (PDI). The working principle of the proposed sensor relies on the
fact that a pressure variation induces a change in the lens curvature and hence in its focal length which can be tracked
and measured with the interferometer. The pressure is then measured by recording and processing the interferometric
images. The calibration of the sensor in this proposal demonstrated a working range of 0-26 kPa with an accuracy of less
than 0.1 kPa in the whole range.
In this work we present an efficient proposal to evaluate optical surfaces working at infrared wavelengths based
on the Ronchi test and on the concept of synthetic wavelength. The implementation is performed by using a
spatial modulator (XGA2 SLM) and a white Light Emitting Diode (LED) of 5mm. In order to select distinct
wavelengths, different color filters are employed. Thus, for a given selected wavelength, the surface evaluation
is carried out according to the method of Ronchi, registering two perpendicular interferograms for this color;
the process is repeated for a second wavelength (architecture of this proposal allowed us to test the surface in
more than two wavelengths). Then, an equivalent ronchigram is computationally generated with the registered
data which is then analyzed in order to generate the wavefront for the correspondent synthetic wavelength.
Observations of our results show that with an appropriate LED alignment and high intensity, we avoid an
increase of noise due to the employment of longer wavelengths, as well as the alignment problem, often linked
to the evaluation of infrared (IR) surfaces. The simplicity of the optical setup and low cost materials make this
proposal applicable in the area of optical testing.
In this paper, some concepts and results associated with the interferometric concept of effective wavelength have been applied for the evaluation of optical surfaces. This testing technique measures the wavefront slope instead of the contour
of the wavefront, like in the conventional interferometry. Therefore in this paper we present two methods of analysis of
optical surfaces with the Ronchi test. First, we described a procedure to evaluate surfaces employing the effective
wavelength in the Ronchi test [1]. Our results were computationally processed in order to reconstruct the wavefront of a
particular mirror by means of the effective wavelength. A second proposal technique of analysis is based on the change
of the traditional analysis of a ronchigram to a method by a proper scaling of the shearing interferogram, via the
equivalent wavelength. The effective wavelength and equivalent wavelength are distinct concepts and are independent of
the wavelengths used in the image registering process. Comparisons of the Zernike Polynomials for each wavefront with
a reference wavefront show, the differences between both methods. Finally, we discuss some advantages and
disadvantages of each of the proposed analysis and mention the principal factors to improve our results.
The Ronchi test has been consolidated as one of the most successful and powerful techniques applied to determine
the quality of optical surfaces.5 In recent years, the development and availability of LCD's (Liquid Crystal
Displays) have allowed the incorporation of LCD's instead of the traditional static ruling. The easy change of the
characteristics of the fringes in the ruling, such as frequency, position, and geometrical form, transformed this
technique into a dynamic test.1, 8 Its physical interpretation fully connected with a lateral sheared interferometer 5, 6 and some concepts and results associated with the interferometric concept of equivalent wavelenght have
been applied in this proposal for the evaluation of optical surfaces. The procedure described here to evaluate
an optical surface uses the Ronchi test with the equivalent wavelenght.6, 10 This is achieved by registering and
computing Ronchigrams obtained by employing, separately, two distinct wavelengths. For a particular mirror,
some results are shown in order to demonstrate the enhancement of the test with this proposal.
Lattice associative memories also known as morphological associative memories are fully connected feedforward
neural networks with no hidden layers, whose computation at each node is carried out with lattice algebra
operations. These networks are a relatively recent development in the field of associative memories that has
proven to be an alternative way to work with sets of pattern pairs for which the storage and retrieval stages use
minimax algebra. Different associative memory models have been proposed to cope with the problem of pattern
recall under input degradations, such as occlusions or random noise, where input patterns can be composed
of binary or real valued entries. In comparison to these and other artificial neural network memories, lattice
algebra based memories display better performance for storage and recall capability; however, the computational
techniques devised to achieve that purpose require additional processing or provide partial success when inputs
are presented with undetermined noise levels. Robust retrieval capability of an associative memory model is
usually expressed by a high percentage of perfect recalls from non-perfect input. The procedure described here
uses noise masking defined by simple lattice operations together with appropriate metrics, such as the normalized
mean squared error or signal to noise ratio, to boost the recall performance of either the min or max lattice auto-associative
memories. Using a single lattice associative memory, illustrative examples are given that demonstrate
the enhanced retrieval of correct gray-scale image associations from inputs corrupted with random noise.
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