High-accuracy reference standards for two-photon absorption in the 680–1050 nm wavelength range

Abstract

Degenerate two-photon absorption (2PA) of a series of organic fluorophores is measured using femtosecond fluorescence excitation method in the wavelength range, λ_2PA = 680-1050 nm, and ~100 MHz pulse repetition rate. The function of relative 2PA spectral shape is obtained with estimated accuracy 5%, and the absolute 2PA cross section is measured at selected wavelengths with the accuracy 8%. Significant improvement of the accuracy is achieved by means of rigorous evaluation of the quadratic dependence of the fluorescence signal on the incident photon flux in the whole wavelength range, by comparing results obtained from two independent experiments, as well as due to meticulous evaluation of critical experimental parameters, including the excitation spatial- and temporal pulse shape, laser power and sample geometry. Application of the reference standards in nonlinear transmittance measurements is discussed.

Symmetry Breaking in Pyrrolo[3,2‐b]pyrroles: Synthesis, Solvatofluorochromism and Two‐photon Absorption

“…This behavior is characteristic of strongly dipolar chromophores, where parity selection rules do not apply . Note that for 8 and 20 , where the NLT data is directly compared to the 2PEF measurement, the spectral shapes are closely matched, but the absolute cross‐section value obtained by NLT appears as a factor 1.5–2 higher, even though both methods used fluorescein in pH 11 aqueous buffer as 2PA reference standard . This discrepancy may be related to the absorption from the excited state, which effectively increases the NLT response but does not affect directly the 2PEF signal .…”

Synthesis of Bis(arylethynyl)pyrrolo[3,2‐b]pyrroles and Effect of Intramolecular Charge Transfer on Their Photophysical Behavior

“…Two-photon absorption studies:A ll photophysical studies were performed with freshly prepared air-equilibrated solutions at room temperature (298 K). Two-photon-excited fluorescence (TPEF) cross sections were measured using the method described by Xu and Webb [31] and the appropriate solvent-related refractive index corrections. [31c] To span the l = 690-980 nm range, aN d:YLF-pumped Ti :sapphire oscillator was used, generating 150 fs pulses at a 76 MHz rate.…”

“…The two-photon absorption (TPA) properties of dyes 13, 14, 16,a nd 18 were measured by meanso ft wo-photon excited fluorescencee xperiments in solution. [31] Measurements were conducted in the 690-1100 nm range (i.e.,f irst biological spectral region or NIR1). The very low solubility in toluene, or low fluorescenceq uantum yields in alternative solvents in which these dyes show good solubility,p recluded measurements for dyes 15 and 17.T he two-photon absorption spectra are shown in Figure 5a nd Figure S12 (Supporting Information) along with corresponding rescaled one-photon absorption spectra,w hereas the corresponding data are listedi nT able 2.…”

Two-photon spectroscopy of tungsten(0) arylisocyanides using nanosecond-pulsed excitation

“…3,4 Laser excitation wavelength was 811 nm; the beam was collimated to a diameter of 2 mm. Sample luminescence was collected with a 1-mm diameter optical fiber and directed to an Ocean Optics USB-4000 spectrometer.…”

“…Dependence of the emission intensity of [Ru(bpy) 3 ] 2+ and W(CNAr) 6 complexes on laser power at λ = 847.6 nm, displayed on a logarithmic scale. Each data set was fit to a linear function, with slopes varying from m = 1.7-2.3.…”