OAKTrust :: Browsing by Author "Lin, Pao Tai"

Browsing by Author "Lin, Pao Tai"

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Apparatus for detecting a substance and method of operating the same
(United States. Patent and Trademark Office, 2020-08-04T00:00:00Z) Lin, Pao Tai; Gutierrez-Osuna, Ricardo; Texas A&M University System
An apparatus configured to detect a substance, and method of operating and forming the same. In one embodiment, the apparatus includes a tunable resonator including an upper Bragg reflector and a lower Bragg reflector separated by a porous matrix. The tunable resonator is configured to be illuminated by a light source and produce a first spectral optical response from a substance absorbed within the porous matrix. The apparatus also includes a detector positioned proximate the tunable resonator configured to provide a first absorption signal representing the first spectral optical response.
Applications of Light for Biomaterials and Safety
(2019-04-17) Nodurft, Dawson Thomas; Yakovlev, Vladislav; Sokolov, Alexei; Belyanin, Alexey; Welch, George; Lin, Pao Tai
The interaction of light with biological media represents an increasingly important area of research. Recent expansion of ultrafast laser sources in the midinfrared (MIR) regime is driving research in previously unexplored areas. In particular, the applications of these systems to biological materials is significant due to biological materials response to MIR wavelengths. The first two works presented here are motivated by gaps in the American National Standard for Safe Use of Lasers (ANSI) Z136.1 for eye safety. While we are ultimately interested in the nonlinear effects of MIR laser sources and the potential for retinal damage, we began by studying nonlinear behavior in Zinc Selenide (ZnSe) and air. The nonlinear processes examined were that of harmonic and continuum generation. The filament that was generated by the laser pulse in atmospheric air produced enough visible light at several wavelengths that were determined to be hazardous to the retina. Further work is required by the study in ZnSe to determine if maximum permissible exposure limits for retinal tissue was exceeded, despite significant visible light generation having been observed in spectral analysis. Laser light is not only a threat to safety, but a tool for use in diagnosing and understanding complicated biological structures. Raman spectroscopy allows for precise chemical and molecular analysis. The information Raman spectroscopy provides can identify the composition of unknown materials along with quantification of molecular concentration. Analysis of a commercial Raman spectrometer provided information about the most effective operation parameters for signal-to-noise enhancement. Thereafter, the spectrometer was used in determining the effectiveness of a microfluidic device as a cultivation tool for microalgae produced lipids. The results showed that Raman spectroscopy worked as effectively at measuring lipid production for time-course analysis as conventional methods without causing the damage to the algae cell typical of those conventional methods. Finally, a random Raman laser was investigated as a tool for imaging phenomena with lifetimes on the order of nanoseconds. The work determined the random Raman laser to be a more effective imaging tool when compared to two other conventional strobe methods.
Dual-Modal and Dual-Sensing-Mechanism (DMDSM) Acoustic Sensors for Robotic Ranging and Material Differentiation
(2023-05-01) Fang, Cheng; Zou, Jun; Lin, Pao Tai; Righetti, Raffaella; Song, Dezhen
One of the grand challenges in robotics is robust grasping of unknown objects. This is particularly important when robots expand its territory from industry floors to domestic service applications where the object prior knowledge is not often available. As a result, sensor-based grasping is more desirable. Ideally, with the assistance of object sensing, robotic fingers can respond to subtle changes in object pose right before grasping and adjust operations dynamically. Moreover, the object material and structure information can help planners better estimate the force distribution, impact characteristics and friction coefficients for a more robust grasping. However, current sensors have difficulties in satisfying these requirements. Tactile/force sensors may change object poses or even damage the object, which leads to slow or failed grasping. Non-contact long-distance sensors such as camera, LIDAR, radar, sonar suffer from occlusion or blind zones. Therefore, non-contact near-distance sensing is the optimal solution. Unfortunately, existing near-distance sensors based on optical, electric-field, and acoustic signals still cannot satisfy these grasping requirements. Electric-field