Laserli periyodik yüzey yapılandırılma ileyüzey artırımlı raman saçılması

In this study, our aim is to fabricate and characterize efficient substrates of surface enhanced Raman spectroscopy (SERS) utilizing the field enhancement due to hot spots made by recently developed method of laser induced periodic surface structuring (LIPSS). LIPSS is a cost-effective technique for rapid processing of almost any materials compared to conventional lithography methods. Coating of a thin silver film on LIPSS applied substrate surface provides to observe the localized surface plasmon effect for SERS measurement with the use of Raman reporter molecules interacting with silver substrate at the plasmon frequency. In order to characterize the optical properties, diffuse and total reflectivity of the substrates will be measured. Among possible expected applications of such prepared substrates are photonic templates for thin film optoelectronic devices with strong field enhancement properties.Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Physics

Variation of the raman frequency of a soft mode with the pressure (20 oc) for the phase transitions in NH4F

Tarı, Özlem (Arel Author)The Raman frequency of a soft mode (238 cm-1) is analyzed as a function of pressure at 20 oC for NH4F using the experimental data from the literature. This analysis is performed for the pressure dependence of the Raman frequency shifts (1??)(????P)T of the soft mode close to the I - III, III - V and V - VI transitions in NH4F. The frequency shifts increase as the pressure increases toward the phase transitions at T = 20 oC (293 K) in this ammonium structure. From the frequency shifts of the soft mode studied, the pressure dependence of the isothermal compressibility is predicted through the mode Grüneisen parameter. Our calculated isothermal compressibility can be compared with the experimental measurements.The Raman frequency of a soft mode (238 cm-1) is analyzed as a function of pressure at 20 oC for NH4F using the experimental data from the literature. This analysis is performed for the pressure dependence of the Raman frequency shifts (1??)(????P)T of the soft mode close to the I - III, III - V and V - VI transitions in NH4F. The frequency shifts increase as the pressure increases toward the phase transitions at T = 20 oC (293 K) in this ammonium structure. From the frequency shifts of the soft mode studied, the pressure dependence of the isothermal compressibility is predicted through the mode Grüneisen parameter. Our calculated isothermal compressibility can be compared with the experimental measurements

Extraction of dielectric and magnetic material properties for a periodic hole array THz filter

With the increase in optical applications in the terahertz frequency range there is a greater need for devices that work at these frequencies. One such device which has applications which range from spectroscopy to imaging is the band pass filter. The frequency selective nature of this component can be used for filtering noise during signal processing or can be even used for reducing radiation background levels for imaging purposes [1, 2]. The simplest form of this filter structure has been shown to be that of a free-standing metal sheet with a hole array. The frequency selective nature of the filter is realized by changing the structural parameters of the hole array with respect to the propagating input THz wave. Due to the sub-millimeter wave nature of the radiation the patterns are easier to fabricate for low frequency terahertz radiation applications (<1THz). Here, by using a high power Yb:doped pulsed nanosecond fiber laser system with exceptional beam quality, aluminum metal surfaces were machined with high precision leading to a high quality band pass filter that was shown to work in the terahertz frequency range [3]. We modeled the THz transmission through the the structure that was produced using FDTD simulation tools and also characterized them using the existing home-built time-domain terahertz spectrometers in our laboratories. Results of FDTD simulations are found to be consistent with transmission coefficient which is obtained from the experiment. In order to understand the efficiency of the composite structure which can be described as a frequency selective surface, the electrical permittivity (ε) and magnetic permeability (μ) is extracted from the transmission and reflection simulations [4]. The significance of these values is discussed with respect to the width and transmission observed for the fabricated and measured filter