In 2016, with funding from an NSF grant, we purchased a recently commercialized laser-driven
tunable low-energy photon source (Energetiq EQ-1500 LDLS™) which offers distinct advantages
over noble gas plasma sources previously used in photochemical studies involving nanoscale thin
films. The spectral distribution of this photon source ranges from 0.5 eV to 7.4 eV, ensuring that our
photochemistry studies are conducted in the absence of radiation chemistry. A newly installed
movable FGAP71 photodiode (Thorlabs) is used to measure the photon flux. Although the measured
incident flux (~6 × 1015 photons cm−2 s−1 ) of the Energetiq photon source is high, the flux is orders of
magnitude lower than that of laser sources (e.g., ArF excimer lasers) which can initiate two-photon
processes. The incident photon flux is stable, showing a temporal variation of less than 1%. The
Energetiq photon source has spectral radiance approximately independent of photon energy, as
characterized by the manufacturer. When the photon source is coupled with a Czerny-Turner
Monochromator (to be purchased with NSF funding), > 1012 photons/second can be obtained at a
spectral bandwidth of 10 meV, allowing for wavelength-dependent photochemistry studies to probe
fundamental molecular processes.
