Yiin Kuen FUH^* and Jia Ren FAN

Institute of Opto-mechatronics Engineering, National Central University, Jhongli, Taoyuan 32001, Taiwan

(Received April 23, 2013; Revised June 7, 2013; Accepted June 10, 2013)

The induced optical aberration of laser beam passing through a transparent flowing fluid layer on a metal specimen is experimentally and empirical formula studied. The proposed study presents an experimental investigation of metal surface roughness measurement by combining an optical probe of laser-scattering phenomena and adaptive optics (AO) for aberration correction. In the absence of the AO correction scheme, induced flow velocity of 0.278 m/s can severely degrade the residual wavefront root mean square (RMS) error to 0.58 μm and decrease the scattered laser intensity. Real-time AO correction in closed-loop at a sampling rate of 8 Hz can reduce the wavefront RMS error to 0.19 μm and improve the attenuation of scattered laser intensity. The maximum relative error of the estimated roughness (R_a) is less than 7.8% compared with the stylus method. The experimental results show satisfactory correction in the presence of a flowing fluid layer using the AO system.

Key words: adaptive optics, scattering, surface roughness

^*E-mail address: mikefuh@ncu.edu.tw