We demonstrate a compact diode-pumped Yb:KGW femtosecond oscillator-Yb:YAG Innoslab amplifier master oscillator power amplifier (MOPA) with nearly transform-limited 636 fs pulses at 620 W average output power, 20 MHz repetition rate, and beam quality of M(x)(2) = 1.43 and M(y)(2) = 1.35. By cascading two amplifiers, we attain an average output power of 1.1 kW, a peak power of 80 MW, and a 615 fs pulse width in a single linearly polarized beam. The power-scalable MOPA is operated at room temperature, and no chirped-pulse amplification technique is used.
We demonstrate a scheme for nonlinear pulse compression at high average powers based on self-phase modulation in a multi-pass cell using fused silica as the nonlinear medium. The scheme is suitable for compression of pulses with peak powers exceeding the threshold for critical self-focusing. At >400 W of input power, the pulses of a Yb:YAG-Innoslab laser system (10 MHz repetition rate, 850 fs pulse duration) are spectrally broadened from 1.6 to >13.5 nm bandwidth while maintaining almost diffraction-limited beam quality. The chirp is removed with a dispersive mirror compressor, and pulse durations of 170 fs at an output power of 375 W are achieved. The compression unit reaches an overall transmission of >90%.
The Innoslab design, already established for neodymium doped laser crystals, was applied to ytterbium doped laser materials. Recent progresses in brightness of high power diode lasers facilitate efficient pumping of quasi-three-level laser materials. Innoslab amplifiers are compared to competing thin-disk and fiber fs-amplifiers. A compact diode-pumped Yb:YAG Innoslab fs-oscillator-amplifier system, scalable to the kilowatt range, was realized. Numerical simulations result in conditions for high efficiency and beam quality. Nearly transform and diffraction limited 680 fs pulses at 400 W average output power and 76 MHz repetition rate without using CPA technology have been achieved at room temperature so far.
The Innoslab amplifier comprises a diode-laser partially end-pumped thin slab crystal and a folded single-pass optical amplification path. While this configuration differs in many respects from other slab amplifiers, it shares characteristics with partially end-pumped rod amplifiers. It combines outstanding thermal management, efficiency, and beam quality in the 100 W to 1 kW power range. In this paper, we review amplifiers for a wide range of operation regimes and laser materials.
We report on single-pass high-harmonic generation (HHG) with amplified driving laser pulses at a repetition rate of 20.8 MHz. An Yb:YAG Innoslab amplifier system provides 35 fs pulses with 20 W average power at 1030 nm after external pulse compression. Following tight focusing into a xenon gas jet, we observe the generation of high-harmonic radiation of up to the seventeenth order. Our results show that state-of-the-art amplifier systems have become a promising alternative to cavity-assisted HHG for applications that require high repetition rates, such as frequency comb spectroscopy in the extreme UV.
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...
Laser-dressed photoelectron spectroscopy, employing extreme-ultraviolet attosecond pulses obtained by femtosecond-laser-driven high-order harmonic generation, grants access to atomic-scale electron dynamics. Limited by space charge effects determining the admissible number of photoelectrons ejected during each laser pulse, multidimensional (i.e. spatially or angle-resolved) attosecond photoelectron spectroscopy of solids and nanostructures requires high-photon-energy, broadband high harmonic sources operating at high repetition rates. Here, we present a high-conversion-efficiency, 18.4-MHz-repetition-rate cavity-enhanced high harmonic source emitting 5 × 105 photons per pulse in the 25-to-60-eV range, releasing 1 × 1010 photoelectrons per second from a 10-µm-diameter spot on tungsten, at space charge distortions of only a few tens of meV. Broadband, time-of-flight photoelectron detection with nearly 100% temporal duty cycle evidences a count rate improvement between two and three orders of magnitude over state-of-the-art attosecond photoelectron spectroscopy experiments under identical space charge conditions. The measurement time reduction and the photon energy scalability render this technology viable for next-generation, high-repetition-rate, multidimensional attosecond metrology.
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