Mechanisms of femtosecond laser-induced refractive index modification of poly(methyl methacrylate)

Baum, Alexandra; Scully, Patricia; Perrie, Walter; Liu, Dun; Lucarini, Valerio

doi:10.1364/josab.27.000107

Cited by 41 publications

(25 citation statements)

References 17 publications

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“…The n which results has previously been shown to be due to a combination of de-polymerisation (chain scission, yielding monomer MMA) and crosslinking combined with an observed change of the absorption edge of the material towards the visible, effects which can alter the refractive index in the visible region [20]. Cross linking will pull molecules together, increasing local density and thus n. The photochemistry generates lower molecular weight fragments with unsaturated end groups which also give a positive n. The monomer MMA, soluble in PMMA can diffuse out over time, and stress relaxation may also be important.…”

Section: Resultsmentioning

confidence: 94%

Multi-beam second-harmonic generation in beta barium borate with a spatial light modulator and application to internal structuring in poly(methyl methacrylate)

et al. 2012

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Parallel beam frequency doubling of 170 fs, NIR pulses is demonstrated by placing a thin beta barium borate (BBO) nonlinear crystal after a spatial light modulator. Computer-generated holograms applied to the spatial light modulator create 18 parallel diffracted beams at the fundamental wavelength λ = 775 nm, then frequency doubled to λ = 387 nm and focussed inside the poly(methyl methacrylate) (PMMA) substrate for refractive index structuring. This procedure, demonstrated for the first time in PMMA, requires careful attention to phase matching of multiple beams and opens up dynamic parallel processing at UV wavelengths where nematic liquid crystal devices are more sensitive to optical damage. By overlapping filamentary modifications, an efficient, stable volume phase grating with dimensions 5 × 5 × 2.0 mm 3 and pitch Λ = 15 µm was fabricated in 18 minutes and reached a first-order diffraction efficiency of 70 % at the Bragg angle.

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Section: Resultsmentioning

confidence: 94%

Multi-beam second-harmonic generation in beta barium borate with a spatial light modulator and application to internal structuring in poly(methyl methacrylate)

et al. 2012

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“…To further investigate the formation procedure of the spherical cavity, the thermal interaction between the PMMA and femtosecond laser pulses is taken into consideration. Although complex nonlinear effects are believed to occur during the laser irradiation process because the laser energy used for CMBL fabrication (25 J cm −2 per pulse) is much larger than the ablation threshold of PMMA (0.446 J cm −2 ), we conjecture that the energy balance of heat diffusion prevails in determining the absorbed energy of a laser beam by the material with an efficiency η . Despite the fact that the ultrafast procedure of femtosecond laser nonlinear absorption is correlated to the disassociation of polymer molecules, the formation of ball lens is mainly due to subsequent gas generation and polymer melting, which are much slower steps associated with thermal diffusion.…”

Section: Resultsmentioning

confidence: 90%

“…It is well known that the direct cleavage of the polymer backbone occurs even in a loose focusing condition . Random scission is also demonstrated in the process of photomodification of PMMA with a femtosecond laser . It is important to note that, the molecular dissociation dynamics of PMMA due to multiphoton absorption is unclear since the femtosecond laser induced nonlinear effect is not studied in detail.…”

Section: Resultsmentioning

confidence: 99%

Femtosecond Laser Fabrication of Cavity Microball Lens (CMBL) inside a PMMA Substrate for Super-Wide Angle Imaging

Zheng

Kihm

et al. 2015

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Since microlenses have to date been fabricated primarily by surface manufacturing, they are highly susceptible to surface damage, and their microscale size makes it cumbersome to handle. Thus, cavity lenses are preferred, as they alleviate these difficulties associated with the surface-manufactured microlenses. Here, it is shown that a high repetition femtosecond laser can effectively fabricate cavity microball lenses (CMBLs) inside a polymethyl methacrylate slice. Optimal CMBL fabrication conditions are determined by examining the pertinent parameters, including the laser processing time, the average irradiation power, and the pulse repetition rates. In addition, a heat diffusion modeling is developed to better understand the formation of the spherical cavity and the slightly compressed affected zone surrounding the cavity. A micro-telescope consisting of a microscope objective and a CMBL demonstrates a super-wide field-of-view imaging capability. Finally, detailed optical characterizations of CMBLs are elaborated to account for the refractive index variations of the affected zone. The results presented in the current study demonstrate that a femtosecond laser-fabricated CMBL can be used for robust and super-wide viewing micro imaging applications.

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“…Later, significant attention was paid onto ablation of both pristine PMMA [28-32] and PMMA doped with different compounds [33-37]. Wochnowski et al [38] and Scully et al [39] investigated the modification mechanism of PMMA induced by excimer laser irradiation at different wavelengths. The threshold value of the laser energy for the creation of periodical structure on pristine PMMA surface was found to be 400 mJ cm −2 (at 248 nm).…”

Section: Introductionmentioning

confidence: 99%

Preparation of periodic surface structures on doped poly(methyl metacrylate) films by irradiation with KrF excimer laser

et al. 2014

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In this work, we describe laser modification of poly(methyl methacrylate) films doped with Fast Red ITR, followed by dopant exclusion from the bulk polymer. By this procedure, the polymer can be modified under extremely mild conditions. Creation of surface ordered structure was observed already after application of 15 pulses and 12 mJ cm−2 fluence. Formation of grating begins in the hottest places and tends to form concentric semi-circles around them. The mechanism of surface ordered structure formation is attributed to polymer ablation, which is more pronounced in the place of higher light intensity. The smoothness of the underlying substrate plays a key role in the quality of surface ordered structure. Most regular grating structures were obtained on polymer films deposited on atomically ‘flat’ Si substrates. After laser patterning, the dopant was removed from the polymer by soaking the film in methanol.

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Mechanisms of femtosecond laser-induced refractive index modification of poly(methyl methacrylate)

Abstract: The mechanisms of refractive index change in poly(methyl methacrylate) by frequency doubled femtosecond laser pulses are investigated. It is demonstrated that positive refractive index modificaton can be caused by a combination of depolymerization and crosslinking.

Cited by 41 publications

References 17 publications

Multi-beam second-harmonic generation in beta barium borate with a spatial light modulator and application to internal structuring in poly(methyl methacrylate)

Multi-beam second-harmonic generation in beta barium borate with a spatial light modulator and application to internal structuring in poly(methyl methacrylate)

Femtosecond Laser Fabrication of Cavity Microball Lens (CMBL) inside a PMMA Substrate for Super-Wide Angle Imaging

Preparation of periodic surface structures on doped poly(methyl metacrylate) films by irradiation with KrF excimer laser

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