FIG 1 (IMAGE)
Caption
Fig. 1. Schematic and comparison of PA responses from microsecond pulse laser and modulated square wave laser excitation. (a) Schematic of the molecular-level PA process, encompassing vibrational excitation, non-radiative relaxation, and thermal diffusion. (b) Simulated temporal profiles of pulse and modulated CW laser and the corresponding heat source. SW; modulated square wave. (c) Transient acoustic pressure response of the first-order longitudinal mode in the resonant PA cell for both excitation methods. (d) A detailed view of the steady-state response of (c). (e) Fourier transform of the steady-state signals, quantifying that the fundamental frequency amplitude of the low duty-cycle pulsed response is 1.57 times that of the modulated square wave. (f) Theoretical and experimental PA excitation efficiency at various modulation duty cycles, normalized to the signal at 50%.
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