Soft X-ray Laser Research Articles

Demonstration of an all-diode-pumped soft x-ray laser

We have demonstrated an 18.9 nm Ni-like molybdenum soft x-ray laser, pumped by a compact all-diode-pumped Yb:YAG laser. The solid-state pump laser produces 8.5 ps pulses with up to 1 J energy at 10 Hz repetition rate. This diode-pumped laser has the potential to greatly increase the repetition rate and the average power of soft x-ray lasers on a significantly smaller footprint.

High resolution full-field imaging of nanostructures using compact extreme ultraviolet lasers

Recent advances in the development of high peak brightness table-top extreme ultraviolet (EUV) and soft x-ray (SRX) lasers have opened new opportunities for the demonstration of compact full-field EUV/SXR microscopes capable of capturing images with short exposures down to a single laser shot. We demonstrate the practical application of table-top zone plate EUV microscopes that can image nanostructures with a spatial resolution of 54 nm and below and exposure times as short as 1.2 ns, the duration of a single laser shot.

Optimization of soft x-ray amplifier by tailoring plasma hydrodynamics

Plasma-based seeded soft x-ray lasers have the potential to generate a high-energy, highly coherent, short pulse beam. Owing to their high density, plasmas created by interaction of an intense laser with a solid target should store the highest amount of energy among all plasma amplifiers. However, to date output energy from seeded solid amplifiers remains as low as 60 nJ. We demonstrated that careful tailoring of the plasma shape is crucial for extracting energy stored in the plasma. With 1-mm-wide plasma, energy as high as 20 microJ in sub-ps pulses is achievable. With such tailored plasma, gain and pumping efficiency have been increased by nearly a factor of 10 as compared to the narrower plasma amplifiers studied here.

Method to eliminate the damage aroused by intrinsic prepulse of Blumlein transmission line in capillary discharge soft X-ray laser system

To raise the utilization ratio of the energy power, and meanwhile, guarantee the waveform of the main discharge current to obtain X-ray laser, our capillary discharged Ne-like Ar soft X-ray laser system adopts Blumleim transmission line (BTL) and a 300 kV-Marx generator; and by using our self-developed intrinsic-prepulse elimination device and extrinsic-prepulse generator, we successfully removed the intrinsic prepulse of BTL, and thus eliminated its deteriorative effect towards Z-pinch plasma. By this means, we obtained stable X-ray laser output; and the voltage transmission rate of our system nearly reaches 122%, which provides a guarantee for the miniaturization of the power source and the whole system.

An optimized kHz two-colour high harmonic source for seeding free-electron lasers and plasma-based soft x-ray lasers

Free-electron lasers (FEL) and plasma-based soft x-ray lasers (PSXL) have been recently evolving very fast from the vacuum ultraviolet to the soft x-ray region. Once seeded with high harmonics, these schemes are considered as the next generation soft x-ray light sources delivering ultrashort pulses with high temporal and spatial coherence. Here, we present a detailed experimental study of a kHz two-colour high harmonic generation performed in various gases and investigate its potential as a suitable evolution of the actual seeding sources. It turns out that this double harmonic content source is highly tuneable, controllable and delivers intense radiation (measured here with a calibrated photodiode) with only one order of magnitude difference in the photon yield from 65 to 13 nm. Then, first and foremost, injections could be achieved at wavelengths shorter than what was previously accessible in FEL and PSXL and/or additional energy could be extracted. Also, such a strong and handy seed could allow the saturation range of FEL devices to be greatly extended to shorter wavelengths and would bring higher spectral as well as intensity stabilities in this spectral zone.

Soft X-ray laser emission from W46+

Using published atomic data, the populations of the excited states 1s22s22p63s23p63d94l (l= s, p, d, and f) – 1s22s22p63s23p63d10of Ni-like W have been calculated for electron densities in the range 1020–1023 cm-3and electron temperatures in the range 0.5–1 keV. For those transitions with positive population inversion factor, the gain coefficients are determined and plotted against the electron density.

