A multi-color in-line digital holographic microscope (DHM) has been developed for high speed profile measurement of
micro-structures. The in-line architecture of the proposed DHM offers a high spatial resolution compared with the
conventional off-axis DHM. The multi-color DHM captures the three color hologram simultaneously in one-shot
recording by using a color CCD sensor and three RGB LED sources. The measurement range without phase ambiguity
of the multi-color DHM is extended up to 5 micrometers compared with the 0.3 micrometer of the conventional single
wavelength DHM technology. The real-time reconstruction rate of 3D profile is estimated around 20fps when using a
100 frame/sec CCD camera and a simple three-step phase shifting algorithm. The high reconstruction rate is important
for the measurement in the shop floor where fast measurement and immunity to the environment disturbance are
demanded. The air turbulence and floor vibration effects are further reduced by the near common-path architecture of
the proposed DHM. A phase stability of better than 5nm is achieved without any need of anti-vibration instrument table
and air turbulence protection cover.
A polarization-sensitive optical coherence microscope (PS-OCM) has been developed to non-destructively measure
birefringence distribution at the surface and internal interfaces of multi-layer structures. The PS-OCM can make twodimensional
en face measurement by exploiting the parallel sensing capability of the CCD sensors. PS-OCM utilizes the
low coherence interference principle to enable the depth-resolved mapping of the birefringence distribution inside the
materials. By simultaneous detection of interference fringes in two orthogonal polarization states allows determination
of the Strokes parameters of light. Comparison of the Strokes parameters of the incident state to that reflected light from
the sample can yield a depth-resolved map of optical properties such as birefringence and refractive index. Because
many semiconductor and optic materials such as ceramic/wafer/polymer/glass are stress-induced birefringence materials,
changes in birefringence distribution may, for instance, indicate changes in material uniformity and stress inside the
materials. The PS-OCM has the capability to measure the spatial stress-field distribution of a material caused by the
residual stress or applied load. Using the high numerical aperture of the objective lens and the broad bandwidth of the
light source, the PS-OCM has the 1.5micrometer and 1.6 micrometer resolutions respectively in the lateral direction and
longitudinal (or depth) direction.
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