Life on Earth relies on chiral molecules-that is, species not superimposable on their mirror images. This manifests itself in the selection of a single molecular handedness, or homochirality, across the biosphere. We present the astronomical detection of a chiral molecule, propylene oxide (CH3CHCH2O), in absorption toward the Galactic center. Propylene oxide is detected in the gas phase in a cold, extended molecular shell around the embedded, massive protostellar clusters in the Sagittarius B2 star-forming region. This material is representative of the earliest stage of solar system evolution in which a chiral molecule has been found.

We report three-dimensional trapping of an oxide molecule (YO), using a radio-frequency magneto-optical trap (MOT). The total number of molecules loaded is ∼1.5×10 4 , with a temperature of 7(1) mK. This diversifies the frontier of molecules that are laser coolable and paves the way for the second-stage narrow-line cooling in this molecule to the microkelvin regime. Futhermore, the new challenges of creating a 3-D MOT of YO resolved here indicate that MOTs of more complex non-linear molecules should be feasible as well.

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We present 2D terahertz-terahertz-Raman (2D TTR) spectroscopy, the first technique, to our knowledge, to interrogate a liquid with multiple pulses of terahertz (THz) light. This hybrid approach isolates nonlinear signatures in isotropic media, and is sensitive to the coupling and anharmonicity of thermally activated THz modes that play a central role in liquid-phase chemistry. Specifically, by varying the timing between two intense THz pulses, we control the orientational alignment of molecules in a liquid, and nonlinearly excite vibrational coherences. A comparison of experimental and simulated 2D TTR spectra of bromoform (CHBr 3 ), carbon tetrachloride (CCl 4 ), and dibromodichloromethane (CBr 2 Cl 2 ) shows previously unobserved off-diagonal anharmonic coupling between thermally populated vibrational modes.ultrafast dynamics | terahertz | coherent multidimensional spectroscopy D etailed molecular pictures of the structure and dynamics of liquids drive our understanding of chemistry and biology. Nonlinear 2D infrared and NMR spectroscopies have revealed many specifics of liquid behavior, monitoring the coupling, spectral diffusion, and homogeneous linewidths of intramolecular vibrations and nuclear spins (1, 2). However, the motions that directly participate in solvation and chemical reactivity are manifest in the terahertz (THz) region of the spectrum, making 2D THz studies especially valuable. To date, no 2D technique has been demonstrated that incorporates multiple THz interactions with a liquid.Recent advances in pulsed, high-power THz sources with electric fields exceeding 100 kV/cm have enabled a new generation of nonlinear THz spectroscopy, in which THz radiation is used to both manipulate and record the response of matter (3). It is now possible, for example, to control the alignment of gasphase molecules (4) and antiferromagnetic spin waves (5), drive an insulator-to-metal transition in oxides such as VO 2 (6), and break up Cooper pairs in a superconductor with intense THz pulses (7). Nonlinear THz interactions have also enabled the first demonstrations of 2D THz spectroscopy in a double quantum well system and graphene (8, 9).With weak transition dipole moments yet high THz absorptivity, liquids present many challenges with respect to the development of 2D THz spectroscopy. Initial successes with 2D Raman spectroscopy were later shown to suffer from the interference of cascaded processes (10-12), but new schemes using optical pulse shaping have eliminated the cascaded contributions (13). An alternative approach is resonant 2D THz spectroscopy, analogous to 2D IR spectroscopy. However, this method is hindered by a lack of THz directional phase matching, leading to signals that can be easily overwhelmed by a strong linear background. In the last few years, hybrid optical-THz techniques that circumvent these challenges have emerged, including 2D Raman-THz spectroscopy and THz Kerr effect spectroscopy (14-16). Here, we present the complementary 2D TTR spectroscopy, a natural extension of these hybrid te...

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Broadband spectroscopy is an invaluable tool for measuring multiple gas-phase species simultaneously. In this work we review basic techniques, implementations, and current applications for broadband spectroscopy. We discuss components of broad-band spectroscopy including light sources, absorption cells, and detection methods and then discuss specific combinations of these components in commonly-used techniques. We finish this review by discussing potential future advances in techniques and applications of broad-band spectroscopy.

Fundamental properties of molecular liquids are governed by long-range interactions that most prominently manifest at terahertz (THz) frequencies. Here we report the detection of nonlinear THz photon-echo (rephasing) signals in liquid bromoform using THz-THz-Raman spectroscopy. Together, the many observed signatures span frequencies from 0.5 to 8.5 THz and result from couplings between thermally populated ladders of vibrational states. The strongest peaks in the spectrum are found to be multiquantum dipole and 1-quantum polarizability transitions and may arise from nonlinearities in the intramolecular dipole moment surface driven by intermolecular interactions.

The generation and detection of a decade-spanning terahertz (THz) frequency comb is reported using two Ti:sapphire femtosecond laser oscillators and asynchronous optical sampling THz time-domain spectroscopy. The comb extends from 0.15 to 2.4 THz, with a tooth spacing of 80 MHz, a linewidth of 3.7 kHz, and a fractional precision of 1.8 × 10 −9 . With time-domain detection of the comb, we measure three transitions of water vapor at 10 mTorr between 1-2 THz with an average Doppler-limited fractional accuracy of 6.1 × 10 −8 . Significant improvements in bandwidth, resolution, and sensitivity are possible with existing technologies.