We investigate the amplification of mid-infrared nanosecond laser pulses in a single-mode Er-doped fluoride fibre amplifier. The seed laser pulses in the wavelength range around 2790 nm are generated in a wavelength-tuneable, PPLN-based OPO, with sub-10 ns pulse durations and pulse energies of few 100 nJ at a repetition rate of 10 kHz. The single-stage fibre amplifier consists of a double-clad, single-mode Er-doped fluoride fibre with a doping concentration of 70000 ppm, pumped at 980 nm in counter-propagation to the laser signal. The sub-10 ns laser pulses are amplified to pulse energies above 35 µJ, resulting in gain values of more than 20 dB and peak powers above 5 kW. The gain bandwidth and wavelength range of the fibre amplifier are investigated at different gain values and wavelength tuning is demonstrated over the range from 2711 nm to 2818 nm.
The lifetime and the efficiency of EUV source collector optics will have direct impact on the cost effectiveness of
the EUV lithography semiconductor production. Therefore the collector optics was identified as a critical issue
in EUVL. To continually improve and optimize the source collector optics precise measurements of the optics
characteristics are required as well as life time studies.
Adequate measuring equipment must be designed to perform these measurements on-site, at-wavelength and
under realistic conditions. Moreover, the measurement accuracy must be sufficient to allow the detection of small
changes in reflectivity and homogeneity of the EUV source collector optics. This makes it possible to predict
the lifetime of an EUV source collector operated with a high power EUV source after a fraction of the specified
pulse number, e.g. after a couple of hours.
A reflectometer for the investigation of full EUV source collectors was developed, designed and set up. As an
EUV source a commercial microfocus EUV tube was used. This source is particularly suitable for application in
metrology, as it is very stable in its output parameters (namely power, spectrum, spot size, spot position), and
it does not emit debris.
The radiation cone emitted by the EUV source is tailored with a Schwarzschild objective to the spectral and
geometrical requirements of the Wolter-shell EUV source collector optics
At the time of this contribution the measurement system presented here is in operation since 18 months,
and a large number of collector measurements was performed. It is used for the quality control of factory-new
EUV source collectors as well as for repeated measurements within the context of lifetime tests. With this
device the efficiency of debris filters, which prevent the EUV source collector optics from contamination, could
be determined and improved.
The concept of the device and the implementation together with measurement results are described.
The detection of damages at optics for the extreme ultraviolett (EUV) requires precise tools for at-wavelength-metrology.
Excellent stability of the probe radiation is a precondition for precise measurements. As an EUV-source
we use an electron-based microfocus EUV-tube. This EUV-source is debris-free, and it provides a output
of up to 300&mgr;W at 13.5 nm. The metrology setup benefits from the very good long-time stability and spatial
stability of this tube. Optical samples were characterized in reflectivity and transmission. Optical defects of
EUV-optics were analyzed at-wavelength. The incidence angle of the EUV-radiation was varied from grazing
incidence to nearly normal incidence. Our reflectivity measurements were compared with a calibrated synchrotron
measurement at the German national metrology institute (PTB). The absolute accuracy of the reflectivity
measurement was found to be better than 3% for any incidence angle. The reproducibility of the measurement
was found to be better than 0.5%. Investigations are performed to further improve the reproducibility and
absolute accuracy. The metrology setup is flexible, thus it can be fit to different types of measurement for
different applications. The concept of the metrology setup is discussed and recent results are presented. The
devices can be purchased from the Laser Zentrum Hannover e.V.
Developers and users of EUV-optics need precise tools for the characterization of their products. Often a
measurement accuracy of 0.1% or better is desired to detect and study slow-acting aging effect or degradation by
organic contaminants. To achieve a measurement accuracy of 0.1% an EUV-source is required which provides an
excellent long-time stability, namely power stability, spatial stability and spectral stability. Naturally, it should
be free of debris. An EUV-source particularly suitable for this task is an advanced electron-based EUV-tube.
This EUV source provides an output of up to 300 μW at 13.5 nm. Reflectometers benefit from the excellent long-time stability of this tool. We design and set up different
reflectometers using EUV-tubes for the precise characterisation of EUV-optics, such as debris samples, filters,
multilayer mirrors, grazing incidence optics, collectors and masks. Reflectivity measurements from grazing
incidence to near normal incidence as well as transmission studies were realised at a precision of down to 0.1%.
The reflectometers are computer-controlled and allow varying and scanning all important parameters online.
The concepts of a sample reflectometer is discussed and results are presented. The devices can be purchased
from the Laser Zentrum Hannover e.V.
