• Journal of Microbiology and Biotechnology
• /
• v.26 no.7
• /
• pp.1285-1289
• /
• 2016

A split-column photobioreactor (SC-PBR), consisting of two bubble columns with different sizes, was developed to enhance the photon utilization efficiency in an astaxanthin production process from Haematococcus lacustris. Among the two columns, only the smaller column of SC-PBR was illuminated. Astaxanthin productivities and photon efficiencies of the SC-PBRs were compared with a standard bubble-column PBR (BC-PBR). Astaxanthin productivity of SC-PBR was improved by 28%, and the photon utilization efficiencies were 28-366% higher than the original BC-PBR. The results clearly show that the effective light regime of SC-PBR could enhance the production of astaxanthin.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.29 no.7 s.238
• /
• pp.998-1004
• /
• 2005

A nano-stereolithography (NSL) process has been developed for fabrication of 3D shell structures which can be applied to various nano/micro-fluidic devices. By the process, a complicated 3D shell structure on a scale of several microns can be fabricated using lamination of layers with a resolution of 150 nm in size, so it does not require the use of my sacrificial layer or any supporting structure. A layer was fabricated by means of solidifying liquid-state monomers using two-photon absorption (TPA) induced using a femtosecond laser processing. When the polymerization process is finished, unsolidified liquid state resins can be removed easily by dropping several droplets of ethanol fur developing the fabricated structure. Through this work, some 3D shell structures, which can be applied to various applications such as nano/micro-fluidic devices and MEMS system, were fabricated using the developed process.

• ETRI Journal
• /
• v.24 no.3
• /
• pp.221-225
• /
• 2002

We performed nonlinear transmission measurements and quantum-chemical calculations on dithienothiophene(DTT)-based molecules to gain insight into the effect of acceptor and donor groups on two-photon absorption(TPA) properties. The TPA intensity showed dispersion characteristics of the single-photon absorption spectrum. When the molecules included an asymmetric donor-acceptor pair, the single- and two-photon absorption maximum wavelengths were red-shifted more than when the molecules had a symmetric donor-donor structure. We interpreted this result as indicating that the $S_2$ state plays the dominating role in the absorption process of molecules with a symmetric structure. The experimental TPA ${\delta}$ values at the absorption peak wavelength showed a dependence on the structural variations. We found the self-consistent force-field theory and Hartree-Fock Hamiltonian with single configuration interaction formalism to be valid for evaluating TPA ${\delta}$. Although the quantum-chemical calculations slightly underestimated the experimental ${\delta}$ values obtained from nonlinear trans -mission measurements, they reasonably predicted the dependence of the ${\delta}$ value on the structural variations. We confirmed the role of molecular symmetry by observing that donor-donor substituted structure gave the highest experimental and theoretical TPA ${\delta}$ values and that the donor-acceptor substituted structure showed a greater red-shift in the TPA absorption maximum wavelength. Overall, the theoretical ${\delta}$ values of DTT-based molecules were in the order of $10^{-46}\;cm^4{\cdot}s{\cdot}photon^{-1}$ and are higher than that of AF-50 by nearly two orders of magnitude.

• International Journal of Precision Engineering and Manufacturing
• /
• v.8 no.4
• /
• pp.63-69
• /
• 2007

The two-photon stereolithography (TPS) process is a promising technique for the fabrication of real three-dimensional (3D) nano/micro-structures via application of a femto-second laser, In TPS, when a near-infrared ultrashort-pulsed laser is closely focused onto a confined volume of photocurable resin, only the local area at the center of the focus is cured. Therefore, real 3D microstructures with resolution under the diffraction limit can be fabricated through a layer-by-layer accumulative technique, This process provides opportunities to develop neo-conceptive nano/micro devices in IT/BT industries, However, a number of issues, including development of effective fabrication methods, highly sensitive and functional materials, and neo-conceptive devices using TPS, must be addressed for the realization of industrial application of TPS. In this review article, we discuss our efforts related to TPS: effective fabrication methods, diverse two-photon curable materials for high functional devices, and applications.

• Journal of the Korean Society for Precision Engineering
• /
• v.33 no.4
• /
• pp.265-270
• /
• 2016

Recently, many studies have been conducted on the nano-scale fabrication technology using twophoton- absorbed polymerization induced by a femtosecond laser. The nano-stereolithography process has many advantages as a technique for direct fabrication of true three-dimensional shapes in the range over several microns with sub-100 nm resolution, which might be difficult to obtain by using general nano/microscale fabrication technologies. Therefore, two-photon induced nano-stereolithography has been recently recognized as a promising candidate technology to fabricate arbitrary 3D structures with sub-100 nm resolution. Many research works for fabricating novel 3D nano/micro devices using the two-photon nano-stereolithography process, which can be utilized in the NT/BT/IT fields, are rapidly advancing.

