Phase-dependent ultrafast third-order optical nonlinearities in metallophthalocyanine thin films

Abstract

We present a comprehensive study on the impact of phase transformations of metallophthalocyanine thin films on their third-order nonlinear optical (NLO) properties. The metallophthalocyanine thin films are prepared by thermally evaporating the commercially available Copper(II)2,9,16,23-Tetra-tert-butyl-29H,31H-phthalocyanine (CuPc) and Zinc(II) 2,9,16,23-Tetra-tert-butyl-29H,31H-phthalocyanine (ZnPc) powder on glass substrate. Thermal annealing causes a phase transformation which has a distinct signature in powder X-ray diffraction and UV-Vis-NIR spectroscopy. The NLO characteristics which include nonlinear refractive index n2, as well as nonlinear absorption coefficient (βeff), were measured by using a single beam Z-scan technique. An ultrashort pulsed fiber laser emitting femtosecond pulses (Δτ ≈ 250 fs) at 1064 nm central wavelength is used as a source for the Z-scan experiment. The βeff values in as prepared thin films were ascertained to be smaller as compared to the annealed one due to the smaller value of saturation intensity (Is) which, in turn, is a consequence of ground-state bleaching in the thermally unstable amorphous state of the molecule. Interestingly, the nonlinear refractive indices bear opposite sign for CuPc and ZnPc. The variations in the third-order nonlinearity in CuPc and ZnPc are discussed in terms of molecular packing and geometries of metallophthalocyanine molecules.

Synthesis, Optical, Electrochemical, DFT Studies, NLO Properties, and Ultrafast Excited State Dynamics of Carbazole-Induced Phthalocyanine Derivatives

“…The uncertainties in the NLO coefficients and cross sections were estimated (error percentage) to be ±10% arising predominantly from (a) errors in the estimation of beam waist (at focus) and thereby leading to errors in the peak intensities, which is a crucial parameter (b) fluctuation in the input laser power (c) fitting errors, etc. We have attempted to compare the NLO coefficients obtained for the present set of molecules with recent reports in the literature. − There are several mechanisms reported and discussed in the literature for the sign and magnitude of n 2 . Some of the mechanisms include (a) one purely electronic in nature, (b) thermal nonlinearity due to absorption/heating and (c) due to excited state population, (d) electrostriction, (e) formation of nuclear/vibrational contributions, etc.…”

Charge Transfer and Ultrafast Nonlinear Optical Properties above Percolation Threshold in Graphene-Induced ZnTTBPc

“…As a member of the phthalocyanine family, ZnPc’s NLO behavior has been considerably studied in previous reports. ,− , We further compared the NLA coefficients of our samples with the reported Pc molecules as well as Pc–RGO compositions, and the results are tabulated in Table . With MHz repetition rate, even though the pulse width is small (∼150 fs), the measured NLA coefficient is much higher owing to thermoaccoustic effect .…”

“…The NLO properties of phthalocyanine derivatives have been reported by several groups. ,− Most of the reports presented either two-photon absorption (2PA) or three-photon absorption (3PA) behavior with both femtosecond (fs) ,, and nanosecond (ns) , pulse excitation. Similar measurements have been performed on RGO-based composites as well as heterojunctions.…”

Impact of Pauli-blocking effect on optical limiting properties of WSe2 thin films

“…However, the asymmetry in the peak-to-valley transmittance is essentially brought about by a strong SA characteristics exhibited by all the thin-films at 515 nm excitation wavelength. In order to estimate n 2 , the normalized CA transmittance curves were fitted using the relation [53,63,64] ∆T = 1 − 4x∆φ 0 (x 2 + 9)(x 2 + 1) − 2(x 2 + 3)∆Ψ 0 (x 2 + 1)(x 2 + 9) (4) where ∆φ 0 = kn 2 I 0 L ef f is the phase change due to nonlinear refraction at the focus, k=2π/λ is propagation wavevector and ∆Ψ 0 = βI 0 L ef f /2 is phase change due to nonlinear absorption. The real part of third order nonlinear susceptibility (χ (3) ) and n 2 exhibit a relation given by [33] χ The values of n 2 and χ…”