Motoyoshi Baba

Low- and high-order harmonic generation in the extended plasmas produced by laser ablation of zinc and manganese targets

The systematic studies of the harmonic generation of ultrashort laser pulses in the 5-mm-long Zn and Mn plasmas (i.e., application of nanosecond, picosecond, and femtosecond pulses for ablation, comparison of harmonic generation from atomic, ionic, and cluster-contained species of plasma, variation of plasma length, two-color pump of plasmas, etc.) are presented. The conversion efficiency of the 11th–19th harmonics generated in the Zn plasma was ∼5u2009×u200910−5. The role of the ionic resonances of Zn near the 9th and 10th harmonics on the enhancement of harmonics is discussed. The enhancement of harmonics was also analyzed using the two-color pump of extended plasmas, which showed similar intensities of the odd and even harmonics along the whole range of generation. The harmonics up to the 107th order were demonstrated in the case of manganese plasma. The comparison of harmonic generation in the 5-mm-long and commonly used short (≤0.5u2009mm) plasma plumes showed the advanced properties of extended media.

Correlation between Lamina Cribrosa Tilt Angles, Myopia and Glaucoma Using OCT with a Wide Bandwidth Femtosecond Mode-Locked Laser

Purpose To measure horizontal and vertical lamina cribrosa (LC) tilt angles and investigate associated factors using prototype optical coherence tomography (OCT) with a broad wavelength laser light source. Design Cross sectional study. Methods Twenty-eight no glaucoma eyes (from 15 subjects) and 25 glaucoma eyes (from 14 patients) were enrolled. A total of 300 optic nerve head B-scans were obtained in 10 µm steps and the inner edge of Bruchs membrane opening (BMO) was identified as the reference plane. The vertical and horizontal angles between BMO line and approximate the best-fitting line for the surface of the LC were measured and potential associated factors were estimated with univariate and multivariate logistic regression analyses. Results The median (interquartile range) horizontal and vertical tilt angles were 7.10 (2.43–11.45) degrees and 4.15 (2.60–6.85) degrees in eyes without glaucoma and 8.50 (4.40–14.10) degrees and 9.30 (6.90–14.15) degrees in glaucoma eyes, respectively. The refractive errors had a statistically significant association with horizontal LC tilt angles (coefficients, −1.53 per diopter) and glaucoma had a significant correlation with vertical tilt angles (coefficients, 6.56) using multiple logistic regression analysis (p<0.001). Conclusions OCT allowed evaluation of the internal tilting of the LC compared with the BMO. The horizontal internal LC tilt angle was correlated with refractive errors, corresponding to myopic physiological changes, and vertical internal LC tilt was correlated with glaucoma, corresponding to glaucomatous pathological changes. These parameters have important implications for investigation of the correlation between myopia, glaucoma and LC morphological features.

Morphology of laser-produced carbon nanoparticle plasmas and high-order harmonic generation of ultrashort pulses in clustered media

We analyse the morphology of the laser plasmas produced on surfaces containing various carbon clusters (nanotubes, nanofibres, fullerenes, and nanoparticles). It is shown that the presence of C5–C25 nanoparticles in the laser plasmas coincides with the enhancement of harmonics in the spectral range of 40–80 nm. We suggest that these nanoparticles, rather than larger clusters, play a decisive role in the observed growth of harmonic yield.

Application of carbon cluster-contained extended plasmas for the high-order harmonic generation of ultrashort pulses

We present the studies of the high-order harmonic generation of 802-nm, 64-fs pulses in the extended plasmas contained the carbon-based clusters (fullerenes, nanofibers, nanoparticles, and nanotubes). Our studies show that the 11th–19th harmonics in the 15–33u2009eV range may originate from the low-sized nanoparticles produced during ablation of large clusters and agglomerates. The conversion efficiency of the 11th harmonic generated from the 5-mm-long fullerene plasma was estimated to be 2u2009×u200910−5.

