Fringe generation and phase shifting with LCDs in projection moiré topography

Abstract

Structured light projection techniques are an important and popular approach for whole-field surface topography. Within this branch, projection moire interferometry is our preferred optical metrology method. The use of liquid crystal display (LCD) projectors to produce structured light patterns has been proposed and used before in projection moire. It allows fast and easy adaptation of the grid pitch and thus measurement sensitivity. In this paper we will show how using a second liquid crystal panel makes the projection moire technique even more versatile and performant: The setup incorporates optical demodulation (OD) which in turn allows for accurate phase-shifting and the use of phase-shifting algorithms (PSAs). The Z-resolution is high and no filtering or interpolation is needed in X-Y by using the gray scale value variations through the phase-shifting and optical demodulation. Thus, we make optimal use of the camera pixel resolution and achieve an uncompromised measuring resolution. Furthermore, the setup is entirely digitally controlled, needs no physical interaction and avoids mechanically moving component. The low-cost setup, technique and theory will be covered in this talk. The resolution and other performance properties will be discussed and demonstrated. And to conclude, an application to achieve elasticity parameters of membranes will be shown. interferometry is our preferred optical metrology method. The use of liquid crystal display (LCD) projectors to produce structured light patterns has been proposed and used before in projection moire. It allows fast and easy adaptation of the grid pitch and thus measurement sensitivity. In this paper we will show how using a second liquid crystal panel makes the projection moire technique even more versatile and performant: The setup incorporates optical demodulation (OD) which in turn allows for accurate phase-shifting and the use of phase-shifting algorithms (PSAs). The Z-resolution is high and no filtering or interpolation is needed in X-Y by using the gray scale value variations through the phase-shifting and optical demodulation. Thus, we make optimal use of the camera pixel resolution and achieve an uncompromised measuring resolution. Furthermore, the setup is entirely digitally controlled, needs no physical interaction and avoids mechanically moving component. The low-cost setup, technique and theory will be covered in this talk. The resolution and other performance properties will be discussed and demonstrated. And to conclude, an application to achieve elasticity parameters of membranes will be shown.