Broadband terahertz pulse generation driven by an ultrafast thin-disk laser oscillator

Abstract

We demonstrate broadband THz generation driven by an ultrafast thin-disk laser (TDL) oscillator. By optical rectification of 50-fs pulses at 61 MHz repetition rate in a collinear geometry in crystalline GaP, THz radiation with a central frequency at around 3.4 THz and a spectrum extending from below 1 THz to nearly 7 THz are generated. We realized a spectroscopic characterization of a GaP crystal and a benchmark measurement of the water-vapor absorption spectrum in the THz range. Sub-50-GHz resolution is achieved within a 5 THz bandwidth. Our experiments show the potential of ultrafast TDL oscillators for driving MHz-repetition-rate broadband THz systems.

Fiber laser-driven gas plasma-based generation of THz radiation with 50-mW average power

“…The measured spectra corresponding to the field-traces extend up to about , limited by the detection bandwidth of the EOS measurement. Due to the limited phase matching, decreasing nonlinear index towards higher frequencies as well as absorption of THz radiation in GaP [3, 28], the detection can not retrieve the full spectrum of the generated radiation. From the simulation depicted in Fig.…”

MHz-repetition-rate, sub-mW, multi-octave THz wave generation in HMQ-TMS

“…Sources based on ytterbium active media occupy an operating range around 1030 nm, restricting the choice of nonlinear crystals suitable for THz generation. Figure 1(a) shows the relationship between the coherence length and the optical pump wavelength for GaP, where we consider the optical group index dispersion from [21] and the THz index from [22]. It is clear to see that for pump wavelengths around 1030 nm, a 1 mm thick crystal will support THz wave generation up to nearly 4 THz because the group index of the pump (n g = 3.31) and the refractive index of the THz wave (n THz ≈ 3.36) in this wavelength region are relatively well matched [22].…”

“…Here, we adopt a non-depleted, plane-wave pump approximation, account for the frequency dependent Fresnel transmission at each crystal-air interface, assume a transform limited 30 fs input pump and probe pulse, measurement of the generated THz waveform in time using air-biased coherent detection (i.e. a broadband detection scheme that does not impose a spectral response function), and realistic material parameters including the dispersion of the refractive index and absorption in the THz and optical range for GaP [21,22] and for HMQ-TMS [16,17], respectively. It can be seen from Figs.…”

Optical rectification of ultrafast Yb lasers: pushing power and bandwidth of terahertz generation in GaP

“…The green curve demonstrates the results with a thinner crystal, where the phase mismatch frequency cutoff at 7.3 THz is no longer the main limiting factor, and the THz spectrum is mostly limited by the pulse duration of the driving laser. The PM conditions between the IR and THz pulse in GaP were calculated according to [28] based on a Sellmeier fit of the THz refractive indices presented in [19] and a group refractive index for the IR pulse n g = 3.31 calculated from [29] (see Table 1 in Appendix A).…”

“…Recently, we demonstrated the generation of broadband THz radiation with a gap-less spectrum extending to 5 THz at a few microwatts of average power [19]. This was achieved by optical rectification in GaP of 50 fs pulses, delivered by a 4 W TDL oscillator.…”