Generation of 60-nJ sub-40-fs pulses at 70 MHz repetition rate from a Ti:sapphire chirped pulse-oscillator

We have studied the influence of the intracavity dispersion on the mode-locking characteristics of pure-Kerr-lens mode-locked Ti:sapphire chirped-pulse oscillators. Using the results of this study, we have built chirped-pulse oscillators that can be mode-locked when pumped with the highest pump powers commercially available at 532 nm. We generated 62 nJ pulses at 70 MHz repetition rate, with a Fourier limited duration of 33 fs. PACS 42.60.Fc; 42.60.Lh; 42.65.Re     

Some remarks on mechanism and kinetics of the coulometric variant of the Karl-Fischer titration reaction

The quasi-lattice model for quaternary reciprocal systems of molten salts, previously developed for association processes in mixed solvents, has been modified to apply to an association process involving a “mixed ligand” in a pure salt as solvent. The association energies, determined from e.m.f. measurements in the range 620–720 K, for the association of silver(I) with chloride-bromide mixtures in molten sodium nitrate, are in satisfactory agreement with the predictions of the model. The very small, but significant, discrepancies between calculated and experimental association energy values show the same trend as those previously found for the mixed solvent systems.     

Patterned retarders prepared by photoisomerization and photopolymerization of liquid crystalline films

Isomerizable diacrylates derived from cinnamic acid are designed, synthesized and mixed with liquid crystalline diacrylates with the aim of making films with alternating birefringent and isotropic domains by applying the E–Z isomerization process at room temperature. The effects of the structure of the isomerizable‐mesogenic group on the isotropization efficacy, the efficiency of the E–Z isomerization reaction, and film formation are discussed. Compounds derived from cyclohexyl cinnamate are proved to be good candidates that meet a whole set of parameters related to processing and application. These compounds exhibit a low nematic‐to‐isotropic transition temperature. In addition, they show no yellowing upon irradiation, unlike similar compounds derived from phenyl cinnamate. To elucidate the origin of isotropization of the film by irradiation, the pure Z‐isomer is prepared by photolysis of the E‐isomer and subsequent chromatographic separation of both isomers. Analysis of reference samples containing the pure isomers reveals that the decrease in transition temperature can be attributed exclusively to the E–Z photoisomerization process. Finally, thin films with alternating birefringent and isotropic parts of 100×100 µm² are obtained by using a combination of photoisomerization in air and photopolymerization in a nitrogen atmosphere, which is referred to as photo‐patterning.     

Pulse fidelity control in a 20-μJ sub-200-fs monolithic Yb-fiber amplifier

We discuss nonlinearity management versus energy scalability and compressibility in a three-stage monolithic 100-kHz repetition rate Yb-fiber amplifier designed as a driver source for the generation and tunable parametric amplification of a carrier-envelope phase stable white-light supercontinuum.     

Mechanism and reaction rate of the karl-fischer titration reaction: Part III. Rotating ring-disk electrode measurements— comparison with the aqueous system

A platinum disk-platinum ring electrode was used to investigate the oxidation of sulfur dioxide by iodine and triiodide in aqueous solutions. Contrary to methanolic solutions, where the monomethyl sulfite ion is the only oxidizable species, in aqueous solutions both the hydrogen sulfite ion and the sulfite ion can be oxidized. The reaction rate was generally so high, that the method for measurements of homogeneous second order reactions had to be used. At pH values >5, the reaction proceeded too fast to be measured reliably. In a solution “diluted” with ethanol (50% of weight), however, the reaction rate was within the range where a rotating ring-disk electrode can be applied to measure fast homogeneous reactions. At very low pH values both the first order calculation technique and the second order method could be used. The results with both methods were in fair agreement.     

Mechanism and reaction rate of the karl fischer titration reaction: Part V. Analytical Implications

The Karl Fischer titration procedure for the determination of water has been studied. In view of the results of previous investigations, a methanolic sodium acetate—sulfur dioxide solution is recommended as solvent and an iodine solution in methanol as titrant. The advantages of this procedure over a conventional Karl Fischer titration are: a much more rapidly reacting reagent, the possibility of a visual end-point detection, a titrant of constant titre over a long period of time, and the absence of the disagreeable odour of pyridine.     

Optical detection of attosecond ionization induced by a few-cycle laser field in a transparent dielectric material

We observe an optical signature induced by the modulation of electron density inside a bulk transparent solid that is quasiperiodically ionized on an attosecond time scale by electric field peaks of a focused few-cycle laser pulse. The emitted optical signal resulting from the attosecond ionization dynamics is spatially, temporally and spectrally isolated from concomitant optical responses through the use of a noncollinear pump-probe technique. The method holds promise for developing an attosecond metrology for bulk solids, in which, unlike in the established attosecond metrology of gases and surfaces, direct detection of charged particles is unfeasible.     

Compression of the pulses of a Ti:sapphire laser system to 5 femtoseconds at 0.2 terawatt level

High intensity contrast ratio, pre-pulse free pulses with pulse duration of 5 fs and pulse energy of 1 mJ were generated at a repetition rate of 1 kHz by compressing the output pulses of a multi-stage Ti:sapphire laser amplifier system in a Ne-gas-filled hollow fibre. The spatial and temporal properties of the output laser beam were fully characterised. PACS 42.60.Jf; 42.65.Re; 42.81.Qb     

Few-cycle carrier envelope phase-dependent stereo detection of electrons

The spatial distribution of electrons emitted from atoms by few-cycle optical fields is known to be dependent on the carrier envelope phase, i.e., the phase of the field with respect to the pulse envelope. With respect to Paulus et al. [Phys. Rev. Lett.91, 253004 (2003)] we propose a greatly simplified device to measure and control the carrier envelope phase of few-cycle pulses with an accuracy of better than pi/10 based on this principle. We compared different schemes to control the carrier envelope phase of our pulses.     

Ultrabroadband, coherent light source based on self-channeling of few-cycle pulses in helium

Self-channeling of few-cycle laser pulses in helium at high pressure generates coherent light supercontinua spanning the range of 270-1000 nm, with the highest efficiency demonstrated to date. Our results open the door to the synthesis of powerful light waveforms shaped within the carrier field oscillation cycle and hold promise for the generation of pulses at the single-cycle limit.