Background and Objective: 6.05-μm-laser is strongly absorbed by means of both the OH bending of water and
the amide-I of proteins. In order to prove the usefulness of dentin ablation by laser irradiation with λ = 6.05 μm, we
investigated an ablative behavior of bovine dentin without a water spray.
Study Design/Materials and Methods: The dehydrated bovine dentin was irradiated without a water spray by the
mid-infrared Free Electron Laser at λ = 6.05 μm and λ = 9.7 μm, while varying the laser parameters, such as the
incident fluence and the number of pulse. We observed the configurational changes in the irradiated dentin surface
using a scanning electron microscope and estimated the removed volume using a laser confocal microscope. Also,
we measured the temperature rise using a radiation thermometer and the emission spectrum using a fiber optics
spectrometer during laser irradiation.
Results: We found the followings: (1) the dentin was ablated by the evaporation of proteins at the maximum
temperature rise of ~400 degC; (2) the irradiated dentin surface had dentinal tubules and was not melted; (3) the
extent of the ablative behavior was proportional to the laser parameters used; (4) the tensile bonding strength
between the irradiated dentin surface and the composite resin was significantly higher than that for Er:YAG laser
irradiation.
Conclusion: We can conclude that 6.05-μm-laser can thermo-mechanically excise dentin by the evaporation of proteins even without a water spray. We showed the applicability of a 6.05-μm-laser to a non-invasive laser treatment.
Background and Objective: The surface modification of root dentin by mid-infrared (MIR) pulsed-laser irradiation is a potential candidate for non-invasive treatment to prevent root surface caries. The purpose of this study is to compare the relative acid resistance of root dentin treated with an MIR Free Electron Laser emitting at between 9.0 μm and 9.7 μm.
Study Design/Materials and Methods: The average power density was varied over the range 7.5-51.5 W/cm2. After irradiation, the samples were immersed in a 0.1 M lactic acid solution. Acid resistance was estimated as the quantity of Ca dissolved in the solution after immersion times (tim) of 1-22 h.
Results: The acid resistance of all samples increased markedly, but only until tim = ~3 h. It did not depend significantly on the laser parameters used.
Conclusion: The surface modification of root dentin leads to improved acid resistance, but this only persists for a few hours and therefore represents a poor treatment for root surface caries.
For non-invasive laser dental treatmet, a real-time and non-contact monitoring technique is needed. We have investigated the extent of the surface modification of root dentin using photoacoustic spectroscopy (PAS) and pulsed-photothermal radiometry (PPTR), and have discussed the applicability of each technology to in vivo monitoring during laser treatment. Root dentins were used as specimens. The wavelength, average power density, and exposure time used were varied within the ranges λ = 9.0-10.6 μm, Pav = 7-28 W/cm2, and τ = 0-10 s respectively. The temporal behaviors of the laser-induced acoustic waves and the temperature rise were measured with an audible microphone and a radiation thermometer, respectively. The extent of the surface modification was evaluated by using information on the ablation depth and the absorption spectrum of the irradiated dentin. The morphological and chemical changes of the irradiated dentin can be made available to assist in dentinal tubule sealing and increased acid resistance for root surface caries therapy. It was found that time-resolved measurements of the acoustic waves and the temperature are useful for a real-time understanding of the extent of the morphological and chemical changes, respectively. We have demonstrated that applicability of an in vivo monitoring technique using PAS and PPTR for root surface caries therapy.
Recrystallization of tooth dentin by the application of mid- infrared (MIR) pulsed-laser irradiation is one candidate for a novel, non-invasive treatment for the prevention of tooth decay. Recrystallized dentin functions in a similar way to dental enamel. To recrystallize the dentin effectively and non-invasively it is essential to estimate quantitatively and qualitatively the laser parameters, such as the wavelength and the average power density, required for recrystallization. The laser-tissue interaction is initiated effectively by selective excitation of phosphate acid ions (PO4) in the dentin. Using a tunable, MIR Free Electron Laser (FEL) in the wavelength region of 8.8- 10.6micrometers , corresponding to intense absorption bands due to PO4 vibration modes, we have investigated macroscopically extent of surface modification of dentin, and we have obtained experimental results related to the ablation depth, the MIR absorption spectrum, and the elemental chemical composition. From these results, it was found that (1) the laser parameters at which efficient surface modification, without enhanced ablation effects, occurred were estimated to be approximately in the wavelength and average power density regions of ~9.4- 10.3micrometers and ~10-20 W/cm2, and that (2) in this region PO4 vibration modes with lower binding energy were preferentially excluded from the dentin.
Indocyanide green (ICG) is widely used as a tracer for the non-invasive estimation of liver function. ICG has properties of binding with plasma protein, and has a large absorption peak at 805 nm. There were no reports, however, about the IR absorption peak of ICG at 7.1 micrometers , which absorption coefficient amounts to approximately 13000cm-1. In this study, ICG was exposed to free electron lasers (FELs) with wavelength of 7.1 micrometers and usefulness of ICG as an IR-marker was discussed. ICG film sample was formed on IR-transparent BaF2 crystal substrate and exposed to FELs with the wavelength of 7.1micrometers . After exposure the sample was analyzed by FT-IR and film thickness measurements. As results, ICG ablated with the FEL of the power density of more than 5 W/cm2(equalsPdth), and that the molecular structure of ICG was still stable for the power density of less than Pdth, 3 W/cm2. Therefore, ICG can be considered as a novel infrared marker (IR marker) to the living tissue which absorbs FEL photon energy without changing the IR absorption peak.
