Browsing by Author "Sennaroglu, A."

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    Development of a thulium (Tm:YAP) laser system for brain tissue ablation
    (2011) Bilici, T.; Mutlu, S.; Kalaycioglu H.; Kurt, A.; Sennaroglu, A.; Gulsoy, M.
    In this study, a thulium (Tm:YAP) laser system was developed for brain surgery applications. As the Tm:YAP laser is a continuous-wave laser delivered via silica fibers, it would have great potential for stereotaxic neurosurgery with highest local absorption in the IR region. The laser system developed in this study allowed the user to set the power level, exposure time, and modulation parameters (pulse width and on-off cycles). The Tm:YAP laser beam (200-600 mW, 69-208 W/cm 2) was delivered from a distance of 2 mm to cortical and subcortical regions of ex-vivo Wistar rat brain tissue samples via a 200-μm-core optical fiber. The system performance, dosimetry study, and ablation characteristics of the Tm:YAP laser were tested at different power levels by maximizing the therapeutic effects and minimizing unwanted thermal side-effects. The coagulation and ablation diameters were measured under microscope. The maximum ablation efficiency (100 × ablation diameter/coagulation diameter) was obtained when the Tm:YAP laser system was operated at 200 mW for 10 s. At this laser dose, the ablation efficiency was found to be 71.4% and 58.7% for cortical and subcortical regions, respectively. The fiber-coupled Tm:YAP laser system in hence proposed for the delivery of photothermal therapies in medical applications. © 2011 Springer-Verlag London Ltd.
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    Femtosecond pulse generation from an extended cavity Cr4+: Forsterite laser using graphene on YAG
    (Optical Society of America, 2013) Baylam I.; Ozharar, S.; Natali Cizmeciyan, M.; Balcı, Osman; Pince, Erçağ; Kocabaş, Coşkun; Sennaroglu, A.
    A room temperature, multipass-cavity, femtosecond Cr4+:forsterite laser was modelocked with a single-layer graphene saturable absorber on a YAG substrate. The resonator produced nearly transform-limited 92 fs pulses near 1250 nm with 53 kW of peak power. © OSA 2013.
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    Femtosecond pulse generation with voltage-controlled graphene saturable absorber
    (Optical Society of America, 2014) Baylam, M. N.; Cizmeciyan, S.; Ozharar, S.; Polat, E. O.; Kocabas, C.; Sennaroglu, A.
    We report, for the first time to our knowledge, the demonstration of a graphene supercapacitor as a voltage-controlled saturable absorber for femtosecond pulse generation from a solid-state laser. By applying only a few volts of bias, the Fermi level of the device could be shifted to vary the insertion loss, while maintaining a sufficient level of saturable absorption to initiate mode-locked operation. The graphene supercapacitor was operated at bias voltages of 0.5-1V to generate sub-100 fs pulses at a pulse repetition rate of 4.51 MHz from a multipass-cavity Cr4+:forsterite laser operating at 1255 nm. The nonlinear optical response of the graphene supercapacitor was further investigated by using pump-probe spectroscopy. (C) 2014 Optical Society of America
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    Fluence of thulium laser system in skin ablation
    (IEEE, 2010) Bilici, T.; Tabakoğlu, O.; Kalaycıoğlu, Hamit; Kurt, A.; Sennaroglu, A.; Gülsoy, M.
    Tm:YAP laser system at power levels up to 1.2 W at 1980 nm was established in both continuous-wave and modulated modes of operation. The fluence effect of the laser system for skin ablation was analyzed by histology analysis with Wistar rat skin tissues. Thermally altered length, thermally altered area, ablation area, and ablation depth parameters were measured on histology images of skin samples just after the laser operation and after four-day healing period. Continuous-wave mode of operation provided higher thermal effects on the skin samples. Lower fluence levels were found for efficient ablation effect. © 2010 IEEE.
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    Generation of Sub-20-fs Pulses From a Graphene Mode-Locked Laser
    (OSA - The Optical Society, 2017) Canbaz, F.; Kakenov, N.; Kocabas, C.; Demirbas, U.; Sennaroglu, A.
    We demonstrate, what is to our knowledge, the shortest pulses directly generated to date from a solid-state laser, mode locked with a graphene saturable absorber (GSA). In the experiments, a low-threshold diode-pumped Cr3+:LiSAF laser was used near 850 nm. At a pump power of 275 mW provided by two pump diodes, the Cr3+:LiSAF laser produced nearly transform-limited, 19-fs pulses with an average output power of 8.5 mW. The repetition rate was around 107 MHz, corresponding to a pulse energy and peak power of 79 pJ and 4.2 kW, respectively. Once mode locking was initiated with the GSA, stable, uninterrupted femtosecond pulse generation could be obtained. In addition, the femtosecond output of the laser could be tuned from 836 nm to 897 nm with pulse durations in the range of 80-190 fs. We further performed detailed mode locking initiation tests across the full cavity stability range of the laser to verify that pulse generation was indeed started by the GSA and not by Kerr lens mode locking. � 2017 Optical Society of America.
