R. Poprawe - Academia.edu (original) (raw)

Papers by R. Poprawe

The influence of gain-saturation on Kerr-lens mode locking of a Cr:LiSAF laser

Conference Digest. 2000 Conference on Lasers and Electro-Optics Europe (Cat. No.00TH8505), 2000

MS412 Development and Evaluation of a Novel Poly-L-Lactic Acid/Caprolactone Copolymer Coronary Stent Manufactured by Selective Laser Melting

Atherosclerosis Supplements, 2010

Development and application of miniaturized scanners for laser beam micro-welding

Microsystem Technologies, 2008

Nowadays, flexible production systems for laser joining of micro parts require high dynamics and ... more Nowadays, flexible production systems for laser joining of micro parts require high dynamics and precision, as well as increased flexibility regarding the working space. The combination of miniaturized scanner-based laser joining systems and high-performance assembly systems is a new approach for a high accuracy compact micro assembly system with an increased flexibility. Using highly dynamic oscillation techniques leads to a

Precise ablation of dental hard tissues with ultra-short pulsed lasers. Preliminary exploratory investigation on adequate laser parameters

Lasers in Medical Science, 2013

This study aimed to evaluate the possibility of introducing ultra-short pulsed lasers (USPL) in r... more This study aimed to evaluate the possibility of introducing ultra-short pulsed lasers (USPL) in restorative dentistry by maintaining the well-known benefits of lasers for caries removal, but also overcoming disadvantages, such as thermal damage of irradiated substrate. USPL ablation of dental hard tissues was investigated in two phases. Phase 1--different wavelengths (355, 532, 1,045, and 1,064 nm), pulse durations (picoseconds and femtoseconds) and irradiation parameters (scanning speed, output power, and pulse repetition rate) were assessed for enamel and dentin. Ablation rate was determined, and the temperature increase measured in real time. Phase 2--the most favorable laser parameters were evaluated to correlate temperature increase to ablation rate and ablation efficiency. The influence of cooling methods (air, air-water spray) on ablation process was further analyzed. All parameters tested provided precise and selective tissue ablation. For all lasers, faster scanning speeds resulted in better interaction and reduced temperature increase. The most adequate results were observed for the 1064-nm ps-laser and the 1045-nm fs-laser. Forced cooling caused moderate changes in temperature increase, but reduced ablation, being considered unnecessary during irradiation with USPL. For dentin, the correlation between temperature increase and ablation efficiency was satisfactory for both pulse durations, while for enamel, the best correlation was observed for fs-laser, independently of the power used. USPL may be suitable for cavity preparation in dentin and enamel, since effective ablation and low temperature increase were observed. If adequate laser parameters are selected, this technique seems to be promising for promoting the laser-assisted, minimally invasive approach.

Facet temperature reduction by a current blocking layer at the front facets of high-power InGaAs/AlGaAs lasers

Journal of Applied Physics, 2003

High-power broad-area laser diodes have been improved during the last years in terms of lifetime ... more High-power broad-area laser diodes have been improved during the last years in terms of lifetime and output power. They are already used for many different applications, but there is still an urgent demand for increasing the output ...

IEEE Journal of Quantum Electronics, 2002

A new type of band-edge aligned carrier barriers is introduced into InGaAs-AlGaAs single quantum-... more A new type of band-edge aligned carrier barriers is introduced into InGaAs-AlGaAs single quantum-well (SQW) high-power diode laser structures in order to prevent thermionic emission and the overflow of carriers at elevated operating temperatures. These barriers, which are located in the direct vicinity of the active zone of the laser, are undoped to avoid free-carrier absorption. An InGaAs-AlGaAs SQW laser structure with a 10-nm-thick AlGaAsSb electron-blocking layer on the p-side of an In 0 2 Ga 0 8 As quantum well was realized. The composition of this layer was adjusted so that its valence-band edge matches that of the adjacent AlGaAs waveguide layer. This is to prevent any additional voltage drop or series resistance due to the injection of holes into the quantum well through the electron blocking layer. These lasers show a high characteristic temperature 0 of about 225 K for 1500-m-long as-cleaved devices, which is about 60 K higher than the same laser structure without the blocking layer. Simultaneously low internal losses ( 1 5 cm 1 at 20 C) and high internal quantum efficiencies ( 93% at 20 C) are achieved. No additional voltage drop or series resistance was measured. The higher temperature stability is mainly attributed to the suppression of carrier leakage and a reduced free-carrier absorption at elevated temperatures.

