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Contact person |
Bálint Kiss |
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The MIR laser emits extremely short (few optical cycle) light pulses in the mid-infrared around 3 µm wavelength at a very high repetition rate of 100 kHz. One very important feature is that the pulses are “phase-stable”, meaning that the phase of the actual electric field is almost the same for each shot and can be set to the desired value via a precise control system.
The MIR laser proposes a combination of unique parameters whose relevance depends on the experiments. The unusual wavelength of 3.2 µm allows to benefit from the power scaling laws (λN) specific to strong field physics like for instance the extension of the harmonics plateau varying like (λ2) in High Order Harmonic Generation (HHG). Equivalently, during the interaction with the high intensity laser, electrons from atoms or molecules experience a quiver motion and acquire an energy proportional to the ponderomotive energy scaling again like . Therefore, the MIR laser long wavelength allows to produce high-photon energy as well as high-electron energy for high harmonics spectroscopy or light induced electron diffraction (LIED).
The very high repetition rate of 100 kHz allows to record data on extremely short times with very good statistics while the stability of the system provides potential for long acquisitions of very low cross-section phenomena. Finally, the post-compressed version down to below 2 cycles together with stable CEP (carrier-envelope phase) is very well adapted to the excitation of semiconductor crystals for the study of CEP sensitive HHG in solids.
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The MIR system has been delivering 140 µJ, 4-cycle pulses centred at 3.2 µm at 100 kHz repetition rate with < 1% RMS stability over 8+ hours of operation per day since November 2017 (Fig. 1). The system has unique c.a. 100 mrad CEP stability together with precise CEP control during experiments [1].
Schematic layout of the MIR System
The output parameters are shown in Table 1. The energy can be varied continuously from 0 µJ to 90 µJ via a pair of wire grid polarizers. The CEP target can be adjusted continuously between 0 and 2 π. The pulse duration can be optimized on-target via the pulse shaper or via material dispersion.
| Typical parameters after beam delivery* | Tuning range | |
| Peak power | >2.4 GW | 0 - 2.1 GW |
| Pulse energy | >120 µJ | 0 – 90 µJ** |
| Pulse duration | <50 fs (4.8 optical cycles) | 42 fs - 150 fs (negatively chirped) |
| Repetition rate | 100 kHz | not tunable |
| CEP stability | <150 mrad | Setpoint: 0 - 2 π |
| Energy stability | <1.0% RMS | not tunable |
| Strehl ratio | >0.7 | not tunable |
| Central wavelength | 3200±30 nm (optimal) | 2500 nm - 3900 nm*** |
| Beam pointing | 5% of total divergence | not tunable |
| Beam profile | Gaussian, 14 mm diameter, s or p-pol | 6 to 30 mm, s or p-pol |
Table 1: Measured laser parameters
*By taking into account the optical losses related to beam steering and manipulation (telescoping, periscope/dogleg, chirp compensation and/or sampling for in-line diagnostics) required for user experiments in general.
**Via pair of wire grid polarizers.
***Upon detuning the central wavelength, the available power is in the ~4-9 W regime with ~2.5 % stability, and the compressed pulse duration increases to the ~150 fs range. Active CEP stabilisation is available based upon best effort.
Figure 2: TIPTOE measured and reconstructed ionization yield (top) and deduced pulse profile (bottom) of the MIR OPCPA after beam delivery. It corresponds to 4.4 optical cycles at 3.2 µm.
Figure 3: MIR OPCPA output pulse energy plot over a day of operation (19/01/2023).
Post-compressed sub-2-cycle output
The pulses of the MIR OPCPA are compressed below 2-cycles in a compact post-compression stage [2]. Spectral broadening is performed in mm-thick dielectric (BaF2) and semiconductor (Si) windows in a confocal geometry, followed by recompression in bulk dielectric (BaF2/CaF2) windows/wedges combined with custom dispersive mirrors. We provide sub-2-cycle pulses (Fig. 4) with energies up to 75 µJ (7.5 W) with long-term CEP (240 mrad) and power stability (2%) for several hours without interruption (see Fig. 5). The parameters are listed in Table 2 below.
Figure 4: TIPTOE measured and reconstructed ionization yield (top) and deduced pulse profile (bottom) of the post-compressed MIR pulses.
