An Yb-based 78-MHz repetition rate fiber-amplified frequency comb is used to investigate the power scaling
limitations of a standard-design bow tie high-finesse enhancement cavity for XUV generation. With a Xenon
gas jet in the 22-μm-radius focus, the 200-fs intra-cavity circulating pulse reaches a maximum of 20 kW of time-averaged
power. A novel cavity design is presented, conceived to overcome the observed enhancement limitations
and offering the prospect of few-nm high-power high-harmonic generation. Several applications which come into
reach for the first time are discussed.
Results on the detection of traces of trinitrotoluene (TNT) on different substrate-materials like Aluminum and
standard car paint are presented. We investigated different samples with a movable imaging standoff detection
system at angles of incidence far away from specular reflection. The samples were illuminated with a tunable
mid-infrared external-cavity quantum cascade laser. For collection of the diffusely backscattered light a highperformance
infrared imager was used. Trace concentrations of TNT corresponding to fingerprints on realworld-
substrates were detected, while false alarms of cross-contaminations were successfully suppressed.
We present experimental results on a Quantum cascade laser (QC laser) embedded in an external cavity. These results were obtained with a broadly tunable laser exceeding 80 cm-1 covering a characteristic absorption band of trinitrotoluene
(TNT). By combining the laser source with a high performance IR imager a stand-off detection setup based on multi-
spectral MIR backscattering spectroscopy has been realized. With this technique TNT surface-contaminations of as low
as 10 μg/cm2 could be detected on surfaces such as an aluminum-sheet and standard car paint. The contrast of the
detection technique depends on the reflectance of the surface. A surface leading to mirror-like reflectance of the IR laser radiation leads to absorbance-like signatures of the TNT contamination, while surfaces showing high absorbance of the laser light may induce a contrast-reversal in the resulting image of the TNT coverage. This effect can be explained by a theoretical model for thin film coated substrates taking into account differences in the reflectance. Limitations and
further work needed to explore the full potential of the IR backscattering technique are also discussed.