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Extremely fast processes happening on sub picosecond time scale can be captured by the well-known pump-probe scheme using ultrashort x-ray pulses as shutter. XFELs and femtosecond slicing beam lines on synchrotrons together-with ultra-short laser driven plasma x-ray sources (LPXs) as an attractive supplement offer exceptional parameters to unleash ultra-fast phenomenon. As pump-probe techniques based on the compact LPXs attract attention being jitter free, more precise knowledge of their emission duration, determining the measurement temporal resolution, became indispensable. We report here, for the first time, x-ray pulse duration from LPX using NIR pump x-ray probe cross-correlation method. The underlying mechanism is ultrafast relaxation of femtosecond laser-induced non-thermal electrons generated on the surface of transition metals. The emission duration of x-ray pulse is estimated by the evolution of transmission (110 ±6 fs) and fluorescence signals (129 ± 19 fs) and found in good agreement with the theoretical prediction of ≤100 fs for LPXs.

It is commonly accepted that X-ray lasers, as the devices based on amplified spontaneous emission (ASE), did not show any specific polarization in the output beam. The theoretical analysis within the uniform (single-mode) approximation suggested that the output radiation should show some defined polarization feature, but randomly changing from shot-to-shot. This hypothesis has been verified by experiment using traditional double-pulse scheme of transient inversion. Membrane beam-splitter was used as a polarization selector. It was found that the output radiation has a significant component of p-polarisation in each shot. To explain the effect and place it in the line with available, but scarce data, propagation and kinetic effects in the non-uniform plasma have been analysed.

In microscopy, where the theoretical resolution limit depends on the wavelength of the probing light, radiation in the soft X-ray regime can be used to analyze samples that cannot be resolved with visible light microscopes. In the case of soft X-ray microscopy in the water-window, the energy range of the radiation lies between the absorption edges of carbon (at 284 eV, 4.36 nm) and oxygen (543 eV, 2.34 nm). As a result, carbon-based structures, such as biological samples, posses a strong absorption, whereas e.g. water is more transparent to this radiation. Microscopy in the water-window, therefore, allows the structural investigation of aqueous samples with resolutions of a few tens of nanometers and a penetration depth of up to 10μm. The development of highly brilliant laser-produced plasma-sources has enabled the transfer of Xray microscopy, that was formerly bound to synchrotron sources, to the laboratory, which opens the access of this method to a broader scientific community. The Laboratory Transmission X-ray Microscope at the Berlin Laboratory for innovative X-ray technologies (BLiX) runs with a laser produced nitrogen plasma that emits radiation in the soft X-ray regime. The mentioned high penetration depth can be exploited to analyze biological samples in their natural state and with several projection angles. The obtained tomogram is the key to a more precise and global analysis of samples originating from various fields of life science.

X-ray microscopy in the water window has become a valuable imaging tool for a wide field of applications with a resolution in the nanometer regime. The emergence and the development of laboratory based transmission X-ray microscopes (LTXM) can be of great benefit to users, since LTXM provides access to a method previously limited to synchrotron facilities only. In recent years, measuring times in the laboratory have been reduced to the point, where tomography of aqueous cryofixated samples has become feasible. We report on a laboratory full-field transmission X-ray microscope based on a laser induced plasma source located at the Berlin Laboratory for innovative X-ray Technologies. A short introduction on full-field X-ray microscopy in the water window is given. We demonstrate that, with a thin disk laser-system (TDL), which provides an average power of ~15 W a spatial resolution of Δx = 41 nm ± 3 nm (half-pitch) is feasible. An image of a diatom recorded at 15 W average laser power with a magnification of 1125x captured in 5 min is presented.

Using the x-ray lasers as amplifiers of ultrashort x-ray pulses has been investigated as a scheme for ultimate light sources. For successful implementation, the characteristics of the scheme should be taken into account in designing the amplifiers. In this paper, the basic physics and characteristics of the scheme were analyzed by using the Maxwell-Bloch equations incorporating time-dependent gain, random spontaneous emission, atomic level degeneracy, and radiation polarization. The variation of the pulse parameters such as energy, bandwidth, pulsewidth, and polarization were explained based on a simple mechanism of pulse growth and also compared to that in the conventional x-ray lasers. These results should be the basic information for a practical implementation of the scheme.

High-harmonic-seeded x-ray laser became an important issue in x-ray laser development due to the possibility to obtain a highly coherent and polarized soft x-ray source. We performed theoretical investigations into amplification of high harmonic pulses in an x-ray lasing medium by using a model based on Maxwell-Bloch equations. From the theoretical works, we analyze characteristics of energy extraction and temporal profile of output pulse. In addition, preliminary experimental results and ongoing experiments related the harmonic-seeded x-ray lasers are reported.

Technological reasons stimulated enormous interest in the spectral range between 10 nm and 15 nm. One of the most important, apart from the potential to be applied in the microlithography, was the existence of the high-efficiency, spectrally highly selective (narrow-band) reflective multi-layer (ML) optics in this spectral range. Applying these optics to plasma based XUV (extreme ultra violett) sources the debris from the plasma is a serious problem. For transmissive multi-layer optics we have additionally the low figures of merit. For example, the best beam splitters have an efficiency of about 30% (energy in both parts of the splitted beam). This type of element is crucial for efficient single-shot interferometry being the main application using table-top soft x-ray lasers. We applied capillary optical elements, to our knowledge for the first time, to XUV radiation at 13.9 nm. These optical elements help overcome the limits discussed above or at least remarkably reduce the existing difficulties. A capillary beam splitter and a focussing capillary were applied to an incoherent XUV radiation source. For the beam splitter we measured a throughput of about 80%. With the focussing capillary we obtained a spot size of 27 μm (FWHM) with a gain (intensity in the focal spot compared to the intensity behind a pinhole of the focal spot size) of 600. Advantages and disadvantages of these optics in the discussed spectral range are analyzed.