sensors have difficulties in targets with low dielectric contrast to air. The optical ones lack lateral resolution and are not effective for optically-transparent or highly-reflective targets. Acoustic-based sensors could work on distance ranging and material/structure sensing, but fail on thin-film, porous, or sound-absorbing targets. To address these issues, a new finger-mounted non-contact dual-modal and dual-sensing-mechanism (DMDSM) sensor for near-distance ranging and material/structure differentiation is studied and developed, which is based on two modalities and sensing mechanisms: pulse-echo ultrasound (US) and optoacoustics (OA). In both modalities, the object distance is estimated from the Time-of-Flight (ToF) of the US/OA signal, whose frequency spectra are used to extract the distinctive features of the material/structure. The development of the DMDSM sensor is conducted as follows. First, the prototype of the DMDSM sensor is designed, fabricated, and characterized. Testing is conducted on conventional objects and optically and/or acoustically challenging targets (OACTs) to characterize its performance. Second, to simplify the DMDSM sensor design and operation, a single wideband ultrasound transmitter and receiver is investigated where both US and OA collection can be initiated by a single laser pulse. Third, to expand to areal mapping or imaging, a new self-focused US/OA transceiver and a flat scanning mirror are studied to steer laser and ultrasound beams over the target with customized patterns. At last, optically-transparent focused (OTF) ultrasound transducers are explored, which are helpful to miniaturize the DMDSM sensors while enhancing their performances.
Flexible mid-infrared photonics for chemical sensing
(United States. Patent and Trademark Office, 2020-03-17T00:00:00Z) Lin, Pao Tai; The Texas A&M University System
A flexible waveguide structure including a waveguide on a flexible substrate, both having transparent windows in the mid-infrared range, may serve as a photonic chemical sensor for measuring characteristic absorptions of analytes brought in physical contact with the waveguide. Such a sensor may, in accordance with some embodiments, be formed by an aluminum-nitride waveguide on a borosilicate substrate.
Improving the Performance of Perovskite Solar Cells Fabricated in Ambient Atmosphere
(2021-08-13) Chadaram, Naga Abhilash Abhilash; Wong, Zi Jing; Qian, Xiaofeng; Lin, Pao Tai
The metal halide perovskites have proven their potential in being the active absorption layer for the third-generation perovskite solar cells (PSCs). Their reported power conversion efficiency (PCE) is one of the fastest growths in the last decade, closing in towards the Shockley-Queisser limit and the silicon solar cell’s highest recorded PCE. This was possible by exploiting properties, like tunable band gap, excellent photon absorption, and long carrier diffusion lengths. One of the possible ways to further improve the performance of the PSCs is by fabricating high-quality, defect-free perovskite films and optimizing the PSC’s architecture accordingly. Ambient fabrication (Avg. 45% relative humidity) of PSCs usually causes non-uniform morphology and unequal crystal growth of the perovskite thin film leading to bad performance of the PSC. The motivation for this research is to fabricate high-efficiency metal halide perovskite solar cells with good optoelectronic and photovoltaic properties in complete ambient conditions i.e., without the use of an inert gas environment/glove box. Fabrication in such an environment leads to the formation of larger grains and defects. Hence, optimizing the fabrication process to minimize the defects, results in uniform deposition of perovskite active layer with larger grain size, which will aid in faster carrier transportation. By fine-tuning the growth conditions of every layer in the PSC and optimizing their fabrication variables, one can achieve improved performance from a PSC. Hence, choosing the most effective source materials and deposition conditions that work in ambient conditions for both electron transport layer (ETL) and hole transport layer (HTL) and optimizing the thin films for best extraction and transportation of charge carriers while also blocking the opposite charge carrier is essential. We took measures to improve the quality of the perovskite active layer by using mixed anti-solvent to increase the grain size and depositing a passivation layer on perovskite thin film before the HTL to lower the surface defects. Therefore, a synergistic effect from various individual optimizations done at each layer and interface level was anticipated, which successfully improved the PCE of our PSCs fabricated in ambient conditions from around 7% to above 15%.