Figure 5: Four-hour measurement of the CEP (top), power (middle) and the spectrum (bottom)
| Typical values after beam delivery* | Tuning range | |
| Peak power | 3.5 GW | 0 - 2.5 GW |
| Pulse energy | 70 µJ | 0 - 50 µJ ** |
| Pulse duration | <20 fs (<2 optical cycles) | 18 fs - 100 fs (chirped) |
| Repetition rate | 100 kHz | not tunable |
| CEP stability | <250 mrad | Setpoint: 0 - 2 π |
| Energy stability | <1.5% | not tunable |
| Strehl ratio | >0.7 | not tunable |
| Central wavelength | 3100 nm | not tunable |
| Beam pointing | <8% of total divergence | not tunable |
| Beam profile | Gaussian, 7 mm diameter, s or p-pol | 5 mm – 20 mm, s or p-pol |
Table 2: Measured laser parameters of the post-compressed output
*By taking into account the optical losses related to beam steering.
**By using 2-wire grid polarizers.
Two main configurations are offered to Users as follows (see the Fig. 6.). In configuration A, the OPCPA output (4 cycles, 120 µJ) is delivered to the User setup. In configuration B, the OPCPA output is injected into the post-compression unit in order to bring down the pulse duration below 2 optical cycles with 70 µJ energy per pulse. Further configurations are subject to discussion.
Figure 6: The standard configurations of MIR.
We are offering a compact arrangement dedicated to the generation and study of VIS-UV harmonics from semiconductor crystals such as ZnO [3,4] or various types of metamaterials. The interaction can be driven by both configurations (4 cycle or 2 cycle pulses) with continuous power, chirp and CEP control.
Laser metrology:
Spectrometer 1.5-5 um (Mozza, Fastlite)
Scanning SH-FROG, all reflective, down to sub-2 cycles @ 3.1µm
TIPTOE, down to single cycle (0.5-5 um)
Single-shot CEP detection (Fringeezz, Fastlite)
Beam profilers (IRC912 MIR CCD camera, Ophir Nanoscan, Pyroview DIAS Infrared Bolometric camera)
Wavefront sensor (SID4-DWIR, Phasics)
Power meter heads and console (Gentec, Ophir)
Fast photodetectors
VIS-UV HHG metrology:
UV-VIS spectrometer (Avantes 200-1100 nm)
Optical Spectrum Analyser (Yokogawa 350-1200 nm)
[1] N. Thiré, R. Maksimenka, B. Kiss, C. Ferchaud, T. Pinoteau, H. Jousselin, S. Jarosch, P. Bizouard, V. Di Pietro, E. Cormier, K. Osvay and N. Forget, “Highly-stable, 15 W, few-cycle, 65 mrad CEP-noise mid-IR OPCPA for statistical physics”, Optics Express 26(21), 26907-26915 (2018)
https://doi.org/10.1364/OE.26.026907
[2] R. Flender, M. Kurucz, T. Grosz, A. Borzsonyi, U. Gimzevskis, A. Samalius, D. Hoff and B. Kiss, “Dispersive mirror characterization and application for mid-infrared post-compression”, Journal of Optics 23 (2021) 065501 (9pp)
http://dx.doi.org/10.1088/2040-8986/abf88e
[3] N. Tsatrafyllis, S. Kühn, M. Dumergue, P. Foldi, S. Kahaly, E. Cormier, I. A. Gonoskov, B. Kiss, K. Varju, S. Varro, and P. Tzallas, “Quantum Optical Signatures in a Strong Laser Pulse after Interaction with Semiconductors”, Phys. Rev. Lett. 122, 193602 (2019)
https://doi.org/10.1103/PhysRevLett.122.193602
[4] R. Hollinger, D. Hoff, P. Wustelt, S. Skruszewicz, Y. Zhang, H. Kang, D. Würzler, T. Jungnickel, M. Dumergue, A. Nayak, R. Flender, L. Haizer, M. Kurucz, B. Kiss, S. Kühn, E. Cormier, C. Spielmann, G. G. Paulus, P. Tzallas, and M. Kübel, “Carrier-envelope-phase measurement of few-cycle mid-infrared laser pulses using high harmonic generation in ZnO”, Optics Express Vol. 28, Issue 5, pp. 7314-7322 (2020)
https://doi.org/10.1364/OE.383484
