Measurement of the Transient Spatial Profiles of Refractive Index and Lattice Temperature during Femtosecond Pulse Inscription in Fused Silica

Since its experimental invention in 1996 femtosecond~(fs) laserinduced modification of refractive index in variety of transparentmaterials has been of growing interest. The physical processesinvolved in the inscription processes are not fully understood and ifinscription techniques are to improve and become more repeatable it isimportant that measurement techniques to characterise and understandthe processes be further developed.This program seeks to develop techniques to measure the transientspatial profiles of refractive index and lattice temperature duringthe femtosecond optical pulse inscription process in planar silicadevices. This investigation will lead to improvements in theinscription process and to on-line monitoring tools whichcould offer significant improvements in the repeatability and controlof femtosecond laser inscription systems.Two particular techniques which we intend to develop are NomarskyDifferential Interference Contrast (DIC) microscopy to provide aqualitative measurement of refractive index variation on a micrometerscale and pump/probe experiments using Yb$^{3+}$ doped glass tomeasure the spatial transient lattice temperature profile - somethingwhich to the best of our knowledge has not previously been observed infused silica. The major cost of this project is to fund 4 visits (amounting to a oneyear of his time spread over two years in total) by visiting fellowOleksandr Turchyn who has significant experience in performing opticalmeasurements on solid state materials important for this project. Someadditional resources are required in terms of additional components toenable us to construct the experimental equipment necessary to performthe proposed measurements.