11 research outputs found
Polarization-insensitive wide-angle resonant acousto-optic phase modulator
Phase modulators are commonly used devices in optics. Free-space phase
modulators are typically constructed from optically anisotropic crystals
exhibiting the Pockels effect. To preserve the light's polarization state as it
propagates through the crystal, it is essential to align the polarization and
angle of incidence of the light with respect to the crystal. In this study, we
demonstrate the feasibility of constructing free-space resonant phase
modulators with a broad acceptance angle and minimal dependence on the
polarization state of light using an acousto-optic approach. These modulators
operate in the megahertz frequency range, require modest power levels, have
aperture sizes exceeding one square centimeter, and feature sub-millimeter
thickness.Comment: 8 pages, 6 figure
Optically isotropic longitudinal piezoelectric resonant photoelastic modulator for wide angle polarization modulation at megahertz frequencies
Polarization modulators have a broad range of applications in optics. The
acceptance angle of a free-space polarization modulator is crucial for many
applications. Polarization modulators that can achieve a wide acceptance angle
are constructed by attaching a piezoelectric transducer to an isotropic
material, and utilize a resonant transverse interaction between light and
acoustic waves. Since their demonstration in the 1960s, the design of these
modulators has essentially remained the same with minor improvements in the
following decades. In this work, we show that a suitable single crystal with
the correct crystal orientation, functioning as both the piezoelectric
transducer and the acousto-optic interaction medium, could be used for
constructing a highly efficient free-space resonant polarization modulator
operating at megahertz frequencies and exhibiting a wide acceptance angle. We
construct the modulator using gallium arsenide, an optically isotropic and
piezoelectric crystal, and demonstrate polarization modulation at 6 MHz with an
input aperture of 1 cm in diameter, acceptance angle reaching ,
and modulation efficiency exceeding 50%. Compared to state-of-the-art resonant
photoelastic modulators, the modulator reported in this work exhibits greater
than 50 fold improvement in modulation frequency for the same input aperture,
while simultaneously reducing the thickness by approximately a factor of 80.
Increasing the modulation frequency of photoelastic modulators from the
kilohertz to the megahertz regime and substantially reducing their thickness
lead to significant performance improvements for various use cases. This
technological advancement also creates opportunities for utilizing these
devices in new applications.Comment: 19 pages, 10 figure
Longitudinal piezoelectric resonant photoelastic modulator for efficient intensity modulation at megahertz frequencies
Intensity modulators are an essential component in optics for controlling
free-space beams. Many applications require the intensity of a free-space beam
to be modulated at a single frequency, including wide-field lock-in detection
for sensitive measurements, mode-locking in lasers, and phase-shift
time-of-flight imaging (LiDAR). Here, we report a new type of single frequency
intensity modulator that we refer to as a longitudinal piezoelectric resonant
photoelastic modulator. The modulator consists of a thin lithium niobate wafer
coated with transparent surface electrodes. One of the fundamental acoustic
modes of the modulator is excited through the surface electrodes, confining an
acoustic standing wave to the electrode region. The modulator is placed between
optical polarizers; light propagating through the modulator and polarizers is
intensity modulated with a wide acceptance angle and record breaking modulation
efficiency in the megahertz frequency regime. As an illustration of the
potential of our approach, we show that the proposed modulator can be
integrated with a standard image sensor to effectively convert it into a
time-of-flight imaging system.Comment: 23 pages, 11 figure
III/V-on-lithium niobate amplifiers and lasers
We demonstrate electrically pumped, heterogeneously integrated lasers on thin-film lithium niobate, featuring electro-optic wavelength tunability. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen
Supplementary document for Polarization-insensitive wide-angle resonant acousto-optic phase modulator - 6913674.pdf
Supplementary Materia
Y-Z cut lithium niobate longitudinal piezoelectric resonant photoelastic modulator
The capability to modulate the intensity of an optical beam has scientific
and practical significance. In this work, we demonstrate Y-Z cut lithium
niobate acousto-optic modulators with record-high modulation efficiency,
requiring only for 100% modulation at 7 MHz. These
