Research
|
Generation and Applications of Terawatt-Peak-Power Single-Cycle Infrared Fields In this project, we pursue a hybrid OPCPA/filamentation scheme to realize a terawatt-peak-power single-cycle IR source. Such an IR source will find numerous intriguing applications in attosecond and high-field science including the production of attosecond XUV/soft-X-ray pulses by high-harmonic generation (HHG), tomographic imaging of molecular orbitals (making the "molecular movie"), laser-induced electron diffraction, and attosecond spectroscopy on solid surfaces. Most importantly, HHG driven by multi-mJ few-cycle IR sources holds great promise for the realization of bright coherent sources in the soft- and potentially even hard-X-ray region.
1. Infrared Optical Parametric Chirped-Pulse Amplification (OPCPA) Our four-stage IR OPCPA is based on a fusion of femtosecond diode-pumped solid-state (DPSS) Yb:KGW technology and a picosecond 100-mJ Nd:YAG pump amplifier. The front-end shown in Figure 1, a two-stage optical parametric amplifier (OPA) driven by a femtosecond Yb:KGW master-oscillator power amplifier (MOPA), delivers carrier-envelope phase (CEP)-stable 4-μJ pulses at 1.5 μm signal wavelength (for details, see Ref. [1]). In the amplification stages 2-4, we use Type-II parametric amplification in KTP crystals.
Fig.1: CEP-stable two-stage OPA seed source driven by a femtosecond Yb:KGW MOPA. In the power-amplification stages 3 and 4 (see Ref. [2]) depicted in Figure 2, the CEP-stable 1.5-μm pulses are boosted from the μJ-level up to pulse energies exceeding 10 mJ before recompression.
Fig.2: Booster amplification stages 3 and 4 pumped by a 100-mJ Nd:YAG amplifier. An IR DAZZLER is used for programmable higher-order dispersion compensation. Figure 3 shows SHG-FROG characterization data of recompressed 3.5-mJ, 1.57-μm pulses with 62 nm bandwidth from our four-stage IR OPCPA. The measured 74.4-fs pulse duration is close to the transform limit (TL) of 72.6 fs.
Fig.3: SHG-FROG characterization of the 20-Hz four-stage IR OPCPA.
2. Spectral broadening and pulse self-compression via filamentation in noble gases For many applications in attosecond science, in particular for the generation of isolated attosecond XUV/soft-X-ray pulses, few-cycle driver waveforms are required. To achieve few-cycle durations, we spectrally broaden the multi-mJ 1.5-μm pulses from the IR OPCPA by filamentation in noble gases. When a sufficiently intense ultrashort pulse propagates in a noble gas, a self-guiding channel ("filament") can occur due to the balance between self-focusing by the nonlinear Kerr effect and defocusing by the plasma created by multi-photon ionization. During the nonlinear propagation, the pulse spectrum can be significantly broadened. In Figure 4, the filament channel can nicely be seen through the output window by the blue 5th harmonic created within the filament channel.
Fig.4: Filamentation of recompressed 1.4-mJ 1.57-μm pulses in xenon at 0.5 atm. In argon and krypton, we have generated ~3-mJ 600-nm wide IR supercontinua of high spatial quality supporting 8-fs pulse durations, which corresponds to less than two optical cycles at 1.5 μm [3]. The filamentation regime involving plasma-induced pulse self-compression is particularly attractive for the pursuit of a terawatt-peak-power single-cycle IR source. By lowering the input pulse energy and tuning the gas pressure in the cell, we achieved the regime of pulse self-compression. In the experiment shown in Fig. 5, CEP-stable 2.2-mJ 74.4-fs 1.57-μm input pulses were compressed in a single filament in argon down to a 19.8-fs duration. This represents a temporal compression of the input pulses by a factor of ~4. The output pulse energy was 1.5 mJ, corresponding to the energy throughput of 66% [2,3].
Fig.5: SHG-FROG data of 1.5-mJ pulses self-compressed in argon at 5 bar to a 19.8-fs pulse duration. The corresponding Wigner distribution function in Fig. 6 reveals a rather flat spectral phase over the whole pulse bandwidth.
Fig. 6: Wigner distribution functions computed from the SHG-FROG data in Fig. 5. The grey curve indicate the retrieved group delay (GD). The panels above and on the right indicate the temporal intensity profile and pulse spectrum, respectively. In the coming months, we want to use these CEP-stable multi-mJ IR pulses in long-wavelength HHG experiments and for attosecond surface spectroscopy. The project is funded by the Austrian Science Fund (FWF).
References [1] O. D. Mücke, D. Sidorov, P. Dombi, A. Pugžlys, A. Baltuška, S. Ališauskas, V. Smilgevičius, J. Pocius, L. Giniūnas, R. Danielius, and N. Forget [2] O. D. Mücke, S. Ališauskas, A. J. Verhoef, A. Pugžlys, A. Baltuška, V. Smilgevičius, J. Pocius, L. Giniūnas, R. Danielius, and N. Forget [3] O. D. Mücke, S. Ališauskas, A. J. Verhoef, A. Pugžlys, V. Smilgevičius, J. Pocius, L. Giniūnas, R. Danielius, and A. Baltuška [4] O. D. Mücke, S. Ališauskas, A. J. Verhoef, A. Pugžlys, A. Baltuška, V. Smilgevičius, J. Pocius, L. Giniūnas, R. Danielius, and N. Forget, Toward TW-Peak-Power Single-Cycle IR Fields for Attosecond Physics and High-Field Science, in Advances in Solid-State Lasers: Development and Applications, edited by M. Grishin, 279 (INTECH, 2010, ISBN 978-953-7619-80-0). Information View Download Latest update March 2010 |
