The objective of this project funded by the German BMBF was to show that security relevant substances can be detected
in complex matrices at low concentrations using single photon ionization ion trap mass spectrometry (SPI-ITMS). The
advantage of such a soft ionization technique is a reduction of unwanted fragment ions in mass spectra allowing
identification of signals from complex matrices and enabling MS/MS capability. The MS/MS studies permit low false-positive
and false-negative rates. Additionally, the accumulation of the ions in the ion trap decreases the detection limit.
To obtain low detection limits the ionization potentials (IPs) of the relevant substances have to be below the IPs of the
bulk matrix components. That enables the utilization of a photon energy unaffecting the matrix components resulting in
increased sensitivity due to essentially non-existent background signals. As literature values for many ionization
potentials are unavailable, IPs of several security relevant substances were determined using monochromatized
synchrotron radiation from BESSY, Germany. All analyzed substances exhibited IPs significantly below the IPs of
common matrix molecules such as water, nitrogen and oxygen. First measurements with a pre-demonstrator show that it
is possible to shield matrix substances using a well chosen photon energy for soft ionization.
During the recent years extensive development of laser tube and pulsed power module in compact excimer laser systems has been done. Aim of all development was the enlargement of lifetimes and reduction of cost of ownership. Therefore, new laser chamber designs have been developed, tested and optimized. Especially the discharge unit was new designed. Additionally, a new generation of pulsed power modules has been developed. By replacing the solid state switch element by a faster device the efficiency of the module was enlarged and the matching to the discharge was improved. Due to the reduction of electrode erosion the lifetime of the laser chamber is enlarged. These new components were integrated in a new experimental laser system and tested to verify the estimated prolongation of laser tube lifetime. In long-term tests of this new laser tube connected with the newest generation of the pulsed power module at 193 nm wavelength, 8 mJ constant energy and 1 kHz repetition rate have been done. A laser chamber lifetime of more than 5 billion pulses was achieved during the first long-term tests. Implementing further improvement the lifetime of the laser chamber could enhanced to more than 6 billion pulses under these test conditions. The lifetime of the pulsed power module exceeds this high lifetime, no degradation of components in the pulsed power module was found.
American and European statistics have shown that 1-2 per cent of the human population is affected by the skin disease psoriasis. Recent research reports promising treatment results when irradiating skin areas affected by psoriasis with high powered excimer lasers with a wavelength of 308 nm. In order to apply the necessary high energy dose without hurting healthy parts of the skin new approaches regarding the system technology must be considered. The aim of the current research project is the development of a sensor-based, automated laser treatment system for psoriasis. In this paper we present the algorithms used to cope with the diffculties of irradiating irregularly shaped areas on curved surfaces with a predefined energy level using a pulsed laser. Patients prefer the treatment to take as little time as possible. This also helps to reduce costs. Thus the distribution of laser pulses on the surface to achieve the given energy level on every point of the surface has to be calculated within a limited time frame. The remainder of the paper will describe in detail an efficient method to plan and optimize the laser pulse distribution. Towards the end, some first results will be presented.
Compact excimer laser systems were developed for industrial applications especially for micro-machining applications. Therefore all components and modules are designed for long-term operation and long maintenance intervals. By using new designs and technologies the performance of these laser systems could be improved in comparison to the well-known compact excimer lasers. The result of the first tests of the prototype are presented. The laser tube lifetime could be more than doubled in comparison to the former laser design. Additionally maximum repetition rates of 2kHz were demonstrated for the prototype 193 nm laser systems. A maximum pulse energy of about 40 mJ was measured. The pulse-to-pulse stability was reduced below 1% (one sigma) in the working area of the laser. The state-of-the-art of compact excimer lasers will be presented and outlook for the future will be given.
The compact class of excimer lasers has been developed originally for the ophthalmology (vision correction). These table-top excimer lasers have output energies below 50 mJ, typically up to 20 mJ depending on the emitted wavelength. Due to the continual development in the recent years these laser systems are now available with lifetimes of some billion pulses and repetition rates up to two kHz. All commercially used wavelengths between 351 nm and 157 nm are realized in this laser class. For generating the high voltage pulses to initiate the laser emission a solid state pulsed power module (SSPPM) is installed. This module has a nearly unlimited lifetime. Further work is done to enlarge the life time of all sub-modules especially of the laser tube and the resonator optics. These laser systems can be applied as light sources in metrology and inspection systems especially for the lithography. The state of the art of compact excimer lasers will be presented and especially the results at 193 nm and 157 nm will be discussed. An outlook of the future trends of development of compact excimer lasers will be given, too.
