Femtosecond laser writing of phase-tuned volume gratings for symmetry control in 3D photonic crystal holographic lithography

Abstract

Volume diffractive optical elements promise widespread application in laser beam shaping, imaging and optical data storage by structuring refractive index modulation in the third axial dimension. Femtosecond laser direct writing has been exploited inside fused silica to assemble multiple 1D grating layers on Talbot planes and overcome the inherent weak diffraction efficiency otherwise found in low-contrast volume gratings. Here, we extend laser structuring from linear (1D) to orthogonally crossed (2D) gratings with the aim to write 3D photonic crystal templates in photoresist by 3D interference lithography. The formation of crossed grating structures present challenges in balancing the efficiency of diffraction orders owing to blazing and index overwriting effects requiring compensation by tuning the grating design and laser power exposure. In this way, six-layer grating designs have been fabricated and applied to exposure of thick photoresist, enabling the formation of 3D photonic crystal templates with bicontinuous structure. A systematic offsetting of orthogonal grating layers to establish phase offsets over 0 to π/2 range presents a precise means for controlling the photonic crystal structure symmetry between body centered tetragonal (BCT) and woodpilelike tetragonal (wTTR).

Laser Scanning Holographic Lithography for Flexible 3D Fabrication of Multi-Scale Integrated Nano-structures and Optical Biosensors

“…Compared with previous approaches of HIL with stationary beams 7 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 , both top-hat and nonuniform Gaussian beam can be used to form uniform 3D structures in laser scan HIL. Further, scanning an undersized exposure beam over a larger mask area until the full mask has been uniformly and completely exposed has been demonstrated such as the linearly shaped beams found in laser projection lithography 56 .…”

“…The present scanning method should extend readily to other phase mask designs that control the 3D nanostructure symmetry and motif and form, for example, TTR 17 , woodpile 18 19 to diamond-like 20 21 22 35 3D PC templates, offering isotropic directional stopbands 33 34 or monodisperse nanoporosity 49 . The prospects for embedding finer structures such as localized defects to form optical waveguides and cavities within the present 3D photonic crystal network may be further explored with a second direct writing step 15 40 to add functionality such as with photonic, surface plasmonic and metamaterials integrated devices.…”

“…On the other hand, today’s highly powered lasers are highly favored in holographic interference lithography (HIL) for expanding the fabrication area and speeding the process time of 3D PC templates with resolution at one half optical wavelength 7 . Various configurations of free space and phase mask beam splitting have permitted flexible tuning of the crystal symmetry between Tetragonal (TTR) 17 , woodpile 18 19 and diamond-like 20 21 22 structures, and from simple Bravais lattices 23 24 25 to compound 26 , chiral 27 and quasi-crystalline structures 28 . However, traditional free-space methods for beam splitting and combining 7 20 29 have given way to the more stable methods of beam interference with prismoids 18 26 , transmission gratings 30 , and proximity phase mask 17 31 32 33 34 techniques that firmly lock together the phases of multiple diffracted beams to stabilize the 3D interference fringe pattern 17 18 19 26 29 30 31 32 33 34 .…”

Tunable Antireflection Coating to Remove Index‐Matching Requirement for Interference Lithography

“…In a negative photoresist (e.g., SU‐8), this leads to polymerization and hardening in regions of constructive interference, while the resist is left soluble in regions of destructive interference, forming a porous structure matching the interference pattern. The fact that the interference pattern can be controlled through the wavelength, propagation direction, intensity, and polarization of the interfering beams, enables a diversity of structures to be formed . In principle, all Bravais lattices can be made using 4 beams .…”

Controlling the optical creation of gold nanoparticles in a PVA matrix by direct laser writing

“…The 2-PDLW technique has been successfully exploited for the realization of biomimetic materials [2,3], mechanical and pho-tonic materials [4,5], and optical metamaterials [6]. Nevertheless, beyond the "bare" topographic structuring of 3D objects, more specific applications would require the possibility to get a physical or chemical patterning of the structure on the sub-micrometric scale.…”