X-ray harmonics made with long-wavelength lasers reach higher fluxes and photon energies when plasma effects dominate.

We describe the elimination of the astigmatism of a Czerny–Turner imaging spectrometer, built using spherical optics and a plane grating, over a broad spectral region. Starting with the principle of divergent illumination of the grating, which removes astigmatism at one chosen wavelength, we obtain design equations for the distance from the grating to the focusing mirror and the detector angle that remove the astigmatism to first order in wavelength. Experimentally, we demonstrate near diffraction-limited performance from 740 to 860 nm and over a $5\mathrm{mm}$ transverse spatial extent, while ray-tracing calculations show that barring finite-aperture and detector size limitations, this range extends from 640 to 900 nm and over $10\mathrm{mm}$ transversely. Our technique requires no additional optics and uses standard off-the-shelf components.

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We demonstrate a simplified arrangement for spatiotemporal ultrashort pulse characterization called Hartmann–Shack assisted, multidimensional, shaper-based technique for electric-field reconstruction. It employs an acousto-optic pulse shaper in combination with a second-order nonlinear crystal and a Hartmann–Shack wavefront sensor. The shaper is used as a tunable bandpass filter, and the wavefronts and intensities of quasimonochromatic spectral slices of the pulse are obtained using the Hartmann–Shack wavefront sensor. The wavefronts and intensities of the spectral slices are related to one another using shaper-assisted frequency-resolved optical gating measurements, performed at particular points in the beam. This enables a three-dimensional reconstruction of the amplitude and phase of the pulse. We present some example pulse measurements and discuss the operating parameters of the device.

Dispersive wave emission (DWE) in gas-filled hollow-core dielectric waveguides is a promising source of tuneable coherent and broadband radiation, but so far the generation of few-femtosecond pulses using this technique has not been demonstrated. Using in-vacuum frequency-resolved optical gating, we directly characterize tuneable 3 fs pulses in the deep ultraviolet generated via DWE. Through numerical simulations, we identify that the use of a pressure gradient in the waveguide is critical for the generation of short pulses.