A micropulse-picking system attached to a free electron laser (FEL) opens a broad range of potential applications of ultrafast phenomena in medicine and biology. This paper reports the micropulse-picking system of a mid-infrared (IR) FEL at iFEL, Osaka University. We have designed the system with a germanium acousto-optic modulator (Ge-AOM), which can effectively deflect the direction of the FEL propagation due to Bragg diffraction of the FEL and radio frequency (RF) waves. The system includes a reducing optics for the FEL beam, a focusing optics onto the Ge- AOM and a micropulse-picking device (including the Ge-AOM and the RF driver). The system, which is independent on wavelength in the mid-IR region, can be realized by using the following technique: the RF frequency is carefully controlled to satisfy the Bragg angle matching over the mid-IR region. As a result, the micropulse-picking system can supply single and/or some FEL micropulses at an arbitrary repetition rate over the mid-IR region (equals 2 - 12 micrometers ) and can control the resulting peak power and average power in the ranges of approximately 1 - 2 MW and approximately 50 (mu) W - 20 mW, respectively.
An imploded plasma core is irradiated by a 100 ps laser pulse in a model experiments of fast ignition. Additional laser pulses for drilling and heating are introduced co- axially with the laser beams for the implosion. The preformed imploded core is created by the 12 beams of 0.53 micrometers laser with the total energy of 800 J. The additional heating pluses contain 100 ps pulses separated by 300 ps at the wavelength of 1.06 micrometers with the total energy of 320J. The first pulse is intended for drilling the coronal pulses surrounding the core and the second is for addition heating of the core. We measured the imploded core additionally heated with 100 ps pulses.
Ultra-fast x-ray imaging is of great importance for diagnosing laser-driven inertial confinement fusion (ICF) plasmas. Typical required spatial and temporal resolutions are 10 micrometer and 10 ps, respectively. We have developed variety of one- (1D) and two-dimensional (2D) image sampling technique for ultrafast time-resolved x-ray imaging with x-ray streak cameras. Moire imaging of an x-ray-backlit target has been developed as 1D image sampling of an objective with 1D repetitive structure with a spatial resolution of 5 micrometer for use in experiments on hydrodynamic instabilities in laser- accelerated targets. With 1D sampling of repetitive 2D images, a multi-imaging x-ray streak camera (MIXS) with temporal- and spatial-resolutions of 10 ps and 15 micrometer, respectively, has been developed and successfully utilized for diagnosing uniformity and heating process of the imploded core plasmas. Two types of spectroscopic applications of the MIXS have been developed. One is multi-channel MIXS (McMIXS) which has three MIXS channels with various spectral responses for time- resolved 2D temperature measurement. Another is monochromatic MIXS (M-MIXS) for temperature, density and material mixing measurement, in which monochromatic images with Bragg crystals are coupled to MIXS. Finally, 2D image sampling of a 2D image on an x-ray streak camera (2D-SIXS) was also developed.
Indirect/direct-hybrid drive scheme to suppress the initial imprint of the laser irradiation nonuniformities has been proposed and investigated as a new drive scheme for inertial fusion. In direct drive inertial confinement fusion, initial imprinting of laser irradiation nonuniformity is considered to cause seeding of the perturbation on target surface in the very beginning of the irradiation which may be amplified by Rayleigh-Taylor instability in the acceleration phase of the implosion and be deleterious to efficient heating of the hot spark at the center of the compressed fuel core plasma. In indirect/direct-hybrid drive scheme, the target is first irradiated very uniformly with low-intensity soft x-ray prepulse from external sources apart from the target. Indirect x-ray pre-irradiation of the surface causes a pre- expansion layer of the plasma before the irradiation of the direct drive laser beam. When the drive beam comes later, the target has a substantial stand-off distance between the ablation front and the beam absorption region. Thus the thermal smoothing effect is expected to occur in this transport layer, and the initial imprint can be significantly reduced. We have demonstrated planar target experiments on the indirect/direct hybrid scheme and observed reduction of the initial imprint. Implosion experiments the indirect/direct hybrid drive spherical capsules with external x-ray sources has been started. Overall implosion was performed successfully.
IN order to directly observe low-mode implosion nonuniformities, especially of l equals 1, which prevents stable formation of a hot spark in the compressed core plasma at the final stage of the implosion, a series of direct-drive implosion experiments has been performed at the Gekko-XII glass laser facility by using gas-filled plastic- shell targets. Partially coherent light (PCL) was used as a drive laser to suppress middle- to higher-modes of the irradiation nonuniformity down to approximately 1 percent. A clear shift from the center of the chamber and a slight crosswise structure were seen in the time- and space- resolved shape of the shell in the accelerating phase with an x-ray framing camera and absorbed laser intensity were also estimated by using a rocket equation. In order to confirm the property of these results, separate experiments under similar laser conditions were performed by using Au- coated sapphire spheres as surrogate target. The x-ray intensity distribution on the circumference of the target in the XFCs image, which is strongly dependent on the drive nonuniformity in the accelerating shell resulted from the l equals 1 drive nonuniformity. In our experiments, the l equals 1 drive nonuniformity due to some reproducible factors was found to be of the order of approximately 10-20 percent.
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