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Title: Polarisation dependent NUV femtosecond laser inscription of high grade Volume Bragg Gratings in poly(methyl)methacrylate with a spatial light modulator
Author: Ye, Lingyi
ISNI:       0000 0004 5363 2925
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2014
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Parallel near-ultraviolet(NUV)beam, 387nm femtosecond laser pulses with linear and circular polarisations were used to inscribe high efficiency Volume Bragg Gratings (VBGs) in clinical grade poly(methyl)methacrylate (PMMA) with the aid of a Spatial Light Modulator (SLM). Large, high quality VBGs with dimensions of 5mm x 5mm in size with (1-7)mm thickness and 20µm pitch were created at high speed, fabricated in 36 minutes, showing a first order diffraction efficiency 1 >94% with 4mm thickness. This is the highest diffraction efficiency observed to date in the undoped polymer, PMMA. Linear polarisation produced a higher refractive index contrast than circular polarisation, was found to be due to polarisation dependent non-linear filamentation, initiated through self-focusing. Using the threshold for supercontinuum, the ratio of critical power for self-focusing in PMMA was measured to be Pc lin/Pc circ  1.5, in accord with theoretical expectations. The pulse energy uniformity of the multiple beams was also dramatically improved by a camera based feedback system which was integrated into a LabVIEW based hologram calculation and display system, reducing the non-uniformity of parallel NUV and NIR beams significantly, thus improving the inscription process.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available