## 2 Experimental Setup and Materials  
The experimental setup of active HSI system is shown in Figure 1a. The active HSI uses a home-made SC laser as the broadband coherent illuminator and a commercial visible/near-infrared hyperspectral imager (Sichuan Dualix Spectral Image Technology Co.Ltd, GaiaField-F-V10) as the imaging instrument. An off-axis parabolic silver-plated mirror is mounted on a XYZ translation stage to reflect the SC laser beam to the objects. A diaphragm installed behind the parabolic mirror is used to remove the weak illumination at the edge of the laser spot.  
The spectral detection range of the hyperspectral imager is 400-1000 nm with a spectral resolution of 3.5 nm. The image obtained by the imager has a spatial size of \(568\times 696\) and a spectral bands number of 174 after down-sampling. The SC laser has a size of about \(270\times 250\times 80\) mm\({}^{3}\), driven by a direct  
Figure 1: Experimental setup and characterization: (**a**) Photo of the active HSI system in laboratory. (**b**) Output spectrum of the SC laser at the range of 400–200 nm. (**c**) False-color image of the SC laser spot by the hyperspectral imager. (**d**) Spectral profiles of the 13 points (A–J) marked in (**c**) recorded by the hyperspectral imager.  
current power supply. It has an average optical output power of 4 W and a rough spectral range of 500-2400 nm. The output spectrum of the SC laser at the wavelength range of 400-1200 nm is shown in Figure 1b, which is measured by a commercial spectrograph. Figure 1c shows the photo of the SC laser spot captured by the hyperspectral imager in the dark. The laser beam diameter on the plane of targets placed -5 m away from the SC laser is -12 cm, measured by the squares (0.5 \(\times\) 0.5 cm) drawn on a piece of white paper. The spectral profiles of the 13 points (A-J) marked in Figure 1c is shown in Figure 1d. It is obvious that the measured illumination spectra at different locations of the spot are totally different from each other, showing a non-uniform distribution of intensity and spectrum. Conversely, the ambient light of sun is more uniform, which makes the passive HSI classification and spectral analysis much easier. Doubtlessly, the problem limits the development and application of active HSI systems.  
In the experiments, different materials are selected as the objects of interest, including fresh leaves, plastic leaves, blue plastic flowers, white plastic flowers, a green plastic bottle cap, red wood and a calibrated Spectralon reflectance standard plate (Labsphere Inc., USA); they are shown in Figure 2. To avoid the effect of sunlight, active HSI experiments are conducted in darkness. The objects are placed -5 m away from the active HSI system. At such close distances, the radiation power level of SC laser is enough for illuminating and reflected signal receiving [20]. In actual scenarios, the hyperspectral imager and SC laser may be kept at long distances from the targets, therefore, a higher-power SC laser is needed to ensure sufficient reflected signals can be received by the hyperspectral imager. Under this situation, the radiation power level of SC lasers should be considered seriously by matching the solar irradiance on the ground surface at the spectral range required [11]. The long-distance experiments and applications will be a future research orientation with a high-power SC laser developed.