This work deals with label free multiphoton imaging of the human lung tissue extra-cellular matrix (ECM) through
optical fibers. Two devices were developed, the first one using distal scanning associated to a double clad large mode
area (LMA) air-silica microstructured fiber, the second one using proximal scanning of a miniature multicore image
guide (30000 cores inside a 0.8 mm diameter). In both cases, the main issue has been efficient linear and nonlinear
distortion pre-compensation of excitation pulses. By inserting before the delivery fiber a compact (10 cm × 10 cm
footprint) grisms-based stretcher (a grating in close contact with a prism) made of readily available commercial
components, we achieved as short as 35-femtosecond-duration pulses that were temporally compressed at the direct exit
of a 2-meter-long fiber. Interestingly, this femtosecond pulse fiber delivery device is also wavelength tunable over more
than 100 nm inside the Ti: Sapphire emission band. With the help of distal scan system, those unique features allowed us
to record elastin (through two-photon fluorescence) and collagen (through second harmonic generation) fibered network
images. These images were obtained ex-vivo with only 15 mW @ 80 MHz of IR radiation delivered to the alveoli or
bronchus tissues. 3D imaging with 400-μm-penetration depth inside the tissue was possible working with a 2-meter-long
LMA fiber. With the help of proximal scanning, the miniature image guide allowed us to perform endoscopic real time
microimaging of the ECM ex vivo.
During glioblastoma surgery, delineation of the brain tumour margins remains difficult especially since
infiltrated and normal tissues have the same visual appearance. This problematic constitutes our research
interest. We developed a fibre-optical fluorescence probe for spectroscopic and time domain measurements.
First measurements of endogenous tissue fluorescence were performed on fresh and fixed rat tumour brain
slices. Spectral characteristics, fluorescence redox ratios and fluorescence lifetime measurements were analysed.
Fluorescence information collected from both, lifetime and spectroscopic experiments, appeared promising for
tumour tissue discrimination. Two photon measurements were performed on the same fixed tissue. Different
wavelengths are used to acquire two-photon excitation-fluorescence of tumorous and healthy sites.
The optical properties of the cornea have been a research subject of great interest for many years. Several
early theories have been put forward to explain with more or less success the optical transparency of this
tissue, but it was not until Maurice demonstrated in a very elegant way during the 50s that this optical
transparency could be explained by the regular ultrastructure of the cornea. When becoming edematous, the
cornea's ultrastructure is perturbed and the tissue becomes a strongly scattering medium.
With the emergence of ophthalmologic surgery by ultrashort pulse lasers in recent years, a regain of interest in
the subject of corneal transparency arose. However, relatively little and no recent data of transparency spectra
measurements covering a large wavelength range is available in the literature. The purpose of this study is to
provide quantitative values for light scattering and its relation to the degree of edema by measuring the
spectrum of transmitted light through corneas presenting different degrees of edema. This paper focus on the
comparison of laboratory measurements published earlier with a new simple method we propose We also for
eye banks to quantitatively measure the degree of transparency of corneal grafts by measuring the modulation
transfer function of a Siemens star viewed through a corneal graft. Indeed, there is no current method to
determine the transparency of corneal graft but the subjectivity of the laboratory technician or the ophthalmic
surgeon.
Femtosecond laser surgery in the volume of corneal tissue is typically performed wavelengths of about 1 μm,
which gives excellent results on transparent corneas. However, the outcome is much worse in the case of
oedematous or pathological corneas as the laser beam propagation is disturbed by optical scattering. Our studies
suggest that this phenomenon can be greatly reduced by using a better suited laser wavelength. Best results are
obtained at 1.65 μm.
Currently, no compact femtosecond laser at this wavelength is commercially available. We have developed a
new simple, compact and stable laser source consisting of a non linear crystal pumped by a compact commercial
solid-state laser emitting at 1.03 μm in a configuration of an Optical Parametric Generation (OPG). The output
wavelength of this system can be tuned in the spectral range of 1.45 - 1.8 μm. A series of ex vivo penetrating
incisions using energies of the order of a few microjoules on corneal tissues have been performed while varying
the wavelengths from 1.45 μm to 1.7 μm. The results have been compared to experiments performed at 0.8 μm
and 1 μm. The use of longer infrared wavelengths around 1.65 μm for femtosecond laser keratoplasty
significantly improves the quality and the penetration depth of incision in case of pathological tissues, without
inducing any additional side effects.
We are developing a non-linear fibered endomicroscope for imaging the extracellular
matrix collagen and elastin fibrillar networks during bronchoscopy. As a proof of concept, laser pulses at
the output of a standard 2 meter long single-mode fibre have been obtained with pulse duration of about
50 fs and pulse energy up to 50 uJ, using a specially designed grism line for the dispersion compensation.
With these pulses, we performed a spectroscopic characterization of the non-linear endogenous signal,
consisting of two-photon fluorescence and second harmonic generation, and originated from human
pulmonary tissue of various thickness, both in forward and backward geometry of signal collection, with
excitation at 830 nm.
Femtosecond laser surgery in the volume of corneal tissue is difficult in the case of oedematous or pathological corneas: in those corneas, the propagation of the laser beam is perturbed by the optical scattering. This phenomenon can be greatly reduced by using a better suited laser wavelength.
A series of ex vivo surgical experiments has been conducted at wavelengths around 1600 nm. The results have been compared to experiments performed at 800 nm and 1000 nm. We have compared penetration depth and incision quality as a function of wavelength and energy.
The specular transmittance spectrum of human corneas is studied using a confocal geometry set-up. The comparison of the obtained spectrum with the total transmittance spectrum permits the determination of the stromal scattering spectrum of pathological corneas. The dependence of the scattering cross section on
wavelength dependence is analyzed.
