An analysis is presented of the detailed effects of varying the write parameters in Co/Pt multilayer films. Domains written thermomagnetically by laser modulation have been imaged using the modified differential phase contrast mode of Lorentz electron microscopy. The effects of different laser powers and bias fields were investigated. While the domain size increases with laser power, the bias field is found to have a profound effect on domain regularity. The periodicity of the irregular circumference of the domains written at high‐bias fields closely resembles the mean repeat in the ac‐demagnetized state suggesting that it arises as a relaxation phenomenon.