Subcycle spectral structures of light-induced states in attosecond transient absorption of helium dressed by an orthogonally polarized laser field

We present the subcycle spectral structures from attosecond transient absorption spectra of helium by accurately solving the full three-dimensional time-dependent Schrödinger equation in extreme ultraviolet attosecond pulse and an orthogonally polarized infrared (IR) laser field. We discover that the subcycle spectral features associated with the dressed 1<i>snp</i> (<i>n</i> ≥ 4) states and light-induced states, referred to as <i>ns</i> ^-, <i>nd</i> ^-, <i>np</i> ^- and <i>nf</i> ^-, can be strongly modified or even enhanced when the strength ratio of the orthogonal laser field in two polarized laser directions changes. To understand the spectral evolution of the subcycle structures, we perform calculations of the time-dependent population and time-frequency analysis. The results indicate that more quantum channels can be opened by the attosecond pulse combined with the orthogonally polarized IR laser field, leading to robust absorption spectra of light-induced states. Our theoretical findings predict that the orthogonally polarized laser field is useful for manipulating subcycle transition dynamics in the transient absorption process.