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Publication Metadata only 1200 nm pumped Tm3+:Lu2O3 ceramic lasers(Optical Soc Amer, 2018) Özharar, Sarper; N/A; Department of Physics; Toker, Işınsu Baylam; Sennaroğlu, Alphan; PhD Student; Faculty Member; Department of Physics; N/A; College of Sciences; N/A; 23851We report on an experimental demonstration of a 1200-nm pumped Tm3+:Lu2O3 ceramic laser. By using a gain-switched, tunable Cr4+:forsterite laser, the excitation spectrum was measured, with optimum pumping bands centered near 1198 nm, 1204 nm, and 1211 nm. The highest slope efficiency of 21.5% was obtained at the pump wavelength of 1204 nm. Comparative energy efficiency measurements performed near 1200-nm and 800-nm pumping further showed that nearly 40% improvement was obtained in slope efficiency measured with respect to the incident pump energy for 1200-nm pumping. A transition was further observed from single-wavelength operation at 2066 nm to dual-wavelength operation near 2066 nm and 1967 nm for absorbed pump energies above 50 mu J. In this regime, two consecutive output pulses were observed in the time domain. The shortest temporal duration of the first pulse was 1.1 mu s at the incident pulse energy of 105 mu J. The duration and build-up time of the second pulse remained around 5.9 mu s and 18.5 mu s. We believe that the improved energy efficiency demonstrated for the 1.5% Tm3+:Lu2O3 ceramic with 1200-nm pumping can be used as an alternative scheme for the excitation of Tm3+:Lu2O3 ceramic lasers.Publication Metadata only 2.3-μm Tm3+: YLF laser passively Q-switched with a Cr2+: ZnSe saturable absorber(Optical Soc Amer, 2017) N/A; N/A; Canbaz, Ferda; Yorulmaz, İsmail; Sennaroğlu, Alphan; PhD Student; PhD Student; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 23851We report, what is to our knowledge, the first passively Q-switched operation of a 2.3-mu m Tm3+ : YLF laser by using a Cr2+ : ZnSe saturable absorber. In the experiments, a tunable Ti3+ : sapphire laser was used to end pump the Tm3+ : YLF gain medium inside an x cavity. A Cr2+ : ZnSe saturable absorber was also included in the cavity to initiate passive Q switching. At all pump power levels above lasing threshold, passively Q-switched operation of the Tm3+ : YLF laser could be obtained at 2309 nm with pulse durations and repetition frequencies in the ranges of 1.21.4 mu s and 0.3-2.1 kHz, respectively. Analysis of power dependent repetition rate data further gave an estimated value of 3.1% for the round-trip saturable loss of the Cr2+ : ZnSe saturable absorber.Publication Metadata only 21 fs Cr:LiSAF laser mode locked with a single-walled carbon nanotube saturable absorber(Optical Soc Amer, 2019) Bae, Ji Eun; Rotermund, Fabian; Demirbaş, Ümit; N/A; N/A; N/A; Department of Physics; Tanısalı, Gökhan; Toker, Işınsu Baylam; Taşçı, Mısra; Sennaroğlu, Alphan; PhD Student; PhD Student; Undergraduate Student; Faculty Member; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; School of Medicine; College of Sciences; N/A; N/A; N/A; 23851We report the shortest femtosecond pulses directly generated from a solid-state laser that is mode locked by using a single-walled carbon nanotube saturable absorber (SWCNT-SA). In the experiments, we used a 660 nm diode-pumped, low-threshold extended-cavity Cr:LiSAF laser operating around 850 nm with a repetition rate of 47.9 MHz. The SWCNT-SA mode-locked Cr:LiSAF laser produced 21 fs pulses with a time-bandwidth product of 0.56 by using only 210 mW of pump power. Pump-probe spectroscopy measurements showed that the SWCNT-SA exhibited saturable absorption with slow and fast decay times of 2.7 ps and 0.4 ps. The single-pass modulation depth and saturation fluence of the SWCNT-SA were further determined as 0.3% and 45 mu J/cm(2) at the pump wavelength of 850 nm.Publication Metadata only 5-nj Femtosecond Ti3+:sapphire laser pumped with a single 1 W green diode(Iop Publishing Ltd, 2018) N/A; N/A; Department of Physics; Department of Physics; Muti, Abdullah; Kocabaş, Aşkın; Sennaroğlu, Alphan; PhD Student; Faculty Member; Faculty Member; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 227753; 23851We report a Kerr-lens mode-locked, extended-cavity femtosecond Ti3+:sapphire laser directly pumped at 520 nm with a 1 W AlInGaN green diode. To obtain energy scaling, the short x-cavity was extended with a q-preserving multi-pass cavity to reduce the pulse repetition rate to 5.78 MHz. With 880 mW of incident pump power, we obtained as high as 90 mW of continuous-wave output power from