Ozone can be synthesised by corona discharge where oxygen molecules are subjected to a high level of high electrical potential excitation. This imparts higher energy to the oxygen molecules. This results in high level of excitation of oxygen molecules and split them in to atomic oxygen. These single free atoms recombine with other oxygen molecules to form triatomic oxygen, better known as ozone; under the same high energy excitation.
Ozone can also be synthesised by exposing oxygen molecules to UV radiation at 185 nm wavelength which excite oxygen molecules in the same way as corona discharge does to form ozone. However, ozone formed this way is very weak and has a very low concentration.
The most common method to synthesise ozone for any useful application is using corona discharge.