Composite Yb : YAG/Cr4+: YAG ceramics picosecond microchip lasers

Efficient laser-diode pumped picosecond self-Q-switched all-ceramic composite Yb: YAG/ Cr4+: YAG microchip lasers with 0.72 MW peak power has been developed. Lasers with nearly diffraction-limited beam quality (M-2 < 1.09), oscillate at stable single- and multi- longitudinal-modes due to the combined etalon effects in the Yb:YAG and Cr4(+:) YAG parts of its binary structure. (C) 2007 Optical Society of America

Effect of ytterbium concentration on Yb : YAG microchip laser performance at ambient temperature

The microchip laser performance of Yb:YAG crystals doped with different ytterbium concentrations (10, 15, and 20 at.%) has been investigated at ambient temperature. Efficient laser oscillation for 1-mm-thick YAG doped with 10 at.% Yb3+ ions was achieved at 1030 and 1049 nm with slope efficiencies of 85 and 81%, correspondingly

The Effect of a Music Program on Phonological Awareness in Preschoolers

The present experiment investigated the effect of a music program on phonological awareness in preschoolers. In particular, the effects of a music program and a phonological skills program on phonological awareness were compared. If language and music share basic processing mechanisms, the effect of both programs on enhancing phonological awareness should be similar. Forty-one preschoolers (22 boys) were randomly assigned to a phonological skills program, a music program, and a control group that received sports training (from which no effect was expected). Preschoolers were trained for 10 min on a daily basis over a period of 20 weeks. In a pretest, no differences were found between the three groups in regard to age, gender, intelligence, socioeconomic status, and phonological awareness. Children in the phonological skills group and the music group showed significant increases in phonological awareness from pre- to post-test. The children in the sports group did not show a significant increase from pre- to post-test. The enhancement of phonological awareness was basically driven by positive effects of the music program and the phonological skills program on phonological awareness for large phonological units. The data suggests that phonological awareness can be trained with a phonological skills program as well as a music program. These results can be interpreted as evidence of a shared sound category learning mechanism for language and music at preschool age

Transient temperature profile in the gain medium of CW- and end-pumped passively Q-switched microchip laser

The transient temperature profile in CW- and end-pumped passively Q-switched (PQS) microchip laser is investigated qualitatively by treating the population inversion (thereby the thermal load) as the sawtooth function of the time. The numerical results reveal not only the dynamics of thermal buildup, but also the dependence of the quasi-steady-state temperature rise and the repetitively oscillatory amplitude on the incident pump power and the pulse repetition rate of PQS laser. The abruptly ascending branch of the repetitive temperature oscillation is synchronized with the pulsing stage of PQS laser. As the result, the abrupt temperature transition during the pulsing stage would introduce the fluctuation into the PQS pulse parameters (pulse energy, pulse width, and peak power) via temperature-dependent stimulated emission and thermal lensing effect. (c) 2006 Elsevier B.V. All rights reserved

Maximum value of the pulse energy of a passively Q-switched laser as a function of the pump power

The finite recovery time T-s of the bleached absorber is presented as one of the possible mechanisms accounting for the increase-maximum-decrease in pulse energy E with the pumping rate W-p in cw-pumped passively Q-switched solid-state lasers. by analytically evaluating the sign of the derivative partial derivative E/partial derivative W-p. The results show that. in the low punipinie (T > T-s, T is the interpulse period). the initial repopulation density n, remains constant. the final population density n(i) decreases with W-p. and this results in a monotonic increase of E with W-p. In the high pump regime (T < T-s). n, decreases but n(i) remains the same with W-P; this results in a monotonic decrease of E with W-p. At the critical region (T approximate to T), E reaches its maximum value. A cw-pumped Yb:YAG laser passively Q switched by a Cr4-:YAG absorber is demonstrated to confirm this model. The theoretical model is also applied to the analysis of three previously reported passive Q switching solid-state [Nd:GdVO4, Nd-:LaSc3(BO3)(4) (Nd-:LSB), and Nd:YAG] lasers experiments. (c) 2006 Optical Society of America

Near-diffraction-limited passively Q-switched Yb : Y3Al5O12 ceramic lasers with peak power > 150 kW

Laser-diode pumped nearly diffraction-limited beam quality (M-2 < 1.05), high peak power, subnanosecond passively Q-switched Yb:Y3Al5O12 ceramic miniature laser with Cr4+:Y3Al5O12 ceramic as saturable absorber has been achieved. The slope efficiency is as high as 36% for 80% initial transmission of Cr4+:Y3Al5O12 ceramic. The pulse width of 335 ps and peak power of over 150 kW at repetition rate of 5 kHz were obtained. Laser oscillates at single-longitudinal-mode oscillation and wide-separated multilongitudinal-mode oscillation due to the combined etalon effect of the Cr4+:YAG thin plate and thin glass plate as output coupler. (c) 2007 American Institute of Physics

Laser-diode pumped heavy-doped Yb : YAG ceramic lasers

Laser performance of heavy-doped Yb:YAG ceramics was investigated using a two-pass pumping miniature laser configuration. Slope efficiency of 52% and optical-to-optical efficiency of 48% have been achieved for 1-mm-thick YAG ceramic doped with 20 at. % ytterbium ions. Laser spectra of Yb:YAG ceramic and single-crystal lasers were addressed under different intracavity laser intensities. Heavy-doped Yb:YAG ceramic is more suitable for a thin disk laser than a single-crystal with the same Yb3+-ion lasants. (c) 2007 Optical Society of America

Ytterbium and chromium doped composite Y3Al5O12 ceramics self-Q-switched laser

Composite Yb:Y3Al5O12/Cr:Y3Al5O12 ceramics were fabricated by using vacuum sintering technique and nanocrystalline technology. Self-Q-switched composite Yb:Y3Al5O12/Cr:Y3Al5O12 ceramic lasers with pulse energy of 125 mu J and peak power of over 105 kW at repetition rate of 3.8 kHz have been demonstrated. Nearly diffraction-limited beam quality with M-2 less than 1.35 was achieved in this composite Yb:Y3Al5O12/Cr:Y3Al5O12 ceramic self-Q-switched lasers. (C) 2007 American Institute of Physics

CD226 (DNAM-1) Is Involved in Lymphocyte Function–associated Antigen 1 Costimulatory Signal for Naive T Cell Differentiation and Proliferation

Upon antigen recognition by the T cell receptor, lymphocyte function–associated antigen 1 (LFA-1) physically associates with the leukocyte adhesion molecule CD226 (DNAM-1) and the protein tyrosine kinase Fyn. We show that lentiviral vector-mediated mutant (Y-F322) CD226 transferred into naive CD4+ helper T cells (Ths) inhibited interleukin (IL)-12–independent Th1 development initiated by CD3 and LFA-1 ligations. Moreover, proliferation induced by LFA-1 costimulatory signal was suppressed in mutant (Y-F322) CD226-transduced naive CD4+ and CD8+ T cells in the absence of IL-2. These results suggest that CD226 is involved in LFA-1–mediated costimulatory signals for triggering naive T cell differentiation and proliferation. We also demonstrate that although LFA-1, CD226, and Fyn are polarized at the immunological synapse upon stimulation with anti-CD3 in CD4+ and CD8+ T cells, lipid rafts are polarized in CD4+, but not CD8+, T cells. Moreover, proliferation initiated by LFA-1 costimulatory signal is suppressed by lipid raft disruption in CD4+, but not CD8+, T cells, suggesting that the LFA-1 costimulatory signal is independent of lipid rafts in CD8+ T cells