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Fiber-based high-power laser systems are advantageous for defense applications due to their intrinsic stability and resilience against challenging environmental conditions. Using single- or few-mode output fibers, an excellent beam quality can be achieved, allowing for tight focusing over long distance. However, thermally induced transverse mode instabilities (TMI) limit the obtainable diffraction-limited output power. We will show how thermally induced mode instabilities can be conveniently detected in-line in an all-fiber system. Towards this aim, we compare different detection locations and methods and show that characteristic signals can be detected in backwards direction. Expanding the system and applying these detection methods, we will investigate Raman-based high-power amplification for spectral shift in a passive fiber. We present the observation and identification of TMI due to Raman amplification and the tracing of their origin, locating it in the passive fiber section. By comparing different fiber and seed laser parameters, we deduce respective limiting parameters.

Laser-dressed photoelectron spectroscopy, employing extreme-ultraviolet attosecond pulses obtained by femtosecond-laser-driven high-order harmonic generation, grants access to atomic-scale electron dynamics. Limited by space charge effects determining the admissible number of photoelectrons ejected during each laser pulse, multidimensional (i.e. spatially or angle-resolved) attosecond photoelectron spectroscopy of solids and nanostructures requires high-photon-energy, broadband high harmonic sources operating at high repetition rates. Here, we present a high-conversion-efficiency, 18.4-MHz-repetition-rate cavity-enhanced high harmonic source emitting 5 × 105 photons per pulse in the 25-to-60-eV range, releasing 1 × 1010 photoelectrons per second from a 10-µm-diameter spot on tungsten, at space charge distortions of only a few tens of meV. Broadband, time-of-flight photoelectron detection with nearly 100% temporal duty cycle evidences a count rate improvement between two and three orders of magnitude over state-of-the-art attosecond photoelectron spectroscopy experiments under identical space charge conditions. The measurement time reduction and the photon energy scalability render this technology viable for next-generation, high-repetition-rate, multidimensional attosecond metrology., Space charge effects can distort the results of photoelectron spectroscopic measurements, and usually limit the allowable photon flux in an experiment. Here, the authors present an 18.4 MHz repetition rate high harmonic source in the 25–60 eV range, with a large count rate improvement over state-of-the-art attosecond setups under identical space charge conditions.

We present our current results on the fabrication of arbitrary shaped fiber tapers on our tapering rig using a CO2-laser as heat source. Single mode excitation of multimode fibers as well as changing the fiber geometry in an LPG-like fashion is presented. It is shown that this setup allows for reproducible fabrication of single-mode excitation tapers to extract the fundamental mode (M2 < 1.1) from a 30 μm core having an NA of 0.09.

We report experimental and numerical results on the new pulse dynamics in a passively mode-locked ytterbium-doped fiber laser operating in the chirped-pulse regime. Due to the negligible nonlinearity of added highly-positive GVD segment in the purely-normal-dispersion regime, highly-positive chirped pulses can be formed through weak intra-cavity temporal and spectral breathing. Numerical simulations reveal intra-cavity pulse evolution with local temporal stretching phenomena and pulse shaping properties.

This chapter reviews the fundamentals and achievements of ultrashort pulse generation and amplification in ytterbium-doped fibers. Compact and ultrastable passively mode-locked fiber oscillators represent an ideal seed source for high performance femtosecond fiber amplification systems, which have been scaled towards kW-level average power and pulse energies well above the mJ-level. These laser systems will have significant impact in numerous scientific and industrial applications.

We report on two low-loss 7:1 single-mode to multi-mode fiber coupler-designs generating more than 5 kW of output power. These all-glass fiber-optical devices have the objective to keep the brightness at its theoretical maximum and the heat load at its technical minimum. To the best of our knowledge, regarding all-fiber geometrical combined power generation, beam quality and heat stability, the presented results had never been reported before.

