Fig. 2
From: A prototype of an optical sensor for the identification of diesel oil adulterated by kerosene
a Schematic diagram of a handheld sensor for fake diesel oil screening. DOE is a diffractive optical element. The dashed lines describe scattering of light due to the surface roughness and refractive index mismatch between the fuel and the glass. b Prototype of a portable sensor for fake diesel oil screening. The microscope slide is above the sensor head (the black plastic cup). Normally, the glass slide is on the bottom of the cup. The reading of 106, shown on the display is from the roughened probe window without a liquid sample. Bellow value 100, the accuracy of the reading is ±0.1