Laser speckle interferometry of semi-Lambertian reflecting surfaces

Area of Science:

• Optics and Photonics
• Interferometry
• Laser Speckle Metrology

Background:

• Semi-Lambertian surfaces exhibit both random (diffuse) and ordered (specular) light reflection characteristics.
• Laser speckle interferometry is a technique used to measure small displacements and surface deformations.
• Understanding the optical recording geometry is crucial for optimizing specklegram quality.

Purpose of the Study:

• To investigate the effect of recording plane distance on laser speckle interferograms of semi-Lambertian surfaces.
• To analyze fringe contrast and spacing variations in specklegrams recorded at different distances.
• To draw an analogy between semi-Lambertian surface speckle fringes and two-point diffraction patterns.

Main Methods:

• Illumination of a semi-Lambertian surface with laser light.
• Recording laser speckle interferograms (specklegrams) at the image plane and at planes farther from the lens.
• Maintaining consistent displacement for all recordings to ensure comparability.

Main Results:

• Specklegrams recorded farther from the image plane showed enhanced fringe contrast.
• A slight reduction in the distance between fringes was observed with increased recording distance.
• The obtained fringe patterns exhibited similarities to those produced by two-point diffraction sources.

Conclusions:

• The distance of the recording plane significantly influences the quality and characteristics of specklegrams from semi-Lambertian surfaces.
• Optimizing the recording geometry can improve fringe visibility and resolution in laser speckle interferometry.
• The study establishes a valuable analogy between semi-Lambertian surface speckle patterns and fundamental diffraction principles.