Browsing by Author "Sennaroğlu, A."
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Item Open Access Effect of Composition on the Spontaneous Emission Probabilities, simulated Emission Cross Sections and Local Environment of Tm+3, in Teo2-Wo3 Glass'(Elsevier Science B.V, 2003-04) Özen, G.; Aydınlı, Atilla; Cenk, S.; Sennaroğlu, A.Effect of composition on the structure, spontaneous and stimulated emission probabilities of various 1.0 mol% Tm2O3 doped (1 - x)TeO2 + (x)WO3 glasses were investigated using Raman spectroscopy, ultraviolet-visible-near-infrared (UV/VIS/NIR) absorption and luminescence measurements. Absorption measurements in the UV/VIS/NIR region were used to determine spontaneous emission probabilities for the 4f-4f transitions of Tm3+ ions. Six absorption bands corresponding to the absorption of the (1)G(4), F-3(2), F-3(3) and F-3(4), H-3(5) and H-3(4) levels from the H-3(6) ground level were observed. Integrated absorption cross-section of each band except that of H-3(5) level was found to vary with the glass composition. Luminescence spectra of the samples were measured upon 457.9 nm excitation. Three emission bands centered at 476 nm ((1)G(4) --> H-3(6) transition), 651 nm ((1)G(4) --> H-3(4) transition) and 800 nm ((1)G(4) --> H-3(5) transition) were observed. Spontaneous emission cross-sections together with the luminescence spectra measured upon 457.9 nm excitation were used to determine the stimulated emission cross-sections of these emissions. The effect of glass composition on the Judd-Ofelt parameters and therefore on the spontaneous and the stimulated emission cross-sections for the metastable levels of Tm3+ ions were discussed in detail. The effect of temperature on the stimulated emission cross-sections for the emissions observed upon 457.9 nm excitation was also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.Item Open Access Graphene supercapacitor as a voltage controlled saturable absorber for femtosecond pulse generation(OSA, 2014) Baylam, I.; Çizmeciyan, M. N.; Özharar, S.; Polat, Emre Ozan; Kocabaş, Coşkun; Sennaroğlu, A.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.Item Open Access Graphene-gold supercapacitor as a voltage-controlled saturable absorber for femtosecond pulse generation(OSA, 2015) Baylam, I.; Balcı, Osman; Kakenov, Nurbek; Kocabaş, Coşkun; Sennaroğlu, A.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.Item Open Access Investigation of the ultrafast response and saturable absorption of voltage-controlled graphene(OSA, 2018) Baylam, I.; Çizmeciyan, M. N.; Kakenov, Nurbek; Kocabaş, Coşkun; Sennaroğlu, A.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.Item Open Access Ultrafast spectroscopy of voltage reconfigurable graphene saturable absorbers in the visible and near infrared(IOP, 2019-04-23) Baylam, I.; Kakenov, Nurbek; Kocabaş, Coşkun; Sennaroğlu, A.; Çizmeciyan, M. N.We describe a detailed experimental investigation of the ultrafast nonlinear response of a voltagecontrolled graphene-gold saturable absorber (VCG-gold-SA) by employing femtosecond pump probe spectroscopy. Visible and near-infrared continuum probe pulses covering the spectral range from 500nm to 1600nm were used. In the experiments, the saturation fluence, modulation depth, ultrafast relaxation times, and the saturable absorption bandwidth of the VCG-gold-SA were measured as a function of the applied bias. We observed both saturable absorption and multi-photon absorption regimes as the applied bias voltage was varied between 0 and 2 V. Measurements indicate that under bias voltages in the range of 0–2 V, it should be possible to adjust the insertion loss of the VCG-gold-SA and at the same time, maintain a sufficient amount of modulation depth as well as an attainable level of saturation fluence over an ultrabroad spectral bandwidth. In particular, at the bias voltage of 1 V, the VCG-gold-SA exhibited fast saturable absorber behavior with adjustable insertion loss from 630nm to 1100nm. These results clearly demonstrate that the VCG-gold-SA can operate as a versatile mode locker for femtosecond pulse generation from lasers operating in the visible and near-infrared wavelengths.