Formulation of diffraction efficiencies of binary phase gratings for array illumination with ultrashort pulse beams.

We present simple formulas for the diffraction efficiencies of a binary phase grating that performs array illumination with ultrashort pulse beams. Using scalar diffraction theory, we formulated the efficiencies as a function of pulse spectral width by Fourier-transforming the complex-modulated frequency spectra of diffracted pulses in the far-field region. From the analytical simulations, we found that pulse array uniformity departs from unity as the spectral width increases, or the pulse duration decreases, thereby limiting the attainable split counts.

Achromatic optical system with diffractive-refractive hybrid lenses for multifocusing of ultrashort pulse beams.

We report an achromatic cascade optical system for multifocusing ultrashort pulse beams with a diffractive beam splitter. Distortion compensation requires the removal of pulse front distortions from arrayed pulses, which originate from beam-radius-dependent group delay dispersions. The inclusion of hybrid diffractive-refractive lenses can effectively manage system dispersions.

Distortion-compensated multifocusing of ultrashort pulse beams using cascade optical system.

We report a cascade optical system for multifocusing ultrashort pulse beams, particularly sub-50-fs pulses. System achromaticity is key to simultaneous compensation of the spatio-temporal pulse distortions. In this system, diffractive and refractive subsystems are optically coupled in cascade to correct chromatic aberrations, which are the primary cause of pulse distortion.

Generation of 120-fs laser pulses at 1-GHz repetition rate derived from continuous wave laser diode.

We report the first demonstration of continuous-wave laser diode based 100-fs-class pulse lasers operating at a gigahertz repetition rate without a mode-locking technique. We describe the performance of a 1-W, 120-fs optical pulse train at 1 GHz and a 1-W, 80-fs optical pulse train at 250 MHz by using a simple configuration. Sub-100-fs pulse durations are achieved by using a progressive expansion of the spectrum in the self-phase modulation process in an erbium-doped fibre amplifier.

Extreme ultraviolet free electron laser seeded with high-order harmonic of Ti:sapphire laser.

The 13th harmonic of a Ti:sapphire (Ti:S) laser in the plateau region was injected as a seeding source to a 250-MeV free-electron-laser (FEL) amplifier. When the amplification conditions were fulfilled, strong enhancement of the radiation intensity by a factor of 650 was observed. The random and uncontrollable spikes, which appeared in the spectra of the Self-Amplified Spontaneous Emission (SASE) based FEL radiation without the seeding source, were found to be suppressed drastically to form to a narrow-band, single peak profile at 61.

Endoscopic submucosal dissection of esophageal lymphangioma: a case report with a review of the literature.

Esophageal lymphangioma is a very rare disease. We report a case of esophageal lymphangioma successfully treated with endoscopic submucosal dissection (ESD), which yielded definitive histological diagnosis and symptom relief. ESD offers a better option for definitive diagnosis as well as complete resection of large esophageal lymphangiomas with flat configuration.

Diagnosis of small flat early gastric cancer by flexible spectral imaging color enhancement.

Current conventional endoscopy often misses flat early gastric cancers (0-IIb) because they are sometimes invisible. We experienced a case of small flat early gastric cancer that had been missed by normal-caliber conventional endoscopy. By small-caliber endoscope, conventional endoscopy showed a subtle reddish change of gastric mucosa, but the image with flexible spectral imaging color enhancement clearly showed a flat reddish lesion with 10 mm diameter, distinct from the surrounding mucosa.

Parallel-aligned GaAs nanowires with 110 orientation laterally grown on [311]B substrates via the gold-catalyzed vapor-liquid-solid mode.

We report parallel aligned GaAs nanowires (NWs) with 110 orientation laterally grown on [311]B substrates via the vapor-liquid-solid mode and demonstrate their controllability and growth mechanism. We control the size, density, and site of the lateral NWs by using size- and density-selective Au colloidal particles and Au dot arrays defined by electron-beam lithography. The lateral NWs grow only along the [110] and [Formula: see text] directions and formation of the stable facets of (111)B and (001) on the sides of the lateral NWs is crucial for lateral NW growth.

Endoscopic submucosal dissection for superficial duodenal neoplasms.

Endoscopic submucosal dissection (ESD) has emerged as a novel technique for achieving en bloc resection for superficial neoplasms limited to the mucosa. ESD was originally developed in Japan as a method of endoscopic resection of superficial gastric cancers. In our hospital, ESD has been used concurrently in other parts of the gastrointestinal tract, including the esophagus and colorectum from the beginning of its development.

Diagnosis of elevated-type early gastric cancers by the optimal band imaging system.

