High-sensitivity photothermal radiometry measurement using a mirrored liquid sample vessel for multireflection of a pumping beam

A method to enhance the sensitivity of photothermal radiometry (PTR) measurement was proposed. This method features multireflection of a pumping laser beam on the inside of a liquid vessel. This is a new, effective, and extremely simple method for measurement of a lowly thermally emissive sample. Our experimental data were compared to that of the conventional PTR method. A dye (IR-140) was used as the impurity in a solvent, and we ascertained superior detectablity of the impurity in the sample vessel—a 12 mm diameter integrating sphere—to that of the conventional method by more than a magnitude of one. A theoretical “limit of detection” value for our technique was estimated to be 0.7 ppb when the power of the pumping beam was 500 mW.