Mid-infrared integrated photonics for chemical sensing
(United States. Patent and Trademark Office, 2020-07-28T00:00:00Z) Lin, Pao Tai; Texas A&M University System
A waveguide structure including a mid-infrared-transparent waveguide on a mid-infrared-transparent undercladding may serve as a photonic chemical sensor for measuring characteristic absorptions of analytes brought in physical contact with the waveguide. In some embodiments, a sensor including an amorphous-silicon waveguide on a barium-titanate undercladding can operate at wavelengths ranging from 2.5 .mu.m to about 7 .mu.m; this sensor may be manufactured by epitaxial growth of the undercladding on a substrate, followed by CMOS-compatible creation of the waveguide. Additional embodiments are disclosed.
Nanostructured Photonic Chips for High Throughput Biomolecule Sensing
(2023-03-07) Makela, Megan Hope; Lin, Pao Tai; Cote, Gerard; Kolluru, Pavan; Park, Hangue
Optical biosensors have emerged as primary candidates to realize integrated, self-contained analytical systems capable of replacing or out-performing traditional benchtop set-ups for applications requiring high-throughput or ultra-sensitive biomolecular detection. As such, this work investigated the use of photonic waveguide-based sensing devices for the detection of chemical and biological compounds via fluorescence and Raman scattering modalities. Aluminum nitride (AlN) optical waveguides were fabricated and used to excite Raman scattering of benzene derivative mixtures, from which characteristic peaks and concentrations could be resolved. Low-index optical waveguides were combined with metallic nanoparticle-conjugated molecular reporters for waveguide-assisted, surface-enhanced Raman detection of an immobilized cardiac biomarker assay. Further, the use of a nano-slot silicon nitride (Si3N4) fluidic waveguide to detect a tagged oligonucleotide with a viral DNA sequence was also demonstrated, showing sensitivity enhancement of 9 x over a strip waveguide. A resin mate-rial platform was used for direct-write fabrication of waveguides and micro-ring resonators, where the low index contrast and reduced coupling loss allowed for increased excitation of a fluorescence-labeled biomolecule, resulting in an overall 12 x signal over a titanium dioxide (TiO2) waveguide. The work also examined methods for further improving the performance of photonics-based biosensors. A surface functionalization scheme to immobilize probe molecules for affinity-based sensing with high selectivity was applied, utilizing a self-assembled silane layer and linker molecule to covalently bond biomolecules to the device surface. Nanoporous anodic aluminum oxide (AAO) membranes were employed for further improvement of detection sensitivity, owing to their extensive surface area. Surface-functionalized AAO membranes were demonstrated for detection of fluorophore-labeled DNA and RNA sequence targets, yielding an increase in signal nearly 100 x compared to a non-porous substrate. Moreover, direct fabrication of AAO from thin films to create AAO-clad optical waveguides was presented and used to facilitate antibody and unlabeled DNA detection assays. Further improvement to AAO-waveguide devices through fabrication and a functionalization strategy for orientation-specific protein immobilization is proposed.
