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During the last decades laser micromachining became a valuable tool for many applications in automotive, medicine, tool construction, or mobile technology. Beside the quality, processing time and production costs are crucial questions. A promising approach to achieve high throughput combined with good processing quality represent laser ablation by an assisting magnetic-field. Therefore, we studied the influence of an applied magnetic field to the ablation behaviour of silicon by using short and ultrashort laser pulses. Based on the experimental results we report on a first theoretical model that addresses the energy distribution of the heated electrons in the irradiated area.

We present a new fabrication method to realize smooth structures in lithium niobate. Therefore a detailed study on laser micro-polishing using ultrashort laser pulses is carried out by separating the effects of spatial pulse overlap and temporal pulse overlap. The adventage of this approach is the smoothing of the processed area by a simultaneous ablation. That will allow ablation depths between 1 µm and 4 µm with rms-roughness values of ≈20 nm.

We compare conventional bursts with GHz bursts in respect of their applicability for surface treatments such as polishing, hardening or surface alloying. It turns out that GHz bursts are more suitable than conventional bursts, especially with respect of energy efficiency and thus for gentle surface treatments with less thermal load for the bulk material. The temporal delay between the pulses is the key factor for surface melting. It is shown that the application of GHz bursts corrects the surface degradation caused by heat accumulation during ablation. This allows a dual process strategy to increase the ablation rates while maintaining the surface quality.

Guiding light is an essential issue in telecommunication or sensor applications, in optical metrology and integrated optic circuits. Each application has different demands on waveguide dimensions, properties, electromagnetic field distribution, and transmission characteristics. Here, we present an overview on different waveguide designs and design criteria, fabrication technologies, as well as selected applications.

In this study, using ultrafast lasers of 10 ps pulse duration as a precise and efficient method for cutting edge preparation is researched. Cutting edge preparation is an important step within cutting tool manufacturing, while unprepared sharp cutting edges show low stability, which leads to tool failure by high mechanical and thermal loads during the turning processes [C. F. Wyen, W. Knapp, and K. Wegener, Int. J. Adv. Manuf. Technol. 59, 899–914 (2012)]. The rounding of the edges requires laser manufacturing with high precision and minimal heat accumulation; thus, ultrafast lasers have been used in other investigations [M. Stolze, T. Herrmann, and J. L'huillier, Proceedings of ICALEO, Orlando, USA, ICALEO, Orlando, FL, October 23–27 (J. Laser Applications, Orlando, 2011)]. In the authors’ study, the effects of edge roundness on the cutting tool material WC-Co alloy were experimentally investigated. Samples with three different grain sizes and percentages of cobalt were used in the authors’ study. The experiments were carried out on the free surfaces of cutting tools under varying laser parameters including laser wavelength, fluence, and spatial pulse overlap (PO) in air or by using process gases (helium and oxygen). The impact of all these different laser parameters on the various material sorts was investigated. As a result, no reduction of the hardness of the original material was observed that could have a negative effect on the cutting ability of laser rounded cutting tools. By analyzing the surface quality of the ablated areas processed with different laser parameters mentioned above, a surface roughness below Ra = 0,15 μm was generated by using optimal fluence at both wavelengths of 1064 nm (IR) and 532 nm (VIS) and using a 70% spatial PO. Thus, a well-defined cutting edge with radii of 20–40 μm could be prepared.

A spintronic bilayer structure of 2-nm Fe and 3-nm Pt grown by molecular beam epitaxy on MgO substrate was evaluated as a viable THz radiation source for different excitation wavelengths and various average pump power levels. We demonstrate that this optimized Fe/Pt structure is an efficient THz emitter for 800-nm and 1550-nm pump wavelengths even with low excitation power.

