Grafen-tabanlı hızlı doyabilen soğurucular ve katıhal lazerlerinin kip-kilitlenmesindeki uygulamaları

Graphene and other carbon-based nanomaterials have emerged as alternative saturable absorbers to other semiconductor saturable absorbers due to their favorable optical characteristics and relatively simple growth schemes. It has been demonstrated that the graphene saturable absorbers (GSAs), can be used as effective modulators to generate femtosecond pulses from lasers, operating in the near and mid infrared. Therefore, it is of great interest to explore the mode locking performance of the GSAs, grown on different substrates, in power-scaled lasers. However, one possible drawback of a monolayer graphene saturable absorber stems from its small-signal optical insertion loss of 5%, which leads to challenges in operating low gain lasers. Such challenges can be obviated by using graphene-based supercapacitor structures so that when a voltage bias is applied, the Fermi level of graphene can be shifted to reduce the absorption via Pauli blocking. The first part of this thesis focuses on the linear and nonlinear optical characterization of the GSAs grown on different substrates (quartz and YAG) and their application to mode locking of an energy-scaled multipass-cavity (MPC) Cr4+:forsterite laser operating near 1250 nm. The Cr4+:forsterite resonator, mode-locked with the GSA on quartz or the GSA on YAG, produced nearly transform-limited pulses with sub-100 fs durations and 53-kW pulse peak powers. To the best of our knowledge, both results report the highest peak powers obtained from a GSA mode-locked femtosecond solid-state laser. The remaining parts of this thesis investigate the optical characterizations and mode locking applications of the graphene-based supercapacitors as fast saturable absorbers with voltage-controllable optical insertion losses. The first supercapacitor design (voltage-controlled graphene saturable absorber, VCG-SA) consisted of a high dielectric electrolyte, sandwiched between two graphene electrodes. Linear and non-linear optical characterizations of the device were performed to explore its voltage-dependent optical properties and the results indicated that the supercapacitor architecture enabled the modulation of absorption up to the visible region (2.4 eV) even with few volts (0-3V) of applied bias. The VCG-SA was further employed in the MPC Cr4+:forsterite laser to investigate the voltage-dependent mode-locked operation. The MPC Cr4+: forsterite laser produced, 84-fs pulses with a time-bandwidth product of 0.32 at 1V of applied bias. To further reduce the insertion losses at zero bias, a second graphene-based supercapacitor architecture with the same electrolyte sandwiched between a graphene and a notched gold electrode was fabricated. Mode locking performance of the voltage-controlled graphene-gold saturable absorber (VCG-gold-SA) was investigated again in the MPC Cr4+:forsterite laser, operating near 1250 nm. Since one of the graphene electrodes of the previous design was replaced with a notched gold electrode, the optical insertion loss of the VCG-gold-SA was reduced at zero bias with respect to the previous design involving two graphene electrodes. In this case, the resonator generated 80-fs nearly transform-limited pulses with a pulse peak power of 42 kW at 0.8V of applied bias. Finally, to push the mode locking capability of these supercapacitor devices to as low a wavelength as possible, a Ti3+:sapphire laser, operating near 800 nm was used. The Ti3+:sapphire resonator successfully produced femtosecond pulses at wavelengths as short as 795 nm. To our knowledge, this is the shortest wavelength, where a graphene-based supercapacitor was used as a fast saturable absorber to generate femtosecond pulses. The novel graphene supercapacitor devices, first demonstrated as fast saturable absorbers in this thesis, have the potential to be used for femtosecond pulse generation from lasers operating over a broad wavelength range and with different levels of gain.