Copper is a promising material to replace aluminum In some microelectronlc applications. However, the interaction of copper with contacting materials in multilevel metallization schemes, especially copper diffusion in dielectrics, is an important issue that needs to be addressed before it can be utilized in certain applications. The influence of different deposition parameters on film properties was studied. Optical and structural properties of deposited films were characterized by ellipsometry and infrared absorption spectroscopy, respectively. The interaction of copper with dielectrics was investigated by different analytical and electrical methods. To accelerate the Cu-migration the samples were exposed to various thermal and electrical stresses. These measurements were performed on MIS structures with Cu dots.

We present the coherent combination of high-energy ultrashort pulses from two fiber CPA channels. We achieved a combining efficiency of 91% with a compressed pulse duration of 800 fs and 120 µJ pulse energy.

We report on environmentally stable mode-locked Yb-doped all-fiber lasers operating in the wave-breaking-free and stretched-pulse regime. The compact linear cavity is constructed with saturable absorber mirror directly glued to the fibers end-facet as nonlinear mode-locking mechanism and chirped fiber Bragg grating for dispersion management, thus, without any free-space optics. In the wave-breaking-free regime the laser generates positively-chirped pulses with a pulse duration of 15.4 ps. These pulses are compressed to 218 fs in a hollow-core photonic bandgap fiber spliced to the output port. Adaptation of dispersion management has led to operation in the stretched-pulse regime, where a parabolic spectral profile is obtained as well. In this regime pulses are compressible to 213 fs. Numerical simulations are presented which confirm the wave-breaking-free and stretched-pulse evolution inside the fiber laser cavity. Both regimes are compared in terms of pulse quality.

We demonstrate a femtosecond fiber laser system delivering >5-μJ, sub-400-fs pulses at a pulse repetition rate of 200 kHz. At constant average power the pulse repetition rate of this Watt-level femtosecond laser can be adjusted up to several MHz. The laser is monolithically integrated from the oscillator to the booster amplifier stage. The system was applied for structuring metallic as well as transparent media as e.g. biological tissues in ophthalmology.

Indium solders are frequently used for interconnections in cooled systems because of their high ductility down to very low temperatures. Very fine contact pitches are required for hybrid mosaic radiation sensors compared with those for conventional flip‐chip technology. This paper presents solutions for bumping and bonding indium bumps based on the measured properties of indium solders in relation to the requirements of, and possibilities for, manufacture of fine pitch solder bump features.

We report experimental and numerical results on the pulse dynamic of passively modelocked Yb-doped fiber laser operating in the chirped-pulse regime. A newly design cavity with a CFBG provides positive dispersion with negligible nonlinearity.

We report on environmentally-stable mode-locked Yb-doped all-fiber lasers operating in the wave-breaking-free and stretched-pulse regime. The laser generates positively-chirped pulses with parabolic spectral profile in both regimes. Numerical simulations confirm the intra-cavity pulse evolution.

We report on a self-starting passively mode-locked fiber laser operating in the chirped-pulse regime for the first time. A chirped fiber Bragg grating provides positive dispersion with negligible nonlinearity.

This article reports both numerically and experimentally the generation of wave-breaking-free pulses from an environmentally stable Yb-doped all-fiber laser. To the authors' knowledge, this is the first realization of an environmentally stable all-fiber mode-locked laser operating in the wave-breaking-free regime.

We present a self-starting passively mode-locked fiber laser operating in the chirped-pulse regime for the first time. A chirped fiber Bragg grating in the cavity provides positive dispersion with negligible nonlinearity. The laser generates positively-chirped pulses with a pulse duration of 22 ps at a repetition rate of 44 MHz, which are compressible down to 1.5 ps. We believe that the presented approach reveals a pulse energy scaling potential of mode-locked fiber lasers as nonlinear effects are significantly diminished compared the other known operation regimes.

Flip chip technology is familar for hybridization of mosaic sensors. In the case of cooled applications solder bumps made of In or In-alloys are preferred. The high density of pixels necessary for radiation detectors results in sharp claimings on patterning sufficiently high bumps that can be accomplished by electrodeposition. Solder alloys necessary for sensors susceptible to higher temperatures are plated sandwich-like. Special requirements on joining technology, too arise from materials, geometries and working conditions. Both cold pressure welding and reflow soldering are practicable with In-bumps. Technological variants of hybridization techniques are discussed, results are demonstrated on phantom devices.