Solution glow discharge plasma chamber with lens

A solution electrode glow discharge (SEGD) apparatus comprising:

• a solution electrode;
• a solid electrode;
• and
• a plasma chamber comprising:
• a hollow body configured to enclose a plasma generated between a solid electrode and a solution electrode, the hollow body at least one viewing port for letting light generated from the plasma leave the hollow body;
• and
• a lens at or near the viewing port, the lens being configured to collect light from the plasma and direct the light onto a light receiving unit;
• and
• a holder unit configured to hold the light receiving unit at a predetermined distance from the lens parallel to a focal axis of the lens, wherein at least one of the lens and the light receiving unit is movable with respect to the other, perpendicularly to the focal axis of the lens and parallel to an axis of the gap between the solid electrode and the solution electrode.