http://hdl.handle.net/20.500.12566/17 2026-04-06T06:02:33Z http://hdl.handle.net/20.500.12566/2379 Development of a flexible piezoelectric biosensor that integrates BaTiO₃–poly(dimethylsiloxane) for posture correction applications Aslan, Menduh Furkan; Özbek, Cem; Yiğit, Gökhan; Tosun, Mehmet; Demirel Topel, Seda The prolonged issue of poor posture due to desk work has led to innovative technologicalremedies. This study shows the development of a flexible piezoelectric biosensor integrating BaTiO3nanoparticles within a Polydimethylsiloxane (PDMS) matrix for practical posture correction. Thebiosensor is capable of real-time posture monitoring and correction by leveraging the piezoelectricproperties of BaTiO3. Comprehensive synthesis and characterization using X-ray diffraction analysis(XRD) and transmission electron microscopy (TEM) validated the ideal particle size and crystallinestructure of the composite. COMSOL Multiphysics simulations showed a peak potential of 0.87 voltsunder mechanical stress, which further confirmed the sensor’s efficiency. Electrical testing revealedthat the sensor with 35 wt.% BaTiO3exhibited a higher output voltage of 0.87 V compared to 0.34 Vfor the sensor with 30 wt.% BaTiO3, emphasizing its exceptional potential for addressing posture-related issues. 2024-01-01T00:00:00Z http://hdl.handle.net/20.500.12566/2324 Pushing the tuning limits of femtosecond Yb-based solid-state lasers to 1 µm: a Yb:YVO4 laser tunable down to 1004 nm Kılınç, Muharrem; Demirbaş, Ümit; Thesinga, Jelto; Kellert, Martin; Yakovlev, Alexey; Kärtner, Franz X.; Pergament, Mikhail We have obtained what we believe to be the shortest fs tuning wavelength (1004 nm) from a Yb-based solid-state laser system. As the working horse, we have chosen Yb:YVO4 due to its blueshifted gain spectrum. While using a single 10 W 952 nm diode for pumping and a semiconductor saturable absorber mirror (SESAM) for mode-locking, we have achieved 266 fs long pulses with up to 1.24 W of output power around 1021 nm. Using an intracavity birefringent filter, the central wavelength of the fs pulses could be tuned smoothly between 1004–1038 nm and 1009–1061 nm while employing the E//a and E//c axis of the material, respectively. By using an additional hard aperture to increase the modulation depth, we have also attained 100 fs level pulses in the 1012.5–1019 nm range, which shows the suitability of the system in seeding cryogenic Yb:YLF-based amplifiers. 2024-01-01T00:00:00Z http://hdl.handle.net/20.500.12566/2313 Fractional thermal load in cryogenically cooled Yb:YLF and Yb:YAG lasers Kılınç, Muharrem; Demirbaş, Ümit; Thesinga, Jelto; Kellert, Martin; Kärtner, Franz X.; Pergament, Mikhail We present a method for the direct measurement of the fractional thermal load (FTL) in cryogenically cooled laser crystals. The experimental methodology involves characterizing the liquid nitrogen evaporation rate in a dewar containing the laser crystals, allowing for the accurate determination of FTL. The FTL is measured to be 1.7 × quantum defect (QD) for Yb:YLF and 1.5 × QD for Yb:YAG under continuous wave lasing conditions. The measured FTL values are then used to calculate the temperature distribution inside the crystals as a function of pump power, and the simulation results are found to be in very good agreement with the in-situ temperature measurements using contactless optical luminescence thermometry. The method and findings presented in this work hold great potential to benefit laser engineers and scientists working with cryogenic lasers to address and overcome temperature-dependent handicaps. 2024-01-01T00:00:00Z http://hdl.handle.net/20.500.12566/2310 Advantages of pulse-train excitation in narrow-band terahertz generation: mitigation of undesired nonlinear effects Demirbaş, Ümit; Rentschler, Christian; Zhang, Zhelin; Pergament, Mikhail; Matlis, Nicholas H.; Kärtner, Franz X. In this work, we have studied the limitations of narrowband multi-cycle (MC) terahertz (THz) generation via optical rectification (OR) in periodically poled lithium niobate (PPLN) crystals. Detailed investigation of the transmitted beam profile, THz conversion efficiency (CE), and parasitic second-harmonic generation (SHG) strength as a function of incident pump beam size showed that Kerr-lensing is a significant bottleneck in the efficiency scaling of MC THz generation. We have also demonstrated that compared to the usage of a single pump pulse, excitation of the PPLN crystal via a pulse train, not only boosts up THz CE and narrows down the bandwidth of the achieved THz beam but also helps to mitigate the effect of undesired nonlinearities, such as Kerr-lensing and parasitic SHG. 2024-01-01T00:00:00Z