The effect of pulse duration on writing photonic structures in poly(methyl methacrylate) using femtosecond lasers

A Baum, P J Scully, W Perrie, D Jones, R. Issac, D.A. Jaroszynski

    Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

    Abstract

    There is currently great interest in writing photonic structures into polymers, and femtosecond (fs) lasers can fabricate micronsized, 3-D, permanent refractive index structures in transparent media for photonic devices, but work to date has been carried out in glasses. Polymethyl methacrylate (PMMA) or perspex is a polymeric transparent material exploited in integrated optics, microfluidics and polymer optoelectronics due to its low processing temperature, biocompatibility and ease of injection moulding and extrusion. Pulse duration, which has to date received little attention in material modification below the ablation threshold, is shown to be important for efficient modification of poly (methyl methacrylate) and writing conditions determined by wavelength and pulse length and the associated photochemistry for refractive index modification were investigated. Refractive index modification of pure PMMA is investigated as a function of pulse duration using femtosecond lasers at 800 and 387 nm wavelength. At 800 nm, the refractive index is modified more efficiently as the pulse duration decreases below 100 fs, whereas at 387 nm, efficient index modification is accomplished with longer, 180 fs pulses. It is suggested that three- and two-photon absorption mechanisms are responsible for modification of pure PMMA at 800 nm and 387 nm, respectively. Repeated irradiation using short pulses at low laser fluence, facilitate photo-modification control via incubation, reducing bulk damage. The paper concludes that efficient fs laser modification relies on a suitable combination of laser pulse duration and wavelength in relation to the material bandgap.
    Original languageEnglish
    Title of host publicationPhoton 08: Optics & Photonics Conference.
    Place of PublicationBristol
    PublisherIOP Publishing Ltd
    Publication statusPublished - Aug 2008
    EventPhoton 08: Optics & Photonics Conference. - Heriot Watt University, Edinburgh
    Duration: 25 Aug 200829 Aug 2008

    Conference

    ConferencePhoton 08: Optics & Photonics Conference.
    CityHeriot Watt University, Edinburgh
    Period25/08/0829/08/08

    Keywords

    • photonic structures
    • PMMA
    • poly methyl methacrylate
    • femtosecond laser writing
    • pulse duration
    • refractive index modification

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