Recent studies in spintronics have highlighted ultrathin magnetic metallic multilayers as a novel and very promising class of broadband terahertz radiation sources. Such spintronic multilayers consist of ferromagnetic (FM) and non-magnetic (NM) thin films. When triggered by ultrafast laser pulses, they generate pulsed THz radiation due to the inverse spin-Hall effect, a mechanism that converts optically driven spin currents from the magnetized FM layer into transient transverse charge currents in the NM layer, resulting in THz emission. As THz emitters, FM/NM multilayers have been intensively investigated so far only at 800-nm excitation wavelength using femtosecond Ti:sapphire lasers. In this work, we demonstrate that an optimized spintronic bilayer structure of 2-nm Fe and 3-nm Pt grown on 500 {\mu}m MgO substrate is just as effective as a THz radiation source when excited either at {\lambda} = 800 nm or at {\lambda} = 1550 nm by ultrafast laser pulses from a fs fiber laser (pulse width close to 100 fs, repetition rate around 100 MHz). Even with low incident power levels, the Fe/Pt spintronic emitter exhibits efficient generation of THz radiation at both excitation wavelengths. The efficient THz emitter operation at 1550 nm facilitates the integration of such spintronic emitters in THz systems driven by relatively low cost and compact fs fiber lasers without the need for frequency conversion. Accepted version

We present a visually intuitive method for higher-order dispersion compensation based on multi-photon interpulse interference pulse scans. The dispersion values obtained from these scans are fed back as a correction to an acousto-optical programmable dispersive filter to compensate residual higher-order dispersions up to fifth order. This method is applied to the dispersion management of a non-collinear optical parametric chirped-pulse amplifier. A grism-pair stretcher is designed based on a global dispersion balance which provides a large stretching factor and supports a spectral bandwidth of up to 320 nm. It is implemented in a two-stage three-pass non-collinear optical parametric chirped-pulse amplifier and stretches 6-fs seed pulses to about 80 ps from 700 to 1,000 nm. The amplified pulses are compressed by material dispersion. Pulses of less than 10-fs duration with a pulse energy of 125 μJ are obtained at 20-kHz repetition rate.

The mode-locking technique using nonlinear polarization rotation via Type I second-harmonic generation (SHG) is demonstrated on the femtosecond timescale. The narrow spectral bandwidth of the loss modulation was broadened via a double crystal approach, which allows for mode-locking broadband gain media. We prove the predicted advantages of the technique to be correct utilizing intrinsic dispersion compensation and group-velocity mismatch management to produce 193 fs pulses. This eliminates the need for dispersion compensating elements. The technique can be applied to high-power lasers at any wavelength where a suitable SHG process is possible.

A new generation of resonant scanners in the kHz-range shows ultra-high deflection speeds of more than 1000m/s but suffer from an inherent nonlinear mirror oscillation. If this oscillation is not compensated, a typical bitmap, written point by point, would be strongly distorted because of the decreasing spot distance at the turning point of the scanning mirror. However, this can be avoided by a dynamic adaption of the repetition rate (RR) of the ultrafast laser. Since resonant scanners are operated in the 10 kHz-range, this means that the RR has to be continuously swept up to several 10 000 times per second between e.g. 5MHz and 10 MHz. High-speed continuous adaption of the RR could also optimize laser micromachining of narrow curved geometries, where nowadays a time consuming approximation with numerous vectors is required. We present a laser system, which is capable of sweeping the RR more than 32 000 times per second between 5MHz and 10MHz at an average output power of more than 120W at 515nm with a pulse duration of about 40 ps. The laser consists of a semiconductor oscillator, a 3-stage fiber pre-amplifier, a solid state InnoSlab power amplifier and a SHG stage. We systematically analyzed the dynamic of the laser system as well as the spectral and temporal behavior of the optical pulses. Switching the repetition rate typically causes a varying pulse energy, which could affect the machining quality over one scanning line. This effect will be analyzed and discussed. Possible techniques to compensate or avoid this effect will be considered.

