Abstract
The physics of attosecond pulse generation requires using infrared driving wavelength to reach the soft X-rays. However, with longer driving wavelength, the harmonic conversion efficiency drops significantly. It makes the conventional attosecond pulse measurement using streaking very difficult due to the low photoionization cross section in the soft X-rays region. In-situ measurement was developed for precisely this purpose. We use in-situ measurement to characterize, in both space and time, an attosecond pulse produced by ultrafast wavefront rotation of a 1.8 μm fundamental beam. We confirm what models suggest – that each beamlet is an isolated attosecond pulse in the time domain. We get almost constant flat wavefront curvature through the whole photon energy range. The measurement method is scalable to the soft X-ray spectral region.
Highlights
The physics of attosecond pulse generation requires using infrared driving wavelength to reach the soft X-rays
We report the first temporal characterization of isolated attosecond pulses produced by an infrared driver
We show that isolated attosecond pulses can be created with infrared drivers and we measured their spatial-temporal characteristics
Summary
The detector records the spectrum of the XUV emission along its horizontal axis, and the angle of the XUV emission (from the gas jet to the MCP plate) along the vertical axis. The laser beam is focused by a silver-coated concave mirror behind the gas jet. The attosecond pulses generated at different time propagate to different direction. The transmitted beam is used for the isolated attosecond pulse generation. This beam creates the spatially well-separated XUV radiation beamlets extending from 30 eV to 68 eV. The angle of the perturbation beam is 6.7 mrad and its intensity was 10-3 of the fundamental. Because of the small angle, the perturbation beam only modifies the wavefront along the vertical direction.
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