Optical properties of femtosecond laser-treated diamond

Abstract

A laser-induced periodic surface structure (LIPSS) has been fabricated on polycrystalline diamond by an ultrashort Ti:Sapphire pulsed laser source (k = 800 nm, P = 3 mJ, 100 fs) in a high vacuum chamber (\10 -7 mbar) in order to increase diamond absorption in the visible and infrared wavelength ranges. A horizontally polarized laser beam had been focussed perpendicularly to the diamond surface and diamond target had been moved by an automated X-Y translational stage along the two directions orthogonal to the optical axis. Scanning electron microscopy of samples reveals an LIPSS with a ripple period of about 170 nm, shorter than the laser wavelength. Raman spectra of processed sample do not point out any evident sp 2 content, and diamond peak presents a right shift, indicating a compressive stress. The investigation of optical properties of fs-laser surface textured diamond is reported. Spectral photometry in the range 200/2,000 nm wavelength shows a significant increase of visible and infrared absorption (more than 80 %) compared to untreated specimens (less than 40 %). The analysis of optical characterization data highlights a close relationship between fabricated LIPSS and absorption properties, confirming the optical effectiveness of such a treatment as a light-trapping structure for diamond: these properties, reported for the first time, open the path for new applications of CVD diamond.

Large-area fabrication of low- and high-spatial-frequency laser-induced periodic surface structures on carbon fibers

“…The photograph reveals that the areas containing HSFL appear darker than the non-structured areas under illumination with white light. This can be explained based on the results reported by Calvani et al concerning the optical properties of HSFL on fs-laser treated diamond[36]. Total transmission and reflection measurements using an integrating sphere demonstrated that HSFL…”

“…9 Based on the findings concerning the formation of HSFL in dependence on F, we used F = 0.7 J/cm 2 with  = (170  10) nm enhance light trapping so that absorbance strongly increases to a maximum of about 80% in a wide spectral range, in particular in the visible and IR spectral ranges. In these investigations, the increased absorbance was shown to be mainly correlated to a decreased reflectance of the materials surface [36]. Moreover, contributions by scattering effects at the sub-wavelength structures cannot be excluded here.…”

Solar energy conversion with photon-enhanced thermionic emission

“…Absorption of sunlight in a polycrystalline diamond film is significant, but highly selective towards higher energy photons [47]. It is possible to increase absorption by modifying the surface of polycrystalline diamond with femtosecond laser pulses, creating ripples with controllable magnitude and spacing [52]. Absorptance of 0.8-0.9 was measured for the treated diamond in the wavelength range of 200-2000 nm, compared to <0.4 in most of this spectral range for the untreated material.…”

Defect engineering of diamond cathodes for high temperature solar cells

“…On its directly illuminated surface, periodic textured structures with periodicity of hundreds of nanometers, comparable to the solar radiation wavelengths, are developed. It was demonstrated that 1D textures drastically increase the diamond solar absorptance from 20% to values >90% [8]. The absorbed radiation heats the photocathode at a temperature not exceeding 800 °C to avoid hydrogen desorption from diamond surface.…”

“…the absorptance integrated over all the solar spectrum) > 90 % [8,18]. In addition to a pure optical trapping mechanism, the surface texturing introduces in the diamond bandgap a broad peak of defect energy states acting as traps [9].…”