A single-mode deep-UV laser at 191.7 nm is demonstrated by seventh-harmonic generation of a single-mode 1342 nm Nd:YVO₄ laser. The fundamental laser is an injection-locked, Q-switched ring laser at 10 kHz pulse repetition frequency. By cascaded second-harmonic and sum-frequency generation, an average power of 230 mW at 191.7 nm is achieved. At 185 mW, the setup features a Gaussian beam with a beam quality factor of M²1.5. A pulse duration of 9 ns with pulse energy fluctuations of σ3% is obtained. The long-term spectral width is approximately 240 MHz full width at half-maximum, measured with a homemade scanning confocal Fabry-Perot interferometer. This work opens possibilities in fiber Bragg grating production, allowing the inscription of long gratings.

Characteristics by laser micromachining of congruent, stoichiometric and doped lithium niobate by using ultrashort laser pulses with different wavelengths from ultraviolet up to infrared were investigated. The ablation thresholds were determined in dependence of c+-side and accordingly c−-side. The strong impact of crystal orientation by micromachining lithium niobate will be additionally shown by the use of a high pulse repetition rate of 1000 kHz. Furthermore, we demonstrate the advantage of processing smooth ridges with high-repetition UV picosecond laser-pulses in combination of post-processing thermal annealing and a low-loss ridge waveguide in congruent LiNbO3 will be demonstrated.

Ridge waveguides in ferroelectric materials like LiNbO3 attended great interest for highly efficient integrated optical devices, for instance, electro-optic modulators, frequency converters and ring resonators. The main challenges are the realization of high index barrier towards the substrate and the processing of smooth ridges for minimized scattering losses. For fabricating ridges a variety of techniques, like chemical and wet etching as well as optical grade dicing, have been investigated in detail. Among them, laser micromachining offers a versatile and flexible processing technology, but up to now only a limited side wall roughness has been achieved by this technique. Here we report on laser micromachining of smooth ridges for low-loss optical waveguides in LiNbO3. The ridges with a top width of 7 µm were fabricated in z-cut LiNbO3 by a combination of UV picosecond micromachining and thermal annealing. The laser processing parameters show a strong influence on the achievable sidewall roughness of the ridges and were systematically investigated and optimized. Finally, the surface quality is further improved by an optimized thermal post-processing. The roughness of the ridges were analysed with confocal microscopy and the scattering losses were measured at an optical characterization wavelength of 632.8 nm by using the end-fire coupling method. In these investigations the index barrier was formed by multi-energy low dose oxygen ion implantation technology in a depth of 2.7 μm. With optimized laser processing parameters and thermal post-processing a scattering loss as low as 0.1 dB/cm has been demonstrated.

Irradiation of focused laser pulses to transparent materials leads to structural changes and can be used for the fabrication of e.g. LED light guiding components. In these applications both small spot sizes and a high lateral resolution in the μm range are absolutely essential. In order to achieve the industrially required throughput of nearly one million laser markings per second, ultrafast lasers with 100 W of average power and pulse repetition frequencies of several MHz are required. Laser machining of polymers additionally necessitates a wide spatial separation of the markings to avoid heat accumulation effects. Therefore, neither commercially available galvanometer based nor Polygon based scanners with their limited scan speed can be used for beam deflection. In our work, we developed an experimental setup based

We demonstrate a continuous wave single-frequency laser at 671.1 nm based on a high-power 888 nm pumped Nd:YVO4 ring laser at 1342.2 nm. Unidirectional operation of the fundamental ring laser is achieved with the injection-locking technique. A Nd:YVO4 microchip laser serves as the injecting seed source, providing a tunable single-frequency power of up to 40 mW. The ring laser emits a single-frequency power of 17.2 W with a Gaussian beam profile and a beam propagation factor of M2

In this paper we report on the realization of a single-mode Q-switched Nd:YVOsub4/subring laser at 1342 nm. Unidirectional and single-mode operation of the ring laser is achieved by injection-locking with a continuous wave Nd:YVOsub4/submicrochip laser, emitting a single-frequency power of up to 40 mW. The ring laser provides a single-mode power of 13.9 W at 10 kHz pulse repetition frequency with a pulse duration of 18.2 ns and an excellent beam quality (Msup2/sup1.05). By frequency doubling of the fundamental 1342 nm laser, a power of 8.7 W at 671 nm with a pulse duration of 14.8 ns and a beam propagation factor of Msup2/sup1.1 is obtained. The 671 nm radiation features a long-term spectral width of 75 MHz.

