Researcher:
Toker, Işınsu Baylam

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PhD Student

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Işınsu Baylam

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Toker

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Toker, Işınsu Baylam

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2012 - 2019222020 - 20228

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Now showing 1 - 10 of 31
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    Investigation of the ultrafast response and saturable absorption of voltage-controlled graphene
    (Optica Publishing Group (formerly OSA), 2018) Kakenov N.; Kocabas C.; N/A; N/A; Department of Physics; Toker, Işınsu Baylam; Çizmeciyan, Melisa Natali; Sennaroğlu, Alphan; PhD Student; PhD 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; College of Sciences; N/A; N/A; 23851
    Ultrafast pump-probe measurements show that at a bias voltage of 1V, voltage reconfigurable graphene supercapacitors can operate as fast saturable absorbers with adjustable insertion loss over an ultrabroad spectral range from 630 to 1100 nm.
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    Sub-100-fs pulse generation from a Kerr-lens mode-locked Alexandrite laser
    (Optica Publishing Group (formerly OSA), 2018) Demirbaş Ümit; N/A; N/A; N/A; Department of Physics; Cihan, Can; Muti, Abdullah; Toker, Işınsu Baylam; Sennaroğlu, Alphan; PhD Student; PhD Student; PhD 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; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 23851
    We report, to the best of our knowledge, the shortest pulses obtained from a Kerr-lens mode-locked multipass-cavity Alexandrite laser operating near 750 nm. The resonator produced 70-fs pulses with a time-bandwidth product of 0.331.
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    Femtosecond laser written continuous-wave Nd3+:BaY2F8 waveguide laser at 1.3 mu m
    (Elsevier, 2022) Di Lieto, Alberto; Cittadino, Giovanni; Damiano, Eugenio; Tonelli, Mauro; Department of Physics; N/A; N/A; N/A; Department of Physics; Morova, Yağız; Morova, Berna; Jahangiri, Hadi; Toker, Işınsu Baylam; Sennaroğlu, Alphan; Researcher; Researcher; Researcher; PhD Student; Faculty Member; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; N/A; N/A; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; N/A; 23851
    We experimentally demonstrate, for the first time to our knowledge, robust operation of a Nd3(+:)BaY(2)F(8) waveguide laser at 1.3 mu m without any parasitic lasing at any other wavelength. The best power performance was obtained with a depressed cladding waveguide, having a diameter of 70 mu m, which was fabricated by employing femtosecond laser writing. The propagation loss of the waveguide was measured as 0.33 dB/cm at the wavelength of 761 nm. The power performance of the waveguide laser was investigated for E//z and E//y pumping polarizations by using butt-coupled flat resonator mirrors. Higher power performance was obtained for E//z pumping, where the resonator with the 6.2% transmitting output coupler produced 157 mW of continuous-wave output power at 1318 nm with 882 mW of pump power at 800 nm. The measured power slope efficiency was 19% with respect to the incident pump power. By using a different set of cavity optics, 1050-nm lasing performance was also studied, where E//z pumping at 800 nm with the 12% transmitting output coupler yielded 307 mW of output power with 31% slope efficiency. Use of a host medium with relatively low refractive index around 1.5 was instrumental in reducing the facet reflectivity and eliminating the possibility of parasitic lasing at 1.05 mu m during 1.3-mu m lasing.
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    Graphene supercapacitor as a voltage controlled saturable absorber for femtosecond pulse generation
    (Optical Society of America (OSA), 2014) Ozharar, Sarper; Ozan Polat E.; Kocabas, Coskun; N/A; N/A; Department of Physics; Toker, Işınsu Baylam; Çizmeciyan, Melisa Natali; Sennaroğlu, Alphan; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A, N/A; 23851
    For the first time to our knowledge, we employed a graphene supercapacitor as a voltage controlled saturable absorber at bias voltages of 0.5-1V to generate 84-fs pulses from a solid-state laser near 1255 nm.
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    Dual-wavelength temporal dynamics of a gain-switched 2-mu m Tm3+:Lu2O3 ceramic laser
    (IEEE-Inst Electrical Electronics Engineers Inc, 2018) N/A; N/A; Department of Physics; Toker, Işınsu Baylam; Canbaz, Ferda; Sennaroğlu, Alphan; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 23851
    We provide a detailed experimental investigation of the energy efficiency and rich temporal dynamics of a gain-switched 2-mu m Tm3+:Lu2O3 ceramic laser pumped near 800 nm. A tunable Ti3+:sapphire laser was used to determine the full excitation spectrum and the optimum pumping bands for the 1.5% Tm3+:Lu2O3 ceramic gain medium. These bands were centered at 774, 796, and 811 nm. The highest output pulse energy was obtained when the pump wavelength was set to 796 nm. In the experiments, a free-running x-cavity was used to investigate the energy efficiency of the Tm3+:Lu2O3 ceramic laser. Extracavity grating-dispersed output and prism-tuned resonator were used to further assess the role of cross-relaxation for the 1.5% Tm3+:Lu2O3 ceramic. Finally, we demonstrate that as the pump energy was increased, a transition occurred from-single-wavelength output (2068 nm) to dual-wavelength multipulse output (2068 and 1968 nm). We performed systematic temporal and spectral characterization measurements by using the free-running resonator, extracavity-grating-dispersed laser output, and prism-tuned resonator to investigate how the laser pulses at 1968 and 2068 nm evolved in time. A plane-wave rate equation model was further used to investigate the temporal dynamics of the Tm3+:Lu2O3 ceramic laser and provided predictions in qualitative agreement with experimental data.
