*2.1. AOTF-HSL Design and Components*

Figure 1 presents the design and diagram of the AOTF-HSL, which employs a super-continuum (SC) laser source covering 450–2350 nm. Figure 2 presents the relationship between the wavelength and power density of the employed SC laser source. An AOTF is installed in front of the SC source. AOTF is capable of consciously selecting and filtering laser beam with 10 nm spectral resolutions from 430–1450 nm. After the laser beam passing through AOTF, the emitted broadband laser beam is collimated and then reflected towards the target by a reflecting mirror. A Cassegrain telescope optical

system is employed to collect the energy of the reflected laser pulses from the targets. An APD sensor module with an integrated amplifier is placed on the focal point of the Cassegrain telescope to collect the back-scattered laser echoes and transform them to electronic signals, which are sampled and recorded by a linked high-speed oscilloscope (20 GHz sampling rate, which equals 7.5 mm range resolution). Spectral information can be extracted from the recorded raw waveform. Meanwhile, the triggering signal indicating the emission of SC source is collected by the linked high-speed oscilloscope. Distance information is obtained by measuring the time difference between the triggering signal and reflected signal from the target. More details on the spectral and ranging information acquiring capacity could be found in our recent paper [32]. The remainder of this section will present the specifications of different parts of the AOTF-HSL.

**Figure 2.** The supercontinuum laser source and the power density against the wavelength.