With the development of EUV lithography there is an increasing need for high-accuracy at-wavelength metrology. In particular, there is an urgent need for metrology at optical components like mirrors or masks close to the production line. Sources for metrology have to fit different demands on EUV power and spectral shape than sources for steppers systems. We present the results of the radiometric characterization of a laser produced plasma (LPP)-source, newly developed at Max-Born-Institute Berlin for use in an EUV reflectometer. It is operated with a high-power pointing-stabilized laser beam (energy per pulse up to 700 mJ, 10 ns pulse duration, < ± 25 μrad pointing stability) at 532 nm which is focussed on a rotating Au target cylinder. The incident angle of the laser beam is set to 63°, the detecting angle 55° to the target normal. The source has been characterized regarding spectral photon flux, source size and source point stability. Two independently calibrated instruments, an imaging spectrometer and a double multilayer tool for in-band power measurements were used to obtain highly reliable quantitative values for the EUV emission of the Au-LPP source. Both instruments were calibrated by Physikalisch-Technische Bundesanstalt in its radiometry laboratory at the electron storage ring BESSY II. We obtained a source size of 30 μm by 50 μm (2s horizontal by vertical) and a stability of better than 2s=5 μm horizontally and 2s=9 μm vertically. A spectral photon flux of 1*10e14 /(s sr 0.1 nm) at 13.4 nm at a laser pulse energy of 630 mJ is obtained. The shot-to-shot stability of the source is about 5% (1s) for laser pulse energies above 200 mJ. For pulse energies between 200 mJ and 700 mJ, there is a linear relation between laser pulse energy and EUV output. The spectrum shows a flat continuos emission in the EUV spectral range, which is important for wavelength scanning reflectometry. High stability in total flux and spectral shape of the plasma emission as well as low debris was only obtained using a new target position for each shot. There is also a trade off between source size and EUV power. For a slightly defocused laser, an increase in EUV power up to a factor of two is obtained, while the source size also increases by about a factor of two. It is shown that an Au-LPP source provides spectrally flat reproducible emission with sufficient power at low debris conditions for the operation of a laboratory based EUV reflectometer.

The quality assurance for production of optical components for EUV lithography strongly requires at-wavelength metrology. Presently, at-wavelength characterizations of mirrors and masks are done using the synchrotron radiation of electron storage rings, e.g. BESSY II. For the production process of EUV optics, however, the immediate access to metrology tools is necessary and availability of laboratory devices is mandatory. Within the last years a stand alone laboratory EUV reflectometer for large samples has been developed It consists of a laser produced plasma (LLP) radiation source, a monochromator and a large goniometer systme. The manipulation system of the reflectometer can handle samples with diameters of up to 500 mm, thicknesses of up to 200 mm and weights of up to 30 kg. The wavelength can be varied from 10 nm to 16 nm. The spot size on the sample surface is about 2mm. The angle of incidence can be varied from 3° to 60°. In this paper, we describe the laboratory reflectometer in detail and discuss the achieved performance. First measurements of 4 inch mirrors are presented and discussed in comparison to the results obtained at the PTB soft x-ray radiometry beamline at BESSY II.

In this contribution we describe a laser plasma source for Extreme Ultraviolet Lithography (EUVL) based on a Xe-cluster target. Although Xe-clusters as target systems for EUVL are known for some time, no attempts have been made for a systematic study of the influence of the laser parameters on the EUV-emission at a well defined Xe-aggregation. The MBI burst mode laser used offers some unique features: Within one burst (duration 800 μs) the repetition rate of single laser pulses can be adjusted between 30 and 1000 kHz. The average power per burst is about 5 kW at the maximum energy of 4 J/burst. The pulse duration of a single pulse can be adjusted from the ps- to ns-range. We have examined the EUV-emission from the Xe-cluster target within one burst of the laser as a function of single pulse intensity and repetition rate. Based on the measured EUV-spectra the conversion efficiency at 13.4 nm wavelength in dependence on pulse duration in the range from 30 ps to 3 ns were estimated.

Large Xe-clusters have been excited with 50 fs and 2 ps pulses from a Ti:Sa multi - TW laser at 800 nm wavelength. Additionally a 10 ns Nd:YAG laser at 1064 nm wavelength was used to heat Xe-cluster/gas and a liquid Xe-spray target. Absolute yield measurements of EUV-emission in a wavelength range between 10 nm and 15 nm in combination with target variations were carried out. The ps-laser pulse has resulted in about 30 percent enhanced and spatially more uniform EUV-emission compared to fs-laser excitation. Similar emission has been obtained with ns-pulse exposure of different target modifications which also act back to the EUV-source size. Absolute emission efficiencies at 13.4 nm of up to 0.8 percent in 2pi sr and 2.2 percent bandwidth were measured.

In this article we describe a laser plasma source for Extreme Ultraviolet Lithography (EUVL) based on a liquid water jet target. Although jet targets are known for some time now, no attempts have been made to prove the functionality of the target under conditions similar to an EUVL production-line facility, that means illumination with high average power laser systems (in the multi-kW regime) at repetition rates in the kHz region. Such systems are currently under development. We used the MBI-burst laser to simulate these extreme illumination conditions. We examined the hydrodynamic stability of the target as a function of the laser repetition rate at different average laser powers (0.6kW and 5kW per burst). Additionally, the dependence of the conversion efficiency on pulse duration in the range from 30ps to 3ns was investigated. From our results one can conclude parameters for future design of driver lasers for EUVL systems.