Applied Spectroscopy, 2010

Multiphoton microscopy is a promising technique to detect spatially and temporally resolved conce... more Multiphoton microscopy is a promising technique to detect spatially and temporally resolved concentration gradients of chemical compounds, e.g., reactants in hydrogel-encapsulated biocatalysts. In contrast to current techniques, the improved spatial and temporal resolution of this method in data acquisition and its ability to measure hydrogel beads facilitates the identification of various kinetic phenomena. To our knowledge, multiphoton microscopy is used here for the first time to examine diffusion, mass transfer, and reaction in immobilized hydrogel systems. In a first step, the phenomena of diffusion and diffusion-coupled mass transfer through the phase interface are investigated in the bead center. Finally, the complete system-consisting of diffusion, mass transfer, and enzymatic reaction-is observed by measuring concentration gradients along the bead radius with temporal and spatial resolution. This metrology enables a subsequent mechanistic model identification, which in turn leads to an enhanced knowledge of reaction kinetics and supports the design of biotechnological processes. This task was only possible due to excellent spatial (25 lm) and temporal (5 s) resolution and the accuracy (61%) achieved by using a multiphoton microscopy setup.

Online control of penetration depth in laser beam welding

IECON '98. Proceedings of the 24th Annual Conference of the IEEE Industrial Electronics Society (Cat. No.98CH36200), 1998

Q-Switch Behaviour of Different Solid State Laser Hosts

CLEO/Europe Conference on Lasers and Electro-Optics, 1998

ABSTRACT

A 500W High Brightness Diode end pumped

Advanced Solid-State Lasers, 2002

Removal and Drilling of Metals by Excimer Laser Radiation

Laser/Optoelektronik in der Technik / Laser/Optoelectronics in Engineering, 1990

“New ultrafast high power kW class lasers open next generation applications&#x201D

22nd IEEE International Semiconductor Laser Conference, 2010

In this paper we present compact laser sources with a high flexibility in pulse energy (μJ to mJ)... more In this paper we present compact laser sources with a high flexibility in pulse energy (μJ to mJ) and pulse repetition rate (kHz to ~ 100MHz), delivering an average power of more than 400W. Additionally, a broad range of application examples and parameter sets will be presented, from micro- and nanostructuring of various materials to volume processing of dielectrics.

Inline-Verfahren

VDI-Buch, 2005

A Nd:YAG slab is partially end pumped by a diode laser stack with three diode laser bars. The pum... more A Nd:YAG slab is partially end pumped by a diode laser stack with three diode laser bars. The pumped volume has a rectangular cross section. A hybrid resonator, which is stable in the plane of small dimension and is off-axis unstable in the plane of large dimension of the gain cross section, was used to yield highly efficient laser operation at diffraction-limited beam quality. The laser design and experimental results are reported.

Ytterbium Innoslab amplifiers - The high average power approach of ultrafast lasers

Efficient Generation of Tunable Visible Light by Means of DFG of aTi:Al2O3 and a Nd:YAG Laser

Advanced Solid-State Photonics, 2005

Abstract DFG of a frequency doubled Titanium: Sapphire and a Nd: YAG laser provides tunable outpu... more Abstract DFG of a frequency doubled Titanium: Sapphire and a Nd: YAG laser provides tunable output in the spectral range between 520 nm and 680 nm. Using BBO crystals, conversion efficiencies of up to 32% have been achieved.

New advances in process control for laser materials processing: Japan Welding Society. 7th International Symposium. Proceedings. Today and tomorrow in science and technology of welding and joining. Vol. 1

Regenerative amplification of laser diode pulses with variable pulse duration from ps to ns range

A laser diode seeded Nd:YAG regenerative amplifier is demonstrated. The pulse duration of the las... more A laser diode seeded Nd:YAG regenerative amplifier is demonstrated. The pulse duration of the laser diode is variable from 150 ps to 3 ns. Pulse energies of 0.5 mJ at kHz repetition rate are measured.

UV beam sources for double pulse generation

Filtration Industry Analyst, 2000

Summary form only given. The concept of two laser sources has been developed whose pulse generati... more Summary form only given. The concept of two laser sources has been developed whose pulse generation signals and light paths are synchronized. This can be realized with an accuracy in the nanosecond range, so the two temporally shifted pulses act onto the material with a separation significantly shorter than the thermal dissipation time of several microseconds, hence appearing to the

295-MHz, diode-pumped, mirror-dispersion-controlled femtosecond laser

Technical Digest. Summaries of Papers Presented at the Conference on Lasers and Electro-Optics. Conference Edition. 1998 Technical Digest Series, Vol.6 (IEEE Cat. No.98CH36178), 1998

ABSTRACT We present, to our knowledge, the first results of a very compact femtosecond laser deli... more ABSTRACT We present, to our knowledge, the first results of a very compact femtosecond laser delivering sub-100-fs pulses with almost 300-MHz repetition rate approaching the 100-mW level. Our Kerr-lens mode-locking setup employs a 5-mm-long, 2.2%-doped Cr:LiSAF crystal and a pair of identical Gires-Tournois interferometer mirrors (GTI) to compensate the positive group velocity dispersion (GVD) of the gain medium. GTI mirrors were chosen because of the larger amount of negative GVD together with lower scatter loss compared to chirped mirrors