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Publication Open Access Angular-momentum-driven chaos in small clusters(American Physical Society (APS), 1998) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129The effects of the rotational motion on the chaotic behavior of triatomic Lennard-Jones clusters are studied. A set of initial momentum distributions with tunable parameters is chosen to correspond to various rigid-body rotations around symmetry axes of the cluster. By smoothly varying the direction of the initial kicks given to the cluster, periodic transitions between regular and chaotic regimes are obtained. A study of initial conditions leading up to such transitions shows that the major factor that determines the extent of the chaotic behavior is the initial partitioning of the kinetic energy between the rotational and vibrational motion. From the analysis of the time evolution of various properties it is concluded that the basic role of this initial partitioning is to control the energy transfer between the kinetic and the potential energy.Publication Open Access Chaotic behavior of triatomic clusters(American Physical Society (APS), 1997) Elmacı, N.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129The dynamics of triatomic clusters is investigated employing two-body Lennard-Jones and three-body Axilrod-Teller potential functions. Lyapunov exponents are calculated for the total energy range of -2.70 epsilon <E< -0.72 epsilon. The effects of the initial geometry of the cluster, its angular momentum, and the magnitude of three-body interactions are analyzed. It has been found that the dominating factor for the extent of chaotic behavior is the energy assigned to vibrational modes. The introduction of the rotational motion regularizes the dynamics in spite of a higher degree of nonlinearity. The three-body terms in the potential function affect the extent of the chaos in different manners depending on the initial geometry of the cluster. Finally, the time evolution of heterogeneous clusters generated by varying the size, mass, and the interaction strength of a single atom is observed. Their Lyapunov exponent spectra show that the additional nonlinearity reduces the chaotic behavior of the system in most of the cases.Publication Open Access Comment on “Identical motion in classical and quantum mechanics”(American Physical Society (APS), 1999) Department of Mathematics; Department of Physics; Mostafazadeh, Ali; Faculty Member; Department of Mathematics; Department of Physics; College of Sciences; 4231Makowski and Konkel [Phys. Rev. A 58, 4975 (1998)] have obtained certain classes of potentials which lead to identical classical and quantum Hamilton-Jacobi equations. We obtain the most general form of these potentials.
Publication Metadata only Comparative experimental investigation of thermal loading in continuous-wave cr4+: forsterite lasers(Optical Society of America (OSA), 1998) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851Results of a detailed experimental study aimed at reducing the thermal loading effects in room-temperature continuous-wave Cr4+:forsterite lasers are presented. By using a Nd:YAG pump laser operated at 1.06 mu m, the effect of the absorption coefficient and crystal cross-sectional area on the power performance of three crystals was compared between 12 and 36 degrees C. Experiments indicated that a low differential absorption coefficient significantly reduces the pump-induced thermal effects and cavity losses that would otherwise give rise to inefficient operation and increased temperature sensitivity. In particular, a Cr4+:forsterite crystal with an absorption coefficient of 0.57 cm(-1) yielded as much as 900 mW of output power at 1.26 mu m and a crystal temperature of 15 degrees C with an incident pump power of only 7.6 W. To the author's knowledge, the demonstrated slope efficiency of 30% represents the highest continuous-wave power performance reported to date from this laser system at elevated temperatures. (C) 1998 Optical Society of America.Publication Metadata only Continuous wave thermal loading in saturable absorbers: theory and experiment(Optical Society of America (OSA), 1997) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851Theoretical and experimental results of a study that investigates cw thermal loading in solid-state saturable absorbers with low heat conductivities are presented. In addition to the temperature dependence of the refractive index, the proposed model considers the temperature dependence of the fluorescence lifetime to account for the local variations in the saturation intensity resulting from thermal gradients. In the calculations an iterative scheme is employed to calculate first the temperature distribution produced by the pump beam subject to saturable absorption with a constant saturation intensity and then the resulting modifications in the propagation parameters that are due to the presence of the calculated temperature distribution. Excellent agreement is obtained between the numerically calculated results and experimentally measured cw transmission data obtained with use of a Cr:YAG saturable absorber. Because the absorption cross section of the medium is used as one of the fitting parameters to yield the best fit between theory and experiment, the model further offers an accurate method whereby the cw power transmission data can be used to determine the absorption cross section of a saturable absorber subject to thermal loading. (C) 1997 Optical Society of America.Publication Metadata only Continuous-wave operation of a 3.5-W diode-pumped Nd : YVO4 laser at 1342 nm(Optical Society of America (OSA), 1999) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851Different end pumping configurations were used to investigate the continuous-wave power performance of a diode-pumped Nd:YVO4 laser at 1342 nm. By using a high-power diode array at 806 run, A compact resonator with a 3.6% transmitting output coupler produced as high as 3550 mW of continuous-wave output power with an absorbed power slope efficiency of 28.1%. the focal length of the pump-induced thermal lens was measured as a function of the absorbed pump power. Results further showed that the laser output was insensitive to variations in the crystal boundary temperature between 20 and 40 degreesC.Publication Metadata only 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; 23851Rate-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.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.Publication Metadata only Determination of the optimum absorption coefficient in Cr4+: forsterite lasers under thermal loading: errata(Optical Soc Amer, 1999) 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/AIn our recent Letter,[1] in which we analyzed the effects of thermal loading in room-temperature Cr4+:forsterite lasers, a scaling error was made in the best-fit and optimization calculations. In the comparison of theory with experiment (Fig. 2), the correct best-fit value of the stimulated-emission cross section 𝜎𝑒 should have been 0.98×10−19 cm2. In addition, the correct optimum value of the small-signal absorption coefficient that minimizes the incident threshold pump power (see Fig. 3) should have been 0.34 cm−1, corresponding to a net unsaturated pump absorption of 49% for a 2-cm-long crystal. The corrections did not affect any of the trends predicted by the theory.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.
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