Terahertz wave absorption via preformed air plasma

• The plasma absorbs terahertz when it propagates through the preformed plasma.
• Terahertz and preplasma beams focus on the same spot.
• The mechanism relies on energy level transition.
• Polarization of preplasma beam affects the terahertz absorption.

Terahertz wave generation from laser-induced air plasma has continued to be an exciting field of research over the course of the past decade. In this paper, we report on an investigation concerning terahertz wave absorption with preformed plasma created by another laser pulse. We examine terahertz absorption behavior by varying the pump power and then analyze the polarization effect of the preplasma beam on terahertz wave absorption. The results of experiments conducted in which a type-I beta barium borate (BBO) crystal is placed before the preformed air plasma indicate that the fundamental (ω) and second harmonic (2ω) pulses can also influence terahertz absorption.