Pulsed-laser deposition scheme (PLD) is one of feasible coating methods and we applied this method to hydroxyapatite coating on medical implants. Our previous study showed that ablated droplets disturbed to coat dense, high purity, and high crystallinity hydroxyapatite layer at low annealing temperature. Therefore, we applied “eclipse-type” PLD scheme, which could capture ablated droplets by an obstacle ball and only tiny particles as atoms, ions, and molecules were deposited on a substrate. Raman spectrum from the coating layer showed coating layer changed to crystal layer over 360 ℃, and as increase the annealing temperature crystallinity became better. The adhesion strength of the coating layer was also measured by a scratched test. As increasing of the annealing temperature, the adhesion also became strength stronger. We concluded this high-quality coating layer is suitable for medical implants coating.
Calcium phosphate coatings were employed for medical implants such as dental or orthopedic for bone bonding. Essentially, these layers were dissolved by osteoclast and replaced with newly formed bone by osteoblast. Finally, the implant is fixed with bone without a gap in vivo, which is called “osseointegration”. In this situation, the implant and bone are fixed only by an anchor effect, therefore they aren’t fixed microscopically. If this coating layer isn’t dissolved easily, enhances bone formation, and adheres strongly with implants, implants will be expected much stronger bone bonding than osseointegration. We reported that dense without holes, high purity, and high crystallinity hydroxyapatite coating layer was fabricated on zirconia substrate by droplets eliminated type pulsed-laser deposition scheme, which was similar geometric configuration with the solar eclipse. Pressed and sintered -Tricalcium phosphate target was irradiated by a 4th harmonic of YAG laser in H2O gas at 0.1 T
Laser processing of polymeric materials by means of 100-mW class QCL lasers with emission wavelength of 7.728 and 4.329 μm were examined. Polymeric materials show absorption bands based on transitions between vibronic levels in mid-infrared (MIR) wavelength. Since such absorption bands are very sharp, resonant conditions with laser wavelength are critical. Quantum cascade laser (QCL) is a promising laser source for mid-infrared laser processing; emission wavelength can be customized by changing the heterostructure. In this work, we have employed 100-mW class QCLs and applied for focused irradiation at several polymeric materials, polypropylene (PP), polycarbonate (PC), polyacetal (POM).
Three-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) is a fine engineering ceramic that offers high fracture resistance and flexural strength. Thus, it is often applied in mechanical components and medical implants. The surface roughness can be controlled to improve the device characters in some applications. Ultrashort pulse lasers can form laser-induced periodic surface structures (LIPSS) on 3Y-TZP, which have never been investigated in detail. Therefore, this paper reports the formation and characteristics of LIPSS formed on 3Y-TZP, focusing on the pulsewidth dependence. The LIPSS was formed by a Ti:sapphire chirped-pulse amplification system, which generates 810 nmcentered 80-fs pulses at a 570 Hz repetition rate. The measured ablation threshold peak fluence was ~1.5 J/cm2 and the LIPSS was formed at the peak fluence of 2.7–7.7 J/cm2. For linearly polarized pulses, the lines of the LIPSS were oriented parallel to the polarization direction, and their period was comparable to or larger than the center wavelength of the laser. These characteristics differ from the reported characteristics of LIPSS on metals and dielectrics. The pulsewidth dependence of the ablation and LIPSS was investigated for different pulsewidths and signs of chirp. Under the investigated fluence condition, the LIPSS period increased with increasing pulsewidth for both signs of chirp. Similar pulsewidth dependencies were observed for circularly polarized pulses.
We are developing a multi-kHz repetition rate high-average power Ti:sapphire regenerative amplifier as a pumping laser of a laser-plasma X-ray source. With an optimally designed ring resonator with a cryogenically-cooled laser rod, the average output power of 54 W before compression was achieved when pumped by a 180-W green laser at 10 kHz repetition rate. The focusability of the output beam was better than two times of the diffraction limit and can be compressed to 82 fs. Possibility of scaling to higher output power is discussed.
We present a novel 3D display that can show any 3D contents in free space using laser-plasma scanning in the air. The
laser-plasma technology can generate a point illumination at an arbitrary position in the free space. By scanning the
position of the illumination, we can display a set of point illuminations in the space, which realizes 3D display in the
space. This 3D display has been already presented in Emerging Technology of SIGGRAPH2006, which is the basic platform of our 3D display project. In this presentation, we would like to introduce history of the development of the laser-plasma scanning 3D display, and then describe recent development of the 3D contents analysis and processing technology for realizing an innovative media presentation in a free 3D space. The one of recent development is performed to give preferred 3D contents data to the 3D display in a very flexible manner. This means that we have a platform to develop an interactive 3D contents presentation system using the 3D display, such as an interactive art presentation using the 3D display. We would also like to present the future plan of this 3D display research project.
