A. Voss

Bio: A. Voss is an academic researcher from University of Stuttgart. The author has contributed to research in topics: Laser & Fiber laser. The author has an hindex of 11, co-authored 37 publications receiving 1484 citations.

Scalable concept for diode-pumped high-power solid-state lasers

Abstract: A new, scalable concept for diode-pumped high-power solid-state lasers is presented The basic idea of our approach is a very thin laser crystal disc with one face mounted on a heat sink This allows very high pump power densities without high temperature rises within the crystal Together with a flat-top pump-beam profile this geometry leads to an almost homogeneous and one-dimensional heat flux perpendicular to the surface This design dramatically reduces thermal distortions compared to conventional cooling schemes and is particularly suited for quasi-three-level systems which need high pump power densities Starting from the results obtained with a Ti:Sapphire-pumped Yb:YAG laser at various temperatures, the design was proved by operating a diode-pumped Yb:YAG laser with an output power of 44 W and a maximum slope efficiency of 68% From these first results we predict an exctracted cw power of 100 W at 300 K (140 W at 200 K) with high beam quality from a single longitudinally pumped Yb: YAG crystal with an active volume of 2 mm3 Compact diode-pumped solid-state lasers in the kilowatt range seem to be possible by increasing the pump-beam diameter and/or by using several crystal discs

Multiwatt diode-pumped Yb:YAG thin disk laser continuously tunable between 1018 and 1053 nm.

Abstract: A new powerful source of broadly (35-nm) tunable laser radiation in the near-infrared (near 1030 nm) wavelength range is presented. Inserting a birefringent filter into a 10-W diode-pumped Yb:YAG thin disk laser resonator gives several watts of narrow-linewidth (0.07-nm) continuously tunable cw output power. By taking advantage of the power scalability of the thin disk concept, even hundreds of watts of tunable power with near-diffraction-limited beam quality and high efficiency are feasible. Generation and amplification of subpicosecond pulses with high average and peak powers are also promising applications of the Yb:YAG thin disk laser.

Illuminating the proton radius conundrum: The mu He+ Lamb shift

Abstract: We plan to measure several 2S–2P transition frequencies in μ4He+ and μ3He+ by means of laser spectroscopy with an accuracy of 50 ppm. This will lead to a determination of the corresponding nuclear rms charge radii with a relative accuracy of 3 × 10−4, limited by the uncertainty of the nuclear polarization contribution. First, these measurements will help to solve the proton radius puzzle. Second, these very precise nuclear radii are benchmarks for ab initio few-nucleon theories and potentials. Finally when combined with an ongoing measurement of the 1S–2S transition in He+, these measurements will lead to an enhanced bound-state QED test of the 1S Lamb shift in He+.

100 W TEM00 Operation of Yb:YAG Thin Disc Laser with High Efficiency

Abstract: We report on the power scalability of the thin disc laser design with high efficiency and good beam quality. Nearly 100 W of TEM00 power (M2 = 1.2) with an electrical to optical efficiency of more than of 13% is obtained. A maximum laser power of 346 W was extracted from one single disc with an electrical to optical efficiency of 16.8%.

Recent developments in compact ultrafast lasers

Abstract: Ultrafast lasers, which generate optical pulses in the picosecond and femtosecond range, have progressed over the past decade from complicated and specialized laboratory systems to compact, reliable instruments. Semiconductor lasers for optical pumping and fast optical saturable absorbers, based on either semiconductor devices or the optical nonlinear Kerr effect, have dramatically improved these lasers and opened up new frontiers for applications with extremely short temporal resolution (much smaller than 10 fs), extremely high peak optical intensities (greater than 10 TW/cm2) and extremely fast pulse repetition rates (greater than 100 GHz).

Semiconductor saturable absorber mirrors (SESAM's) for femtosecond to nanosecond pulse generation in solid-state lasers

Abstract: Intracavity semiconductor saturable absorber mirrors (SESAM's) offer unique and exciting possibilities for passively pulsed solid-state laser systems, extending from Q-switched pulses in the nanosecond and picosecond regime to mode-locked pulses from 10's of picoseconds to sub-10 fs. This paper reviews the design requirements of SESAM's for stable pulse generation in both the mode-locked and Q-switched regime. The combination of device structure and material parameters for SESAM's provide sufficient design freedom to choose key parameters such as recovery time, saturation intensity, and saturation fluence, in a compact structure with low insertion loss. We have been able to demonstrate, for example, passive modelocking (with no Q-switching) using an intracavity saturable absorber in solid-state lasers with long upper state lifetimes (e.g., 1-/spl mu/m neodymium transitions), Kerr lens modelocking assisted with pulsewidths as short as 6.5 fs from a Ti:sapphire laser-the shortest pulses ever produced directly out of a laser without any external pulse compression, and passive Q-switching with pulses as short as 56 ps-the shortest pulses ever produced directly from a Q-switched solid-state laser. Diode-pumping of such lasers is leading to practical, real-world ultrafast sources, and we will review results on diode-pumped Cr:LiSAF, Nd:glass, Yb:YAG, Nd:YAG, Nd:YLF, Nd:LSB, and Nd:YVO/sub 4/.

