Laser shaping of diamond for IR diffractive optical elements

Abstract

Recently a new technique for laser-induced generation of phase relief to manufacture diamond diffractive lenses for the mid IR range has been proposed. In the present paper the realization of more complicated diamond diffractive optical elements (DOEs) is considered, able to transform a CO2 laser beam into arbitrary pre-given focal domains. Two DOEs for completely different tasks of laser beam focusing have been manufactured and finally investigated by means of various optical techniques. Measured intensity distributions in the DOEs focal planes as well as diffraction efficiencies have been compared with related results of computer simulation, and have been found to be in a good mutual concordance. The obtained results indicate that laser ablation technique can be effectively used to manufacture high quality diamond DOEs for laser beam focusing. Special attention is paid to the diamond surface graphitization in the process of laser ablation. Main parameters of excimer laser ablation are investigated and density of laser-induced graphite-like layer is defined. It was demonstrated experimentally that graphitized layer formed at different regimes of irradiation remains almost constant in thickness, but has different crystal structure.

High-damage-threshold antireflection coatings on diamond for CW and pulsed CO2lasers

“…With prolonged continuous irradiation (more than 100 s), no signs of destruction or damage were observed on the surface of the antireflection coating throughout the available intensity range. The intensities that the coatings have withstood are comparable with the results on the radiation resistance of uncoated polycrystalline diamond windows in [1] and significantly exceed the peak intensities of ~100 kW cm −2 for DOEs [2]. The difference in damage thresholds in [1,2] can be related to the fact that in [2] part of radiation was absorbed in a graphitized surface layer.…”

“…The intensities that the coatings have withstood are comparable with the results on the radiation resistance of uncoated polycrystalline diamond windows in [1] and significantly exceed the peak intensities of ~100 kW cm −2 for DOEs [2]. The difference in damage thresholds in [1,2] can be related to the fact that in [2] part of radiation was absorbed in a graphitized surface layer. Such a layer appears in the process of diamond surface ablative microstructuring by excimer KrF laser and partially remains on the surface even after thermal annealing in an air atmosphere.…”

“…It was found that CVD diamond can withstand extremely high radiation loads. For example, it was shown that watercooled diamond windows [1] can operate at intensities of a coherent-wave (CW) CO 2 laser up to 2 MW cm −2 , while diamond DOEs [2] retained their functional ability at radiation intensities of 50 -100 kW cm −2 . In the case of a shorter wavelength (λ ≈ 1 µm [3]) of CW radiation, the damage threshold of diamond windows increases up to ≈10 MW cm −2 .…”

“…Besides, the above-mentioned methods of surface post-growth processing cannot be used for bleaching of a shaped diamond (curved) surface, e.g. a DOE [2,[5][6][7], which fundamentally limits the prospects for their practical use. An alternative approach, consisting of applying thin-film antireflection coatings, is free of such a disadvantage and can be applied to both flat and structured diamond surfaces.…”

Pulsed femtosecond-laser Machining and deep reactive ion etching of diamond

“…Diamond is a well-studied material, with many favorable attributes for numerous applications [1][2][3][4][5]. In reference to the use of lasers on diamond substrates, the applications have included surface treatments [6][7][8], growth and ablation/etching of diamond [9][10][11], diffraction gratings and other elements for high power optical systems [12][13][14], and graphitic/conductive channel formation [8,[15][16][17][18][19][20][21]. The potential for directly writing conductive channels onto or into diamond for electronic applications is appealing, given the potential speed and high-dielectric constant of diamond, which are utilized in applications such as high-power switches [4].…”