Multipass spectral broadening of 18  mJ pulses compressible from 13  ps to 41  fs

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

“…This 3D Bintegral is calculated by taking the on-axis value divided by 2, which should be equal to the average value of the 1D model in the case of perfect Gaussian beam and homogenization. Although it might be surprising that this very large nonlinearity does not induce significant spatio-spectral couplings [19], it has also been observed experimentally that a B-integral per roundtrip of 2.4 rad does not result in the onset of spatio-spectral couplings in intensity, as revealed by an imaging spectrometer characterization [9]. We would like to point out that this is in contradiction with the result reported at the end of our earlier report [15] that showed a rapid increase of the spatio-spectral coupling for the concentric configuration as the nonlinearity is increased.…”

“…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.…”

Spectral compression in a multipass cell

“…A solid or gas nonlinear medium is inserted inside the cell, allowing easy tuning of the nonlinearity level through the gas pressure or bulk medium thickness, while dispersion properties may be easily tailored through appropriate mirrors coatings. This concept has been used mostly to implement temporal compression in a wide range of pulse energies and durations [13][14][15][16][17]. In the case of experiments that make use of a bulk medium inserted in the MPC the peak power scaling is not limited by the critical power because the pulses exit the nonlinear medium before catastrophic collapse at each pass.…”