Background: The endoscopic diagnosis of an elevated-type early gastric cancer is often difficult. The optimal band imaging (OBI) system can reconstruct the best spectral images decomposed from ordinary endoscopic images with free selection of 3 wavelengths and provide unmagnified images with high light intensity as well as magnified images.

Objective: To evaluate whether the OBI system facilitates detection of the demarcation lines between an elevated-type early gastric cancer and surrounding tissue and thus is more helpful for performing endoscopic therapy.

Growth of GaInAs/AlInAs heterostructure nanowires for long-wavelength photon emission.

We investigated the growth of GaInAs/AlInAs heterostructure nanowires on InP(111)B and Si(111) substrates in a metalorganic vapor phase epitaxy reactor. Au colloids were used to deposit Au catalysts 20 and 40 nm in diameter on the substrate surfaces. We obtained vertical GaInAs and AlInAs nanowires on InP(111)B surfaces.

Demonstration of carrier envelope offset locking with low pulse energy.

We demonstrate a carrier-envelope-offset (CEO)- locked frequency comb with 230-pJ fiber coupling pulse energy by using a passively mode-locked Er-fiber amplifier laser. For the generation of an octave-bandwidth spectrum in a highly nonlinear fiber and the second harmonic in a self-referenced interferometer with the lower pulse energy, we use a tellurite photonic crystal fiber and a direct-bonded quasi-phasematched LiNbO3 ridge waveguide, respectively. Our method is feasible for locking the CEO with a lower pulse energy to obtain a low-noise and highaccuracy optical frequency comb at telecommunications wavelengths.

Optimal band imaging system can facilitate detection of changes in depressed-type early gastric cancer.

Background: The endoscopic diagnosis of depressed-type early gastric cancers is difficult because these cancers manifest as subtle changes in color and shape. The newly developed optimal band imaging (OBI) system can reconstruct the best spectral images derived from ordinary endoscopic images and enhances the mucosal surface without the use of dyes. This imaging technique is based on narrowing the bandwidth of conventional image arithmetically by using spectral estimation technology.

Dynamical study of femtosecond-laser-ablated liquid-aluminum nanoparticles using spatiotemporally resolved x-ray-absorption fine-structure spectroscopy.

We study the temperature evolution of aluminum nanoparticles generated by femtosecond laser ablation with spatiotemporally resolved x-ray-absorption fine-structure spectroscopy. We successfully identify the nanoparticles based on the L-edge absorption fine structure of the ablation plume in combination with the dependence of the edge structure on the irradiation intensity and the expansion velocity of the plume. In particular, we show that the lattice temperature of the nanoparticles is estimated from the L-edge slope, and that its spatial dependence reflects the cooling of the nanoparticles during plume expansion.

Two-body Coulomb explosion and hydrogen migration in methanol induced by intense 7 and 21 fs laser pulses.

Two-body Coulomb explosion with the C-O bond breaking of methanol induced by intense laser pulses with the duration of Delta t=7 and 21 fs is investigated by the coincidence momentum imaging method. When Delta t=7 fs, the angular distribution of recoil vectors of the fragment ions for the direct C-O bond breaking pathway, CH(3)OH(2+)-->CH(3) (+)+OH(+), exhibits a peak deflected from the laser polarization direction by 30 degrees -45 degrees , and the corresponding angular distribution for the migration pathway, CH(2)OH(2) (+)-->CH(2) (+)+H(2)O(+), in which one hydrogen migrates from the carbon site to the oxygen site prior to the C-O bond breaking, exhibits almost the same profile. When the laser pulse duration is stretched to Delta t=21 fs, the angular distributions for the direct and migration pathways exhibit a broad peak along the laser polarization direction probably due to the dynamical alignment and/or the change in the double ionization mechanism; that is, from the nonsequential double ionization to the sequential double ionization.

Sampling measurement of soft-x-ray-pulse shapes by femtosecond sequential ionization of Kr+ in an intense laser field.

We propose a sampling technique for measuring the shape of ultrashort soft-x-ray pulses. The technique uses the transient state of Kr+ ions that is produced by the femtosecond sequential evolution of Kr ions during optical-field-induced ionization as an ultrafast x-ray-absorption sampling gate. We demonstrate the technique by measuring the pulse shape of the 51st harmonic (15.

Effects of pump propagation and absorption on the gain distribution of longitudinally pumped Ni-like molybdenum x-ray lasers.

We reveal from simulations that in longitudinally pumped Ni-like Mo x-ray lasers, deformation of the temporal gain profile can occur, causing the x-ray laser pulse to have a steep rising edge. This is shown to be due to the rapid change in the inverse bremsstrahlung absorption when the main picosecond pulse pumps the cold preplasma.