Mechanics-free speckle contrast optical spectroscopy with liquid-lens-based adaptive illumination

Speckle contrast optical spectroscopy (SCOS) is often limited by short exposure bias and a reduced dynamic range at a long exposure time. We present a mechanics-free SCOS approach that simultaneously adjusts the exposure time and illumination spot size using an electrically tunable liquid lens (-3 to +3 dpt), redistributing photons across a broader exposure range. Using independently the measured field autocorrelation functions g₁(τ), we validate the SCOS model and identify a reliable operating range of the normalized mean intensity between 0.2 and 0.5. Measurements acquired under different optical conditions are normalized by their respective speckle contrast factor β and combined into a single composite dataset, enabling joint analysis across multiple exposure times. The extracted correlation time (τ_c) agrees with the reference value to within <1%. These results show that adaptive spot control with unified data combination enables a robust multi-exposure-time SCOS analysis.