We present a new type of combiner based on a fused pump/signal fiber bundle. We obtain a record high signal-to-pump isolation of more than 46dB from a device optimized for high power counter directional pumping of Ytterbium-doped large mode area airclad fibers. The compact device combines more than 100W of light from 14 pcs. of 105μm NA=0.15 fibers into the pump cladding of an airclad fiber with a coupling efficiency of 90%. The signal light is delivered through the center of the combiner ensuring the exceptional isolation. The high level of isolation, measured for a 60W amplifier configuration, is essential to ensure the reliability of the pump diodes in a high power pulsed system. The combiner is compatible with PM and non-PM systems and we demonstrate both a CW and a pulsed configuration.

We report on the monolithic integration of frequency converter and amplitude modulator in a single lithium niobate (LiNbO 3 ) chip by the use of focussed ultrashort laser pulses. The waveguiding structures are obtained by femtosecond-laser induced internal modification and the electrodes are ablated out of a gold-layer sputtered onto the sample surface.

Single tracks and pairs of tracks were written into undoped and Nd-doped YAG crystals using a commercial femtosecond laser system delivering pulses with pulse duration of 140 fs and pulse energies up to 10 μJ. The pulses were focused by a 50× microscope objective below the surface of the crystals. Due to the elasto-optical effect, stress-induced birefringence was observed in domains surrounding the single tracks and between the pairs of tracks. Waveguiding was demonstrated in certain channels in these domains. To investigate the underlying guiding mechanism highly selective chemical etching of the modified material was performed with etching rates up to 5 μm/h. Pumped at 808 nm, laser operation at a wavelength of 1064 nm was achieved. The maximum output power was 25.5 mW at 261 mW of launched pump power with a slope efficiency of 23%.

We report on ultrashort pulse laser micromachining experiments on different metals at average powers up to 70 W and repetition rates up to 1 MHz. The laser pulses with subpicosecond duration were generated by an ultrafast fiber CPA laser system. The influence of particle shielding and heat accumulation on the ablation efficiency and on the processing quality will be discussed.

We report on laser drilling experiments on copper and stainless steel samples using a novel ultrafast fiber CPA laser amplifier. Effects of particle shielding and heat accumulation at high average powers are discussed.

We present an experimental study on the drilling of metal targets with ultrashort laser pulses at high repetition rates (from 50 kHz up to 975 kHz) and high average powers (up to 68 Watts), using an ytterbium-doped fiber CPA system. The number of pulses to drill through steel and copper sheets with thicknesses up to 1 mm have been measured as a function of the repetition rate and the pulse energy. Two distinctive effects, influencing the drilling efficiency at high repetition rates, have been experimentally found and studied: particle shielding and heat accumulation. While the shielding of subsequent pulses due to the ejected particles leads to a reduced ablation efficiency, this effect is counteracted by heat accumulation. The experimental data are in good qualitative agreement with simulations of the heat accumulation effect and previous studies on the particle emission. However, for materials with a high thermal conductivity as copper, both effects are negligible for the investigated processing parameters. Therefore, the full power of the fiber CPA system can be exploited, which allows to trepan high-quality holes in 0.5mm-thick copper samples with breakthrough times as low as 75 ms.

We report on an ytterbium-doped fiber based chirped-pulse amplification system delivering 100 microJ pulse energy at a repetition rate of 900 kHz, corresponding to an average power of 90 W. The emitted pulses are as short as 500 fs. To the best of our knowledge, this is the highest average power ever reported for high-energy femtosecond solid-state laser systems.

We report on an Yb-doped photonic crystal fiber based CPA system delivering 90.4 W average power of 500 fs pulses at a repetition rate of 0.9 MHz corresponding to a pulse energy of 100 mu J.

In this contribution we report a high repetition rate optical parametric amplifier (OPA) pumped by a chirped pulse fiber amplifier system. Fiber CPA systems have demonstrated power scaling and open the route to OPAs at repetition rates in the 100 kHz-10MHz range. The OPA stage is seeded by a continuum generated in a Sapphire plate and more than 50 nm bandwidth is efficiently amplified, resulting in 3 &mgr;J, 29 fs pulses.

We report on a Q-switched short-length fiber laser producing 100 W of average output power at 100 kHz repetition rate and pulse durations as short as 17 ns. Up to 2 mJ of energy and sub-10-ns pulse duration are extracted at lower repetition rates. This performance is obtained by employing a rod-type ytterbium-doped photonic crystal fiber with a 70 microm core as gain medium, allowing for very short pulse durations, high energy storage, and emission of a single-transverse-mode beam.

We will review the achievements and the scaling potential of high average power and high energy ultrafast ytterbium-doped fiber laser systems

For the first time to the authors’ knowledge, laser activity has been achieved in low-phonon-energy, moisture-resistant bromide host crystals, neodymium-doped potassium lead bromide (Nd3+:KPb2Br5) and rubidium lead bromide (Nd3+:RbPb2Br5; RPB). Laser activity at 1.07??m was observed for both crystalline materials. Laser operation at the new wavelengths 1.18 and 0.97??m that resulted from the F5?24+H9?22–IJ4 transitions (J=13?2 and J=11?2) in Nd:RPB was achieved in a solid-state laser material. Rare-earth-doped MPb2Br5(M=K,Rb) is a promising candidate for long-wavelength infrared applications because of its low phonon frequencies and other favorable features. In principle, Nd3+:MPb2Br5 has high potential for laser operation at new wavelengths as well as for the achievement of short-wavelength lasing as a result of upconversion.