A novel compact EUV-reflectometer recently developed is presented. The designconcept relies on a flexible approach, thus this reflectometer can be set up as a compact table-top tool for a specified task as well as a full all-purpose reflectometer. As an EUV-source an electron-based microfocus EUV-tube is used. This EUV source is debris-free and provides a typical output of 30μW at 13.5 nm. The reflectometer benefits from the very good long-time stability and spatial stability of this tube. Reflectivity measurements from grazing incidence to nearly normal incidence as well as transmission studies can be realized in the same setup at a typical precision of measurements of 0.5%. A precise computer-controlled positioning unit allows to vary and scan all important parameters online, allowing for example complex surface scans and angle variations. The concept of the reflectometer is discussed and recent results are presented. This device can be purchased from the Laser Zentrum Hannover e.V.
Two applications of an electron-based EUV-tube are presented: the set up of a grazing incidence EUV reflectometer with high reproducibility and accuracy, and our works towards the realization and application of a Schwarzschild objective for EUV imaging. Both applications benefit form the use of the table-top EUV-source, which is debris-free, long-term stable, and compact.
Novel ultrashort EUV and hard x-ray sources have been developed
and characterized. Radiation pulses were produced by combining
femtosecond laser technology with a specially designed EUV and
x-ray diode. At first, ultrashort electron pulses are generated by
photoemission from a photocathode. Then, these electron pulses are
accelerated over a short distance towards an high-Z anode. EUV
radiation is produced with a silicon anode via L-shell emission,
hard-x-rays are generated with a copper anode.
Measurements of the pulse duration were performed for hard-x-rays
using an advanced streak camera. For high electron pulse charges
(several pC), hard-x-ray pulse durations of less than 10 ps were
observed.
In this contribution we present the concept of our EUV and hard
x-ray source. A wide range of experimental parameters is
investigated: Different cathode and anode materials were tested,
femtosecond laser systems with different parameters are used, the
dependence of the radiation pulse length on experimental
parameters e.g. laser energy and acceleration voltage is studied.
Recently, an electron-based ultrashort hard-x-ray source has been developed at the Laser Zentrum Hannover e.V. In this source x-ray pulses are produced by combining femtosecond laser technology with a specially designed x-ray diode. At first, ultrashort electron pulses are generated by photoemission from a photocathode. Then, these electron pulses are accelerated over a short distance towards a high-Z anode. Hard-x-rays are produced via Bremsstrahlung and characteristic line emission. Now detailed measurements of the hard-x-ray pulse duration have been performed using an advanced streak camera. The streak camera has a sub-picosecond time resolution in the keV range. With this camera hard-x-ray pulse durations of less than 5 ps were observed for electron pulse charges of the order of several pC. In this contribution we present our results on the x-ray pulse duration measurements and their dependence on different experimental parameters. A comparison with theoretical simulations is given.
Recently, an electron-based ultrashort hard-x-ray source has been developed at the Laser Zentrum Hannover e.V. In this source x-ray pulses are produced by combining femtosecond laser technology with a specially designed x-ray diode. At first, ultrashort electron pulses are generated by photoemission from a photocathode. Then, these electron pulses are accelerated over a short distance towards a high-Z anode. Hard-x-rays are produced via Bremsstrahlung and characteristic line emission.
Now detailed measurements of the hard-x-ray pulse duration have been performed using an advanced streak camera. The streak camera has a sub-picosecond time resolution in the keV range. With this camera hard-x-ray pulse durations of less than 10 ps were observed for electron pulse charges of the order of several pC.
In this contribution we present our results on the x-ray pulse duration measurements and their dependence on different experimental parameters. A comparison with theoretical simulations is given.
Investigations of resonant spectral structures of four wave mixing (FWM) in molecular sodium are presented. For a double- (Lambda) configuration with strong-weak-strong-weak fields, split components in FWM spectra induced by the strong pump fields are observed. It is shown, that the split components merge into a single peak for a certain ratio of the strong field intensities. A strong correlation between the level splitting effect and saturation behavior of the FWM-signal is experimentally demonstrated.
Interactive numerical simulator, based on MATLAB/SIMULINK platform, for virtual experimentation and optimization of frequency tunable optically pumped dimer laser has been created. Nonperturbative theory considering features of quantum coherence and interference effects at Doppler broadened transitions under two strong driving fields accounting for collisions and other kinetic processes in vapor-gas mixture as well as for propagation effects in optically thick medium is developed. The results are in good agreement with real experiments.
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