Malzeme karakterizasyonu için yakın ve orta kızılaltı darbeli lazerlerin geliştirilmesi

This thesis investigates the experimental development of novel advanced pulsed lasers in the near and mid infrared and use of pulsed lasers in the optical characterization of quantum dots. In particular, the development of solitary and chirped-pulse Cr4+:Forsterite laser, Nd doped tellurite glass laser and continuous-wave injection-seeded gain-switched Cr:ZnSe laser was investigated. In the second part, pulsed Ti:sapphire lasers operated in the nanosecond and femtosecond regimes were used to measure the two-photon absorption characteristics of CdTe-CdS quantum dots.The first part of the thesis focuses on the experimental demonstration of a mode-locked, low-threshold, room-temperature, multipass-cavity femtosecond Cr4+:Forsterite laser. The repetition rate was lowered to 11.7 MHz by introducing a q-preserving multipass cavity. Pulse formation could be achieved by using the Kerr-lens mode-locking technique. Nearly transform-limited 5.1-nJ pulses with a duration of 68 fs were generated at an output power of only 60 mW. Furthermore, as short as 41-fs pulses could be obtained with a pulse energy of 3.4 nJ at an absorbed pump power of only 1.1 W.In the second part of the thesis, the Cr4+:Forsterite laser was operated in the positive dispersion regime. We obtained record 81-nJ pulses directly from the Cr4+:Forsterite oscillator at a pulse repetition rate of 4.9 MHz. In that case, pulse duration at the output was 5.5 ps. By using an external grating compressor , the pulses were then compressed to 607 fs. High-energy mode-locked oscillators operating in this wavelength range should be important in various biomedical applications including deep-tissue multi-photon microscopy as well optical coherence tomography.In the third part, lasing action in a novel, neodymium-doped tellurite-based glass with the host composition (0.8)TeO2-(0.2)WO3 was demonstrated. To our best knowledge, this is the first time laser operation from Nd:Tellurite glass with this composition was reported in the literature. During gain switched operation, the glass laser produced 11 µJ of output energy at 1065 nm with 114 µJ of pump energy. The slope efficiency with respect to the incident energy was 12%. Then, the laser was operated at 1370 nm by using the other laser transition of the Nd3+ ion . To our best knowledge, lasing action at 1370 nm was demonstrated for the first time in a bulk tellurite glass host for the energy transition 4F3/2?4I13/2 of the Nd3+ ion. The laser was operated in gain-switched regime at 1 kHz with a threshold pulse energy of 59 ? J. The slope efficiency was further determined to be 5.5 %. As high as 6 ? J-pulses with a duration of 1.74 ? s were obtained. From the threshold analysis, the emission cross section came to 1.57 x 10-20 cm2 in the presence of excited-state absorption. These results indicate that doped tellurite glasses have the potential of being used in the development of efficient bulk glass lasers and fiber lasers in the near infrared.In the fourth part of the thesis, we reported a narrow-linewidth, tunable, gain-switched Cr:ZnSe laser operating between 2255 and 2455 nm. The spectral width of the laser was reduced from 125 nm to 0.65 nm by using injection seeding. Seeding was achieved with another tunable, continuous-wave Cr:ZnSe laser. The wavelength of the laser was controlled by tuning the wavelength of the seed laser. The seeded gain-switched oscillator produced as high as 157 µJ-pulses with 598 µJ incident pump pulse energy at a repetition rate of 1 kHz.Finally, we demonstrated an application of pulsed Ti:sapphire lasers in the optical characterization of quantum dots. By using pulse lasers, we analyzed the two-photon absorption and resulting emission of core-shell CdTe-CdS q-dots. We showed that emission strength of the sample was independent of the wavelength of the pump laser in the range of 740-860 nm. Moreover, we found out the luminescence efficiency to be 60.7 % with respect to Rodamin 6G. Furthermore, the two-photon absorption cross-section was determined to be 4.1x106 GM.