The application of magnetic field at low pressure for optimal laser-induced plasma spectroscopy

• With magnetic field, LIBS signal enhancement is sensitive to the laser energy
• At low pressure, signal enhancement with magnetic field is insensitive to the laser energy
• The electron density is analyzed to explain the observed signal intensity variation

The application of magnetic field in controlling the charged particles of the laser induced plasma is considered. The chara\cteristics of the plasma depend on the electron density and its recombination. The magnetic field effects as well as the ambient pressure are the key factors for determining the electron density of the plasma. Two different laser energies (Low: 30 mJ/pulse, High: 140 mJ/pulse) and the pressure range between 760 Torr and 10 Torr are used when focusing a Nd:YAG laser beam (1064 nm, 6 ns) onto the metal samples where the applied magnetic field varied between 0.1 and 0.5 Tesla. At 760 Torr, the plasma signal enhancement was obtained in the presence of magnetic field when the laser energy was low. With a lowered pressure however, the signal enhancement due to a magnetic field was achieved regardless of the laser energy. The enhancement of the signal in the presence of magnetic field is related to the electron density and the high frequency instability which are controlled by the ambient pressure and magnetic field intensity. In this paper, the optimal conditions for the laser-induced plasma spectroscopy in the magnetic field at various low pressures are discussed.