Transverse Coherence Limited Coherent Diffraction Imaging using a Molybdenum Soft X-ray Laser Pumped at Moderate Pump Energies.

Coherent diffraction imaging (CDI) in the extreme ultraviolet has become an important tool for nanoscale investigations. Laser-driven high harmonic generation (HHG) sources allow for lab scale applications such as cancer cell classification and phase-resolved surface studies. HHG sources exhibit excellent coherence but limited photon flux due poor conversion efficiency. In contrast, table-top soft X-ray lasers (SXRL) feature excellent temporal coherence and extraordinary high flux at limited transverse coherence. Here, the performance of a SXRL pumped at moderate pump energies is evaluated for CDI and compared to a HHG source. For CDI, a lower bound for the required mutual coherence factor of |µ 12| ≥ 0.75 is found by comparing a reconstruction with fixed support to a conventional characterization using double slits. A comparison of the captured diffraction signals suggests that SXRLs have the potential for imaging micron scale objects with sub-20 nm resolution in orders of magnitude shorter integration time compared to a conventional HHG source. Here, the low transverse coherence diameter limits the resolution to approximately 180 nm. The extraordinary high photon flux per laser shot, scalability towards higher repetition rate and capability of seeding with a high harmonic source opens a route for higher performance nanoscale imaging systems based on SXRLs.

10-Hz grazing--incidence pumped Ni-like Mo x-ray laser.

The operation of a Ni-like Mo x-ray laser at 18.9 nm with a repetition rate of 10 Hz has been demonstrated. The laser has been pumped applying the grazing incidence pump arrangement, where a short (picoseconds) pulse irradiates a Mo plasma column generated by a long (a few hundred picoseconds) pulse. The delayed short pulse is incident at a grazing angle on the plasma to heat it efficiently. We used a total energy of less than 450 mJ ( 150 mJ in the long and 250-300 mJ in the short pulse) in a line focus of 7 mm by 50 microm .

High-repetition-rate chirped-pulse-amplification thin-disk laser system with joule-level pulse energy.

We are reporting on the development of a diode-pumped chirped-pulse-amplification (CPA) laser system based on Yb:YAG thin-disk technology with a repetition rate of 100 Hz and output pulse energy in the joule range. The focus lies with the first results of the preamplifier--a regenerative amplifier (RA) and a multipass amplifier (MP). The system consists of a front end including the CPA stretcher followed by an amplifier chain based on Yb:YAG thin-disk amplifiers and the CPA compressor. It is developed in the frame of our x-ray laser (XRL) program and fulfills all requirements for pumping a plasma-based XRL in grazing incidence pumping geometry. Of course it can also be used for other interesting applications. With the RA pulse energies of more than 165 mJ can be realized. At a repetition rate of 100 Hz a stability of 0.8% (1sigma) over a period of more than 45 min has been measured. The optical-to-optical efficiency is 14%. The following MP amplifier can increase the pulse energy to more than 300 mJ. A nearly bandwidth-limited recompression to less than 2 ps could be demonstrated.

Transverse spatial coherence of a transient nickellike silver soft-x-ray laser pumped by a single picosecond laser pulse.

The degree of spatial coherence in the direction perpendicular to the target surface is reported for a transient nickellike silver x-ray laser at 13.9 nm. An x-ray laser plasma column was produced by irradiating a slab silver target with a single shaped picosecond laser pulse with energy less than 3 J. Young's double-slit method was applied to measure the fringe visibility as a function of the slit separation for different target lengths. The diameter of the equivalent incoherent source and the coherence radius of the output radiation were determined as well.