Abstract
Ultrafast terahertz (THz) spectroscopy is a potent tool for studying the fundamental properties of matter. Limitations of current THz sources, however, preclude the technique being applied in certain advanced configurations or in the measurement of, e.g., strongly absorbing samples. In response to this problem, here we demonstrate the generation of 1.38 mW broadband THz radiation at 10 MHz repetition rate by combining the highly efficient nonlinear organic crystal HMQ-TMS with ultrafast pump pulses generated using a simple and stable external pulse compression of a high power, near-infrared (NIR) femtosecond ytterbium-doped fiber (Yb:fiber) laser. Utilizing spectral broadening in a large core, polarization maintaining photonic crystal fiber and a pair of SF11 prisms, we achieve a tenfold pulse compression of the Yb:fiber laser, yielding compressed 0.35 µJ pulses with a full-width at half maximum pulse duration of 22 fs, exerting a peak power of 13.8 MW at a repetition rate of 10 MHz. THz generation through optical rectification of the NIR pulses is explored in two distinct thicknesses of the organic crystal, leading to a maximum conversion efficiency of ∼5.5 · 10−4, an order of magnitude higher than that achieved with inorganic nonlinear crystals, e.g., gallium phosphide, for similar pump parameters. The focused THz beam has a peak on-axis field strength greater than 6.4 kV cm−1 in unpurged atmosphere. We believe that our moderately strong-field THz source is well suited to a variety of applications in ultrafast THz spectroscopy, in particular THz-enabled scattering-type near-field, and scanning tunneling spectroscopy, where multi-MHz repetition rate sources are required.
Highlights
Advances in the development of ultrafast laser-based generation of high intensity pulses in the terahertz (THz) range (0.2–30 THz) over the last two decades have enabled a wealth of new application areas in both fundamental and applied science.1 In particular, time-domain and time-resolved time-domain spectroscopic techniques have proven a powerful approach for the characterization of novel materials in physics, chemistry, and biology, as well as for uncovering the non-equilibrium dynamics in such material systems.2 To this end, there has been a significant focus placed on improving the operational bandwidth, source acquisition speed, peak field strength, and average power to extend the scope and improve the quality of possible studies
In response to this problem, here we demonstrate the generation of 1.38 mW broadband THz radiation at 10 MHz repetition rate by combining the highly efficient nonlinear organic crystal HMQ-TMS with ultrafast pump pulses generated using a simple and stable external pulse compression of a high power, near-infrared (NIR) femtosecond ytterbium-doped fiber (Yb:fiber) laser
In terms of compression ratio and pulse duration, our system compares to similar approaches using large mode area (LMA)-photonic crystal fiber (PCF) in combination with Yb-doped laser sources operating at multi-watt power levels and MHz repetition rates that report pulse durations between 19 fs and 33 fs
Summary
Advances in the development of ultrafast laser-based generation of high intensity pulses in the terahertz (THz) range (0.2–30 THz) over the last two decades have enabled a wealth of new application areas in both fundamental and applied science.1 In particular, time-domain and time-resolved time-domain spectroscopic techniques have proven a powerful approach for the characterization of novel materials in physics, chemistry, and biology, as well as for uncovering the non-equilibrium dynamics in such material systems.2 To this end, there has been a significant focus placed on improving the operational bandwidth, source acquisition speed, peak field strength, and average power to extend the scope and improve the quality of possible studies. In response to this problem, here we demonstrate the generation of 1.38 mW broadband THz radiation at 10 MHz repetition rate by combining the highly efficient nonlinear organic crystal HMQ-TMS with ultrafast pump pulses generated using a simple and stable external pulse compression of a high power, near-infrared (NIR) femtosecond ytterbium-doped fiber (Yb:fiber) laser.
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