Nearly transform-limited sub-20-fs pulses at 1065 nm and >10 nJ enabled by a flat field ultrafast pulse shaper.

Using a low-nonlinearity fiber and pulses from a nonlinear fiber amplifier seeded by a modelocked Yb-doped fiber oscillator, we generate 19-fs pulses centered at 1065 nm with 11.5 nJ of pulse energy (700 mW average power). The short (<15 cm) 10-µm core, polarization maintaining fiber minimizes deleterious nonlinear effects and eliminates fiber damage, while still producing pulse bandwidths well beyond the Yb gain bandwidth limit. A flat-field pulse shaper, utilizing a Plössl lens, compresses the pulse to within 92% of the transform-limited peak power. The total power transmission efficiency is as high as 67%, including fiber coupling losses and pulse shaper transmission, due to the novel pulse shaper design allowing the incorporation of a high-efficiency transmission grating.

Time-resolved coherent Raman spectroscopy by high-speed pump-probe delay scanning.

Using a spinning window pump-probe delay scanner, we demonstrate a means of acquiring time-resolved vibrational spectra at rates up to 700 Hz. The time-dependent phase shift accumulated by the probe pulse in the presence of a coherently vibrating sample gives rise to a Raman-induced frequency shifting readily detectable in a balanced detector. This rapid delay scanning system represents a 23-fold increase in averaging speed and is >10× faster than state-of-the-art voice coil delay lines. These advancements make pump-probe spectroscopy a more practical means of imaging complex media.

Temporal coherence and spectral linewidth of an injection-seeded transient collisional soft x-ray laser.

The temporal coherence of an injection-seeded transient 18.9 nm molybdenum soft x-ray laser was measured using a wavefront division interferometer and compared to model simulations. The seeded laser is found to have a coherence time similar to that of the unseeded amplifier, ~1 ps, but a significantly larger degree of temporal coherence. The measured coherence time for the unseeded amplifier is only a small fraction of the pulsewidth, while in the case of the seeded laser it approaches full temporal coherence. The measurements confirm that the bandwidth of the solid target amplifiers is significantly wider than that of soft x-ray lasers that use gaseous targets, an advantage for the development of sub-picosecond soft x-ray lasers.