Researcher:
Sennaroğlu, Alphan

Profile Picture
ORCID

Job Title

Faculty Member

First Name

Alphan

Last Name

Sennaroğlu

Name

Name Variants

Sennaroğlu, Alphan

Email Address

Birth Date

Filters

Advanced Search

Filter by

Settings

Researcher Of Publications: search.filters.isAuthorOfPublication.26055499-e895-461f-97af-e219ac6d31cc

Search Results

Now showing 1 - 10 of 248
  • Placeholder
    PublicationMetadata 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; 23851
    We 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.
  • Placeholder
    PublicationMetadata only
    Spectroscopic characterization of Tm3+:TeO2-K2O-Nb2O5 glasses for 2- μm lasing applications
    (Elsevier Science Bv, 2012) Kurt, Adnan; Speghini, Adolfo; Bettinelli, Marco; Department of Physics; Department of Physics; Department of Physics; Görgülü, Adil Tolga; Çankaya, Hüseyin; Sennaroğlu, Alphan; Master Student; Researcher; Faculty Member; Department of Physics; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; 23851
    We have performed detailed experiments to investigate the spectroscopic properties of a new type of tellurite based host doped with thulium: Tm2O3:(0.70)TeO2-(0.15)K2O-(0.15)Nb2O5 having Tm2O3 concentrations of 0.125, 0.25, 0.5, and 1.0 mol%. By performing a Judd-Ofelt analysis of the absorption bands, we obtained average radiative lifetimes of 2.57 +/- 0.20 and 0.35 +/- 0.01 ms for the H-3(4) and F-3(4) levels, respectively. Furthermore, we also observed that an increase in the Tm2O3 concentration from 0.125 to 1.0 mol% results in a decrease of the measured fluorescence lifetime from 814 to 439 mu s and from 258 to 47 mu s for the H-3(4) and F-3(4) levels, respectively, due to efficient non-radiative decay. The highest quantum efficiency of 32% was obtained for the sample doped with 0.125 mol% Tm2O3 for the H-3(4) level. Results show that cross relaxation becomes important as the ion concentration is increased, leading to the quenching of the 1460-nm band and enhancement of the 1860-nm emission. The highest emission cross section of 6.85 x 10(-21) Cm-2 measured for the 1860-nm band reveals the potential of this host for the development of 2-mu m lasers in bulk glass as well as fiber media. (C) 2011 Published by Elsevier B.V.
  • Placeholder
    PublicationMetadata only
    Graphene mode-locked Cr:ZnSe laser
    (Optical Society of America (OSA), 2013) Kim J.W.; Bae S.; Hong B.H.; Rotermund F.; N/A; Department of Physics; Çizmeciyan, Melisa Natali; Sennaroğlu, Alphan; 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; College of Sciences; N/A; 23851
    We report a graphene mode-locked Cr:ZnSe laser which produces femtosecond pulses with duration as short as 176 fs and pulse energy as high as 2.4 nJ at a 78-MHz repetition rate near 2400 nm.
  • Placeholder
    PublicationMetadata only
    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.
  • Placeholder
    PublicationMetadata only
    Concentration dependence of the infrared luminescence efficiencies in TEO-CDCL2 : TM3+ glass
    (Optica Publishing Group, 2003) Özalp, M. Reha; Özen, Gönül; Department of Physics; Department of Physics; Sennaroğlu, Alphan; Kurt, Adnan; Faculty Member; Teaching Faculty; Department of Physics; College of Sciences; College of Sciences; 23851; 194455
    Using exper imental methods, the characteristics of the 1450-nm and 1800-nm luminescence bands of Tm3+ doped TeO2-CdCl2 glasses were studied as a function of the Tm3+ doping level.
  • Placeholder
    PublicationMetadata only
    Investigation of the factors affecting the photothermal therapy potential of small iron oxide nanoparticles over the 730-840 nm spectral region
    (Royal Soc Chemistry, 2018) N/A; N/A; N/A; Department of Physics; Department of Chemistry; Bilici, Kübra; Muti, Abdullah; Duman, Fatma Demir; Sennaroğlu, Alphan; Acar, Havva Funda Yağcı; PhD Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; 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; 178902
