Research Outputs
Permanent URI for this communityhttps://hdl.handle.net/20.500.14288/2
Browse
7 results
Search Results
Publication Restricted Development of near infrared emitting cationic Ag2S quantum dots as drug-gene delivery and optical imaging agents(Koç University, 2017) Duman, Fatma Demir; Acar, Havva Funda Yağcı; 0000-0001-5601-8814; Koç University Graduate School of Sciences and Engineering; Materials Science and Engineering; 178902Publication Restricted Development of ultrasmall near infrared emitting colloidal PbS and PbS/CdS quantum dots with enhanced stability in liquid petroleum products(Koç University, 2019) Durmuşoğlu, Emek Göksu; Acar, Havva Funda Yağcı; 0000-0001-5601-8814; Koç University Graduate School of Sciences and Engineering; Materials Science and Engineering; 178902
Publication Metadata only Direct experimental determination of the optimum chromium concentration in continuous-wave Cr2(+): ZnSe lasers(Institute of Electrical and Electronics Engineers (IEEE), 2007) Demirbaş, Ümit; Department of Physics; Department of Chemistry; Department of Chemistry; Sennaroğlu, Alphan; Somer, Mehmet Suat; Kurt, Adnan; Faculty Member; Faculty Member; Teaching Faculty; Department of Physics; Department of Chemistry; College of Sciences; College of Sciences; College of Sciences; 23851; 178882; 194455We employed several experimental techniques to measure the concentration dependence of the important laser parameters, and directly determine the optimum ion concentration for continuous-wave (CW) operation in room temperature Cr2+:ZnSe lasers. By using diffusion doping, 40 polycrystalline Cr2+ :ZnSe samples with ion concentrations in the range of 0.8 x 10(18) to 66 x 10(18) ions/cm(3) were prepared and used in this paper. Based on the spectroscopic measurements, empirical formulae showing the concentration dependence of the passive laser losses, fluorescence lifetime, and the fluorescence efficiency were obtained. By using the fluorescence efficiency data, the optimum chromium concentration, which maximizes the 2400-nm fluorescence intensity at a fixed excitation power, was determined to be 6 x 10(18) ions/cm(3). The dependence of the optimum concentration on sample length was further discussed. The CW power performance of the samples was also evaluated. At an incident pump power of 2.1 W, the optimum concentration for lasing was determined to be 8.5 X 10(18) ions/cm' that was in good agreement with the fluorescence measurements. The predictions of the fluorescence analysis and laser power measurements were in good agreement at low chromium concentrations. The observed discrepancy at higher doping levels was attributed to thermal loading.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 Restricted InP quantum dot based light-emitting and neuro-stimulating optoelectronic devices(Koç University, 2019) Karatüm, Onuralp; Nizamoğlu, Sedat; 0000-0003-0394-5790; Koç University Graduate School of Sciences and Engineering; Electrical and Electronics Engineering; 130295Publication Metadata only Low-threshold diode-pumped 2.3-mu m Tm3+:YLF lasers(IEEE-Inst Electrical Electronics Engineers Inc, 2018) N/A; Department of Physics; Yorulmaz, İsmail; Sennaroğlu, Alphan; PhD Student; Faculty Member; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; N/A; 23851We demonstrate low-threshold diode-pumped operation of a continuous-wave Tm3+:YLF laser near 2.3 mu m and provide a detailed experimental investigation of its lasing characteristics. A narrow-line, tunable Ti3+:sapphire laser was first used to measure the excitation spectrum and investigate the absorption saturation behavior of the 1.5 at.% Tm3+:YLF gain medium. A single-mode, 120-mW laser diode operating at 792 nm was then used as a pump source to demonstrate low-threshold lasing at 2.3 mu m. With a 1% output coupler, diode-pumped operation could be obtained with as low as 25 mW of incident threshold pump power. With 119 mW of pump power, as high as 10.5 mW of out-put power could be obtained at 2305 nm with a slope efficiency of 11.4%. By using a second, 250-mW laser diode, a resonator with variable output coupling was constructed to measure the threshold pump power and power slope efficiency as a function of output coupling. The minimum threshold pump power at output coupling levels approaching 0% was measured to be 4 mW. Results further showed that the slope efficiency decreased with increasing output coupling beyond 0.7%. The stimulated emission cross section at 2305 nm was further determined to be 0.68 x 10(-20) cm(2) from lasing threshold data.Publication Restricted Spectroscopic investigation of CdS quantum dots and Fe2+: ZnSe(Koç University, 2007) Erdamar, Ahmet Koray; Sennaroğlu, Alphan; 0000-0003-4391-0189; Koç University Graduate School of Sciences and Engineering; Physics; 23851