Polarisation dependent NUV femtosecond laser Inscription of high grade Volume Bragg Gratings in poly(methyl)methacrylate with a spatial light modulator


Ye, L (2014) Polarisation dependent NUV femtosecond laser Inscription of high grade Volume Bragg Gratings in poly(methyl)methacrylate with a spatial light modulator. PhD thesis, University of Liverpool.

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Abstract

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.

Item Type: Thesis (PhD)
Additional Information: Date: 2014-10 (completed)
Depositing User: Symplectic Admin
Date Deposited: 05 Aug 2015 07:47
Last Modified: 17 Dec 2022 01:33
DOI: 10.17638/02011959
Supervisors:
URI: https://livrepository.liverpool.ac.uk/id/eprint/2011959
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