Current Search:   microfabrication (x)

View All Items

  • CSV Spreadsheet
(1 - 4 of 4)
DESIGN AND OPTIMIZATION OF NANO-OPTICAL ELEMENTS BY COUPLING FABRICATION TO OPTICAL BEHAVIOR
Title
DESIGN AND OPTIMIZATION OF NANO-OPTICAL ELEMENTS BY COUPLING FABRICATION TO OPTICAL BEHAVIOR.
Creator
Rumpf, Raymond, Johnson, Eric, University of Central Florida
Abstract / Description
Photonic crystals and nanophotonics have received a great deal of attention over the last decade, largely due to improved numerical modeling and advances in fabrication technologies. To this day, fabrication and optical behavior remain decoupled during the design phase and numerous assumptions are made about "perfect" geometry. As research moves from theory to real devices, predicting device behavior based on realistic geometry becomes critical. In this dissertation, a set of numerical tools...
Show morePhotonic crystals and nanophotonics have received a great deal of attention over the last decade, largely due to improved numerical modeling and advances in fabrication technologies. To this day, fabrication and optical behavior remain decoupled during the design phase and numerous assumptions are made about "perfect" geometry. As research moves from theory to real devices, predicting device behavior based on realistic geometry becomes critical. In this dissertation, a set of numerical tools was developed to model micro and nano fabrication processes. They were combined with equally capable tools to model optical performance of the simulated structures. Using these tools, it was predicted and demonstrated that 3D nanostructures may be formed on a standard mask aligner. A space-variant photonic crystal filter was designed and optimized based on a simple fabrication method of etching holes through hetero-structured substrates. It was found that hole taper limited their optical performance and a method was developed to compensate. A method was developed to tune the spectral response of guided-mode resonance filters at the time of fabrication using models of etching and deposition. Autocloning was modeled and shown that it could be used to form extremely high aspect ratio structures to improve performance of form-birefringent devices. Finally, the numerical tools were applied to metallic photonic crystal devices.
Show less
Date Issued
2006
Identifier
CFE0001159, ucf:46849
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001159
SYNTHESIS OF NOVEL FLUORENE-BASED TWO-PHOTON ABSORBING MOLECULES AND THEIR APPLICATIONS IN OPTICAL DATA STORAGE, MICROFABRICATION, AND STIMULATED EMISSION DEPLETION
Title
SYNTHESIS OF NOVEL FLUORENE-BASED TWO-PHOTON ABSORBING MOLECULES AND THEIR APPLICATIONS IN OPTICAL DATA STORAGE, MICROFABRICATION, AND STIMULATED EMISSION DEPLETION.
Creator
Yanez, Ciceron, Belfield, Kevin, University of Central Florida
Abstract / Description
Two-photon absorption (2PA) has been used for a number of scientific and technological applications, exploiting the fact that the 2PA probability is directly proportional to the square of the incident light intensity (while one-photon absorption bears a linear relation to the incident light intensity). This intrinsic property of 2PA leads to 3D spatial localization, important in fields such as optical data storage, fluorescence microscopy, and 3D microfabrication. The spatial confinement that...
Show moreTwo-photon absorption (2PA) has been used for a number of scientific and technological applications, exploiting the fact that the 2PA probability is directly proportional to the square of the incident light intensity (while one-photon absorption bears a linear relation to the incident light intensity). This intrinsic property of 2PA leads to 3D spatial localization, important in fields such as optical data storage, fluorescence microscopy, and 3D microfabrication. The spatial confinement that 2PA enables has been used to induce photochemical and photophysical events in increasingly smaller volumes and allowed nonlinear, 2PA-based, technologies to reach sub-diffraction limit resolutions. The primary focus of this dissertation is the development of novel, efficient 2PA, fluorene-based molecules to be used either as photoacid generators (PAGs) or fluorophores. A second aim is to develop more effective methods of synthesizing these compounds. As a third and final objective, the new molecules were used to develop a write-once-read many (WORM) optical data storage system, and stimulated emission depletion probes for bioimaging. In Chapter I, the microwave-assisted synthesis of triarylsulfonium salt photoacid generators (PAGs) from their diphenyliodonium counterparts is reported. The microwave-assisted synthesis of these novel sulfonium salts afforded reaction times 90 to 420 times faster than conventional thermal conditions, with photoacid quantum yields of new sulfonium PAGs ranging from 0.01 to 0.4. These PAGs were used to develop a fluorescence readout-based, nonlinear three-dimensional (3D) optical data storage system (Chapter II). In this system, writing was achieved by acid generation upon two-photon absorption (2PA) of a PAG (at 710 or 730 nm). Readout was then performed by interrogating two-photon absorbing dyes, after protonation, at 860 nm. Two-photon recording and readout of voxels was demonstrated in five and eight consecutive, crosstalk-free layers within a polymer matrix, generating a data storage capacity of up to 1.8 x 1013 bits/cm3. The possibility of using these PAGs in microfabrication is described in Chapter III, where two-photon induced cationic ring-opening polymerization (CROP) crosslinking of an SU8 resin is employed to produce free-standing microstructures. Chapter IV describes the investigation of one- and two-photon stimulated emission transitions by the fluorescence quenching of a sulfonyl-containing fluorene compound in solution at room temperate using a picosecond pump-probe technique. The nature of stimulated transitions under various fluorescence excitation and quenching conditions were analyzed theoretically, and good agreement with experimental data was demonstrated. Two-photon stimulated transitions S1 to S0 were shown at 1064 nm. The two-photon stimulated emission cross section of the sulfonyl fluorophore was estimated as aproximately 240 - 280 GM, making this compound a good candidate for use in two-photon stimulated emission depletion (STED) microscopy.
