  Resonance states of axion-like particles were searched for via four-wave
mixing by focusing two-color pulsed lasers into a quasi-vacuum. A
quasi-parallel collision system that allows probing of the sub-eV mass range
was realized by focusing the combined laser fields with an off-axis parabolic
mirror. A 0.10 mJ/34 fs Ti:Sapphire laser pulse and a 0.14 mJ/9 ns Nd:YAG laser
pulse were spatiotemporally synchronized by sharing a common optical axis and
focused into the vacuum system. No significant four-wave mixing signal was
observed at the vacuum pressure of $3.7 \times 10^{-5}$ Pa , thereby providing
upper bounds on the coupling-mass relation by assuming exchanges of scalar and
pseudoscalar fields at a 95 % confidence level in the mass range below 0.21 eV.
For this search, the experimental setup was substantially upgraded so that
optical components are compatible with the requirements of the high-quality
vacuum system, hence enabling the pulse power to be increased. With the
increased pulse power, a new kind of pressure-dependent background photons
emerged in addition to the known atomic four-wave mixing process. This paper
shows the pressure dependence of these background photons and how to handle
them in the search.
