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High aspect ratio micro-explosions in the bulk of sapphire generated by femtosecond Bessel beams

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ABSTRACT

Femtosecond pulses provide an extreme degree of confinement of light matter-interactions in high-bandgap materials because of the nonlinear nature of ionization. It was recognized very early on that a highly focused single pulse of only nanojoule energy could generate spherical voids in fused silica and sapphire crystal as the nanometric scale plasma generated has energy sufficient to compress the material around it and to generate new material phases. But the volumes of the nanometric void and of the compressed material are extremely small. Here we use single femtosecond pulses shaped into high-angle Bessel beams at microjoule energy, allowing for the creation of very high 100:1 aspect ratio voids in sapphire crystal, which is one of the hardest materials, twice as dense as glass. The void volume is 2 orders of magnitude higher than those created with Gaussian beams. Femtosecond and picosecond illumination regimes yield qualitatively different damage morphologies. These results open novel perspectives for laser processing and new materials synthesis by laser-induced compression.

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(a) SEM imaging of a nano-void inside sapphire created by a single 2 μJ femtosecond pulse. The structure is fully enclosed within the sapphire and has been opened by FIB milling. (b–d) Are magnified views of the void for the regions indicate in (a). The white dashed line corresponds to the cross section cut shown in Fig. 3 below.
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f1: (a) SEM imaging of a nano-void inside sapphire created by a single 2 μJ femtosecond pulse. The structure is fully enclosed within the sapphire and has been opened by FIB milling. (b–d) Are magnified views of the void for the regions indicate in (a). The white dashed line corresponds to the cross section cut shown in Fig. 3 below.

Mentions: Figure 1(a) shows a high resolution SEM image of a void created in the bulk of sapphire and opened by FIB milling. The void is ~300 nm in diameter and extends over 30 +/− 3 μm, with a progressive reduction of the diameter at the extremities. The large error bar is due to the difficulty of determining the boundaries of the void in the vertical direction. Figure 1(b–d) show magnified views of the inside of the channel: it is very clear that the channel is free from debris with vertical parallel walls. While damages and compression zone around the void are expected it appeared to be difficult to observe them with the SEM. The volume of the void is ~2 femtolitres, which is 2 orders of magnitude larger than the voids created from Gaussian beams (~10 attolitres)4.


High aspect ratio micro-explosions in the bulk of sapphire generated by femtosecond Bessel beams
(a) SEM imaging of a nano-void inside sapphire created by a single 2 μJ femtosecond pulse. The structure is fully enclosed within the sapphire and has been opened by FIB milling. (b–d) Are magnified views of the void for the regions indicate in (a). The white dashed line corresponds to the cross section cut shown in Fig. 3 below.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037470&req=5

f1: (a) SEM imaging of a nano-void inside sapphire created by a single 2 μJ femtosecond pulse. The structure is fully enclosed within the sapphire and has been opened by FIB milling. (b–d) Are magnified views of the void for the regions indicate in (a). The white dashed line corresponds to the cross section cut shown in Fig. 3 below.
Mentions: Figure 1(a) shows a high resolution SEM image of a void created in the bulk of sapphire and opened by FIB milling. The void is ~300 nm in diameter and extends over 30 +/− 3 μm, with a progressive reduction of the diameter at the extremities. The large error bar is due to the difficulty of determining the boundaries of the void in the vertical direction. Figure 1(b–d) show magnified views of the inside of the channel: it is very clear that the channel is free from debris with vertical parallel walls. While damages and compression zone around the void are expected it appeared to be difficult to observe them with the SEM. The volume of the void is ~2 femtolitres, which is 2 orders of magnitude larger than the voids created from Gaussian beams (~10 attolitres)4.

View Article: PubMed Central - PubMed

ABSTRACT

Femtosecond pulses provide an extreme degree of confinement of light matter-interactions in high-bandgap materials because of the nonlinear nature of ionization. It was recognized very early on that a highly focused single pulse of only nanojoule energy could generate spherical voids in fused silica and sapphire crystal as the nanometric scale plasma generated has energy sufficient to compress the material around it and to generate new material phases. But the volumes of the nanometric void and of the compressed material are extremely small. Here we use single femtosecond pulses shaped into high-angle Bessel beams at microjoule energy, allowing for the creation of very high 100:1 aspect ratio voids in sapphire crystal, which is one of the hardest materials, twice as dense as glass. The void volume is 2 orders of magnitude higher than those created with Gaussian beams. Femtosecond and picosecond illumination regimes yield qualitatively different damage morphologies. These results open novel perspectives for laser processing and new materials synthesis by laser-induced compression.

No MeSH data available.


Related in: MedlinePlus