modulators use a simple fabrication process; coating the top and bottom
surfaces of a thin lithium niobate wafer with transparent electrodes. The
fundamental shear acoustic mode of the wafer is excited through the transparent
electrodes by applying voltage with frequency corresponding to the resonant
frequency of this mode, confining an acoustic standing wave to the electrode
region. Polarization of light propagating through this region is modulated at
the applied frequency. Polarization modulation is converted to intensity
modulation by placing the modulator between polarizers. To showcase an
important application space for this modulator, we integrate it with a standard
image sensor and demonstrate 4 megapixel time-of-flight imagingComment: 18 pages, 8 figure
1989 Bulgaristan göçünün göçmenler üzerindeki ekonomik etkileri
Ankara : İhsan Doğramacı Bilkent Üniversitesi İktisadi, İdari ve Sosyal Bilimler Fakültesi, Tarih Bölümü, 2014.This work is a student project of the The Department of History, Faculty of Economics, Administrative and Social Sciences, İhsan Doğramacı Bilkent University.by Karabağ, Müzeyyen
Impact of hyperbaric oxygen therapy on irradiated autogenous bone grafts in rats
Amaç: Radikal radyoterapinin kullanımı, yol açtığı doku hasarı nedeniyle kısıtlıdır. Ek hiperbarik oksijen tedavisi potansiyel olarak radyasyonun yarattığı devaskülarizasyon sürecini engelleyebilir ve biyolojik rekonstrüksiyon modellerinin dezavantajlarını ortadan kaldırabilir. Bu çalışmada radyasyonun ve hiperbarik oksijen uygulamasının kemik iyileşmesi üzerine etkileri araştırıldı. Çalışma planı: Yüz yirmi adet Wistar cinsi sıçan rastgele dört gruba ayrıldı. Kontrol grubunda, tibia diafizinden çıkartılan segment tekrar implante edildi. İkinci gruptaki sıçanlara, rezeksiyon ve reimplantasyondan sonra hiperbarik oksijen tedavisi uygulandı. Üçüncü gruba ait diafizer kemik segmentleri tekrar implante edilmeden önce irradiye edildi. Dördüncü grupta ise irradiye segmentler tekrar implante edildikten sonra, deneklere ek olarak hiperbarik oksijen tedavisi uygulandı. Sonuçlar: Hiperbarik oksijen tedavisi konvansiyonel otogreftlerin kemik iyileşmesini altıncı haftanın sonunda anlamlı derecede artırdı. Tek fraksiyonda uygulanan tümörisidal dozda radyasyon, kemik iyileşmesini kronik fazda engelledi. On ikinci haftanın sonunda, histolojik ve radyolojik bulgular, dördüncü grup örneklerinde üçüncü gruba göre anlamlı derecede daha iyi kemik iyileşmesi ortaya koydu. Çıkarımlar: Hiperbarik oksijen tedavisi, radyasyonun kemik iyileşmesi üzerindeki kötü etkilerini engelleyebilir ve habis kemik tümör cerrahisinde rezeksiyonu takiben, tümörlü segmentin irradiye edilip tekrar implante edilmesi ile yapılan biyolojik rekonstrüksiyonlarda yararlı olabilir.Objectives: Limited tissue tolerance precludes the use of radical radiotherapy. Adjuvant hyperbaric oxygen therapy potentially can revert the devascularization process in radiation-induced injuries and eliminate the disadvantages of biologic reconstruction methods. The aim of this experimental study is to evaluate the effects of irradiation and hyperbaric oxygen therapy on bone healing. Methods: One hundred-twenty Wistar rats were randomly allocated into four groups. A tibial diaphyseal segment was resected and reimplanted in one group as controls. Rats in the second group received adjuvant hyperbaric oxygen therapy following resection and reimplantation. In the third group, reimplantation was performed following irradation of bone segments. The fourth group was treated with adjuvant hyperbaric oxygen therapy after reimplantation of an irradiated bone segment. Results: Hyperbaric oxygen therapy significantly increased healing of conventional bone autografts after six weeks. Tumoricidal irradiation administered at a single fraction caused marked impairment in bone healing at the chronic phase. Histologic and radiologic findings after 12 weeks revealed substantial improvement in bone healing in the fourth group in comparison to the third group. Conclusion: Hyperbaric oxygen therapy may have a relevant role in eliminating deleterious effects of irradiation on the biologic potential of bone tissue and may be used as an adjunct for bone segments resected and irradiated to be used in biological reconstruction
Dealing with the gray zones in the management of gastric cancer: The consensus statement of the Istanbul Group
The geographical location and differences in tumor biology significantly change the management of gastric cancer. The prevalence of gastric cancer ranks fifth and sixth among men and women, respectively, in Turkey. The international guidelines from the Eastern and Western countries fail to manage a considerable amount of inconclusive issues in the management of gastric cancer. The uncertainties lead to significant heterogeneities in clinical practice, lack of homogeneous data collection, and subsequently, diverse outcomes