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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3

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    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.
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    Efficient continuous-wave operation of a diode-pumped Nd:YVO4 laser at 1342 nm
    (Elsevier Science Bv, 1999) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851
    The experimental study described in this paper investigates the continuous-wave power performance of an efficient diode-pumped Nd:YVO4 laser at 1342 nm by employing four different end pumping configurations. When pumped by a high-power fiber-coupled diode array at 806 nm, the compact resonator consisting of a 9.25-mm long Nd:YVO4 crystal and a 3.6% transmitting output coupler produced as high as 3550 mW of output power. The absorbed power slope efficiency was measured to be 28.1%. By using the experimentally measured threshold data, the stimulated emission cross-section of the gain medium was determined to be 13 X 10(-19) cm(2) at 1342 nm. Above absorbed pump powers of 11 W, strong thermal loading caused saturation of the output power and the focal length of the induced thermal lens was measured as a function of the pump power. Results further showed that the laser output was insensitive to variations in the crystal boundary temperature between 20 degrees C and 40 degrees C.
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    Experimental and numerical investigation of thermal effects in end-pumped Cr/sup 4+/: forsterite lasers near room temperature
    (IEEE-Inst Electrical Electronics Engineers Inc, 1998) Department of Physics; Department of Physics; Sennaroğlu, Alphan; Pekerten, Barış; Faculty Member; Undergraduated Student; Department of Physics; College of Sciences; College of Sciences; 23851; N/A
    The results of a study which employs both experimental and theoretical methods to investigate the role of thermal effects in room-temperature Cr4+:forsterile lasers are presented. A novel model was developed to calculate the incident threshold pump power required to attain oscillation by taking into account absorption saturation and pump-induced thermal loading in the gain medium, Experimentally, the incident threshold pump power was measured as a function of the crystal boundary temperature for three Cr4+:forsterite laser crystals with different small-signal differential absorption coefficients alpha(p0) and/or cross-sectional areas. Excellent agreement was obtained between theory and experiment for values of the stimulated emission cross section comparable to those from previously reported data. The model was then used to numerically determine the optimum value of alpha(p0) which minimizes the incident threshold pump power in room-temperature Cr4+:forsterite lasers, At a crystal boundary temperature of 15 degrees C, the optimum value of alpha(p0) was determined to be 0.64 cm(-1) for a 2-cm-long Cr4+:forsterite crystal, corresponding to an unsaturated absorption of 72%. The use of crystals with an optimum absorption coefficient should lead to the realization of highly efficient CW Cr4+:forsterite lasers at room temperature.
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    Experimental determination of fractional thermal loading in an operating diode-pumped Nd: YVO4 minilaser at 1064 nm
    (Optical Soc Amer, 1999) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851
    A practical in, situ method is described and used for determination of the fractional thermal-loading parameter eta(h) in an operating diode-pumped Nd:YVO4 minilaser at 1064 nm. Readily applicable to the thermal characterization of other solid-state media, the method is based on the fact that thermally induced lensing will cause the laser oscillation to be quenched at a critical pump power whose magnitude depends on the cavity configuration, thermo-optical properties of the gain medium, and, in particular, on the value of eta(h). In the experiments described here, a 0.5-mm-long coated Nd:YVO4 crystal with 3-at. % Nd concentration was used to construct the diode-pumped laser with a flat highly reflecting end mirror and an intracavity lens. For the method to be effective, the resonator was set up close to the edge of the stability range. Above the oscillation threshold, the pump power at which lasing was quenched because of the onset of the thermally induced resonator instability was measured as a function of the intracavity lens position. A numerical model that accounted for absorption saturation and pump-induced thermal lensing was then used to analyze the experimentally measured data with eta(h) as an adjustable parameter. The average best-fit value of eta(h) was determined to be 0.40 with an estimated statistical variation of 8%.
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    Femtosecond optical parametric oscillator based on periodically poled KTiOPO(4)
    (1998) Kartaloğlu, Tolga; Köprülü, Kahraman G; Aytur, Orhan; Risk, William; Department of Physics; Sundheimer, Michael; Faculty Member; Department of Physics; College of Sciences; N/A
    We report a femtosecond optical parametric oscillator based on a periodically poled KTiOPO4 crystal for which quasi-phase matching is achieved with a 24−µm poling period. The singly resonant parametric oscillator, synchronously pumped by a Ti:sapphire laser at a wavelength of 758 nm, generates a signal at 1200 nm and an idler at 2060 nm. The maximum signal power conversion efficiency of the device is 22% with a pump depletion of 69%. We tune the signal wavelength over a 200-nm band by changing the cavity length. In addition, pump wavelength tuning provides output tunability in the 1000–1235-nm range. 
