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Publication Metadata 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; 23851Results 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.Publication Metadata only Comparison between difference-frequency generation and parametric fluorescence in quasi-phase-matched lithium niobate stripe waveguides(IEEE, 1996) Baldi, P.; El Hadi, K.; De Micheli, M. P.; Ostrowsky, D.B.; Department of Physics; Sundheimer, Michael; Faculty Member; Department of Physics; College of Sciences; N/ATuning curves and gain are two relevant parameters for integrated optical parametric oscillators. We show in this paper that they can be determined with a good precision without building a high-finesse cavity by measurement of the optical parametric fluorescence and difference-frequency generation. In the first part of this paper, we compare theoretically the guided optical parametric fluorescence and the guided difference-Frequency generation in the quasi-phase matching configuration. In the second part, we compare experimental results on optical parametric fluorescence in the 1.2-2.2-μm region and optical difference-frequency generation from a 1.55-μm laser diode using a pump wavelength between 775-795 nm in quasi-phase-matched lithium niobate stripe waveguides. This comparison shows that the gain measured by both methods is identical, but, while parametric fluorescence allows us to obtain the quasi-phase-matching curve, the difference-frequency generation gives a simpler and more accurate measurement of the gain. The combination of these two techniques provides therefore a powerful tool for evaluating the different fabrication processes of the nonlinear waveguides, without actually fabricating a parametric oscillator.Publication Metadata only 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; 23851The 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.Publication Metadata only 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/AThe 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.Publication Metadata only 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; 23851A 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%.Publication Metadata only Efficient continuous-wave operation of a radiatively cooled CR4+: forsterite laser at room temperature(Optical Society of America, 1997) Department of Physics; Department of Physics; Sennaroğlu, Alphan; Kurt, Adnan; Faculty Member; Teaching Faculty; Department of Physics; College of Sciences; College of Sciences; 23851; 194455Results of a detailed experimental investigation aimed at reducing the thermal loading problem in a cw Cr(4+):forsterite laser at elevated temperatures are presented. From a Cr(4+):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 mum and at a crystal boundary temperature of 15 degrees C with an absorbed pump power of only 4.5 W at 1.06 mum. No chopping of 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 Cr(4+):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 Cr(4+):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.Publication Metadata only 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/AWe 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.Publication Metadata only The sensitivity of conformational free energies of the alanine dipeptide to atomic site charges(Wiley, 1997) Maye, Peter V.; Mezei, Mihaly; Department of Physics; Reşat, Haluk; Faculty Member; Department of Physics; College of Sciences; N/ADifferent atomic point charge sets are obtained for the are and C7,eq conformations of the alanine dipeptide by fitting the charges of each conformation to the respective ab initio electrostatic potential surfaces both individually and simultaneously, in both the united atom and the all-atom representations. Using these charge sets, the sensitivity of the relative conformational aqueous free energies to the atomic site charges is investigated. For this particular system, we find that the solute-water contributions to the conformational free energy differences have a rather weak dependence on site charges; the calculated intramolecular contributions, however, show a rather strong dependence on the atomic site charges. It is suggested that the calculated results for the alanine dipeptide using a single, simultaneously fit set of charges for both conformations are in better agreement with experiments than the calculations carried out with charges determined individually for each conformation. © 1997 John Wiley & Sons, Inc.Publication Metadata only 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; 23851A 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%.Publication Metadata only 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/AWe 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.