Broadband terahertz detection with selected gases

We present a combined theoretical and experimental investigation of the detection of pulsed terahertz waves via field-induced second-harmonic generation in gaseous media. The effects of the probe pulse energy, bias field strength, nonlinear susceptibility of the gases, phase matching, and focusing conditions of the terahertz and optical beams are discussed. The analytical calculation, which is based on a Gaussian-beam approximation, allows for the easy identification of the parameters important for the sensitivity of the terahertz gas sensor. A figure of merit is introduced to characterize the sensitivity of gases. The experimental results are found to be in good agreement with the calculation. (C) 2009 Optical Society of America