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

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.


Side view SEM image of the sapphire sample with opened nanochannels using single pulse illumination.The opening was made by FIB milling, and the depth of beam focus was linearly varied by 4 μm between each pulse. The incident laser beam direction is marked as the white arrow, and the depth variation is indicated as the white dashed line. The energy per pulse was 2 μJ at 140 fs and a wavelength of 800 nm.
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f2: Side view SEM image of the sapphire sample with opened nanochannels using single pulse illumination.The opening was made by FIB milling, and the depth of beam focus was linearly varied by 4 μm between each pulse. The incident laser beam direction is marked as the white arrow, and the depth variation is indicated as the white dashed line. The energy per pulse was 2 μJ at 140 fs and a wavelength of 800 nm.

Mentions: Figure 2 shows structures produced at varying input positions of the beam with respect to the surface. The spacing between the pulses used was 20 μm. No noticeable difference was observed in the void diameters obtained. However, we observed that the void with an exit hole (numbered #1) is slightly longer than the other ones by ~3 μm. This can be understood because of the smaller energy density necessary to remove material in this configuration compared to bulk focusing. The energy density threshold to evacuate the material is reached over a longer distance than for the bulk focusing.


High aspect ratio micro-explosions in the bulk of sapphire generated by femtosecond Bessel beams
Side view SEM image of the sapphire sample with opened nanochannels using single pulse illumination.The opening was made by FIB milling, and the depth of beam focus was linearly varied by 4 μm between each pulse. The incident laser beam direction is marked as the white arrow, and the depth variation is indicated as the white dashed line. The energy per pulse was 2 μJ at 140 fs and a wavelength of 800 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Side view SEM image of the sapphire sample with opened nanochannels using single pulse illumination.The opening was made by FIB milling, and the depth of beam focus was linearly varied by 4 μm between each pulse. The incident laser beam direction is marked as the white arrow, and the depth variation is indicated as the white dashed line. The energy per pulse was 2 μJ at 140 fs and a wavelength of 800 nm.
Mentions: Figure 2 shows structures produced at varying input positions of the beam with respect to the surface. The spacing between the pulses used was 20 μm. No noticeable difference was observed in the void diameters obtained. However, we observed that the void with an exit hole (numbered #1) is slightly longer than the other ones by ~3 μm. This can be understood because of the smaller energy density necessary to remove material in this configuration compared to bulk focusing. The energy density threshold to evacuate the material is reached over a longer distance than for the bulk focusing.

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.