Recently, there has been much interest in the capability of low cost glow discharge detectors (GDDs) for detection of terahertz radiation. To utilize them in applications such as terahertz imaging these studies have typically focused on the response of the GDD at specific frequencies. To better understand the spectral behavior of glow discharges, we examine the interaction mechanism of GDDs with terahertz radiation using terahertz time domain spectroscopy in a broader range of frequencies between 0.05 and 0.5 THz. Our results show that in addition to terahertz-induced oscillations in the plasma charge density, the structure of the GDD itself plays an important role in the detection mechanism. We observe that by increasing the bias voltage on the gap, not only can we greatly reduce the transmission at a specific frequency, but we can also tune it as well, suggesting that these devices can be used as hybrid plasma filters.

The laser crystallization (LC) of amorphous silicon thin films into polycrystalline silicon (pc-Si) thin films on glass substrates is an active field of research in the fabrication of Si-based thin film transistors and thin film solar cells. Efforts have been, in particular, focused on the improvement of LC technique. Adhesion promoters of the crystallized Si thin films at the glass interface play a crucial role in the stability and device performance of fabricated structures. The crystalline Si thin films are required to be produced free of contamination risks arising from impurity diffusion from the glass substrate. Moreover, it is preferable to fabricate pc-Si thin films at temperatures as close as possible to the ambient temperature for an effective cost reduction. In this work, we demonstrate the successful use of a commercially available nanosecond pulsed laser marker at 1064 nm wavelength for Si crystallization at ambient conditions compared to the common method of pre-elevated substrate temperatures used in continuous wave laser irradiation technique. As a result, our technique results in a better energy balance than that in previous works. The second main purpose of this study is to enhance the crystallinity of Si thin films and to determine the best choice of an intermediate dielectric layer (IDL) comparatively among four thin buffer layers, namely, SiN_x, SiO₂, ZnO, and TiO₂, for the sake of obtaining improved adhesion and larger crystalline domains as compared to that on a direct Si–glass interface. The crystalline qualities of samples containing IDLs of SiN_x, SiO₂, ZnO, and TiO₂ were compared via Raman spectroscopy analysis and electron backscatter diffraction method against the direct Si–glass interface reference. The analyses quantitatively showed that both the crystallinity and the domain sizes can be increased via IDLs.

Interest in laser crystallization (LC) of silicon (Si) thin films has been on the rise in fabrication of polycrystalline silicon (pc-Si) based thin/ultrathin photovoltaic solar cells and Si based thin film transistors (TFT). Laser based fabrication of device quality pc-Si thin films at room temperature is expected to be a key enabling technology because of its low energy, material and process time budget. Fabrication of high-quality pc-Si thin films without pre-/post-treatment at large is a disruptive technology which has the potential to revolutionize the Si thin film industry. We hereby describe in detail a multi-wavelength laser processing platform specially developed for crystallization of amorphous silicon (a-Si) thin films into pc-Si thin films. The platform has three main stages. The first stage consists of a nanosecond pulsed ytterbium (Yt³⁺) doped fibre-laser with a master oscillator power amplifier architecture, operating at a wavelength of 1064 nm with an adjustable repetition rate between 80 kHz–300 kHz. The output beam has a maximum power of 18 W with a pulse energy of 90 µJ. The pulse durations can be set to values between 15 ns–40 ns. The second stage has free-space optical elements for second harmonic generation (SHG) which produces an emission at a wavelength of 532 nm. Conversion efficiency of the SHG is 25% with an output pulse energy of 20 µJ. The platform provides two wavelengths at either 1064 nm or 532 nm in crystallization of a-Si films for different crystallization regimes. The last stage of the platform has a sample processing assembly with a line-focus, which has an x-y motorized stage on a vibration isolated table. Speed of the motorized stage can be set between 1 mm/s–100 mm/s. Stage speed and repetition rate adjustments help to adjust overlap of successive pulses between 97.22–99.99%. Our platform has variety of tune parameters that make it a uniquely flexible system for delicate Si thin film crystallization. A large selection of operational parameter combinations, the wavelength selection and simultaneous x-y scanning capability allow users to crystallize Si films on various substrates optimally. The operation wavelength choice can be done by considering optical absorption and thickness of a-Si films on different types of substrates. Hence, delivering precise amount of absorbed energy in the line-focus irradiation is useful in increasing the average size of crystalline domains; moreover, nucleation of crystallites can be initiated either from the top or bottom interface of the film. Continuous and simultaneous motion of the stage in two dimensions allows to process arbitrary continuous pc-Si geometries in a-Si film. In summary, our multi-wavelength laser processing platform offers all-in-one LC utility for intricate LC-Si processing.

Son yıllarda anti-bakteriyel direnç olgusu, bakterilerin neden olduğu hastalıklarla mücadelede daha fazla sorun haline gelmiştir. Biz bu çalışmayla, açık yara ve yanıkların fırsatçı patojeni olan Pseudomonas aeruginosayı daha etkili bir yöntemle inaktive etmeyi ve fotodinamik inaktivasyon(PDI) gelişimine katkıda bulunmayı hedefledik. Pseudomonas aeruginosa bakterisini, vitamin B kompleksi ve lazer ile inaktive olduğunu spektrofotometrik ölçümler ve antimikrobiyal madde etkinliği analiz yöntemleriyle gösterdik. Ayrıca PDI'nin bakteri üremesi üzerindeki etkisi hem kalitatif hem de kantitatif olarak değerlendirilmiştir. Escherichia coli ve Pseudomonas aeruginosa suşları karşılaştırılarak ölüm oranları belirlendi. Koloni oluşturma birimi oranlarında Escherichia coli bakteri suşlarının karanlık ve ışık deneyinde vitamin B kompleksinin 0,25 mg/mL ve 0,125 mg/mL konsantrasyonlarında % 20’lik bir ölüm oranı görülmüştür. Pseudomonas aeruginosa bakteri suşlarının karanlık deneyinde vitamin B kompleksinin 0,5 mg/mL ve 0,125 mg/mL konsantrasyonlarında çok az bir ölüm oranı görülürken lazer maruziyet sonrası ölüm oranları sırasıyla % 60 ve % 50 çıktığı görülmüştür. Bu ölüm oranlarını doğrulama amaçlı akış sitometresi canlılık deneyleri yapılmış ve çıkan sonuçlar birbiriyle paralellik göstermiştir. Bu çalışmadan elde edilen veriler ışığında; kırmızı lazer diyotun, vitamin B kompleksi ile birlikte Pseudomonas aeruginosa bakterisinin inaktivasyonu için uygun bir aday olduğunu öngörmekteyiz. Yaptığımız bu çalışma, bakteriyel enfeksiyonların tedavisi için hastane, tıp ve mikrobiyoloji alanlarında yapılacak alternatif tedavi yöntemlerine ışık tutacaktır.