Roadmap to ultra-short record high-energy pulses out of laser oscillators

Highly-chirped dissipative solitons of the cubic-quintic Ginzburg-Landau equation found in this work may provide a roadmap to design passively mode-locked laser oscillators that generate pulses of extremely high energy. We provide a region in the space of the system parameters where high-energy dissipative solitons are found, along with their typical spectral and temporal features.     

Experimental implementation of ultrashort laser pulses in the von Neumann picture

The characterization and interpretation of ultrashort laser pulses is most intuitive in the joint time–frequency domain, where structures like multiple pulses become immediately apparent. For practical reasons, ultrafast femtosecond laser pulse shaping, however, is commonly carried out in the frequency domain. Here we implement pulse shaping of optical fields defined in the von Neumann representation, which is a joint time–frequency distribution with complex-valued Gaussian basis functions. We discuss the feasibility as well as the principal limitations of this technique, show illustrative examples, and propose possible applications in coherent control.     

Substitution, dimerization, metalation, and ring-opening reactions of N-fused porphyrins

A variety of reactions such as substitution, dimerization, rhenium(I) metalation, and ring-opening reactions of N-fused porphyrin (NFP) and optical properties of the products are presented. Palladium-catalyzed cross-coupling reactions under Suzuki or Stille conditions afford aryl and arylethynyl-substituted NFPs (12, 14) and an ethynyl-bridged dimer (15) from 3-bromo-substituted NFP (3b) in 40-98% yields. Treatment of NFP with silver(I) trifluoroacetate in CHCl₃ affords a dimer (22) linked at both C21-positions of the fused rings and its bis-Re(I) metal complex (24) is synthesized. X-ray structures of the 3-trifluoromethyl and 3-phenyl NFP derivatives (9e and 12a) reveal the three-center hydrogen bondings in the core. All the new NFP derivatives display unique absorption spectra, and particularly, ethyne-bridged NFP-dimer (15) shows a remarkable bathochromic shift into a near-infrared region showing an absorption band at 1020 nm with tailing up to 1100 nm. Moreover, alkoxide nucleophiles convert NFP into NCP derivatives by the cleavage of C-N bond in the fused ring, which is useful for the preparation of various C3-substituted NCPs and C21,C21′-linked NCP dimers from NFPs.     

Evolution of the N = 20 and N = 28 shell closures in neutron-rich nuclei

The isospin dependence of shell closure phenomena is studied for light neutron-rich nuclei within a microscopic self-consistent approach using the Gogny force. Introducing configuration mixing, ³²Mg is found to be dynamically deformed, although the N = 20 spherical shell closure persists at the mean-field level for all N = 20 isotones. In contrast, the N = 28 spherical shell closure is found to disappear for N - Z≥ 10 whereas deformed shell closures are preserved and lead to shape coexistence in ⁴⁴ S. Configuration mixing shows that the ground state of this nucleus is triaxially deformed. The first 2⁺ excitation energy E_x = 1.46 MeV and the reduced transition probability B(E2;0⁺ _gs→ 2⁺ ₁)= 420 e ² fm ⁴ obtained with our approach are in good agreement with experimental data. Received: 26 July 2000 / Accepted: 30 August 2000     

Configuration assignments and decay of 126La high-spin bands

High spin states of ¹²⁶La have been populated using the reaction ¹¹⁶Sn+¹⁴N at 68 MeV. γ-rays and conversion electrons were detected with the GAREL array. Multipolarities of the lowest-lying in-band dipole transitions have been determined from the deduced internal conversion coefficients. Experimental B(M1)/B(E2) ratios have been derived for the bands and compared with calculated values using the D?nau-Frauendorf geometrical model. Configurations are proposed for the bands comparing them with cranked shell model calculations and on the basis of the measured B(M1)/B(E2) ratios. The β-decay of ¹²⁶La has also been revisited. The population of the ¹²⁶Ba levels gives a probable spin value of five for the decaying high-spin ¹²⁶La state with T _1/2≈ 64 s which may indicate a signature inversion in the πh_11/2νh_11/2 band. Received: 12 October 1999     