Nonlinear Optical Effects in the Picosecond Regime for Chemical Sensing and Polycrystalline Semiconductor Frequency Conversion
(2023-07-11) Marble, Christopher Brian; Yakovlev, Vladislav V; Lin, Pao Tai; Scully, Marlan O; Sokolov, Alexei V
In this work, we employ nonlinear optical spectroscopic techniques using picosecond visible, near-IR, and mid-IR laser pulses to resolve knowledge gaps in light-matter interactions of organic molecules and semiconductors. Nonlinear optics provides an array of different and unique capabilities compared to linear optics including dual-detection of IR-active vibrational modes and Raman-active modes of biomolecules and the generation of broadband IR continuum using high harmonic generation in polycrystalline semiconductors like zinc selenide. Sections 2-4 utilize hyper-Raman scattering to study biomolecules in solution. In Section 2, we outline the design of a hyper-Raman microscope and present early work on dual detection of Raman and hyper-Raman scattered light from biomolecules. In Section 3, the hyper-Raman microscope system was used to explore the hyper-Raman allowed transitions of organic molecules in solution, and polarization resolved spectra of biomolecules was reported. In Section 4, we utilize the sensitivity of hyper-Raman to water librations to study water solvation chemistry in a mixed solution of water with dimethyl sulfoxide. Sections 5-6 study high harmonic generation (HHG) in poly-crystalline Zinc Selenide (poly-ZnSe). Sections 5 and 6 contrast each other by performing the same experiment in different laser excitation regimes. In Section 5/6, the experiment is performed using high power (TW/cm2)/lower power (GW/cm2), broadband/narrowband, femtosecond (100 fs)/picosecond (30 ps), mid-IR laser pulses. In Section 5, we observe efficient frequency conversion via HHG resulting in a broad supercontinuum spanning the near-IR and visible region, a result that has been replicated by other research groups. However, understanding this efficient conversion is complicated by numerous nonlinear effects simultaneously occurring in the material. In Section 6, we approach frequency conversion in poly-ZnSe at lower power at the threshold of HHG generation to study the different nonlinear effects that contribute to broadband continuum generation. We find that random quasi-phase matching is an essential ingredient to the efficient frequency conversion in disordered, polycrystalline semiconductors like poly-ZnSe.
Optical Studies on the Photophysical Properties of Strongly Quantum Confined Lead Bromide Perovskite Nanocrystals
(2023-04-09) Tang, Xueting; Son, Dong; Banerjee, Sarbajit; Sheldon, Matthew T.; Lin, Pao Tai
Recently, lead halide perovskite (LHP) materials have drawn great research interest in the fields of photonics and photovoltaics as sources of photon and charge carriers thanks to their high defect tolerance and carrier mobility. In contrast to traditional semiconductor materials where the band gap is mostly tuned through size, LHP materials showed tunability in the band gap through continuously variable halide components, which eases the synthesis and device fabrication processes. However, recent advances in the synthetic methods of strongly quantum confined LHP nanocrystals (NCs) have largely expanded the research potential of these materials. In addition to altering the band gap, imposing strong quantum confinement to LHP materials also modifies their electronic properties as a result of increased interaction of the electron and hole pair and excitons with other degree of freedom due to increased spatial overlap. For instance, strong quantum confinement is known to modify the fine structures of exciton states as a result of increased exchange energy of electron and hole, inverting the relative ordering of the bright and dark exciton states of LHP NCs as compared to their weakly quantum confined counterparts. In hybrid LHP NCs, the presence of an organic A-site cation, usually methylammonium (MA+) or formamidinium (FA+), introduces in additional degrees of freedom from the rotational and librational motions of the organic cations. In order to explore the role of the organic cations on the exciton transitions, the photoluminescence (PL) spectra and dynamics of strongly quantum confined FAPbBr3 NCs were investigated. These FAPbBr3 NCs showed intense emission from the dark exciton ground state, with significantly shorter dark exciton lifetime in comparison to CsPbBr3 NCs of the same size, suggesting the stronger mixing of bright and dark state. Moreover, the inter-particle electronic coupling in the arrays of strongly quantum confined CsPbBr3 NCs were investigated by means of PL spectra and dynamics as well. The electronic coupling alters the level structure and relaxation dynamics of bright and dark exciton. The results of electronically coupled CsPbBr3 NCs resembles individual NCs of increased sizes, suggesting delocalization of exciton wavefunction beyond borders of NCs in the electronically coupled arrays.
