The spatial phase shifting digital speckle pattern shearing interferometry (DSPSI) system has been widely used to determine map of deformation. In this paper a common-path DSPSI setup is introduced for in-plane strain measurement under dynamic loading, using two laser beams with different wavelengths that symmetrically illuminate the test object, and a single detector. The simplicity, stability and efficiency of the arrangement are provided using a glass plate as a shearing device which is capable of tuning the sensitivity continuously. The phase is recovered from a single frame by the Fourier method. In this setup the spatial carrier frequencies can be adjusted independent of the lateral shearing amount. Ultimately, the desired field of view can easily be achieved by simple imaging optics. To validate the feasibility and the flexibility of our technique, the proposed setup is used to evaluate the strain map of an aluminum plate which is deformed under dynamic stress in its plane. Experimental results are presented and discussed.
When the emitted light from a small object illuminates a rough interface, the image of the object is formed in reflection if the incident angle of the light is larger than a threshold angle. The threshold angle is the angle beyond which the specularly scattered light acquires a coherent component. The threshold angle depends on interface roughness and light wavelength. In transmission mode, the incident angle on the rough interface has an upper limit for image formation. The latter angle depends also on the refractive indices of the media surrounding the rough interface. We have determined the threshold angles and corresponding roughness for three different wavelengths using rough sheet-glass surfaces that were prepared by grinding sheet-glass surfaces by powders of different grain size. The roughnesses obtained by this method are in good agreement with those obtained by other methods. Our experimental studies also show that the threshold angle is practically independent of the illumination intensity. The presented method has the potential to be used in process measurement due to simplicity of the required optical system.
It is generally accepted that mirage is formed when temperature of the ground surface, in a flat area like desert, is higher
than the temperatures of the over ground air layers. In this case, light emerging from a distant object makes total internal
reflection in the air layers and forms the image of the object that is called mirage. Our investigation on mirage formation
in desert indicates that there is no meaningful relation between mirage formation and temperature change over the
ground. In addition, we show that, the interference of the lights reflected from different air layers destroys the coherency
of the image forming light. This happens because the temperature change occurs in an interval larger than a wavelength.
In the second part of the report we demonstrate theoretically and experimentally that flat rough surfaces behave like
mirrors at very large incident angles. We show that there is a threshold incident angle for observation of image in a rough
surface that depends on the surface roughness and light wavelength. The shortest distance between observer and the
image is determined by the threshold incident angle. Mirage is such an image. Image formation is studied in rough sheet
glass surfaces that prepared by grinding with powders of different sizes.
Different effects induce spectral changes; for example, correlation of the fluctuations in source, propagation of light, random
changes of optical properties of medium, diffraction and scattering from objects and rough interfaces. In this report we
review the spectral changes that occur as result of light diffraction from phase steps and particularly we emphasize on the
effect of phase singularities on spectral changes. We also review the redshift and blueshift in the spectra of the lights
coherently and diffusely scattered from rough interfaces. In addition, we study the effect of roughness and incident angle on
spectral profile of light scattered in reflection and transmission modes.
As the emitted light from an object strikes a rough interface the scattered light in specular direction can form
image only at incident angles beyond a threshold angle that depends on surface roughness and light wavelength.
This is also the case in transmission mode, but in this case the image is observed below a threshold angle that
depends also on refractive indices of the media surrounding the rough interface. In this work we show that the
threshold angle is the angle beyond which the scattered light acquires coherent component in specular direction.
Using glass surfaces roughened by powders of different grain sizes we have measured the threshold angles for
roughnesses in the range of 0.420-4.23 μm with the precision of 5 arc minutes, which provides the measurement
of the roughness, σ, with a precision in the range 0.002-0.15 μm. Our experimental studies show that the
threshold angle is practically independent of the illumination intensity. We have also studied the dependence
of the threshold angle on wavelength and the change in the image color with the change of incident angle in
reflection and transmission. The theoretical predictions and experimental results are in good agreement.