R. Szipocs

Compression of high-energy laser pulses below 5 fs.

High-energy 20-fs pulses generated by a Ti:sapphire laser system were spectrally broadened to more than 250 nm by self-phase modulation in a hollow fiber filled with noble gases and subsequently compressed in a broadband high-throughput dispersive system. Pulses as short as 4.5 fs with energy up to 20-microJ were obtained with krypton, while pulses as short as 5 fs with energy up to 70 microJ were obtained with argon. These pulses are, to our knowledge, the shortest generated to date at multigigawatt peak powers.

Chirped multilayer coatings for broadband dispersion control in femtosecond lasers

Optical thin-film structures exhibiting high reflectivity and a nearly constant negative group-delay dispersion over frequency ranges as broad as 80 THz are presented. This attractive combination makes these coatings well suited for intracavity dispersion control in broadband femtosecond solid-state lasers. We address design issues and the principle of operation of these novel devices.

Sub-10-fs mirror-dispersion-controlled Ti:sapphire laser

We demonstrate the generation of nearly bandwidth-limited 8-fs optical pulses near 0.8 microm from a self-mode-locked Ti:sapphire laser oscillator, using chirped dielectric mirrors for dispersion control. The mode-locking performance is described, and limitations are discussed.

Generation of 11-fs pulses from a Ti:sapphire laser without the use of prisms

The generation of highly stable optical pulses as short as 11 fs from a Kerr-lens mode-locked Ti:sapphire laser containing no intracavity prisms is demonstrated. In the femtosecond oscillator design reported, novel dielectric mirrors provide broadband dispersion control for solitonlike pulse formation.

Ultrabroadband ring oscillator for sub-10-fs pulse generation

A four-mirror ring cavity formed by chirped dielectric mirrors is proposed for self-mode-locked solid-state lasers. It offers, for the first time to our knowledge, the potential for approaching the gain-bandwidth limit in Ti:sapphire and related broadband lasers. Using this concept, we produced nearly bandwidth-limited 7.5-fs pulses from a feedback-initiated, self-mode-locked Ti:sapphire ring oscillator. Our experiments provide new insight into the physics and limitations of sub-10-fs oscillators.

Ultrabroadband chirped mirrors for femtosecond lasers

We report on the performance of widely tunable femtosecond and continuous-wave Ti:sapphire lasers that use a newly developed ultrabroadband mirror set. The mirrors exhibit high reflectivity (R>99%) and smooth variation of group delay versus frequency over a wavelength range from 660 to 1060 nm. Mode-locked operation with pulse durations of 85 fs was achieved from 693 to 978 nm with only one set of ultrabroadband mirrors.

Dendritic nicotinic receptors modulate backpropagating action potentials and long-term plasticity of interneurons

Stratum radiatum interneurons, unlike pyramidal cells, are rich in nicotinic acetylcholine receptors (nAChRs); however, the role of these receptors in plasticity has remained elusive. As opposed to previous physiological studies, we found that functional α7‐subunit‐containing nAChRs (α7‐nAChRs) are abundant on interneuron dendrites of rats. Moreover, dendritic Ca2+ transients induced by activation of α7‐nAChRs increase as a function of distance from soma. The activation of these extrasynaptic α7‐nAChRs by cholinergic agonists either facilitated or depressed backpropagating action potentials, depending on the timing of α7‐nAChR activation. We have previously shown that dendritic α7‐nAChRs are involved in the regulation of synaptic transmission, suggesting that α7‐nAChRs may play an important role in the regulation of the spike timing‐dependent plasticity. Here we provide evidence that long‐term potentiation is indeed boosted by stimulation of dendritic α7‐nAChRs. Our results suggest a new mechanism for a cholinergic switch in memory encoding and retrieval.

Reduced inflammatory threshold indicates skin barrier defect in transglutaminase 3 knockout mice

Recently, a transglutaminase 3 knockout (TGM3/KO) mouse was generated that showed impaired hair development, but no gross defects in the epidermal barrier, although increased fragility of isolated corneocytes was demonstrated. Here we investigated the functionality of skin barrier in vivo by percutaneous sensitization to FITC in TGM3/KO (n=64) and C57BL/6 wild-type (WT) mice (n=36). Cutaneous inflammation was evaluated by mouse ear swelling test (MEST), histology, serum IgE levels, and by flow cytometry from draining lymph nodes. Inflammation-induced significant MEST difference (P<0.0001) was detected between KO and WT mice and was supported also by histopathology. A significant increase of CD4+ CD25+-activated T cells (P<0.01) and elevated serum IgE levels (P<0.05) in KO mice indicated more the development of FITC sensitization than an irritative reaction. Propionibacter acnes-induced intracutaneous inflammation showed no difference (P=0.2254) between the reactivity of WT and KO immune system. As in vivo tracer, FITC penetration from skin surface followed by two-photon microscopy demonstrated a more invasive percutaneous penetration in KO mice. The clinically uninvolved skin in TGM3/KO mice showed impaired barrier function and higher susceptibility to FITC sensitization indicating that TGM3 has a significant contribution to the functionally intact cutaneous barrier.

Random access three-dimensional two-photon microscopy

We propose a two-photon microscope scheme capable of real-time, three-dimensional investigation of the electric activity pattern of neural networks or signal summation rules of individual neurons in a 0.6 mm x 0.6 mm x 0.2 mm volume of the sample. The points of measurement are chosen according to a conventional scanning two-photon image, and they are addressed by separately adjustable optical fibers. This allows scanning at kilohertz repetition rates of as many as 100 data points. Submicrometer spatial resolution is maintained during the measurement similarly to conventional two-photon microscopy.

Measurement of the group delay of laser mirrors by a Fabry-Perot interferometer

The group delay of multilayer laser mirrors was measured by determining the spectral position of transmission maxima of a Fabry–Perot interferometer formed by the mirrors to be characterized. By optimizing the spacer thickness, we obtained an accuracy of the group-delay measurement of better than 0.23 fs. To our knowledge, this is the most precise direct measuring method reported.