Quantum electrodynamics

Abstract: THE subject of quantum electrodynamics is extremely difficult, even for the case of a single electron. The usual method of solving the corresponding wave equation leads to divergent integrals. To avoid these, Prof. P. A. M. Dirac* uses the method of redundant variables. This does not abolish the difficulty, but presents it in a new form, which may be dealt with in two ways. The first of these needs only comparatively simple mathematics and is directly connected with an elegant general scheme, but unfortunately its wave functions apply only to a hypothetical world and so its physical interpretation is indirect. The second way has the advantage of a direct physical interpretation, but the mathematics is so complicated that it has not yet been solved even for what appears to be the simplest possible case. Both methods seem worth further study, failing the discovery of a third which would combine the advantages of both.

The size of the proton

Abstract: Considering that the proton is a basic subatomic component of all ordinary matter — as well as being ubiquitous in its solo role as the hydrogen ion H+ — there are some surprising gaps in our knowledge of its structure and behaviour. A collaborative project to determine the root-mean-square charge radius of the proton to better than the 1% accuracy of the current 'best' value suggests that those knowledge gaps may be greater than was thought. The new determination comes from a technically challenging spectroscopic experiment — the measurement of the Lamb shift (the energy difference between a specific pair of energy states) in 'muonic hydrogen', an exotic atom in which the electron is replaced by its heavier twin, the muon. The result is unexpected: a charge radius about 4% smaller than the previous value. The discrepancy remains unexplained. Possible implications are that the value of the most accurately determined fundamental constant, the Rydberg constant, will need to be revised — or that the validity of quantum electrodynamics theory is called into question. Here, a technically challenging spectroscopic experiment is described: the measurement of the muonic Lamb shift. The results lead to a new determination of the charge radius of the proton. The new value is 5.0 standard deviations smaller than the previous world average, a large discrepancy that remains unexplained. Possible implications of the new finding are that the value of the Rydberg constant will need to be revised, or that the validity of quantum electrodynamics theory is called into question. The proton is the primary building block of the visible Universe, but many of its properties—such as its charge radius and its anomalous magnetic moment—are not well understood. The root-mean-square charge radius, rp, has been determined with an accuracy of 2 per cent (at best) by electron–proton scattering experiments1,2. The present most accurate value of rp (with an uncertainty of 1 per cent) is given by the CODATA compilation of physical constants3. This value is based mainly on precision spectroscopy of atomic hydrogen4,5,6,7 and calculations of bound-state quantum electrodynamics (QED; refs 8, 9). The accuracy of rp as deduced from electron–proton scattering limits the testing of bound-state QED in atomic hydrogen as well as the determination of the Rydberg constant (currently the most accurately measured fundamental physical constant3). An attractive means to improve the accuracy in the measurement of rp is provided by muonic hydrogen (a proton orbited by a negative muon); its much smaller Bohr radius compared to ordinary atomic hydrogen causes enhancement of effects related to the finite size of the proton. In particular, the Lamb shift10 (the energy difference between the 2S1/2 and 2P1/2 states) is affected by as much as 2 per cent. Here we use pulsed laser spectroscopy to measure a muonic Lamb shift of 49,881.88(76) GHz. On the basis of present calculations11,12,13,14,15 of fine and hyperfine splittings and QED terms, we find rp = 0.84184(67) fm, which differs by 5.0 standard deviations from the CODATA value3 of 0.8768(69) fm. Our result implies that either the Rydberg constant has to be shifted by −110 kHz/c (4.9 standard deviations), or the calculations of the QED effects in atomic hydrogen or muonic hydrogen atoms are insufficient.

Fifteen Years of Work on Thin-Disk Lasers: Results and Scaling Laws

Abstract: The principal ideas of the thin-disk laser design will be illustrated and the advantages for operating different laser materials will be explained. The results for continuous-wave (CW) and Q-switched operation as well as for amplification of short (nanosecond) and ultrashort (picosecond, femtosecond) pulses demonstrate the potential of the thin-disk laser design. The scaling laws for this laser design show that the power limit for CW operation is far beyond 40 kW for one single disk and the energy limit is higher than 3 J from one disk in pulsed operation. Also, the applicability of the thin-disk laser concept to optically pumped semiconductor structures will be discussed. When pumping directly into the quantum wells, the energy defect between the pump photon and the laser photon can be smaller than 5%, thus reducing the waste heat generated inside the semiconductor structure. First results demonstrate the potential of this new concept. Finally, a short overview of the industrial realization of the thin-disk laser technology will be given.