Photoelectron FROG in the VUV

"Quantitative" methods in photoelectron spectroscopy

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Paul Hockett
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Photoelectron FROG in the VUV

Post by Paul Hockett »

A topic of current, moderate, interest for me: applying FROG-type reconstructions (FROG == frequency resolved optical gating) to two-photon photoelectron measurements for pulse metrology, and (maybe) photoelectron metrology (==characterising photoemission). I don't yet know a whole lot about this, but did have a quick play a while back on the method development (see this Jupyter Notebook for details).

In short, if you can factor out (or otherwise fudge away) the medium response, then things look pretty much identical to optical FROG, and the same type of methods can be used. This is probably reasonable for atomic photoionization over (relatively) limited bandwidths (say 100s meV) in many case, although obviously depends on the photoionization dynamics for the case at hand. For some test data, for non-resonant ionization of Xe with 160 + 266nm fields, this seemed to work for field reconstruction with blind FROG (see figure) - in the preliminary experimental test case this returned pulses that looked as expected (but more research is required, of course!).

An interesting extension here is whether one can determine anything about the photoionization dynamics in cases where this doesn't hold, which is likely possible if you know at least one of the fields a priori.

As far as I can tell, the first demonstration in the literature is from 2002, under the "TPI-FROG" moniker (TPI = two-photon ionization):

“Measurement of the Intensity-Dependent Atomic Dipole Phase of a High Harmonic by Frequency-Resolved Optical Gating.” Sekikawa, Taro, Tomotaka Katsura, Satoshi Miura, and Shuntaro Watanabe. 2002. Physical Review Letters 88 (19): 193902.

One of the techniques commonly used for characteriz-
ing the ultrashort pulses fully is frequency-resolved optical
gating (FROG) [10]. It involves measuring the time-
dependent spectrum of the autocorrelation or cross correla-
tion (spectrogram) and solving the pulse retrieval problem
mathematically. The nonlinear optical processes used so
far, however, require bulk materials as nonlinear media,
through which XUV and VUV pulses cannot propagate.
Another nonlinear process is necessary for the pulse mea-
surement in the VUV and XUV regions.

In this paper, we propose two-photon ionization (TPI)
FROG for the full characterization of XUV and VUV
pulses and demonstrate the intensity and phase measure-
ment of the fifth harmonic pulses of a Ti:sapphire (TiS)
laser for the first time. TPI FROG is free from phase
matching and is scalable to XUV and soft x-ray pulses.
Here we focus on the fifth harmonic to demonstrate the
versatility of TPI FROG, because the phase manipulation
is easier by using the transport dispersive materials and
because the validity of the measurement can be checked.

... but there doesn't seem to be much since, although I'm still looking into it (slowly).

Here's my reading list so far, comments or suggestions appreciated! (This will update as things progress.)

Key refs

Full reading list so far (based on some Scopus/Google Scholar searches)

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