Optimizing the photothermal signal: effects of the detector position and pinhole radius in mode-mismatched <i>Z</i> -scan

The pump-probe mode-mismatched thermal lens <i>Z</i>-scan technique is used to investigate the effects of detector position (L) and pinhole radius (<i>ρ</i>₀) on the thermal lens (TL) signal. Theoretical analysis shows that the TL signal is sensitive to both parameters, with optimal performance at a detector distance of ∼20<i>c</i><i>m</i> and a pinhole radius of 0.02 cm. As the pinhole radius increases, the TLS peak shifts to higher L values and the signal amplitude decreases. Experimental measurements with pinhole radii of 0.02, 0.05, 0.075, and 0.1 cm, using an ethanol solution, exhibit good agreement with the theoretical model, validating its reliability. Experimental optimization validated the theoretical model, revealing the significant influence of aperture size and detector position.