We report on a parametric Kerr-lens mode-locked 888 nm pumped Nd:YVO4 1342 nm oscillator using cascaded second-order nonlinearities in LBO. Stable ps-pulse-operation was achieved. For an output coupling of T=25% high average output power of 6.5 W, emitting Fourier-limited pulses with a duration of 10 ps was reached. By changing the output coupling to T=10%, we achieved much shorter pulses with a pulse duration of 4 ps for less lower average power of 4.8 W. The beam was diffraction limited with an M2 parameter better than

A degenerate optical parametric oscillator (OPO) using an MgO:PPLN crystal and a volume Bragg grating (VBG) output coupler is presented. By changing the temperature of the VBG, the resonance of the OPO can be tuned exactly on the degeneracy point. A single-longitudinal and a multi-longitudinal mode pump scheme as well as the performance of the optical parametric oscillator on and off degeneracy are compared. It was found that the multi-longitudinal mode pump setup provides superior results with respect to spectral width and stability at degeneracy. At 2128.4 nm, a spectral width of less than 0.7 nm, an output power of 1.7 W with a slope efficiency of 31.8%, and low power fluctuation of 0.3% were achieved.

We present a diode laser pumped continuous wave, pump-enhanced singly-resonant optical parametric oscillator (OPO). The cavity is stabilized by a Pound–Drever–Hall scheme using direct modulation of the diode laser. The system provides stable signal powers of up to 220 mW. The wavelength can be tuned between 1.40–1.60 μm for a ring or a linear cavity design by changing the crystal temperature. The relative fluctuations of the stabilized OPO’s wavelength are less than 10−7 for more than one hour. Using a self-heterodyne technique, we measure a linewidth of the signal wave of 3.5 MHz.

We report on an experimental study of 888 nm pumped, passively mode-locked, high-power Nd:YVO4 lasers with an enhanced cavity design, involving spatial hole burning (SHB) in the active medium. We observed a significant pulse shortening due to the concept of “Gain-at-the end,” despite using long gain length up to 30 mm. A 31.6 W average output power TEM00 Nd:YVO4 oscillator, providing 16.2 ps pulses at an repetition rate of 96 MHz is presented. The pulse duration turns out to be primarily a function of the effective gain length, which can be explained by means of SHB. A further pulse shortening with decreasing gain length down to 9.5 ps at 11.1 W average output power is demonstrated.

We report a highly efficient optical parametric generator (OPG) in lithium triborate (LBO). A frequency-doubled passively mode-locked diode-pumped Nd:YVO4 oscillator amplifier (MOPA) system is used as the pump radiation source. Focussing according to the theory of Boyd and Kleinman leads to a pump power density of 50 GW/cm2, which is well below the damage threshold of LBO of 80 GW/cm2. The overall conversion efficiency reaches a value of 72% measured at degeneracy. The tuning range of the OPG ranges from 760 nm (signal) to 1770 nm (idler) when referring to an overall conversion efficiency of 50%. The beam quality is excellent for conversion efficiencies below 40% (M2

The generation of tunable mid-infrared picosecond laser radiation in a synchronously pumped optical parametric oscillator (OPO) based on periodically poled lithium niobate (PPLN) is reported. Numerical calculations were used to optimize the crystal length in order to balance the parametric gain and the absorption losses in the high-absorption regime of lithium niobate. Due to the numerical results, the system was systematically optimized for the mid-infrared output power. An output power of 1.1 W at 4.5 μm and of more than 3 W at 3 μm were achieved for 6-ps-long pulses with a repetition rate of 160 MHz and an M2

We report on the generation of 267 fs long pulses with a peak power of 661 W emitted by an InGaAs diode laser master-oscillator power-amplifier (MOPA) system with an external grating compressor. The oscillator emits strongly chirped picosecond pulses with several nanometer of bandwidth, which can be amplified without significant phase modulation and are compressed to femtosecond pulses after leaving the amplifier. We used a diode laser module for asymmetric colliding pulse mode-locking and optimized the collision point and the relative intensity of the counter-propagation pulses.

