Femtosecond laser processing of biopolymers at high repetition rate

Abstract

The large intensities available with femtosecond (fs) laser pulses allow permanent structural modifications in transparent materials with high spatial resolution. Irradiation of self-standing transparent biopolymer films, such as collagen, pure and curcumin doped gelatine employing a 60-fs high-power 11 MHz Ti-Sapphire oscillator laser system linked to an optical microscope led to modifications and ablation. Swelling modifications consisting in the foaming of the irradiated area and formation of a single layer of bubbles arranged around the narrow ablation crater were investigated by optical, scanning force (SFM) and scanning electron (SEM) microscopy. These modifications occur at fluences below the respective ablation thresholds, i.e. ablation processes take place on modified swelled phases. The results are discussed in terms of local temperature increase, generation of thermoelastic stress, physico-chemical effects, and in terms of an incubation model, i.e. the accumulation of these phenomena upon successive pulse irradiation.

Microfoams of Biopolymers by Laser-Induced Stretching: Mechanisms and Applications

“…Moreover the ejected matter which is still poorly known can be solid particles and gases and is probably more abundant at high fluence. Results obtained during experiments with fs laser are reported in details in (Sionkowska et al, 2007;Gaspard et al, 2007Gaspard et al, , 2008aGaspard et al, and 2008b. As shown below they show strong similarity with the ns laser results.…”

Three dimensional microstructuring of biopolymers by femtosecond laser irradiation

“…Chemical effects taking place in the free electron plasma can be discussed in terms the fragmentation of the organic molecular solid initiated by capture of electrons into antibonding orbitals and, in the case of materials with water content ͑4% in gelatine͒ by ionization and dissociation of water molecules. 12 These effects would contribute to the generation of gaseous products inside the voxels. Additionally, generated free radicals and reactive oxygen species can initiate the oxidation and reduction of the organic material.…”

“…10 Femtosecond multipulse irradiation at MHz repetition rates and pulse energies of the order of nJ focused through a microscope objective can be used to achieve high-precision submicrometer scale modifications in polymers and biological tissues. [11][12][13][14] If sufficiently high numerical apertures ͑NA͒ are used, the focus diameter is reduced and unwanted nonlinear effects leading to filamentation and streak formation can be avoided; at the same time the nonlinear absorption allows the production of precisely localized modified areas of submicrometer dimensions inside the bulk of transparent materials. 15,16 In addition to bulk structuring, some examples of superficial fs laser processing of biopolymers and polymer-biopolymer blends have been reported.…”

Femtosecond laser induced damage characterization of transmission volume phase gratings

“…The fitting values ð/ 1 ; nÞ are close to those found in uniform materials, see, for example, Refs. [16][17][18][19]. Notice that since damage occurs at x NI , the LIDT found in the photopolymerizable glass refers to damage threshold on the less resistant locations to irradiation.…”

“…It has been applied to ns- 15 and fs-pulse irradiation for various uniform material classes. [16][17][18][19] Based on this model, we develop a formalism to interpret the damage mechanism to chemically non-uniform materials, including the case of transmission gratings. For the photopolymerizable glass grating, its chemical composition changes locally with the variation of the MS concentration.…”