Fig. 3
From: Pockels laser directly driving ultrafast optical metrology
Ranging and velocimetry performance. a Schematic illustration of the time-dependent optical (left) and beatnote (right) frequency in an FMCW LiDAR. Top, middle, and bottom panels show three operational regimes with fd = 0, fd < fr, and fd > fr, respectively. b Experimental setup for distance and velocity measurement. Photos of the objects are provided in SI. EDFA erbium-doped fiber amplifier, CIRC circulator, COL collimator, Galvo. Galvo mirror, PC polarization controller, PD photodetector, OSC oscilloscope, ESA electrical spectrum analyzer. c Left: Spectrum of the measured beat-not signal as a function of target velocity, with a fixed laser frequency modulation speed of 100 kHz. Right: As a function of laser frequency modulation speed, at a fixed target velocity of 3 m/s. The shaded areas indicate the false-detection regime due to insufficient laser frequency chirping rate. The red dashed line marks the case with a modulation speed of 100 kHz and a target velocity of 3 m/s, whose detailed spectrogram is shown in (d). d Time–frequency spectrogram of the beating signal at four different target velocities of 0.3, 3, 30, and 40 m/s. To showcase the effect of laser frequency modulation speed, the four spectrograms are measured with different laser-frequency modulation speeds of 10, 100 kHz, 1, and 2 MHz, respectively. The right figure compares the measured velocity by the device with the set velocity of the object. e Theoretical maximum measurable velocity for our laser. f 2D scanned ranging image of a static object. g Spectrum of the beatnote as a function of the relative position of an object, with a step of 2 mm. The red area is highlighted at right to show the ranging resolution
