Mass transport following impulsive optical excitation

Abstract

Transition from reverse-saturable absorption to saturable absorption of the chloroaluminum phthalocyanine solution excited by a giant laser pulse is ascribed not just to the saturation of excited state absorption, but also to the outward migration of the solute molecules at the laser beam center. While the saturation of excited state absorption occurs within a single picosecond laser pulse, the beam center population decrease is sustained much longer than the pulse duration. We distinguish these two mechanisms with the Z-scan technique, utilizing picosecond pulses with pulse-to-pulse separations ranging from 0.1 to 5.0 s.

Collective migration of solute caused by excited state absorptions

“…As a result, we verify that a 19 ps laser pulse with energy E > 6.6 ,uJ can induce the solute migration [1]; however, a 2.8 ns pulse depositing more energy to the solute can not. We proposed a microscopic potential well model to explain the observed results.…”

Study of solute migration-induced negative lensing effect in chloroaluminum phthalocyanine–ethanol

“…s md at the beam waist is hence estimated, in the manner described in Ref. [14], to be 0.3 s, longer than the shortest available s p-p of 0.1 s. This enables us to tune s p-p across s md .…”

“…Contrarily, when e was below e T , Z-scan curves were independent of s p-p and symmetrical about the beam waist. Accordingly, we attributed the skewness of the curves obtained with e > e T and s p-p s < s md to absorption weakening induced by the outward solute migration, a cumulative effect sustaining across neighboring pulses [14]. Moreover, we modeled each solute molecule as an oscillator confined within a potential well to explain that the migration demands e to exceed e T .…”

“…Moreover, we modeled each solute molecule as an oscillator confined within a potential well to explain that the migration demands e to exceed e T . Only when e exceeds e T , the solute molecules, particularly those near the beam center, gain sufficient translational excess energy, via intramolecular vibronic-translational relaxation, to overcome the potential well barrier and then to migrate out of the laser beam center [14,15]. In this report, we reason that a negative lensing effect is additionally induced by the outward solute migration and verify our reasoning by comparing the divided Z-scan curves obtained with pulses of equal energy and various s p-p s with respect to s md .…”

Mechanism for the photoreduction of poly(vinylpyrrolidone) to HAuCl4 and the dominating saturable absorption of Au colloids

“…This process is almost nonradiative, so the large amount of excess energy of Au NPs is converted from the energy that is absorbed from the laser. 43,50,51 The highly concentrated excess energy leads to an ''explosion'' in the colloid, 50,51 which pushes the Au NPs laterally outward from the center of the laser beam, leading to the migration of Au NPs. The migration causes the concentration gradient of Au NPs in the colloid.…”