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We present a novel all-fiber pumped OPCPA architecture to generate self-CEP stable, sub-8 optical cycle duration pulses at 7-micron wavelength approaching millijoulelevel pulse energy at 100 Hz repetition rate. The system yields a peak power of 1.1 GW and, if focused to the diffraction limit, would reach a peak intensity of 7x10 14 W/cm 2. The OPCPA is pumped by a 2-micron Ho:YLF chirped pulse amplifier to leverage the highly efficient and broadband response of the nonlinear crystal ZGP. The 7-micron seed at 100 MHz is generated via DFG from an Er:Tm:Ho multi-arm fiber frequency comb and a fraction of its output optically injects the Ho:YLF amplifier. While the pulse bandwidth at 7 micron is perfectly suited for nonlinear and spectroscopic applications, current parameters offer, for the first time, the possibility to explore strong field physics in an entirely new wavelength range with a ponderomotive force 77 times larger than from an 800 nm source. The overall OPCPA system is very compact and provides a new tool for investigations directly in the molecular finger print region of the electromagnetic spectrum or to drive high harmonic generation to produce fully coherent X-rays in the multi-keV range and possibly zeptosecond temporal waveforms.

Recent developments in laser sources operating in the mid-IR (3 -8 µm), have been motivated by the numerous possibilities for both fundamental and applied research. One example is the ability to unambiguously detect pollutants and carcinogens due to the much larger oscillator strengths of their absorption features in the mid-IR spectral region compared with the visible. Broadband sources are of particular interest for spectroscopic applications since they remove the need for arduous scanning or several lasers and allow simultaneous use of multiple absorption features thus increasing the confidence level of detection. In addition, sources capable of producing ultrashort and intense mid-IR radiation are gaining relevance in attoscience and strong-field physics due to wavelength scaling of re-collision based processes. In this paper we review the state-of-the-art in sources of coherent, pulsed mid-IR radiation. First we discuss semi-conductor based sources which are compact and turnkey, but typically do not yield short pulse duration. Mid-IR laser gain material based approaches will be discussed, either for direct broadband mid-IR lasers or as narrowband pump lasers for parametric amplification in nonlinear crystals. The main part will focus on mid-IR generation and amplification based on parametric frequency conversion, enabling highest mid-IR peak power pulses. Lastly we close with an overview of nonlinear post-compression techniques, for decreasing pulse duration to the sub-2-optical-cycle regime.

We present the state of the art of a compact high-energy midinfrared laser system for TW-level 8-cycle pulses at 7 µm. This system consists of an Er:Tm:Ho:fiber MOPA which serves as the seeder for a ZGP-based OPCPA chain in addition to a Ho:YLF amplifier which is Tm:fiber pumped. Featuring all-optical synchronization, the system delivers 260-mJ pump energy at 2052 nm, 16-ps duration at 100 Hz with a stability of 0.8 % rms over 20 min. We show that chirp inversion in the OPCPA chain leads to excellent energy extraction and aids in compression of the 7-µm pulses to 8 optical cycles (188 fs) in bulk BaF 2 with 93.5 % efficiency. Using 21.7 mJ of the available pump energy, we generate 0.75-mJ-energy pulses at 7 µm due to increased efficiency with a chirp-inversion scheme. The pulse quality of the system's output is shown by generating high harmonics in ZnSe which span up to harmonic order 13 with excellent contrast. The combination of the passive carrier-envelope phase stable midinfrared seed pulses and the high-energy 2052 nm picosecond pulses makes this compact system a key enabling tool for the next generation of studies on extreme photonics, strong field physics and table-top coherent X-ray science.

A 2-μm wavelength laser delivering up to 39-mJ energy, ∼10 ps duration pulses at 100-Hz repetition rate is reported. The system relies on chirped pulse amplification (CPA): a modelocked Er:Tm:Ho fiber-seeder is followed by a Ho:YLF-based regenerative amplifier and a cryogenically cooled Ho:YLF single pass amplifier. Stretching and compressing are performed with large aperture chirped volume Bragg gratings (CVBG). At a peak power of 3.3 GW, the stability was <1% rms over 1 h, confirming high suitability for OPCPA and extreme nonlinear optics applications. ultra-short mid-IR pulses, but further progress is hampered by the near exclusive usage of ∼1 μm pump lasers. These pump lasers impose an unfavorable photon ratio between pump and signal/idler that limits efficiency, prevents accessing the highly efficient class of non-oxide crystals, and presents serious power scaling limitations due to linear and two-photon absorption [12]. These limitations can be mitigated using powerful pump lasers emitting at 2-μm wavelength thereby reducing the photon ratio mismatch and allowing the use of highly nonlinear non-oxide crystals such as ZGP [13]. While the technology of such lasers, based on Q-switched Ho:YLF (or Ho:LuLiF) and Ho:YAG, is very mature for generating high-energy nanosecond pulses [14][15][16][17][18][19][20], amplification of few picosecond pulses from such systems to the multi-tens of mJ has not been reported. In this Letter, we report on a compact and stable laser system operating at 2-μm wavelength, delivering ∼10 ps duration optical pulses with up to 39-mJ output energy at 100-Hz repetition rate. Highly efficient temporal compression of narrow-band picosecond pulses was performed at the multi-tens of mJ energy-level in a chirped volume Bragg grating (CVBG).The laser system relies on chirped pulse amplification (CPA) architecture consisting of a fiber seeder, a CVBG stretcher, two consecutive amplification stages, and a large aperture CVBG compressor (Fig. 1). The all-fiber seeder is a multi-stage system (Menlo Systems GmbH) starting with an amplified modelocked Er:fiber oscillator delivering femtosecond optical pulses at 100-MHz repetition rate and 1.5-μm wavelength. These pulses are frequency shifted to 2052-nm wavelength and spectrally narrowed to ∼1.5 nm bandwidth before seeding a series of Tm:Ho fiber amplifiers [21]. The 4-nJ energy, picosecond duration pulses emerging from these amplifiers at 100 MHz form the seed for the CPA chain thereby removing the problem of modelocking Ho-based systems directly. These pulses are temporally stretched to 170-ps duration in a double-pass, CVBG-based stretcher. The CVBG (OptiGrate Corp.) used in this stretcher is broadband AR-coated around 2052 nm, has a 5 mm × 8 mm clear aperture, a chirp rate of 150 ps/nm, and a design wavelength of 2053.5 nm. Upon stretching, the 100-MHz train is passed through a rubidium titanyle phosphate (RTP) pulse picker to reduce the repetition rate to 100 Hz. The pulses are then passed through an optical isolator and directed toward a regen...