• Current Optics and Photonics
• /
• v.6 no.4
• /
• pp.381-391
• /
• 2022

Two-photon-polymerization additive-manufacturing systems feature high resolution and precision. However, there are few reports on specific methods and possible problems concerning the use of small lasers to independently build such platforms. In this paper, a femtosecond-laser two-photon-polymerization additive-manufacturing system containing an optical unit, control unit, monitoring unit, and testing unit is built using a miniature femtosecond laser, with a detailed building process and corresponding control software that is developed independently. This system has integrated functions of light-spot detection, interface searching, micro-/nanomanufacturing, and performance testing. In addition, possible problems in the processes of platform establishment, resin preparation, and actual polymerization for two-photon-polymerization additive manufacturing are explained specifically, and the causes of these problems analyzed. Moreover, the impacts of different power levels and scanning speeds on the degree of polymerization are compared, and the influence of the magnification of the object lens on the linewidth is analyzed in detail. A qualitative analysis model is established, and the concepts of the threshold broadening and focus narrowing effects are proposed, with their influences and cooperative relation discussed. Besides, a linear structure with micrometer accuracy is manufactured at the millimeter scale.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.2
• /
• pp.277-280
• /
• 2002

Mass-analyzed threshold ionization (MATI) spectra of 2-hydroxypyridines existing as lactims (2-pyridinol) in a molecular beam are obtained via (1+1') two-photon process to give accurate ionization energies of 8.9344${\pm}$0.0005 and 8.9284${\pm}$0.0005 eV for 2-pyridinol (2Py-OH) and its deuterated analogue (2Py-OD), respectively. Resonantly-enhanced two-photon ionization spectra of these compounds are also presented to give vibrational structures of their $S_1$ states. Vibrational frequencies of 2Py-OH and 2Py-OD in ionic ground states are accurately determined from MATI spectra taken via various $S_1$ intermediate states, and associated vibrational modes are assigned with the aid of ab initio calculations.

• Journal of Astronomy and Space Sciences
• /
• v.38 no.1
• /
• pp.55-63
• /
• 2021

The universe is well known to be consists of dark energy, dark matter and the standard model (SM) particles. The dark matter dominates the density of matter in the universe. The dark matter is thought to be linked with dark photon which are hypothetical hidden sector particles similar to photons in electromagnetism but potentially proposed as force carriers. Due to the extremely small cross-section of dark matter, a large amount of data is needed to be processed. Therefore, we need to optimize the central processing unit (CPU) time. In this work, using MadGraph5 as a simulation tool kit, we examined the CPU time, and cross-section of dark matter at the electron-positron collider considering three parameters including the center of mass energy, dark photon mass, and coupling constant. The signal process pertained to a dark photon, which couples only to heavy leptons. We only dealt with the case of dark photon decaying into two muons. We used the simplified model which covers dark matter particles and dark photon particles as well as the SM particles. To compare the CPU time of simulation, one or more cores of the KISTI-5 supercomputer of Nurion Knights Landing and Skylake and a local Linux machine were used. Our results can help optimize high-energy physics software through high-performance computing and enable the users to incorporate parallel processing.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.7
• /
• pp.999-1005
• /
• 2004

A new stamp fabrication technique for the soft lithography has been developed in the range of several microns by means of a nano-replication printing (nRP) process. In the nRP process, a figure or a pattern can be replicated directly from a two-tone bitmap figure with nano-scale details. A photopolymerizable resin was polymerized by the two-photon absorption which was induced by a femtosecond laser. After the polymerization of master patterns, a gold metal layer (about 30 ㎚ thickness) was deposited on the fabricated master patterns for the purpose of preventing a join between the patterns and the PDMS, then the master patterns were transferred in order to fabricate a stamp by using the PDMS (poly-dimethylsiloxane). In the transferring process, a few of gold particles, which were isolated from the master patterns, remained on the PDMS stamp. A gold selective etchant, the potassium iodine (KI) was employed to remove the needless gold particles without any damage to the PDMS stamp. Through this work, the effectiveness of the nRP process with the PDMS molding was evaluated to make the PDMS stamp with the resolution of around 200 ㎚.

• Polymer(Korea)
• /
• v.29 no.4
• /
• pp.418-421
• /
• 2005

Three-dimensional (3D) microfabrication process using two-photon polymerization (TPP) is developed to fabricate the curved microstructures in a layer, which can be applied potentially to optical MEMS, nano/micro-devices, etc. A 3D curved structure can be expressed using the same height-contours that are defined by symbolic colors which consist of 14 colors. Then, the designed bitmap figure is transformed into a multi-exposure voxel matrix (MVM). In this work a multi-exposure voxel matrix scanning method is used to generate various heights of voxels according to each laser exposure time that is assigned to the symbolic colors. An objective lens with a numerical aperture of 1.25 is employed to enlarge the variation of a voxel height in the range of 1.2 to 6.4 um which can be controlled easily using the various exposure time. Though this work some 3D curved micro-shapes are fabricated directly to demonstrate the usefulness of the process without a laminating process that is generally required in a micro-stereolithography process.