Nowadays, femtosecond lasers are routinely used in refractive eye surgery. Until recently, commercialised clinical systems
were exclusively based on ytterbium or neodymium-doped solid state lasers emitting sub-picosecond pulses at a
wavelength of about 1 μm and repetition rates of a few 10 kHz. These systems use pulse energies in the μJ range and
focussing optics of NA = 0.3 to 0.5. Recent developments have provided a variety of alternative and equally viable approaches:
systems are now available using nJ pulses at high numerical apertures and MHz repetition rates - an approach
so far only used for femtosecond cell surgery - and fibre laser technology is now being used for femtosecond laser corneal
surgery.
Recent research has also provided more insight in side effects occurring in present systems: self focusing phenomena and
so far unexplained periodical structures have been observed even at high numerical apertures (NA >> 0.5) and moderate
pulse energies. The interaction of femtosecond laser pulses with strongly scattering tissue has been studied in view of
extending the application of femtosecond lasers to keratoplasty for opaque corneas and to glaucoma surgery. The use of
new laser wavelengths and adaptive optics has been proposed.
Despite the reputation of femtosecond surgical systems for their precision, repeatability and the absence of secondary
effects or complications, a closer examination reveals the presence of subtle phenomena which merit further investigation.
We present three of these phenomena: the influence of optical aberration on the quality of the incision, the occurrence
of filamentation effects, and the deposit of microscopic glass fragments when performing penetrating incisions.
Two processes explain radioluminescence of organic and inorganic materials. Exposition of organic materials to ionizing particles leads to the excitation of the molecules of the matrix. The relaxation leads to photon emission. In the case of the inorganic materials a self-trapped exciton (STE) propagates in the crystal until it reaches and excites an impurity; the relaxation of this impurity may be radiative.
We observed that lanthanides (ErIV or NdIV) doped materials (porous or ED2 glasses) show some characteristic emission rays. The spectra are quite similar to the expected ones for inorganic materials, while these materials are organic. We developed a model explaining how the radioluminescence of the organic materials excites the lanthanide ions, and then the observed radioluminescence emission spectra can be explained by the Judd-Ofelt theory.
Several materials have been studied: erbium doped porous glass (ErIV:PG), neodymium doped ED2 glass (NdIV:ED2), and also a sample of titan sapphire (Ti:Sa) as a comparison sample for inorganic materials. These samples have been exposed to H2+, 4He++, 12C++ ions accelerated up to 4.1 MeV with a Van de Graaff accelerator.
The emission spectra have been measured and a study of the luminescence lifetime of the material has been made. Luminescence lifetime of the characteristic rays is dependent on the radiation dose. These observations allow us to conclude that the lanthanide ions are well excited by the standard radioluminescence of the undoped material. Also, studies have been made as a function of the deposited energy to investigate the potential applications. All these results will be presented and discuted.
Evaporated films of the azo-material DR 1 have been investigated. In the as-grown state partly crystalline films with low transmittance are obtained. Using homogeneous exposure transparent regions may be formed. The recording of holographic gratings in thin films (< 1 μm) of the azo dye is investigated for the case of more-dimensional
light-intensity patterns. The mechanism of the photo-isomerisation of the azo-compounds is used to form dual gratings with a refractive index grating and a surface-relief grating. The grating-formation is investigated in case of 1D-gratings first. The time dependent diffraction efficiency is discussed in a model of 2 processes with different time-constants. A material transport process is involved in the formation of relief patterns. The enhancement of the modulation-depth of the surface-relief gratings is investigated for the application of a Corona discharge and a thermal treatment after the holographic recording. 2D-gratings are formed using either a 3-beam holographic set-up or a consecutive method. The resulting light patterns are simulated. Diffraction patterns and AFM-measurements are used to confirm these simulated structures. The modulation of the surface-relief gratings can be enhanced by thermal treatment after the holographic recording.
Studies of some optical materials, like fluored glass, crystals or polymers, show an important luminescence in the visible spectrum, near UV, due to high energy radiation (α, β, n, X-rays or γ). This phenomenon, known as radioluminescence or scintillation, is especially used for medical physics and dosimetry. Those materials can be doped by heavy metal ions, like rare-earth elements. Recent studies show that the irradiation of such rare-earth doped scintillators, can emit visible spectral rays. Those are corresponding to rare-earth transitions, in addition to the normal radioluminescence of the undoped material. Those peaks cannot correspond to the propagation of the self-trapped exciton in the inorganic scintillator. We actually believe the rare-earth ions are just excited by the light (blue) emitted by the scintillator, and that finally this phenomenon is not electronic but photonic, thus a kind of radioluminofluorescence.
The effective refractive index of a guided wave depends on its polarization due to the anisotropic phase shift during the total internal reflection. Thus the grating-coupling angle is in general different for TM and TE polarized light. The compensation of this anisotropy is a difficult task. Some optical materials may present a significant birefringence when exposed to a polarized light. We would like to compensate the optical anisotropy using this photo-induced birefringence phenomenon, which would allow us to bring back the TM grating-coupling angle to the TE one. During these studies, we have developed an optical material, which allows us the formation of a relief grating via traditional light exposure techniques. At the same time, this material exhibits a significant photo-induced birefringence. This takes place thanks to the molecular reorientation phenomena after that the recording of the grating coupler is over. It is important to note that this last process does not affect significantly the grating-coupler. Furthermore we have observed that photo-induced birefringence present a strong reminiscence after the pump beam deactivation. The grating coupling experiments with and without the photo-induced phenomena were conducted.
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