A new generation of compact Fluorine lasers has been developed for repetition rates up to 2 kHz. The output powers are in the range of 3 W at 157 nm. Due to the introduction of new concepts for the laser tube and the pulsed power module it was possible to increase the maximum repetition rate from 1 kHz to 2 kHz without any loss in the performance of the laser output parameters. The pulse-to-pulse stability of the laser energy is improved in comparison to previous laser generations. The results of long term tests and measurements of the laser output characteristic will be reported in detail. The state-of-the-art of compact excimer lasers will be presented and an outlook for future trends will be given.
A mini-excimer laser with a specially designed laser tube was operated at a constant energy of 8 mJ and a constant repetition rate of 500 Hz at 193 nm. A long-term test of this laser system was done. The output energy was constant over the test interval of 1.5 billion pulses. The pulse-to-pulse stability was constant over the total test period. The test was done without changing or cleaning the resonator optics.
The discharge pumped excimer laser is a gas laser providing ultra violet (UV) radiation with well defined spectral, temporal and spatial properties. The fast development of excimer lasers in recent years has succeeded in designing very compact, table-top and turn-key systems delivering up to 20 W of radiation at 248 nm, 10 W at 193 nm and 2 W at 157 nm with repetition rates up to 2000 Hz (1, 5). Due to their short emission wavelength and compactness they are continuously replacing other light sources, like lamps and ion lasers, in applications as metrology, inspection, direct writing and material testing. Spatial and temporal beam properties of compact excimer lasers are very suitable to be utilized as illumination source in these applications. The compact excimer laser is combining the advantages of both, lamp and laser sources. It displays low temporal and spatial coherence, but has a narrow spectral emission range of a few hundred pm. The beam area is approximately 1/2 cm2, the divergence is in the order of 1 mrad. Variation of beam position and beam direction are negligible for most illumination applications. Compact excimer lasers are easy to integrate in measurement and inspection systems. Typically their footprint area is 0.25 m2. The power consumption is less than 1 kW, enabling single phase electrical supply and air cooling. State-of-the-art compact excimer lasers are compliant to all relevant SEMI regulations. The laser optics exceeds the life time of the laser tube, thus no optics cleaning and exchange is necessary in a whole life time of a laser tube of a few billion pulses (6).
For new industrial applications, mini excimer lasers with a wavelength of 157 nm were developed. The main goal was to extend the component lifetime. The laser tube is designed in metal-ceramic technology. An erosion-free corona preionization is installed. The pulsed-power module contains a solid state switch with additional compression stages to generate the high current rise at the electrodes of the laser tube. All of the modules in the laser system are designed for long lifetime. At 157 nm the mini excimer laser reaches a maximum single-pulse energy of 2 mJ up to a repetition rate of 1000 Hz. An overview of the results of long-term testing of these stateÑofÑtheÑart mini excimer lasers at 157 nm will be given.
In this paper, we report on our investigations of radiation induced processes in optical interference coatings for 193 nm applications with respect to the microstructure of the coating. Experimental studies revealed that fluoride coatings contribute the main source for radiation induced optical changes during its exposure to 193 nm laser irradiation due to their porous microstructure. NIR spectroscopy could identify the origin of optical changes in interference coatings as a reversible hydrocarbon contamination which occurs within the coatings from storage in air atmosphere. Additionally, Laser Induced Damage Threshold measurements show a direct influence of the hydrocarbon contamination on the radiation durability of the multilayer systems during laser exposure. Experiments were carried out by using several characterization techniques including DUV spectrophotometry, ATR-IR-spectroscopy, x-ray diffractometry, and the determination of the '1-on-1' laser induced damage threshold. Test methods were applied to DUV coatings before and after exposure to 193 nm radiation with irradiation doses of up to 108 laser pulses at a fluence of 70mJ/cm2. Test samples consisted of several coating designs, primarily of high reflective multilayer systems.
