SLAC MeV-UED has led to a new paradigm in ultrafast electron scattering: higher electron beam energy means stronger diffraction and significantly reduced space-charge effects, leading to atomic spatial resolution together with subpicosecond temporal resolution. Furthermore, MeV electrons experience less multiple-scattering, and possess a near-flat Ewald-sphere; MeV-UED makes it possible to achieve quantitatively-understood observables to validate physical modeling. MeV-UED has enabled broad scientific opportunities in ultrafast structural dynamics and chemical dynamics, such as the first direct observations of bond dissociation, non-adiabatic dynamics through conical intersections, coherent ground state wavepacket motion after electrocyclic ring-opening in real space and time, and simultaneous observation of electronic and nuclear structure changes in a molecule undergoing non-adiabatic dynamics (SLAC-MeV-UED Pub).
SLAC MeV-UED run 4 will focus on gas-phase chemical dynamics. It will build on the success of the previous gas-phase UED run (run 2), using the same GUED sample chamber and incorporating improvements in the MeV UED facility since then. The run will build on successful sample delivery methods such as the flow cell and pulsed nozzles, while R&D efforts will focus on new high-repetition rate delivery.
- Sample Delivery
- Sample Delivery R&D
- Optical Laser Properties
- P43 phosphor screen & Andor iXon Ultra 888 EMCCD
- ePIX detector - direct electron detection*
Two ‘standard’ sample delivery methods are offered in run 4: (1) A flow cell which has proved ideally suited for systems with moderate vapor pressure, and (2) a Parker valve pulsed nozzel which allows sample heating to ~180 Celcius.
In the past, we achieved the best results for samples with vapor pressures of >0.5 mbar at room temperature using the flow cell. Samples requiring higher temperatures to increase their vapor pressure can only be used in combination with the Parker valve operating at 50% of the maximum repetition rate (180 Hz). In previous, successful experiments, samples were heated to temperatures where they exhibit 50-100 mbar of vapor pressure. The gas phase UED team is constantly enhancing sample delivery capacities, which will be offered to users on a best effort basis.
Sample Delivery R&D
MeV UED is committed to continuing development of its sample delivery options. Some new delivery systems are planned for development. In particular, we are planning R&D efforts on heatable cw slit jets which will allow experiments with samples, which have to be heated to achieve >0.5 mbar vapor pressures, at the full 360 Hz repetition rate. If there is interest in using such a sample source on a best effort basis, please contact the gas phase UED team.
Optical Laser Properties
Single shot → 360 Hz
200 nm, 266 nm, 400 nm, 800nm, 240 nm - 2 µm tunable, 3-15 µm tunable
Typical optical pulse energy
> 8 mJ @ 800 nm
Nominal pulse duration
75 fs (FWHM)
0 - 3 ns (physical delay stage)
Optical spot size
200 - 1500 µm (FWHM)
P43 phosphor screen & Andor iXon Ultra 888 EMCCD
85 µm (rms)
13 x 13 µm2
1024 x 1024
Pixel well depth
ePIX detector - direct electron detection*
100 x 100 um2
~8 x 8 cm2 (Partially shadowed)
3 fixed plus 2 with auto ranging and programmable switch point
S/N in High Gain per MeV electron
*Offered under a commissioning/best-effort basis. Contact UED staff for details.