Surface Functionalization for Selective Mid-Infrared On-Chip Sensing
(2022-07-10) Al Husseini, Diana; Sukhishvili, Svetlana A; Coté, Gerard L; Gutierrez-Osuna, Ricardo; Lin, Pao Tai; Qian, Xiaofeng
We report on the development of conformal nanoparticle (NP)-based coatings, with flexible chemical modification, applied to the surface of mid-infrared (MIR) waveguide (WG)-based sensors, to simultaneously achieve sensitivity and selectivity enhancement of gaseous analytes. Traditional organic polymeric coatings are incompatible with MIR waveguide sensing because of the spectral overlap and the limited ability of hosting analyte molecules close to the evanescent field (EF) due to the lack of inherent porosity. On the other hand, commonly designed inorganic 3D porous coatings cannot be seamlessly integrated within the WGs due to the inability to conform to theWG within thin films of controlled thickness. Here, we construct conformal nanocoatings on the WGs that can be deposited at a nanometer-scale-controlled thickness. The coatings have high surface area readily available for adsorption and concentration of the analytes in the vicinity of the EF for improved sensitivity, as well as variable surface chemistry for improved selectivity. The nanocoatings were deposited on the WGs using our newly developed hybrid deposition technique incorporating a controlled substrate withdrawal speed within the layer-by-layer (LbL) method. Two types of LbL systems were explored: NP/NP and polymer/NP. The NP/NP system consisted of spherical ZnO₂ and SiO₂ NPs with diameters of 4.2 nm and 20 nm, respectively. The polymer/NP system was composed of branched polyethylenimine and mesoporous silica NPs of a~150-nm diameter and was calcinated prior to use. We investigated the effect of deposition conditions, such as withdrawal speed and solution pH, on the thickness, porosity and morphology of the coatings. The substrate withdrawal speed was a critical factor, where uniform coatings were only achieved in the convective regime (≤ 0.001 cm/s). In addition to enhanced detection sensitivity, these coatings improved the selectivity of the WGs due to the preferential interaction of polar gas molecules with the polar surfaces of the metal oxide NP-based coatings. Moreover, silane functionalization of such inorganic coatings was successfully achieved to enhance the selectivity of gas molecules with different polarities. Using LbL-coated MIR WGs, we demonstrated selective and reversible sensing of methane, acetone and ethanol using the C-H stretching vibrational bands of these analytes.
The Development of a Multi-Modal Raman and Fluorescence Spectroscopic Platform for Point-of-Care Applications
(2023-04-09) Soliman, Cyril George; Cote, Gerard; Maitland, Kristen; Mabbott, Samuel; Lin, Pao Tai
The development of optical biosensors has enabled sensitive and specific detection of target analytes associated with diseases. Fluorescence is a commonly used optical modality for biosensing applications due to its high efficiency and the availability of labels to tag target analytes. Another sensitive optical modality is its spectroscopy which can enable specific detection of a target analyte based on its chemical composition. The inherently weak Raman scattering signals can be enhanced using metallic nanostructures through surface-enhanced Raman scattering (SERS). Many sensing probes and detection schemes have been developed for fluorescence, SERS, and dual fluorescence and SERS-based techniques. Spectroscopy-based instrumentation is required for Raman signal readout, however, fluorescence-based techniques can be readout through spectroscopy- or intensity-based approaches. The development of compact optical readout platforms has the potential to impact diagnostic and sensing needs at the point of care (POC). POC platforms can be used for chronic disease biomarker detection for applications such as cardiovascular disease (CVD). CVD has a disproportionate burden on low-income communities and POC technologies can aid in providing earlier biomarker detection. In this work, a multi-modal Raman and fluorescence spectroscopic platform was developed for POC applications. The developed spectroscopic platform was miniaturized from a portable, benchtop form factor to a handheld device by utilizing innovative optical designs and grating manufacturing techniques. The portable system utilized separate excitation and collection arms to minimize signal crosstalk and improve detection sensitivity. The Raman arm used a spectroscopy-based detection method, and the fluorescence arm was intensity-based. The first handheld design utilized two separate detection arms, but both were spectroscopy-based methods. The final handheld design utilized a single spectrometer bench to separate both optical signals and measure their intensities using a single detector. A compound grating was designed and manufactured with an industry collaborator, Wasatch Photonics, to enable the separation of the Raman and fluorescence signals onto different regions of interest of the same detector area. Lastly, commercial Raman spectrometers were used to measure the assay response of a paper-fluidic platform for CVD biomarker sensing to determine the potential clinical utility at the POC.

Browsing by Author "Lin, Pao Tai"

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