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

Good, Jacob T. and Holland, Daniel B. and Finneran, Ian A. and Carroll, P. Brandon and Kelley, Matthew J. and Blake, Geoffrey A. (2015) A decade-spanning high-resolution asynchronous optical sampling terahertz time-domain and frequency comb spectrometer. Review of Scientific Instruments, 86 (10). Art. No. 103107. ISSN 0034-6748. https://resolver.caltech.edu/CaltechAUTHORS:20151019-084242563

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Abstract

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.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1063/1.4932567DOIArticle
ORCID:
AuthorORCID
Holland, Daniel B.0000-0002-3404-4939
Finneran, Ian A.0000-0003-2506-4652
Carroll, P. Brandon0000-0002-3191-5401
Blake, Geoffrey A.0000-0003-0787-1610
Additional Information:© 2015 AIP Publishing LLC. Received 30 July 2015; accepted 24 September 2015; published online 14 October 2015. The authors are grateful to Jun Ye (NIST-JILA) for loaning equipment and for many helpful discussions. The authors thank M. A. Allodi (Caltech) for edits to this manuscript and for advice regarding alignment of optics and Jeff Groseth (Caltech) for advice and assistance with electronics. This work was supported by the National Science Foundation (Grant Nos. CHE-1214123 and CHE-0722330). I. A. Finneran acknowledges the NSF Graduate Research Fellowship Program for financial support.
Funders:
Funding AgencyGrant Number
NSFCHE-1214123
NSFCHE-0722330
NSF Graduate Research FellowshipUNSPECIFIED
Issue or Number:10
Record Number:CaltechAUTHORS:20151019-084242563
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20151019-084242563
Official Citation:A decade-spanning high-resolution asynchronous optical sampling terahertz time-domain and frequency comb spectrometer Good, Jacob T. and Holland, Daniel B. and Finneran, Ian A. and Carroll, P. Brandon and Kelley, Matthew J. and Blake, Geoffrey A., Review of Scientific Instruments, 86, 103107 (2015), DOI:http://dx.doi.org/10.1063/1.4932567
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:61240
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:19 Oct 2015 16:37
Last Modified:10 Dec 2020 20:50

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