ET-SLM neurons · Electrothermal Spatial Light modulator for neuronal tissue imaging in depth

Electrothermal Spatial Light modulator for neuronal tissue imaging in depth

The development of new technics for controlling light propagation has always been the source of major innovations and discoveries in imaging. With their ability to control actively and spatially the light components, the spatial light modulators (SLMs) represent the ultimate goal in light shaping. They allowed substantial growth in the display sector thanks to recent innovations such as liquid crystal display (LCD), or the digital light processing (DLP) video projector. In the research field, phase-only SLMs are central tools in modern imaging domains ranging from astronomy to microscopy. Liquid crystal SLMs (LC-SLM) have become the essential tool for beam shaping in microscopy featuring high resolution (few µm) and high definition (several millions of pixels). While LC-SLMs provide outstanding achievement in superresolution, 3D localization, or optogenetics, their limited performances still remain a roadblock in many applications. Indeed, LC-SLMs are polarization sensitive, suffer from strong chromatic diffractive effects, and have an intrinsic response time of several ms. To overcome these limitations, spatial light modulation using thermo-optic effects has been recently proposed. Such an approach relies on heating materials displaying strongly temperature-dependent refractive indices, which refractive index is highly sensitive to temperature increase. To overcome these limitations, an Electrothermal Spatial Light Modulator (ET-SLM) called SmartLens has been developped. These SmartLenses are polarization-insensitive since they involve non-birefringent thermo-optical index modulations. As they operate in a refractive rather than diffractive regime, they are also relatively achromatic (unlike LC-SLMs) and can be used over a broad wavelength range. Despite its great promises, the SmartLens concept is still in its infancy, with several limitations that currently prevent several applications such as the response time, the number of actuators, or the sharpness of the modulation. The first objective of the project relies in improving these performances. They are particularly desired in the domain of imaging through dynamic scattering mediums such as in vivo brain tissues. Besides being one of the biggest scientific challenges of our times, deciphering how the brain works constitutes a priority research line for the European Union. Among the different optical tools employed, the use of SLM has revolutionized the field of optogenetics by enabling parallel stimulation. In this context, the second objective of the project aims to combine an ET-SLM with advanced microscopes systems and perform neuronal imaging. The last step of the project relies in pushing the capabilities of the ET-SLM in order to perform fast thermal wavefront applied in in imaging in complex media such as in brain depths.

Data: CORDIS, © European Union