Plume monitoring system as a stabilizer for laser ablation method

Abstract: We constructed a laser-plume monitoring system to stabilize fabrication process of high-temperature superconducting (HTS) circuits with films and junctions prepared by a laser ablation method. The system utilizing a CCD camera with wide band sensitivity accumulates intensity of ultraviolet ray for many plumes as an averaged matrix data of 256×256. Using the matrix data, we successfully estimated the magnitude or length of plumes objectively with a measurement error of ±0.15mm. We found that target temperature, laser gas condition and target consumption have strong influences on the magnitude of plumes even if the laser power monitor shows the same output power. We found the conditions to obtain a stable magnitude of plumes and successfully controlled the magnitude of plumes even in unstable conditions of laser ablation. The junctions fabricated by using the stable plumes had resistively shunted junction (RSJ) type current–voltage (I–V) characteristics with a percentage of success of 93%. [Copyright &y& Elsevier]