IMAGING IN TURBID MEDIA
California Institute of Technology (USA)
Title: Deep tissue imaging and analysis by optical time-reversal
We appear opaque because our tissues scatter light very strongly. Interestingly, optical scattering is deterministic and can be time-reversed in much the same way a ricocheting billiard ball can be made to retrace its trajectory if nudged appropriately. I will discuss out recent results in using ultrasound tagging in combination with digital optical phase conjugation to focus light tightly and deeply within biological tissues. I will also report on our experiments using digital optical phase conjugation to tightly focus light on a moving target in a scattering medium. This technology can potentially enable incisionless laser surgery, targeted optogenetic activation, high-resolution biochemical tissue imaging and more.
Astronomic Observatory of Padova INAF (Italy)
Title: Large and extremely large: Field of View and telescope sizes in AO for Astronomy
The narrow Field of View of AO systems in Astronomy is one (among with complexity and sky coverage) of the main operational limiting factors. With the advent of the large (i.e. 8 to 10m class) telescopes and the coming era of extremely large telescopes (in the 20 to 40m range of diameter) the quest for a larger Field of View becomes more and more relevant. I describe the past and current efforts in wide field AO systems in astronomy and the ongoing developments for a new paradigm, where the sensed Field of View is going to surpass the scientifically usable Field of View in order to give access to diffraction limited capabilities with a sky coverage approaching the whole celestial sphere.
ADAPTIVE OPTICS DEVICE DEVELOPMENT
Queen Mary University of London, School of Engineering & Materials Science (UK)
Title: Electrically tuneable lenses made of electromechanically active polymers
F.Carpi, M.Pieroni, C.Lagomarsini and D.De Rossi
Electrical control of optical focalisation is important in several fields, such as consumer electronics, medical diagnostics and optical communications. As an alternative to complex, bulky and expensive state-of-the-art approaches based on shifting constant-focus lenses, we are currently developing electrically tuneable lenses made of a highly-performing class of electromechanically active polymers, known as dielectric elastomers. This original approach allows focusing tuneability to be achieved with compact size, low weight, fast and silent operation, shock tolerance, no overheating, low power consumption, and inexpensive off-the-shelf materials. The presentation will show ongoing progress and future challenges.
Italian Institute of Technology (Italy)
Title:Sound driven optofluidic lenses for high-speed focusing
The requirement of accurate z-focus control constitutes a time limiting step for applications as important as laser processing or imaging. Several approaches have been developed to circumvent this problem including mechanical sample translation or the use of varifocal lenses for focal plane shifting. However, in all cases the capacity to control focus is fundamentally limited by inertia to speeds well above 1 ms. In this talk, I will present an optofluidic lens that uses acoustic waves to periodically modulate the refractive index of a fluid and achieve focus scanning speeds at microsecond time scales. Such high speed enables one to simultaneously capture multiple focal planes in brightfield and confocal microscopy, or to uniformly process irregular surfaces for high-throughput laser microfabrication.
Janelia Research Campus (USA)
Title: From stars to neurons – adaptive optical microscopy for deep brain imaging
Imaging neurons deep within the brain of a living mouse shares many similarities with gazing at distant stars with a telescope. In both cases, imaging quality is limited by optical aberration and scattering. Wavefront shaping using adaptive optics (AO) has revolutionized astronomy by allowing us to obtain sharp images of celestial objects through the turbulent atmosphere. Similar technology can be applied to microscopy for optically transparent samples but not mammalian brains, which are highly scattering. In this talk, I will describe our work to extend AO microscopy to these more optically challenging systems, which has allowed us to image both the input and output of mouse cerebral cortex with diffraction-limited resolution.
University of Oxford (UK)
Title: Adaptive Optics in Microscopy
High resolution microscopy relies on the use of high quality optics with the goal of obtaining diffraction-limited operation, working at the physical limits imposed by the wavelength of the light. Yet in many cases this goal is not achieved as aberrations, distortions in the optical wavefront, blur the focus and reduce the resolution of the system. Aberrations can arise from imperfections in the optics, but are often introduced by the specimen, particularly when imaging thick specimens. One common source is a planar mismatch in refractive index, such as that between the microscope coverslip and the specimen mounting medium, which introduces spherical aberration. Biological specimens also exhibit variations in refractive index that arise from the three-dimensional nature of cells and tissue structures. In general, these aberrations become greater in magnitude and more complex in form as the focusing depth is increased. The induced wavefront aberrations distort the focus causing a reduction in resolution and, often more importantly, reduced signal level and contrast. These effects limit the observable part of the specimen to a region near the surface.
Adaptive optics systems enable the dynamic correction of aberrations through the reconfiguration of an adaptive optical element, for example a deformable mirror or liquid crystal spatial light modulator. Various adaptive schemes have been developed for a range of different modalities including confocal, multiphoton and widefield microscopes. Some systems employ wavefront sensors to measure aberrations, whereas others use indirect sensing to determine the wavefront distortions. We review the methods and applications of these systems in biological sciences and other areas. We also present recent developments in adaptive optical methods for super-resolution nanoscopy – methods through which resolutions far below the diffraction limit of the microscope are achieved through combinations of optical and photo-physical effects.
Simon Fraser University, BORG Lab (Canada)
Title: Wavefront sensorless adaptive optics optical coherence tomography for retinal imaging in mice and in humans
We present our work on wavefront sensorless adaptive optics optical coherence tomography (WSAO-OCT) as a technique for in vivo high-resolution depth-resolved imaging that mitigates some of the challenges encountered with use of wavefront sensors. In WSAO-OCT, the Hartmann Shack wavefront sensor is replaced by a depth-resolved image-driven optimization algorithm, with the metric based on the OCT volumes acquired in real-time. A high-speed GPU processing platform and fast modal optimization algorithm was developed for real-time, in vivo retinal imaging. Image quality improvements with WSAO OCT are presented for both pigmented and albino mouse retinal data. We also describe WSAO-OCT for imaging the human photoreceptor mosaic in vivo at several eccentricities, and demonstrate the improvement in photoreceptor visibility with WSAO aberration correction.
Centre for Vision in the Developing World, St Catherine's College, Oxford (UK)
Title: How can we get several billion people in the world to see with 20/20 Vision?
A consensus is beginning to emerge that between two and three billion people in the world need corrective eyewear if they are to see as clearly as possible. Whilst one solution to this problem is to provide them with conventional eyeglasses to correct their refractive error, that turns out to be impossible to achieve without training a very large number of optometrists , and putting in place a large infrastructure, something which would be both expensive and lengthy.
An alternative approach is to take advantage of the fact that everyone has an eye-brain adaptive optical system which has evolved over time to function very well. If a wearer is equipped with eyeglasses with simple lenses whose focus can be easily changed manually, then the wearer can effectively " piggy-back" on their own eye-brain adaptive optical system to find best focus, and thereby correct their own refractive error with such glasses. Our clinical research has shown that this approach can work extremely well, as I will explain. Several challenges remain, and I will suggest how they might be dealt with.
ADAPTIVE OPTICS FOR HIGH POWER LASERS
Bruno Le Garrec
ELI Beams (Czech Republic)
Title:Adaptive optics for High Power Lasers
Using adaptive optics in lasers is only less than 20 years old. Everything started in the 90’s when people where dreaming at powerful laser beams propagating over long distances and still being able to damage some flying device. The first laser systems to be equipped with adaptive optics are the fusion lasers: NIF in the US and LMJ in France. This was possible because wavefront sensors were becoming available and because many attempts were made to successfully design and operate large size deformable mirrors. I will give an overview of the different techniques used together with some specific tricks coming from using adaptive optics in laser systems.