Three-dimensional optic nerve head images using optical coherence tomography with a broad bandwidth, femtosecond, and mode-locked laser

PurposeThe aim of this study was to demonstrate the fine laminar structure of the optic nerve head (ONH), in vivo, using a broad wavelength, ultra-high resolution, and optically coherent tomography (OCT) system.MethodsThis high-resolution OCT system, based on a 200xa0nm bandwidth spectrometer and an 8 femtosecond ultra-short, mode-locked, coherent laser light source, enabled in vivo cross-sectional ONH imaging with 2.0xa0μm axial resolution. A total of 300 optic disc B-scans, which consisted of 300u2009×u20092048xa0pixels, were obtained in 10xa0μm steps. Three-dimensional images were rendered from these images to obtain n face images of the optic disc. Fundus photography, scanning laser ophthalmoscopy (SLO), and standard OCT were also performed for all subjects.ResultsThirty-six eyes of normal subjects and ten eyes of glaucoma patients with mean age of 40.0u2009±u200910.0xa0years were enrolled in this study. Sequential en face images, from the ONH surface to deeper layers, were reconstructed in 2.0xa0μm steps. Observation of the images indicated variations in the shape and arrangement of the lamina pores at different depths. Clear lamina pores were identified by this technique in 44 eyes, compared with the fundus camera (identified in six eyes), SLO (identified in 14 eyes), and standard OCT (identified in 24 eyes) (all comparisons, pu2009<u20090.001).ConclusionsThe fine structure of the ONH could be resolved in vivo using our OCT, providing improved imaging that can be used in research and clinical applications for a better characterization of the anatomical and pathological features associated with glaucoma.

The observation of a transient surface morphology in the femtosecond laser ablation process by using the soft x-ray laser probe (Withdrawal Notice)

We have improved a soft x-ray laser (SXRL) interferometer synchronized with a Ti:Sapphire laser pulse to observe the single-shot imaging of the nano-scaled structure dynamics of the laser induced materials. By the precise imaging optics and double time fiducial system having been installed, the lateral resolution on the sample surface and the precision of the temporal synchronization between the SXRL and Ti:Sapphire laser pulses were improved to be 700 nm and 2 ps, respectively. By using this system, the initial stage (t < 200 ps) of the ablation process of the Pt surface pumped by 80 fs Ti:Sapphire laser pulse was observed by the comparison between the soft x-ray reflective image and interferogram. We have succeeded in the direct observation of the unique ablation process around the ablation threshold such as the rapid increase of the surface roughness and surface vibration.

Rarefaction after fast laser heating of a thin metal film on a glass mount

Understanding the physics of laser-matter interactions in ultrashort pulses is important for many well-acknowledged applications from material modifications to biology. We numerically and experimentally consider the effect of sub-picosecond Ti:sapp laser actions on 60-100u2005nm gold films mounted onto a fused silica substrate. The pulse energy is sufficient to ablate the films. For the first time, we show that there are different regimes of ablation, and the formation of the 3D structures depends on the value of the absorbed fluence Fabs and the adhesion strength padh between the film and the substrate. Namely, a delamination threshold Fdelam and an ablation threshold Fabl (Fdelam < Fabl) exist if adhesion is weak. Above the lower threshold Fdelam, the whole film delaminates from the substrate. Above the higher threshold Fabl, the thin film ruptures near its middle plane. The external half of the film flies away, while the internal half remains on the glass substrate. There are two thresholds Fdelam and Fabl...

The Observation of Transient Thin Film Structures During the Femto-Second Laser Ablation Process by Using the Soft X-Ray Laser Probe

We modified a soft X-ray laser (SXRL) interferometer synchronized with a Ti:sapphire laser to observe a single-shot image of the nanoscale structure dynamics of materials induced by an optical laser pulse. The lateral resolution on the sample surface was improved to 0.7 μm using precise imaging optics. Using this system, we succeeded in observing thin film structures above the solid (or liquid) surface in the femtosecond laser ablation process of metals (Au). The thin film worked as soft X-ray beam splitter. This result shows a thin film was smooth and dense (with a roughness of a few nanometers and near sold density). Furthermore, it gave rise to the possibility of generating novel transient soft X-ray optics .