Isinsu Baylam

Femtosecond pulse generation with voltage-controlled graphene saturable absorber.

We report, for the first time to our knowledge, the demonstration of a graphene supercapacitor as a voltage-controlled saturable absorber for femtosecond pulse generation from a solid-state laser. By applying only a few volts of bias, the Fermi level of the device could be shifted to vary the insertion loss, while maintaining a sufficient level of saturable absorption to initiate mode-locked operation. The graphene supercapacitor was operated at bias voltages of 0.5-1V to generate sub-100 fs pulses at a pulse repetition rate of 4.51 MHz from a multipass-cavity Cr(4+):forsterite laser operating at 1255 nm. The nonlinear optical response of the graphene supercapacitor was further investigated by using pump-probe spectroscopy.

Energy scaling of a carbon nanotube saturable absorber mode-locked femtosecond bulk laser

We report successful energy scaling of a room-temperature femtosecond Cr4+: forsterite laser by using a single-walled carbon nanotube saturable absorber (SWCNT-SA). By incorporating a q-preserving multipass cavity, a repetition rate of 4.51 MHz was realized, and the oscillator produced 121 fs, 10 nJ pulses at 1247 nm, with an average output power of 46 mW. To the best of our knowledge, the peak power of 84 kW is the highest generated to date from a SWCNT-SA mode-locked oscillator. Furthermore, energy scaling of a femtosecond multipass-cavity laser, mode-locked using a SWCNT-SA, is demonstrated for the first time.

Graphene-gold supercapacitor as a voltage controlled saturable absorber for femtosecond pulse generation.

For the first time to our knowledge, we employed a graphene supercapacitor as a voltage controlled saturable absorber at bias voltages of 0.5-1V to generate 84-fs pulses from a solid-state laser near 1255 nm.

Femtosecond pulse generation from a Ti^3+:sapphire laser near 800 nm with voltage reconfigurable graphene saturable absorbers

We experimentally show that a voltage-controlled graphene-gold supercapacitor saturable absorber (VCG-gold-SA) can be operated as a fast saturable absorber with adjustable linear absorption at wavelengths as low as 795 nm. This was made possible by the use of a novel supercapacitor architecture, consisting of a high-dielectric electrolyte sandwiched between a graphene and a gold electrode. The high-dielectric electrolyte allowed continuous, reversible adjustment of the Fermi level and, hence, the optical loss of the VCG-gold-SA up to the visible wavelengths at low bias voltages of the order of a few volts (0-2 V). The fast saturable absorber action of the VCG-gold-SA and the bias-dependent reduction of its loss were successfully demonstrated inside a femtosecond Ti3+:sapphire laser operating near 800 nm. Dispersion compensation was employed by using dispersion control mirrors and a prism pair. At a bias voltage of 1.2 V, the laser operated with improved power performance in comparison with that at zero bias, and the VCG-gold-SA initiated the generation of nearly transform-limited pulses as short as 48 fs at a pulse repetition rate of 131.7 MHz near 830 nm. To the best of our knowledge, this represents the shortest wavelength where a VCG-gold-SA has been employed as a mode locker with adjustable loss.

Graphene-Gold Supercapacitor As a Voltage-Controlled Saturable Absorber for Femtosecond Pulse Generation

We report, for the first time to our knowledge, a voltage-controlled graphene-gold supercapacitor saturable absorber, as a modulator with adjustable insertion loss for low-gain mode-locked lasers. Nearly transform-limited, 80-fs pulses were generated near 1240 nm.

Energy scaling of a multipass-cavity mode-locked femtosecond bulk laser with a carbon nanotube saturable absorber

In the design of mode-locked lasers, single-walled carbon nanotube saturable absorbers (SWCNT-SAs) have emerged as important alternatives to semiconductor saturable absorber mirrors (SESAMs) due to their favorable optical characteristics, low cost, and relatively simple fabrication scheme. Therefore, it is of great interest to explore the limits of energy scaling in solid-state lasers mode-locked with SWCNT-SAs. Due to their unique wavelength range for biomedical applications, a room-temperature Cr4+:forsterite laser operating near 1.3 μm was used in the mode-locking experiments. The laser was end-pumped with a continuous-wave Yb-fiber laser at 1064 nm. Furthermore, a q-preserving multipass-cavity (MPC) was added to the short resonator to lower the pulse repetition rate to 4.51 MHz and to scale up the output pulse energy at low average power. The SWCNT-SA was fabricated with SWCNTs grown by the highpressure CO conversion (HiPCO) technique. With dispersion compensation optics, the net group delay dispersion of the resonator was estimated to be around -4440 fs2. When mode-locked with the SWCNT-SA, the resonator produced 10-nJ, 121-fs pulses at 1247 nm with a spectral bandwidth of 16 nm, corresponding to a time-bandwidth product of 0.37. To our knowledge, this represents the highest peak power (84 kW) generated to date from a bulk femtosecond solid-state laser, mode-locked by using a SWCNT-SA. The results also suggest that the peak power achieved in our experiments was limited only by the self-focusing in the Cr4+:forsterite gain medium and further increase in output energy should in principle be possible in other gain media mode-locked with SWCNT-SAs.