High-power two-cycle ultrafast source based on hybrid nonlinear compression

Abstract

We demonstrate a hybrid dual-stage nonlinear compression scheme, which allows the temporal compression of 330 fs-pulses down to 6.8 fs-pulses, with an overall transmission of 61%. This high transmission is obtained by using a first compression stage based on a gasfilled multipass cell, and a second stage based on a large-core gas-filled capillary. The source output is fully characterized in terms of spectral, temporal, spatial, and short-and long-term stability properties. The system's compactness, stability, and high average power makes it ideally suited to drive high photon flux XUV sources through high harmonic generation. IntroductionFew-cycle laser sources are the subject of intense research efforts worldwide since they allow efficient high-harmonic generation (HHG) and the emission of isolated attosecond pulses. This results in compact and highly coherent radiation sources in the extreme ultraviolet (XUV) and soft X-ray ranges, with a rapidly increasing number of scientific and industrial applications such as ultrafast spectroscopy, nanoscale imaging, and attosecond science [1-3]. Laser sources based on titanium-doped sapphire (Ti:Sa) have, for a long time, been almost exclusively used to drive the HHG process and to pioneer attosecond physics. The pulse duration typically available from such lasers is 25 fs, so that a single stage of nonlinear compression in a gas-filled capillary result in few-cycle pulses [4]. Despite extraordinary material properties such as gain bandwidth and thermal conductivity, Ti:Sa systems suffer from the short upper state lifetime, their large quantum defect and the fact that they must be pumped with high brightness green lasers. This limits the efficiency, output average power, and prevents repetition rate scaling to drive strong field physics experiments.Laser physicists have been working on more efficient and power scalable ultrafast sources for strong field physics for over a decade. In particular, optical parametric chirped pulse amplifier systems appear as a particularly promising solution [5,6], since they can deliver extremely short pulses in various wavelength ranges and are less impacted by thermal effects because they are based on a non-resonant nonlinear process. However, in order to obtain good spatial and temporal quality, the energy transfer from the pump to the signal is around 10%, so that the pump laser energy must be scaled accordingly, with stringent requirements in terms of spatial and temporal quality.Currently, the most mature and powerful ultrafast source technology is undoubtedly ytterbium-based systems, with average power levels beyond 1 kW [7-9] and numerous industrial applications. These lasers have been used to drive the HHG process as early as 2009 [10], but the long pulse duration delivered by these sources (300 fs -2 ps) limits their relevance to this application field. Therefore, nonlinear compression setups have been used successfully to reduce the pulse duration and obtain XUV photon flux among the highest ever reported for HHG-based sources [11...

Multipass cells: 1D numerical model and investigation of spatio-spectral couplings at high nonlinearity

“…Recently, multipass cells (MPC) either including a bulk medium [6] or filled with a rare gas [7][8][9] have been used to perform nonlinear temporal compression of femtosecond pulses in various regimes (normal dispersion [6][7][8][9], soliton compression in anomalous dispersion [10]), in a large range of pulses energies (from µJ [6,11] to mJ [7,9]), and output pulse durations (from >100 fs [6] to few cycles [10,12]). In all these demonstrations, it was observed that the MPC essentially acts like a 1D nonlinear object, with negligible impact of the nonlinearity on the spatial properties of the beams.…”

The amazing progress of high-power ultrafast thin-disk lasers

“…Ongoing efforts to improve the quality of this and other Yb-doped broadband gain materials are expected to bring further improvements to the achievable levels. In parallel to these efforts, large progress has been made in finding paths for efficient external pulse compression of these high-average power laser systems using hollow-core fibers [48], multi-pass cells [49][50][51][52], hybrid setups including multi-plate compressors [53], and even spectral broadening in the amplifier itself [54] bringing these applications one step closer. Additionally, as the pulse durations from these systems keeps getting shorter and approach the few-cycle regime, carrier-envelope phase control becomes increasingly relevant, in particular for high-power oscillators which can be used as powerful seeds for booster amplifiers [55,56].…”

“…Whereas the latest obtained results still remain moderate for the thin-disk geometry (13 W) [58], this represents an important first milestone in the potential direct generation of high-power few-cycle pulses at high average power. Furthermore, external pulse compression obviously allows for reaching few-fs pulse durations even starting from the (sub-) picosecond regime [51,52]. Finally, extending the wavelength coverage available from TDLs to longer wavelengths also represents a very promising research direction for ultrafast thin-disk oscillators and amplifiers, which would expand the application possibilities of these sources even further.…”

Multioctave supercontinuum generation and frequency conversion based on rotational nonlinearity

“…Shorter driving pulses allow exposure of the neutral gas atoms to higher laser intensities, or, alternatively, the use of heavier gases with larger n 2 , both resulting in larger nonlinear phase shifts  nl (t) ∝ n 2 I(t). To this end, substantial effort has been invested into the development of few-cycle laser amplifiers (13,14) and two-stage compression schemes (15)(16)(17), which mitigate the effects of ionization and plasma generation on the efficiency and compressibility of broad supercontinuum spectra.…”