More Like this

1. Enabling MHz-Level Tailored Ultrafast Photoemission via Simultaneous Laser Mixing and Shaping

   https://doi.org/10.1364/CLEO_SI.2023.SM2F.4  

   Lemons, Randy; Hirschman, Jack; Neveu, Nicole; Duris, Joseph; Marinelli, Agostino; Durfee, Charles; Carbajo, Sergio (January 2023, Optica Publishing Group)

   We present a novel, versatile framework to generate W-level temporally shaped UV picosecond pulses via non-colinear sum frequency generation and demonstrate it producing temporally flattop, high-power UV pulses capable of enhancing femtosecond- and attosecond-level X-ray free electron lasers. 

   more » « less
2. Time-resolving state-specific molecular dissociation with XUV broadband absorption spectroscopy

   https://doi.org/10.1126/sciadv.adk1482  

   Magunia, Alexander; Rebholz, Marc; Appi, Elisa; Papadopoulou, Christina C; Lindenblatt, Hannes; Trost, Florian; Meister, Severin; Ding, Thomas; Straub, Michael; Borisova, Gergana D; et al (November 2023, Science Advances)

   The electronic and nuclear dynamics inside molecules are essential for chemical reactions, where different pathways typically unfold on ultrafast timescales. Extreme ultraviolet (XUV) light pulses generated by free-electron lasers (FELs) allow atomic-site and electronic-state selectivity, triggering specific molecular dynamics while providing femtosecond resolution. Yet, time-resolved experiments are either blind to neutral fragments or limited by the spectral bandwidth of FEL pulses. Here, we combine a broadband XUV probe pulse from high-order harmonic generation with an FEL pump pulse to observe dissociation pathways leading to fragments in different quantum states. We temporally resolve the dissociation of a specific O₂⁺state into two competing channels by measuring the resonances of ionic and neutral fragments. This scheme can be applied to investigate convoluted dynamics in larger molecules relevant to diverse science fields. 

   more » « less
3. Subadditive femtosecond laser-induced electron emission from a GaAs tip

   Newman, William; Jones, Eric; Brunkow, Evan; Batelaan, Herman; Gay, Timothy (May 2024, Physical review B)

   Multiphoton emission of electrons has been observed from sharp tips of heavily p-doped GaAs caused by laser pulses with, nominally, 800-nm wavelength, 1-nJ/pulse energy, and 90-fs duration. The emission is mostly due to four-photon processes, with some contribution from three-photon absorption as well. When the electron emission current due to two pulses separated by delay 200 fs << τ << 1 ns is integrated over all electron energies, it is less than that observed for the sum of the emission from the two individual pulses. This subadditive behavior is consistent with a fast electron emission process, i.e., one in which the electron emission occurs over a time comparable to the laser pulse width. The subadditivity results from Pauli blocking of electron emission by the second pulse due to a population increase of the GaAs conduction band caused by the first pulse. Such subadditive photoemission is a sensitive probe of excited-carrier dynamics. We employ the use of an excited-level population model to characterize the photon absorption process and give us a clearer understanding of the electron dynamics in GaAs associated with multiphoton electron emission. Possible applications of this subadditivity effect to control photoemitted electron spin are discussed. 

   more » « less
4. Implementation of Broadband near-UV Pump Pulses for Ultrafast 2D Electronic-Vibrational Spectroscopy

   https://doi.org/10.1364/UP.2020.Tu2A.2  

   Sandwisch, Jason W.; Gaynor, James D.; Khalil, Munira (January 2020, Optica Publishing Group)

   We present the generation of efficient, tunable sub-20 fs broadband near UV pulses. The tunable pulses are used in two-dimensional electronic-vibrational spectroscopy and reveal additional vibronic states in an excited state intramolecular proton transfer process. 

   more » « less
5. Dynamic optical spectroscopy and pyrometry of static targets under optical and x-ray laser heating at the European XFEL

   https://doi.org/10.1063/5.0142196  

   Ball, O_B; Prescher, C.; Appel, K.; Baehtz, C.; Baron, M_A; Briggs, R.; Cerantola, V.; Chantel, J.; Chariton, S.; Coleman, A_L; et al (August 2023, Journal of Applied Physics)

   Experiments accessing extreme conditions at x-ray free electron lasers (XFELs) involve rapidly evolving conditions of temperature. Here, we report time-resolved, direct measurements of temperature using spectral streaked optical pyrometry of x-ray and optical laser-heated states at the High Energy Density instrument of the European XFEL. This collection of typical experiments, coupled with numerical models, outlines the reliability, precision, and meaning of time dependent temperature measurements using optical emission at XFEL sources. Dynamic temperatures above 1500 K are measured continuously from spectrally- and temporally-resolved thermal emission at 450–850 nm, with time resolution down to 10–100 ns for 1–200 μs streak camera windows, using single shot and integrated modes. Targets include zero-pressure foils free-standing in air and in vacuo, and high-pressure samples compressed in diamond anvil cell multi-layer targets. Radiation sources used are 20-fs hard x-ray laser pulses at 17.8 keV, in single pulses or 2.26 MHz pulse trains of up to 30 pulses, and 250-ns infrared laser single pulses. A range of further possibilities for optical measurements of visible light in x-ray laser experiments using streak optical spectroscopy are also explored, including for the study of x-ray induced optical fluorescence, which often appears as background in thermal radiation measurements. We establish several scenarios where combined emissions from multiple sources are observed and discuss their interpretation. Challenges posed by using x-ray lasers as non-invasive probes of the sample state are addressed. 

   more » « less