Spatial and spectral properties of the high-order harmonic emission in argon for seeding applications

We characterize and control the harmonic emission in the spectral and spatial domains in order to define in which conditions the harmonic radiation can be a high-quality seed for soft x-ray and x-ray free-electron lasers. The length of the gas cell, where harmonics are generated, was optimized and the energy per pulse was determined in absolute value with a calibrated x-ray photodiode. The beam spatial profile was measured and, in some conditions, a very collimated beam with a half-angle divergence below 1 mrad could be obtained. We also show that increasing the intensity of the fundamental laser field leads to a considerable broadening of the bandwidth of the harmonic radiation, allowing us to cover a large spectral range. This effect is due to fundamental reshaping leading to an efficient phase matching of both short- and long-trajectory contributions.

Low-threshold ablation of dielectrics irradiated by picosecond soft x-ray laser pulses

Ablation of LiF crystal by soft x-ray laser (XRL) pulses with wavelength λ=13.9 nm and duration TL=7 ps is studied experimentally and theoretically. It is found that a crater appears on a surface of LiF for XRL fluence, exceeding the ablation threshold Fa∼10.2 mJ/cm2 in one shot, or 5 mJ/cm2 in each of the three XRL shots. This is substantially below the ablation thresholds obtained with other lasers having longer pulse duration and/or longer wavelength. A mechanism of thermomechanical ablation in large bandgap dielectrics is proposed. The theory explains the low Fa via small attenuation depth, absence of light reflection, and electron heat conductivity.

Demonstration of Mo Soft X-Ray Lasers with a Grazing Incidence Pumping Scheme in the XL-II Facility

A Ni-like Mo soft x-ray laser (SXRLs) operating at 18.9nm has been demonstrated by employing a grazing incidence pumping scheme with 120mJ in the 200ps pre-pulse and 140mJ in the 200fs main pulse. The SXRL gain is estimated to be 1.5–3cm−1 when a grazing incidence angle of 14° is applied. Numerical simulations are also performed to investigate the dynamics of the ion distribution. It is found that a high intensity at 2.4 × 1014 W/cm2 of the 200 fs main pulse could heat the pre-plasma rapidly to an appropriate temperature for population inversion, and could compensate for the shortage of the total pump energy to a certain extent.

Quantum Monte Carlo study on speckle variation due to photorelaxation of ferroelectric clusters in paraelectric barium titanate

Time-dependent speckle pattern of paraelectric barium titanate observed in a soft x-ray laser pump-probe measurement is theoretically investigated as a correlated optical response to the pump and probe pulses. The scattering probability is calculated based on a model with coupled soft x-ray photon and ferroelectric phonon mode. It is found that the speckle variation is related to the relaxation dynamics of ferroelectric clusters created by the pump pulse. Additionally, critical slowing down of cluster relaxation arises on decreasing temperature toward the paraelectric-ferroelectric transition temperature. The relation between critical slowing down, local dipole fluctuation, and crystal structure is revealed by quantum Monte Carlo simulation.

Bow shocks formed by plasma collisions in laser irradiated semi-cylindrical cavities

The formation of shocks in plasmas created by short pulse laser irradiation ( λ = 800 nm, I ≈ 1 × 10 12 W cm −2) of semi-cylindrical cavities of different materials was studied combining visible and soft X-ray laser interferometry with simulations. The plasma rapidly converges near the axis to form a dense bright plasma focus. Later in time a long lasting bow shock is observed to develop outside the cavity, that is shown to arise from the collision of plasmas originating from within the cavity and the surrounding flat walls of the target. The shock is sustained for tens of nanoseconds by the continuous arrival of plasma ablated from the target walls. The plasmas created from the heavier target materials evolve more slowly, resulting in increased shock lifetimes.

