Strong optical nonlinearity of ultrathin graphitic films synthesized on dielectric substrates

Abstract

We propose and demonstrate a scalable technique to grow a thin polycrystalline graphitic film directly onto a fused silica substrate. The technique is based on the pyrolysis of a photoresist in the presence of a sacrificial 10 nm thick nickel catalyst layer. The synthesized graphitic film with a thickness of about 50 nm possesses almost constant 40% absorptance over visual and near infrared spectral regions. By using Raman characterization, third harmonic generation spectroscopy, and the Z-scan technique we perform a comparative study of the films pyrolyzed with and without a Ni catalyst. We show that the amorphous carbon dominates the linear and nonlinear optical properties of the resist film pyrolyzed without the Ni catalyst. In contrast, in presence of a Ni catalyst layer, the pyrolysis leads to a graphitic film that demonstrates a strong saturable absorption behavior at 1550 nm wavelength and has a nonlinear refractive index comparable with that of graphene. Thus, the developed, transfer-free synthesis technique provides an alternative route towards the controllable growth of wafer scale graphitic films on the dielectric substrates for photonics applications.

Electrical, Transport, and Optical Properties of Multifunctional Graphitic Films Synthesized on Dielectric Surfaces by Nickel Nanolayer-Assisted Pyrolysis

“…Under pump fluence of 625 MW/cm 2 we observed about 1.5 % change in transmittance in both GRF(Ni+) and GRF (Ni-) samples. No pronounced ΔT/T signal was obtained from PPF in agreement with our earlier studies of amorphous carbon films 17,33 . The biexponential fitting of normalized ΔT/T kinetics taken at 1300 nm probe wavelength revealed fast and slow components associated with intra-(T1) and interband (T2) relaxation: T1 (Ni+) = (450 ± 60) fs , T1 (Ni-) = (320 ± 50) fs and T2 (Ni+) = (2500 ± 150) fs, T2 (Ni-) = (1850 ± 120) fs for GRF(Ni+) and GRF(Ni-), respectively.…”

“…In the experiment, we used 1 kHz repetition rate and a fluence of about 100 μJ/cm 2 at the peak irradiance of 625 MW/cm 2 . It is 1 order of magnitude below the level when two-photon absorption can be observed and 2 orders of magnitude lower than the optical damage threshold of the GRF . The time delay between the probe and pump pulses was controlled by a rapid motorized delay line.…”

“…Specifically, it has been shown that pyrolysis at the temperature of 800 °C transforms several hundred nanometers thick photoresist layer into tens of nanometers thick GRF embedded with Ni nanoparticles . Such ultrathin GRFs have already exhibited an impressive performance in surface-enhanced Raman spectroscopy and nonlinear optics, , although relationship between their properties and synthesis conditions is still unclear.…”

Coherent Detection of Terahertz Radiation with Graphene

“…It is worth noticing that the synthesis of GRF ribbons is a wafer-scale process and the number of THz detectors was limited by the size of the Ni–Au electrodes. A detailed description of the transfer-free synthesis and characterization of the ultrathin graphitic material is presented in the Supporting Information and in refs and . The image of 15 detectors on a 0.5 mm thick fused silica substrate is shown in Figure .…”

Biomedical Optical Sensors

“…To simultaneously image various fluorophores with optimum sensitivity and selectivity, a multiwavelength femtosecond source is required. Such a multiphoton microscope design will expand its applications in genetics (DNA sequencing) [22], [23], analyzing neural network architecture [24], examining various immune cells behavior [25], [26], tracking tumor cell [27], and material characterization and processing [28]- [30]. To make a compact and flexible endoscope, we need to miniaturize the scanning mechanism, optical system, signal collection assembly and femtosecond laser.…”