Cost-effective time-stretch terahertz recorders, using 1550 nm probes

Time-stretch electro-optic detection allows THz waveforms to be recorded in single-shot, up to megahertz acquisition rates. This capability is required in accelerator physics, and also opens new applications in table-top THz time-domain spectroscopy. However, the technique has also been notoriously known for the need for high-speed - and high-cost - ADCs or oscilloscopes for the readout. Furthermore, the resulting cost considerably increases with the number of samples that are needed per THz waveform, an issue that has severely limited the widespread use of the technique so far. In this article, we show that particularly cost-effective designs can be obtained by using 1550 nm probes, by taking advantage of the high dispersion per dB loss of fibers at this wavelength. With respect to previous achievements, this strategy enables us to decrease the cost of time-stretch recorders (by decreasing the required oscilloscope bandwidth), or to increase the effective number of recorded samples for a given budget. We present the performances of an experimental design that uses only standard components (in particular, a telecommunication dispersion compensation fiber) and a standard commercial probe laser without additional pulse broadening. We tested the time-stretch recorder with 100 ps THz pulses (≈0.75 THz bandwidth) provided by the synchrotron SOLEIL facility. In these conditions, our THz time-stretch recorder (with ≈40 ns final stretch duration) could already record coherent THz pulses over an unprecedented number of samples (a time-bandwidth product of ≈100), and a ≈130 ps window, using oscilloscopes and ADC boards with only 1-3 GHz bandwidth. The sensitivity (measured as the detectable birefringence in the crystal) is in the 0.5 mrad range.