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    Experimental determination of fractional thermal loading in an operating diode-pumped nd:yvo4 minilaser at 1064 nm
    (Optica Publishing Group, 1999) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851
    A practical in, situ method is described and used for determination of the fractional thermal-loading parameter eta(h) in an operating diode-pumped Nd:YVO4 minilaser at 1064 nm. Readily applicable to the thermal characterization of other solid-state media, the method is based on the fact that thermally induced lensing will cause the laser oscillation to be quenched at a critical pump power whose magnitude depends on the cavity configuration, thermo-optical properties of the gain medium, and, in particular, on the value of eta(h). In the experiments described here, a 0.5-mm-long coated Nd:YVO4 crystal with 3-at. % Nd concentration was used to construct the diode-pumped laser with a flat highly reflecting end mirror and an intracavity lens. For the method to be effective, the resonator was set up close to the edge of the stability range. Above the oscillation threshold, the pump power at which lasing was quenched because of the onset of the thermally induced resonator instability was measured as a function of the intracavity lens position. A numerical model that accounted for absorption saturation and pump-induced thermal lensing was then used to analyze the experimentally measured data with eta(h) as an adjustable parameter. The average best-fit value of eta(h) was determined to be 0.40 with an estimated statistical variation of 8%.
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    Determination of the optimum absorption coefficient in Cr4+: forsterite lasers under thermal loading
    (Optical Soc Amer, 1998) Department of Physics; Department of Physics; Sennaroğlu, Alphan; Pekerten, Barış; Faculty Member; Undergraduated Student; Department of Physics; College of Sciences; College of Sciences; 23851; N/A
    We present the results of a novel experimental and numerical investigation aimed at minimizing thermal loading effects in room-temperature Cr4+:forsterite lasers. In the model we numerically calculated the incident primp power required for oscillation threshold to be attained by taking into account pump absorption saturation, pump-induced thermal gradients inside the crystal, and the temperature dependence of the upper-state fluorescence lifetime. Excellent agreement was obtained between model predictions and experimental threshold data. We then used the model to calculate the optimum absorption coefficient that minimizes the incident threshold pump power. At a crystal boundary temperature of 15 degrees C the optimum value of the absorption coefficient was numerically determined to be 0.64 cm(-1). Such optimization studies, which are readily applicable to other laser systems, should make a significant contribution to the improvement of the power performance of Cr4+:forsterite lasers at room temperature.
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    Continuous-wave power transmission and thermal lensing of a saturable absorber subject to excited-state absorption
    (Optical Soc Amer, 1999) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851
    Rate-equation analysis has been used in an investigation of the role of saturation and excited-state absorption in the power transmission characteristics and thermal lensing of an absorber. Use of an iterative approach gives explicit analytical results for power transmission and thermal focal length in the presence of excited-state absorption. Sample calculations indicate that pump absorption can increase or decrease with increasing incident pump power, depending on the relative strength of the excited-state absorption cross section with respect to the ground-state absorption cross section. In the case of thermal lensing, results further indicate that saturation and excited-state absorption act as two competing effects, the former reducing the strength of the thermal lens and the latter causing the opposite effect. The analytical was derived in this analysis should prove useful to experimentalists in determination of ground-state and excited-state absorption cross sections from experimental power transmission and lensing data.
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    Infrared parametric fluorescence in segmented KTP channel waveguides
    (Optica Publishing Group, 1998) Aschieri Pierre; Baldi, Pascal; Bierlein, John; Department of Physics; Sundheimer, Michael; Faculty Member; Department of Physics; College of Sciences; N/A
    In this article results of measurements of infrared parametric fluorescence in segmented KTP channel waveguides are presented, showing the dependence of optical parametric oscillator tuning curves and fluorescence conversion efficiency (parametric gain) on segmentation duty-cycle.
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    Optimum crystal parameters for room-temperature Cr4+: Forsterite lasers: threshold and finite-power analysis
    (Optical Soc America, 1999) Department of Physics; Department of Physics; Sennaroğlu, Alphan; Konca, Ali Özgün; Faculty Member; Undergraduate Student; Department of Physics; College of Sciences; College of Sciences; 23851; 156098
    A novel model was used to analyze the experimental threshold and efficiency data of continuous-wave Cr4+:forsterite lasers operated around room temperature by taking into account the temperature dependence of the fluorescence lifetime, pump absorption saturation, and excited-state absorption at the lasing wavelength. The best-fit values of the stimulated emission cross-section and the excited-state absorption cross-section were determined to be 1.23x10(-19) cm(2) and 0.26x10(-19) cm(2), respectively. The numerical calculations further predict the optimum crystal length and absorption coefficient to be 2 cm and 0.34 cm(-1) for room-temperature Cr4+:forsterite lasers.