Uniform illumination of optically dense NMR samples.

We demonstrate a simple, inexpensive method for in situ laser illumination of NMR samples using a stepwise tapered optical fibre to deliver light uniformly along the axis of a 5 mm NMR tube. The optical path length of the incident light inside the sample is about 3 mm, allowing efficient illumination of optically dense samples. The degradation in spectral resolution and the reduction in filling factor are both minimal. Probe modifications are not required.