Deflectometry Challenges Interferometry: 3D-Metrology from Nanometer to Meter

Abstract

We will discuss deflectometry from the physicist's and from the information theoretical point of view. The intrinsic features of deflectometry-incoherence, source encoding, high dynamical range, simplicity, and scalability-enable new sensors and unexpected applications. We will demonstrate that deflectometry is a novel imaging principle with a wide spectrum of new applications. The local slope of specularly reflecting surfaces can be measured for objects from µm-size to meter-size. With simple means, it is possible to find shallow (nm-) grooves or defects and to generate SEM-like images with high dynamical range. Microdeflectometry in transmission supplies extremely sensitive quantitative "phase contrast". Macroscopic deflectometry in transmission allows us to measure local refractive power with an accuracy better than 1 mD.

Surface Shape Distortion Online Measurement Method for Compact Laser Cavities Based on Phase Measuring Deflectometry

“…In a practical PMD system, the fringes reflected by the mirror captured in the CCD camera are used to calculate the wavefront distortion. However, limited by the wavefront reconstruction principle and algorithm, the LCD screen has to be placed in parallel with the surface of the mirror under test, which will take up a large measurement space [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][31][32][33][34][35][36][37]. It leads these mentioned methods to be primarily constrained in offline tests and not applicable for real-time measurement in the compact laser.…”

“…Based on the reference wavefront, the surface shape distortion will be accurately measured. Similar to the PMD method [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], the COPMD method is also based on sinusoidal fringe pattern projection and detection to acquire the wavefront slope through a phase-shift algorithm and then numerical integration to reconstruct the wavefront distortion. In the measurement process of the COPMD, the surface shape of the mirror before laser operation is measured first and taken as the reference.…”

“…It could be used to accurately measure the surface shape of a single optical element with the unique advantages of a high dynamic range, full field of view, and non-null measurement [13] on the basis of the triangulation law [14], Scheimpflug principle [15], and diffuse-versus-specular reflections principle [16]. Based on the synergy between deflectometry and ray-tracing, the PMD method was employed for the on-site evaluation of the free-form mirrors with a high speed, high accuracy, and cost reduction [17][18][19]. The software configurable optical test system (SCOTS), an upgraded phase measuring deflectometry, is presented to achieve a high-accuracy surface shape measurement of large astronomical telescopes and ellipsoidal X-ray mirrors with a flexible configuration and high dynamic range [20,21].…”

“…In 2018, the phase measuring deflectometry system combined with a laser resonator was designed to achieve a high-precision online thermal distortion measurement of crystals in the high-power laser [27]. However, limited by the wavefront reconstruction principle and algorithm, the screen of the liquid crystal display (LCD) has to be placed in parallel with the surface of the mirror under test, which takes up a large measurement space [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Thus, these mentioned methods are primarily constrained in offline tests and not applicable for real-time measurement in the enclosed laser facility.…”