the short cavity by using a 3% output coupler. In the Kerr-lens mode-locked regime, the extended cavity produced nearly transform-limited 95 fs pulses at 776 nm. The resulting energy and peak power of the pulses were 5.1 nJ and 53 kW, respectively. To our knowledge, this represents the highest pulse energy directly obtained to date from a mode-locked, single-diode-pumped Ti3+:sapphire laser.Publication Metadata only 70 femtosecond Kerr-lens mode-locked multipass-cavity Alexandrite laser(Optical Soc Amer, 2018) Demirbaş, Umit; N/A; N/A; N/A; Department of Physics; Department of Physics; Cihan, Can; Muti, Abdullah; Toker, Işınsu Baylam; Kocabaş, Aşkın; Sennaroğlu, Alphan; PhD Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; 227753; 23851We report, to the best of our knowledge, the shortest femto-second pulses generated from a Kerr-lens mode-locked (KLM) Alexandrite laser operating near 750 nm. The Alexandrite gain medium was pumped with a continuous-wave (cw), 532 nm laser, and the performance of both the short and extended resonators was investigated. The use of an extended cavity eliminated the multi-wavelength spectral instabilities observed during the cw operation of the short cavity. Furthermore, since the repetition rate of the Alexandrite laser was reduced from 107 to 5.6 MHz, the resulting increase in the intracavity pulse energy provided enhanced Kerr nonlinearity and eliminated the Q-switching instabilities during mode- locked operation. The KLMMPC Alexandrite laser produced nearly transform-limited, 70 fs pulses at a pulse repetition rate of 5.6MHz with only 1 W of pump power. The time-bandwidth product was further measured to be 0.331. (C) 2018 Optical Society of AmericaPublication Metadata only A 35--μm pitch IR thermo-mechanical MEMS sensor with AC-coupled optical readout(IEEE-Inst Electrical Electronics Engineers Inc, 2015) Ferhanoğlu, Onur; Torun, Hamdi; N/A; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Adiyan, Ulaş; Çivitçi, Fehmi; Ürey, Hakan; PhD Student; Researcher; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; 194282; 8579A thermo-mechanical MEMS detector with 35-mu m pixel pitch is designed, fabricated, and characterized. This fabricated design has one of the smallest pixel sizes among the IR thermo-mechanical MEMS sensors in the literature. The working principle of the MEMS detector is based on the bimaterial effect that creates a deflection when exposed to IR radiation in the 812-mu m waveband. The nanometer level out of plane mechanical motion is observed in response to IR heating of the pixel, which is detected by a diffraction grating-based optical readout. Performance of MEMS sensor arrays with optical readout have been limited by a large DC bias that accompanies a small AC signal. We developed a novel optical setup to reduce the DC term and the related noise using an AC-coupled detection scheme. Detailed noise characterization of the pixel and the readout system is reported in this paper. The noise equivalent temperature difference of our detector is measured as 216 mK using f/0.86 lens with the AC-coupled optical readout. Finally, we obtained a thermal image using a single MEMS pixel combined with a scanning configuration. Despite the reduced pixel size, the measured noise levels are comparable to the state-of-the-art thermo-mechanical IR sensors.Publication Metadata only A magnetically actuated resonant mass sensor with integrated optical readout(Ieee-Inst Electrical Electronics Engineers Inc, 2008) N/A; N/A; Department of Electrical and Electronics Engineering; N/A; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Department of Mechanical Engineering; Öztürk, Alibey; Ocaklı, Hüseyin İlker; Özber, Natali; Ürey, Hakan; Kavaklı, İbrahim Halil; Alaca, Burhanettin Erdem; Master Student; Researcher; Master Student; Faculty Member; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; 8579; 40319; 115108Nickel cantilevers with integrated diffraction gratings are used as resonant mass sensors with a resolution of 500 femtograms. Their applicability to biosensing is demonstrated with human opioid receptors. The device is fabricated through a single-mask lithographic process. The microoptical readout provides a simple measurement platform with one external photodiode. Thanks to its ac operation principle, the device is immune to environmental noise and entails a high tolerance to fabrication defects. Obtained signal-to-noise ratio is comparable to that of a high-end Doppler vibrometer. The device with these aspects for systems integration and