New electrode configuration for measurements of the induced current from a laser plasma and its application to monitoring laser processing

An electromagnetic phenomenon in terms of the induced current in a laser ablation process has been studied, and its potential application has been demonstrated. A new electrode configuration for measuring the induced current emerged due to the interaction between the electric lines of force and the laser-produced plasma has been devised. In this new electrode configuration, the induced current is detected by employing a circuit of electrodes, supplied with several hundred DC volts and placed above the sample surface in parallel, which is called the parallel configuration. This parallel configuration provides a far higher flexibility in comparison with the sandwiched configuration developed in our previous work. The induced current signal can be detected from various samples of any size, including metals and nonmetals. We found that the source of the induced current was the outer electrons in the plasma. This induced current is very useful as a unique monitoring method and promises many applications in laser microprocessing. In this work, this induced current method was applied for several monitoring purposes in laser material processing, such as for estimating the ablated amount, monitoring the penetration of a laser beam into processed materials, and determining the precise tight focusing position of the lens, in real time.