Measurement of fusion excitation functions of 27, 29, 31Al + 197Au

A systematic study of the sub-barrier fusion reactions with neutron-rich projectiles has been carried out for three isotopes ^27,29,31Al bombarding a ¹⁹⁷Au target. A target chamber equipped with a target stack and sets of MWPC was employed in order to enhance the efficiency of the radioactive beam experiment. Coupled-channel calculations including the quadrupole excitations do not well fit the measured fusion excitation functions, whereas flat barrier distributions to represent the coupling to the neutron transfer largely account for the observed enhancement of the sub-barrier fusion cross-sections. Received: 13 March 2001 / Accepted: 27 April 2001     

Superconducting gap anisotropy in Nd1.85Ce0.15CuO4: results from photoemission

We have performed angle resolved photoelectron spectroscopy on the electron doped cuprate superconductor Nd1.85Ce0.15CuO4. A comparison of the leading edge midpoints between the superconducting and normal states reveals a small, but finite shift of 1.5-2 meV near the ( pi,0) position, but no observable shift along the zone diagonal near ( pi/2, pi/2). This is interpreted as evidence for an anisotropic superconducting gap in the electron doped materials, which is consistent with the presence of d-wave superconducting order in this cuprate superconductor.     

Speech recognition in noise as a function of the number of spectral channels: comparison of acoustic hearing and cochlear implants

Speech recognition was measured as a function of spectral resolution (number of spectral channels) and speech-to-noise ratio in normal-hearing (NH) and cochlear-implant (CI) listeners. Vowel, consonant, word, and sentence recognition were measured in five normal-hearing listeners, ten listeners with the Nucleus-22 cochlear implant, and nine listeners with the Advanced Bionics Clarion cochlear implant. Recognition was measured as a function of the number of spectral channels (noise bands or electrodes) at signal-to-noise ratios of + 15, + 10, +5, 0 dB, and in quiet. Performance with three different speech processing strategies (SPEAK, CIS, and SAS) was similar across all conditions, and improved as the number of electrodes increased (up to seven or eight) for all conditions. For all noise levels, vowel and consonant recognition with the SPEAK speech processor did not improve with more than seven electrodes, while for normal-hearing listeners, performance continued to increase up to at least 20 channels. Speech recognition on more difficult speech materials (word and sentence recognition) showed a marginally significant increase in Nucleus-22 listeners from seven to ten electrodes. The average implant score on all processing strategies was poorer than scores of NH listeners with similar processing. However, the best CI scores were similar to the normal-hearing scores for that condition (up to seven channels). CI listeners with the highest performance level increased in performance as the number of electrodes increased up to seven, while CI listeners with low levels of speech recognition did not increase in performance as the number of electrodes was increased beyond four. These results quantify the effect of number of spectral channels on speech recognition in noise and demonstrate that most CI subjects are not able to fully utilize the spectral information provided by the number of electrodes used in their implant.     

Soliton self-frequency shift in a short tapered air-silica microstructure fiber

We report a soliton self-frequency shift of more than 20% of the optical frequency in a tapered air-silica microstructure fiber that exhibits a widely flattened large anomalous dispersion in the near infrared. Remarkably, the large frequency shift was realized in a fiber of length as short as 15 cm, 2 orders of magnitude shorter than those reported previously with similar input pulse duration and pulse energies, owing to the small mode size and the large and uniform dispersion in the tapered fiber. By varying the power of the input pulses, we generated compressed sub-100-fs soliton pulses of ~1-nJ pulse energy tunable from 1.3 to 1.65 mum with greater than 60% conversion efficiency.     

Ultrahigh-resolution optical coherence tomography using continuum generation in an air-silica microstructure optical fiber

We demonstrate ultrahigh-resolution optical coherence tomography (OCT) using continuum generation in an air-silica microstructure fiber as a low-coherence light source. A broadband OCT system was developed and imaging was performed with a bandwidth of 370 nm at a 1.3-mu;m center wavelength. Longitudinal resolutions of 2.5 microm in air and ~2 microm in tissue were achieved. Ultrahigh-resolution imaging in biological tissue in vivo was demonstrated.     

An azo-isomerization-induced Freedericksz transition of a nematic liquid crystal

We observed an azo-isomerization-induced Freedericksz transition of the 5CB liquid crystal doped with 1% double-azo. In experiment, we found that the Freedericksz transition threshold occurred at optical intensity level of 0.3 mW/mm² for the 12.5 μm-thickness planar alignment doped 5CB, which is four orders of magnitude lower as that for the pure 5CB. Using optical phase retardation, we measured the relations between the Freedericksz transition threshold and the pump beam polarization. The maximum twist angle of liquid crystal molecules under different pump beam intensity is given. The experiment indicated that trans–cis isomerization plays an important role in the decrease of the Freedericksz transition threshold.     

Spectral stabilization of amplified pulses from synchronously-pumped dye laser systems

We demonstrate an effective scheme for passively stabilizing the single shot spectrum of the amplified pulses from a synchronously pumped dye laser system. This scheme is easy to implement and inexpensive. Data from resonant and nonresonant coherent transient experiments are shown to illustrate its effectiveness.     

Irradiated rare‐earth‐doped powellite single crystal probed by confocal Raman mapping and transmission electron microscopy

The irradiation‐induced damages and structure modifications of rare earths doped powellite single crystal have been precisely studied using optical and electron microscopy techniques, including optical interferometry, confocal micro‐Raman spectroscopy and transmission electron microscopy. The surface of powellite crystal pops out anisotropically after exposing under Ar ion beam, with a saturation swelling value of 2.0% along a‐axis and 1.3% along the c‐axis of powellite at high dose. Raman mapping on focused ion‐beam sections (5 × 3 µm²) perpendicular to the irradiated surface reveals that irradiation damage induces orientation‐dependent compressive stresses in powellite. However, no significant anisotropic effect has been found on the irradiation‐induced structural disorder in powellite. At low dose (0.012 dpa), the main irradiation‐induced defects created in powellite crystal are small defect clusters. By comparison, the dominant kinds of defects in high‐dose (5.0 dpa) sample are dislocations loops and networks. Copyright © 2014 John Wiley & Sons, Ltd.     

Zirconium-doped hybrid films patterned by soft lithography for distributed-feedback lasers

Zirconium (Zr)-doped hybrid films containing Rhodamine 6G (Rh6G) were prepared by spin-coating on glass substrates with different Zr–Si molar ratio. Second-order distributed-feedback (DFB) resonators with large surface-relief modulation depth over 160 nm could be fabricated by soft lithographic technique using a polydimethylsiloxane (PDMS) replica. Optically pumped by a pulsed frequency-doubled Q-switched Nd:YAG laser, the emission wavelength of the DFB-lasers can be tuned over 16 nm by changing the grating period. With the optimization of the Zr–Si molar ratio, low laser threshold of 3 μJ/mm² was obtained.