Technologies for materializing our cotton-cake like tin target scheme are being developed. With the scheme, we expect to achieve 4% conversion efficiency into 2π sr supported by our experimental data. In order to implement EUVL, EUV power exceeding 100 W is considered to be required to be sent to an illumination box. Large collection solid angle and high conversion efficiency are the mandatory requirements for a source for EUVL. A route to the goal is not yet clear. With our scheme, we can expect EUV exceeding 100 W at the entrance of an illuminator is obtained with a 15 kW YAG laser. Difficulties we encountered when we tried plasma production by shooting droplets of a SnO2 suspension were preparation of a long life SnO2 suspension and stable droplet generation with the suspension. In these few years our technologies are highly improved, and we are now able to supply the suspension for several hours without stop, and concentration of a suspension is now increased to as high as 40 wt %. EUV intensity dependence on concentration was studied by shooting a jet of a suspension. We found the EUV intensity saturated at around several at %, which corresponds to several tens wt%, and the EUV intensity comparable to that from a Sn plate was observed. By introducing active synchronization of laser pulses with droplets, we can now shoot droplets running at 10 kHz with a 10 Hz YAG laser with no miss shot. We are now ready to challenge formation of cotton-cake like tin target to demonstrate a very high CE.
In this paper, we described a laser plasma source for Extreme Ultraviolet Lithography (EUVL) based on a water droplet target. We successfully generated stable multi-kHz water droplets with several hundred μm diameter using our experimentaql setup. We realized a good synchronization of laser with droplet by employing droplet-probing photo diode (PD) signal to trig YAG laser timely. We got EUV emission with pulse to pulse stability of 3.4% (1σ) from this droplet region without being destroyed due to hot laser plasma formation from the previous droplet.
Particle-cluster tin target is presented as the solution of a 100W EUV source for EUVL. Theory for maximizing conversion efficiency of a laser-produced plasma is derived and the theory is experimentally confirmed by using a dispersed SnO2 particles. The EUV intensity 4 times higher than that from a plasma on a solid Sn plate target is observed at the optimized density. The achieved conversion efficiency for dispersed particles is estimated to be as high as 3%/(2π str 2%BW) or higher from the value for a Sn plate of 0.8% measured by using two multilayer mirrors and a calibrated photodiode. Theoretical consideration reveals that larger diameter plasma enables higher EUV power. The particle-cluster can be delivered at multi kHz rep-rate by using water droplet. Experimental confirmation of delivering particles by droplets is also reported.
In order to protect a multilayer mirror from sputtering or ion implantation, high-energy ions ejected from EUV source plasma are to be blocked. We propose use of a laser-produced plasma as an ultra-fast shutter. Ion signal form an ion-source plasma dropped abruptly by two orders of magnitude to a noise level after the shutter plasma generation. The stopping effect for the high-energy ions was observed to reduce as the distance of shutter plasma expansion increases, but the suppression of ions below detection level was observed up to 10 mm. We concluded that reduction of ion signal was caused by in-take of the source plasma flow into the stream of the shutter plasma.
We succeeded in generating a strong narrowband peak at 13.7 nm in a cavity confined Sn plasma. Fraction of the energy within 2% bandwidth at 13.7 nm against the total radiation spectrum was 11.3%. In our experiment, the plasma is generated not on a solid plate but in a cavity as described below. A YAG laser pulse ablates the surface of a concave structure Sn target in order to supply the material for plasma generation. The next laser pulse with 1064nm wavelength heats the ablated material to generate a high temperature plasma. The ablation YAG laser is focused to 600μm diameter with a flux of 10 J/cm2. The heating YAG laser is focused to 100μm diameter at a delay time of 30 ns after the laser ablation. Emission spectra are observed using a grazing incidence Hitachi flat-field grating and a back side illuminated CCD detector. Fraction of the energy at 13.7nm within 2% bandwidth in the whole radiation energy was 11.3%. However, the intensity of the spectrum peak was about 1/10 against the plane Sn target LPP source. When nano (less than 200 nm diameter) particle SnO2 deposited on a 100nm-thick Si3N4 membrane were irradiated, a sharp peak was observed. The intensity of the spectral peak of the nano particle SnO2 target LPP source was as high as that of the plane Sn target LPP source. The EUV energy within 2% bandwidth at around 13.7 nm to the whole radiation energy of the nano particle SnO2 target LPP source was 7.4%.