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    Graphene mode-locked Cr:LiSAF laser at 850 nm
    (OSA - The Optical Society, 2015) Canbaz F.; Kakenov, N.; Kocabas, C.; Demirbas, U.; Sennaroglu, A.
    We report, for the first time to our knowledge, a mode-locked femtosecond Cr:LiSAF laser initiated with a high-quality monolayer graphene saturable absorber (GSA), synthesized by chemical-vapor deposition. The tight-focusing resonator architecture made it possible to operate the Cr:LiSAF laser with only two 135 mW, 660 nm low-cost single-mode diode lasers. At a pump power of 270 mW, the laser produced nearly transform-limited 68 fs pulses with an average power of 11.5 mW at 850 nm. The repetition rate was around 132 MHz, corresponding to a pulse energy and peak power of 86 pJ and 1.26 kW, respectively. Once mode locking was initiated with the GSA, stable, uninterrupted femtosecond pulse generation could be sustained for hours. The saturation fluence and the modulation depth of the GSA were further determined to be 28 μJ/cm2 and 0.62%, respectively. 2015 Optical Society of America.
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    Graphene mode-locked diode-pumped Cr:LiSAF laser at 857 nm
    (IEEE, 2015) Canbaz, F.; Kakenov, Nurbek; Kocabaş, Coşkun; Demirbaş, U.; Sennaroglu, A.
    The Cr:LiSAF gain medium, belonging to the class of Cr:colquiirite lasers, possesses a broad gain bandwidth suitable for the generation of femtosecond pulses near 850 nm [1]. Because the nonlinear refractive index of these media is typically low, Kerr lens mode locking alone does not provide sufficient modulation for stable mode locking. To increase the effective modulation depth for mode-locked operation, gain matched output couplers [2], semiconductor saturable absorber mirrors (SESAM) [3], and single-walled carbon nanotubes (SWCNT) [4] have been used in previous studies. One drawback of SESAMs and SWCNTs is the narrow operation bandwidth which limits the pulse widths as well as the mode-locked tuning range. An attractive alternative involves use of the graphene saturable absorber (GSA) which provides constant absorption over a very broad wavelength range due to the zero band-gap energy [5]. However, one challenge remains in the case of Cr.colquiirite lasers since the relatively low optical gain may not be sufficient to overcome the small signal loss of the GSA (around 5% per round trip), especially in low-power systems. In previous studies, GSA has been used to generate mode-locked pulses from bulk solid-state lasers between 800 and 2500 nm [6, 7].
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    Graphene mode-locked femtosecond Alexandrite laser
    (OSA - The Optical Society, 2018) Cihan, C.; Kocabas, C.; Demirbas U.; Sennaroglu, A.
    We report for the first time, to the best of our knowledge, graphene mode-locked operation of a femtosecond Alexandrite laser at 750 nm. A multipass-cavity configuration was employed to scale the output energy and to eliminate spectral/Q-switching instabilities. By using a monolayer graphene saturable absorber, mode locking could be obtained. With 5W of pump at 532 nm, nearly transformlimited, 65 fs pulses with a time-bandwidth product of 0.319 were generated. The mode-locked laser operated at a pulse repetition rate of 5.56 MHz and produced 8 mW output power, corresponding to a pulse energy and peak power of 1.4 nJ and 22 kW, respectively. These experiments further show that graphene can be used to initiate mode locking at wavelengths as low as 750 nm.
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    Graphene mode-locked femtosecond Cr: LiSAF laser
    (Optical Society of America (OSA), 2015) Canbaz F.; Kakenov, N.; Kocabas, C.; Demirbas, U.; Sennaroglu, A.
    We report the first demonstration of femtosecond pulse generation from a Cr:LiSAF laser mode-locked with a monolayer graphene saturable absorber. Nearly transform-limited 72-fs pulses were generated at 850 nm with only two 135-mW pump diodes.
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    Graphene mode-locked multipass-cavity femtosecond Cr4+:forsterite laser
    (Optical Society of America, 2013-04-19) Ozharar, S.; Baylam, I.; Cizmeciyan, M. N.; Balci, O.; Pince, E.; Kocabas, C.; Sennaroglu, A.
    We report, for the first time to our knowledge, the use of graphene as a saturable absorber in an energy-scaled femtosecond Cr4+: forsterite laser. By incorporating a multipass cavity, the repetition rate of the original short resonator was reduced to 4.51 MHz, which resulted in the generation of 100 fs, nearly transform-limited pulses at 1252 nm with a peak power of 53 kW. To the best of our knowledge, this is the highest peak power obtained from a room-temperature, femtosecond Cr4+: forsterite laser mode locked with a graphene saturable absorber. The corresponding pulse energy was 5.3 nJ with only 24 mW of average output power. The saturation fluence and modulation depth of the GSA were measured to be 25 mu J/cm(2) and 0.74%, respectively. The nonlinear effects in the Cr4+: forsterite medium that limit further power scaling were also investigated by using different output couplers. (c) 2013 Optical Society of America
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    Graphene-gold supercapacitor as a voltage controlled saturable absorber for femtosecond pulse generation
    (Optical Society of America, 2016-02) Baylam, I.; Balci, O.; Kakenov, N.; Kocabas, C.; Sennaroglu, A.
    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 μm.