Rabah Mokdad

Fringe pattern analysis with a parametric method for measurement of absolute distance by a frequency-modulated continuous optical wave technique

Interferometry associated with an external cavity laser of long coherence length and broad wavelength tuning range shows promising features for use in measurement of absolute distance. As far as we know, the processing of the interferometric signals has until now been performed by Fourier analysis or fringe counting. Here we report on the use of an autoregressive model to determine fringe pattern frequencies. This concept was applied to an interferometric device fed by a continuously tunable external-cavity laser diode operating at a central wavelength near 1.5 microm. A standard uncertainty of 4 x 10(-5) without averaging at a distance of 4.7 m was obtained.

Phase analysis with autoregressive modeling in holographic interferometry

An autoregressive method to analyze the fringe pattern observed in holographic interferometry is reported. Considering the impact of a 30 dB signal-to-noise ratio, we have shown that the reconstruction of the simulated symmetric profiles with 3, 4, and 5 fringes produces a maximum error of 0.300, 0.520, and 1.015 rad, respectively. The reconstruction of an asymmetric profile gives a larger error. The method was also applied to a recent fringe pattern. Our results are in qualitative agreement with those obtained using other methods.

Holographic interferometry deformations metrology by using AR modeling

The frequency of the holographic fringe signal is proportional to the measured object deformation or displacement. Fast Fourier transform (FFT) is the most commoly used signal processing technique for analyzing output fringes. One problem with this approach is that a long data acquisition is required to achieve adequate deformation resolution, typically 5 to 10 fringes are needed. We propose using an autoregressive (AR) model to obtain with the same advantages deformation of an opaque object using holographic interferometry. This deformation will be estimated directly from the model parameters. The theoretical and experimental results obtained indicate that the proposed method has a good accuracy by using a small number of fringes.

Modeling of a passively Q-switched Nd3+∶Cr4+ all-fiber laser

A numerical model of an all-fiber Nd 3þ laser passively Q- switched with Cr 4þ is presented. The repetition rate, average output power, and pulse width have been calculated with the same parameters as those of an experimental setup of another group. We found a qualitative agreement between the two results. The validated model has been used on another proposed setup to investigate and optimize laser parameters. The low and high self-impulse amplitude regimes were found for different Cr 4þ ion densities. The optimal efficiency of the high regime was estab- lished when the saturable absorber density increases.

Fringe analysis in scanning frequency interferometry for absolute distance measurement

The deterministic FTT gives good results whereas the parametric method implemented needs proper settings of the parameters. Also, we have observed no degradation of the uncertainty in the case of two targets with the FTT.

Investigation of the laser pumping power impact on the operating regimes of a laser passively Q-switched by a saturated absorber

We have adapted the point model for the study of an all-fiber laser doped with Nd3+ and Q-switched by a saturable fiber absorber doped with Cr4+. Calculations of the output power of the 1084 nm laser are considered as a function of the pump power supplied by a 790 nm laser diode. The analysis of the simulation results reveals the existence of pulsed, sinusoidal, and dc operating regimes.

Position measurement of in-line microbid holograms using an autoregressive method

The work developed and presented in this communication, relates to the restitution of frequency chirp of an interferometric signal deduced from a measured diffraction pattern relating to a spherical micro-particle. For this purpose, analysis were achieved by implementing a parametric method with a sliding window. These frequencies allows us to reconstruct the axial position of the corresponding object. The study, achieved in the far field approximation, allows us to validate preceding methods based on simulation results. The principle consists to generate optically in-line diffraction patterns of a spherical particle with radii of 39μm and measured with a microscope ZEISS. The collimated coherent light was generated from a He-Ne laser that the wavelength is λ = 632.8 nm. The generated diffraction pattern was recorded by using a 2D-CCD camera Ophir having 1024 x768 pixels with a pitch of 4.65 μm connected to a computer. Since the variation of the chirp frequency is linear, the knowledge of its variation slop, resulting from a linear fit, enables us to deduce the z-position of the particle. This is achieved with a resolution of 1.2 %.

Size measurements of an optical fiber by diffraction pattern analysis in Fraunhofer approximation

This study concerns the determination of the diameter of an optical fiber by analysis of a 2D measured diffraction pattern relative to this linear object, falling within the scope of the Fraunhofer approximation. In this approach, when considering a small line-shaped aperture, with a radius α, or a diffractive object placed at the y-axis, an amplitude of the in-line Fraunhofer hologram can be achieved by a mathematical expression, for a given wavelength of the illuminating light λ and a distance z between the particle and the recording plane. The interferometric signal depends on an Airy curve expressed by a Sinc function whose determination of the zeros makes it possible to deduce an argument giving the radius of the fiber. The measurement is carried out for an object-CCD distance equal to z = 60 mm, with a wavelength of illumination λ = 635nm. The zeros of the Airy function appearing in the analytic expression of the interferometric signal allows us to achieve the value of the measured diameter. Knowing that the fiber radius is α = 62.5 μm, the measured value is acquired with an error of 1.7%.

Modeling with the progressive wave model passively Q-switched and gain-switched dual-cavity fiber laser doped Yb:Yb

This work focuses on the simulation and modeling of a passively Q-switched dual-cavity fiber laser doped Yb:Yb, to our knowledge, it is for the first time that the progressive wave model is applied to this type of laser, a good agreement between our simulation results and the experimental results published by another team is obtained, two pulse trains are produced by this laser, the first is at the wavelength of 1064 nm, and the second is at 1100 nm, we also show that certain parameters such as the concentration of Yb ions and their length are an important parameters for the optimization of the two laser signals at 1064 nm and 1100 nm.