Doğrusal olmayan yöntemler kullanılarak kızılaltı bölgesinde çalışan laser kaynaklarının geliştirilmesi

This thesis investigates the development of an efficient and robust femtosecond laser which produces mid infrared pulses by employing different mode locking techniques. In particular, Kerr lens mode locking and graphene saturable absorber mode locking techniques were successfully applied to the Cr:ZnSe laser which operates around 2.45 μm. In the second part of the thesis, linear and non-linear optical properties of a gated graphene based supercapacitor were experimentally characterized, and voltage dependent optical and ultrafast properties were discussed. The first part of the thesis is the demonstration of a Kerr lens mode-locked Cr:ZnSe laser and evaluation of the performance of four different cost-effective and practical dispersion compensation methods. The highest pulse energy was obtained with a 6% output coupler and a CaF2 prism pair, where as high as 1.81 nJ was obtained with 2 W of pump power. When a 1% output coupler was used with the CaF2 prism pair, higher intracavity energy led to the generation of pulses as short as 92 fs. Based on the mode locking parameters of the laser, the nonlinear refractive index (n2) of ZnSe was estimated as (1.2±0.2)×10−18 m2/W by using the soliton area theorem. The second part of the thesis involves the demonstration of graphene saturable absorber mode-locked operation of a stable femtosecond Cr:ZnSe laser. The laser produced 176-fs pulses at a repetition rate of 78 MHz with an average power of 80 mW. The measured time-bandwidth product was 0.39 with a 3% output coupler. With a 6% output coupler, 2.4-nJ, 200-fs pulses were generated near 2400 nm at a pulse repetition frequency of 78 MHz. The average mode-locked output power was 185 mW. This work was the first demonstration of a femtosecond Cr:ZnSe laser passively mode locked with a graphene saturable absorber. The third part of the thesis focuses on the optical characterization of graphene samples grown on quartz, YAG and CaF2. We determined the saturation fluence and modulation depth of the samples as 34 μJ/cm2 and 0.6%, 60 μJ/cm2 and 0.8%, 39 μJ/cm2 and 0.6% for graphene on quartz, YAG and CaF2, respectively. The final part is the linear and non-linear characterization of the optical properties of a voltage controlled saturable absorber based on graphene super capacitors. Pump-probe measurements revealed that the ultrafast response of the graphene has similar dynamics with an average fast and slow time constants of 283 fs and 1.9 ps up to 1V of applied voltage. The saturation fluence at 1250 nm monotonically increases with the applied bias, becoming 456 μJ/cm2 at 1V and the modulation depth decreases from 1.09% at 0V to 0.69% at 1V. Hence, the modulation depth of the device was adjusted in the range of 1.1-0.7%.Our results indicate that, utilization of cost effective dispersion techniques as well as novel saturable absorbers such as graphene will lead to the development of practical sources of mid-infrared femtosecond pulse sources suitable for spectroscopic, medical and nonlinear optical applications.