Electrical discharges are widely used in applications such as electric welding, micromachining and fuel ignition in combustion engines, to name just a few examples. Despite their ubiquity, the ability to control and shape the exact path of a discharge along a specific trajectory remains a significant challenge. Now, Matteo Clerici and colleagues from Canada, the UK, China, France and the USA have shown that specially shaped laser beams can perform this feat (Sci. Adv. 1, e1400111; 2015).

Three kinds of beam shapes — a standard Gaussian beam, a Bessel beam and an Airy beam — were investigated in the study. All beams were produced by an amplified Ti:sapphire laser system and sent between two wire electrodes. The beams were 10 mm in size (full width at half-maximum), featured an input energy of 15 mJ and were pulsed with a pulse duration of 50 fs.

The concept of the scheme is to use the laser pulses to ionize the air between the electrodes and create a preferred path for a discharge, which is created by applying a high voltage (nearly 15 kV over a 5 cm gap) between the electrodes.

The Bessel and Airy beams were able to create well-defined discharge paths (pictured), whereas in the case of the Gaussian beam the trajectory of electric discharges is heavily disordered and effectively unpredictable.

Credit: MATTEO CLERICI

The differences in behaviour are thought to be due to the different electric field strength of the beams. The central high-intensity peaks of the sub-diffractive Bessel beam and Airy beam were ∼7 μm and ∼20 μm, respectively, considerably smaller than the diameter of the Gaussian optical filament (∼50 μm). The international team further investigated the electric breakdown for the three cases and observed that the breakdown field was 3.5 and 10 times lower for the cases of the Airy and Bessel beams, respectively.

Surprisingly, the team found that laser-guided discharge could take place even when the laser beam encountered an obstacle between the electrodes (pictured). In the cases of a Bessel-type and an Airy-type propagation, the beam restored itself after the obstacle and the electric discharge occurred along an almost unaffected trajectory.

According to Matteo Clerici, one of the authors of the study, the next challenge is to find the limits of this technique. Two questions that he says need answering are: “How much can we bend a discharge and how high is the current we can transport in a controlled way?”