Ion acceleration with mixed solid targets interacting with circularly polarized lasers

The interaction of a circularly polarized laser pulse with a mixed solid target containing two species of ions is studied by particle in cell simulations and analytical model. After the interaction tends to be stable, it is demonstrated that the acceleration is more efficient for the heavier ions than that in plasmas containing a single kind of heavy ion and the acceleration efficiency is higher when its proportion is lower. To obtain monoenergetic heavy-ion beams, a sandwich target with a thin mixed ion layer between two light ion layers and a microstructured target are proposed. The influences of parameters of the laser pulse and target on ion acceleration are discussed in detail. It is found that, when the target is thick enough, a cold target is more appropriate for heavy-ion acceleration than a warm target, and the velocity of the reflected heavy ions is proportional to the laser amplitude.

激光二极管抽运的国产Yb:YAG陶瓷激光器

研究了国产Yb:YAG陶瓷的激光输出特性。激光器采用激光二极管(LD)纵向同轴抽运Yb:YAG陶瓷样品,样品的掺杂原子数分数为1%,一端面镀940 nm和1030 nm双增透膜,另一端面镀1030 nm增透膜,激光器在1031 nm处获得了近红外激光输出。实验中分别测试了Yb:YAG陶瓷在不同输出透射率(T=4%,8%,10%)条件下的激光输出特性。整个实验过程中,激光器维持基横模运转。当输出透射率为10%,吸收的抽运功率为9 W时,激光器获得最大的激光输出功率为1.63 W,相应的斜率效率为23.2%。

Ultrafast dynamics in ZnO thin films irradiated by femtosecond lasers

The damage morphologies, threshold fluences in ZnO films were studied with femtosecond laser pulses. Time-resolved reflectivity and transmissivity have been measured by the pump-probe technique at different pump fluences and wavelengths. The results indicate that two-phase transition is the dominant damage mechanism, which is similar to that in narrow band gap semiconductors. The estimated energy loss rate of conduction electrons is 1.5 eV/ps. (c) 2005 Elsevier Ltd. All rights reserved.

Optical breakdown of 6H SiC induced by wavelength-tunable femtosecond laser pulses

The damage mechanisms and micromachining of 6H SiC are studied by using femtosecond laser pulses at wavelengths between near infrared (NIR) and near ultraviolet (NUV) delivered from an optical parametric amplifier (OPA). Our experimental results indicate that high quality microstructures can be fabricated in SiC crystals. On the basis of the dependence of the ablated area and the laser pulse energy, the threshold fluence of SiC is found to increase with the incident laser wavelength in the visible region, while it remains almost constant for the NIR laser. For the NIR laser pulses, both photoionization and impact ionization play important roles in electronic excitation, while for visible lasers, photoionization plays a more important role.

Angular distributions of multiphoton detachment of H- in various infrared laser fields

Using a nonperturbative quantum scattering theory, the photoelectron angular distributions (PADs) from the multiphoton detachment of H- ions in strong, linearly polarized infrared laser fields are obtained to interpret recent experimental observations. In our theoretical treatment, the PADs in n-photon detachment are determined by the nth-order generalized phased Bessel (GPB) functions X-n(Z(f),eta). The advantage of using the GPB scenario to calculate PADs is its simplicity: a single special function (GPB) without any mixing coefficient can express PADs observed by recent experiments. Thus, the GPB scenario can be called a parameterless scenario.

Infrared luminescence properties of bismuth-doped barium silicate glasses

Infrared (IR) luminescence covering 1.1 to similar to 1.6 mu m wavelength region was observed from bismuth-doped barium silicate glasses, excited by a laser diode at 808 nm wavelength region, at room temperature. The peak of the IR luminescence appears at 1325 nm. A full width half-maximum (FWHM) and the lifetime of the fluorescence is more than 200 nm and 400 mu s, respectively. The fluorescence intensity increases with Al2O3 content, but decreases with BaO content. We suggest that the IR luminescence should be ascribed to the low valence state of bismuth Bi2+ or Bi+, and Al3+ ions play an indirect dispersing role for the infrared luminescent centers.

Transparent Ni2+-doped ZnO-Al2O3-SiO2 system glass-ceramics with broadband infrared luminescence

We report transparent Ni2+-doped ZnO-Al2O3-SiO2 system glass-ceramics with broadband infrared luminescence. After heat-treatment, ZnAl2O4 crystallite was precipitated in the glasses, and its average size increased with increasing heat-treatment temperature. No infrared emission was detected in the as-prepared glass samples, while broadband infrared luminescence centered at 1310 nm with full width at half maximum (FWHM) of about 300 nm was observed from the glass-ceramics. The peak position of the infrared luminescence showed a blue-shift with increasing heat-treatment temperature, but a red-shift with an increase in NiO concentration. The mechanisms of the observed phenomena were discussed. These glass-ceramics are promising as materials for super broadband optical amplifier and tunable laser. (c) 2006 Elsevier Ltd. All rights reserved.

Fluorescent Ag nanoclusters in glass induced by an infrared femtosecond laser

We report a method for the selective introduction of fluorescent Ag nanoclusters in glass. Extinction and photoluminescence spectra show that a fraction of the Ag atoms are generated through femtosecond laser induced multiphoton reduction and then aggregate to form Ag nanoclusters after heat treatment. Red luminescence from the irradiated region is observed under blue or green laser excitation. The fluorescence can be attributed to interband transitions within Ag nanoclusters. This method provides a novel route to fabricate fluorescent nanomaterials in 3D transparent materials. (c) 2007 Elsevier B.V. All rights reserved.