Temporal resolution of a transient pumping X-ray laser

We report on a time-resolved study of a Ni-like transient collisionnal X-ray laser with a resolution as high as 1.9 ps. The FWHM duration of the Ni-like x-ray laser pulse at 13.99 nm Ag J = 0→1 4d-4p line is measured to be as short as ∼2 ps at optimum conditions of pump laser irradiation. This is about four times shorter than was estimated in previous experiments. The x-ray laser signal appears in the rising edge of the continuum emission. The x-ray laser duration rises significantly when the short (heating) pulse duration is increased and when doubling the peak-to-peak delay of the two irradiation pulses. It does not change when the short pulse energy is increased. The results presented are the first direct measurements of the temporal profile of the x-ray laser output at a high resolution.