Applications of digital speckle pattern shearing interferometry in characterization of fluids.

Digital speckle pattern shearing interferometry is a robust optical technique mostly used for measuring small deformations in solid objects. In this paper we focus on applications of this technique in characterization of liquid and gaseous samples. We demonstrate this by a few examples: measurement of the density (temperature) profiles inside a candle flame and around a hot wire in air.

Digital speckle shearography setup to measure the field-induced strain map in piezoelectric materials.

Residual or induced strains are important factors in the performance of electronic devices, actuators, and sensors. In this paper, we report the application of digital speckle shearography to obtain the two-dimensional field-induced out-of-plane strain maps in a piezoelectric slab under a varying electric field. Both the free-standing and loaded (pinned) states are investigated.

Measurement of the full complex degree of coherence using Fresnel diffraction from a phase discontinuity.

A field-portable, single-shot and very simple method is presented for measuring the full complex degree of coherence (CDC) of a quasi-monochromatic Schell-model field using the Fresnel diffraction from a phase discontinuity. To validate the proposed technique, the CDC of the light emitted from an incoherent source with variable size is investigated. The results are in excellent agreement with theoretical predictions of the Van Cittert-Zernike theorem.

Determination of the spectral line profile using a phase gradient step and stationary Fourier transform spectroscopy.

This paper introduces a new, to the best of our knowledge, simple, fast, and affordable spectroscopy technique, in which Fresnel diffraction caused by a phase gradient step is used to determine the spectral profile of light sources by Fourier transformation of the interferogram data. To realize the phase gradient step, a Fresnel biprism or double mirror can be used. In principle, a single interferogram is sufficient to obtain the line profile.

Application of white light Fresnel diffractometry to film thickness measurement.

In this work we present the theoretical background and experimental procedure to measure the thickness of thin films by analyzing Fresnel diffraction patterns obtained from polychromatic illumination of phase-step samples. As examples of this technique, we measured the thicknesses of thin aluminum layers on glass substrates using three different broad-spectrum light sources. The results are in excellent agreement with independent interferometric measurements within less than 5% relative uncertainties.

Nanometer displacement measurement using Fresnel diffraction.

We introduce a relatively simple and efficient optical technique to measure nanoscale displacement based on visibility variations of the Fresnel diffraction fringes from a two-dimensional phase step. In this paper we use our technique to measure electromechanical expansions by a thin piezoelectric ceramic and also thermal changes in the diameter of a tungsten wire. Early results provide convincing evidence that sensitivity up to a few nanometers can be achieved, and our technique has the potential to be used as a nanodisplacement probe.

High precision refractometry based on Fresnel diffraction from phase plates.

When a transparent plane-parallel plate is illuminated at a boundary region by a monochromatic parallel beam of light, Fresnel diffraction occurs because of the abrupt change in phase imposed by the finite change in refractive index at the plate boundary. The visibility of the diffraction fringes varies periodically with changes in incident angle. The visibility period depends on the plate thickness and the refractive indices of the plate and the surrounding medium.

Application of Fresnel diffraction from a phase step to the measurement of film thickness.

When a thin film that is prepared in a step form on a substrate and coated uniformly with a reflective material is illuminated by a parallel coherent beam of monochromatic light, the Fresnel diffraction fringes are formed on a screen perpendicular to the reflected beam. The visibility of the fringes depends on film thickness, angle of incidence, and light wavelength. Measuring visibility versus incident angle provides the film thickness with an accuracy of a few nanometers.