Approaching the transform limit for X-ray laser pulses

Below saturation, X-ray laser output shows a reduction in pulse duration and frequency bandwidth as the gain-length product increases. Above saturation, both quantities can be expected to rebroaden. The duration of gain can be close to an order-of-magnitude longer than the output pulse duration. With gain-length products just below saturation, X-ray lasing at 13.9 nm in nickel-like silver has been measured with a pulse duration Δt of 3 - 4 ps and an estimated frequency bandwidth Δv of 5 × 10¹¹ Hz. Such values imply that the pulses are close to transform limited with Δt Δv ≈ 1.5. Measurements of x-ray laser pulse-lengths and gain duration will be described in this paper.