Scientists from Tokyo Metropolitan University have uncovered a way to improve the efficiency of plasma technology, which has diverse applications, including sterilization and surface treatment in the semiconductor industry. Their research focused on oxygen plasma, a type of plasma made by breaking down oxygen gas into highly reactive atomic oxygen. By mapping the production of atomic oxygen under different pressure conditions, the team found that reducing the pressure slightly below atmospheric levels increased the availability of atomic oxygen for chemical reactions. This discovery could lead to more efficient and powerful plasma-based technologies. Plasma, often called the fourth state of matter, consists of charged particles such as ions and electrons, and it is the most common form of matter in the universe. It can be artificially created by applying high voltage across a gas, which generates nonthermal plasma. In this type of plasma, only the electrons are heated to high temperatures, while the gas atoms remain in a reactive state known as radicals. These nonthermal plasmas are used in various fields, such as killing bacteria, modifying material surfaces, and removing pollutants. Oxygen plasma is especially valuable because it produces atomic oxygen, a powerful oxidizing agent. However, its effectiveness is limited by the short lifespan of atomic oxygen at atmospheric pressure, where frequent collisions with other gas molecules prevent it from reacting with the desired target. To overcome this challenge, a team led by Associate Professor Yusuke Nakagawa from Tokyo Metropolitan University investigated the effects of lowering the pressure during plasma generation. Their study, published in the Journal of Physics D: Applied Physics, used laser-induced fluorescence to track the production of atomic oxygen at various points in the plasma. Contrary to expectations, the team found that reducing the pressure did not decrease the number of atomic oxygen radicals but instead increased the number available for reactions. This was due to the extended lifetime of the radicals and the involvement of electrons with moderate energy in radical production, which occurred not only in glowing parts of the plasma but also in dark regions near the electrodes. This insight provides a new understanding of how atomic oxygen is generated and could lead to more effective plasma treatments across various industries.