Debris-free generation of a tin plasma was demonstrated in the cavity-confined configuration. Narrow band emission at 13.7-nm was observed in an emission spectrum of a cavity confined tin plasma. The spectral efficiency was as high as 12% and we found the conversion efficiency could reach 6%/2π str ultimately while lots of works are required to achieve this value. We also confirmed a magnetic field has some effect of stopping a plasma.
Magnetic field shield for laser produced plasma (LPP) had been investigated. The interaction between expanding LPP and magnetic field is not described by Lorentz force, but, may be described by magneto hydro dynamics. When a magnetic field strength of 0.6T was placed between LPP and a faraday cup, attainment ratio of plasma to a faraday cup was decrease to 20%. The attainment ratio was decreased from 0.4 to 0.25 with varying the distance between the plasma and the magnetic field from 10 mm to 70 mm. And, it was observed that plasma detoured around a magnetic field.
Laser plasma light source using double pulses laser irradiation and through-hole method is proposed as a mass-limited target srouce for extreme UV (EUV) radiation. After minimum necessary material is supplied using the ablation laser from a solid target, only ablated material is irradiated with the heating laser to produce a high-temperature plasma, and EUV radiation is extracted passing through the hole formed in the solid target. Fundamental concept of this scheme, EUV radiation and great reduction of particle debris were experimentally confirmed.
For realizing a table-top x-ray laser or a compact short wavelength x-ray laser, improvement of the pumping efficiency is one of the most important points. Thermal conduction into inside of the target should suppress rising up of electron temperature of a laser-produced plasma. Then, the plasma produced on a very thin membrane target gets rid of this energy loss, and the efficiency of the high temperature plasma production will be increased. Moreover, density of the plasma from a membrane decreases very rapidly because of the small amount of target limited by the membrane thickness. These features of membrane plasma are suitable in recombination x- ray laser. To confirm the advantages of this pumping scheme, we produced the plasma on a thin membrane and the heating and expansion was evaluated. Experimentally observed spectral lines of H-like and He-like Si ions show effective heating and ionization of the plasma for a membrane target. Electron density evaluations and plasma expansion velocity measurements confirm rapid plasma expansion from the membrane target. Theoretical hydrodynamic simulation also showed the effective heating and ionization of the plasma from the membrane target.
A new pumping scheme named exploding pumping is proposed for realizing recombination x-ray lasers with high excitation efficiency. In the new scheme, a very thin membrane is employed as a target and it is heated instantaneously before the plasma starts to move by a high peak power sub- picosecond pumping laser. In the scheme, the plasma heating efficiency is improved by being free from heat conduction loss to bulk, and by suppressing the energy loss to hydrodynamic motion. Inertia of the mass delays the start of the plasma motion and gives sufficient time for full ionization. Owing to the extreme thinness of the initial high density plasma, only a few micrometers expansion leads to great reduction of the density and cools down rapidly to produce large gain. Efficient heating of a membrane plasma is confirmed in experimentally observed x-ray spectra and charge collector signals. It is discussed that the most serious problem for realizing water window x-ray lasers is conventional ablation pumping is density gradient which causes refraction of x-rays and limits gain length. The new pumping scheme can solve this refraction problem. The density profile of the expanding plasma in this scheme is fairly uniform because all material expand explosively and because no mass is supplied during the expansion. According to a numerical simulation, 3.34-nm water window of gain length product of 10 will be realized with the 6 J/ 0.3 ps laser irradiation. Longer wavelength x-ray lasers around 13- nm will be realized with a few J/ a few ps pulse pumping. The key technology in the new pumping scheme is suppression of pre-pulse. The effect of pre-pulse is experimentally observed, and means for pre-pulse suppression is discussed.
Amplified spontaneous emissions of Li-and Be-like Al ions and Li-like Si ions were observed in recombining plasmas produced by a low-power driving laser. These were achieved by heating plasma with a train of laser pulses of short interval, and sharply focusing a pumping laser to a line 40 micrometers wide onto a slab target for rapid cooling of plasmas through adiabatic expansion. Mechanism of plasma heating and the optimum shape of the laser pulse for pumping soft X-ray lasers were also investigated.
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