We report on a high-power 888-nm-pumped continuous-wave Nd:YVO4 laser at 1342 nm. An output power of 24 W emitted into a diffraction limited beam with an M 2 parameter better than

This paper reports the generation of fs light pulses by a passively mode-locked InGaAs master oscillator power amplifier (MOPA) system. The laser system generates chirped pulses with 6.2 ps duration, a center wavelength of 922 nm and 4 GHz repetition rate. Pulse compression by an external grating compressor reduces the pulse duration to 580 fs. The average power of the compressed pulses of 851 mW corresponds to a peak power of 366 W.

This paper reports on the generation of picosecond (ps) laser pulses by self-phase-adjusting additive-pulse-mode-locking (PSA) at wavelengths of 0.9 and 1.3 μm. The main objective of this work was to investigate and compare the characteristic optical properties of ps lasers based on different Nd-doped laser crystals like Nd:YAG, Nd:YAlO3, Nd:YVO4 and Nd:GdVO4. As a result of these investigations a mode-locked Nd:YVO4 laser for example, generated, ps pulses at 1.3 μm with a duration of 7 ps, a repetition rate of 160 MHz and an average power of 4.7 W. At 0.9 μm pulses with a duration of 1.9 ps were obtained at a repetition rate of 158 MHz and an average power of 2.8 W.

This paper reports on efficient generation of cw laser radiation at 0.9 and 1.3 μm in different neodymium doped laser hosts. The thermal, mechanical and optical properties as well as the laser performance of Nd:YAG, Nd:YAlO3, Nd:YVO4 and Nd:GdVO4 are studied in numerical simulations as well as in experimental investigations. For example an output power of more than 4.0 W is generated in Nd:YVO4 at the 914 nm 4F3/2→4I9/2 transition using a pump power of 19 W. In Nd:GdVO4 more than 6.0 W are obtained at the 1342 nm 4F3/2→4I13/2 laser transition by using a pump power of 19.3 W. The spatial beam quality of both lasers is diffraction limited with an M2 value of less than 1.1.

The amplification of ps and fs pulses with peak powers of up to 4.5 kW has been investigated in a single quantum well InGaAs tapered amplifier. The pulses with durations of 100 fs or 2 ps were generated by a modelocked titanium–sapphire laser. The amplified pulses indicate strong gain saturation and carrier generation due to photon absorption in the laser active region which causes a temporal broadening of the amplified pulses as well as modifications of the optical spectrum. The gain recovery time was measured by a pump–probe experiment. The experimental results are analyzed with respect to the sub-ps gain dynamics which is described by a relaxation time approximation.

We present an improved Schlieren method to measure the optical quality of crystals, defined by it’s optical homogeneity and the surface roughness of it’s facets. The method is based on a combination of Schlieren, interferometric and tilting angle measurements. It is especially appropriate for the optical characterization of crystals with small clear apertures. The theory and an application of this improved technique on a BIBO crystal are given. Spatial resolution and sensitivity of the method are mainly defined by the Schlieren setup, which offers a spatial resolution as high as 27 μm and a minimum deflection angle as low as 2.3×10-6.

We report on a frequency resolved optical gating (FROG) system which allows the reconstruction of amplitude and phase of picosecond pulses generated by mode-locked diode laser oscillators and amplifiers. The main challenge of developing such a FROG system is the required high spectral resolution. In the spectrometer a cylindrical grating with 1200 lines/mm and a radius of curvature of 3 m is used. A width of the illuminated area of 15 cm provides in a spectral resolution exceeding 2 GHz (1.4 pm) at 460 nm. The FROG system is, thus, well suited for analyzing ps-pulses with durations of up to 80 ps and a corresponding fourier-limited spectral width of 0.017 nm.