The exposure of optical interference coatings to low-fluence DUV-radiation reveals changes of thin layer properties due to interactions between radiation field and thin film structure. An experimental set up for irradiating antireflective as well a high reflective coatings with 193nm excimer laser was used in order to study permanent cumulative changes in optical coatings at fluences ranging from 20mJ/cm2 with up to 240 106 laser pulses. The optical ex-situ monitoring of radiation induced modifications enabled the differentiation of coating specific and substrate inherent alteration effects. The identification of conditions as well as degradation processes during the exposure could be achieved for several types of DUV-coating materials. They were deposited with an ultra low loss evaporation process onto calcium fluoride and fused silica substrates. Fluoride coating included LaF3, Na3AlF6, MgF2, AlF3 oxide coatings consisted of SiO2 and Al2O3 exclusively.
We report on our investigations on the long-term behavior of optical coatings under 193 nm laser irradiation in dependence on coating materials, radiation conditions, and substrate properties. A wide variety of different highly reflective dielectric mirrors and antireflective coatings, deposited by an ultra low loss evaporation process onto calcium fluoride and fused silica, has been tested. Irradiation experiments with highly reflective coatings show that fluoride coatings exhibit nearly no changes of their optical function in air as well as in argon atmosphere due to low initial absorption levels. Temporal atmospheric contaminations can be removed by using appropriate irradiation conditions. Oxide layers tend to post-oxidize during 193 nm exposure in air and the DUV absorption level will be reduced. Effectively, reflectance of multilayer coatings on the basis of oxide materials can be improved through laser irradiation. Irradiation experiments with antireflective coatings point out the dominant role of bulk and surface properties of the substrate for prolonged laser irradiation. In addition, we present laser induced damage thresholds to demonstrate upper limits of laser radiation resistance that can be achieved nowadays with several types of coatings.
Sealed-off, metal-ceramic pseudospark switches are currently being developed as a replacement for conventional thyratrons in pulsed gas discharge lasers. In this contribution the performance of different type of pseudospark switches at different load conditions typical for pulsed gas discharge lasers is discussed. Experiments were performed at a low inductive 1 (Omega) water pulse line at holdoff voltages of up to 32 kV with a dI/dt of 6 X 1011 A/s (10% - 90%) and a maximum current of 30 kA. Switch parameters were continuously recorded at repetition rates of up to 100 Hz. In a second experiment the long-term behavior of a pseudospark switch in an excimer laser test circuit was investigated. At a repetition rate of 233 Hz and a charging voltage of 22 kV a nearly unipolar current pulse of about 10 kA in amplitude with a length of 170 ns (FWHM) was obtained. Again switch parameters were on- line recorded. Further the power loss to the electrodes could be determined. Performance of those type of pseudospark switches and the application in real laser systems are discussed.
Longterm tests with several electrode materials and discharge channel arrangements were performed. Two possible geometries were tested, a radial and a coaxial one. Optical fast shutter technique, and spectroscopic and interferometric methods were used to get more information about the discharge-character, the pinching of the discharge channels due to magnetic forces, and the erosion mechanism. The homogeneous ignition and the equal distribution of the current into the individual discharge channels was proved by fast photography and current measurements. At currents exceeding some kA the pseudospark transforms from a specific hollow cathode discharge into a metal-vapor-arc like behavior. Measurements of the forward voltage drop provide values of less than 100 V which are typical for metal-vapor-arcs. Also cathode spots and their traces on the electrode surface were observable. The performance of these switches in pulsed power devices will be reported.
The experimental results of high-repetition-rate pseudospark switch testing are reported, with particular interest in applications like high-repetition- rate, high-average power excimer lasers and pulsed TEA CO2 lasers. Typical test parameters are hold-off voltage of about 20 kV, peak currents around 15 kA, and pulse durations of less than 100 ns, discharge conditions that are typical for high average power excimer lasers. These were realized in a low inductive discharge circuit using discrete ceramic capacitors of up to 10 nF total capacitance and an impedance of about 1 (Omega) . The resulting peak currents were about 19 kA in the short-circuited, ringing discharge. A special feature of the switch is being capable to withstand severe current reversal, high rates of current rise of about 5*1011 A/s and peak currents above 20 kA. Some 107 shots have been performed with a sealed-off metal-ceramic pseudospark switch with integrated hydrogen reservoir without degradation of the switch performance. In this setup, repetition rates of up to 1.8 kHz were achieved. The switch-triggering behavior and measurements of the switch resistance in dependence of the peak current are reported.