Phase unwrapping is a very important processing step in phase shift interferometry. In this work, we propose a new
method which combines the branch-cut method with error correcting. The method can avoid the propagation of the phase
errors and have higher reliability. The experiment proves the proposed method is feasible and effective.
This study proposes the auto-focusing procedure and the scan-range determining algorithm for white-light scanning
interferometry. During white-light scanning interferometry, the interference fringe must be located and to the best-focus
interferogram identified. The vertical-scan range must also be determined prior to the scanning procedure. A series of
images, either in-focus or out-of-focus, are collected in a proposed interference-fringe searching step. The contrast and
the sharpness indices of each image are calculated and applied in the auto-focusing scheme, and the vertical-scan range
is determined accordingly. Some preliminary experiments are performed to demonstrate that the best-focus
interferogram can be located precisely and the vertical-scan range can be determined.
A dynamic 3-D nano-scale surface profilometer using stroboscopic white light interferometry with novel image
deconvolution and automatic identification of structure resonant modes was successfully developed. As micro
electromechanical systems (MEMS) increase rapidly towards industrial application, the needs of accurate dynamic
characterization are extremely important to optimal design and fabrication. To meet the demands, an optical microscopy
based on stroboscopic interferometry was developed to achieve full-field vibratory out-of-plane surface profilometry
and system characterization. A novel deconvolution strategy with correction of the light response function was
established to remove the potential image blurs caused by the unavoidable vibration of the tested parts. With this
technical advance, the bandwidth of dynamic measurement can be significantly increased up to 10 MHz without
sacrificing measurement accuracy. Meanwhile, an innovative detection algorithm based on image contrast measure was
developed for automatic identification of accurate resonant modes. The detection method provides the simplest and
most economic way to detect accurate resonant peaks without adding any significant hardware in a stroboscopic
interferometric framework. To verify the effectiveness of the developed methodology, AFM cantilever beams were
measured to analyze the full-field resonant vibratory modes and dynamic characteristics. The experimental results
confirm that the resonant vibration behavior of the tested microcantilever beams can be accurately characterized and 5
nm of vertical measurement accuracy as well as tens micrometers of vertical measurement range can be achieved. The
measured results were satisfactorily consistent with the theoretical simulation outcomes from ANSYS.
The results of combining the wrapped phase with the fringe order of this phase to increase the precision of white-light interferometry at high scanning speed are presented. Monochromatic phase data are calculated using the Fourier method and the fringe order is determined using a general coherence peak sensing method. A wide scanning interval of 5λ/8 and a narrow-band color filter with a bandwidth of 70 nm are adopted to acquire interferograms. Experiments with an rms repeatability of step height measurement of below 1 nm and a scanning speed of 40 μm/s are performed.
A static and dynamic 3-D surface profilometer with nano-scale measurement resolution was successfully developed using stroboscopic illumination and white-light vertical scanning techniques. Microscopic interferometry is a powerful technique for static and dynamic characterization of micro electromechanical systems (MEMS). As MEMS devices move rapidly towards commercialization, the issue of accurate dynamic characterization has emerged as a major challenge in design and fabrication. In view of this need, an interferometric microscopy based on white-light stroboscopic interferometry using vertical scanning principle was developed to achieve static and dynamic full-field profilometry and characterization of MEMS devices. A micro cantilever beam used in AFM was characterized using the developed instrument to analyze its full-field resonant vibratory behavior. The first five mode resonant vibration can be fully characterized and 3-5 nm of vertical measurement accuracy as well as tens micrometers of vertical measurement range can be achieved. The experimental results were consistent with the theoretical simulation outcomes from ANSYS. Using white-light stroboscopic illumination and white-light vertical scanning techniques, our approach has demonstrated that static and dynamic 3-D nano-scale surface profilometry of MEMS devices with tens-micrometer measurement range and a dynamic bandwidth up to 1MHz resonance frequency can be achieved.
A miniature sensor based on extrinsic Fabry-Perot interferometry is proposed. In this setup, two optical fibers are integrated into a miniature sensing head to produce a pair of quadrature signals for solving direction ambiguity problem. It can also achieve nanometer resolution and at least 10kHz dynamic range after electronic subdivision. Comparing with capacitive senor, it has advantages including electromagnetic interference immunity and long distance measurement capability. In this paper, related theoretical descriptions are introduced and the comparisons with capacitive sensor are conducted. An experiment for detecting the characteristics of hard disk drive with this novel sensor is depicted. Furthermore, a new method of measuring liquid refractive index is described. All the experiment results show that this novel sensor is excellent in displacement and vibration measurement and many other applications.
A planar encoder using conjugate optics is proposed for sensing the 2-D displacement of a 2-D grating. A Doppler frequency shift of diffracted light is generated when the grating moves. The optical conjugate path can compensate for the error arising from the relative tilt between the optical head and the scale (head-to-scale tilt). Additionally, the optical head is easily integrated, having high tolerance in component-to-component placement. The 2-D displacement system with the 2-D grating, which has period of 1.6 µm in both the X and Y directions, provides a signal period of 0.4 µm by using a double-diffraction configuration. This system and associated electronics provide interpolation with a factor of 400, corresponding to a measurement resolution of 1 nm.
A new profiling algorithm is proposed for the scanning white-light interferometry. A series of white-light interferograms are acquired by traditional vertical scanning process. The collected intensity data of the interferograms are then Fourier-Transformed with respect to the ordinate, or the scanning axis, into the wave number domain, where two or more wave numbers are selected for further calculation. The multi-wavelength phase-unwrapping technique is then used to solve for the surface profile. Preliminary experiment has been carried out with a Mirau-type white-light interferometer on two sets of step-height standards. The proposed algorithm works as well even when the spectrum of the white-light source is not Gaussian distributed, while the conventional peak sensing algorithms do not.
Laser encoders overcome the fundamental resolution limit of geometrical optical encoders by cleverly converting the diffraction limit to phase coded information so as to facilitate nanometer displacement measurement. As positioning information is coded within the optical wavefront of laser encoders, interferometry principles must be adopted in the design of the laser encoders. This effect has posed a very strong alignment tolerance among various components of the whole laser encoder, which in turn imposes a serious user adaptation bottleneck. Out of all alignment tolerances, the head-to-scale alignment tolerance represents the most important hindrance for wider ap-plications. This paper presents a novel laser planar encoder, which serves as a two-dimensional position detection apparatus for precision machine applications and can provide a measuring resolution less than 1 nm. Improving the IBM laser optical encoder design by taking into consideration manufacturing tolerance of various optical components, an innovative two-dimensional laser encoder with ultra high head-to-scale tolerance is presented. It was identified that this newly proposed laser encoder design could avoid the effect of differences in polarization diffraction efficiencies for the 2-D grating scale used. Optimizing the system performance by cleverly designing the profile of the 2-D grating scale was also detailed. The effect of non-uniform temperature field within the head-to-scale range that can yield a nonzero initial phase so as to decrease the system measurement accuracy was analyzed. In addition, misalignment of the polarizers located in front the photodiodes were identified to be the main cause for imperfect Lissajous circles, which may lower the measuring resolution when traditional arctangent algorithm was adopted for circular polarization interferometers. The resolution of the newly developed laser planar encoder was verified by experiments and was found to agree well with the theoretical predictions.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.