Vibrational bands of luminescent zinc(II)‐octaethylporphyrin using a polarization‐sensitive ‘microscopic’ multiplex CARS technique

Abstract

Polarization-sensitive, multiplex coherent anti-Stokes Raman scattering (ps-MCARS) has been used to detect the vibrational bands of the highly luminescent zinc(II)-octaethylporphyrin (Zn-OEP). We show here that ps-MCARS can be used to measure the vibrational bands under resonant conditions. Polarization-sensitive CARS further helps to resolve composite and overlapping Raman bands on the basis of variations in vibrational symmetry. This paper also exemplifies the advantages of multiplex CARS (MCARS) spectroscopy carried out under tight focusing conditions as proposed earlier. We demonstrate that a 'microscopic' CARS focusing and collection system in combination with the multiplex technique allows a reduction in the amount of sample and a shortening of the measurement time. We analyse the relationship between the coherent vibrational phases and the symmetry of the different vibrational band of Zn-OEP skeletal modes. The values of the coherent vibrational phases are similar for vibrational bands with the same symmetry.

Direct extraction of Raman line-shapes from congested CARS spectra

“…These spectra are generally characterized by well-separated vibrational resonances. Multiplex CARS spectroscopy has also been used in the study of the vibrational structure of protein complexes under resonant excitation conditions, where the different non-linear susceptibility tensor elements have been analyzed separately using polarization sensitive techniques [21]. In the latter case, like for biological samples in general, elaborate data analysis based on a priori knowledge of the vibrational (Raman) spectrum is generally required to extract the information contained in the CARS spectra, in particular when attempting to quantify different constituents [18].…”

Coherent anti‐Stokes Raman Scattering Microscopy

“…This explains why this method has found only limited use in CARS microscopy, [35,61] while it is frequently employed in CARS spectroscopy. [62][63][64][65] …”

“…One possibility to extract the required information from complex multiplex CARS spectra is using a least-squares fit of the theoretical expression for the CARS spectrum to the experimental data. [34,37,64,86,[88][89][90][91] This approach requires sufficient starting information about the vibrational spectrum of the sample components. Recently, it was demonstrated [36,37] that it is also possible to extract the imaginary part of the CARS spectrum (equivalent to the spontaneous Raman spectrum) directly from the measured spectral data.…”

Ultra-Broadband Time-Resolved Coherent Anti-Stokes Raman Scattering Spectroscopy and Microscopy with Photonic Crystal Fiber Generated Supercontinuum

“…In order to effectively distinguish different molecules, a method for simultaneously obtaining the complete molecular vibrational spectra is required. For this purpose, many methods for extending the simultaneously detectable spectral range of CARS spectroscopy and 171 microscopy are presented [34][35][36][37][38] . With the advent and the progress of supercontinuum (SC) generated by photonic crystal Fibre (PCF) pumping with ultra-short laser pulses [39] , the broadband CARS microscopy based on SC has been developed that provided better feasibilities [40][41][42][43][44] .…”

“…The recent progress in wavelengthtunable ultra-short pulse laser has been giving a powerful momentum to the development of M-CARS. The M-CARS micro-spectroscopy has been developed for fast spectral characterization of microscopic samples [35,99,100] . But because of the used laser limitation to the line-width, M-CARS is still unable to simultaneously obtain wider molecular vibrational spectra as required.…”