High average power Yb:CaF2 femtosecond amplifier with integrated simultaneous spatial and temporal focusing for laser material processing.

A watt level, 10-kilohertz repetition rate chirped pulse amplification system that has an integrated simultaneous spatial and temporal focusing (SSTF) processing system is demonstrated for the first time. SSTF significantly reduces nonlinear effects normally detrimental to beam control enabling the use of a low numerical aperture focus to quickly treat optically transparent materials over a large area. The integrated SSTF system has improved efficiency compared to previously reported SSTF designs, which combined with the high repetition rate of the laser, further optimizes its capability to provide rapid, large volume processing.

Hybrid plasmon/dielectric waveguide for integrated silicon-on-insulator optical elements.

VLSI compatible optical waveguides on silicon are currently of particular interest in order to integrate optical elements onto silicon chips, and for possible replacements of electrical cross-chip/inter-core interconnects. Here we present simulation and experimental verification of a hybrid plasmon/dielectric, single-mode, single-polarization waveguide for silicon-on-insulator wafers. Its fabrication is compatible with VLSI processing techniques, and it possesses desirable properties such as the absence of birefringence and low sensitivity to surface roughness and metallic losses. The waveguide structure naturally forms an MOS capacitor, possibly useful for active device integration. Simulations predict very long propagation lengths of millimeter scale with micron scale confinement, or sub-micron scale confinement with propagation lengths still in excess of 100 microns. The waveguide may be tuned continuously between these states using standard VLSI processing. Extremely long propagation lengths have been simulated: one configuration presented here has a simulated propagation length of 34 cm.

Preservation of the carrier envelope phase during cross-polarized wave generation.

The preservation of carrier envelope phase (CEP) during Cross-Polarized Wave Generation (XPWG) is demonstrated through two independent experiments based on the spatially and spectrally resolved interference fringes formed by the XPW beam and its fundamental. In a first measurement, we found that the vertical fringe position on the spatial detector was maintained over many consecutive laser shots, implying practically no change in relative CEP between the XPW and the fundamental. In a second experiment, we measured the change in relative CEP between the XPW and fundamental beam by systematically varying the amount of material dispersion inside the XPW arm of the interferometer. The recorded rate of relative phase change was in excellent agreement with the theoretical value.

Linear spatio-temporal characterization of a UV microscope objective for nonlinear imaging and spectroscopy by using two-dimensional spectral interferometry.

Two-dimensional Fourier transform spectral interferometry is used to characterize the spatio-temporal aberrations of a UV microscope objective. The spatial and temporal profiles of a 420 nm, 38 fs pulse at the focus of a 0.32 NA UV objective are then deduced using a wave propagation code incorporating the measured aberrations.

Simultaneous imaging of multiple focal planes using a two-photon scanning microscope.

Despite all the advances in nonlinear microscopy, all existing instruments are constrained to obtain images of one focal plane at a time. In this Letter we demonstrate a two-photon absorption fluorescence scanning microscope capable of imaging two focal planes simultaneously. This is accomplished by temporally demultiplexing the signal coming from two focal volumes at different sample depths. The scheme can be extended to three or more focal planes.

Complete characterization of a spatiotemporal pulse shaper with two-dimensional Fourier transform spectral interferometry.

Spatiotemporal pulse shaping is characterized with two-dimensional Fourier transform spectral interferometry. A deformable-mirror-based bidimensional pulse shaper is used to create simple spatiotemporal structures on a femtosecond pulse, structures that are directly calculated from the measured spatiospectral phases and intensities.

Simultaneous visualization of spatial and chromatic aberrations by two-dimensional Fourier transform spectral interferometry.

We demonstrate the use of a simple tool to simultaneously visualize and characterize chromatic and spherical aberrations that are present in multiphoton microscopy. Using two-dimensional Fourier transform spectral interferometry, we measured these aberrations, deducing in a single shot spatiotemporal effects in high-numerical-aperture objectives.

Adaptive correction of a tightly focused, high-intensity laser beam by use of a third-harmonic signal generated at an interface.

By using the third-harmonic signal generated at an air-dielectric interface, we demonstrate a novel way of correcting wavefront aberrations induced by high-numerical-aperture optics. The third harmonic is used as the input physical parameter of a genetic algorithm working in closed loop with a 37-actuator deformable mirror. This method is simple and reliable and can be used to correct aberrations of tightly focused beams, a regime where other methods have limitations. Improvement of the third-harmonic signal generated with an f/1.2 parabolic mirror by 1 order of magnitude is demonstrated.

Magnetostatic effects in the nucleation of rare earth ferromagnetic phases.

It has been reported that superheating, supercooling, and explosive kinetics coupled to other degrees of freedom occur at the ferromagnetic transitions of Er and Dy, and that metastable phases occur during the transition kinetics of Er. We explain these observations in terms of magnetostatic energy, which requires highly eccentric nuclei in the homogeneous nucleation of magnetic transitions in heavy rare earths. The magnetostatics favor transitions through ferrimagnetic intermediaries. The unusual kinetics derive from effective spin lattice relaxation.

Generation of broadband VUV light using third-order cascaded processes.

We report the first demonstration of broadband VUV light generation through cascaded nonlinear wave mixing in a gas. Using a hollow-fiber geometry to achieve broad-bandwidth phase-matching, frequency conversion of ultrashort-pulse Ti:sapphire laser pulses from the visible into the deep UV around 200 and 160 nm is achieved. A new type of quasi-phase-matching is also observed in the VUV for the first time. Conversion using cascaded processes exhibits higher efficiencies, shorter pulse durations, and broader bandwidths than other schemes for generating light in the deep UV, and will enable many applications in science and technology.

Intense 8-fs pulse generation in the deep ultraviolet.

By use of the recently developed technique of guided-wave frequency conversion, the generation of sub-10-fs light pulses in the UV has been demonstrated for what is believed to be the first time. Cross-phase modulation of the light in a hollow waveguide produced a bandwidth of 16 nm, with a center frequency of 270 nm, at 1 kHz. A simple grating pair was used to compress the pulses to a duration of 8 fs, as measured by self-diffraction frequency-resolved optical gating. In the experiment the compressed energy was greater than 1 muJ , with a peak power of >100 MW ; the technique can be scaled to higher energy. Further improvements should make it possible to generate pulses as short as approximately 3 fs with this technique.