High-Resolution Terahertz Spectrometer

Klatt, Gregor; Gebs, Raphael; Schäfer, H.; Nagel, M.; Janke, C.; Bartels, A.; Dekorsy, Thomas

doi:10.1109/jstqe.2010.2047635

Cited by 46 publications

(26 citation statements)

References 41 publications

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“…For stronger absorption lines, such as at 2.977, 3.020, and 3.138 THz, the signals are relatively weak, and the different sensitivity levels between the two systems also cause the discrepancy. The frequency of each absorption line can be identified with high accuracy, and these absorptions also correspond to previous reports [16,17] . In conclusion, we demonstrate the performance of two detection methods of broadband THz-TDS -THz-ABCD and EO detection -at different relative humidity levels.…”

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confidence: 85%

Study of broadband THz time-domain spectroscopy at different relative humidity levels

Zhang

2012

中国光学快报

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Two detection techniques of broadband terahertz (THz) time-domain spectroscopy-THz air-biased coherent detection (THz-ABCD; from 0.3 to 14 THz) and electro-optical (EO) detection (from 0.3 to 7 THz) -are both performed at several different relative humidity levels. The THz power exponentially decays with the increase in relative humidity. The dynamic range of the main pulse in the time domain linearly decreases as the relative humidity increases from 0% to 40%, and linear fittings show that the slopes are -0.017 and -0.019 for THz-ABCD and EO detection, respectively. Because of the multiple reflections caused by the crystal in the common EO detection, THz-ABCD has better spectral resolution (17 GHz) than that of EO detection (170 GHz). The spectrum of water vapor absorption measured by THz-ABCD is also compared with that measured by the Fourier transform infrared spectroscopy (FTIR).OCIS codes: 300.6495, 320.7150, 300.6500. doi: 10.3788/COL201210.043001.Terahertz (THz) waves have brought benefits to a variety of applications, including biomedical investigation, non-destructive inspection, and material characterization [1−3] . This is because most rotational and vibrational resonances of molecules and chemical compounds are located in such frequency range. However, water vapor attenuates THz waves when it propagates in the atmosphere. Grischkowsky et al. have reported a number of research about water vapor absorption in the THz range, especially from 0.2 to 2 THz [4,5] . On the other hand, the astronomical observations at THz frequencies are significantly impacted by daily weather, varying seasons, as well as different altitudes and geographical locations. To reduce the attenuation by water vapor over an absorbing propagation path, many groups have driven submillimeter-wave telescopes to the highest, driest, and coldest sites for ground-based astronomical telescopes operating at THz frequencies [6,7] . THz time-domain spectroscopy (THz-TDS) using selected gases as an emitter and sensor now provides an intense THz field, a broadband spectrum, and sensitive detection capabilities for studying material properties [8,9] . In terms of remote sensing, a promising technique is the use of gases as the emitter and the sensor [10,11] . To investigate the performance of broadband THz-TDS in various environments, this study uses nitrogen gas as THz emitter along with two broadband detection techniques -THz air-biased coherent detection (THz-ABCD) and electro-optical (EO) sampling with a GaP crystal [12,13] -to measure the absorption spectra of water vapor at different relative humidity (RH) levels.The broadband THz spectrometer with THz-ABCD and EO sampling with a GaP crystal is schematically shown in Fig. 1. A Ti-sapphire amplified laser (Coherent Libra) with a central wavelength of 800 nm, 50-fs pulse duration, 1.3-mJ pulse energy, and 3-kHz repetition rate is used as the optical source. The laser beam is split into two by an optical beam splitter. One beam has 85% of the energy passed through a 100-µm-thick type I beta b...

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confidence: 85%

Study of broadband THz time-domain spectroscopy at different relative humidity levels

Zhang

2012

中国光学快报

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“…This will increase the useful spectroscopic bandwidth of the instrument from 3.2 THz to at least 7 THz. 19 Further optimization of THz emission efficiency at high frequencies by implementing a reflection emitter geometry and detection by multiple inorganic crystals or poled EO sensitive polymers 35 should enable gap-free measurement of gas phase signatures to at least 10 THz, covering nearly a century of bandwidth. 11 Thus, this instrument overcomes many limitations of past THz-TDS and ASOPS-THz-TDS systems and demonstrates future paths to high precision, high dynamic range gas-phase spectroscopy covering the entire THz region.…”

Section: Discussionmentioning

confidence: 99%

“…17 Frequency content is extracted from the time-domain data by a fast Fourier transform (FFT) allowing THz-TDS to overcome broadband detector noise through the multiplex principle. To highlight the potential of ASOPS based THz-TDS, the capabilities of two recent ASOPS-THz-TDS instruments are listed here: a high-speed 1 GHz oscillator ASOPS-THz-TDS system with 7 THz of bandwidth that has achieved a mean frequency deviation of 142 MHz when measuring the line centers of water vapor absorptions from 0.2 to 6.3 THz, 18,19 and a high-resolution ASOPS-THz-TDS system based on two Er-doped fiber lasers achieved a mean frequency deviation of 4 MHz when measuring line centers of acetonitrile absorptions from 642.0 GHz to 643.2 GHz. 20 We stress that a single system has yet to demonstrate the ideal combination of high frequency resolution applicable to Doppler-limited spectroscopy while maintaining multi-decade spanning THz bandwidth.…”

