Fig. 1. Principle diagram of optical path. (a) Traditional rainbow; (b) rainbow refractometer

Fig. 2. Three-dimensional view ofrainbow refractometer

Fig. 3. Experimental setup of spray droplet measurement with compact rainbow refractometer

Fig. 4. Rainbow picture of deionized water

Fig. 5. Inversion results of refractive index of deionized water

Fig. 6. Rainbow pictures of ethanol solution with volume fractions of 0-100%

Fig. 7. Measurement results of refractive index of ethanol solution different volume fractions