Lensless diffractive imaging using tabletop coherent high-harmonic soft-X-ray beams.

We present the first experimental demonstration of lensless diffractive imaging using coherent soft x rays generated by a tabletop soft-x-ray source. A 29 nm high harmonic beam illuminates an object, and the subsequent diffraction is collected on an x-ray CCD camera. High dynamic range diffraction patterns are obtained by taking multiple exposures while blocking small-angle diffraction using beam blocks of varying size. These patterns reconstruct to images with 214 nm resolution. This work demonstrates a practical tabletop lensless microscope that promises to find applications in materials science, nanoscience, and biology.

Unified microscopic-macroscopic formulation of high-order difference-frequency mixing in plasmas.

We investigate high-order difference-frequency mixing in plasmas, taking into account the microscopic rescattering physics and propagation effects for the first time. We show that phase matching can occur over a broad frequency range, up to very high photon energies, and that it is confined to specific temporal and spatial windows. This gated phase matching mechanism is driven by the continuous phase slip between two driving fields and can be employed for manipulating the temporal, spatial, and spectral properties of high harmonic emission.

Efficient reflection grisms for pulse compression and dispersion compensation of femtosecond pulses.

Efficient reflection grisms for pulse-compression and material-dispersion compensation have been designed and demonstrated in a 40 fs, 300 microJ, 5 kHz downchirped pulse amplification system for the first time to our knowledge. A grism design for 800 nm femtosecond laser pulse dispersion compensation applications is realized by using standard, commercial diffraction gratings.

High-order harmonic generation from ions in a capillary discharge.

We demonstrate a significant extension of the high-order harmonic cutoff by using a fully-ionized capillary discharge plasma as the generation medium. The preionized plasma dramatically reduces ionization-induced defocusing and energy loss of the driving laser due to ionization. This allows for significantly higher photon energies, up to 150 eV, to be generated from xenon ions, compared with the 70 eV observed previously. We also demonstrate enhancement of the harmonic flux of nearly 2 orders of magnitude at photon energies around 90 eV when the capillary discharge is used to ionize xenon, compared with harmonic generation in a hollow waveguide. The use of a plasma as a medium for high-order harmonic generation shows great promise for extending efficient harmonic generation to much shorter wavelengths using ions.

Multi-kilohertz repetition rate Ti:sapphire amplifier based on down-chirped pulse amplification.

We present a novel ultrafast multipass laser amplifier design optimized for sub-millijoule output energy and capable of being operated at repetition rates exceeding 40 kHz. This ti:sapphire based system makes use of a grism based stretcher, a cryogenically cooled ti:sapphire crystal and an astigmatically compensated multipass amplifier design that allows for pumping with significantly lower pump pulse energies than has been demonstrated to date. We also make use of the downchirped pulse amplification scheme to minimize loss in the pulse compression process. Preliminary experiments demonstrate an output pulse energy of 290 muJ at 10 kHz and 270 muJ at 15 kHz with a pulse duration of 36 fs.

11-W average power Ti:sapphire amplifier system using downchirped pulse amplification.

We demonstrate a high-power laser system that employs a new scheme in which pulses with negative chirp are amplified and then recompressed by dispersion in a block of transparent material. This scheme has significant advantages for amplification of intermediate energy pulses at high average power, including insensitivity to small misalignments of the pulse compressor, elimination of compressor gratings and their thermal loading issues, low compressor energy and bandwidth throughput losses, and a simplified optical design. Using this scheme, we demonstrate what we believe is the highest-average-power single-stage Ti:sapphire amplifier system with 11-W compressed output.