Browsing by Author "Agusanto, Kusuma"

Now showing 1 - 2 of 2

Effect of oblique retroreflection from a vibrating mirror on laser Doppler shift
(2019-03-20)
Agusanto, Kusuma
;
Lau, Gih-Keong
;
Liu, Ting
;
Zhu, Chuangui
;
機械工程學系
A laser Doppler vibrometer (LDV) fails to measure a large out-of-plane vibration of a rotating mirror when the mirror obliquely reflects the laser beam away, causing a signal loss from being detected. To solve this problem, an external retroreflective tape was used to recover the oblique reflection. However, the reading of LDV obtained from the recovered signal is not right because the retroreflection adds extra Doppler frequency shifts to the oblique reflection. Here, we first derive the relationship of Doppler shift to the oblique angle of retroreflection. For the first time with the help of retroreflection, a standard LDV can measure the largely vibrating mirror as well as a high-speed camera, albeit without the need for heavy computation. (C) 2019 Optical Society of America
Radial and tangential velocity effects of a probed scanning mirror on laser Doppler frequency shift
(2020-04-20)
Agusanto, Kusuma
;
Lau, Gih-Keong
;
Liu, Ting
;
Zhu, Chuangui
;
機械工程學系
A laser Doppler vibrometer (LDV) is precise and fast in measuring the translational velocity of a vibrating diffuse surface. However, it could fail to measure the tangential velocity of a rotating mirror. While the specular reflection away from the mirror can be recovered by a retroreflective collector, the recovered LDV reading is found to deviate from the true tangential velocity of the probed scanning mirror. This happens because the probed spot shifts radially along the rotating mirror surface and thus introduces extra Doppler shift, while the laser beam is aimed at a constant height on the scanning mirror. Here, we derive an analytical relationship between the laser Doppler shift and the tangential velocity of the measured spot. With the input of the prescribed scan profile, we recover the true reading of tangential velocity of the scanning mirror even at a large rotational angle. This corrected LDV reading is as precise as the measurement by a high-speed camera. (C) 2020 Optical Society of America