QIF-T0078

LiDAR remote pulse detection (laser Doppler vibrometry for cardiac waveform extraction)

The iPhone LiDAR scanner uses a VCSEL (vertical-cavity surface-emitting laser) array emitting pulsed 940nm infrared laser light and a SPAD (single-photon avalanche diode) detector array measuring time-of-flight. In normal operation, it measures depth for AR applications. However, the same hardware can function as a simplified laser Doppler vibrometer (LDV): when the laser beam reflects off skin, the pulse wave from cardiac activity causes micro-vibrations (amplitude ~1-10 µm) on the skin surface. These vibrations create measurable Doppler shifts or time-of-flight variations in the reflected laser signal. Extracting the cardiac pulse waveform from LiDAR data requires raw access to the SPAD photodetector output (timing resolution in picoseconds) rather than the processed depth map. This requires either a jailbreak, hardware teardown, or compromised firmware. The extracted pulse waveform contains: heart rate, heart rate variability (HRV), pulse transit time (correlated with blood pressure), and potentially cardiac arrhythmia signatures. Unlike QIF-T0075 (ultrasonic sonar), this is optical and directional, requiring line-of-sight but working at greater precision for skin-surface vibrations. Range is limited to ~5m (LiDAR operational range) but could be extended with higher-power laser sources.