Supplementary document for Transient field-resolved reflectometry at 50-100 THz - 5538130.pdf

Abstract

Supporting Information on 'Transient field-resolved reflectometry at 50-100 THz' MARCEL NEUHAUS et al. 1. Further details on the experimental setup 1.1. NOPAThe experimental setup for MIR field-resolved transient reflectometry is based on a non-collinear optical parametric amplifier (NOPA) delivering sub-8 fs pulses at around 800 nm, cf. Fig. 1. The NOPA is driven by a commercial fiber laser (Active Fiber Systems) source with an output of 1030 nm in wavelength and 540 fs pulse length, cf. Fig. 1 (a). The tunable repetition rate of the fiber laser (0.05-19 MHz) was set to 2.1 MHz and a pulse energy of 20 J.A part of the fiber laser output is used for producing the seed via super-continuum generation (SCG) in an 8 mm long YAG crystal with 1.5 J of the 1030 nm beam using a numerical aperture of 0.019. As the wavelength range around the fundamental is incompressible due to phase ripples, a 1000 nm short-pass filter was used to clip the SC at the long wavelength side. To optimize the SC, the crystal was adjusted with respect to the focus, resulting in minimal fluctuations of about 0.3% in shot-to-shot rms, similar to the fluctuations of the fiber laser itself. The excellent stability arises from intensity clamping, which is well known in bulk SC generation [1,2]. The remaining power of the fiber laser output was frequency doubled by second harmonic generation (SHG) to produce the pump beam for the NOPA in a 1-mm thick BBO crystal, resulting in 10 J per pulse of SHG output.The SC was combined with the frequency doubled part of the fiber laser output in a 3.5 mm thick BBO crystal under an angle of 2.3 • . A broadband NIR pulse is achieved spanning from 650-980 nm (see Fig. 1(b)). The NIR pulses are compressed by a combination of fused-silica wedges and a set of complementary chirped mirror pairs to a pulse duration below 8 fs at an energy of around 2 J (Fig. 1(c)). The spectral phase and pulse duration of NOPA output pulses are measured and retrieved using the dispersion scan (D-scan) technique.The shot-to-shot rms power stability of the NIR was as low as 0.4% with long-term (8 hours) power stability below 1% as can be seen in Fig. 2. To improve the pointing stability of the pulses, a beam pointing stabilizer (Aligna, TEM) is placed between the NOPA and successive iDFG stage.