Enhancement limit of sensitivity in laser absorption spectroscopy using a multipass cell composed of spherical concave mirrors

The upper limit of sensitivity enhancement in a multipass process was investigated. In the calculation of 3.7 × 10 13 ray-trace analysis, the sensitivity enhancement was increased to 13 510 for the mirror diameter of 75 mm with the mirror diameter. In the experiment, the sensitivity was enhanced by a factor of 1790 ± 160 for an effective mirror diameter of 50 mm, which was one-third of the numerical prediction. The lower enhancement could be attributed to the insufficient spatial and angular resolution of alignment optics. Therefore, this multipass cell has the potential to improve the sensitivity by three to four orders of magnitude.