We report on a non-collinear, 1064 nm pumped, 10 kHz repetition rate ns-OPO which consists of a 13 mm long periodically poled lithium niobate (PPLN) crystal in a hemispherical optical cavity. The non-collinear phase-matching is achieved by tilting the domains by 60° with respect to the pump beam. This phase-matching avoids back conversion of signal and idler radiation into pump radiation and thus improves the spatial quality of the generated OPO radiation considerably. At a pump power of 5.5 W the OPO provided a conversion efficiency of up to 34%. The generated OPO pulses with a total power of up to 1.85 W were emitted in an almost diffraction limited beam with a M2-value of 1.1. The beam quality did not change when the pump power was varied in the range of 2–5 W.

This paper reports on a mode-locked InGaAs master oscillator power amplifier (MOPA) system that generates at 920 nm 14-ps-long pulses with a repetition rate of 4.3 GHz and an average power of 2.7 W. Single-pass frequency doubling in a periodically poled KTP crystal provides 550 mW of blue 460-nm radiation. The power of the blue output, which corresponds to a conversion efficiency of more than 20%, was optimized by a detailed investigation of the influence of various system parameters like injection current and repetition rate on pulse power, pulse duration, and spectral shape of the infrared laser pulses.

We present a concept for a femtosecond laser based on a passively mode-locked semiconductor diode laser and a tapered amplifier. The absorption in the monolithically integrated quantum well absorber is controlled by a reverse voltage bias. Excellent mode-locking stability was observed without any rf modulation applied to gain current or absorber voltage. To avoid fast gain saturation and strong nonlinear pulse distortions within the tapered amplifier the technique of chirped pulse amplification is applied. In contrast to common chirped pulse amplification setups the oscillator emits pre-chirped pulses and a stretcher stage can be omitted. A pulse duration of 267 fs was achieved after compression in the colliding pulse mode-locking regime. For the first time we adapted this technique to the generation of tailored chirped pulses and investigated the influence of the collision point in an asymmetric two-section oscillator. This diode laser system is suited as a ultrafast pulse source for high power bulk or fiber amplifiers and paves a road to highly integrated laser systems.

We report on the influence of self-focusing and self-defocusing in the phase-mismatched frequency doubling crystal on the third harmonic generation (THG) efficiency in a two crystal frequency tripling scheme. By detuning the temperature of the doubling crystal, the impact of a phase-mismatch in second harmonic generation (SHG) on the subsequent sum frequency mixing process was investigated. It was found that adjusting the temperature not only affected the power ratio of the second harmonic to the fundamental but also the beam diameter of the fundamental beam in the THG crystal, which was caused by self-focusing and self-defocusing of the fundamental beam, respectively. This self-action was induced by a cascaded χ(2) : χ(2) process in the phase-mismatched SHG crystal. Self-defocusing was observable for positive detuning and self-focusing for negative detuning of the phase-matching temperature. Hence, the THG efficiency was not symmetric with respect to the point of optimum phase-matching. Optimum THG was obtained for positive detuning and the resulting self-defocusing in combination with the focusing lens in front of the THG stage was also beneficial for the beam quality of the third harmonic.

We report on the creation of Fiber Bragg Gratings (FBGs) based sensors in large mode area (LMA) fibers. By using a quintupled Nd:YVO4 laser at 213 nm wavelength, FBGs are produced in conventional double clad fibers with core diameters of up to 50 µm. Bragg wavelength shifts depending on applied tensile strain as well as temperature changes are recorded and operating ranges of strain sensors identified. The ease of coupling with light sources into LMA fibers as well as their comparatively elevated robustness makes them promising sensor solutions for harsh environments.

