Understanding Pound-Drever-Hall locking using voltage controlled radio-frequency oscillators: An undergraduate experiment

We have developed a senior undergraduate experiment that illustrates frequency stabilization techniques using radio-frequency electronics. The primary objective is to frequency stabilize a voltage controlled oscillator to a cavity resonance at 800 MHz using the Pound-Drever-Hall method. This technique is commonly applied to stabilize lasers at optical frequencies. By using only radio-frequency equipment it is possible to systematically study aspects of the technique more thoroughly, inexpensively, and free from eye hazards. Students also learn about modular radio-frequency electronics and basic feedback control loops. By varying the temperature of the resonator, students can determine the thermal expansion coefficients of copper, aluminum, and super invar.Comment: 9 pages, 10 figure

Ultrafast isomerization initiated by X-ray core ionization

Rapid proton migration is a key process in hydrocarbon photochemistry. Charge migration and subsequent proton motion can mitigate radiation damage when heavier atoms absorb X-rays. If rapid enough, this can improve the fidelity of diffract-before-destroy measurements of biomolecular structure at X-ray-free electron lasers. Here we study X-ray-initiated isomerization of acetylene, a model for proton dynamics in hydrocarbons. Our time-resolved measurements capture the transient motion of protons following X-ray ionization of carbon K-shell electrons. We Coulomb-explode the molecule with a second precisely delayed X-ray pulse and then record all the fragment momenta. These snapshots at different delays are combined into a ‘molecular movie’ of the evolving molecule, which shows substantial proton redistribution within the first 12 fs. We conclude that significant proton motion occurs on a timescale comparable to the Auger relaxation that refills the K-shell vacancy

Soft-x-ray-induced ionization and fragmentation dynamics of Sc3N@C80 investigated using an ion-ion-coincidence momentum-imaging technique

Citation: Xiong, H., Obaid, R., Fang, L., Bomme, C., Kling, N. G., Ablikim, U., … Berrah, N. (2017). Soft-x-ray-induced ionization and fragmentation dynamics of ${\mathrm{Sc}}_{3}\mathrm{N}@{\mathrm{C}}_{80}$ investigated using an ion-ion-coincidence momentum-imaging technique. Physical Review A, 96(3), 033408. https://doi.org/10.1103/PhysRevA.96.033408The fragmentation dynamics of an endohedral fullerene, Sc3N@C80, after absorption of a soft-x-ray photon, has been studied with an ion-ion-coincidence momentum-imaging technique. Molecular inner-shell ionization at 406.5 eV, targeting the Sc (2p) shell of the encapsulated Sc3N moiety and the C (1s) shell of the C80 cage, leads to the cage fragmentation through evaporation of C2, emission of small molecular carbon ions (Cn+, n≤24), and release of Sc and Sc-containing ions associated with the carbon cage opening or fragmentation. The predominant charge states of Sc and Sc-containing ionic fragments are +1 despite an effective Sc valence of 2.4, indicating that charge transfer or redistribution plays an important role in the fragmentation of the encaged Sc3N. Sequential emission of two out of the three Sc atoms of the encaged moiety, via Coulomb explosion in the form of Sc+ or Sc-containing ions, is significant. We also find that the resonant excitation of the Sc (2p) shell electrons significantly increased the yield of the parent Sc3N@C80 and its fragment ions, partially attributed to the collision of the energetic Auger electrons from the Sc site with the carbon cage

Reactivity of Aromatic Radical Cations. Rate Constants for Reactions of 9-Phenyl- and 9,10-Diphenylanthracene Radical Cations with Acyclic Amines

Peer reviewed: YesNRC publication: Ye