Ersin Kayahan

Autocorrelation analysis of spectral dependency of surface roughness speckle patterns

When a surface is illuminated with a highly coherent light such as a laser beam, the speckle pattern of bright and dark regions is observed. It depends on the surface parameters and carries important information about the roughness of the surface. Various methods and techniques are employed for the determination of surface roughness parameters from speckle pattern properties. In this paper, an experimental approach for surface roughness evaluation based on the autocorrelation analysis of the spectral properties of speckle patterns caused by milled metal surfaces is reported. The speckles at three 633, 604 and 543 nm wavelengths of He-Ne laser were analyzed. It was found that autocorrelation analysis is very sensitive to small variations in speckle sizes, caused by spectral properties of speckle patterns such as increasing the wavelength lead to increased speckle sizes. The results are in good agreement with the results obtained from the mechanical stylus profilometer for the milled metal surfaces with roughness values Ra; 0.36µm (low roughness) and 1.98µm (high roughness). The technique reported here has a great potential for precise and non-contact optical measurements of rough surfaces.

Aging effect on photoluminescence of p-type porous silicon

Visible photoluminescence (PL) in anodized porous Si (PS) at room temperature has opened the way to realize different types of quantum electronics devices based on silicon technology. Such devices require a strong PL intensity and a controlled shift of the PL peak on the energy scale. Porous silicon is produced by electrochemical etching of either p- or n-type crystalline silicon. Illumination is one of the most complicated parameters in PS formation, because it changes the properties of microporous as well as macroporous layers. It is necessary to illuminate the wafer during the anodization in order to create the holes required by the chemical reaction to form the PS. In this paper we present the results of the effects of illumination level during fabrication on the PL properties of p-type PS and it time degradation dynamics.

Wavelength Depended Speckle Correlation Analyses of Engineered Metal Surfaces

Light source selection using rough surface illumination is crucial when especially high accuracy roughness measurements are required. It is therefore important to establish an extensive relationship between the wavelength of the illuminations, speckle size and roughness. Therefore, in this paper, an experimental approach for surface roughness evaluation based on the autocorrelation analysis of the spectral properties of speckle patterns caused by milled metal surfaces is reported. The speckle patterns obtained by the illumination of three 633, 604 and 543 nm wavelengths of He–Ne laser were also analyzed. It was found that wavelength depended speckle correlation analysis (WDSCA) is very sensitive to small variations in speckle sizes caused by spectral properties of speckle patterns such as increasing the wavelength lead to increased speckle sizes. The results are in good agreement with the results obtained from the mechanical stylus profilometer for the milled metal surfaces with roughness values between Ra; 0.36 and 1.98 µm. The technique reported here has a great potential for precise and non-contact optical measurements of rough surfaces.

The Photoluminescence Quenching of Porous Silicon

In this study, time‐depended photoluminescence (PL) quenching of porous silicon (PS) produced in different solutions by electro‐chemical method under UV light was investigated. A two‐time‐constant exponential function characterizing the quenching of PL intensity was developed and found to be in good agreement with experimental results. Spectra were performed in millisecond intervals since the intensity and wavelength of maximum peak of tile PL spectra were affected by excitation light of PL. It was observed that spectroscopic results of UV and FTIR were coherent and especially Si–O‐Si bonds, Si‐Hx stretch and deformation bonds in the PL quenching played a crucial role.