How Nitrogen and Argon Create Bidirectional Air Lasing

Researchers at the University of California Los Angeles (UCLA) and Max Born Institute have recently made a significant breakthrough in cavity-free lasing in atmospheric air. Traditionally, lasers require optical cavities—pairs of mirrors—to amplify light. However, this new study, published in Physical Review Letters, explores how laser-like light can be generated in open air without these cavities.

The study, led by Chan Joshi and his team, reveals a new physical mechanism where photon-mediated energy transfer occurs between nitrogen (N2) and argon (Ar). The researchers discovered that 3-photon resonant absorption of 261 nm photons in argon leads to cascaded superfluorescence. This process results in bidirectional and laser-like emission of light without the need for traditional optical cavities.

In their experiments, the team observed that the cascaded superfluorescence could switch wavelengths when air contained 1% argon, uncovering a novel air lasing mechanism. This new mechanism facilitates the radiative energy transfer from nitrogen to argon, enabling bidirectional, two-colored lasing in atmospheric air.

Joshi and his colleagues found that the coupling between argon and nitrogen was crucial for this effect. Mixing argon with other gases, such as oxygen or helium, did not produce the same results, indicating that the interaction between argon and nitrogen is key to this air lasing phenomenon.

The team’s research also showed that N2 molecules in an excited state absorb photons at slightly shifted frequencies compared to argon, which helps explain the observed superfluorescence. Their theoretical model provides insight into the mechanisms underlying this phenomenon.

Misha Ivanov, another co-author, highlighted the potential applications of this discovery, such as remote sensing, where achieving lasing in both directions—sending a laser into the air and receiving a laser-like burst back—is highly desirable.

The study’s findings open new possibilities for backward air lasing, which could advance the development of remote sensing technologies. Future research aims to explore the detailed physics of this mechanism and improve the efficiency of backward air lasing to bring this technology closer to practical applications.