Development of practical methods to create nitrogen-vacancy (NV) centres in diamond for quantum emitters is an active field of research. Femtosecond laser direct writing is one promising technique, able to inscribe graphitised, electrically conductive structures inside diamond and to create single structural defects by a maskless approach. High-temperature annealing is the key missing technology for defect control: annealing those which are not required and leaving the quantum emitters. This control can also be applied by pre-heating the diamond host during laser inscription. Here we report the first demonstration of thermal control inside diamond. Pristine diamond couples negligibly to a 2.45 GHz field. We show that femtosecond-laser inscription of a buried graphitic (sp²) architecture makes a 4 × 4 × 2 mm³ N-doped (100 ppm) high-pressure high-temperature (HPHT) crystal absorb strongly, and that the absorption is switched by the orientation of the inscribed structure relative to the cavity electric field. For a concentric grating  at 90 W, an abrupt excursion to ∼ 900^◦C with surface roughening and terraced oxidation.  The depolarisation factors L of the sub-wavelength tracks are responsible for energy deposition; the screening parameter S = Lσ/(ωε₀ε_h), where σ is conductivity, ω the cyclic frequency and ε_h,0 the permittivity of host and vacuum, respectively. The model attributes the effect almost entirely to the single continuous axial line, predicts a conductivity optimum at S = 1 near the resistivities actually achieved by laser writing, and turns element length, diameter and writing regime into design variables for microwave absorption in a transparent host.

We will discuss localisation of energy deposition using microwaves for nanostructured black-Si and oxidation of metal  nanofilms.