    The use of superparamagnetic iron oxide nanoparticles (SPIONs) as a sensitizer in photothermal therapy (PTT) is relatively new and the origin of such a phenomenon is not known. Usually, large crystals and aggregated particles are preferred in the literature, suggesting that these increase the absorbance of particles at the irradiation wavelength, and hence, provide a larger temperature increase. This study has two major goals: identification of the key factors that affect the photo-induced temperature increase in well-controlled experiments and the influence of laser irradiation on nanoparticle properties. Small, biocompatible poly(acrylic acid) coated SPIONs (PAA/SPIONs) were used since they are more practical for future medical use than large aggregates. We studied the impact of three major laser-dependent variables, namely the wavelength (between 728 and 838 nm), intensity (1.85-9.76 W cm(-2)) and power (105-800 mW) as well as attenuation at the irradiation wavelength, on photothermal heating achieved with PAA/SPIONs. Within the studied range of these variables, only the laser power plays a critical role on the magnitude of photothermal heating in solutions. There is no strong correlation between the attenuation at the excitation wavelength and the temperature increase. In addition, extensive characterization of SPIONs before and after irradiation revealed no significant difference, which supports the re-usability of SPIONs. Lastly, the PTT potential of these small PAA/SPIONs was demonstrated in vitro on HeLa cells. At these low laser powers no temperature increase in SPION-free water or cell death in SPION-free cells was detected. Hence, this study provides a new insight into the photothermal effect of SPIONs, provides a clear and repeatable experimental procedure and demonstrates great potential for small SPIONs to be exploited in PTT.
  • Placeholder
    PublicationMetadata only
    Effect of thermal lensing on the mode matching between pump and laser beams in Cr4+: forsterite lasers: a numerical study
    (IOP Publishing, 2000) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851
    The numerical study presented in this paper investigates the role of thermal lensing on the mode matching between the pump beam and the cavity beam in continuous-wave end-pumped Cr4+:forsterite lasers. A suitable mode overlap function was first derived to calculate the degree of overlap between the pump beam and the fundamental mode of the resonator. The effect of thermal lensing on mode matching was then numerically investigated by calculating the changes in the average value of the mode overlap function due to variations in pump power and crystal boundary temperature. Thermal lensing was taken into account by calculating the pump-induced thermal gradients and by approximating the gain medium as a distributed quadratic lens. Finally, the model was used to offer guidelines about how one of the resonator lenses should be readjusted in order to maintain optimum mode matching as the boundary temperature and pump power are varied.
  • Placeholder
    PublicationMetadata only
    Efficient continuous-wave radiatively cooled Cr4+: forsterite lasers at room temperature
    (Optical Soc Amer, 1998) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851
    Results of a detailed experimental investigation aimed at reducing the thermal loading problem in a cw Cr4+:forsterite laser at elevated temperatures are presented. From a Cr4+:forsterite crystal with a differential absorption coefficient of 0.57 cm(-1), as much as 900 mW of cw output power has been obtained at 1.26 mu m and at a crystal boundary temperature of 15 degrees C with an absorbed pump power of only 4.5 W at 1.06 mu m. No chopping of the the pump beam was necessary. An efficient radiative cooling technique was further employed to cool the laser and no subsequent power fading was observed. To the author's knowledge, the measured absorbed power slope efficiency of 29.5% represents the highest cw power performance reported to date: from a Cr4+:forsterite laser pumped by a Nd:YAG laser around room temperature. The role of the low differential absorption coefficient in the reduction of thermal loading is further elucidated by presenting comparative cw power performance data with a second Cr4+:forsterite crystal having a differential absorption coefficient of 1.78 cm(-1) in the temperature range between 12 and 35 degrees C. Finally, some interesting multipulse effects of the laser observed in the millisecond regime during quasi-cw operation at 50% duty cycle are described.
  • Placeholder
    PublicationMetadata only
    Femtosecond laser written Tm3+:BaY2F8 waveguide laser operating near 1.9 μm
    (Optica Publishing Group (formerly OSA), 2021) Tonelli, Mauro; Department of Physics; Department of Physics; Sennaroğlu, Alphan; Morova, Yağız; Faculty Member; Researcher; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; College of Sciences; College of Sciences; 23851; N/A
    We report the first experimental demonstration of continuous-wave laser action near 1.9 μm in a femtosecond laser written Tm3+ ion-doped BaY2F8 crystal waveguide laser with incident lasing threshold pump power as low as 23 mW.
  • Placeholder
    PublicationMetadata only
    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.