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 language | English |
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Title of host publication | Photon 08: Optics & Photonics Conference. |
Place of Publication | Bristol |
Publisher | IOP Publishing Ltd |
Publication status | Published - Aug 2008 |
Event | Photon 08: Optics & Photonics Conference. - Heriot Watt University, Edinburgh Duration: 25 Aug 2008 → 29 Aug 2008 |
Conference
Conference | Photon 08: Optics & Photonics Conference. |
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City | Heriot Watt University, Edinburgh |
Period | 25/08/08 → 29/08/08 |
Keywords
- photonic structures
- PMMA
- poly methyl methacrylate
- femtosecond laser writing
- pulse duration
- refractive index modification