High-average-power femtosecond laser at 258 nm

We present an ultrafast fiber laser system delivering 4.6 W average power at 258 nm based on two-stage fourth-harmonic generation in beta barium borate (BBO). The beam quality is close to being diffraction limited with an M2 value of 1.3×1.6. The pulse duration is 150 fs, which, potentially, is compressible down to 40 fs. A plain BBO and a sapphire-BBO compound are compared with respect to the achievable beam quality in the conversion process. This laser is applicable in scientific and industrial fields. Further scaling to higher average power is discussed

Table-Top Milliwatt-Class Extreme Ultraviolet High Harmonic Light Source

Extreme ultraviolet (XUV) lasers are essential for the investigation of fundamental physics. Especially high repetition rate, high photon flux sources are of major interest for reducing acquisition times and improving signal to noise ratios in a plethora of applications. Here, an XUV source based on cascaded frequency conversion is presented, which delivers due to the drastic better single atom response for short wavelength drivers, an average output power of (832 +- 204) {\mu}W at 21.7 eV. This is the highest average power produced by any HHG source in this spectral range surpassing precious demonstrations by more than a factor of four. Furthermore, a narrow-band harmonic at 26.6 eV with a relative energy bandwidth of only {\Delta}E/E= 1.8 x 10E-3 has been generated, which is of high interest for high precision spectroscopy experiments.Comment: 4 Pages, 4 Picture

High power ultra-short pulse lasers based on fiber driven OPCPA

Ultrashort laser pulses enable fundamental studies on small length and time scales. Additionally, high pulse energies allows the access to new regimes of light matter interaction and the investigation of nanometer scale structures on attosecond time scales by XUV pulses produced via high harmonic generation (HHG). Unfortunately, the XUV photon flux is typically very low. Hence, high power and high repetition rate driving laser sources are required in order to improve the performance of current studies and to open the way for new exiting applications, such as seeding of free electron lasers. Regrettably, conventional (Ti:Sa) laser technology is limited in output power due to the thermo optical effects in the amplifier crystals. The objective of this thesis is the development of a new power scalable laser concept merging OPCPA technology with state-of-the-art high power fiber lasers. Based on modeling of the optical parametric amplifier, important requirements on the OPCPA pump are found which are adopted in choice and development of the pump laser later. Furthermore, the geometry of the optical parametric amplifier is optimized for ultra-broadband amplification. Gain narrowing and saturation effects are investigated in order to achieve high conversion efficiency. In addition, parasitic nonlinear effects, such as second harmonic generation of signal and idler wave, are studied and configurations are found which effectively avoid these unwanted effects. Experimentally, pulse durations of 8 fs and a pulse peak power as large as 6 GW are achieved with an optimized ultra-broadband OPCPA system. In addition, this few-cycle OPCPA system delivers an average output power as large as 6.7 W, which represents a record value for few-cycle lasers. Finally, high harmonic generation is demonstrated with this laser system and further scaling potential to higher peak and average powers is discussed

High photon flux table-top coherent extreme ultraviolet source

High harmonic generation (HHG) enables extreme ultraviolet radiation with table-top setups. Its exceptional properties, such as coherence and (sub)-femtosecond pulse durations, have led to a diversity of applications. Some of these require a high photon flux and megahertz repetition rates, e.g. to avoid space charge effects in photoelectron spectroscopy. To date this has only been achieved with enhancement cavities. Here, we establish a novel route towards powerful HHG sources. By achieving phase-matched HHG of a megahertz fibre laser we generate a broad plateau (25 eV - 40 eV) of strong harmonics, each containing more than $10^{12}$ photons/s, which constitutes an increase by more than one order of magnitude in that wavelength range. The strongest harmonic (H25, 30 eV) has an average power of 143 $\mu$W ($3\cdot10^{13}$ photons/s). This concept will greatly advance and facilitate applications in photoelectron or coincidence spectroscopy, coherent diffractive imaging or (multidimensional) surface science

Electrically Tunable Multiwavelength Bragg Grating Filter Acoustically Induced in a Highly Birefringent Suspended Core Fiber

Multiwavelength reflection spectra induced by an acoustically modulated fiber Bragg grating (FBG) in a highly birefringent suspended core fiber are experimentally investigated. Longitudinal acoustic waves interacting with a grating generate side lobes in the reflectivity spectrum and produce a superposed reflection band. The reflectivity of up to five wavelength peaks can be actively tuned by the voltage of the electrical signal inducing the acoustic waves. This indicates new possibilities for compact and fast multiwavelength dynamic and fiber-integrated reflection filters

Shell effects and free-electrons in electromigrated oxidized Cu-nanocontacts

Electromigration in interconnects continues to be an important field of study in integrated circuits as the interconnects are planned to shrink in size at comparable pace as the semiconductor functional elements. Through shrinking the interconnects approach the regime where quantum size effects become important. The observation of quantum size and shell effects is usually restricted either to low-temperatures or vacuum conditions or to chemically inert materials such as Au. Here, we show that in electromigrated Cu nanocontacts such effects can be observed at room temperature and room pressure even in the presence of oxidation. Our data provide evidence that the nanocontacts are nearly spherical objects with a triangular-cylindrical symmetry of their electronic wave functions with a stronger free-electron-like character compared to previous results. We do not observe a detrimental effect of oxygen. The presence of shell effects has implications for the technological use of Cu nanocontacts as interconnects in integrated circuits and could lead to the use of electronic wave functions of shells in such interconnects

Codiffused Bifacial n-type Solar Cells (CoBiN)

AbstractWe present codiffused bifacial n-type (CoBiN) solar cells on 156 mm Czochralski grown (Cz) Si wafers with peak efficiencies of 19.6 % fabricated using a lean industrial process. Simultaneous diffusion of phosphorus back surface field (BSF) and boron emitter in one single tube furnace process, the so called codiffusion, leads to a significant process simplification. Manipulation of the borosilicate glass (BSG) layer, deposited by atmospheric pressure chemical vapor deposition (APCVD) prior to the POCl3 based codiffusion process, allows for emitter profile tuning, without influencing the phosphorus doped BSF. Analytical simulations concerning the BSF identify the dark saturation current density of the passivated part of the BSF J0pass, BSF as the parameter that allows for maximum improvement of cell efficiency

Reflectivity and Bandwidth Modulation of Fiber Bragg Gratings in a Suspended Core Fiber by Tunable Acoustic Waves

The acousto-optic modulation of fiber Bragg gratings in a four-hole suspended core fiber is experimentally demonstrated. Strong modulations with a reflectivity amplitude decrease by up to 67% and a 57% bandwidth increase in the Bragg resonance are obtained for gratings of 0.26- and 1-nm 3-dB bandwidths, respectively. The reduction of the required acoustic power for achieving the acousto-optic modulation compared to conventional solid-core single-mode fibers points to more efficient modulator devices in suspended core fibers