Homodyne Solid-State Biased Coherent Detection of Ultra-Broadband Terahertz Pulses with Static Electric Fields

Abstract

We present an innovative implementation of the solid-state-biased coherent detection (SSBCD) technique, which we have recently introduced for the reconstruction of both amplitude and phase of ultra-broadband terahertz pulses. In our previous works, the SSBCD method has been operated via a heterodyne scheme, which involves demanding square-wave voltage amplifiers, phase-locked to the THz pulse train, as well as an electronic circuit for the demodulation of the readout signal. Here, we demonstrate that the SSBCD technique can be operated via a very simple homodyne scheme, exploiting plain static bias voltages. We show that the homodyne SSBCD signal turns into a bipolar transient when the static field overcomes the THz field strength, without the requirement of an additional demodulating circuit. Moreover, we introduce a differential configuration, which extends the applicability of the homodyne scheme to higher THz field strengths, also leading a two-fold improvement of the dynamic range compared to the heterodyne counterpart. Finally, we demonstrate that, by reversing the sign of the static voltage, it is possible to directly retrieve the absolute THz pulse polarity. The homodyne configuration makes the SSBCD technique of much easier access, leading to a vast range of field-resolved applications.

Solid-State Biased Coherent Detection of Ultra-Broadband Terahertz Pulses for high repetition rate, low pulse energy lasers

“…The damage threshold of the bias voltage was not investigated, as it could lead to permanent device failure. Compared to previous publications on the SSBCD technique [8][9][10] we use significantly shorter pulse durations (40 fs compared to 155 fs). While we expect the shorter pulse duration to be beneficial to the SSBCD technique, the larger peak intensities might contribute to the lower damage threshold in probe pulse energy.…”

“…While the SSBCD device is capable of a DR two orders of magnitudes larger, it is conventionally used with much larger probe energies (50-100 nJ compared to 32 nJ) [8][9][10]. As the DR and SNR scale quadratically with the probe energy, such low SNR and DR values are expected for the combination of low probe energy and low THz field used in this setup.…”

“…In high field setups, the combination of two-color plasma sources with ABCD has been established to cover the 0.1-10 THz range and can be further simplified through the use of SSBCD [8][9][10]. In the context of low field setups, we show here that the combination of a spintronic emitter and SSBCD is a very promising approach to obtain a system covering the entire 0.1 -10 THz region.…”

“…A new detection technique has recently been discovered, building upon the EFISH process used in ABCD. In solid-state biased coerent detection (SSBCD) the EFISH process takes place in a thin layer of silicon nitride (SiN) instead of a gas [8][9][10]. The benefit is a much larger χ (3) coefficient compared to the gases used in ABCD, which allows the use of bias voltages and probe energies several orders of magnitude lower compared to ABCD.…”

“…In the context of low field setups, we show here that the combination of a spintronic emitter and SSBCD is a very promising approach to obtain a system covering the entire 0.1 -10 THz region. While the SSBCD technique has very successfully been used to replace an existing ABCD setup in high field setups driven by a plasma source at a repetition rate of 1 kHz [8][9][10], its suitability for setups with high repetition rates and low THz fields has not yet been demonstrated. In this work we examine the performance of a SSBCD device in a low THz field setup with a repetition rate of 250 kHz and use it to study three test samples.…”