FMCW lidar-enabled stabilization for range-selective digital holographic imaging of vibrating objects

Range-selective digital holography (RSDH) is a coherent imaging technique that enables the reconstruction of digital holograms at tunable distances while suppressing the contributions from objects at other ranges. This selectivity is achieved by combining digital holography with frequency-modulated continuous-wave (FMCW) signals commonly found in lidar to produce a temporally modulated interference pattern. By tuning the local-oscillator frequency according to the object distance, a temporally stable hologram is formed at the desired range, which can then be recorded on a sensor array. The resulting range resolution can be substantially finer than the non-diffraction-limited depth of field. However, holographic systems are inherently sensitive to object motion and vibration, which introduce phase variations that can degrade the quality of the hologram. In particular, radial motion exceeding half the optical wavelength during the sensor integration time can induce phase shifts that lead to signal washout, requiring the use of short integration times that degrade the image signal-to-noise ratio (SNR). We demonstrate an FMCW lidar-enabled stabilization system that preserves high-fidelity holographic reconstructions outdoors at distances up to 90 m, with long integration times and significantly higher SNR, even when the object displacement exceeds 18 optical wavelengths during integration. The developed RSDH architecture enables a theoretical holographic imaging range window of multiple kilometers while providing stabilization over a similarly broad range of object distances.