Millijoule 265 fs Tm:YAP regenerative amplifier for driving ultrabroad band collinear mid-infrared optical parametric amplifiers.

Generation of 265-fs millijoule pulses at 1940 nm from a solid-state regenerative amplifier has been demonstrated. The amplification chain consists of a thulium-doped fluoride (Tm:ZBLAN) fiber oscillator, a two stage Tm:ZBLAN fiber preamplifier, and a regenerative amplifier with a thermoelectrically cooled thulium-doped yttrium aluminium perovskite crystal. The newly developed light source is used for pumping an ultra broadband mid-infrared optical parametric amplifier based on a gallium selenide crystal. The 2.5-4 µm range of a multioctave supercontinuum, generated in a polarization-maintaining ZBALN fiber, is used as the MIR seed. The amplified signal in combination with the corresponding idler pulses spread from 2.5 to 10 µm in a collinear geometry.

Generation and characterization of mid-infrared supercontinuum in polarization maintained ZBLAN fibers.

We present mid-infrared (MIR) supercontinuum generation in polarization-maintained ZBLAN fibers pumped by 2 µm femtosecond pulses from a Tm:YAP regenerative amplifier. A stable supercontinuum that spreads from 380 nm to 4 µm was generated by coupling only 0.5  µJ pulse energy into an elliptical core ZBLAN fiber. The supercontinuum was characterized using cross-correlation frequency-resolved optical gating (XFROG). The complex structure of the XFROG trace due to the pulse-to-pulse spectrum instability have been fixed by reducing the length of the applied fibers or improving the quality of the incident pulse spectrum.

Millijoule femtosecond pulses at 1937 nm from a diode-pumped ring cavity Tm:YAP regenerative amplifier.

We present an infrared source operating at 1937 nm center wavelength capable of generating 1.35 mJ pulse energies with 1 kHz repetition rate and 2 GW peak power based on a diode-pumped Tm:YAP regenerative amplifier. The obtained pulses after 45 round trips have been compressed down to 360 fs. Using only a small portion (15 µJ) of the output of the system we managed to generate a white light continuum in a 3 mm YAG window that exhibits the viability of the system as a suitable candidate for a pumping source of a mid-infrared optical parametric amplifier.

Ultrabroadband microjoule 1.8 µm laser pulse from a single-stage broadband pumped OPA.

We propose a broadband pumped optical parametric amplification scheme for the generation of a micojoule few-cycle pulse centered at 1.8 µm. Owing to the opposite chirp of the broadband pump and seed pulses, an idler pulse with an FWHM bandwidth of 434 nm is obtained, which can be effectively compressed to a near-transform-limited duration of 13.1 fs by simply compensating for the linear chirp. The picojoule-level seed is amplified to microjoule level in a single stage with a pump pulse of 100 µJ, corresponding to an overall conversion efficiency of 9%. The presented scheme is potentially applicable in various nonlinear crystals with different kinds of femtosecond laser systems, which provides not only an efficient approach of down-converting a near-infrared laser with moderate energy to the mid-infrared region, but also a suitable seeding source in high-energy OPCPA systems.

Ultrabroadband tunable OPA design using a spectrally broadened pump source.

A robust optical parametric amplifier (OPA) scheme is proposed in which we have experimentally achieved broadband bandwidth for a collinear OPA design that exhibits good beam quality and spatial distribution using a type-I ß barium borate crystal. The applied pump pulses are simultaneously spectrally broadened and temporally stretched in a multi-plate system before being used to amplify the temporally stretched white light. In this case, the phase matching can be obtained for a broad range of wavelengths, and we have managed to achieve bandwidths three times broader than a conventional narrowband pumped collinear OPA. With a bandwidth as broad as 400 nm centered at 1400 nm, as well as a broadband angular dispersion-free idler, the signal bandwidth supports transform-limited pulses as short as 7.5 fs which correspond to sub-two optical cycles for this center wavelength. Furthermore, the system is easily tunable over a 400 nm range of bandwidths starting from 1100 to 1500 nm. The proposed scheme provides a versatile near-infrared/middle-infrared source with a broad bandwidth and fine tuning capability which paves the way for ultrafast spectroscopy and strong field applications.

Tunable broadband intense IR pulse generation at non-degenerate wavelengths using group delay compensation in a dual-crystal OPA scheme.

A robust group delay compensated dual-crystal optical parametric amplification (DOPA) scheme is proposed that will be used to prove the positive effect of group delay compensation on a DOPA as predicted by the simulations in the previously published literature. Through simple adjustments, it is also capable of providing 20 fs pulses (theoretically compressible to 12 fs, corresponding to sub-four-cycle for 1300 nm components), broadband IR pulses at non-degenerate wavelengths using short pulse (broadband) pump laser. In our table-top DOPA system, group delay compensation has been realized using a simple optical crystal. Our design provides output power in order of 100 mW. We managed to achieve minimum 20 nm improvement on the bandwidth, compared to single-crystal OPA (SOPA) structure whilst keeping total conversion efficiency above 30%. Adjusting our configuration by optimizing the phase-matching angles of the two BBO crystals, we also have realized a practical scheme that benefitting from group delay compensation can obtain 75 nm bandwidth improvement while keeping the conversion efficiency constant. This achievement will open the doors to the realm of multiple crystals OPA systems and provide a solution to the imposed limitation on the effective lengths of applicable non-linear crystals and hence limited power gain of such broadband OPA systems.