The resolution of ultrafast studies performed at extreme ultraviolet and X-ray free-electron lasers is still limited by shot-to-shot variations of the temporal pulse characteristics. Here we show a versatile single-shot temporal diagnostic tool that allows the determination of the extreme ultraviolet pulse duration and the relative arrival time with respect to an external pump-probe laser pulse. This method is based on time-resolved optical probing of the transient reflectivity change due to linear absorption of the extreme ultraviolet pulse within a solid material. In this work, we present measurements performed at the FLASH free-electron laser. We determine the pulse duration at two distinct wavelengths, yielding (184 ± 14) fs at 41.5 nm and (21 ± 19) fs at 5.5 nm. Furthermore, we demonstrate the feasibility to operate the tool as an online diagnostic by using a 20-nm-thin Si 3 N 4 membrane as target. Our results are supported by detailed numerical and analytical investigations.

The pulse duration, and, more generally, the temporal intensity profile of free-electron laser (FEL)\ud pulses, is of utmost importance for exploring the new perspectives offered by FELs; it is a nontrivial\ud experimental parameter that needs to be characterized. We measured the pulse shape of an extreme\ud ultraviolet externally seeded FEL operating in high-gain harmonic generation mode. Two different methods\ud based on the cross-correlation of the FEL pulses with an external optical laser were used. The two methods,\ud one capable of single-shot performance, may both be implemented as online diagnostics in FEL facilities.\ud The measurements were carried out at the seeded FEL facility FERMI. The FEL temporal pulse\ud characteristics were measured and studied in a range of FEL wavelengths and machine settings, and they\ud were compared to the predictions of a theoretical model. The measurements allowed a direct observation of\ud the pulse lengthening and splitting at saturation, in agreement with the proposed theory

Extreme-ultraviolet to x-ray free-electron lasers (FELs) in operation for scientific applications are up to now single-user facilities. While most FELs generate around 100 photon pulses per second, FLASH at DESY can deliver almost two orders of magnitude more pulses in this time span due to its superconducting accelerator technology. This makes the facility a prime candidate to realize the next step in FELs-dividing the electron pulse trains into several FEL lines and delivering photon pulses to several users at the same time. Hence, FLASH has been extended with a second undulator line and self-amplified spontaneous emission (SASE) is demonstrated in both FELs simultaneously. FLASH can now deliver MHz pulse trains to two user experiments in parallel with individually selected photon beam characteristics. First results of the capabilities of this extension are shown with emphasis on independent variation of wavelength, repetition rate, and photon pulse length.

Applications in life sciences and information technology require all-optical solutions. In the inevitable race towards miniaturized optical circuits, all-integrated solutions will prevail against bulk setups. Because of its outstanding nonlinear properties, lithium niobate (LiNbO3) emerged as the key platform for integrated optics. In this paper, we discuss the direct femtosecond (fs) laser inscription technique whose flexibility enables the realization of two- and three-dimensional embedded optical waveguides in various optical materials. Linear and nonlinear components for monolithic and hybrid waveguide devices are characterized and their perspectives are reviewed, e.g. couplers, Bragg reflectors, frequency converters, amplitude modulators and gain modules. Finally, we demonstrate a monolithic LiNbO3 waveguide chip that combines a frequency doubling and a modulating unit. Thumbnail image of Schematic of a hybrid fs laser written chip that comprises a rare-earth-doped laser section (a), a frequency doubling unit (b), Bragg reflectors (c), waveguide splitters (d) and an amplitude modulator (e)

We report on a Yb:YAG Innoslab laser amplifier system for generation of subpicsecond high energy pump pulses for optical parametric chirped pulse amplification (OPCPA) at high repetition rates. Pulse energies of up to 20 mJ (at 12:5 kHz) and repetition rates of up to 100 kHz were attained with pulse durations of 830 fs and average power in excess of 200 W. We further investigate the possibility to use subpicosecond pulses to derive a stable continuum in a YAG crystal for OPCPA seeding. © 2011 Optical Society of America OCIS codes: 140.4480, 190.4410, 190.4970. High repetition rate free electron lasers (FELs) [1], attosecond metrology [2], and coherent control [3] are examples of applied physics fields that require stable laser amplifier systems with very high repetition rates, high pulse energies, and ultrashort pulse durations. Free electron lasers such as FLASH would tremendously benefit when combining extreme UV (XUV) pulses and a laser amplifier with millijoule-level pulse energies, 5-20 fs pulse duration, and an intraburst repetition rate of 0:1-1 MHz to perform pump-probe experiments. Another application is the FEL seeding with similar pulse parameters [4]. Such a state-of-the-art laser system is difficult to develop, most of all because of the additional longterm stability requirements for operation at large scale facilities [5]. Optical parametric chirped pulse amplification (OPCPA) [6,7] is to date the only technique to offer a way to amplify broadband pulses at high pulse energies with several hundreds of watts average power level. An increase of the average output power of an OPCPA system requires novel concepts for the pump amplifier system. Experimental OPCPA pump amplifiers have been successfully used, either to amplify pulses at low repetition rates and high peak powers [8,9] or high repetition rates and lower pulse energies [10,11]. An avenue in the multikilohertz repetition rate regime is the regenerative thin-disk amplifier that can provide millijoule pulse energy in the picosecond regime [12]. The concept has its limitations at high average powers given by difficult cavity outcoupling. Fiber chirped pulse amplification (CPA) laser amplifiers have emerged to be powerful tools for amplification to highest average powers of up to 830 W at femtosecond pulse durations [13,14]. However, combining the fiber laser amplifier with a Yb:YAG Innoslab amplifier [15] is a promising approach to push the average power beyond the kilowatt level with multimilljoule pulse energies. A striking advantage of this amplifier combination is the attainable subpicosecond pulse duration, avoiding complicated and lossy stretcher-compressor schemes for OPCPA [16]. Recent developments have also shown the potential to use a subpicosend pump amplifier driven continuum [17] generated in bulk media to seed optical parametric amplification (OPA) [18]. Additionally, higher peak intensities can be used to drive the OPCPA system due to the inherent scaling of the damage threshold with shorter pulse duration [19]. The current st...

High harmonic generation (HHG) is a central driver of the rapidly growing field of ultrafast science. We present a novel quasiphase-matching (QPM) concept with a dual-gas multijet target leading, for the first time, to remarkable phase control between multiple HHG sources (>2) within the Rayleigh range. The alternating jet structure with driving and matching zones shows perfect coherent buildup for up to six QPM periods. Although not in the focus of the proof-of-principle studies presented here, we achieved competitive conversion efficiencies already in this early stage of development.

An Yb:YAG thin-disk multipass laser amplifier system was developed operating in a 10 Hz burst operation mode with 800 µs burst duration and 100 kHz intra-burst repetition rate. Methods for the suppression of parasitic amplified spontaneous emission are presented. The average output pulse energy is up to 44.5 mJ and 820 fs compressed pulse duration. The average power of 4.45 kW during the burst is the highest reported for this type of amplifier.

The potential of borate crystals, BBO, LBO and BiBO, for high average power scaling of optical parametric chirped-pulse amplifiers is investigated. Up-to-date measurements of the absorption coefficients at 515 nm and the thermal conductivities are presented. The measured absorption coefficients are a factor of 10-100 lower than reported by the literature for BBO and LBO. For BBO, a large variation of the absorption coefficients was found between crystals from different manufacturers. The linear and nonlinear absorption coefficients at 515 nm as well as thermal conductivities were determined for the first time for BiBO. Further, different crystal cooling methods are presented. In addition, the limits to power scaling of OPCPAs are discussed.