Measurements of opacity and temperature of warm dense matter heated by focused soft X-ray laser irradiation

The transmission of plasma-based soft X-ray lasers through thin targets can be used to measure the target opacity. Measurements of warm dense matter transmission obtained using a focused 59 eV photon energy laser irradiation on thin targets of polyimide (C 22H 10N 2O 5) and aluminum are shown to produce simultaneous heating and probing enabling opacity and temperature measurements of warm dense matter. It is shown that the opacity of the warm dense matter considered in the experiments follows closely tabulated cold ‘room temperature’ opacities at temperatures below ∼10 eV. Transmission measurements of thin iron targets which are highly opaque to the X-ray laser radiation are also presented.

Submicrometer-resolution in situ imaging of the focus pattern of a soft x-ray laser by color center formation in LiF crystal

We demonstrate high quality, single-shot in situ imaging of the focused Ag x-ray laser (XRL) at 13.9 nm with 700 nm spatial resolution by color center formation in LiF. The flux and intensity for the color center formation in LiF are evaluated from the experimental data. Comparisons with previous reports show that the threshold x-ray flux for the color center formation in LiF for the 13.9 nm, 7 ps Ag XRL is 3 orders of magnitude less than that with the 46.9 nm, 2 ns capillary discharge Ar XRL.

Reactions of Neutral Vanadium Oxide Clusters with Methanol

Reactions of neutral vanadium oxide clusters with methanol and ethanol in a fast-flow reactor are investigated by time-of-flight mass spectrometry. Single-photon ionization through soft X-ray (46.9 nm, 26.5 eV) and vacuum ultraviolet (VUV, 118 nm, 10.5 eV) lasers is employed to detect both neutral cluster distributions and reaction products. In order to distinguish isomeric products generated in the reactions V(m)O(n) + CH(3)OH, partially deuterated methanol (CD(3)OH) is also used as a reactant in the experiments. Association products are observed for most vanadium oxide clusters in reaction with methanol. Products VOD, V(2)O(3)D, V(3)O(6)D, and V(4)O(9)D are observed for oxygen-deficient vanadium oxide clusters reacting with methanol, while oxygen-rich and the most stable clusters can extract more than one hydrogen atom (H/D) from CD(3)OH to form products VO(2)DH(0,1), V(2)O(4)DH(0,1), V(2)O(5)DH(0,1), V(3)O(7)DH(0,1), and V(4)O(10)DH(0,1). Species VO(2)(CH(3))(2), VO(3)(CH(3))(2), V(2)O(5)(CH(3))(2), V(3)O(7)(CH(3))(2), and V(3)O(8)(CH(3))(2) are identified as some of the main products generated from a dehydration reaction for V(m)O(n) + CH(3)OH. A minor reaction channel that generates VOCH(2)O (VOCD(2)O) and VO(2)CH(2)O (VO(2)CD(2)O) can also be identified. An obviously different behavior appears in the reaction V(m)O(n) + C(2)H(5)OH. The main observed products for this reaction are association products of the form V(m)O(n)C(2)H(5)OH. In order to explore the mechanism of V(m)O(n) + CH(3)OH reactions, DFT calculations are performed to study the reaction pathways of VO(2) + CH(3)OH and VO + CH(3)OH reaction systems. The calculation results are in good agreement with the experimental observations.

Observation of a plasma waveguide in a preformed plasma pumped by double-pulse laser irradiation for the efficient soft x-ray amplification

A molybdenum slab target was irradiated by double pulses of a line-focused chirped-pulse-amplification Nd:glass laser. A probe beam was injected in the plasma in the longitudinal direction, and we found that the probe beam was guided in the plasma with the plasma length of up to 4.3 mm at the time of 0.8-1.5 ns after the peak of the second pulse. Comparison with hydrodynamics code implied that the electron-density dip or flat region was formed, which was favorable for the efficient soft x-ray lasing under the coupling of the seed x-ray and the x-ray amplifier.

