Browsing by Subject "Optical imaging"
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Item Open Access Computer-generated holograms embedded in bulk silicon with nonlinear laser lithography(IEEE, 2016) Turnalı, Ahmet; Tokel, Onur; Makey, Ghaith; Pavlov, Ihor; İlday, Fatih ÖmerRecently, we have showed a direct laser writing method to form subsurface structures inside silicon by exploiting nonlinear interactions. Here, we demonstrate utilization of this phenomenon to create computer-generated holograms buried in silicon.Item Open Access Cumulant-based parametric multichannel FIR system identification methods(Elsevier, 1994) Özgen, M. T.; Alshebeili, S. A.; Çetin, A. Enis; Venetsanopoulos, A. N.In this paper, “least squares” and recursive methods for simultaneous identification of four nonminimum phase linear, time-invariant FIR systems are presented. The methods utilize the second- and fourth-order cumulants of outputs of the four FIR systems of which the common input is an independent, identically distributed (i.i.d.) non-Gaussian process. The new methods can be extended to the general problem of simultaneous identification of three or more FIR systems by choosing the order of the utilized cumulants to be equal to the number of systems. To illustrate the effectiveness of our methods, two simulation examples are included.Item Open Access Harmonic cantilevers for nanomechanical sensing of elastic properties(IEEE, 2003-06) Şahin, O.; Yaralıoğlu, G.; Grow, R.; Zappe, S. F.; Atalar, Abdullah; Quate, C.; Solgaard, O.We present a micromachined scanning probe cantilever, in which a specific higher order flexural mode is designed to be resonant at an exact integer multiple of the fundamental resonance frequency. We have demonstrated that such cantilevers enable sensing of nonlinear mechanical interactions between the atomically sharp tip at the free end of the cantilever and a surface with unknown mechanical properties in tapping-mode atomic force microscopy.Item Open Access Hızlı seyrekleştirici dönüşüm öğrenme ile görüntü ters evrişimi(IEEE, 2018-05) Akyön, Fatih Çağatay; Kamacı, U.; Öktem, F. S.Görüntü ters evrişimi görüntülemede sık karşılaşılan ters problemlerden biridir. Doğal görüntüler bir dönüşüm uzayında seyrek olarak ifade edilebildikleri için seyreklik önsellerinin bu problemleri etkili bir şekilde düzenlileştirebildikleri ve yüksek kaliteli yeniden oluşturmayı mümkün kıldıkları bilinmektedir. Bu çalışmada, görüntü ters evrişimi için dönüşüm öğrenmeye dayalı adaptif bir seyrek görüntü geri kazanım yaklaşımı geliştirilmektedir. Bu yaklaşımda adaptif olarak yama tabanlı bir seyrekleştirici dönüşüm öğrenilir ve eş zamanlı olarak gürültülü, bulanık ölçümlerden görüntü geri kazanılır. Ortaya çıkan optimizasyon problemi kapalı formda ifade edilebilen ve hızlı bir şekilde hesaplanabilen adımlar içeren almaşık enküçültme (alternating minimization) algoritması kullanılarak çözülmektedir. Geliştirilen algoritmanın performansı, farklı optik bulanıklıkları ve gürültü seviyeleri için incelenmektedir. Sonuçlar, geliştirilen yöntemin toplam değişim (total variation) temelli yaklaşımla karşılaştırıldığında, görüntü geriçatım kalitesini arttırdığını, aynı zamanda da hızlı olduğunu göstermektedir.Item Open Access Object detection using optical and LiDAR data fusion(IEEE, 2016-07) Taşar, Onur; Aksoy, SelimFusion of aerial optical and LiDAR data has been a popular problem in remote sensing as they carry complementary information for object detection. We describe a stratified method that involves separately thresholding the normalized digital surface model derived from LiDAR data and the normalized difference vegetation index derived from spectral bands to obtain candidate image parts that contain different object classes, and incorporates spectral and height data with spatial information in a graph cut framework to segment the rest of the image where such separation is not possible. Experiments using a benchmark data set show that the performance of the proposed method that uses small amount of supervision is compatible with the ones in the literature. © 2016 IEEE.Item Open Access Optical waveguides written deep inside silicon by femtosecond laser(OSA, 2017) Pavlov, Ihor; Tokel, Onur; Pavlova, S.; Kadan, V.; Makey, Ghaith; Turnalı, Ahmet; Çolakoğlu, T.; Yavuz, O.; İlday, Fatih ÖmerSummary form only given. Photonic devices that can guide, transfer or modulate light are highly desired in electronics and integrated silicon photonics. Through the nonlinear processes taking place during ultrafast laser-material interaction, laser light can impart permanent refractive index change in the bulk of materials, and thus enables the fabrication of different optical elements inside the material. However, due to strong multi-photon absorption of Si resulting delocalization of the light by free carriers induced plasma defocusing, the subsurface Si modification with femtosecond laser was not realized so far [1, 2]. Here, we demonstrate optical waveguides written deep inside silicon with a 1.5-μm high repetition rate femtosecond laser. Due to pulse-to-pulse heat accumulation for high repetition rate laser, additional thermal lensing prevents delocalization of the light around focal point, allowing the modification. The laser with 2-μJ pulse energy, 350-fs pulse width, operating at 250 kHz focused in Si produces permanent modifications. The position of the focal point inside of the sample is accurately controlled with pumpprobe imaging during processing. Optical waveguides of ~20-μm diameter, and up to 5.5-mm elongation are fabricated by translating the beam focal position along the optical axis. The waveguides are characterized with a 1.5-μm continuous-wave laser, through optical shadow-graphy (Fig. 1 a-b, e) and direct light coupling (Fig.1 c-d, f). The measured refractive index change obtained by quantitative shadow-graphy is ~6×10 -4 . The numerical aperture of the waveguide measured from decoupled light is 0.05.