Time-dependent thermal lens signal with tightly focused laser beam excitation

This work theoretically and numerically explores the effects of varying the excitation beam radius along the propagation axis on time-dependent thermal lensing phenomena. We investigate how changes in sample length and geometrical parameters of the setup influence the thermal lens signal. Specifically, for samples obeying the Beer–Lambert law of optical absorption, an exponential relation between sample length and excitation beam waist is found to accurately describe the point of maximum magnitude of the steady-state signal, offering a reliable route for signal optimization. Understanding the photothermal effects under tightly focused beam excitation is essential to enhance overall sample characterization, being particularly relevant to modern applications in thermal lens microscopy.