High-sensitivity absorption measurement in water and glass samples using a mode-mismatched pump-probe thermal lens method

We report on a mode-mismatched pump-probe thermal lens experiment performed to measure absorption coefficients as small as 10−8 cm−1 in liquid and solid samples. We take advantage of the large axial dimension of the thermal lens by focusing the pump beam in the presence of a collimated probe beam. We measure an absorption coefficient at 533 nm of (6.8±0.1)×10−4 cm−1 and of (3±0.3)×10−6 cm−1 for distilled water and BK7 optical glass, respectively.