A pair of photons called signal and idler photons, respectively, are produced through the nonlinear process of type I spontaneous parametric down conversion in BBO crystal pumped by the second harmonic wave of a Ti∶sapphire femtosecond laser pulse. The two order interference phenomenon of the signal photon in Michelson interferometer is observed and give an analysis in detail.

中国激光(英文版)Jan 1, 20000 citations

Nature Nanotechnology

Harmonizing single photons with a laser pulse

Liang Zhai, Alisa Javadi

Published Apr 26, 2022• 3 citations

Publisher

DOI: 10.1038/s41565-022-01117-0

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We theoretically study multiphoton ionization of the Ca atom irradiated by the second (photon energy

3.1

eV) and third (photon energy 4.65 eV) harmonics of Ti:sapphire laser pulses (photon energy

1.55

eV). Because of the dense energy level structure the second and third harmonics of a Ti:sapphire laser are nearly single-photon resonant with the

4s4p

{}^{1}{P}^{o}

and

4s5p

{}^{1}{P}^{o}

states, respectively. Although two-photon ionization takes place through the near-resonant intermediate states with the same symmetry in both cases, it turns out that there are significant differences between them. The photoelectron energy spectra exhibit the absence or presence of substructures. More interestingly, the photoelectron angular distributions clearly show that the main contribution to the ionization processes by the third harmonic arises from the far-off-resonant

4s4p

{}^{1}{P}^{o}

state rather than the near-resonant

4s5p

{}^{1}{P}^{o}

state. These findings can be attributed to the fact that the dipole moment for the

4{s}^{2}

${}^{1}{S}^{e}\ensuremath{-}4s5p$

{}^{1}{P}^{o}

transition is much smaller than that for the

4{s}^{2}

${}^{1}{S}^{e}\ensuremath{-}4s4p$

{}^{1}{P}^{o}

transition.