Mechanical and optical properties are the main criteria for assessing the health of dental tissue in contemporary dentistry. Dentinal pathological changes can be detected by visuo-tactile and radiographic methods to guide clinicians in establishing a relevant diagnosis and an adapted therapy. However, such approaches cannot give information on the dentinal microstructure. Recently, laser ultrasonic techniques have been deployed to evaluate the mechanical properties of enamel [1,2] However, such techniques lack the resolution to reveal the transitions differences between tissue layers.
In this work, we used Brillouin light scattering spectroscopy as a non-contact alternative to probe mechanical changes in dentin and dentin-resin interface at GHz hypersonic frequencies. We obtained maps of the Brillouin frequency shift and linewidth that can be interpreted as maps of sound velocity and viscosity. In addition, we observed the specimens by a homemade nonlinear microscopy setup [3]. A 730 nm wavelength Titanium-sapphire laser was used as an excitation source for two-photon excitation fluorescence microscopy (TPEF), while 1040 nm wavelengthYb:KGW laser was used for second harmonic generation (SHG).
Our results show significant changes between healthy tissues and pathological lesions. Such results can help to precisely delineate destructed dentin during clinical procedures, paving the way to minimally invasive strategies. In addition, our simultaneous analysis of Brillouin maps and nonlinear images brings valuable information on structure-related mechanical properties of dentin and dentin-resin adhesive interface.
1. Wang et al, Experimental and numerical studies for nondestructive evaluation of human enamel using laser ultrasonic technique. Appl Opt 52, 6896-6905 (2013).
2. Wang et al., Laser ultrasonic evaluation of human dental enamel during remineralisation treatment. Biomed Opt Express 2, 345-355 (2011).
3. Rabasović M et al. Nonlinear microscopy of chitin and chitinous structures: a case study of two cave-dwelling insects. J Biomed Opt 20, 016010 (2015)
The present study describes utilization of two photon excitation fluorescence (2PE) microscopy for visualization of the hemoglobin in human and porcine erythrocytes and their empty membranes (i.e., ghosts). High-quality, label- and fixation-free visualization of hemoglobin was achieved at excitation wavelength 730 nm by detecting visible autofluorescence. Localization in the suspension and spatial distribution (i.e., mapping) of residual hemoglobin in erythrocyte ghosts has been resolved by 2PE. Prior to the 2PE mapping, the presence of residual hemoglobin in the bulk suspension of erythrocyte ghosts was confirmed by cyanmethemoglobin assay. 2PE analysis revealed that the distribution of hemoglobin in intact erythrocytes follows the cells’ shape. Two types of erythrocytes, human and porcine, characterized with discocyte and echinocyte morphology, respectively, showed significant differences in hemoglobin distribution. The 2PE images have revealed that despite an extensive washing out procedure after gradual hypotonic hemolysis, a certain amount of hemoglobin localized on the intracellular side always remains bound to the membrane and cannot be eliminated. The obtained results open the possibility to use 2PE microscopy to examine hemoglobin distribution in erythrocytes and estimate the purity level of erythrocyte ghosts in biotechnological processes.
Mihailo Rabasović, Dejan Pantelić, Branislav Jelenković, Srećko Ćurčić, Maja Rabasović, Maja Vrbica, Vladimir Lazović, Božidar P. Ćurčić, Aleksandar Krmpot
We performed a study of the nonlinear optical properties of chemically purified chitin and insect cuticle using two-photon excited autofluorescence (TPEF) and second-harmonic generation (SHG) microscopy. Excitation spectrum, fluorescence time, polarization sensitivity, and bleaching speed were measured. We have found that the maximum autofluorescence signal requires an excitation wavelength below 850 nm. At longer wavelengths, we were able to penetrate more than 150-μm deep into the sample through the chitinous structures. The excitation power was kept below 10 mW (at the sample) in order to diminish bleaching. The SHG from the purified chitin was confirmed by spectral- and time-resolved measurements. Two cave-dwelling, depigmented, insect species were analyzed and three-dimensional images of the cuticular structures were obtained.
We describe a method for dual-view biomechanical strain measurements of highly asymmetrical biological objects, like teeth or bones. By using a spherical mirror, we were able to simultaneously record a digital hologram of the object itself and the mirror image of its (otherwise invisible) rear side. A single laser beam was sufficient to illuminate both sides of the object, and to provide a reference beam. As a result, the system was mechanically very stable, enabling long exposure times (up to 2 min) without the need for vibration isolation. The setup is simple to construct and adjust, and can be used to interferometrically observe any object that is smaller than the mirror diameter. Parallel data processing on a CUDA-enabled (compute unified device architecture) graphics card was used to reconstruct digital holograms and to further correct image distortion. We used the setup to measure the deformation of a tooth due to mastication forces. The finite-element method was used to compare experimental results and theoretical predictions.
We have measured non-linear Faraday effects for dark and bright long-lived Zeeman coherences in the D2 resonance line of 85Rb, for linearly polarized input laser light. Zeeman coherence in the bright state show enhanced nonlinear effects, larger values for the angle of polarization rotation and higher rates of the polarization rotation, similar to recent results for higher refractive index and dispersion in the bright state of Cs 1. Dark and bright states also show different dependence of both polarization rotation angle and of polarization rate on the laser intensity, while the resonance width for both states varies similarly with the laser intensity. We show small enhancement of such non-linear effects when the laser beam diameter increases from 1 mm to 5 mm. Ellipticity of transmitted laser beam vary strongly for amplitudes of the external magnetic field smaller then 50 mG, but the maximum value of the ellipticity remains below &pgr;/300.
