Spectral behavior of second harmonic signals from organic and non-organic materials in multiphoton microscopy

Abstract

Multimodal nonlinear microscopy allows imaging of highly ordered biological tissue due to spectral separation of nonlinear signals. This requires certain knowledge about the spectral distribution of the different nonlinear signals. In contrast to several publications we demonstrate a factor of 122 relating the full width at half maximum of a gaussian laser pulse spectrum to the corresponding second harmonic pulse spectrum in the spatial domain by using a simple theoretical model. Experiments on monopotassium phosphate crystals (KDP-crystals) and on porcine corneal tissue support our theoretical predictions. Furthermore, no differences in spectral width were found for epi- and trans-detection of the second harmonic signal. Overall, these results may help to build an optimized multiphoton setup for spectral separation of nonlinear signals.

Ultrafast mid-infrared high harmonic and supercontinuum generation with n2 characterization in zinc selenide

“…Potential reasons for the lack of broadening dynamics in the fundamental include: energy losses from linear absorption, free carrier absorption [27], depletion from harmonics generation, or inaccuracy of cr P due to lack of MIR data [12]. In perturbative harmonic generation with perfect phase matching, the ideal FWHM bandwidth of generated harmonics ( ( ) n λ Δ where n is the harmonic order) is related to the FWHM of the fundamental ( [28]. Table 1 outlines the FWHM spectral broadening of the spectra shown in Fig.…”

Two-photon spectral fluorescence lifetime and second-harmonic generation imaging of the porcine cornea with a 12-femtosecond laser microscope

“…The obtained SHG spectrum was narrower (17 nm) than the SHG spectrum expected for transformed limited pulses. 26,27 This is most likely a result of a residual chirp of the pulse. Nevertheless, the SHG spectrum is broader than each individual channel of the PMT, and a strong SHG signal can be detected in the first two channels.…”

Understanding laser desorption with circularly polarized light

“…. 41 The decay of the SHG intensities over time is observed independent of the crystallization state of the sample. The decay indicates successful removal of material, as the SHG response of the sample is depending on its thickness.…”