C. D. Macchietto

Generation of millijoule-level soft-x-ray laser pulses at a 4-Hz repetition rate in a highly saturated tabletop capillary discharge amplifier

Laser pulses with energies of as much as 1 mJ were generated at a wavelength of 46.9 nm by single-pass amplification in a 34.5 cm-long Ne-like Ar capillary discharge plasma. The large gain–length product of this plasma column allows for soft-x-ray amplification in a highly saturated regime, resulting in efficient energy extraction. Average laser output pulse energy of 0.88 mJ and peak power of 0.6 MW were obtained at a repetition rate of 4 Hz. With an estimated peak spectral brightness of ?1×1023 photons/(s mm2 mrad2 0.01% bandwidth) this tabletop laser is one of the brightest soft-x-ray sources to date.

Lasing in Ne-like S and other new developments in capillary discharge ultrashort wavelength lasers

We report our most recent progress in the development of capillary discharge soft x-ray lasers. This includes the first observation of discharge-pumped ultrashort wavelength lasing in a material that is solid at room temperature (S), and preliminary results of discharges in Ca. Excitation by a capillary discharge of S vapor generated by discharge ablation of a solid target resulted in amplification in Ne-like S at 60.8 nm with a gain-length product of 7.5. Overheating of the electron temperature respect to steady-state ionization conditions and transient population effects significantly increased the gain above the steady state-value. The results of two-dimensional near-field and far-field imaging of a saturated table-top Ne-like Ar laser and the measurement of its spatial coherence as a function of amplifier length are also reported and compared with model calculations. The generation of a capillary discharge plasma waveguide is to be used in combination with ultrashort pulse laser excitation for the generation of a new kind of efficient collisional soft x- ray laser is discussed.

Demonstration of a 1 mW average power, 7 Hz table-top soft X-ray laser

Summary form only given. Important motivations for the development of high average power table-top sources of coherent soft X-ray radiation can be found in applications belonging to several disciplines of science and technology. To date, the leading sources of high average power coherent soft X-ray radiation have been undulators in modern storage rings, so-called third generation synchrotrons. High average power beams of soft X-ray coherent radiation can in principle also be generated with much more compact devices using either nonlinear optical techniques for frequency up-conversion of optical laser radiation, or the direct amplification of spontaneous emission in a plasma (an X-ray laser). Soft X-ray lasers have the advantage of a high energy per pulse and therefore the potential to produce very high average power. Soft X-ray lasers pumped by large optical lasers of the type used in fusion research have generated output pulse energies of up to several mJ but are limited to a repetition frequency of only a few pulses per hour at best. We report a 2 to 3 orders of magnitude increase in the average power of table-top soft X-ray lasers.

Plasma probing with a table-top soft X-ray laser

Summary form only given. Due to their short wavelength, high brightness, and good spatial coherence soft X-ray lasers are excellent sources for the diagnostics of dense plasmas. We report the demonstration of plasma imaging and interferometry using a very compact table-top soft X-ray laser. A capillary discharge pumped 46.9 nm laser was used to obtain a sequence of high resolution shadowgrams of the plasma of a microcapillary discharge (380 /spl mu/m diameter, 8 mm long evacuated channel in polyacetal excited by a /spl sim/1.5 kA peak amplitude current pulse of 155 ns duration). The plasma was illuminated on-axis with the soft X-ray laser, and was imaged with 24/spl times/ magnification into an MCP/CCD detector using a 60 cm radius of curvature concave mirror coated with an iridium film. The plasma is observed to rapidly evolve from a nonuniform plasma into a remarkably uniform plasma column with minimum density on axis. These measured plasma characteristics confirm the excellent properties of these discharges as waveguides for laser radiation.

Applications of high-repetition-rate tabletop soft x-ray laser: laser ablation with a focused beam and reflectometry of materials

We report the first applications of a soft x-ray laser in materials processing and diagnostics. We have focused a Ne- like Ar capillary discharge laser ((lambda) equals 46.9 nm) operating at a repetition rate of 1 Hz using a spherical Si/Sc multilayer coated mirror. The energy density obtained significantly exceeded the threshold for the ablation of metals. Ablation of stainless steel, aluminum and brass samples is reported. The laser ablation patterns on brass were used in combination with ray tracing computations to characterize the focused beam. The radiation intensity within the 2 micrometers central region of the focal spot is estimated to be is congruent to 1011 W/cm2, with a corresponding energy density of is congruent to 100J/cm2. In a separate experiment we have conducted laser reflectometry measurements for a number of different samples. These measurements resulted in the characterization of the reflectivity of Si/Sc multilayer mirrors as a function of angle and in the determination of optical constants for Si, GaP, InP, GaAs, GaAsP and Ir. The measurements of InP and GaAsP resulted in the first experimental values to our knowledge for these materials at this wavelength.

Generation of a high-average-power and millijoule-level pulses with a tabletop soft x-ray laser

Millijoule-level laser pulses and multi-milliwatt average power have been obtained for the first time from a table-top soft x-ray laser. Laser pulses with energy up to 1 mJ and an average power of approximately equals 3.5 mW were generated at a wavelength of 46.9 nm by single pass amplification in a 34.5 cm long Ne-like Ar capillary discharge plasma. The large gain-length product of this plasma column allows for soft x-ray amplification in a highly saturated regime, resulting in very efficient energy extraction. An average laser output pulse energy of 0.88 mJ and peak power of 0.6 MW were obtained at a repetition rate of 4 Hz. The spatially coherent average power emitted by this 26.5 eV laser is comparable to that generated at this photon energy in a similar bandwidth ((Delta) (lambda) /(lambda) equals 10-4) by a third-generation synchrotron beam-line, which its peak spatially coherent power exceeds that of the undulator by several orders of magnitude. With an estimated peak spectral brightness of approximately equals 1 X 1023 photons/(s mm2 mrad2 0.01% bandwidth) this table-top laser is one of the brightest soft x-ray sources to date.

Two-dimensional near-field and far-field imaging of a Ne-like Ar capillary discharge table-top soft X-ray laser

We have performed systematic measurements and numerical modeling of the divergence and exit beam size of a 46.9 nm Ne-like Ar capillary discharge pumped soft-x-ray amplifier. Two-dimensional near-field and far-field measurements were obtained over a wide range of discharge parameters. The spot size and divergence of the laser beam were observed to increase significantly with decreasing discharge pressure. Simultaneously, the beam intensity distribution changed from a single peak pattern to an annular profile. These effects are shown to be the result of increased refraction of the soft-x-ray beam, caused by larger density gradients in the plasma columns of the lower pressure discharges. The spatial images are nearly cylindrically symmetric, and have less structure than those reported in the literature for laser-driven soft-x-ray lasers. Beam profiles synthesized by model calculations are found to be in good agreement with the recorded images. The obtained images in combination with the model computations clarify the origin of the different beam patterns that are observed in capillary discharge soft-x-ray laser experiments. @S1050-2947 ~98!09208-7#