We present a new scheme for a pump-probe mode-mismatched thermal lensing experiment aimed at extracting the value of low-absorbing components in the presence of a high-absorbing background. The method allows for the use of large path-length samples. Changes in the background absorption of a column of ethanol of 20 cm of 1% and a pollutant concentration detection limit of 0.04 ppm are obtained when using a pump light power of 34 mW.
A. Marcano O., J. Hung, L. Rodríguez, and L. Borrero, "Differential Thermal Lensing in Extended Samples," Appl. Spectrosc. 57, 1278-1281 (2003)