Section: B Asynchronous Optical Sampling Based Thz Time-domain Spectmentioning

confidence: 99%

A decade-spanning high-resolution asynchronous optical sampling terahertz time-domain and frequency comb spectrometer

Good

Holland

Finneran

et al. 2015

Review of Scientific Instruments

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Terahertz heterodyne spectrometer using a quantum cascade laser Appl. Phys. Lett. 97, 161105 (2010) We present the design and capabilities of a high-resolution, decade-spanning ASynchronous OPtical Sampling (ASOPS)-based TeraHertz Time-Domain Spectroscopy (THz-TDS) instrument. Our system employs dual mode-locked femtosecond Ti:Sapphire oscillators with repetition rates offset locked at 100 Hz via a Phase-Locked Loop (PLL) operating at the 60th harmonic of the ∼80 MHz oscillator repetition rates. The respective time delays of the individual laser pulses are scanned across a 12.5 ns window in a laboratory scan time of 10 ms, supporting a time delay resolution as fine as 15.6 fs. The repetition rate of the pump oscillator is synchronized to a Rb frequency standard via a PLL operating at the 12th harmonic of the oscillator repetition rate, achieving milliHertz (mHz) stability. We characterize the timing jitter of the system using an air-spaced etalon, an optical cross correlator, and the phase noise spectrum of the PLL. Spectroscopic applications of ASOPS-THz-TDS are demonstrated by measuring water vapor absorption lines from 0.55 to 3.35 THz and acetonitrile absorption lines from 0.13 to 1.39 THz in a short pathlength gas cell. With 70 min of data acquisition, a 50 dB signal-to-noise ratio is achieved. The achieved root-mean-square deviation is 14.6 MHz, with a mean deviation of 11.6 MHz, for the measured water line center frequencies as compared to the JPL molecular spectroscopy database. Further, with the same instrument and data acquisition hardware, we use the ability to control the repetition rate of the pump oscillator to enable THz frequency comb spectroscopy (THz-FCS). Here, a frequency comb with a tooth width of 5 MHz is generated and used to fully resolve the pure rotational spectrum of acetonitrile with Doppler-limited precision. The oscillator repetition rate stability achieved by our PLL lock circuits enables sub-MHz tooth width generation, if desired. This instrument provides unprecedented decade-spanning, tunable resolution, from 80 MHz down to sub-MHz, and heralds a new generation of gas-phase spectroscopic tools in the THz region. C 2015 AIP Publishing LLC. [http://dx

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“…Due to the trigger dead time only every second transient is acquired increasing the theoretical possible measurement time by a factor of two. Performing terahertz time-domain spectroscopy at high repetition rates is an interesting application [4,24] as the relevant time window usually only covers a few tenth of picoseconds and a 10 GHz frequency resolution is still sufficient for many samples. The high scan rate is also advantageous for experiments on two time scales using the setup for kinetic terahertz absorption spectroscopy [25].…”

Section: Characterization Of the System Performancementioning

confidence: 99%

Ultrafast time-domain spectroscopy system using 10 GHz asynchronous optical sampling with 100 kHz scan rate

2016

Self Cite

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An ultrafast time-domain spectroscopy system employing asynchronous optical sampling at a repetition rate of 10 GHz is presented. Two ultra-compact Ti:sapphire femtosecond ring lasers allow to achieve scan rates as high as 100 kHz for a 100 ps long time window and a time-delay resolution of 100 fs. The feasibility of this high-speed ASOPS system is evaluated by performing THz time domain spectroscopy on molecular gases where signal-to-noise ratios exceeding 30 dB for averaging times in the millisecond range have been obtained. In order to demonstrate the benefits of this system for ultrafast pump-probe spectroscopy we demonstrate the high-sensitivity detection of coherent acoustic phonons with dephasing times in the range of the 100 ps time window. Konstanzer Online-Publikations-System (KOPS) URL: http://nbn-resolving. de/urn:nbn:de:bsz:352-0-395845 Erschienen in: Optics Express ; 24 (2016 24 ( ), 26. -S. 22930-22940 http://dx.doi.org/10.1364 Graham, "Terahertz cyclotron resonance spectroscopy of an algan/gan heterostructure using a high-field pulsed magnet and an asynchronous optical sampling technique," Appl. Phys. Lett. 108, 212101 (2016). 18. A. Bruchhausen, R. Gebs, F. Hudert, D. Issenmann, G. Klatt, A. Bartels, O. Schecker, R. Waitz, A. Erbe, E. Scheer, J.-R. Huntzinger, A. Mlayah, and T. Dekorsy, "Subharmonic resonant optical excitation of confined acoustic modes in a free-standing semiconductor membrane at GHz frequencies with a high-repetition-rate femtosecond laser," Phys. Rev. Lett. 106, 077401 (2011).

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High-Resolution Terahertz Spectrometer

Cited by 46 publications

References 41 publications

Study of broadband THz time-domain spectroscopy at different relative humidity levels

Study of broadband THz time-domain spectroscopy at different relative humidity levels

A decade-spanning high-resolution asynchronous optical sampling terahertz time-domain and frequency comb spectrometer

Ultrafast time-domain spectroscopy system using 10 GHz asynchronous optical sampling with 100 kHz scan rate

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