M1 and M2 internships at Wavefront engineering microscopy group. Photonics Departement of the Institut de la Vision, Paris

Background. Optogenetics has revolutionized neuroscience by making it possible to control neurons with light1. The current technological challenge lies in the field of optics and photonics as advanced techniques to precisely address hundreds of individual neurons in large volumes with high spatial and temporal precision are necessary to decrypt the neuronal code. Our group has been one of the main actors in developing similar techniques, mainly based on the wavefront shaping of ultrafast laser pulses and twophoton (2P) effects 2–4. Today, a major challenge to the use of light in neuroscience is scattering from biological tissues that prevents deep brain structures to be studied. We propose here two different approaches to overcome scattering, suitable for two master projects.

Project 1: Three-Photon Circuit Optogenetics
Due to the its better axial confinement and higher penetration depth, two-photon excitation (2PE) 5 is currently the gold standard for in vivo functional imaging and optogenetic photo-stimulation, as opposed to single photon excitation. Yet, light scattering limits 2PE investigations to superficial cortical areas extending only few hundred microns in the brain. The aim of this project is to study and implement new strategies for deep all-optical brain interrogation by using three photon excitation (3PE) 6,7. 3PE has some major advantages over 2PE: (i) reduction of scattering as well as of brain tissue absorption thanks to the optimal excitation wavelength used (around 1700 nm); (ii) higher excitation confinement in the axial direction, which falls off as ~1/z4 (with z distance from the focal plane), compared to 1/z2 in 2PE. The candidate will work on the design, realization and validation of 3PE light delivery systems based on novel laser sources for 3PE. The research outcomes are expected to extend beyond neurobiology and provide more insights in nonlinear light-matter interactions and the control of light in turbid media.



Project 2: An optimal two-photon micro-endoscope
3PE is an elegant solution to reach deep layers in the mouse visual cortex. However, there are many different and important brain structures that lie at larger depths, which cannot be reached today with standard microscopy. We recently made the first step towards the study of deeper regions by developing a basic micro-endoscope (ME) through which advanced wavefront shaping could be performed 8. However, such first implementation still suffers from important limitations that need to be overcome. In this project the candidate will develop a new class of optimal two-photon micro-endoscopes for the simultaneous 2P imaging and precise 2P optogenetic photo-stimulation of many neurons in large volumes in depth. The following steps in this direction include: (i) the development of dedicated wavefront shaping solutions (e.g. computer generated holography, adaptive optics, pulse shaping) to control the propagation of ultrafast laser pulses through the ME; (ii) the design and test (both experimentally and through simulations) of optimized optical probes to outperform currently available ones, including new types of optical fibers and micro-lenses; (iii) the construction of the optical setup comprising two different ultrafast laser sources.



Projects in computational optics could also be proposed



Possibility of PhD thesis on similar subjects for which 3 year funding is already secured

Host lab
The project will be carried out at  the Vision Institute.
The Vision Institute / 15-20 National Ophthalmology Hospital also gathers many scientists, mostly biologists or clinicians, around the function and diseases of the vision and eye.

1. Emiliani et al. (2015), J. Neurosci., 35, 13917, DOI: 10.1523/JNEUROSCI.2916-15.2015
2. Papagiakoumou et al. (2010), Nat. Methods, 7, 848, DOI: 10.1038/nmeth.1505
3. Accanto et al. (2018), Optica, 5, 1478, DOI: 10.1364/OPTICA.5.001478
4. Ronzitti et al. (2017), J. Opt., 19, 113001, DOI: 10.1088/2040-8986/aa8299
5. Svoboda et al. (2006), Neuron, 50, 823, DOI: 10.1016/j.neuron.2006.05.019
6. Horton et al. (2013), Nat. Photonics, 7, 205, DOI: 10.1038/nphoton.2012.336
7. Xu et al. (1996), J. Opt. Soc. Am. B, 13, 481
8. Accanto et al. (2019), Sci. Rep., 9, 7603, DOI: 10.1038/s41598-019-43933-w