In this webinar hosted by the Optical Fabrication and Testing Technical Group. Wei Gao will first present a three-axis autocollimator that can simultaneously detect the three-axis angular error motions (pitch, yaw, and roll errors) of a precision linear stage with sub-arcsecond resolutions. A collimated laser beam from a laser diode is projected onto a grating reflector mounted on the stage. The reflected 0th-order diffracted beam is received by an autocollimation unit, which consists of a collimator objective and a quadrant photodiode, for detecting the pitch and yaw errors. The reflected 1st-order diffracted beam is received by another autocollimation unit for detecting the roll error.

Next, Prof. Gao will present a three-axis displacement sensor. Instead of plane mirrors in a conventional Michelson interferometer for measurement of Z-directional displacement, the sensor employs two sinusoidal XY-grating mirrors with identical pitches and amplitudes as the stationary reference mirror and the moving scale mirror, respectively. The positive and negative first-order diffraction light beams from the two XY-grids superimposing with each other to generate interference signals, from which the displacements of the scale grid along the X-, Y-, and Z-axes can be simultaneously obtained with sub-nanometric resolutions. Finally, a multi-beam two-axis Lloyd’s mirror interferometer is presented for fabrication of two-axis scale gratings with identical pitches and amplitudes as the stationary reference mirror and the moving scale mirror, respectively.

What You Will Learn:
• You will learn how diffraction gratings can be used for multi-axis measurement. You will also learn some ultraprecision measurement technologies.

Who should attend:
• Researchers interested in optical metrology
• Students interested in optical science and applications.
• Industry scientists interested in precision metrology for manufacturing.

About the Presenter: Wei Gao from Precision Nanosystems Centre, Tohoku University

Wei Gao received his Bachelor from Shanghai Jiao Tong University in 1986, followed by MSc and Ph. D from Tohoku University in 1991 and 1994, respectively. He is currently a professor in Tohoku University. His research interests lie primarily in precision nanometrology. He is an author of the books “Precision Nanometrology” (Springer), “Surface Metrology for Micro- and Nanofabrication” (Elsevier), “Optical Metrology for Precision Engineering” (De Gruyter). He was awarded the Prize for Science and Technology from the Japanese government (MEXT) in 2019. He is a fellow of CIRP, ISNM, JSPE and a fellow of The Engineering Academy of Japan (EAJ).