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 $\pm30^\circ$, 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

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 $1.5~\text{W}/\text{cm}^2$ 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

The prevalence of microalbuminuria and relevant cardiovascular risk factors in Turkish hypertensive patients.

Objectives: A growing body of data illustrates the importance of microalbuminuria (MAU) as a strong predictor of cardiovascular risk in the hypertensive population. The present study was designed to define the prevalence of MAU and associated cardiovascular risk factors among Turkish hypertensive outpatients. Study design: Representing the Turkish arm of the multinational i-SEARCH study involving 1,750 sites in 26 countries around the world, a total of 1,926 hypertensive patients from different centers were included in this observational and cross-sectional survey study. Patients with reasons for a false-positive MAU test were excluded. The prevalence of MAU was assessed using a dipstick test, and patients were inquired about comorbidities, comedication, and known cardiovascular risk factors. Results: The overall prevalence of MAU was 64.7% and there was no difference between genders. Most of the patients (82.5%) had uncontrolled hypertension, 35.6% had dyslipidemia, and 35.5% had diabetes, predominantly type 2. Almost one-third of the patients (26.4%) had at least one cardiovascular-related comorbidity, with 20.3% having documented coronary artery disease (CAD). Almost all patients (96.8%) had one or more risk factors for cardiovascular disease in addition to hypertension, including family history of myocardial infarction or CAD, diabetes, dyslipidemia, lack of physical exercise, and smoking. A trend towards higher MAU values in the presence of CAD was determined. Conclusion: Microalbuminuria tests should be routinely used as a screening and monitoring tool for the assessment of subsequent cardiovascular morbidity and mortality among hypertensive patients. © 2011 Turkish Society of Cardiology