Michael R. Wang

By Angel Flores and Michael R. Wang

Part of the book: Lithography

By Guomin Jiang, Kai Shen and Michael R. Wang

Part of the book: Updates in Advanced Lithography

By James H. Wang and Michael R. Wang

Outside of the medical field, spectral domain optical coherence tomography (SD-OCT) is sparsely used. As such, we explored the possibility and practicality of using SD-OCT as a tool to evaluate fastener flushness and countersink surface profiles. A SD-OCT device was built with a handheld galvanometer scanner that weighed only 0.5 lb. Not only it does not require scan center alignment, but it is also capable of quickly producing measurements of fastener flushness, radius, slant angle, countersink edge radius, and surface angle. With the X-Y two-line scanning method, measurements take only 90 ms. The SD-OCT device used to obtain these measurements uses a lens with 60 mm focal length and a broadband light source of 840 nm center wavelength and 45 nm spectral bandwidth. With these components, the SD-OCT device is able to provide an axial depth resolution of 8.5 μm and a lateral resolution of 19 μm. The axial depth resolution can be improved by using a wider bandwidth light source. Furthermore, the device is able to produce 3D surface profiles of fasteners and countersinks using multi-line scans.

Part of the book: Optical Coherence Tomography and Its Non-medical Applications

By Kai Shen, Hui Lu, Sarfaraz Baig and Michael R. Wang

We report that high lateral resolution and high image quality optical coherence tomography (OCT) imaging can be achieved by the multi-frame superresolution technique. With serial sets of slightly lateral shifted low resolution C-scans, our multi-frame superresolution processing of these special sets at each depth layer can reconstruct a higher resolution and quality lateral image. Layer by layer repeat processing yields an overall high lateral resolution and quality 3D image. In theory, the superresolution with a subsequent deconvolution processing could break the diffraction limit as well as suppress the background noise. In experiment, about three times lateral resolution improvement has been verified from 24.8 to 7.81 μm and from 7.81 to 2.19 μm with the sample arm optics of 0.015 and 0.05 numerical apertures, respectively, as well as the image quality doubling in dB unit. The improved lateral resolution for 3D imaging of microstructures has been observed. We also demonstrated that the improved lateral resolution and image quality could further help various machine vision algorithms sensitive to resolution and noise. In combination with our previous work, an ultra-wide field-of-view and high resolution OCT has been implemented for static non-medical applications. For in vivo 3D OCT imaging, high quality 3D subsurface live fingerprint images have been obtained within a short scan time, showing beautiful and clear distribution of eccrine sweat glands and internal fingerprint layer, overcoming traditional 2D fingerprint reader and benefiting important biometric security applications.

Part of the book: Optical Coherence Tomography and Its Non-medical Applications

By Diego Palacios and Michael R. Wang

Digital holographic microscopy (DHM) with 3D microscopic imaging capability is attractive for biological sampling, particle identification, and surface topographic profiling. The Michelson (Linnik) optical configuration along with microscope objectives is used to create a hologram with the reflections of a sample of 3D spatial structures. Instead of instantaneous volume recording of the hologram in a holographic film, a digital camera is used to sequentially record four phase-step holograms in 2D format, namely the digital holograms (DHs). A piezoelectric actuator was added to implement the formation of the four-phase-step DHs. Using a four-image phase-shifted algorithm, the 3D microscopic image of the object can be extracted. The recording of the DHs is fast, 28 ms, and the phase retrieval computation is fast as well, 24 ms. The DHM has been utilized to examine the surface topography of a lithography sample showing field of view of 312 μm × 234 μm, axial resolution of 3.31 nm, lateral resolution of 488 nm, and a maximum topography height of 270 nm.

Part of the book: Holography and Its Applications