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Growth of strongly textured $\mathrm{FeCO}_{3}$ thin films on substrates was achieved with ultrashort-pulsed laser deposition using 810-nm, 46-fs ablation pulses. The crystallinity and composition were verified with X-ray diffraction and Raman spectroscopy. Using Mössbauer spectroscopy, it is shown that the deposited $\mathrm{FeCO}_{3}$ thin films possess the film quality required for application in research of nuclear quantum optics. It is found that a relatively low substrate temperature is crucial for growing a strongly textured film of $\mathrm{FeCO}_{3}$ while avoiding decomposition of $\mathrm{FeCO}_{3}$ into $\mathrm{Fe}_{2}\mathrm{O}_{3}$ and $\mathrm{CO}_{2}$. This supports the importance of the use of ultrashort-pulsed laser deposition in providing adatoms with high mobility for attaining good crystallinity. The surface morphology was characterized by surface profilometry, scanning electron microscopy and atomic force microscopy. It is found to be significantly affected by changing the ablation laser parameters, including laser fluence, pulse duration, and on-target spot size. The results show that the peak deposition flux must be below approximately 0.03 nm/pulse in order to grow a flat film. [ABSTRACT FROM AUTHOR]

We demonstrate the proof-of-principle experiment on all-optical quasi-phase matching (QPM) of high-order harmonic generation (HHG) via the transverse selective-zoning method. The dephasing length and the out-of-phase region in the interacting medium are identified in advance by applying a tomographic diagnosis of the generation process. Then a transverse disruptive pulse is employed to suppress the harmonic emission in the out-of-phase region to achieve QPM. The final output is enhanced by 35% with just one QPM zone. This proof-of-principle result provides the feasibility of ion-based HHG for higher cut-off energies, where phase matching is difficult to achieve.

We present a phase-matching scheme for efficient high-order harmonic generation in the water-window x-ray spectral region using a 405-nm driving pulse. A high-intensity pulse (∼10 16 W/cm 2 ) is used to produce He 1+ ions as the target medium, increasing the cutoff photon energy to the water-window x-ray spectral region. By adjusting the driving pulse divergence, the positive dipole phase variation balances the negative plasma dispersion and geometrical phase shift, achieving phase matching. Using the electromagnetic envelope equation coupled with the Keldysh ionization model, numerical experiments identify the optimal conditions. Results show that the relative conversion efficiencies of the 95 th harmonic (4.26 nm) and the 169 th harmonic (2.4 nm) reach 66% and 79% of the perfect phase-matching conditions, respectively.