microarray technology is a candidate for low-cost portable sensors.Publication Metadata only A prism-based optical readout method for MEMS bimaterial infrared sensors(IEEE-Inst Electrical Electronics Engineers Inc, 2016) Civitçi, Fehmi; Ferhanoğlu, Onur; Torun, Hamdi; N/A; Department of Electrical and Electronics Engineering; Adiyan, Ulaş; Ürey, Hakan; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 8579This letter demonstrates a novel prism-based optical-readout, which uses a single prism to detect the incoming TM polarized wave just below the critical angle. The method is used with a 35-mu m-pixel pitch MEMS thermal sensor, whose inclination angle changes with the absorbed infrared (IR) radiation that results in an increase in the reflectivity at the prism's glass-air interface. We compared this approach with the conventional knife-edge method. Noise equivalent temperature difference for a single sensor was measured as 200 mK for knife-edge method, and 154 mK for the proposed critical angle approach. Our approach shows a significant improvement for the sensitivity of the IR sensor. Both methods utilize an AC-coupled readout method for a single MEMS pixel using a photodetector, which responds only to changes in the scene. This method can be scaled to achieve smart pixel cameras for read sensor arrays with low-noise and high-dynamic range.Publication Metadata only Absorption saturation analysis of Cr2+: ZnSe and Fe2+: ZnSe(Optical Soc Amer, 2008) N/A; N/A; N/A; Department of Physics; Çankaya, Hüseyin; Demirbaş, Ümit; Erdamar, Ahmet Koray; Sennaroğlu, Alphan; Researcher; Master Student; Master Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; 20328; N/A; 23851We propose several methods for the accurate determination of the cross sections of solid-state saturable absorbers and apply them to the analysis of polycrystalline Cr2+ :ZnSe and Fe2+ :ZnSe. In the case of Cr2+ :ZnSe, both z-scan and power-dependent transmission measurements were made by using a continuous-wave fiber laser at 1800 nm and a pulsed optical parametric oscillator at 1570 nm. The average ground-state absorption cross sections at the wavelengths of 1800 and 1570 nm were determined to be 6.17 x 10(-19) cm(2) and 2.24 x 10(-19) cm(2), respectively. Furthermore, the ratio of the cross sections at these wavelengths (2.75) was close to the value of 2.55 obtained from absorption spectrum measurements. Excited-state absorption was found to be negligible at both wavelengths. In the case of Fe2+ : ZnSe, a tunable, pulsed Cr2+ :ZnSe laser was used to obtain saturation data (z-scan and power-dependent saturation) at the wavelengths of 2645 and 2730 nm. Average ground-state absorption cross sections at 2645 and 2730 nm were determined to be 1.73 x 10(-19) cm(2) and 2.47 x 10(-19) cm(2), respectively, again in very good agreement with those obtained from absorption spectrum measurements. (c) 2008 Optical Society of America.Publication Metadata only Accurate determination of saturation parameters for Cr4+-doped solid-state saturable absorbers(Optical Society of America, 2006) Department of Physics; N/A; Department of Physics; Department of Physics; Sennaroğlu, Alphan; Demirbaş, Ümit; Özharar, Sarper; Yaman, Fatih; Faculty Member; Master Student; Undergraduate Student; Undergraduate Student; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; 23851; 20328; N/A; N/AWe describe a systematic, rigorous procedure for the determination of the optical absorption saturation parameters for Cr4+:YAG and Cr4+:forsterite crystals at 1064 nm. A rate-equation approach was used to analyze the cw and pulsed transmission data of several crystals by accounting for the transverse as well as longitudinal variation of the beam intensity, saturation effects, and excited-state absorption. Use of an iterative procedure whereby the cw and pulsed data were simultaneously analyzed led to a considerable reduction in the error for the determination of cross sections. The average value of the absorption cross section sigma(a) and the normalized excited-state absorption cross section f(p)=sigma(esa)/sigma(a) were determined to be 6.13 X 10(-19) cm(2) and 0.45, respectively, for Cr4+:forsterite and 19.6 X 10(-19) cm(2) and 0.06, respectively, for Cr4+:YAG. Detailed comparison was also made with previous saturation measurements in the literature. Our results further show that lumped models based on the thin-length approximation should be used with caution in the determination of cross sections, especially when the pump beam is tightly focused inside the absorber.