RESUMO
We calibrated and determined the measurement uncertainty of a custom-made Fourier domain short coherence interferometer operated in laboratory conditions. We compared the optical thickness of two thickness standards and three coverslips determined with our interferometer to the geometric thickness determined by SEM. Using this calibration data, we derived a calibration function with a 95% confidence level system uncertainty of (5.9×10(-3)r+2.3) µm, where r is the optical distance in µm, across the 240 µm optical measurement range. The confidence limit includes contributions from uncertainties in the optical thickness, geometric thickness, and refractive index measurements as well as uncertainties arising from cosine errors and thermal expansion. The results show feasibility for noncontacting absolute distance characterization with micrometer-level accuracy. This instrument is intended for verifying the alignment of the discs of an accelerating structure in the possible future compact linear collider.
RESUMO
Stroboscopic scanning white-light interferometry (SSWLI) can be used for 3D imaging of oscillating samples. It allows measurement of micrometer to millimeter size samples with nanometer vertical precision. Unlike coherent light source systems the SSWLI can measure unambiguously samples with vertical steps. Traceability of the vertical displacement measurement is important with SSWLI since the height measurement is not related to any specific monochromatic light wavelength. For static measurements SSWLI can be calibrated using, e.g., step height standards, but to characterize dynamic measurements traceable samples with accurate motion are needed due to error sources related to the frequency response of the SSWLI. In the presented method, SSWLI measurements are performed on dynamic transfer standards, which are characterized using a laser interferometer traceable to the SI meter. In this work dynamic SSWLI measurements at subkilohertz to 10.7 kHz frequencies with micrometer range displacement are characterized. The expanded uncertainty (k=2) was 9.6 nm for a measured displacement of 766 nm at 10.7 kHz. The methodology can be used up to the frequency limits of the SSWLI using suitable samples.
RESUMO
We used a supercontinuum-based scanning white-light interferometer to characterize the oscillation of a MEMS device. The output of a commercially available supercontinuum light source (FiberWare Ilum II USB) was modulated to achieve stroboscopic operation. By synchronizing the modulation frequency of the source to the sample oscillation, dynamic 3-D profile measurements were recorded. These results were validated against those obtained with a white light LED setup. The measured maximum deflection of a 400×25×4 µm(3) microbridge driven with 0-6.8 V sinusoidal voltage at 10 Hz was 1.42±0.03 µm (supercontinuum), which agreed with the LED measurement. The method shows promise for characterization of high-frequency MEMS devices.
