Contrary to the intense debate about brain oxygen dynamics and its uncoupling in mammals, very little is known in
birds. In zebra finches, picosecond optical tomography (POT) with a white laser and a streak camera can measure in vivo
oxy-hemoglobin (HbO2) and deoxy-hemoglobin (Hb) concentration changes following physiological stimulation
(familiar calls and songs). POT demonstrated sufficient sub-micromolar sensitivity to resolve the fast changes in
hippocampus and auditory forebrain areas with 250 μm resolution. The time-course is composed of (i) an early 2s-long
event with a significant decrease in Hb and HbO2, respectively -0.7 μMoles/L and -0.9 μMoles/L (ii) a subsequent
increase in blood oxygen availability with a plateau of HbO2 (+0.3μMoles/L) and (iii) pronounced vasodilatation events
immediately following the end of the stimulus. One of the findings of our work is the direct link between the blood
oxygen level-dependent (BOLD) signals previously published in birds and our results. Furthermore, the early
vasoconstriction event and post-stimulus ringing seem to be more pronounced in birds than in mammals. These results in
bird, a tachymetabolic vertebrate with a long lifespan, can potentially yield new insights for example in brain aging.
VASAO is an ambitious project that explores new conceptual direction in the field of astronomical adaptive optics. In
the era of 8 meter and larger telescopes, and their instrument costs and telescope time pressure, there is a natural niche
for such ground-breaking conceptual development in the 4 meter class telescope. The aim of VASAO is to provide
diffraction limited imaging in the visible with 100% sky coverage; the challenge (but potential rewards) arises from the
simultaneity of these requirements. To this end, CFHT is conducting a feasibility study based on the polychromatic
guide star concept (Foy et al., 1995 ) coupled with a high order curvature AO system, presented in this paper.
A number of experiments have been started (or carried out) to study the challenges and limits of the techniques involved
in an operational setting; these include the FlyEyes detector, and a polychromatic tip-tilt test on natural stars.
Because such a project straddles such a fine line between facility instrument and experimental facility, careful thought
has to be given to the balance between modes of operations and potential astrophysical targets.
A European Laser Guide Star (LGS) test facility is proposed for the 4.2m William Herschel Telescope (WHT) on La
Palma. It will test the next-generation Adaptive Optics (AO) LGS technologies to aid risk mitigation of Extremely Large
Telescope (ELT) LGS AO systems. In particular, critical scaling of current LGS AO technologies to ELT dimensions
will be tested. For example, experiments addressing increased spot elongation, cone effect and the order of correction
A pan-European consortium proposes to construct test facility infrastructure on the WHT for a number of risk mitigating
experiments. The infrastructure includes the construction of a Nasmyth platform based controlled environment 'Ground-based
Adaptive optics Innovative Laboratory' (GRAIL), an experimental test environment 'Testbed integration facility'
(TIF) and some common-experiment equipment such as the Common Re-Imaging AO System.
Experiments that are proposed for this facility cover the areas of laser technologies, spot elongation, LGS wavefront
sensing, parallel launch concepts, Multi-Object AO, atmospheric characterisation, co-phasing and real-time control
system risk mitigation.
The differential atmospheric tip-tilt can be measured using a Polychromatic Laser Guide Star. A two photon excitation
has been proposed. It consists in exciting the 4D5/2 level of mesospheric sodium atoms with two identical lasers operating
at 589 nm and 569 nm. With two modeless lasers of 2×15W at the mesosphere level, this scheme will produce a returned
flux at 330 nm of about 4×104 photons/s/m2. Thanks to our modeless laser, we propose a new method which consists in
exciting directly the 4P3/2 sodium level with one photon excitation, using a single laser operating at 330 nm. This
solution was previously rejected probably because of strong saturation problems using single longitudinal mode lasers.
We show that 1 W modeless laser at 330 nm can produce the same returned flux at 330 nm. This solution will save at
least 400 k€ of equipment. Moreover, our new method is very promising in terms of simplicity but also in terms of flux
because the returned flux above will probably be not sufficient for getting a good Strehl ratio. We propose very efficient
solid state laser systems for the production of tens of watts at 330 nm.
A new ultrafast Diffuse Optical Tomography (DOT) has been developed for real time in vivo brain metabolism monitoring in songbird. The technique is based on space resolved time of flight measurements of the photons across the brain tissues. A three dimensional reconstruction of the brain activity is foreseeable by means of a double space and time sampling of the reflectance signal. The setup and the treatment procedure are described in depth and promising preliminary results showing the response of brain tissues to hypercapnia stimulations (increase of CO2) are presented.
We demonstrate the possibility of using periodically poled lithium
niobate crystals (PPLN) as a direct source of entangled photon
pairs. Two configurations are studied. The first enables the
generation of polarization-entangled states from a one-dimensional
PPLN structure at different frequencies; the second is dedicated
to the production of frequency-entangled states from a
bi-dimensional PPLN structure. The engineering of both of these
PPLN structures are described from a theoretical perspective.