Abstract
Time- and angle-resolved photoemission spectroscopy (trARPES) using femtosecond extreme ultraviolet high harmonics has recently emerged as a powerful tool for investigating ultrafast quasiparticle dynamics in correlated-electron materials. However, the full potential of this approach has not yet been achieved because, to date, high harmonics generated by 800nm wavelength Ti:Sapphire lasers required a trade-off between photon flux, energy and time resolution. Photoemission spectroscopy requires a quasi-monochromatic output, but dispersive optical elements that select a single harmonic can significantly reduce the photon flux and time resolution. Here we show that 400nm driven high harmonic extreme-ultraviolet trARPES is superior to using 800nm laser drivers since it eliminates the need for any spectral selection, thereby increasing photon flux and energy resolution to <150meV while preserving excellent time resolution of about 30fs.
Highlights
Angle-resolved photoemission spectroscopy (ARPES) using synchrotron radiation in the extreme ultraviolet (XUV) region of the spectrum is one of the most powerful techniques used to study the electronic properties of surfaces, interfaces and correlatedelectron materials over the last decade [1,2,3]
The majority (95%) of the output of a single-stage, cryocooled, Ti:Sapphire multipass laser amplifier system [44] operating at 10 kHz, 1.2 mJ, 25 fs, 780 nm is used to generate the second harmonic in a 200 m thick beta barium borate (BBO) crystal, which yields pulses at 390 nm with 300 J energy per pulse
We focus the blue light into a 5 cm long, 150 m inner-diameter capillary waveguide [38,46] filled with 15–20 Torr of Kr gas, where we dominantly generate the 7th harmonic at 22.3 eV
Summary
Angle-resolved photoemission spectroscopy (ARPES) using synchrotron radiation in the extreme ultraviolet (XUV) region of the spectrum is one of the most powerful techniques used to study the electronic properties of surfaces, interfaces and correlatedelectron materials over the last decade [1,2,3]. For shorter wavelength driving lasers, the HHG process is more efficient, so that lower pump intensity is needed to achieve high photon flux in the XUV [21,28,29] This approach is well-suited for trARPES and will be useful for other advanced spectroscopies using HHG such as cold target recoil ion momentum spectroscopy (COLTRIMS) [30,31,32], velocity-map imaging (VMI) [33], magneto-optical experiments [34,35,36], as well as HHG-based coherent diffractive imaging (CDI) applications [9]
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