KEYWORDS: Charge-coupled devices, Molybdenum, Digital holography, Holography, Holograms, Microscopes, 3D image reconstruction, 3D metrology, Optical engineering, 3D image processing
Holography has a considerable advantage of retrieving three-dimensional information of an object from only one interference recording. However, twin images always appear in the reconstruction for the reason of symmetry. Especially, twin images significantly deteriorate the quality of the reconstructed information in on-axis configuration. A solution of the twin-image problem in a digital holographic microscope by using symmetry with quadrantal masks is suggested in this study. This method is effective to most of the measured area without any additional implements, and restrictions on sample or iterations, and is demonstrated by the simulation and experimental results. The ratio of the disturbed area by a twin-image to the total measured area is reduced to the value of 0.82% in a specific case.
Digital holography (DH) has a big advantage to retrieve the
three-dimensional (3D) information of the object from only
one interference recording. Especially, the digital holographic microscope (DHM) using a microscope objective (MO)
has been researched for 3D microscopy. The researches have progressed for compensation of aberrations and
improvement of the resolution in the optical system in recent years. Most of small aberrations caused by a MO are
compensated through various researches. However, the measured phase is distorted in the optical system, which has the
significant wavefront deformation in illuminating wave larger than number of wavelengths. In this paper, the relation
between illuminating wave and the reconstructed phase is studied based on the wave optics and the analysis is confirmed
by the simulations. The analysis of the wavefront compensation is applied to a super-resolution DHM in theory and the
technique for retrieving the distribution of the intensity and phase is demonstrated in simulation.
The digital holographic microscope (DHM) has emerged as a useful tool for verifying the three-dimensional structure of an object. A dual-type inline DHM that can be used with both transmission and reflection imaging in a single device is developed. The proper modes (between transmission and reflection imaging) can be easily changed according to the characteristics of the object in this system. The optimum condition for retrieving the correct phase information is illuminating a plane wave to an object. In contrast to the transmission imaging, it is difficult to illuminate an object using a plane wave without deformations in the reflection imaging. We developed an adequate relay lens module for illumination that can be adapted to any type of microscope objective without significant aberrations in the reflection imaging. The relationship between the illuminating condition and the measured phase based on the wave optics is analyzed. A specially designed and manufactured phase mask is observed in this system, and an alternative method for overcoming the limitation of phase unwrapping is introduced for the inspection of that object.
Holography has a considerable advantage to retrieve the three-dimensional (3D) information of an object from only one
interference recording. For several decades, the technology of digital holography (DH), which uses numerical
reconstruction as opposed to illuminating the reference beam to the hologram plate, has progressed with the assistance of
improvements in 2D array detectors and computers. In this paper, a dual-type inline digital hologram microscope (DHM)
system that can be used with both transmission imaging and reflection imaging in a single device is developed. The
proper method depending on the modes (transmission imaging or reflection imaging) can be changed easily in this
system according to the characteristics of the object. Illumination with a plane wave is the necessary condition for
retrieving the correct phase information. In the case of reflection imaging, unlike in transmission imaging, a special relay
lens in addition to the microscope objectives (MOs) is needed to meet the needs of this condition. However, the quality
of the 3D information can deteriorate significantly due to the overlapping twin image that is inherent in holography. This
study suggests an effective and convenient method for eliminating the twin image that is entangled in the reconstructed
information. The proposed method does not require extra components, numerical iterations, and restrictions on the
object.
Uncooled TIS is in the spotlight for its small size and low-voltage operation for personal and portable use compare to
other TIS. Generally, uncooled TIS using temperature control by TEC converts the gap between TEC temperature and
input-image into voltage by ROIC and outputs the analog image.
For cooled detector, it is possible to block undesirable infrared input since F number of the optics and the detector are
same but for uncooled detector, it is easy to get undesirable infrared input around because the F numbers are different.
It becomes more obvious when temperature gap between the equipment and background gets bigger.
For TIS, background temperature easily changes inside the system and around the detector because the radiating heat
from the electrical circuit inside the system is getting higher as usage time passes, and it makes worse the non-uniformity
output characteristics of the detector.
In particular, the temperature change of the system itself which depends on its setting position and other temperaturechanging
factors like electrical circuit inside the system make the additional non-uniformity worse which caused by
infrared photon radiates from structures which includes optics and detector.
This article would indicate the method of minimizing its image blurring which originates from the F number gap
between optics and detector.
A novel method is employed to eliminate the twin-images in the so called 'in-line' digital
holographic microscope. We could achieve digital holographic microscope which solve the
problems of overlapping of real and imaginary images and eliminating one of them by padding
and removing DC term by averaging method. The entire process needs only one digital
hologram.
We present a digital holographic microscope that has a wide field of view. Off-axis holograms are recorded with a magnified image of microscopic objects and numerically reconstructed by calculation of scalar diffraction in the Fresnel approximation. Holograms are recorded by CCD. The distance between neighbouring pixels of a CCD is only of the order of 5 micrometer. The corresponding maximum resolvable frequency is of the order of 100 linepairs /mm. The maximum angle between the reference and object wave is therefore limited to a few degrees. The higher magnification by an objective lens with the higher power makes the wider angle object beam. Off- axis holograms with the high power objective lens has the limitation of magnification and a field of view. We present a new type of imaging system that overcomes the limitation of magnification and a field of view. It is consisted of an objective lens and additional lens array. It makes the nearly same angle between object beams and a reference beam. The overlapped angles are also less than the maximum limited angle due to CCD pixel size. It also has a maximum field of view which is decided inherently by an objective lens. It therefore overcomes the limitation of the size of CCD.
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