Fig 1 - uploaded by Thomas Dekorsy
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Schematic of the ASOPS TD-THz spectrometer. Optical paths are red lines, THz paths are blue and electronic signals are dashed black lines.
Source publication
We report a terahertz time-domain spectrometer with 6 THz spectral coverage and 1 GHz resolution which is based on high-speed asynchronous optical sampling. High-speed asynchronous optical sampling is based on two femtosecond lasers with approximately 1 GHz repetition rate. The two lasers are stabilized in their repetition rate to an off-set freque...
Contexts in source publication
Context 1
... fs Ti:sapphire ring-lasers with f R = 1 GHz are offset-locked at the third repetition rate harmonic with f R = 10 kHz. The schematic of the set-up is sketched in Figure 1. Four improvements were implemented in order to enhance the bandwidth performance [12]: i) The phase-locked loop electronics which is used to offset-stabilize the two lasers operate at the tenth harmonic of the repetition frequency. ...
Context 2
... in the range of 10 GHz. This is well-matched to the 1 GHz resolution of our THz-TDS system determined by the maximum time delay of 1 ns. Figure 2 shows the comparison between a measured and calculated water vapor absorption spectrum. The acquisition time for the trace with water vapor was 60 s, the reference data are the 9-minute data shown in Fig. 1. The data for the calculation are taken from the latest version of the HITRAN database [15]. The calculation of the spectrum is performed according to the formulas of reference [14]. During the 60 s measurement the ambient parameters were kept constant at a temperature of 20°C, a pressure 1015 hPa, and a relative humidity of 26%. Up to ...
Citations
... To improve the sampling speed, several methods have been proposed. For example, asynchronous optical sampling requires no mechanical time delay stages and avoids the compromise between the data acquisition rate and frequency resolution [7], [8]. However, two expensive femtosecond lasers are needed, and the mode-locked frequencies of these two lasers should be very stable, which will significantly increase the total cost of the whole system. ...
We propose a genetic algorithm (GA) based method to improve the sampling efficiency in THz time domain spectroscopy (THz-TDS). For a typical time domain THz signal, most information are contained in a short region of the pulse which needs to be densely sampled, while the other regions fluctuating around zero can be represented by fewer points. Based on this clustering feature of the THz signal, we can use much fewer sampling points and optimize the distribution by using a GA to achieve an accurate scanning in less time. Both reflection and transmission measurements were conducted to experimentally verify the performance. The measurement results show that the sampling time can be greatly reduced while maintaining very high accuracy both in the time-domain and frequency-domain compared with a high-resolution step scan. This method significantly improves the measurement efficiency. It can be easily adapted to most THz-TDS systems equipped with a mechanical delay stage for fast detection and THz imaging.
... An alternative, ASOPS [40][41][42][43][44] -Asynchronous Optical Sampling -is an optical sampling technique which introduces a delay between successive pump and probe pulses by instead utilising two pulsed lasers with a very small difference in repetition rate such that = -, see Figure 1-6. If is the roundtrip period of a laser with repetition rate such that = 1⁄ , it is the continual temporal offset between successive pump and probe pulses which causes them to interact with the target at a proportionally increasing delay time with respect to each other, thus eliminating the need to manually delay them at a desired step size. ...
... The length of the translation stage -1 Laser -Simple setup -Scan range customisable -Low scan rates limited by mechanical parts ASOPS [40][41][42][43][44] The offset Δf between both lasers ...
... This is in perfect agreement with the simulated model and expressions (41) and (42). ...
