Phase only SLM as a reference element in Twyman-Green laser interferometer for MEMS measurement

Abstract

The active Twyman-Green laser interferometer for MEMS measurement equipped with Spatial Light Modulator (SLM) as a reference element is reported. The SLM is electrically addressed, reflective (made in Liquid Crystal on Silicone technology) and phase-only device which allows to actively shape of the reference beam wavefront in the interferometer. The proper use of the SLM in interferometric MEMS measurement is possible after opto-mechanical modification of the interferometer, performed calibration procedures and special interferogram processing. All these aspects are described. The use of such device benefits extension of measurement range and simplification testing procedures. Usefulness of the SLM is shown at the examples of active microelements testing. Advantages and disadvantages of SLM application are described and potential of this device for interferometry is discussed.

Progress in Phase Calibration for Liquid Crystal Spatial Light Modulators

“…Neglecting the coefficient, the Fraunhofer diffraction pattern could be treated as the spectrum of the grating. The grayscale-phase relation of the 8 × 8-pixel subsection can be measured according to Equation (5). Hence, the nonuniformity could be measured by moving the small grating inside the subsection.…”

“…Liquid Crystal Spatial Light Modulator (LC-SLM) and Digital Micro-Mirror device (DMD) are two of the most successful SLMs. For phase manipulation, the LC-SLM has been widely used in many fields: holographic display [1][2][3], precision metering [4,5], optical tweezers [6,7], lithography [8], beam shaping [9,10], etc. In the listed fields, the accurate phase manipulation is essential, especially for deploying SLM as a programmable diffractive device.…”

Active limited-angle tomographic phase microscope

“…43 Phaseonly, reflective modulators are also used in interferometry for wavefront shaping. 44 In this case, the correction of the object beam wavefront compensates for the shape of the SLM, which is not perfectly flat, and the aberration that is present at angles close to θ max . Also, if a biological sample was measured, the refractive index mismatch between the immersion liquid and the specimen would result in spherical aberration.…”