We present a scalar model to overcome the computation time and sampling interval limitations of the traditional Rayleigh-Sommerfeld (RS) formula and angular spectrum method in computing wide-angle diffraction in the far-field. Numerical and experimental results show that our proposed method based on an accurate nonparaxial diffraction step onto a hemisphere and a projection onto a plane accurately predicts the observed nonparaxial far-field diffraction pattern, while its calculation time is much lower than the more rigorous RS integral. The results enable a fast and efficient way to compute far-field nonparaxial diffraction when the conventional Fraunhofer pattern fails to predict correctly.

In this work, a high performance near-infrared thermal microscope designed to characterize the thermal behaviour of a power metal–oxide–silicon field-effect transistor (MOSFET) is presented. This non-destructive method is based on the measurement of the thermal radiation emitted by the power transistor in the spectral domain close to 800 nm using an intensified CCD camera. Although the intensifier unit is developed specially for low-level radiant applications, an image processing technique based on lock-in thermography method is proposed to improve the signal-to-noise ratio. The method allows absolute temperature distribution measurements for both the static and periodic modes at the micron scale. In the periodic mode, the transistor is heated (by the Joule effect) at a frequency fitting the camera acquisition speed. The minimum threshold temperature value and the temperature sensitivity to the emissivity factor are examined. Microthermographic images of the power MOSFET are presented and discussed for several values of drain current. For both static and periodic modes, good results of temperature resolution and spatial resolution have been achieved confirming the interest of short wavelengths for microthermography applications.

Nanosecond near-IR lasers are commonly used for industrial laser processing. In this paper, we demonstrate that a 70 μm diameter beam generated from a 5 W, 28 ns, near-IR (1064 nm) Nd:YAG laser can etch a silicon wafer with a lateral feature size as small as 1.3 μm. Surprisingly with this laser, microetching can also be achieved on glass, despite the low absorption of this material at this wavelength. This breakthrough is carried out in ambient air by using glass microspheres with diameters between 4 and 40 μm that generate a concentrated beam at their vicinity, a phenomenon referred to as a photonic jet. The roles of parameters such as laser fluence, pulse number, microsphere diameter, and distance between the microsphere and the sample are discussed. A good correlation has been observed between the computed photonic jet intensity distribution and the etched marks' geometry.

A step index multimode optical fiber with a perturbation on a micrometer scale, inducing a periodic deformation of the fiber section along its propagation axis, is theoretically investigated. The studied microperturbation is mechanically achieved using two microstructured jaws squeezing the straight fiber. As opposed to optical fiber microbend sensors, the optical axis of the proposed transducer is not bended; only the optical fiber section is deformed. Further, the strain applied on the fiber produces a periodical elliptical modification of the core and a modulation of the index of refraction. As a consequence of the micrometer scale perturbation period, the resulting mode coupling occurs directly between guided and radiated modes. To simulate the transmission induced by these kinds of perturbations, simplified models considering only total mode couplings are often used. In order to investigate the range of validity of this approximation, results are compared to the electromagnetic mode couplings rigorously computed for the first time, to our knowledge, with a large multimode fiber (more than 6000 linear polarized modes) using the Marcuse model. In addition, in order to have a more complete modeling of the proposed transducer, the anisotropic elasto-optic effects in the stressed multimode fiber are considered. In this way, the transmission of the microperturbed optical fiber transmission and, therefore, the behavior of the transducer are physically explained and its applications as a future stretching sensor are discussed.

Transparent layers such as polymers are complex and can contain defects which are not detectable with classical optical inspection techniques. With an interference microscope, tomographic analysis can be used to obtain initial structural information over the depth of the sample by scanning the fringes along the Z axis and performing appropriate signal processing to extract the fringe envelope. By observing the resulting XZ section, low contrast, sub-\ensuremathμm sized defects can be lost in the noise which is present in images acquired with a CCD camera. It is possible to reduce temporal and spatial noise from the camera by applying image processing methods such as image averaging, dark frame subtraction or flat field division. In this paper, we present some first results obtained by this means with a white light scanning interferometer on a Mylar polymer, used currently as an insulator in electronics and micro-electronics. We show that sub-\ensuremathμm sized structures contained in the layer, initially lost in noise and barely observable, can be detected by applying a combination of image processing methods to each of the scanned XY images along the Z-axis. In addition, errors from optical imperfections such as dust particles on the lenses or components of the system can be compensated for with this method. We thus demonstrate that XZ section images of a transparent sample can be denoised by improving each of the XY acquisition images. A quantitative study of the noise reduction is presented in order to validate the performance of this technique