Application of Nonlinear Optics in Entomology

Up until now, insects have almost exclusively been studied with linear optical methods. However, nonlinear optical techniques, such as multiphoton microscopy, offer many advantages. Most importantly, due to the low probability of two photons interacting with a specimen simultaneously, multiphoton microscopy inherently offers optical slicing. It is therefore very easy to create a 3D image of a sample, with minimal loss of signal and a high penetration depth. In this project, the use of nonlinear optics has been explored for the field of entomology. A wide variety of insects has been studied with some interesting results. Beetle elytra proved to be the easiest subjects. The results confirmed what was already known about the two beetles that were measured, Hoplia coerulea and Trichtenotoma childreni. The presence of a fluorophore was confirmed with two-photon fluorescence (2PF) microscopy in both beetles. Additionally, Second Harmonic Generation (SHG) was observed in T. childreni, probably due to the non-centrosymmetric distribution of fluorophores inside the bristles. Nonlinear spectroscopy confirmed the broad fluorescence peaks in both insects, with an additional Third Harmonic Generation (THG) peak in H. coerulea and an SHG signal in T. childreni. Next to beetles, cicada and butterfly wings have been observed with multiphoton microscopy. Although images were obtained, it proved to be much more difficult than the beetle elytra. More photodamage was observed and contrast was not as good as that from the beetles. Nonlinear optical spectra were not obtained, as the sample was burned too heavily before measuring a signal. Nevertheless, 2PF micrographs were taken, and in the case of the cicadas, also SHG images. The exoskeleton of insects exists mostly out of chitin, which is both 2PF- and SHG-active. It is therefore always visible in multiphoton microscopy. Additionally, many insects are very colorful, and this is often due to the presence of pigments, which generate an additional 2PF signal, and even a SHG signal in case of non-centrosymmetry. In conclusion, nonlinear optics are certainly useful for the characterization of insects, as they offer more information than usual optical methods, such as fluorescence and confocal microscopy.

Jaar van publicatie:2019

Toegankelijkheid:Open