Abstract
We demonstrate a rapid scanning high-resolution THz spectrometer capable of acquiring THz field transients with 1 ns duration without mechanical delay line. The THz spectrometer is based on two 1-GHz Ti:sapphire femtosecond lasers which are linked with a fixed repetition rate difference in order to perform high-speed asynchronous optical sampling. One laser drives a high-efficiency large-area GaAs based THz emitter, the other laser is used for electro-optic detection of the emitted THz-field. At a scan rate of 9 kHz a time resolution of 230 fs is accomplished. High-resolution spectra from 50 GHz up to 3 THz are obtained and water absorption lines with a width of 11 GHz are observed. The use of femtosecond lasers with 1 GHz repetition rate is essential to obtain rapid scanning and high time-resolution at the same time.
Highlights
The generation and detection of THz radiation with femtosecond lasers is a rapidly evolving field due its relevance for the optical characterization of a wide variety of material systems [1].Conventional THz time-domain spectroscopy (THz-TDS) systems are based on pulsed THz radiation that is repetitively generated by a modelocked train of femtosecond laser pulses in a photoconductive switch, via optical rectification or difference frequency mixing
The THz spectrometer is based on two 1-GHz Ti:sapphire femtosecond lasers which are linked with a fixed repetition rate difference in order to perform high-speed asynchronous optical sampling
The spectrometer is based on high-speed asynchronous optical sampling employing a dual modelocked laser system with femtosecond oscillators that have approximately 1 GHz repetition rate
Summary
The generation and detection of THz radiation with femtosecond lasers is a rapidly evolving field due its relevance for the optical characterization of a wide variety of material systems [1]. The field of THz-TDS without mechanical delays and high scan rates has recently been much advanced by high-speed ASOPS systems based on two Kerr-lens mode-locked Ti-sapphire lasers with fR=1 GHz and a scan rate Δ fR in the kHz frequency range. Such systems were demonstrated for the detection of electrical transients on integrated coplanar resonators [2] and all-optical pump-probe spectroscopy [8]. THz absorption spectra of water vapor at frequencies up to 3 THz are obtained with a dynamic range of 30 dB within a total measurement time of only 250 s
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