Microlens and microlens arrays have been successfully produced using sensitized gelatin and Nd:YAG laser at 532 nm.
Obtained microlenses are divergent (negative), with parabolic profile and 600 &mgr;m useful aperture diameter. Microlenses
have near diffraction limited performance with resolution more then 50 cycles/mm for the total field of view
(2&ohgr; = 18°). Single microlens is manufactured in just a few seconds using 60 mW unfocused Nd:YAG laser beam.
Modification of Koester's interferometer is described in this paper, which is used for calibration of gauge blocks up to 100mm in length. Higher precision was obtained by using a camera (for measurement of fringe fractions) and lasers as the source of light. The process of digitalization and processing of the interference pattern images is also described, as well as rejection of noise caused by transmission of laser beams through the optical fiber.
We have studied experimentally and theoretically Hanle EIA on the closed Fg = 3 goes to Fe = 4 D2 transition of 85Rb. Atoms were excited by the laser light with different polarization, from linear to circular. Results of the theoretical calculations of the laser transmission, based on optical Bloch equations for density matrix elements for the same atomic system, show important effects of magnetic field transverse to the laser light. We were not able to control transverse magnetic field in the experiment but the theoretical results are still applicable to our experimental data due the presence of laboratory stray magnetic field in the vicinity of the Rb cell, occurring because of imperfect magnetic shielding.
KEYWORDS: Teeth, Holography, FDA class II medical device development, Polymerization, Composites, FDA class I medical device development, Finite element methods, Light emitting diodes, Polymers, Holographic interferometry
An experimental technique to reveal the effects of dental polymer contraction is established to choose the most appropriate polymerization technique. Tooth deformation following a dental filling polymerization is analyzed using double-exposure holographic interferometry. A caries-free, extracted human molar is mounted in dental gypsum and different cavity preparations and fillings are made on the same tooth. Dental composite fillings are polymerized by an LED light source especially designed for this purpose. Holographic interferograms are made for occlusal (class I), occlusomesial (class II), and mesioocclusodistal (class II MOD) cavities and fillings. Maximum intercuspal deformation ranges from 2 µm for the class I cavity to 14 µm for the MOD class cavity. A finite element method (FEM) is used to calculate von Mises stress on a simplified tooth model, based on experimental results. The stress varies between 50 and 100 MPa, depending on the cavity type.
We have demonstrated that the frequency of the laser radiation can be stabilized by controlling its coherence properties. Theoretical analysis of the laser radiation visibility function was performed and connection with the longitudinal mode structure was established. It was established that laser emission frequency could be stabilized by controlling the visibility of interference pattern. Calculations have shown that, in theory, stability around 4 kHz can be expected. As a proof-of-the-principle, a HeNe laser, stabilized by measurement of the interference pattern visibility in a modified Mechelson interferometer, was built. Stabilization was performed by temperature control of the laser tube in a digital feedback loop and total frequency variation of 3 MHz was obtained. Possible improvements of the experimental setup, together with some applications of multimode stabilized lasers are discussed.
Electromagnetically induced transparency and absorption is observed in a transmission of the coupling laser, locked to transition between hyperfine levels of the ground and excited states of 85Rb. The transmission was monitored in a V, Λ and N-type systems while the probe laser, with similar power as the coupling laser, scans across the hyperfine levels F' of the 2P3/2. The measured width of the EIT resonance increases with a square-root dependence of laser intensity. The EIA was observed only for a cycling transition and for F' = F+1, where F and F' are the angluar momentum of the hyper-fine levels of the 2S1/2 and 2P3/2, respectively. We demonstrated the effect of a three-photon EIA in a four-level scheme that involves the Raman transitions via virtual level.
Tomographic alogithms are modified in order to reconstruct the inf ormation previously stored by focusing laser radiation in a volume of photosensitive media. Apriori information about the position of bits of inf ormation is used. 1. THE PRINCIPLES OF TOMOGRAPHIC MEMORIES Tomographic principles can be used to store and reconstruct the inf ormation artificially stored in a bulk of a photosensitive media 1 The information is stored by changing some characteristics of a memory material (e. g. refractive index). Radiation from the two independent light sources (e. g. lasers) is f ocused inside the memory material. In this way the intensity of the light is above the threshold only in the localized point where the light rays intersect. By scanning the material the information can be stored in binary or nary format. When the information is stored it can be read by tomographic methods. However the situation is quite different from the classical tomographic problem. Here a lot of apriori information is present regarding the p0- sitions of the bits of information profile representing single bit and a mode of operation (binary or n-ary). 2. ALGORITHMS FOR THE READOUT OF THE TOMOGRAPHIC MEMORIES Apriori information enables efficient reconstruction of the memory contents. In this paper a few methods for the information readout together with the simulation results will be presented. Special attention will be given to the noise considerations. Two different
In laser systems where it is impossible or impractical to use
lamps and rod whose effective perimeters are matched, some elements of
construction of cavities using nonimaging optical concentrators can be
used to achieve improved designs in regard to efficiency and pumping uniformity.
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