While whole-organism calcium imaging in small and semi-transparent animals has been demonstrated, capturing the functional dynamics of large-scale neuronal circuits in awake, behaving mammals at high speed and resolution has remained one of the main frontiers in systems neuroscience. Here we present a novel method based on light sculpting that enables unbiased single and dual-plane high-speed (up to 160 Hz) calcium imaging, as well as in vivo volumetric calcium imaging of a mouse cortical column (0.5 × 0.5 × 0.5 mm) at single-cell resolution and fast volume rates (3 – 6 Hz). This is achieved by tailoring the point-spread function of our microscope to the structures of interest, and by maximizing the signal-to-noise ratio by using a home-built fiber laser amplifier and synchronizing its pulses to the imaging voxel speed. This has enabled in-vivo recording of calcium dynamics of several thousand neurons across cortical layers and in the hippocampus of awake behaving mice.

No abstract

We demonstrate a Kerr-lens mode-locked Ti:sapphire oscillator that generates 130-nJ, 26-fs and 220-nJ, 30-fs pulses at a repetition rate of 11 MHz. The generation of stable broadband, high-energy pulses from an extended-cavity oscillator is achieved by the use of chirped multilayer mirrors to produce a small net positive dispersion over a broad spectral range. The resultant chirped picosecond pulses are compressed by a dispersive delay line that is external to the laser cavity. The demonstrated peak powers, in excess of 5 MW, are to our knowledge the highest ever achieved from a cw-pumped laser and are expected to be scalable to tens of megawatts by an increase in the pump power and (or) a decrease in the repetition rate. The demonstrated source permits micromachining of any materials under relaxed focusing conditions.

We generated a series of harmonics in a xenon gas jet inside a cavity seeded by pulses from a Ti:sapphire mode-locked laser with a repetition rate of 10.8 MHz. Harmonics up to 19th order at 43 nm were observed with plateau harmonics at the microW power level. An elaborate dispersion compensation scheme and the use of a moderate repetition rate allowed for this significant improvement in output power of the plateau harmonics of 4 orders of magnitude over previous results. With this power level and repetition rate, high-resolution spectroscopy in the extreme ultraviolet region becomes conceivable. An interesting target would be the 1S-2S transition in hydrogenlike He+ at 60 nm.

A detailed numerical analysis of heavily chirped pulses in the positive-dispersion regime (PDR) is presented on the basis of the distributed cubic–quintic generalized complex nonlinear Ginzburg–Landau equation. It is demonstrated that there are three main types of pulse spectra: truncated parabolic-top, Π- and M-shaped profiles. The strong chirp broadens the pulse spectrum up to 100 nm for a Ti:Sa oscillator, which provides compressibility of the picosecond pulse down to sub-30 fs. Since the picosecond pulse has a peak power lower than the self-focusing power inside a Ti:Sa crystal, the microjoule energies become directly available from a femtosecond oscillator. The influence of the third- and fourth-order dispersions on the pulse spectrum and stability is analysed. It is demonstrated that the dynamic gain saturation plays an important role in pulse stabilization. The common action of dynamic gain saturation, self-amplified modulation (SAM) and saturation of the SAM provides pulse stabilization inside the limited range of the positive group-delay dispersions (GDDs). Since the stabilizing action of the SAM cannot be essentially enhanced for a pure Kerr-lens mode-locking regime, a semiconductor saturable absorber is required for pulse energies of >0.7 μJ inside an oscillator. The basic results of the numerical analysis are in an excellent agreement with experimental data obtained from oscillators with repetition rates ranging from 50 to 2 MHz.

The effects of high-order dispersion on a chirped-pulse oscillator operating in the positive dispersion regime were studied both theoretically and experimentally. It was found that odd and negative even high-order dispersions impair the oscillator stability owing to resonance with the dispersion waves, but can broaden the spectrum as in the case of continuum generation in the fibers. Positive fourth-order dispersion enhances the stability and shifts the stability range into negative dispersion. The destabilization mechanism was found to be a parametrical instability which causes noisy mode locking around zero dispersion.

No abstract

We have developed the first (to our knowledge) femtosecond Tm-fiber-laser-pumped Ho:YAG room-temperature chirped pulse amplifier system delivering scalable multimillijoule, multikilohertz pulses with a bandwidth exceeding 12 nm and average power of 15 W. The recompressed 530 fs pulses are suitable for broadband white light generation in transparent solids, which makes the developed source ideal for both pumping and seeding optical parametric amplifiers operating in the mid-IR spectral range.