Abstract
After 20 years of terahertz cross-correlation spectroscopy (THz-CCS), the performance of the systems has been improved to practical relevance by reaching a bandwidth of ~2 THz. For the development of high-performance THz-CCS systems, it is necessary to get a deeper knowledge of the signal generation from incoherent light sources. In this work, the bandwidth, dynamic range, and peak-to-peak amplitude of a THz-CCS systems using a superluminescent diode as light source and a programmable optical filter for spectral shaping was investigated to obtain a better understanding of the relationship between the optical spectrum and the generated terahertz spectrum. By a periodic structuring of the continuous optical spectrum, an enhancement of the peak dynamic range of more than 10 dB was achieved with a bandwidth of 1.6 THz. The experimental results are confirmed by numerical simulations.
Highlights
Since terahertz cross-correlation spectroscopy (THz-CCS) was introduced in 2000, the researchers dedicated to this research field have made significant progress towards reasonable performance improvements for practical applications
The first step towards compact THz-CCS systems was presented by Morikawa et al (2000), using a commercially available multimode laser diode (MMLD) and photoconductive antennas (PCAs) [1]
THz-QTDS has the disadvantage of discrete frequency components, much lower bandwidth, and lower dynamic range compared to state-of-the-art terahertz time-domain spectroscopy (THz-TDS)
Summary
Since terahertz cross-correlation spectroscopy (THz-CCS) was introduced in 2000, the researchers dedicated to this research field have made significant progress towards reasonable performance improvements for practical applications. The first step towards compact THz-CCS systems was presented by Morikawa et al (2000), using a commercially available multimode laser diode (MMLD) and photoconductive antennas (PCAs) [1] This was the first time that a MMLD was used for broadband terahertz generation instead of an ultrafast mode-locked laser to create terahertz radiation. Inserting single-mode fiber and a fiber-coupled 50:50 beam splitter into the optical path instead of a free space 50:50 beam splitter improved the signal-to-noise ratio (SNR) and the compactness for THz-CCS systems [2,3]. This technique for terahertz generation was later extended and renamed to terahertz quasi time-domain spectroscopy (THz-QTDS) [4]. THz-QTDS has the disadvantage of discrete frequency components, much lower bandwidth, and lower dynamic range compared to state-of-the-art terahertz time-domain spectroscopy (THz-TDS)
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