Self-Saturable Absorption and Reverse-Saturable Absorption Effects in Diamond-Like Carbon Films with Embedded Copper Nanoparticles

Abstract

Nonlinear optical properties (self-saturable absorption and reverse-saturable absorption) of diamond-like carbon films with variable amounts of embedded copper nanoparticle (DLC:Cu) films deposited by high power pulse magnetron sputtering were studied in dependence on deposition conditions. X-ray photoelectron spectroscopy was used to study elemental composition and He ion microscopy to study changes of the size, shape, and concentration of the Cu nanoparticles deposited using different pulse currents as well as argon and acetylene gas ratios. Raman scattering spectra of DLC:Cu films studied were typical of diamond-like carbon (including the films with a high Cu atomic concentration where it was up to 60 atom % and carbon atomic concentration was less than 20 atom %). In all cases, in the absorption spectra of DLC:Cu films, the surface plasmon resonance-related peak was recorded. The position of the plasmonic peak for all the deposited nanocomposite films was in a 590–620 nm range. For the samples containing lower amounts of copper, reverse-saturable absorption was found. Transient optical absorption measurements have shown that the reverse-saturable absorption is typical for the samples with a lower relaxation time. The longer relaxation times recorded during transient optical absorption measurements correlated with the presence of the saturable absorption effect. For DLC:Cu samples containing 58–62 atom % Cu, some optical inhomogeneities were observed. The samples in different places demonstrated either saturable absorption or reverse-saturable absorption. The presence of both saturable and reverse-saturable absorption effects in the same sample is explained by the lateral inhomogeneities of the DLC:Cu films.

Hydrogen-Free Diamond Like Carbon Films with Embedded Cu Nanoparticles: Structure, Composition and Reverse Saturable Absorption Effect

“…It must be noted that such a result is in accordance with the recent findings. In [8], the Raman scattering spectra of the hydrogenated amorphous carbon and copper nanocomposites were typical for DLC, even in the case when carbon atomic concentration in the films was 20 at.%. In [19], Raman scattering spectra that are typical for DLC were reported for amorphous carbon films containing 50 at.% of copper.…”

“…The nonlinear reflectance was also acquired at 1064 nm. More details on the measurement setup used may found elsewhere [8,14].…”

“…For the hydrogenated DLC:Cu films containing 22 at.% of copper, plasmonic peak was clearly seen. In addition, plasmonic absorbance peaks of the hydrogen-free DLC:Cu films are broader and redshifted in comparison with the hydrogenated ones (data on hydrogenated DLC:Cu films, please see in [8,26]). Figure 9 illustrates the typical dependencies of the normalized reflectance of selected samples on laser fluence.…”

“…Particularly, it was supposed that embedding diamond-like carbon particles to the film used for nonlinear optical applications might improve the saturable absorption effect (i.e., larger increase of a light transmittance with increased light beam intensity) [7]. Saturable and reverse saturable absorption phenomena were both observed in hydrogenated diamond like carbon films with embedded Cu nanoparticles (DLC:Cu) [8]. DLC films became a very interesting alternative for presently used nonlinear optical materials, such as semiconductor self saturable absorber mirrors [9], plasmonic nanoparticles of group IB metals (Au, Ag or Cu) [10,11], graphene [9], or carbon nanotubes [12], due to the beneficial combination of the mechanical and optical properties mentioned above as well as room temperature deposition possibility.…”

“…DLC films became a very interesting alternative for presently used nonlinear optical materials, such as semiconductor self saturable absorber mirrors [9], plasmonic nanoparticles of group IB metals (Au, Ag or Cu) [10,11], graphene [9], or carbon nanotubes [12], due to the beneficial combination of the mechanical and optical properties mentioned above as well as room temperature deposition possibility. However, as mentioned above, there are only few studies on diamond like carbon as a nonlinear optical material [8].…”