Rapid, broadband two-photon-excited fluorescence spectroscopy and its application to red-emitting secondary reference compounds

Abstract

We present a methodology for rapidly acquiring broadband twophoton absorption (2PA) spectra by means of a compact two-channel femtosecond fluorescence excitation apparatus. This technique is insensitive to differences in excitation and collection geometries as well as detection efficiencies between the sample and reference, in addition to variations in average power, pulse duration and spatial beam profile, as it utilizes sequential measurement of the sample and reference in each of the two cell positions. Our approach eliminates the need to determine the fluorescence quantum yields of the sample and reference, as it allows measurement of emission from samples at a common specified wavelength. These attributes allow for acquisition of 2PA spectra with an estimated accuracy of ± 15% (limited almost exclusively by the uncertainty in the 2PA cross section for the reference standards) over an excitation range of 550-1600 nanometers with a typical time per spectrum of ~30-60 minutes. We have applied this technique to determine the 2PA spectra of six commercially available organic dyes over a wide range of excitation wavelengths (670-1600 nm), which can be used as secondary reference standards emitting in the red and near-infrared spectral region (600-1000 nm). We have also characterized some of these compounds using the femtosecond-pulsed Z-scan method and found very good agreement with the fluorescence-based measurements.

Two Photon Absorption in II–VI Semiconductors: The Influence of Dimensionality and Size

“…Both σ LDS698 (2) and σ LDS698 (1) are wellcharacterized by Makarov et al 26 by means of z-scan and 2P-PLE measurements.…”

“…We find very good agreement between z-scan and corrected 2P-PLE results, especially if we consider the published error margin given for the TPA cross sections of LDS698. 26 All the dye-derived 2P-PLE results shown in this Letter have been corrected with respect to pulse width effects (see SI for details to pulse-width effects). It must be noted that it is arbitrary to which spectral pulse width the values are corrected and this may be the reason for the differences in reported TPA cross sections, for example for 3.2 nm CdSe QDs at 800 nm Nyk et al 32 (20 × Comparing the TPA spectra determined by reference-dye at each wavelength (closed circles, Figure 3a) with the selfreferenced spectra (open circles, Figure 3a) shows that the spectral course is barely altered by the SR method.…”

Keto-polymethines: a versatile class of dyes with outstanding spectroscopic properties for in cellulo and in vivo two-photon microscopy imaging

“…The TPA spectra of D 1 D 1 O , D 3 AO and AAO were mapped using the two-photon excited fluorescence (TPEF) 20 and, due to the lack of a stable and reliable TPEF standard in NIR, the magnitude of cross sections were calibrated with open-aperture z -scan techniques. 21 As a general feature, all keto-heptamethines present similar TPA spectra composed of two transitions (Fig.…”

Two-Photon Absorption in CdSe Colloidal Quantum Dots Compared to Organic Molecules

“…56 2PA was measured using a two-arm two-photon excited fluorescence spectrometer as described elsewhere. 58 The spectra were referenced using Lucifer Yellow ( 900 < λ nm), Rhodamine 6G 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 molar absorptivities or cross section as well as emission quantum yields. Detailed descriptions of these measurements and their discussion are given in the SI.…”