Femtosecond micro-machining of hydrogels: parametric study and photochemical model including material saturation

The Role of Thermal Accumulation on the Fabrication of Diffraction Gratings in Ophthalmic PHEMA by Ultrashort Laser Direct Writing

“…High-repetition-rate low-pulse energy laser sources, properly combined with high numerical aperture focusing objectives, have been used to induce nonlinear absorption processes in the thermal regime to create permanent structures in transparent materials [ 32 , 33 , 34 , 35 , 36 , 38 , 39 , 40 ]. In this work, normalized frequencies for the Ti:sapphire oscillator were f n ~16 × 10 3 and 4.7 × 10 3 at 750 nm and 400 nm, respectively.…”

“…These phenomena lead to localized micro or sub-micrometric lattice damage, permanent weak local refractive index variation, the formation of nano-voids, crystallization processes, or chemical transformations [ 11 , 12 ]. Short and ultrashort laser radiation has been recently used to modify the refractive power of polymers for ophthalmic applications by inscribing diffractive optical elements on the surface or inside the material [ 15 , 18 , 19 , 22 , 36 , 37 , 38 , 39 , 40 ]. Nevertheless, the role that thermal accumulation plays on the optical properties of diffraction gratings produced by ultrashort direct laser writing for ophthalmic applications has not conclusively been solved.…”

Direct Laser Interference Patterning of Diffraction Gratings in Safrofilcon-A Hydrogel: Fabrication and Hydration Assessment

“…Short and ultrashort pulsed laser radiation has been recently used to structure polymers, crystals, and glasses in applications such as 2D/3D micro/nanostructures [ 11 , 12 ], active and passive waveguides [ 13 , 14 , 15 , 16 , 17 , 18 ], photonic crystals [ 19 , 20 ], beam splitters [ 11 , 19 ], data storage elements [ 11 , 19 , 21 ], and microfluidic components [ 19 , 22 , 23 ]. In addition, in ophthalmology, ultrashort direct laser writing (UDLW) has been applied to vision correction in photo-refractive surgery [ 24 , 25 , 26 ], and more recently, to change the power of refractive optical elements [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. It is well known that diffractive optical elements, such as diffraction gratings, can be used to modify the refractive index and hence the refractive power of an optical device.…”

“…It is well known that diffractive optical elements, such as diffraction gratings, can be used to modify the refractive index and hence the refractive power of an optical device. Specifically, ultrashort laser radiation with laser pulse energy below damage threshold has been employed to fabricate diffraction gratings within dye-doped and non-doped ophthalmic polymers, resulting in refractive index modification ranging from ~6 × 10 −2 to ~8 × 10 −2 [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. Nonetheless, the processing rates reported to date to structure areas of large dimensions, such as the cornea, are low, which hinders their application on a real scale.…”

Simple Estimate of the Impact of M2 and Strehl Ratio on the Effective Focusable Spot Size

“…In between, there is a corridor of increasing/decreasing importance for the effects of M 2 and the SR. For multiphoton absorption (non-linear) processes for which both the single pulse intensity I (suprathreshold process) and pulse overlapping are involved, a formal estimate can be derived [19].…”