We show that illuminating bulk Nd-doped Bk7 glass at 488 nm induces a decrease in refractive index of order 10-4. Using this index change we experimentally demonstrate that it is possible to use self-writing to enhance the divergence of a Gaussian beam. Here simulations with a Laguerre-Gaussian ‘donut’ writing beam show that a depressed-index ‘pipe’ structure can be created. We demonstrate that these complex waveguide structures can subsequently be used to guide light of different wavelengths.
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