The development of coherent light sources with emission in the mid-IR is currently undergoing a remarkable revolution. The mid-IR spectral range has always been of tremendous interest, mainly to spectroscopists, due to the ability of mid-IR light to access rotational and vibrational resonances of molecules which give rise to superb sensitivity upon optical probing [1-3]. Previously, high energy resolution was achieved with narrowband lasers or parametric sources, but the advent of frequency comb sources has revolutionized spectroscopy by providing high energy resolution within the frequency comb structure of the spectrum and at the same time broadband coverage and short pulse duration [4-6]. Such carrier to envelope phase (CEP) controlled light waveforms, when achieved at ultrahigh intensity, give rise to extreme effects such as the generation of isolated attosecond pulses in the vacuum to extreme ultraviolet range (XUV) . Motivated largely by the vast potential of attosecond science, the development of ultraintense few-cycle and CEP stable sources has intensified , and it was recognized that coherent soft X-ray radiation could be generated when driving high harmonic generation (HHG) with long wavelength sources [9-11]. Recently, based on this concept, the highest waveform controlled soft X-ray flux  and isolated attosecond pulse emission at 300 eV  was demonstrated via HHG from a 1850 nm, sub-2-cycle source . Within strong field physics, long wavelength scaling may lead to further interesting physics such as the direct reshaping of the carrier field , scaling of quantum path dynamics , the breakdown of the dipole approximation  or direct laser acceleration . The experimental development of long wavelength light sources therefore holds great promise in many fields of science and will lead to numerous applications beyond strong field physics and attosecond science. In this paper, we present the first mid-IR optical parametric chirped pulse amplifier (OPCPA) operating at a center wavelength of 7 μm with output parameters suitable already for strong-field experiments. It is also the first demonstration of an Optical Parametric Chirped Pulse Amplifier (OPCPA) using a 2 μm laser pump source which enables the use of non-oxide nonlinear crystals with typically limited transparency at 1 mm wavelength. This new OPCPA system is all-optically synchronized and generates 0.55 mJ energy, CEP stable optical pulses. The pulses are currently compressed to sub-8 optical cycles but support a sub-4 cycle pulse duration. The discrepancy in compression is due to uncompensated higher order phase from the grating compressor which will be addressed in the future.
We report a tunable, high-energy, single-pass, optical parametric generator (OPG) based on the new nonlinear material,
cadmium silicon phosphide, CdSiP<sub>2</sub>. The OPG is pumped by a laboratory designed cavity-dumped passively mode-locked,
diode-pumped, Nd:YAG oscillator, providing 25 μJ pulses in 20 ps at 5 Hz. The pump energy is further boosted
by a flashlamp-pumped Nd:YAG amplifier to 2.5 mJ. The OPG is temperature tunable over 1263-1286 nm (23 nm) in
the signal and 6153-6731 nm (578 nm) in the idler, corresponding to a total tuning range of 601 nm. Using the single-pass
OPG configuration, we have generated signal energy as high as 636 μJ at 1283 nm, together with an idler energy of
33 μJ at 6234 nm, for 2.1 mJ of input pump energy. The signal pulses generated from the OPG have a Gaussian pulse
duration of 24 ps and an FWHM spectral bandwidth of 10.4 nm at central wavelength of 1276 nm. The corresponding
idler spectrum has an FWHM bandwidth of 140 nm centered at 6404 nm.