Terminating high-spin bands in 101Rh

High spin states of ¹⁰¹Rh have been populated using the reaction ⁷⁰Zn+³⁶S at 130 MeV. γ-rays were detected with the EUROGAM2 array. New high-spin bands have been observed in this nucleus up to 45/2⁻, 57/2⁻ and 65/2⁺ states. They have been interpreted using the Nilsson-Strutinsky cranking formalism as terminating configurations. Two of the bands were observed up to the predicted terminating states which are built up from g_9/2 protons as well as d_5/2, g_7/2 and h_11/2 neutrons relative to a ⁹⁰Zr core. Received: 30 October 1998     

Observation of superdeformed states in 88Mo

High-spin states in ⁸⁸Mo were studied using the Gammasphere germanium detector array in conjunction with the Microball CsI(Tl) charged-particle detector system. Three γ-ray cascades with dynamic moments of inertia showing similar characteristics to superdeformed rotational bands observed in the neighbouring A= 80 region have been identified and assigned to the nucleus ⁸⁸Mo. The quadrupole moment of the strongest band, deduced by the Residual Doppler Shift Method, corresponds to a quadrupole deformation of β₂≈ 0.6. This confirms the superdeformed nature of this band. The experimental data are interpreted in the framework of total routhian surface calculations. All three bands are assigned to two-quasi-particle proton configurations at superdeformed shape. Received: 20 May 1999 / Revised version: 25 August 1999     

Generation of 10 to 50 fs pulses tunable through all of the visible and the NIR

Noncollinearly phase-matched optical parametric amplifiers (NOPAs) pumped by the blue light of a frequency-doubled Ti:sapphire regenerative amplifier are a convenient source of continuously tunable ultrashort pulses in the visible and near infrared for spectroscopic experiments. We present the underlying principles, report recent improvements and describe the experiences gained from the routine use of a number of NOPAs in our laboratories. We find that the setup can easily be optimized for the given experimental requirements. Typical output-pulse energies in the visible are 5 to 10 μJ and a few μJ in the NIR from 200 μJ regenerative-amplifier pulses at 800 nm. From 460 to 700 nm, pulse lengths between 10 and 20 fs are routinely achieved, while the length increases monotonically from about 20 fs at 900 nm to just below 50 fs at 1600 nm. In all cases this corresponds to a dramatic shortening compared to the length of the pump pulses of around 100 fs. First results show that the 700 to 900 nm region can be accessed with sub-50-fs pulse lengths by use of an intermediate white-light generator in a two-stage setup. Received: 29 November 1999 / Published online: 5 July 2000     

Nd:Ca4ReO(BO3)3(Re=Gd,Y)晶体最佳激光、最佳倍频及最佳自倍频方向的确定

介绍了Nd:Ca4ReO(BO3)3(Re=Gd,Y)晶体最佳激光方向、最佳倍频方向的确定.综合考虑激光受激发射截面、抽运光吸收系数、有效非线性系数的各向异性,分析了自倍频性质的空间分布,并就此确定出最佳自倍频方向 关键词： Nd:Ca4ReO(BO3)3(Re=Gd Y)晶体 激光发射 倍频 自倍频     

Two-dimensional ‘hat-scratch’ periodic structures induced by a single femtosecond laser pulse on silica glass

Two-dimensional ‘hat-scratch’ structures are fabricated on silica glass by the interference of three non-coplanar beams originating from a single femtosecond laser pulse. The scanning electron microscope (SEM) characterizations show that the as-formed structures are composed of hat holes and scratch marks. The experimental results indicate that the structures are dependent on the intensity of laser beam. The formation of the two-dimensional ‘hat-scratch’ structures is mainly due to the combined laser ablation effects including ionization, shock wave, plasma expansion, and phase explosion.