Two-Color Strong-Field Ionization with Non-Classical Light

Strong-field ionization in intense laser fields is commonly described within a tunneling framework based on classical driving fields, where key concepts such as Volkov states, the ponderomotive energy, and the Keldysh parameter rely on a well-defined classical field amplitude and phase. Extending strong-field tunneling ionization to non-classical driving fields raises fundamental questions about how these quantities and the tunneling picture itself are modified when the driving field can no longer be approximated by a coherent state of light.

We generate bright squeezed vacuum (BSV) pulses at 800 nm via parametric down-conversion as a non-classical source for strong-field experiments. We measure the pulse energy distribution and observe strong shot-to-shot intensity fluctuations characteristic of BSV. The source is implemented using walk-off compensation and cascaded amplification to achieve stable operation at high pulse energies.

We combine a weak non-classical 800 nm field with a strong classical 400 nm field in a two-color driving scheme for strong-field ionization. By scanning the relative optical phase between the two fields, we study how a weak non-classical component perturbs tunneling ionization driven by a dominant classical field. Theoretical results predict that tunneling dynamics are modified by the photon statistics of BSV compared with a coherent dressing field. This approach provides a controlled setting to explore the role of non-classical light in strong-field ionization.