Show less
Date Issued
2009
Identifier
CFE0002913, ucf:48003
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002913
Cavitation and heat transfer over micro pin fins
Title
Cavitation and heat transfer over micro pin fins.
Creator
Nayebzadeh, Arash, Peles, Yoav, Chow, Louis, Kassab, Alain, Plawsky, Joel, University of Central Florida
Abstract / Description
With the dramatic increase in the usage of compact yet more powerful electronic devices, advanced cooling technologies are required to maintain delicate electronic components below their maximum allowable temperatures and prevent them from failure. One solution is to use innovative pin finned heat sinks. This research is centered on the evaluation of hydrodynamic cavitation properties downstream pin fins and extended toward single-phase heat transfer enhancement of array of pin fins in...
Show moreWith the dramatic increase in the usage of compact yet more powerful electronic devices, advanced cooling technologies are required to maintain delicate electronic components below their maximum allowable temperatures and prevent them from failure. One solution is to use innovative pin finned heat sinks. This research is centered on the evaluation of hydrodynamic cavitation properties downstream pin fins and extended toward single-phase heat transfer enhancement of array of pin fins in microchannel. In this work, transparent micro-devices capable of local wall temperature measurements were micro fabricated and tested. Various experimental methods, numerical modeling and advanced data processing techniques are presented. Careful study over cavitation phenomena and heat transfer measurement downstream pin fins were performed.Hydrodynamic cavitation downstream a range of micro pillar geometries entrenched in a microchannel were studied. Three modes of cavitation inception were observed and key parameters of cavitation processes, such as cavity length and angle of attachment, were compared among various micro pillar geometries. Cavity angle of attachments were predominantly related to the shape of the micro pillar. Fast Fourier transformation (FFT) analysis of the cavity image intensity revealed transverse cavity shedding frequencies in various geometries and provided an estimation for vortex shedding frequencies.Experimental and numerical heat transfer studies over array of pin fins were carried out to find out the influence of lateral interactions of fluid flow on the enhancement of heat transfer. Local temperature measurements combined with a conjugate fluid flow and heat transfer modeling revealed the underlying heat transfer mechanisms over pin fin arrays.
Show less
Date Issued
2019
Identifier
CFE0007690, ucf:52407
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007690
Photophysical and photochemical factors affecting multi-photon direct laser writing using the cross-linkable epoxide SU-8
Title
Photophysical and photochemical factors affecting multi-photon direct laser writing using the cross-linkable epoxide SU-8.
Creator
Williams Jr., Henry, Kuebler, Stephen, Elsheimer, Seth, Zhai, Lei, Liao, Yi, Heinrich, Helge, University of Central Florida
Abstract / Description
For the past decade, the epoxy based photoresist SU-8 has been used commercially and in the lab for fabricating micro- and nano-structures. Investigators have studied how processing parameters such as pre- and post-exposure bake temperatures affect the resolution and quality of SU-8 structures patterned using ultraviolet or x-ray lithography. Despite the advances in understanding the phenomena, not all of them have been explored, especially those that are specific to multi-photon direct laser...
Show moreFor the past decade, the epoxy based photoresist SU-8 has been used commercially and in the lab for fabricating micro- and nano-structures. Investigators have studied how processing parameters such as pre- and post-exposure bake temperatures affect the resolution and quality of SU-8 structures patterned using ultraviolet or x-ray lithography. Despite the advances in understanding the phenomena, not all of them have been explored, especially those that are specific to multi-photon direct laser writing (mpDLW). Unlike conventional exposure techniques, mpDLW is an inherently three-dimensional (3D) process that is activated by nonlinear absorption of light.This dissertation reports how several key processing parameters affect mpDLW using SU-8 including pre-exposure bake duration, focal depth, incident laser power, focal-point scan speed, and excitation wavelength. An examination of solvent content of films at various stages in the mpDLW by 1H-NMR shows that even moderate solvent content (over 1 wt-%) affects film viscosity and photoacid diffusion lengths, and can greatly affect the overall fidelity of small features. A study of micro-fabricated feature size versus writing depth in the material shows that even slight refractive index mismatch between SU-8 and the medium between it and the focusing objective introduces spherical aberration that distorts the focus, causing feature size to decrease or even increase in size with writing depth, depending on the average exposure power used. Proper adjustment of the average exposure power was demonstrated as a means to fabricate more uniform features with writing depth. Third, when varying the power and scan speed, it was observed that the feature-size scales with these two parameters in a manner that is consistent with a three-photon absorption mechanism at an excitation wavelength of 800 nm. When aniiiexcitation wavelength of 725 nm is used, the feature-size scaling becomes consistent with that of two photon absorption. This shows that the photoinitiators in the SU-8 can be activated by either two- or three-photon absorption over this wavelength range. Using an irradiance of ~2 TW cm-2 and elongated femtosecond pulses resulted in an observed fourth order power dependence. This observation is in agreement with the literature and suggests that the effective absorptive nonlinearity is also sensitive to pulse duration. These findings will be useful for creating accurate models of the process of mpDLW in SU-8. These models could be used to optimize the processing parameters and develop new processing methods and materials for high-resolution fabrication of robust 3D microstructures. Some of the findings were used to develop a method for fabricating functional microlenses on the tip of optical fibers. This approach opens a new route to functional integrated photonic devices.
Show less
Date Issued
2013
Identifier
CFE0005441, ucf:50403
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005441