We have recently demonstrated high repetition rate tabletop lasers operating at wavelengths as short as 10.9 nm
based on collisional transient excitation of ions in plasmas created by laser heating of solid targets. As a further step in
the development of these lasers into very high brightness and fully coherent soft x-ray sources, we have demonstrated
injection seeding of the amplifiers with high harmonic seed pulses. We report results of an experiment in which a 32.6
nm Ne-like Ti amplifier was used to amplify a seed pulse from the 25th harmonic of Ti:Sapphire into the gain saturation
regime. Simultaneous amplification of the 27th harmonic at 30.1 nm was also observed. The seeded soft x-ray laser beam
was measured to approach full spatial coherence. We have demonstrated that this scheme is scalable to shorter
wavelengths and that is capable of producing extremely bright soft x-ray laser pulse with essentially full coherence.
Hafnium oxide (HfO2) is undoubtedly one of the most desirable high-index optical coatings for high power
laser applications. One of the key goals in the fabrication of oxide films with high Laser Induced Damage
Threshold (LIDT) is to minimize the number of film imperfections, in particular stoichiometric defects. For
HfO2 films deposited by ion beam (reactive) sputtering (IBS) of a hafnium metal target, stoichiometry is
controlled by the injection of molecular oxygen, either close to the substrate or mixed with the sputtering
gas or some other combination. Good stoichiometry is important to reduce the density of unoxidized
particles buried in the coatings, which affect the LIDT. This work evaluates the potential advantages of
using pre-activation of oxygen in the IBS of HfO2, with special emphasis on its impact on LIDT and film
stress. For the experiments, oxygen was activated by an independent plasma source and then introduced
into a commercial IBS chamber. The optical properties of the films were characterized using
spectrophotometry and ellipsometry. Their structural quality and composition were determined from x-ray
diffraction and x-ray photoelectron emission spectroscopy. The stress was determined from interferometer
measurements. For optimized conditions, 2.5 J/cm2 LIDT was measured on HfO2 films at λ=800 nm with 1
ps and 25 mJ pulses from a chirped amplification Ti:Sapphire laser. In the range of oxygen variations under
consideration the effects on LIDT are shown to be minimal.
We have acquired images with sub-38 nm spatial resolution using a tabletop extreme ultraviolet (EUV) imaging system operating at a wavelength of 13.2 nm, which is within the bandwidth of Mo/Si lithography mirrors This zone plate-based, full-field microscope has the power to render images in only several seconds with up to a 10,000 μm2 field of view. The ability to acquire such high-resolution images using a compact EUV plasma laser source opens many possibilities for nanotechnology, including in-house actinic inspection of EUV lithography mask blanks.
We have demonstrated gain-saturated operation of high repetition rate table-top soft x-ray lasers producing microwatt average powers at wavelengths ranging from 13.2 to 32.6 nm in transitions of Ni-like and Ne-like ions. Lasing was also observed for shorter wavelength transitions of the 4d1S0→4p1P1 Ni-like isoelectronic sequence, with amplification approaching gain saturation in the 11.9 nm line of Ni-like Sn and progressively reduced gain for wavelengths as low as 10.9 nm in Ni-like Te. The results were obtained heating a pre-created plasma with a picosecond optical laser pulse with an energy of only 1 J impinging at optimized grazing angles of incidence for maximum pump energy deposition efficiency. This pumping geometry takes advantage of the refraction of the pump beam to increase the energy deposition efficiency of the pump beam into the gain region, making it possible to operate soft x-ray lasers in this wavelength range at significantly increased repetition rates. The results demonstrate the feasibility of producing high average powers of coherent radiation in the 100 eV spectral region for applications using a table-top source.
We report high resolution imaging results obtained utilizing small-scale extreme ultraviolet laser sources. A compact capillary-discharge pumped Ne-like Ar laser emitting at a wavelength of 46.9 nm was used to demonstrate imaging with nanometer-scale resolution in transmission and reflection modes. We exploited the large photon fluence of this short wavelength laser to obtain high-resolution images with exposure times as short as 1-10 seconds. Images with a spatial resolution better than 140 nm were obtained using the combination of a Sc/Si multilayer coated Schwarzschild condenser and free-standing objective zone plate. Preliminary results of imaging with a 13.9 nm extreme ultraviolet laser light are also discussed.
In this work we report on the damage threshold of ion beam deposited oxide films designed for high peak power short pulse laser systems. Single layers of ZrO2, SiO2, Al2O3, TiO2, and Ta2O5 and multilayers of Al2O
3/TiO2, SiO2/Ta2O5, and SiO2/ZrO2 were grown on polished borosilicate glass substrates using ion beam sputter deposition. Deposition conditions were optimized to yield fully oxidized films as determined from x-ray photoelectron spectroscopy (XPS). Damage threshold testing was performed using an amplified Ti:Sapphire laser producing a train of 120 picosecond pulses at a wavelength of 800 nm. The laser output was focused with a lens to generate fluences ranging from 0.1 to 24 J/cm2. The highest damage threshold of 15.4 J/cm2 was measured for a single layer film of SiO2. The damage threshold of high reflectance and anti-reflection multilayer coatings fabricated for 800 nm applications was evaluated using the same procedure as for the single layer films. Highest damage thresholds of 2.5 and 3.5 J/cm2 were measured for a 6-pair ZrO2/SiO2 high reflectance coating and a 5 layer anti-reflection coating of the same materials.
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