Recently, laser activity has been achieved in the low phonon energy, moisture-resistant bromide host crystals, neodymium-doped potassium lead bromide (Nd{sup 3+}:KPb{sub 2}Br{sub 5}) and rubidium lead bromide (Nd{sup 3+}:RbPb{sub 2}Br{sub 5}). Laser activity at 1.07 {micro}m was observed for both crystalline materials. Laser operation at the new wavelengths 1.18 {micro}m and 0.97 {micro}m resulting from the {sup 4}F{sub 5/2}+{sup 2}H{sub 9/2} {yields} {sup 4}I{sub J} transitions (J=13/2 and 11/2) in Nd:RPB was achieved for the first time in a solid state laser material. In this paper we present cw pump-probe spectra in order to discuss excited state absorption, reabsorption processes due to the long lived lower laser levels as well as possible depopulation mechanisms feasible for more efficient laser operation in these crystals. The bromides will be compared with potassium lead chloride (Nd{sup 3+}:KPb{sub 2}Cl{sub 5}).

Laser activity has been achieved in low-phonon energy, moisture-resistant neodymium-doped bromide host crystals, also resulting from the F-4(5/2)+2H(9/2) level for the first time in any solid-state material. Pump-probe spectra reveal mechanisms feasible for more efficient laser operation. (c) 2005 Optical Society of America.

For the first time to the authors' knowledge, laser activity has been achieved in low-phonon-energy, moisture-resistant bromide host crystals, neodymium-doped potassium lead bromide (Nd3+:KPb2Br5) and rubidium lead bromide (Nd3+:RbPb2Br5; RPB). Laser activity at 1.07 microm was observed for both crystalline materials. Laser operation at the new wavelengths 1.18 and 0.97 microm that resulted from the 4F5/2 + 2H9/2 - 4IJ transitions (J=13/2 and J=11/2) in Nd:RPB was achieved in a solid-state laser material. Rare-earth-doped MPb2Br5 (M=K, Rb) is a promising candidate for long-wavelength infrared applications because of its low phonon frequencies and other favorable features. In principle, Nd3+:MPb2Br5 has high potential for laser operation at new wavelengths as well as for the achievement of short-wavelength lasing as a result of upconversion.

Crystals of potassium lead bromide (KPB), a moisture-insensitive low-energy phonon laser host, were synthesized and purified. High-quality undoped and Tb3+-doped (nominal doping concentration was 5mol% TbBr3) KPb2Br5 were grown by the vertical Bridgman technique. X-ray diffraction measurements indicated that, at room temperature, the material was monoclinic with space group P21∕c, while at a high temperature the phase transformed to orthorhombic form. A reversible phase transition was observed around 256°C upon the heating and cooling cycle from differential scanning calorimetric measurements. The material was found to be transparent in the broad range from ∼0.4μmto25μm and above. The transmission spectrum of a Tb3+-doped crystal showed different absorption bands of Tb3+ at 4.5μm, 3μm, 2.3μm, and 2μm corresponding to F67–Fα7 transitions, for α=2–5. The maximum phonon energy of undoped KPb2Br5 at room temperature was determined to be 134cm−1 from Raman scattering spectrum.

Laser activity has been achieved in low-phonon energy, moisture-resistant neodymium-doped bromide host crystals, also resulting from the /sup 4/F/sub 5/2/+/sup 2/H/sub 9/2/ level for the first time in any solid-state material. Pump-probe spectra reveal mechanisms feasible for more efficient laser operation.

We report on the optical properties of Nd3+- and Tb3+-doped low-phonon-energy moisture-resistant host crystals, potassium lead bromide (KPb2Br5), and rubidium lead bromide (RbPb2Br5), including absorption, emission, and emission lifetime measurements as well as calculations of the multiphonon decay rate, Judd–Ofelt parameters, and radiative transition probabilities for relevant (laser) transitions in these crystals. The RE3+:MPb2Br5 (M=Rb, K) crystal is a promising candidate for long-wavelength infrared applications because of the low phonon frequencies and other favorable features.

For the first time laser activity has been achieved in the low phonon energy, moisture-resistant bromide host crystals, neodymium-doped potassium lead bromide (Nd{sup 3+}:KPb{sub 2}Br{sub 5}) and rubidium lead bromide (Nd{sup 3+}:RbPb{sub 2}Br{sub 5}). Laser activity at 1.07 {micro}m was observed for both crystalline materials. Laser operation at the new wavelengths 1.18 {micro}m and 0.97 {micro}m resulting from the {sup 4}F{sub 5/2} + {sup 2}H{sub 9/2} {yields} {sup 4}I{sub J} transitions (J=13/2 and 11/2) in Nd:RPB was achieved for the first time in a solid state laser material. Rare earth- doped MPb{sub 2}Br{sub 5} (M=K, Rb) is a promising candidate for long wavelength infrared applications because of its low phonon frequencies and other favorable features. In principle, Nd{sup 3+}:MPb{sub 2}Br{sub 5} has high potential for laser operation at new wavelengths as well as for the realization of short-wavelength lasing due to upconversion processes.