Spectroscopy seminars

Subha Majumdar presents a six-dimensional Milky Way phase-space catalogue designed to map stellar motions and dark matter beyond the reach of Gaia parallaxes alone. Gaia astrometry is combined with spectrophotometric distances and radial velocities from fourteen surveys, including DESI, SDSS-BOSS, APOGEE and LAMOST. The resulting catalogue contains about 33 million tracers and detailed distance–velocity measurements for roughly half a million halo stars. It characterizes distant clusters, dwarf galaxies and stellar streams, enabling mass modeling, kinematic studies, abundance mapping, Galactic archaeology and dark-matter searches. An application constructs a continuous Galactic rotation curve extending to 250 kiloparsecs.

Light-driven synthesis offers opportunities for more sustainable chemistry, but effective reaction design depends on understanding interactions among photons, substrates and catalysts. This seminar combines spectroscopy with kinetic analysis to resolve those mechanisms. It shows how such evidence can guide more efficient transformations and extend the range of molecules accessible through photochemical synthesis.

Anne L’Huillier explains how the interaction of an intense laser with atoms in a gas generates high-order harmonics and, in the time domain, trains of pulses lasting roughly one hundred attoseconds. These pulses provide a way to investigate electron motion in atoms and molecules through pump–probe measurements. The lecture traces major experimental steps from harmonic generation to the measurement of attosecond pulses, then discusses applications of the resulting techniques. It connects the production and characterisation of extremely short light pulses with the physical processes they make accessible, showing how attosecond science supports the study of electron dynamics.

Jun Ye discusses how laser science and increasingly large coherent quantum systems are expanding precision measurement into nuclear physics. Experiments now maintain coherence in thousands of atoms for minutes and resolve quantum states of the thorium-229 nuclear transition. A vacuum-ultraviolet frequency comb enables coherent excitation of that transition and connects its frequency directly to a highly precise atomic clock. The lecture examines how this connection between atomic and nuclear measurement could support new tests of fundamental physics and nuclear clocks containing billions of absorbers, with the prospect of surpassing the timekeeping capabilities of existing atomic clocks.

Stellar magnetism influences a star's structure, evolution, environment and nearby planets. The seminar distinguishes fields generated continuously by dynamos in cool stars from fossil fields retained by hot stars, and explains how spectropolarimetry measures and maps magnetic structure at stellar surfaces.

Sound waves can be used to modify brain activity safely and transiently with unprecedented precision even deep in the brain - unlike traditional brain stimulation methods. In a series of studies in humans and non-human primates, I will show that Transcranial Ultrasound Stimulation (TUS) can have medium- to long-lasting effects. Multiple read-outs allow us to conclude that TUS can perturb neuronal tissues up to 2h after intervention, including changes in local and distributed brain network configurations, behavioural changes, task-related neuronal changes and chemical changes in the sonicated focal volume. Combined with multiple neuroimaging techniques (resting state functional Magnetic Resonance Imaging [rsfMRI], Spectroscopy [MRS] and task-related fMRI changes), this talk will focus on recent human TUS studies.