WHILE engaged in tests on the ‘ageing’ of the permittivity of a sample of ceramic barium titanate, an observation was made which may be of interest in connexion with the theory of this substance.

THE birefringence of barium titanate has been measured over the range 4000–7000 A. Our attention was first directed to this work by the impossibility of obtaining the correct colour sequence in ...

Fig 1: Novel optical modulation mechanism for cryogenic photonics Fig 2: Optimising the trade-off between purity and brightness in cavity-based probabilistic photon sources Characterising non-linear ...