  Laser writing with ultrashort pulses provides a potential route for the
manufacture of three-dimensional wires, waveguides and defects within diamond.
We present a transmission electron microscopy (TEM) study of the intrinsic
structure of the laser modifications and reveal a complex distribution of
defects. Electron energy loss spectroscopy (EELS) indicates that the majority
of the irradiated region remains as $sp^3$ bonded diamond.
Electrically-conductive paths are attributed to the formation of multiple
nano-scale, $sp^2$-bonded graphitic wires and a network of strain-relieving
micro-cracks.
