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Full characterization and optimization of a femtosecond ultraviolet laser source for time and angle-resolved photoemission on solid surfaces
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Image of FIG. 1.
FIG. 1.

(a) Schematic of the experimental setup for FH generation by frequency doubling. (b) Schematic for FH generation by frequency mixing. L: lens with f = 20 cm, DM: dichroic mirror, DL: delay line. The off-axis parabolas have f = 5–10 cm focal lengths depending on their location. Note that the frequency mixing setup uses 50% of the laser energy, i.e., 3 μJ whereas the frequency doubling setup uses only 1.5 μJ.

Image of FIG. 2.
FIG. 2.

(a) Dashed green line: spectrum of the UV beam obtained by frequency doubling, 2ω + 2ω → 4ω, central wavelength λ0 = 204.5 nm (6.04 eV), FWHM bandwidth Δλ = 1.34 nm (40 meV). Full blue line: spectrum obtained by frequency mixing, 3ω + ω → 4ω, λ0 = 197.5 nm (6.28 eV), Δλ = 1.75 nm (56 meV). (b) Data points from a cross correlation by frequency difference 4ω − ω → 3ω, showing a FWHM of 76 ± 3 fs.

Image of FIG. 3.
FIG. 3.

Insert: focal spot of the UV beam at the focus of a f = 50 cm MgF2 lens. The full and dashed lines represent horizontal and vertical line-outs, respectively. The spot size is 48 × 49 μm at FWHM.

Image of FIG. 4.
FIG. 4.

A 3D view of the experimental chambers and the analyzer.

Image of FIG. 5.
FIG. 5.

(a) Photoemission spectra taken on polycrystalline Cu with the femtosecond 6.28 eV beam at various incident flux values. The photon number is increased from N = 2 × 105 to N = 6 × 106 photons/pulse. (b) Shift of the Fermi level ΔE as a function of photons/pulse. (c) Resolution δE as a function of photons/pulse. The instrumental resolution is reached at low photon flux.

Image of FIG. 6.
FIG. 6.

(a) Angle resolved photoemission data taken on Bi(111) surface at 130 K and along the Γ-M direction of the Brillouin zone using the UV femtosecond laser source. The bands crossing the Fermi level are surface states (indicated by arrows), b is a bulk band. (b) The corresponding Fermi surface obtained in the same experimental conditions.

Image of FIG. 7.
FIG. 7.

(a) Photoemission spectrum at normal emission on Bi at 130 K as a function of pump-probe delay. (b) Blue circles: number of counts integrated in the range [100–300] meV as a function of pump-probe delay; green curve: the primitive integral of the experimental cross correlation of Fig. 2(b).


Generic image for table
Table I.

Summary of the main UV source characteristics for the two different setups. Bandwidth Δλ, duration τ, and focal spot size are given at FWHM.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Full characterization and optimization of a femtosecond ultraviolet laser source for time and angle-resolved photoemission on solid surfaces