Browsing by Author "Serhatlioglu, M."

Now showing 1 - 4 of 4

Open Access
CO2 laser polishing of microfluidic channels fabricated by femtosecond laser assisted carving
(Institute of Physics Publishing, 2016-10) Serhatlioglu, M.; Ortaç, B.; Elbuken, C.; Bıyıklı, Necmi; Solmaz, M. E.
In this study, we investigate the effects of CO2 laser polishing on microscopic structures fabricated by femtosecond laser assisted carving (FLAC). FLAC is the peripheral laser irradiation of 2.5D structures suitable for low repetition rate lasers and is first used to define the microwell structures in fused silica followed by chemical etching. Subsequently, the bottom surface of patterned microwells is irradiated with a pulsed CO2 laser. The surfaces were characterized using an atomic force microscope (AFM) and scanning electron microscope (SEM) in terms of roughness and high quality optical imaging before and after the CO2 laser treatment. The AFM measurements show that the surface roughness improves more than threefold after CO2 laser polishing, which promises good channel quality for applications that require optical imaging. In order to demonstrate the ability of this method to produce low surface roughness systems, we have fabricated a microfluidic channel. The channel is filled with polystyrene bead-laden fluid and imaged with transmission mode microscopy. The high quality optical images prove CO2 laser processing as a practical method to reduce the surface roughness of microfluidic channels fabricated by femtosecond laser irradiation. We further compared the traditional and laser-based glass micromachining approaches, which includes FLAC followed by the CO2 polishing technique.
Open Access
Invisible thin-film patterns with strong infrared emission as an optical security feature
(Wiley-VCH Verlag, 2018) Bakan, G.; Ayas S.; Serhatlioglu, M.; Elbuken, Çağlar; Dana, A.
Spectrally selective thermal emission is in high demand for thermophotovoltaics, radiative cooling, and infrared sensing applications. Spectral control of the emissivity is historically achieved by choosing the material with suitable infrared properties. The recent advancements in nanofabrication techniques that lead to enhanced light-matter interactions enable optical properties like infrared emissivity that are not naturally available. In this study, thermal emitters based on nanometer-thick dielectrics on field-enhancement surfaces as optical security features are proposed. Such a function is achieved by generating patterns by ultrathin dielectrics that are transparent in the visible and exhibit strong infrared absorption in the spectral range of thermal cameras. The invisible patterns are then revealed by thermal imaging. The field-enhancement surfaces enhance the emissivity of the patterns, in turn reduce the minimum temperature to detect the thermal emission down to ≈30 °C from >150 °C to exploit ubiquitous heat sources like the human body. The study provides a framework for the use of thermal emitters as optical security features and demonstrates applications on rigid and flexible substrates.
Open Access
Perfectly absorbing ultra thin interference coatings for hydrogen sensing
(OSA - The Optical Society, 2016) Serhatlioglu, M.; Ayas S.; Bıyıklı, Necmi; Dana, A.; Solmaz, M. E.
Here we numerically demonstrate a straightforward method for optical detection of hydrogen gas by means of absorption reduction and colorimetric indication. A perfectly absorbing metal-insulator-metal (MIM) thin film interference structure is constructed using a silver metal back reflector, silicon dioxide insulator, and palladium as the upper metal layer and hydrogen catalyst. The thickness of silicon dioxide allows the maximizing of the electric field intensity at the Air/SiO2 interface at the quarter wavelengths and enabling perfect absorption with the help of highly absorptive palladium thin film (∼7 nm). While the exposure of the MIM structure to H2 moderately increases reflection, the relative intensity contrast due to formation of metal hydride is extensive. By modifying the insulator film thickness and hence the spectral absorption, the color is tuned and eye-visible results are obtained.
Open Access
Sheathless microflow cytometry using viscoelastic fluids
(Nature Publishing Group, 2017) Asghari, M.; Serhatlioglu, M.; Ortaç, B.; Solmaz, M. E.; Elbuken, C.
Microflow cytometry is a powerful technique for characterization of particles suspended in a solution. In this work, we present a microflow cytometer based on viscoelastic focusing. 3D single-line focusing of microparticles was achieved in a straight capillary using viscoelastic focusing which alleviated the need for sheath flow or any other actuation mechanism. Optical detection was performed by fiber coupled light source and photodetectors. Using this system, we present the detection of microparticles suspended in three different viscoelastic solutions. The rheological properties of the solutions were measured and used to assess the focusing performance both analytically and numerically. The results were verified experimentally, and it has been shown that polyethlyene oxide (PEO) and hyaluronic acid (HA) based sheathless microflow cytometer demonstrates similar performance to state-of-the art flow cytometers. The sheathless microflow cytometer was shown to present 780 particles/s throughput and 5.8% CV for the forward scatter signal for HA-based focusing. The presented system is composed of a single capillary to accommodate the fluid and optical fibers to couple the light to the fluid of interest. Thanks to its simplicity, the system has the potential to widen the applicability of microflow cytometers.