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    Graphene-gold supercapacitor as a voltage-controlled saturable absorber for femtosecond pulse generation
    (The Optical Society (OSA), 2015) N/A; Department of Physics; Toker, Işınsu Baylam; Sennaroğlu, Alphan; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 23851
    We report, for the first time to our knowledge, a voltage-controlled graphene-gold supercapacitor saturable absorber, as a modulator with adjustable insertion loss for low-gain mode-locked lasers. Nearly transform-limited, 80-fs pulses were generated near 1240 nm.
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    Tunable continuous-wave laser operation of Tm3+:BaY2F8 near 2.3 µm
    (2020) Tonelli, Mauro; N/A; N/A; Department of Physics; Muti, Abdullah; Toker, Işınsu Baylam; Sennaroğlu, Alphan; PhD Student; PhD 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; College of Sciences; N/A; N/A; 23851
    We report, for the first time to our knowledge, tunable continuous-wave laser action in the Tm3+:BaY2F8 (BYF) crystal near 2.3 mu m. In the experiments, a BYF crystal doped with 3 at. % thulium was end pumped with a narrow-linewidth, tunable Ti3+ :sapplkire laser with up to 920 mW of incident power. Lasing was achieved for the two pump polarizations of E//x and E//y. The best power performance was obtained in the case of E//x, double-end pumping, where 100 mW of output power was obtained at 2290 nm with 920 mW of pump power and 1% output coupler. The laser could be continuously tuned from 2233 to 2385 nm. Excitation spectra for E//x and Elly pumping were measured in the 760-810 nm range, and the optimum pumping wavelength was determined to be 779 nm for E//x. By using the lifetime and lasing threshold data, the stimulated emission cross section at 2290 nm was further determined to be (0.66 +/- 0.06) x 10(-24) m(2).
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    Graphene-gold supercapacitor as a voltage controlled saturable absorber for femtosecond pulse generation
    (Optical Soc Amer, 2016) Balcı, Osman; Kakenov, Nurbek; Kocabaş, Coşkun; N/A; Department of Physics; Toker, Işınsu Baylam; Sennaroğlu, Alphan; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 23851
    We report, for the first time to the best of our knowledge, use of a graphene-gold supercapacitor as a voltage controlled fast saturable absorber for femtosecond pulse generation. The unique design involving only one graphene electrode lowers the insertion loss of the device, in comparison with capacitor designs with two graphene electrodes. Furthermore, use of the high-dielectric electrolyte allows reversible, adjustable control of the absorption level up to the visible region with low bias voltages of only a few volts (0-2 V). The fast saturable absorber action of the graphene-gold supercapacitor was demonstrated inside a multipass-cavity Cr:forsterite laser to generate nearly transform-limited, sub-100 fs pulses at a pulse repetition rate of 4.51 MHz at 1.24 mu m.
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    The fast-track water oxidation channel on BiVO4 opened by nitrogen treatment
    (Amer Chemical Soc, 2020) N/A; N/A; N/A; N/A; Department of Physics; Department of Chemistry; Kahraman, Abdullah; Barzgarvishlaghi, Mahsa; Toker, Işınsu Baylam; Sennaroğlu, Alphan; Kaya, Sarp; PhD Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); 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; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; 23851; 116541
    BiVO4 is one of the most promising photoanode materials for water-splitting systems. Nitrogen incorporation into a BiVO4 surface overcomes the known bottleneck in its charge-transfer kinetics into the electrolyte. We explored the role of nitrogen in the surface charge recombination and charge-transfer kinetics by employing transient photocurrent spectroscopy at the time scale of surface recombination and water oxidation kinetics, transient absorption spectroscopy, and X-ray photoelectron spectroscopy. We attributed the activity enhancement mechanism to the accelerated V5+/V4+ redox process, in which incorporated nitrogen suppresses a limiting surface recombination channel by increasing the oxygen vacancies.
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    Femtosecond pulse generation with voltage-controlled graphene saturable absorbers
    (World Scientific Publishing Co. Pte. Ltd., 2017) Özharar, Sarper; Kakenov, Nurbek; Kocabaş, Coşkun; N/A; Department of Physics; Toker, Işınsu Baylam; Sennaroğlu, Alphan; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 23851
    We describe experiments where voltage controlled graphene supercapacitor devices are used as saturable absorbers to initiate femtosecond pulses from tunable solid-state lasers. The device architectures allow the control of the Fermi level and hence the overall insertion loss of these devices at low operating voltages on the order of a few volts. Hence, they can be readily incorporated into the resonator of low-gain solid-state lasers. After the background sections on laser fundamentals and ultrafast pulse generation, the second part of the Chapter focuses on the spectroscopic characteristics of graphene and use of graphene supercapacitor devices as saturable absorbers to initiate femtosecond pulses. We present comparative, experimental data taken with a multi-pass cavity, Cr4+:forsterite laser, where two different graphene-based supercapacitor device architectures were used to generate sub-100-fs pulses near 1250 nm.