Germanium is a nonpolar semiconductor with missing Reststrahlen band. In spite of other promising properties including low bandgap and small effective mass, its long, µs-scale recombination time has been prohibitive for applications as photoconductive THz emitters. Using Au-implantated Ge, with recombination times reduced to sub-ns values, we have demonstrated a broadband photoconductive THz emitter compatible with modelocked fibre lasers operating at wavelengths of 1.1 and 1.55 µm and with pulse repetition rates of 78 MHz. Reaching up to 70 THz bandwidth, this approach points towards the possibility of compact, high-bandwidth THz photonic devices compatible with Si CMOS technology.
Frequency combs are an enabling technology for metrology and spectroscopic applications in fundamental and life sciences. While frequency combs in the 1 μm regime, produced from Yb-based systems have already exceeded the 100 W – level, high power coverage of the interesting mid-infrared wavelength range remains yet to be demonstrated. Tm- and Ho-doped laser systems have recently shown operation at high average power levels in the 2 μm wavelength regime. However, frequency combs in this wavelength range have not exceeded the 5 W-average power level. In this work, we present a high power frequency comb, delivered by a Tm-doped chirped-pulse amplifier with subsequent nonlinear pulse compression. With an integrated phase noise of <320 mrad, low relative intensity noise of <0.5% and an average power of 60 W at 100 MHz repetition rate (and <30 fs FWHM pulse duration), this system demonstrates high stability and broad spectral coverage at an unrivalled average power level in this wavelength regime. Therefore, this laser will enable metrology and spectroscopy with unprecedented sensitivity and acquisition time. It is our ongoing effort to extend the spectral coverage of this system through the utilization of parametric frequency conversion into the mid-IR, thus ultimately enabling high power fingerprint spectroscopy in the entire molecular fingerprint region (2 – 20 μm).