Broadband horn antennas have been used for Fourier transform microwave spectroscopy for a little over a decade. In this report, we will show a more cost effective alternative in describing the reduced cost tandem cavity - chirped pulse FTMW spectrometer being constructed in Flint, Michigan.

Many interesting and important physical processes such as high-harmonic generation and coherent control are highly sensitive to the absolute Carrier Envelope Phase (CEP) of ultrashort laser pulses. Thus, the control and measurement of the CEP is of immense importance in strong field physics and chemistry. Even though the relative CEP can be measured with few existing technologies, a simple direct insitu technique has not been developed previously. Here we demonstrate a new technique based on angular streaking that can achieve such a goal. The results have been compared directly with well-known f-2f interferometer measurements. This new technique will assist the research on light-matter interactions involving ultrashort pulses and improve attosecond metrology.

Recent experiments in the Grubbs research group at the Missouri University of Science and Technology have shown that it is possible to detect rotational spectra of molecules in a CP-FTMW using multiple horn antennae. This allows for increased sensitivity by sampling a free induction decay twice, each at a separate point. Utilizing the traditional CP-FTMW design of two horns – one for transmitting and one for receiving – it was shown that it is possible to use the transmitting horn to also receive spectra. This is achieved by adding a circulator, switch, and low noise amplifier in the circuit between the transmitting horn and power amplifier. This has been demonstrated on OCS, 1,3-Difluorobenzene, and Chloroacetone in the 6-18 GHz region of the electromagnetic spectrum utilizing a variety of experimental setups. Results of these experiments as well as issues with implementing this setup, such as FID phasing issues and data analysis, will be discussed. R 0pt                                Figure

Traditionally antennas for Fourier transform microwave spectrometers have been the classic "L" shaped antennas. Here we will discuss how 3D printing can be used to quickly prototype various designs and sizes for antennas and antenna arrays to give insight on optimal antenna for FTMW. This work largely focuses on the receiving antenna and fractal designs.

The size, weight, and power requirements of emerging millimeter-wave transmitter and receiver integrated circuit elements make them ideally suited for use in high-resolution in situ gas sensors. Previous work at the Jet Propulsion Laboratory has demonstrated a tunable 90-105 GHz transmitter fabricated in 65 nm complementary metal-oxide semiconductor (CMOS) process having phase noise and output power characteristics suitable for making sub-doppler measurements when deployed as the source in a traditional frequency modulated absorption spectrometer.D. J. Nemchick et al., "Sub-Doppler spectroscopy with a CMOS transmitter," IEEE Trans. THz Sci. Technol., vol. 8, no. 1, pp. 121-126, 2018.hen paired with a heterodyne receiver of complementary bandwidth and cavity end mirror outfitted with embedded coplanar waveguides a miniaturized cavity enhanced pulsed Fourier transform spectrometer can be realized where all source and detection electronics are housed on a single 100 cm² printed circuit board. D. J. Nemchick et al., A 90-102 GHz CMOS based pulsed Fourier transform spectrometer: New approaches for in situ chemical detection and millimeter-wave cavity-based molecular spectroscopy Rev. Sci. Inst., vol. 89, pp. 073109:1-12, 2018his talk will highlight ongoing work to expand our current capabilities in order to target more strategic molecular transitions, such as the 3_1,3 ← 2_2,0 (J^′′_{K^′′a,K^′′c} ← J^′_{K^′a,K^′c} ) H₂O line at 183.310 GHz, with a new Tx/Rx chipset. Unlike the previous generation these integrated circuit elements, now fabricated with 28 nm CMOS techniques, deploy a 90 GHz phase-lock loop the output of which is either frequency doubled, pulse modulated, then amplified (as in Tx) or frequency doubled for use in pumping a down-conversion mixer (as in Rx). Preliminary results will be presented along with a discussion on how the higher frequency radiation generated from these devices can be coupled into (and out of) an optical cavity to allow for exploitation of sensitive pulsed emission schemes.

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Footnotes:

D. J. Nemchick et al., "Sub-Doppler spectroscopy with a CMOS transmitter," IEEE Trans. THz Sci. Technol., vol. 8, no. 1, pp. 121-126, 2018.W D. J. Nemchick et al., A 90-102 GHz CMOS based pulsed Fourier transform spectrometer: New approaches for in situ chemical detection and millimeter-wave cavity-based molecular spectroscopy Rev. Sci. Inst., vol. 89, pp. 073109:1-12, 2018T

r0pt Figure Recent advancements in microwave technology have greatly reduced the prices of microwave circuit hardware and signal processing (digitization components). Using a combination of purchased (refurbished) and existing hardware, a “new” research-grade FTMW spectrometer has been constructed with minimal investment. This instrument has the capability to include multiple microwave excitations/collections (FIDs) on a single gas pulse. These features are hardware controlled, but can easily be integrated into software routines. Testing has been performed to minimize the necessary circuit components while also maximizing signal fidelity. Operation of the instrument, including tests with OCS and Benzonitrile, will be discussed.

r0pt Figure While rotational spectroscopy has become a more prominent field within the past few decades, few laboratory exercises exist that introduce students at the undergraduate level to the concepts and instrumentation used within the field. Here, a physical chemistry laboratory involving the analysis of benzonitrile with a Balle-Flygare type, Fourier Transform microwave spectrometer is introduced as one such exercise. The analysis of benzonitrile is ideally suited for an undergraduate physical chemistry laboratory because it is easily carried out within one lab period and involves a comprehensive introduction into the world of rotational spectroscopy. Within this laboratory, students have the opportunity to make Gaussian calculations, accrue spectra on a research grade FTMW, and perform effective Hamiltonian fits inclusive of nuclear electric quadrupole coupling using analysis software commonly available to the spectroscopic community. The design, implementation, and students’ response to this laboratory will be discussed.

Two-dimensional laser induced fluorescence spectroscopy is typically implemented using a monochromator equipped with an array detector to record segments of the dispersed fluorescence spectra for each laser excitation wavelength. When pulsed laser excitation is used the capabilities of this system for disentangling complex spectra can be further enhanced by time-gating the array detector. In the present work we are using an Intensified Charge-coupled Device (iCCD) that provides nanosecond time resolution and detection sensitivities that are comparable to photomultiplier tubes. We describe the marriage of a refurbished monochromator, an iCCD, and an Arduino microcontroller to collect temporally and spatially resolved emission spectra of transient small molecules. Recent data for the electronic transitions of the hypermetallic oxide MgOMg will be presented.