Optical imaging of surface dynamics in microstructures

Lauri Lipiäinen

Research output: ThesisDoctoral ThesisCollection of Articles


The research summarized in this thesis covers the design, implementation, and use of optical techniques for characterizing surface movements in microstructures. The main focus of the work has been on developing instrumentation and data analysis methods for investigating surface vibrations in micromechanical components that are based on, e.g., microelectro-mechanical systems (MEMS), and surface and bulk acoustic waves. All the scanning single-point and full-field vibration detection setups and methods developed in this work enable phase-sensitive, absolute amplitude measurement of surface vibrations. An unstabilized homodyne interferometry concept is presented for detecting out-of-plane (OP) vibrations with a scanning single-point Michelson laser interferometer. A noninterferometric detection method for measuring in-plane (IP) vibrations is also described that is implemented in this scanning system. The setup enables vibration measurements for frequencies up to 2 GHz, with typical minimum detectable amplitudes of even less than 1 pm and 10 pm for the OP and IP components, respectively. Furthermore, novel methods based on these scanning techniques were implemented to allow for studies of the nonlinear behavior of surface vibrations, which serve to advance the understanding of such effects in microacoustic components. The scanning-based optical imaging methods were applied to two research studies in MEMS resonators that showed unexpected behavior. The full-field interferometric techniques and analysis methods developed in this thesis work push the performance of the camera-based detection of OP vibrations into new limits. The work advances the stroboscopic white-light interferometric technique to be applicable for characterizing high-frequency devices with vibration amplitudes down to less than 100 pm and with frequencies up to 1 GHz. In addition, a stabilized full-field stroboscopic detection concept was developed and the implemented setup was demonstrated to allow for detecting surface vibrations with minimum detectable amplitudes of less than 30 pm. The stabilized full-field interferometer was also developed further for imaging surface dynamics on microstructures in the time domain with even subnanometer vertical resolution. The optical imaging methods described in this thesis contribute substantially to the research and development of micromechanical devices as they offer direct information of the underlying device physics. The benefits of these advanced optical characterization methods are clearly highlighted in the two MEMS resonator study cases, in which the optical characterization revealed the physical mechanisms that adversely affect the device performance.
Translated title of the contributionPintaliikkeiden optinen kuvantaminen mikrorakenteissa
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Kaivola, Matti, Supervising Professor
  • Kokkonen, Kimmo, Thesis Advisor
Print ISBNs978-952-60-7051-3
Electronic ISBNs978-952-60-7052-0
Publication statusPublished - 2016
MoE publication typeG5 Doctoral dissertation (article)


  • laser interferometry
  • microacoustics
  • micromechanical devices
  • surface dynamics


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