In this study, ps-laser micromachining of different types of metals like copper, aluminum, titanium, tungsten and zinc have been investigated. Their single-pulse damage thresholds for the laser wavelengths of 355 nm, 532 nm and 1064 nm were experimentally determined. The laser-induced surface morphology both in the low and high fluence regime, as well as in the transition area, were examined for all investigated metals by scanning electron microscopy. Single pulse experiments and multi-pulse ablation experiments for up to 6 pulses using time-delays between successive pulses of 1 s and 20 ns were carried out. Our observations show that the surface morphologies significantly change from single-pulse ablation to the application of a second pulse. By comparing different separation times in the multi-pulse experiments we show that the burst-mode in ps-laser processing accumulates heat. This results in strong arising melting films, smoothing of the ablation craters and melt splashes outside of the crater. We found out, that copper and aluminum as well as titanium and zinc show similar ablation behavior by using the burst mode.

A new transversal pumping scheme of fiber lasers based on the optimized manufacturing of an array of large scale ridge waveguides in fused silica is presented. Moreover their application as directional couplers interacting with a double clad optical active fiber for laser application is discussed. Conventional broad area emitters without slow axis collimation (SAC) can be used to couple light (wavelength λp = 976 nm) into the waveguide array.

With the advent of high power and narrow bandwidth 969 nm pump diodes, direct pumping into the upper laser level of Yb:YAG and hence quasi-2-level lasers became possible. Pumping directly into the emitting level leads to higher quantum efficiency and reduction of non-radiative decay. Consequently, thermal load, thermal lensing and risk of fracture are reduced significantly. Moreover pump saturation and thermal population of uninvolved energy-levels in ground and excited states are benefical for a homogenous distribution of the pump beam as well as the reduction of reabsorption loss compared to 3-level systems, which allows for high-power DPSS lasers. Beside continuous-wave (cw) operation, nanosecond pulses with a repetition rate between 1 and 5 kHz are an attractive alternative to flashlamp-pumped systems (10-100 Hz) in various measurement applications that require higher data acquisition rates because of new faster detectors. Based on measurements of the absorption and a detailed numerical model for pump beam distribution, including beam propagation and saturation factors, power-scaling of a ceramic rod Yb:YAG oscillator was possible. Finally a cw output power of 50 W with 33 % pump efficiency at 1030 nm has been demonstrated (M2 < 1.2). Nanosecond pulses have been produced by cavity-dumping of this system. The cavity-dumped setup allowed for 3-10 ns pulses with a pulse energy of 12.5 mJ at 1 kHz (M2 < 1.1). In order to achieve these results a systematic experimental and numerical investigation on gain dynamics and the identification of different stable operating regimes has been carried out.

We present mode-locking via nonlinear polarization rotation (NPR) in Yb:YAG. Intrinsic dispersion compensation via negative SPM and normal dispersion in the NPR crystal allowed for 193 fs pulses. The group-velocity-mismatch effects allowed for adjusting the pulse duration between 193 fs - 1 ps.

By detuning the phase-matching temperature of the SHG crystal, cascaded Chi(2)-processes play an important role in the optimization of a two crystal frequency tripling setup. Self-action of the fundamental is beneficial for the THG efficiency and beam quality.

Optical rectification of femtosecond pulses in nonlinear materials is an efficient method to generate ultra-short terahertz (THz) pulses in a wide frequency range extending from 100 GHz to well above 10 THz. Lithium niobate (LN) is well suited for such a purpose despite the high absorption in the THz range. In this part we will focus on the various experimental realizations to produce THz radiation in bulk, periodically, aperiodically and two-dimensionally poled LN. The possible bandwidth, tunability and the techniques to overcome the high absorption will be discussed as well.

We present a temperature-dependent Sellmeier equation for the extraordinary refractive index of 5 mol % MgO doped congruent lithium niobate. This equation is adapted for wavelengths in the range of 1.3–5 μm and temperatures between 40 °C and 200 °C. The calculation of the appropriate Sellmeier coefficients is based on the wavelengths of the signal and idler radiation measured for quasi-phase-matched optical parametric generators excited by 10-ns-long, 1064-nm pulses of a Q-switched Nd:YVO4 laser.