Abstract
Using the Z-scan technique, we studied the nonlinear absorption and refraction behaviors of a dilute toluene solution of a silicon naphthalocyanine (Si(OSi(n-hexyl)(3))(2), SiNc) at 532 nanometer with both a 2.8-nanosecond pulse and a 21-nanosecond (HW1/eM) pulse train containing 11 18-picosecond pulses 7 nanosecond apart. A thermal acoustic model and its steady-state approximation account for the heat generated by the nonradiative relaxations subsequent to the absorption. We found that when the steady-state approximation satisfactorily explained the results obtained with a 21-nanosecond pulse train, only the thermal-acoustic model fit the 2.8-nanosecond experimental results, which supports the approximation criterion established by Kovsh et al.
Highlights
Two-dimensional molecules with π-conjugated electron systems, such as porphyrins, phthalocyanines, and their derivatives, and their nonlinear optical properties have been widely investigated recently [1, 2]
Using a laser pulse with a width of τ = 2.8 nanoseconds (HW1/eM) and a Gaussian distributed train, composed of 11 18-picosecond pulses 7 ns apart, with an envelope width of τenv = 21 ns, nonradiative relaxations induced a thermal lensing effect (∆ntherm), in addition to internal nonlinearities, is expected to contribute to the nonlinearities. ∆ntherm results from a temperature rise (∆θ ), caused by nonradiative relaxation subsequent to optical excitation, and the solvent density change (∆ρ) induced by a ∆θ -driven thermal acoustic wave
Given the acoustic wave speed of νs = 1170 m/s for the solvent[10], we respectively focused a 2.8-ns pulse and a 21-ns pulse train to have a beam waist radius of w0 = 14.1 μm and 18.9 μm (HW1/e2M for both) in this study
Summary
Two-dimensional molecules with π-conjugated electron systems, such as porphyrins, phthalocyanines, and their derivatives, and their nonlinear optical properties have been widely investigated recently [1, 2] These molecules show potential in optical-limiting applications due to their large excited-state absorption cross sections in both singlet and triplet manifolds within the visible spectrum [3,4,5,6]. Given the acoustic wave speed of νs = 1170 m/s for the solvent (toluene)[10], we respectively focused a 2.8-ns pulse and a 21-ns pulse train to have a beam waist radius of w0 = 14.1 μm and 18.9 μm (HW1/e2M for both) in this study This resulted in τac = w0/νs = 12.0 ns for the 2.8-ns pulse and τac = w0/νs = 16.2 ns for the pulse train. As a result, ∆ρ obtained using both approaches yields close ∆ntherm’s for a 21-ns pulse train but causes significantly different ∆ntherm’s for a 2.8-ns pulse (vide infra)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
