Digital holography extends the use of holography with the ability to provide quantitative values of both amplitude and
phase information of object. Digital holography has shown to be applicable in a wide variety of applications from
metrology to bio imaging. As in traditional holography, a variety of setups are possible in reflection and transmission
modes. In transmission digital holography, quantitative phase information of the object can be related to the height
variation of a transparent medium with constant refractive index to provide 3-D surface profile of the specimen. In this
paper the principles and characteristics of transmission digital holographic microscopy (DHM) are discussed specifically
towards microlens measurement. The capability and challenges of DHM for microlens measurement will be tested and
shown. This includes image plane measurement such as microlens diameter, pitch in lateral direction, microlens height
distribution in axial direction and focal length measurement which is in the range between image plane and hologram
plane. Based on experiment results, the capability and challenges of DHM for microlens measurement will be seen and
the effort direction for DHM enhancement will be pointed out.
In-line digital holographic microscopy as a phase measurement tool for the inspection of micro-components is presented.
Light diffracted by the micro-components interferes with the directly propagating beams to give the in-line digital
hologram recorded by the CCD camera. The convolution method is used to calculate the diffractive propagation of the
light in order to reconstruct the wavefront of the test specimen. A reference hologram without the test specimen is
recorded for the phase reconstruction. Finally, the method is applied on a phase grating to test its refractive index of the
coating material.
Digital holography extends the use of holography with the ability to provide quantitative values of both amplitude and
phase information of object. As in traditional holography, a variety of setups are possible in reflection and transmission
modes. Digital holography has shown to be applicable in a wide variety of applications from metrology to bio imaging.
In transmission digital holography, quantitative phase information of the object can be related to the height variation of a
transparent medium with constant refractive index to provide 3-D surface profile of the specimen. The Confocal
microscope is an high resolution technique for optical metrology. By optical sectioning, out-of-focus blur is essentially
absent from confocal imaging and high-resolution quantitative 3D images of specimen can be created. In this paper 3D
profiles of micro-optical diffractive components are recorded with both a transmission digital holographic microscope
(TDHM) and a confocal microscope to explore their capabilities and shortcomings. The principles and characteristics of
TDHM and confocal microscope are discussed specifically towards surface-profiling of micro-optical diffractive
components. For some components, 3-D imaging and profile measurements obtained with TDHM and the confocal
microscope method provide close agreement while for others discrepancies between TDHM and the confocal microscope
method are observed. The reasons for the differences in the 3-D imaging and profile measurement of these two methods
are discussed and analyzed.
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