Measurement of1−pssoft-x-ray laser pulses from an injection-seeded plasma amplifier

We report on a pulsewidth measurement of phase-coherent soft x-ray laser pulses generated by injection seeding a solid-target plasma amplifier with high harmonic pulses. A pulse duration of $1.13\ifmmode\pm\else\textpm\fi{}0.47\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ was measured for a seeded Ne-like Ti plasma amplifier operating at $32.6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ using an ultrafast streak camera. This is the shortest pulse duration reported to date from a table-top soft x-ray laser amplifier. The result agrees with model simulations which suggest that intense femtosecond soft x-ray laser pulses could be obtained by injection seeding a tailored plasma amplifier in which the gain is confined to a high density region.

Non-thermal desorption/ablation of molecular solids induced by ultra-short soft x-ray pulses

We report the first observation of single-shot soft x-ray laser induced desorption occurring below the ablation threshold in a thin layer of poly (methyl methacrylate)--PMMA. Irradiated by the focused beam from the Free-electron LASer in Hamburg (FLASH) at 21.7 nm, the samples have been investigated by atomic-force microscope (AFM) enabling the visualization of mild surface modifications caused by the desorption. A model describing non-thermal desorption and ablation has been developed and used to analyze single-shot imprints in PMMA. An intermediate regime of materials removal has been found, confirming model predictions. We also report below-threshold multiple-shot desorption of PMMA induced by high-order harmonics (HOH) at 32 nm. Short-time exposure imprints provide sufficient information about transverse beam profile in HOH's tight focus whereas long-time exposed PMMA exhibits radiation-initiated surface ardening making the beam profile measurement infeasible.

Phase-Coherent Injection-Seeded Soft X-ray Lasers at Wavelengths Down to 132 nm

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Y. Wang, F. Pedaci, M. Berrill, D. Alessi, E. Granados, B.M. Luther, and J. J. Rocca, "Phase-Coherent Injection-Seeded Soft X-ray Lasers at Wavelengths Down to 13.2 nm," Optics & Photonics News 19(12), 29-29 (2008) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

DYNAMICS OF FERROELECTRIC NANO CLUSTER IN BaTio3 OBSERVED AS A REAL TIME CORRELATION BETWEEN TWO SOFT X-RAY LASER PULSES

We carry out a theoretical investigation to clarify the dynamic property of photo-created nano-sized ferroelectric cluster observed in the paraelectric BaTiO3 as a real time correlation of speckle pattern between two soft X-ray laser pulses, at just above the paraelectric-ferroelectric phase transition temperature. Based on a model with coupled soft X-ray photon and ferroelectric phonon mode, we study the time-dependence of scattering probability by using a perturbative expansion approach. The cluster-associated phonon softening as well as central peak effects are well-reproduced in the phonon spectral function via quantum Monte Carlo simulation. Besides, it is found that the time-dependence of speckle correlation is determined by the relaxation dynamics of ferroelectric clusters. Near the transition point, cluster excitation is stable, leading to a long relaxation time, while at high temperature, cluster structure is subject to the thermal fluctuation, ending up with a short relaxation time.

Capillary discharge soft X-ray lasing in Ne-like Ar pumped by low main current pulses

Under the condition of the low main current pulse, the capillary discharge soft X-ray laser is obtained. The laser energy of the same discharge current amplitude at different Ar pressures and of different current amplitudes at the same Ar pressure are compared, respectively. At different Ar pressures, the amplitude of the main current pulse evidently impacts the soft X ray, especially at a pressure higher than 30 Pa. In order to obtain the laser output at a high Ar pressure, the amplitude should be increased. However, at the same Ar pressure, it might have an optimum current, in which case the laser spike is the highest and the most stationary. The laser achieving time at different amplitudes is also discussed. As far as we know, this is the first time the influence of the amplitude of the main current pulse has been analyzed.